BEFORE INDEPENDENT COMMISSIONERS AND STATEMENT OF EVIDENCE OF DAVID LEONG ON BEHALF OF WAIMEA COMMUNITY DAM LIMITED 12 NOVEMBER 2014

Transcription

1 BEFORE INDEPENDENT COMMISSIONERS IN THE MATTER of Resource Management Act 1991 AND IN THE MATTER of applications for resource consent for the Waimea Community Dam STATEMENT OF EVIDENCE OF DAVID LEONG ON BEHALF OF WAIMEA COMMUNITY DAM LIMITED 12 NOVEMBER 2014 ANDERSON LLOYD LAWYERS CHRISTCHURCH Solicitor: J Crawford / S Eveleigh Anderson Lloyd House, Level 3, 70 Gloucester Street, PO Box 13831, CHRISTCHURCH 8141 DX WX10009 Tel Fax

2 1 1. INTRODUCTION Qualifications and experience 1.1 My name is David Leong. I am a hydrologist and water resources engineer with the qualifications Bachelor of Engineering with 1st class honours in civil engineering gained in 1987 and Master of Engineering with distinction in civil engineering gained in 1988, both from the University of Canterbury. I am a Chartered Professional Engineer in New Zealand (CPEng) and registered on the International Professional Engineers Register (IntPE). I am also a Category A Recognised Engineer, as defined by section 149 of the Building Act, and can undertake dam safety work prescribed in the Building Act. I have been a full member of the Institution of Professional Engineers of New Zealand (IPENZ) since I am also a member of the New Zealand Hydrological Society and served on the society's executive committee from 2003 to I am currently employed as a Project Director with the environmental and engineering consulting firm Tonkin & Taylor Ltd (T&T), and have 25 years of professional experience mostly with the firm's Water Resources group based in Auckland. I joined T&T in 1990 and have been responsible for hydrological and hydraulic investigations and engineering design for a wide range of water resource projects in New Zealand and overseas. These projects include irrigation dams and headworks; hydro-electric power schemes; water supply headworks; drainage infrastructure for landfills and motorways; and floodplain management projects. My involvement in these projects has spanned from conceptual and environmental studies to detailed design, construction monitoring and safety reviews (for dams). 1.3 Before I joined T&T, I worked for two years at the Hydrology Centre in Christchurch, which was then part of the Ministry of Works and Development and the forerunner to NIWA Freshwater. My role at the Hydrology Centre was as a scientist mainly with research responsibilities in catchment hydrology, flood forecasting and sediment transport processes. 1.4 I have completed hydrological assessments and water resource modelling studies for numerous irrigation, water supply and hydropower projects, and in New Zealand these include: (a) the proposed Ruataniwha Water Storage Scheme in Hawke s Bay (83m high dam, 90 million m 3 reservoir) for irrigation, hydropower generation and environmental flow releases; (b) the Opuha Dam in South Canterbury (50m high, 95 million m 3 reservoir) for irrigation, hydropower generation and minimum flow maintenance;

3 2 (c) the currently proposed Lee Dam (52m high, 13 million m 3 reservoir) for flow augmentation and water supply in Tasman District; (d) the existing Wai-iti Dam (20m high, 800,000m 3 reservoir) for groundwater augmentation in Tasman District; (e) (f) (g) (h) the previously proposed Project Aqua (530 MW, 6 station cascade) hydropower project in the lower Waitaki River; the proposed Omaka Dam (34m high, 18 million m 3 ) for private irrigation in Marlborough District; the 10 existing dams for bulk water supply in the Auckland region, ranging in height from 18m to 64m and reservoir capacity from 1.2 million m 3 to 35 million m 3 ; and for 10 potential storage options in the Ruamahanga catchment, ranging in capacity from about 4 million m 3 to 80 million m 3, as part of the Wairarapa Water Use Project in the Greater Wellington Region. 1.5 I have been involved in the safety reviews and dam break hazard assessments of more than 35 existing and proposed dams both in New Zealand and overseas. Internationally these include the majority of the existing large dams over 100m high in the Philippines (i.e. Angat, Magat, Ambuklao, Binga and Pantabangan Dams), and the recently commissioned 250 MW Bujagali hydropower project on the River Nile in Uganda. I am one of the three members of the Dam Safety Panel for the 520 MW Huoi Quang hydropower project in northern Viet Nam, involving a 104m high concrete dam, currently in the fourth year of construction (in a six-year programme). 1.6 In the Nelson and Marlborough areas, besides the currently proposed Waimea Community Dam, my experience has covered dambreak hazard assessments for the following dams: (a) (b) (c) (d) (e) (f) the existing 18m high Taylor Dam which provides flood detention protection for Blenheim; the existing 15m high Barnes Dam, a double-arched concrete dam which provides water supply to Picton; the existing 22m high Delta Dam located 6 km southwest of Renwick, which has a storage capacity of 1.3 million m 3 ; the proposed 34m high Omaka Dam also southwest of Renwick, with storage capacity of 18 million m 3 ; the existing 20m high Wai-iti Dam, which has a storage capacity of 800,000 m 3 ; a proposed 22m high irrigation dam on the Waima River about 12km southwest of Ward with a storage capacity of 4.7 million m 3 ; and

4 3 (g) the existing 40m high Maitai Dam about 7km east of Nelson, which provides the city with its potable water supply. 1.7 With regard to the Lee Dam, my involvement began in November 2004 with T&T's Phase 1 Prefeasibility Study of potential water storage options in the upper Wairoa/Lee catchments for the Waimea Water Augmentation Committee (WWAC). This initial options study was followed by a Phase 2 Feasibility Study in September 2007 that focused on a potential storage dam on the Lee River, and then by preliminary detailed design of the dam beginning in September I have visited the dam site and the river reaches downstream of the dam site on a number of occasions. 1.8 My role in the Phase 1 and Phase 2 studies was as team leader responsible for coordination and technical management of all water resource investigations and associated studies, including: (a) (b) (c) (d) (e) (f) (g) confirmation of the projected water demand for irrigation and urban/industrial needs; hydrology and catchment water availability; analysis of surface water and groundwater interaction in the Waimea Plains; assessment of the storage requirements to meet consumptive water demands and in-stream needs; assessment of flood frequency and spillway design floods; determination of an operating regime for the reservoir both with and without hydro-electric power generation, and its effects on the downstream flow regime; and dam break hazard assessment and mapping. 1.9 At the commencement of the preliminary detailed design, many of the key design parameters from the water resource investigations had already been confirmed. Therefore, my role at preliminary detailed design was generally limited to refining the spillway and diversion design floods and construction flood risk analysis. Scope of evidence 1.10 I confirm that I have read and agree to comply with Code of Conduct for Expert Witnesses (Environment Court Practice Note 2014). This evidence is within my area of expertise except where I state that I am relying on facts or information provided by another person. I have not purposely omitted to consider material facts known to me that might alter or detract from the opinions that I express My evidence is in two parts. The first part summarises the hydrological aspects of the design of the Lee Dam, including associated water resource investigations and modelling of the

5 4 operation of the reservoir, and the second part outlines the dam break analysis for the storage dam on the Lee River Specifically, in the first part of my evidence I address the following matters: (a) Water resource investigations (section 2); (b) Water demand overview (section 3); (c) Groundwater - surface water interaction in the Waimea Plains (section 4); (d) Flow regime and water availability of the Lee River (section 5); (e) Flood hydrology for flood passage design at the dam (section 6); (f) Demand - supply modelling, utilising storage in the Lee Dam (section 7); (g) Reservoir operating regime and dam discharges (section 8); (h) Hydro-electric power generation from dam releases (section 8); and (i) Comments on relevant submissions (section 9) The second part of my evidence, which concerns the dam break analysis, covers the following: (a) (b) (c) (d) (e) (f) (g) Reason for assessing dam break hazard; Dam failure scenarios; Dam breach parameters; Hydraulic modelling of dam break flood wave; Assessment of potential hazard from dam break; Potential impact classification of the Lee Dam; and Comments on relevant submissions. Summary of findings 1.14 My evidence covers a number of different aspects of the application. My overall conclusions in relation to the matters which I cover are as follows: 1.15 The technical basis for establishing the required reservoir capacity at the storage dam is centred on meeting a set of water demand parameters to a desired level of drought resilience, and both in-stream needs and consumptive demands have been appropriately considered for the Lee Dam Groundwater modelling determined the augmented flow required in the Wairoa River to meet the future water demand and maintain a minimum flow of 1,100l/s in the Waimea River at Appleby Bridge.

6 5 Modelling of the groundwater surface water interaction was undertaken to understand the system response to increased recharge from augmented river flows and increased takes in future The modelling also showed that under actual historical abstraction rates, flow at Appleby Bridge would have been continuously below 800l/s for a period of about 62 days in the 2001 drought and for about 38 days in the 1983 drought. These instances highlight the severity of restrictions that existing abstractive users are likely to face under the new minimum flow rules, if the dam does not proceed. These restrictions are projected to increase under future climate change The water resources of the Lee River and wider Wairoa catchment have been studied using available historical flow data. A representative synthetic record of dam inflows has been successfully generated from the long-term Wairoa at Irvines flow record, which extends from 1958 to The estimated long-term mean flow of the Lee River at the proposed dam site is 3.60m 3 /s, which constitutes 22.2% of the river flow at Irvines Design floods for the dam site have been established using a range of methods. The Maximum Design Flood is based on the Probable Maximum Flood (PMF) which has a peak flow of 1,094m 3 /s, and is approximately 2.9 times the 100 year flood of 375m 3 /s (without climate change, and 2.4 times the 100 year flood of 457m 3 /s with climate change adjustment to the year 2090) Reservoir storage behaviour has been modelled using the projected water demand parameters and selected environmental minimum flows together with historical and synthetic flow records. The supplydemand modelling has established a relationship between reservoir capacity and the level of drought security afforded. The reservoir capacity adopted for design of the dam of 13 million m 3, which includes a nominal 1.0 million m 3 allowance for long-term sediment infill and dead storage, provides approximately a 65 year return period drought security, based on historical flow and climate data. While this would appear to provide a relatively high standard of reliability, future climate change is anticipated to progressively diminish the level of drought security provided by the project A relatively modest sediment infill rate of approximately 5200 tonnes/year, which is equivalent to about 3500 m 3 /year, has been estimated for the reservoir. In terms of the effect on downstream river morphology from sediment retention in the reservoir, the removal of gravel supply to the lower river is not expected to have a significant effect in view of the relatively small amount of gravel supplied by the Lee River above the dam site compared with the remainder of the Waimea catchment Operation of the Lee Dam entails regulation of the river flows at the dam site using reservoir storage, resulting in a modified outflow regime compared with the natural flow regime. However, the long-term

7 6 average changes in the monthly mean flows are relatively small, peaking at about +9% for the month of February (flow increase) and at about -4% for the month of April (flow reduction). Dam outflows match the reservoir inflows for the majority of the time. This response occurs when the reservoir is full or nearly full, typically between June and November each year. There would be minimal attenuation in the flood outflow under such circumstances During the operational phase of the project, the actual operation of the reservoir and dam releases would likely be guided by an operating system that would incorporate a contingency plan to manage drought conditions. At the core of this drought management plan would be the trigger levels for rationing of water abstractions and the stepped minimum flow rules for the Waimea River as set out in Table 1A Schedule 31C of the Tasman Resource Management Plan (TRMP) While principally for downstream flow augmentation to meet in-stream needs and consumptive uses, the dam also presents an opportunity for hydropower generation and the design provides for a 3.3m 3 /s capacity turbine and generator, and a nominal buffering storage to enable capture and generation of inflow that would otherwise be spilled when the reservoir is close to full The results of the dam break analysis show that the Lee Dam should be classified as a High Potential Impact Category (PIC) dam. The classification was determined largely from the significant population-atrisk if a dam break were to occur. It is essential to draw the distinction between hazard potential, that is the effects of the dam breach were it to occur, and the risk or probability of the dam breach actually occurring. The risk of failure occurring for a dam engineered, built, maintained and monitored to appropriate standards would be extremely low. 2. WATER RESOURCE INVESTIGATIONS 2.1 As part of the Phase 1 and Phase 2 studies, water resource investigations comprised the following tasks: (a) (b) (c) Review and confirmation of the potential future water demand for irrigation use, as well as long-term community and industrial demands, plus in-stream flow requirements. Modelling of the groundwater-surface water interaction of the Wairoa/Waimea river and Waimea aquifers, and development of a flow augmentation regime for meeting future demand and a residual flow in the Waimea River of 1100 l/s at Appleby Bridge. Confirmation of the natural flow regime of the Lee River and water availability at the proposed dam site.

8 7 (d) (e) (f) (g) Assessment of the flood hydrology and development of flood hydrographs for the design of the dam spillway and construction diversion. Dynamic storage modelling to confirm the storage capacity needed at the dam site in order to meet the identified water demands at the required level of drought resilience with due allowance for long-term sediment infill and environmental flow releases. Development of a preliminary operating regime for the proposed reservoir and assess the flow changes anticipated in the Lee River immediately below the dam and at the Wairoa Gorge. Assessment of the hydro-generation potential at the storage dam together with associated changes to the operating regime with a hydropower add-on. 2.2 In this statement I provide outline summaries and key findings from these investigations. The work I summarise here has incorporated input from the following entities: (a) (b) (c) (d) (e) (f) (g) (h) (i) Tasman District Council (TDC) (hydrometric data; urban and industrial demand); T&T personnel (project management; hydrological modelling and storage demand assessment; flood hydrology); GNS Science (groundwater modelling); AgFirst (consumptive water demand); Landcare Research (irrigation demand scheduling); Cawthron Institute (in-stream habitat needs); Parsons Brinckerhoff (feasibility design of hydropower add-on); Lincoln Ventures (external peer review); and Engineering Geology (external peer review of flood hydrology). 3. WATER DEMAND OVERVIEW 3.1 This section of my evidence provides background on the technical basis for establishing the reservoir capacity of the storage dam. This is determined by the development of a set of water demand parameters. The original demand assumptions at pre-feasibility level are described in the Waimea Water Augmentation Phase 1 Study: Component 1 Report Water Demand and Availability, May 2007, by T&T. These demand parameters were further developed in the Phase 2 study as described in the Water Resource Investigations report, December 2009, also by T&T.

9 8 3.2 During Phase 2, a technical workshop to review water demand was held on 10 October Participants included representatives from WWAC and TDC, and relevant experts from T&T, Landcare Research, AgFirst, Northington Partners and GNS Science. The purpose of this exercise was to update and agree the demand assumptions on which to base the live storage requirement for the dam s reservoir. I understand that consumptive water users will be separately controlled by the TDC but this nonetheless provides useful background to the demand components that were catered for. 3.3 Aspects that were discussed, and a summary of the key decisions made at the workshop by WWAC, are as follows: (a) (b) (c) (d) (e) (f) (g) (h) (i) Extent of irrigable area. Crop mix in the irrigation service area. Design drought and the drought security standard. In-stream minimum flow. Tasman District urban/industrial demand and planning horizon (100 years). Future wider regional demand. Climate change effects. Hydro-electric power generation potential. Distribution to service areas beyond aquifer zone of supply. 3.4 In relation to the design drought standard, a target 60 year return period drought for storage drawdown and refilling reliability was set, to be reviewed once the drought return period versus storage capacity relationship was defined. A relatively high drought standard, assessed against historical climate and flow data, was adopted, with the expectation that the standard may lower with future climate change. 3.5 I provide below further detail on the in-stream flow requirement and assumptions as to consumptive water demands adopted for design. In-stream needs 3.6 As part of the Phase 1 study, Cawthron assessed the minimum flows required to provide in-stream habitat in the lower Wairoa/Waimea rivers and immediately below the dam site. Different minimum flows were identified to span a range from an environmental benchmark minimum flow that would be conservative in terms of environmental protection, to a minimum flow that would be weighted towards out-ofstream values. At Appleby Bridge, and based on the output of Cawthron s investigations, WWAC determined that provision for an in-

10 9 stream minimum flow of l/s was reasonable and appropriate. This minimum flow has now been adopted in the TRMP through plan changes During Phase 2, Cawthron completed additional investigations and habitat modelling for the Lee River in order to assess an appropriate minimum flow below the proposed dam, and to provide an indication of the flushing flows required to flush sediment and algae from this reach of the river. 3.8 As a result of these investigations, the environmental benchmark of the 7-day mean annual low flow (7-day MALF), which is a flow of about 0.5m 3 /s at the proposed dam site, was confirmed as an appropriate minimum flow below the dam. In addition, Cawthron recommended that a 5m 3 /s flushing flow capability be provided at the dam as part of an adaptive management approach to potential algal proliferation. These assessments including earlier Phase 1 studies are presented by Dr Young in his evidence. Consumptive water demand 3.9 Landcare Research was commissioned to compute a time-series of irrigation usage corresponding with the period of available river flow data at the time (1958 to 2008). Daily time-series of water demand for pasture were computed using its irrigation scheduling model for the specific soil types in the irrigation command area and local rainfall and other climate data based on a maximum weekly application rate of 30mm/week. A relatively aggressive (as opposed to modest ) irrigator behaviour, corresponding with a regime where the soil is kept relatively moist all the time, was assumed in order for the computed demands to be comparable with those determined independently by AgFirst A corresponding time-series record of the soil drainage for each of the modelled soil types was also generated from irrigation scheduling, which was used as input to GNS Science s groundwater model of the Waimea Plains which I will discuss later Exhibit DL01 shows a plot by Landcare Research of the daily irrigation demand pattern for the 1982/1983 drought year based on the full irrigable area of 5856 ha being provided for. Exhibit DL02 shows the predicted year to year variation in the irrigation demand volume from 1958 to High demand years, in excess of 25 million m 3 per annum, are indicated by red bars i.e. 1973, 1983 and 2001 (year ending 30 June). By contrast, in low usage years such as 1996 and 2002, the irrigation demand can be as low as 11 million m 3 or less than half the requirement in a drought year. 1 In this statement, various units have been used to describe the rate of water flow, discharge or usage, i.e. units of litres per second (l/s), cubic metres per second (m 3 /s) and cubic metres per day (m 3 /day) have been used. A flow rate of 1 m 3 /s is equal to 1000 l/s and 86,400 m 3 /day.

11 For a 100-year planning horizon, TDC projected an urban and industrial water demand profile with a nominal peak value of 60,000m 3 /day. This demand would be met from the aquifers of the Waimea Plains, which would be recharged by releases from the dam. A generic seasonal demand pattern with a daily resolution was provided by TDC for supply-demand modelling and shown as Exhibit DL03. As can be seen, the demand pattern is strongly seasonal with the peak demand occurring in January (average demand for the month is about 47,000m 3 /day) while the lowest demand is for the month of June (average demand of about 5,000m 3 /day) An allowance for the wider future regional water demand was confirmed by WWAC at the technical workshop on 10 October A constant year-round surface water take from the Wairoa River of 22,000m 3 /day (254l/s) was assumed for this demand component Taking all of the above into account, constituents of the total consumptive demand were: (a) (b) (c) the irrigation demand (from both the Waimea aquifers and the Wairoa River) peaking at 213,400m 3 /day; the urban and industrial demand peaking at 63,800m 3 /day; and a constant surface water take of 22,000m 3 /day for future regional need For the long-term simulation of storage behaviour for the period 1958 to 2008, which I will describe later, the modelled irrigation demand followed the irrigation schedule developed by Landcare, which was based on historical climate data for the same period, and service area assumptions outlined previously. However, a repeating annual pattern was retained for the urban and industrial water demand component Exhibit DL04 provides a plot of the total water demand for the 1982/1983 drought year divided into surface water and groundwater takes. Table 1 summarises the water demand volumes for the water year ended 30 June This is a high usage year and the water demand for other years will typically be substantially lower than shown. Table 1 Total water demand for 1982/1983 water year Irrigation Take Waimea East Irrigation Scheme (Surface Water) (million m 3 ) Groundwater (million m 3 ) Urban and Industrial Take (Groundwater) (million m 3 ) Future Regional Need (Surface Water) (million m 3 ) Total Demand (million m 3 ) Note: 1 Includes Wakefield allowance (6% of total) which is supplied by the Wai-iti Dam.

12 As noted above, I understand that the consumptive water use by abstractors is also separately controlled by the TDC but this nonetheless provides useful background to the demand components that were allowed for by the project. 4. GROUNDWATER SURFACE WATER INTERACTION 4.1 From a hydrological perspective, an unusual feature of the proposed Lee Dam project is the method by which the water released from the dam is ultimately made available for use. The shallow unconfined aquifers of the Waimea Plains, which currently supply irrigation water to agricultural operations of the Waimea Plains and urban and industrial water to the Richmond area, will be part of the anticipated conveyance method. The project does not include the conveyance of water directly to downstream users. 4.2 It was however necessary to understand how the overall aquifer system operated for reliable prediction of the response of the system, including the surface flow at Appleby Bridge, to the increased groundwater abstractions and recharge from augmented river flows, and ultimately for determination of the required storage capacity at the dam. 4.3 Modelling of the groundwater system and its interaction with surface flows in the river system was therefore undertaken by GNS Science and is reported in detail in the Phase 1 2 and Phase 2 3 study reports. I briefly summarise the outcome of GNS Science s work, which formed the basis for the subsequent storage modelling work that I completed. 4.4 In summary, modelling was undertaken to determine the augmented flows required at Wairoa Gorge to sustain a pre-determined residual flow at Appleby Bridge (i.e. 1,100l/s) while meeting unrestricted abstractive demands from the Waimea aquifers. It should be noted that the river reach between dam site and Wairoa Gorge is considered lossless in that surface flows are conserved along this reach. However, below the Gorge, the river channel lies above the interconnected aquifer system and surface flow can be lost to or gained from groundwater. Indeed, the lower Waimea River is prone to drying as a result of significant water losses to groundwater in a prolonged drought, as was observed in February/March 2001 when the river stopped flowing for a period of 2 to 3 weeks. 2 Groundwater-river interaction modelling for a water augmentation feasibility study, Waimea Plains, Nelson. GNS Science Consultancy Report 2006/200, March 2007, attached as Appendix 2 to Waimea Water Augmentation Component 1 - Water Demand and Availability Report, T&T Ref , May Waimea Water Augmentation Project Feasibility Study: Phase 2 Modelling Report. GNS Science Consultancy Report 2008/185, August 2009, attached as Appendix B to Waimea Water Augmentation Phase 2 Water Resource Investigations Report, T&T Ref , December 2009

13 GNS Science s work entailed multiple runs of the Waimea Plains groundwater model, a model that had been developed and calibrated by GNS Science in collaboration with TDC over a number of years. This groundwater model included both the confined and unconfined aquifer systems which underlie the lower Wairoa/Waimea Plains. Special care was exercised in the representation of the river-aquifer interaction. In particular, the model was appropriately configured so that it was able to replicate the observed drying of the Waimea River at Appleby Bridge, e.g. in February/March 2001 under actual historical water abstraction rates. 4.6 Using this model, the sequence of required augmented flows at Wairoa Gorge was determined for a number of scenarios from repeated (trial-and-error) runs of the model. The scenarios covered partial and the full future water demands for three separate water years, being: (a) (b) (c) 1982/1983 which is known to be a significant drought, 2000/2001 which is a somewhat more severe drought, and 2004/2005 which is a more normal year. 4.7 Groundwater modelling showed that, to meet the future water demand and maintain a minimum flow of 1,100l/s at Appleby Bridge, the average augmented river flow required at Wairoa Gorge over the driest part of the 2000/2001 drought (1 February through 31 March 2001) would have been 3,077l/s (upstream of the Waimea East Irrigation Scheme take). Similarly, modelling of the scenario for the 1982/1983 drought (with the driest part of it also being the 1 February through 31 March time frame) showed that an average augmented flow at the Wairoa Gorge of 3,029l/s would have been required to meet the target minimum flow of 1,100l/s at Nursery- Appleby Bridge. In both cases, the releases from the dam would have constituted approximately 65% to 70% of the augmented flow required at Wairoa Gorge. By contrast, in the 2004/2005 irrigation season, with abstractions at the future demand level, and without any augmentation, natural river flow is predicted to be able to maintain a river flow above 1100l/s at Appleby Bridge at all times except for three days. 4.8 The pattern (timing and quantity) of surface flow loss in the river reach between Wairoa Gorge and Appleby Bridge predicted by the groundwater model was analysed to determine its dependence on a range of variables, including the natural river flow sequence at Wairoa Gorge and the rate and sequence of groundwater abstractions. From this assessment, relationships were developed between the flow augmentation required from dam releases and the pre-augmentation flow at Wairoa Gorge for varying levels of groundwater abstraction. These relationships, which are shown in Exhibit DL05, allow the groundwater system behaviour to be coupled with the river flow above the Gorge and therefore with the operation of a storage dam on the

14 13 Lee River. In effect, these relationships determine, on a day-to-day basis, the required flow release from the proposed dam in the upper Lee catchment to meet downstream demands while allowing for other tributary inflows between the dam site and Wairoa Gorge. 4.9 The black box approach adopted here by necessity has its limitations as it simplifies the physical processes involved in the groundwatersurface water interaction and aquifer storage dynamics. However, to the extent possible, limitations inherent in the adopted approach have been addressed through careful calibration against the full groundwater model results. Furthermore, when the flow augmentation scheme is put into operation, it will be possible, and also preferable, to make use of real-time flow monitoring at Appleby Bridge to refine dam flow releases so as to target the in-stream flow requirement of at least 1,100l/s at Appleby Bridge. 5. WATER RESOURCES OF THE LEE CATCHMENT 5.1 The catchment area of the Lee River at the site of the proposed dam is 77.5km 2, which is approximately 10% of the overall Waimea River catchment. TDC installed a flow monitoring station on this river upstream of the dam site (station name: Lee at Waterfall Creek) in April 2007, and this station continues to operate to the present time. The catchment area at the gauging location is 65.3km 2, representing 84% of the catchment area commanded by the proposed dam. Data from this station has been used to confirm the surface water resources of the Lee River and at the dam site, as well as the flood response of the Lee catchment to storm rainfall. 5.2 At the commencement of the dam feasibility study (2008), only one year of flow data was available from the Lee River flow monitoring station. The nearest and most representative flow recorder with a continuous long-term flow record is on the Wairoa River at Gorge/Irvines 4, which commands a catchment area of 463km 2 that includes the entire Lee River catchment. Exhibit DL06 shows the location of the flow and rainfall monitoring sites in the Lee River and wider Wairoa River catchments. 5.3 Exhibit DL07 plots the contemporaneous flows from the Lee at Waterfall Creek and the Wairoa at Irvines. This plot clearly shows that flows in the upper Lee behave in the same way as flows in the Wairoa, and that their flow regimes are very closely correlated, in terms of both 4 The Wairoa at Irvines flow recording station is located just upstream of the Wairoa Gorge and is sometimes referred to as the Wairoa Gorge recorder, although a discontinued recording station called Wairoa at Gorge (located about 900 m downstream of Wairoa at Irvines) operated between November 1957 and December 1992 before being replaced by the current Wairoa at Irvines recorder. The records from both stations have been combined for the current project and the combined record is referred to as Wairoa at Gorge/Irvines or simply as Wairoa at Irvines.

15 14 magnitude and timing of flow events. Therefore, I considered it entirely appropriate to generate a synthetic record of the Lee River flows, dating back to the start of the Wairoa record in November 1957, by simply scaling the historical flows recorded in the Wairoa Gorge. 5.4 The estimated long-term mean flow of the Lee River at the proposed dam site is 3.60m 3 /s, which represents 22.2% of the flow recorded at Wairoa Gorge. This flow rate is equivalent to an inflow volume to the proposed reservoir of about 114 million m 3 per year on average. It is notable that a long-term mean flow at the flow gauging site of 3.20m 3 /s was predicted at the time of the feasibility study, even though the then available flow record (April 2007 to April 2008) showed a mean flow of only 2.31m 3 /s. The up-to-date record for the Lee at Waterfall Creek (April 2007 to October 2014) now indicates a mean flow of 3.45m 3 /s, which is about 7.5% greater than the estimated long-term mean flow. 5.5 Flow in the Lee River is strongly seasonal. Each year, the lowest flows typically occur between January and March, and the highest sustained flows typically occur between June and October. The mean flow over the three drier months of the year (January to March, 2.4m 3 /s) is approximately half the mean flow for the five wetter months (June to October, 4.4m 3 /s). The total flow volume in a year can vary substantially from one year to the next, and has ranged from a minimum of 60 million m 3 for the 2005/2006 water year up to a maximum of 178 million m 3 for the 1998/1999 water year. 5.6 From an analysis of the annual series of low flows recorded at Wairoa at Irvines and correlation with the shorter Lee at Waterfall Creek record, a 7-day MALF of 0.49m 3 /s was estimated for proposed the dam site. As described by Mr Foley in his evidence, before the current proposed dam site was identified, a dam site located about 1.3km downstream was selected as part of the preceding 2006/2007 prefeasibility study. The catchment area at this former downstream site included Anslow Creek and thus had a slightly greater assessed 7-day MALF of 0.51m 3 /s. This higher 7-day MALF has been conservatively retained for the current upstream dam site, and confirmed by Cawthron s Phase 2 assessment as appropriate at the Lee Dam site. 6. FLOOD HYDROLOGY 6.1 Under my direction, flood hydrology of the Lee/Wairoa catchment was analysed by T&T in order to develop flood hydrographs for design of the dam spillway and for construction diversion provisions. The analysis was focussed on flood estimation at the proposed dam site on the Lee River. The methods used to compute the design floods for a range of event return periods and the PMF comprised the following: (a) Method 1: flood frequency analyses based on the long-term flow record at Wairoa at Irvines

16 15 (b) (c) Method 2: flood hydrograph derived from repeated frequency analysis of flood volumes for a range of flood durations Method 3: PMF hydrograph derived from the Probable Maximum Precipitation (PMP) rainstorm using a rainfall-runoff model calibrated to observed storm rainfall and flood events. 6.2 Methods 1 and 3 are traditionally accepted approaches to design flood estimation. Method 1 provides an estimate of only the peak flow for a range of return periods, while Method 3 produces a full hydrograph which can be used for reservoir flood routing and thus design of the dam s spillway. Method 2 is a newer flow-based method which produces a synthetic design hydrograph without requiring storm rainfall data. For a particular return period event, the synthetic hydrograph essentially comprises nested pairs of volume-duration data covering the full duration of the flood hydrograph. Method 2 provides arguably the most accurate and consistent estimates of both flood volume and peak flow in a single hydrograph. Methods 1 and 2 rely on the long-term flow record at Wairoa at Irvines. Correlations between the short-term record for the Lee River (Lee at Waterfall Creek) and this record have been used to translate the results to the dam site. 6.3 Exhibit DL08 shows the flood frequency distribution fitted to the annual maximum flows recorded at Wairoa at Irvines. The one standard error envelope is also shown (68.3% confidence interval). Peak flow estimates for the proposed dam site on the Lee River have been computed from flood parameters for the Wairoa at Irvines site using the transposition equation recommended for New Zealand 5, which assumes flood peaks are related by catchment area ratio raised to the power of 0.8. Table 2 summarises estimated flood peaks for a range of return periods for the Wairoa River at Irvines and at the proposed dam site. 5 McKerchar, A.I. and Pearson, C.P. Flood Frequency in New Zealand, Publication No. 20 Hydrology Centre, DSIR, 1989

17 16 Table 2 Flood peak estimates for the Wairoa at Irvines and Lee dam site (instantaneous peak flows) Parameter Wairoa at Irvines Lee dam site at Chainage Catchment Area (km 2 ) Mean Flow (m 3 /s) 16.2 ~ 3.60 Mean Annual Flood (m 3 /s) 698 ± Year Flood (m 3 /s) 1055 ± Year Flood (m 3 /s) 1410 ± Year Flood (m 3 /s) 1560 ± Year Flood (m 3 /s) 1710 ± Year Flood (m 3 /s) ~ 2050 ± ,000 Year Flood (m 3 /s) ~ 2550 ± It should be noted that extrapolation of a fitted flood frequency distribution to very long return periods, such as to the 1,000 or 10,000 year events, is not generally recommended. This is not only because of the large uncertainty in the flood estimate, but also the extreme sensitivity of the estimate to the selected type of frequency distribution and fitting approach. Nevertheless, design standards for large dams typically require estimates of the 100 year, 1,000 year and 10,000 year return period floods for the design of spillway provisions, depending on the downstream hazard potential of the completed dam, which I address in section 4 of my evidence. Flood frequency analysis, in spite of the large extrapolation required, remains one of the sounder methods to estimate such long return period events, provided the appropriate type of frequency distribution is used. 6.5 As described by Mr Croft in his evidence, the PMF has been adopted as the ultimate design standard (maximum design flood) for the spillway capacity of the Lee Dam. An operational basis flood (OBF) equal to the 200 year return period flood has been specified for the dam spillway design. A flood with a return period of up to 1,000 years has been adopted for the diversion capacity at any stage during construction where there is a risk to public safety from failure of the partially completed dam. Computation of the PMF 6.6 A catchment rainfall-runoff model was developed for the Lee River catchment for the purpose of generating a PMF (method 3). The flood volume frequency method (method 2), described earlier and which has been used to develop flood hydrographs for return periods up to 10,000 years, is not appropriate for computing the PMF because the PMF has to be derived from the PMP rainstorm. A model was set up

18 17 based on the HEC-HMS software 6, calibrated using a series of recorded storm rainfall and flood hydrograph events for the Lee River at Waterfall Creek, and used to simulate the catchment response to storm rainfall and hence generate the PMF from the PMP. Details of the analysis including the model calibration are provided in the Phase 2 study report PMF hydrographs were generated using the calibrated HEC-HMS model for PMP rainstorm of 12 and 24 hour durations. The peak inflows from both storm durations are comparable, at 1,034m 3 /s for the 12 hour storm and 1,094 m 3 /s for the 24 hour storm, and are nearly three times the 100 year return period peak flow of 375m 3 /s. Climate change allowance 6.8 During the preliminary detailed design, I assessed the implication of projected future climate change on the flood frequency for spillway design. For this analysis, the mid-range emission scenario A1B was adopted for projecting the temperature change to the year The flood estimates which I presented earlier were based on flood frequency analysis of historical flow records. These estimates require to be adjusted for the increase to the design rainfall depth per guidance from the Ministry for the Environment (MfE) 8, which recommends a rainfall depth increase of 8% for each degree of warming. Thus, based on a projected temperature increase for the A1B scenario of 2 C (rise between 1990 and 2090, average of models, averaged over all seasons) for the Tasman-Nelson region, design rainfall depths have been increased by 16%. 6.9 The corresponding change to each design flood hydrograph was computed from the increase in runoff depth resulting from the increased rainfall depth. Table 3 compares the climate changeadjusted design floods with the previous flood estimates applicable for the current climate. The climate-adjusted estimates are between 20% and 25% greater than the corresponding current climate estimates. Exhibit DL09 shows the synthetic design flood hydrographs revised to incorporate climate change. 6 HEC-HMS, Hydrologic Engineering Center - Hydrologic Modelling System, by the US Army Corps of Engineers 7 Waimea Water Augmentation Phase 2 Water Resource Investigations, T&T Ref , December Ministry for the Environment, Preparing for Climate Change A Guide for Local Government in New Zealand, May 2008

19 18 Table 3 Peak inflow at the proposed dam site, with and without climate change adjustment Flood Return Period (ARI see note) No Climate Adjustment Peak Inflow (m 3 /s) With Climate Adjustment Mean annual flood years years years years years years years ,000 years Note: PMF 1094 No change ARI = average recurrence interval, usually expressed in years, is equal to the event return period. AEP = annual exceedance probability, usually expressed as a percentage, equal to reciprocal of the ARI or return period. Flood attenuation effect 6.10 As presented by Mr Croft in his evidence, these hydrographs including the PMF have been used in the design of the dam spillway. The design process involves dynamic simulation of the passage of the flood through the dam s reservoir and spillway, a process known as flood routing. For an ungated spillway (i.e. free overflow spillway) such as that proposed for the Lee Dam, the routed peak outflow from the dam will always be lower than the peak inflow to its reservoir, resulting from temporary flood storage as the reservoir water level rises to a peak This flood attenuation effect is more pronounced for smaller floods. For example, in the PMF and assuming a full reservoir (at full supply level) at the start of the flood, the peak outflow of 1,058m 3 /s is only 3.3% less than the peak PMF inflow of 1094 m 3 /s. In comparison, in the considerably smaller mean annual flood, the peak outflow of 179m 3 /s is 15% less than the corresponding peak inflow of 210 m 3 /s. Furthermore, if the flood occurs at a time when the reservoir is below its full supply level, there would be a larger volume of flood storage available, and the inflow flood would be attenuated to a greater degree. The flood attenuation afforded by the dam and its reservoir may provide some benefit to downstream communities by lowering the flood peak in the downstream river system.

20 19 7. RESERVOIR STORAGE MODELLING AND DROUGHT SECURITY 7.1 The live storage required in the reservoir at the dam is dependent on the following parameters and characteristics: (a) consumptive water demand, which I described in section 3 earlier; (b) (c) (d) (e) environmental base flows for maintenance of in-stream values in the Lee and Wairoa/Waimea rivers, which I outlined in section 3 earlier; inter-annual flow variability at the dam site and in the wider Wairoa River catchment, which is effectively represented by the characteristics of the long-term Wairoa flow record at Gorge / Irvines, as outlined in section 5 earlier; system behaviour, which revolves around the catchment characteristics, its drainage pattern and rainfall-runoff response, and the river-aquifer interaction, which I outlined in section 4 earlier; and the level of drought security desired, which I will discuss next. 7.2 A simulation method, which takes into account the parameters and characteristics above, has been used to model the storage behaviour at the proposed dam site over the period of the flow record available for the Wairoa at Irvines. The key to this spreadsheet-based model that operates on a daily time step is the maintenance of a threshold minimum flow at Wairoa Gorge, which varies according to level of demand and natural river flow, and which is computed using the approach I outlined in section 4. This threshold minimum flow ensures that an in-stream flow of at least 1,100l/s is maintained at Appleby Bridge after consumptive water demands are satisfied. 7.3 Predicted shortfalls in the natural river flow at Wairoa Gorge (less the inflow to the reservoir) must be met by controlled dam releases. It is noteworthy that the flow contributed by tributaries between the dam site and Wairoa Gorge represents about 78% of the total natural river flow at Wairoa Gorge. That is, of the 16.2m 3 /s mean flow (or 511 million m 3 per annum on average) at the Wairoa Gorge, some 12.6m 3 /s (or 398 million m 3 per annum on average) is derived from the intervening catchment between the dam site and the Wairoa Gorge. 7.4 Apart from the consumptive demand and the minimum flow requirement at Appleby Bridge, other aspects taken into consideration in modelling of the reservoir storage are maintenance of a minimum residual flow at the toe of the dam of 0.51m 3 /s and net evaporation from the reservoir surface. Net evaporation is a relatively minor component of the reservoir storage water balance. In the model, a repeating annual pattern has been assumed for net evaporation, which

21 20 is based on open water evaporation less direct rainfall on the reservoir surface for a drought year (1982/1983). Drought security 7.5 For a given amount of live storage, the level of drought security provided by the dam and reservoir can be expressed as the ability to meet the unfettered total water demand over the duration of a drought with a particular severity. The severity of this design drought is indicated by its return period; the greater the return period the larger the live storage needed. 7.6 By using a standard approach similar to that applied to estimating floods or low flows, an analysis of the magnitude of the storage fluctuations over time (specifically the minimum level attained in each year of record) produces a relationship between the storage drawdown and the expected recurrence frequency or return period. The live storage required at the dam to meet a particular design drought standard can be determined from such a relationship. 7.7 Exhibit DL10 shows the simulated storage behaviour from 1958 to 2008, from which the magnitude of the storage drawdown in each year of the simulation period is evident - these appear as inverted spikes in the plot. This shows that the greatest need would have been in the 2000/2001 water year where a live storage in the order of 12 million m 3 would have been required. Exhibit DL12 shows the corresponding storage drawdown frequency plot from which the live storage required versus drought return period is determined. Using the 2000/2001 season again as an example, the frequency plot indicates that the 2000/2001 drought had a return period in the order of 65 years. Table 4 summarises the storage requirements from the frequency distribution. Table 4 Required storage capacity versus drought return period Drought Return Period (years) Note: 1 Required Capacity for Lee River Dam at Chainage Live Storage (million m 3 ) 1 Total Storage (million m 3 ) Total storage includes a nominal 1.0 million m 3 allowance for dead storage and long term sediment infill. 7.8 There is an important and fundamental difference in the way the severity of a drought is defined for a river system which has a

22 21 regulated dam storage and for one without (i.e. a run-of-river system). To elaborate: when required, stored water is released from the dam s reservoir to supplement natural river flows according to downstream requirements, typically under low flow conditions. In general, the highest flow releases occur when periods of high demand coincide with very low natural flows. 7.9 While the maximum rate of release is related to the magnitude of this shortfall on an instantaneous or daily basis, the lowest level to which storage in the reservoir is drawn down depends on the sum of all the preceding releases made. That is, the storage drawdown is a reflection of the accumulated shortfall over time. Thus, for a storage reservoir, the critical situation is one in which the total volume of shortfall over an entire season (or longer if the dam were not full at the start of the season) is a maximum. The magnitude of any single shortlived shortfall episode or river low flow event rarely governs the storage requirement For a run-of-river system, the return period of a drought event is typically determined from an analysis of short-term low flow events, such as the instantaneous low flow or the mean 7-day low flow. So, what may be a significant drought event in a run-of-river system may not necessarily have the same level of significance when there is a storage reservoir because of the different timeframes being considered As noted in paragraph 3.4 earlier, WWAC requested that the 60 year return period drought standard from Phase 1 be retained for Phase 2 initially and be reviewed after Phase 2 modelling results became available. Phase 1 studies had shown that a live storage capacity of 12.0 million m 3 would be required to negotiate a 60 year return period drought The current analysis indicates that for the same 60 year return period drought standard, a marginally lower (3% lower) live storage of 11.6 million m 3 would be sufficient. The analysis also showed that there was negligible difference in storage requirements whether the dam was located at the original (Phase 1) dam site below Anslow Creek or at the now proposed dam site above Anslow Creek. Adding a nominal 1.0 million m 3 allowance for long-term sediment infill and dead storage (see next) gives a total required storage for the proposed dam site of 12.6 million m 3. For feasibility and preliminary detailed design of the dam, this has been rounded up to 13 million m 3, which provides a 65 year return period drought security in approximate terms (leaving aside any variations resulting from the effects of climate change). Reservoir sedimentation 7.13 In regard to the long-term sediment accumulation in the reservoir, a nominal allowance of 1 million m 3 was made for sediment and dead

23 22 storage in the reservoir during the Phase 1 study. Subsequently, a more detailed assessment was completed by Hicks 9 in 2009, which included monitoring of water turbidity and suspended sediment concentration in the Lee River. This study indicated a suspended sediment yield of about 45 tonnes/km 2 /year for the Lee River, which corresponds with about 3,500 tonnes/year at the dam site. The total sediment load, assuming that the bed load at the dam site is 50% of the suspended load (no direct estimate of the bed load is available), is approximately 5,200 tonnes/year. Assuming that all of the bed load and suspended load is retained in the reservoir, which is slightly conservative as a small proportion of the suspended load will be discharged past the dam, the annual sediment infill rate is about 3,500m 3 /year based on an average in-situ dry density of 1.5 tonnes/m 3. Over a 100-year period, the total accumulation would be approximately 350,000m 3, equal to 35% of the nominal allowance made This modest rate of sediment accumulation relative to the reservoir storage capacity (about 3,500m 3 /year versus approximately 13 million m 3 ) means that it will be difficult to accurately determine the rate of sediment infill from repeated bathymetric surveys of the reservoir area, unless the surveys are spaced far apart in time to allow sediment to build up. Nevertheless, an accurate baseline survey is required prior to filling of the reservoir and commissioning of the dam. As part of feasibility and detailed design investigations, a LiDAR survey of the reservoir area was completed, and information from this survey was used to develop an accurate water level versus storage capacity relationship over the operating range of the dam. This LiDAR survey is considered to provide an accurate baseline survey against which future surveys may be referenced to estimate the amount of accumulated sediment Full bathymetric resurveys every 10 years seem appropriate given the relatively low rate of sediment infill. In between resurveys, if necessary, a limited aerial or LiDAR survey of the delta build up at the entrance to the reservoir at a time when the reservoir is drawn down (in order to expose the delta), at five yearly intervals, would be appropriate to monitor the accumulation of the coarser sediments (sand and gravel) In terms of the effects of sediment retention at the dam on downstream river morphology, the removal of gravel supply to the lower river is not expected to have a significant effect in view of the relatively small amount of gravel supplied by the Lee River above the dam site compared with the remainder of the Waimea catchment. To 9 Hicks, D.M Analysis of Suspended Sediment Data from Upper Lee River, Nelson. NIWA Client Report: CHC , November 2009

24 23 illustrate the relativity, Hicks (2011) 10 estimated a suspended sediment yield of 62,000 tonnes/year for the Wairoa River at Gorge. No estimate of the bed load is available. However, assuming that the bed load is roughly 25% of the suspended load at the Wairoa Gorge, a gravel supply rate of about 15,500 tonnes/year is indicated, which is about nine times that at the dam site The Wairoa River becomes the Waimea River below the former s confluence with the Wa-iti River, and a further substantial gravel supply from the Wai-iti River (catchment area approximately 290km 2, representing 38% of the total Waimea River catchment is expected to contribute to the overall gravel supply in the Waimea River. Thus, the bed load trapped in the reservoir corresponds with an even smaller reduction in gravel supply to the Waimea River. 8. PRELIMINARY OPERATING REGIME 8.1 Exhibit DL13 shows the reservoir volume versus water level curve developed for the proposed Waimea Community Dam. For a gross storage capacity of 13 million m 3, the storage-elevation curve indicates a full supply level (or normal top water level, NTWL) of RL 197.2m. The previous Exhibit DL10 showed a time-series plot of the simulated storage behaviour at the dam in terms of volume changes from 1958 to Exhibit DL11 shows the corresponding plot of reservoir level behaviour based on a full supply level at the dam of RL 197.2m. 8.2 Exhibit DL14, which is a storage drawdown duration curve, provides an indication of the proportion of time the reservoir would be full and the proportion of time for which the reservoir is above or below a particular level. In effect, this plot is a condensed form of the timeseries data contained in Exhibit DL11, and shows that the reservoir would be virtually full about 83% of the time, and within 1m of full about 90% of the time on long-term average assuming fully allocated supply. 8.3 Exhibit DL15 compares the simulated river flows immediately below the proposed dam site before and after dam implementation for the sample period from 1 July 1981 to 30 June This period was chosen as it reflects both a drought year with a return period of about 33 years (1982/1983) and a more typical year (1981/1982) in terms of flows. Note that the pre-dam flows are represented by the reservoir inflows. Exhibit DL16 compares the flows in the Wairoa River at Irvines before and after implementation of the Lee Dam for the same period. 8.4 As can be seen in Exhibit DL15, the reservoir inflows or natural flows (blue) match the dam outflows (pink) for the majority of the time (i.e. 10 Hicks D.M., Shankar U., McKerchar A.I., Basher L., Lynn I., Page M. and Jessen M. (2011). Suspended sediment yields from New Zealand Rivers. Journal of Hydrology, New Zealand. Volume 50, No 1, pp

25 24 the pink line plots over the blue line). This response occurs when the reservoir is full or nearly full, typically between June and November inclusive each year. There would be only minor attenuation in the flood outflow under such circumstances. 8.5 Periods of flow augmentation provided by the dam are indicated by the dam outflow plotting higher than the reservoir inflow. In 1982, this occurs between late January and early April, while in the 1983 drought year, flow augmentation was provided from early November 1982 to mid-april Reservoir refilling is indicated by periods where the reservoir inflow plots higher than the dam outflow. A clear example of this is seen in mid-january 1983 where a fresh, peaking at about 10,000l/s, is captured entirely to reservoir storage. 8.6 A similar interpretation can be drawn from Exhibit DL16 on the effect of flow augmentation in the lower Wairoa River. That is, flows at Irvines before and after dam implementation are almost identical most of the time, except over summer low flow periods during which the flow augmentation can be clearly seen. However, there is a notable difference between Irvines and the dam site in terms of flow changes. That is, the impact of the reservoir refilling is far less obvious at Irvines. For example, the fresh that occurred in mid-january 1983 and the series of smaller freshes that preceded it are mostly preserved in the simulated flow record for Irvines, albeit with a slight reduction in the peak flows (15% or so less). This is not unexpected and is attributed to the natural inflows from the tributaries below the dam continuing to contribute to the overall river flow. At the dam site, these freshes were absorbed entirely into the reservoir. 8.7 Table 5 shows the predicted changes in the monthly mean river flows at the dam site and at Wairoa at Irvines resulting from operation of the proposed dam based on supplying the full water demand. The tabulated flows are monthly flows averaged over the simulation period from 1958 to The long-term average change in monthly mean flows are relatively small, peaking at about +9% for the month of February (gain in the outflow) and at about -4% for the month of April (loss in the outflow). Table 5 Predicted change in mean monthly river flow from dam operation 1 ( ) Month Dam inflow (l/s) Lee dam site Dam outflow (l/s) Change (l/s) No dam (l/s) Wairoa at Irvines With dam (l/s) Change (l/s) January ,209 12, February March ,403 11, April ,532 15, May ,317 15,

26 25 Month Dam inflow (l/s) Lee dam site Dam outflow (l/s) Change (l/s) No dam (l/s) Wairoa at Irvines With dam (l/s) Change (l/s) June ,522 18, July ,403 19, August ,690 18,687-3 September ,064 21, October ,808 20, November ,023 17, December ,736 14, Assuming no hydropower operation Drought management 8.8 The analysis of drought storage and the preliminary operating regime I described earlier have been based on meeting the full unrestricted abstractive demand. In some years, supplying the full demand would result in a deep drawdown of the storage, such as would have occurred in 1973, 1983 and 2001 if the dam had been in place at the time, as can be seen in Exhibits DL10 and DL11. The modelling shows that the maximum simulated drawdown of million m 3 would have occurred on 6 May 2001, and the return period of this drought event is estimated to be about 65 years. 8.9 However, in practice, it would be highly unusual and also imprudent, depending on the time of year, to continue to operate at full unrestricted supply if the reservoir were already severely drawn down and close to empty. During the operational phase of the project, I envisage that management of the reservoir and dam releases will likely be guided by a real-time operational model of the reservoir, which would determine the optimal water allocation from storage to meet downstream needs while safeguarding the ability for continued supply from storage through critical periods if a major drought were to eventuate Integral in such an operating system would be a drought management plan, which would be initiated if and when the reservoir level were drawn below particular threshold levels. In relation to this, I note that the TRMP Table 1A includes a trigger for consultation at 2.7 million cubic metres, and a trigger for first step rationing at 2 million cubic metres. This will be directed at ensuring that minimum flows in the TRMP continue to be met in significant drought years. Restrictions on abstractive take would be advised to downstream users and applied, depending on the reservoir level, the time of year and the overall level of abstractive demand at the time. It should be noted that the reservoir storage capacity has been assessed assuming a 100-year demand forecast for Tasman District supply and a possible future regional demand both of which may take some time to be realised.

27 The effects, and differences compared with the modelled results I showed earlier, of implementing such a drought management plan, would be as follows: (a) (b) (c) (d) At full uptake, it would be unlikely that a major drought event such as occurred in 1973, 1983 or 2001 would be negotiated without the dam operator imposing any precautionary restrictions on abstractive demands at some point. Restrictions would be staged, and any shortfall in supply as a result of restrictions would be forecastable to an extent and would typically occur relatively late in the growing season. Therefore, depending on nature of the water use, irrigators should be able to manage around the shortfall without incurring significant production losses. It also means that it would be possible to negotiate a more severe drought than the design event (which has a nominal 65 year return period) with modest to moderate restrictions. For significant drought events, the maximum storage drawdown and thus lowest reservoir level reached would be less extreme than indicated by the simulation results (refer Exhibits DL10 and DL11). For example, the minimum reservoir level in the 2001 drought would be higher than the approximately RL 167m shown in Exhibit DL11 if a drought management plan were implemented in the operating system for the reservoir. Hydropower Add-On 8.12 As Mr Croft describes in his evidence, provision has been made for hydropower generation as a secondary function of the storage dam. Generation is treated as an incidental by-product of controlled flow releases to meet other downstream needs. A preliminary optimisation was completed to determine the preferred hydropower add-on arrangements, particularly the size and type of the power plant and the operational storage requirements for the power plant The preferred hydropower add-on comprised: (a) twin below-ground Francis turbines, with total flow capacity of 3.3m 3 /s, comprising 1.1m 3 /s plus 2.2m 3 /s turbine and generator units; and (b) a modest buffering storage of 100,000m 3 comprising the top 0.16m of the reservoir operating range, to enable capture and diversion to the hydroelectric turbines a proportion of the inflow that would otherwise be spilled when the reservoir is close to its full supply level A buffering storage nominally of 100,000 m 3 for operation of the hydropower station is proposed to be set aside within the 13 million m 3 gross storage capacity of the dam s reservoir. No additional storage will be required to operate the hydropower station in addition to the

28 27 release of water to meet downstream flow requirements (i.e. no changes to the design of the dam or spillway are required). However, when the reservoir is close to full, operation of the power station could require increased fluctuation of the reservoir within a 0.16m range, rather than retaining it at a relatively constant level Exhibit DL17 provides a comparison of the simulated reservoir level behaviour from the with hydro versus without hydro options for the sample period 1 July 1981 to 30 June Exhibit DL18 compares the simulated dam outflows for the with hydro and without hydro options over the same period. Flow duration curves of the dam outflow for both options for the full simulation period 1958 to 2008 are compared in Exhibit DL All these plots show that with hydro generation, the outflow pattern from the dam is very similar to that without generation, especially during periods of flow augmentation. There are subtle differences in the dam discharge regime when the reservoir is full or close to being full as a result of storage regulation to maximise flow through the hydro turbines. Evidence of such operation can be seen as horizontal steps at 3.3m 3 /s and 2.2m 3 /s in the with hydro power flow duration curve in Exhibit DL19, which corresponds to the modelled installed capacity of the turbines (i.e. main unit with capacity of 2.2m 3 /s and a smaller unit with capacity of 1.1m 3 /s). Potential for peaking operation 8.17 It has been assumed that any hydropower station would operate as a run-of-river system whereby the amount of generation would be governed by the downstream flow augmentation needs on a daily basis. Nevertheless, there is a potential for the hydropower station to be operated as a peaking station, i.e. to respond in a dynamic way to the intra-day fluctuations in the electricity market price by using the available buffering storage to temporally re-distribute power generation to the higher price periods each day The assessment of potential peaking operation was confined to the winter months, which are the months with little or no irrigation demand and relatively higher flows, namely May to September (noting that the irrigation season extends into the month of April in some years). The summer months were specifically excluded from daily peaking consideration because of: (a) (b) concerns that the resulting diurnal flow variations could result in intra-daily minimum flows significantly lower than that required for protection of in-stream habitat, especially during coincident high demand - low flow periods, which could potentially trigger the need for additional releases from the dam; and potential effects that the cyclical flow variations could have on the groundwater recharge response, plus other possible

29 28 interference to management of the river flow and irrigation operations While the preliminary optimisation of plant output indicated a turbine capacity of 3.3m 3 /s based on economic considerations, further refinement is very unlikely to recommend a turbine capacity greater than the flushing flow of 5m 3 /s. Given the required minimum flow release of 0.51m 3 /s, the maximum flow excursion under peaking operation would be 2.8m 3 /s based on a peak discharge of 3.3m 3 /s, but could be greater if larger plant were installed Based on monitoring data from the Lee at Waterfall Creek gauge, by increasing the flow from a base residual flow of 0.51m 3 /s to the peak flow of 3.3m 3 /s, there will be a modest increase in the flow depth of about 0.2m. However, the average flow velocity increases from about 0.1m/s to about 0.35m/s, which is not insignificant. It should be noted that, for any given step change in the discharge, the corresponding changes in the flow depth and velocity will vary for each location along the river. Notwithstanding, the scope of such changes are not anticipated to create a significant additional hazard for recreational users However, rapid and frequent flow changes of this magnitude have the potential to affect downstream flows and flow variability to a greater extent than has been modelled. I note that Dr Young has recommended a condition which requires a fluctuating flow analysis to be conducted to guide the maximum level of hydro-peaking within a day that is permitted. 9. SUBMISSIONS HYDROLOGICAL ASPECTS 9.1 I have been provided with a copy of the submissions received on the Lee Dam resource consent applications. Relevant to my area of expertise or scope on hydrological matters within this application I address the following issues and concerns raised by the submitters: (a) (b) (c) (d) No proven water demand and thus need for dam; Proposed dam is too large; Various impacts from an altered flow regime, including from hydropower operation, geomorphological changes, increased flooding and erosion, and that the dam would not prevent an extreme low flow event; and Climate change not taken into account. 9.2 I set out in Table 6 the names of the submitters against each of the issues above. I note that The Friends of Nelson Haven and Tasman Bay Inc. and Patricia Ann Palmer were the only two submitters that raised issue 9.1(d), that climate change was not properly taken into account in the hydrology.

30 29 Table 6 Hydrological Issues Raised by Submitters Submitter No. Notes: Submitter (a) No proven water demand Issue (b) Dam too large (c) Altered flow regime 4 Bruce Lester MacDonald 1 9 James Daniel Challies 19 Catherine Gale Hughson 2 20 Robert and Patricia Todd 30 John Martin Todd 38 The Friends of Nelson Haven and Tasman Bay Inc Waimea Irrigators and Water Users 4 41 J D & L M Rust Ltd 42 F J & E A O Connor 44 David Gavin Vanstone 48 Mary Ellen O Connor 50 R B & M J Wagner 5 52 Redwood Valley Irrigators 57 Patricia Ann Palmer 5, 6 58 Jonathan Norman Harrey 59 Matthew Anthony Kenneth Stuart 7 60 David Leigh Irvine 7 61 Stanley Mitchell Irvine 7 64 Kristopher Charles Cumpstone 65 Ian Willetts 7 67 Pearl Creek Farm Partnership 68 Neudorf Investments Ltd 82 Teresa Mary O Connor 83 Ian Paterson 87 Margaret Mary O Connor 88 William Hill 89 Lars Jensen 92 Brownlow John Westbrooke 93 Maxwell Clarke & Shona McBride Bruce Lester MacDonald suggests that the dam may worsen flooding. Catherine Hughson is concerned with impacts of a large dam on river flow and sediment transport. The Friends of Nelson Haven and Tasman Bay Inc. raise concerns regarding hydropower operation, increased erosion, geomorphological impacts, and climate change. Waimea Irrigators and Water Users suggests smaller dam closer to the Wairoa Gorge be considered. RB & MJ Wagner & Patricia Palmer are concerned that the project won t prevent a 60 year drought. Patricia Palmer s other concerns are that the initial reservoir filling should not commence in the month of February, and the inconsistency between the predicted increased flooding from climate change and the assumptions made in predicting the hydrological effects of the project. These submitters, who have interests located upstream from the dam wall, are concerned about effects from reservoir operation on their land, e.g. flooding from rainfall, earthquake and landslides.

31 With regard to the generic concern that there is no proven demand for water from the project, I summarised earlier, in section 3 of this statement, the assumptions that were made and the approach taken for assessing the potential future consumptive water demand in the Waimea Plains. My role in this process was to coordinate the review of the future consumptive and in-stream water needs to be met from reservoir storage, and to format these needs so that they were suitable for input to a computer model of the reservoir storage and river-aquifer system. 9.4 It should be noted that decisions on several of the fundamental parameters that govern the future system water demand, such as the total area to be irrigated, irrigated land use, future urban and industrial water needs, and the level of environmental flow protection desired for the lower Waimea River, were contributed by others, primarily WWAC with input from others including its technical advisors and local authorities responsible for community water supply. 9.5 However, it is my opinion that the Wairoa/Waimea River and aquifer system will clearly not be able to sustain the specified future in-stream needs and water demands in a dry year. Indeed, even under current water allocations, which are considerably less than the projected future water demands, the lower Waimea River has been observed to stop flowing in a dry summer (e.g. in 2000/2001), as described by Mr King in his evidence. Modelling of the river-aquifer interaction by GNS Science 11 has replicated this drying effect in the Waimea River at Appleby Bridge that was observed over a period of two to three weeks in February/March 2001 under the actual historical water abstraction rates. By applying the projected future consumptive takes, GNS Science s modelling showed that the Waimea River would be constantly dry for a much longer period, i.e. from late January to early April 2001, if no flow augmentation from a storage dam in the upper catchment were provided. 9.6 The TRMP stipulates a basic minimum flow in the Waimea River of 1100l/s on the premise that the Lee Dam is constructed 12, and a minimum flow of 800l/s if the dam does not proceed 13. With regard to the no dam case, it is interesting to note that modelling of the 2001 drought by GNS Science showed that under actual historical abstraction rates (no restrictions), the flow at Appleby Bridge would have been continuously below 800l/s for a period of about 62 days from 29 January 2001, and for long periods in April In the 1983 drought, under actual historical abstraction rates, the flow at Appleby Bridge would have been continuously below 800l/s for about 38 days from 13 February These instances illustrate the severity of restrictions that existing abstractive users are likely to face under the 11 GNS Science (2009). Waimea water augmentation project feasibility study: phase 2 modelling report, November Tasman Resource Management Plan, Part V, Chapter 31, Table 1A. 13 Tasman Resource Management Plan, Part V, Chapter 31, Table 1C.

32 31 proposed minimum flow rules (leaving aside future climate change effects) if the dam does not proceed. 9.7 With regard to the other common concern that the dam is too high or its reservoir too large, I have explained earlier, via section 7 of this statement, the approach I used to compute the storage capacity needed at the dam to meet the projected future water demands and instream flow requirements. For a given set of water demand parameters, the storage capacity and thus height of dam needed is dependent on the level of drought security desired, as shown by the modelling results in Table 4 earlier. 9.8 The proposed reservoir with a gross storage capacity of 13 million m 3 would appear to provide a relatively high standard of drought security, i.e. up to about a 65-year return period drought, based on analysis of the historical climate and river flow records from 1958 to However, as noted in paragraph 3.4 earlier, one reason for adopting a high drought standard is as a hedge against future climate change. In this regard, the MfE 14 warns of more frequent and/or intense droughts in eastern parts of the country, which includes parts of the Tasman District (e.g. Clark et al 15 ). Reduced water availability coupled with increased demand would lead to decreased security of water supply, and this would also apply to a storage based system such as that proposed. Therefore, future climate change is anticipated to progressively diminish the level of drought security provided by the project. Without the dam, existing abstractive users will face increasingly severe restrictions on take. 9.9 Nevertheless, even under historical hydrological conditions (let alone potentially drier future conditions), an analysis of the modelled dam outflows shows that flows in the Wairoa/Waimea Rivers would have required augmentation in 70% of years. In about 25% of the years modelled, flow augmentation would have been required for 8 weeks or longer, and for three particularly dry years (i.e. 1972/1973, 1982/1983 and 2000/200) consistent flow augmentation would have been needed over much of the irrigation season, i.e. 14 weeks or longer. Despite that, dam storage is never fully depleted and environmental flows are able maintained at the base of the dam and in the lower Waimea River at all times in all the years modelled Given the above considerations, it is my view that the reservoir capacity and thus dam height remains appropriate for its intended flow augmentation purpose under current and anticipated future climate conditions. 14 Ministry for the Environment (2008). Climate Change Effects and Impacts Assessment: A Guidance Manual for Local Government in New Zealand, 2 nd Edition, May Refer to Table Clark A., Mullan B., Porteous A. (2011). Scenarios of Regional Drought under Climate Change. NIWA Project SLDR093. Report prepared for Ministry of Agriculture and Forestry, June 2011.

33 Bruce Lester MacDonald (submitter #4) suggests that the dam may worsen flooding. However, as I noted in paragraphs 6.10 and 6.11 earlier, the dam and reservoir will in fact provide some flood attenuation, particularly, if the flood occurred when the reservoir is drawn down below its full supply level. This flood detention effect, while incidental to the operation of the project, could provide some downstream benefit by lowering the flood peak below the dam. The attenuated floods would also tend to have reduced erosive power Catherine Gale Hughson (submitter #19) is generally concerned with the environmental impacts of a large dam, including the effects on river flow and sediment transport processes. The Friends of Nelson Haven and Tasman Bay Inc. (submitter #38) also raises a concern about geomorphological impacts from changes to the flow regime. In relation to the effects on river flow, I described in paragraphs 8.1 to 8.7 earlier the likely changes to the flow regime of the Lee River immediately below the dam and in the Wairoa River at Irvines resulting from operation of the dam and reservoir. In his evidence Dr Young presents the potential effects on water quality and aquatic ecology corresponding with these changes In terms of the effects of the dam on sediment transport processes and river morphology, I described in paragraphs 7.13 to 7.17 the approximate quantity of sediment potentially trapped in the reservoir and the proportional reduction in the gravel supply to the Waimea River as a result. Considering the relatively small amount of gravel sourced from the Lee River above the dam site compared with the remainder of the Waimea catchment, I concluded that the reduction in gravel supply should not have a significant effect R B & M J Wagner (submitter #50) and Patricia Ann Palmer (submitter #57) are concerned that the project may not prevent a 1 in 60-year low flow event in the river. In particular, Ms Palmer quotes from the AEE (T&T, July 2014) that in an approximate 1 in 60-year return period drought, no water would be available for release downstream. In response to this concern, I refer to paragraphs 8.8 to 8.11 of this statement, in which I describe a Drought Management Plan as part of the potential operating system for the reservoir that would allow flow augmentation to be sustained through droughts more severe than the 1 in 60-year return period drought To the extent required by the relevant provisions of the TRMP, if maintenance of environmental flows were prioritised above the abstractive demand, the project should be able to meet environmental flow targets at Appleby Bridge and at the base of the dam even under extreme drought conditions while retaining a relatively high level of service to abstractive users through this drought management plan Patricia Ann Palmer (submitter #57) expressed other concerns in her submission, including that the initial reservoir filling should not commence in the month of February, and that the predicted increased

34 33 flooding from climate change was inconsistent with the assumptions made in predicting the hydrological effects of the project. With regard to the former, there is no specific intent to initiate filling of the reservoir in February. Filling would commence at an appropriate time towards the end of the construction programme, itself (the programme) subject to revision and confirmation as part of the project procurement process. The low mean flow for the month of February (about 2m 3 /s) was quoted purely to illustrate how long it would take for the reservoir height to reach the minimum operating level (of RL 166.5m) once filling commenced under such hydrological conditions. By contrast, if the reservoir inflow were equivalent to the mean flow over the months of September and October (about 4.7m 3 /s), then it would take just under three days for the reservoir to reach the minimum operating level The Friends of Nelson Haven and Tasman Bay Inc. and Ms Palmer are concerned that climate change effects have not been taken into account properly. In response to this concern, I refer to paragraphs 6.8 and 6.9 in which I described the approach that was taken, based on guidance issued by MfE 16, to adjust the design floods for the dam to allow for future climate change. These adjustments, of up to a 25% increase in the peak flood flow, are precautionary and apply to large flood events A similar specific adjustment cannot be readily made in the long-term simulation of the reservoir operation, which has been based on flow records synthesised for the Lee River from the actual flow record for the Wairoa River at Irvines from 1958 to The modelled reservoir behaviour has been used to determine the likely overall effects on the flow regime downstream of the dam. Notwithstanding, the potential effects of future climate change on the water resources of the Lee and wider Waimea catchment have been recognised throughout the studies for the water augmentation project, as noted for example in paragraph 3.3(g) earlier. In relation to droughts, a more recent study by NIWA 17 indicates that in New Zealand, parts of the Tasman District, specifically the Waimea and Motueka valleys, would likely experience greater than a 10% increase in the percentage of time spent in drought conditions by 2080 compared with 1990 levels While no specific adjustment to the water availability has been made, a deliberately conservative (conservative as assessed against industry norms, and when based on historical climatic conditions) drought standard was selected on the premise that droughts will increase in 16 Ministry for the Environment (2008). Climate Change Effects and Impacts Assessment: A Guidance Manual for Local Government in New Zealand, 2nd Edition, May Refer to Table Clark A., Mullan B., Porteous A. (2011). Scenarios of Regional Drought under Climate Change. NIWA Project SLDR093. Report prepared for Ministry of Agriculture and Forestry, June 2011.

35 34 frequency, duration and intensity with future climate change. With the passing of time, these changes will lower the drought resilience provided by the project to a more modest but still acceptable level. Indeed, the project will remain an effective buffer against future climate change by sustaining a reliable supply to meet downstream water needs against a backdrop of increased and more variable seasonal moisture deficits The Friends of Nelson Haven and Tasman Bay is also concerned about hydropower operation, which it says could require a different operating regime. As noted earlier in paragraph 8.12, any hydropower generation, if and when a power station is built at the dam, would be an incidental by-product of controlled flow releases to meet other downstream needs. Generation would not dictate the overall pattern of discharges on a seasonal basis. In paragraphs 8.13 to 8.16 I describe the differences in the operating regime with a potential addon hydropower station, and conclude that the outflow pattern from the dam would be very similar compared with the case without generation, especially during periods of flow augmentation However, as noted in paragraphs 8.17 to 8.19, there is a potential for the hydropower station to operate as a peaking station, but only over the winter months, which would have potential to affect downstream flow variability to a greater extent. Even then, preliminary assessments at the time indicated that the additional value of peaking was likely to be modest. Dr Young has recommended a condition which requires a fluctuating flow analysis to be conducted to guide the maximum level of hydro-peaking within a day that is permitted Waimea Irrigators and Water Users Ltd (submitter #39) suggests that a smaller dam closer to the Wairoa Gorge with piped supply to downstream users should be considered as an alternative to the proposed dam, citing that run-of-river type schemes are uncommon. In my experience, while it is unusual for a shallow unconfined aquifer to be an integral part of the water delivery system, it is common practice to use the natural river channel as part of the water conveyance system, especially where the storage dam is located far from its service areas. While a piped system is more controllable and leak proof, it is also considerably more expensive, particularly if the conveyance distance is long and the delivery flow rates are large, as in the case of the Lee Dam With regard to alternative dam sites, from a hydrological perspective, the Wairoa River at the Wairoa Gorge is a significantly larger river than the Lee River (flood flows about four times as large and catchment area about six times as large), and thus the scale of the spillway and construction diversion works for a dam located near the gorge would be significantly greater and more costly Several submitters (#59, #60, #61 and #65) who own commercial forestry located adjacent to and upstream from the dam wall are

36 35 concerned about effects from the operation of the reservoir on their land, including flooding from rainfall, earthquake and landslides. These potential effects are related to geotechnical and seismic aspects and the design of the spillway. Mr Croft and Mr Foley address these concerns in their evidence. 10. DAM BREAK ANALYSIS Purpose of Dam Break Hazard Assessment 10.1 As stated earlier, I was responsible for technical management of the dam break hazard assessment for the Lee Dam. I carried out certain elements of the assessment and oversaw elements of the assessment undertaken by other T&T personnel. The parts of the assessment I completed include: (a) (b) (c) selection of the dam breach parameters and failure scenarios; verification of the dam break outflow hydrograph; and determination of the proposed dam s PIC in accordance with the Building (Dam Safety) Regulations 2008 within the Building Act I have visited the dam site and the general downstream area potentially affected by dam break. I oversaw the hydraulic modelling work undertaken by my colleague Mr Jon Rix to determine the inundation extents and potential damages from dam break flooding As a preface, I will state the purpose and significance of carrying out a dam break analysis for either a proposed or existing water retaining structure. Dam break analyses are undertaken within the dam industry primarily to assess the potential harm to downstream communities from a dam break. In the case of a proposed dam, the hazard potential guides the selection of appropriate standards for design, construction, operation and maintenance of the dam; the higher the potential hazard, the more stringent the applicable standard. The analysis is hypothetical and entirely divorced from the chances of the dam break ever occurring. Mr Croft, the dam designer, will present evidence on the dam design criteria and approach based on the PIC rating of the proposed Lee Dam Apart from determining the PIC rating of the dam, certain information generated from a dam break study, such as a map delineating the potential extent of inundation from an unlikely dam break, will normally be required in an Emergency Action Plan (EAP) for the dam, and typically made available to the local Civil Defence office. The predicted time for the dam break flood wave to reach specific downstream locations provides a helpful indication of the available warning times, and may also be incorporated in the Emergency Action and/or Civil Defence Plans.

37 Before proceeding, I reiterate that the current dam break hazard assessment has not been instigated by any specific concern with the site conditions or any engineering aspect of the proposed dam, but has been undertaken to determine its potential downstream hazard. Dam failure scenarios 10.6 The 53m high Lee Dam will be considered a classifiable large dam under the Building Act An owner of a large classifiable dam is required under the Building (Dam Safety) Regulations 2008 to assess the likely consequences in the event of a dam failure in order to determine a PIC for their dams. These regulations, currently deferred until 1 July 2015 by the Government, in conjunction with the New Zealand Dam Safety Guidelines (NZSOLD 2000), provide guidance for the safe design, construction, operation and management of dams in New Zealand Dam break analyses typically involve two classes of failure scenarios, commonly referred to as a sunny day failure and a rainy day (wet weather) failure. Both types of failures have been examined for the Lee Dam. Modelling of the dam failure generally considers worst-case scenarios For determining the PIC of a dam, an assessment of the incremental damages from dam break is required. Incremental damage is that resulting directly from a dam break event over and above the damage that would occur if the dam did not fail catastrophically. The difference between total and incremental damage is particularly relevant in the case of a failure initiated by an extreme flood. It is clear that a flood approaching the magnitude of the PMF, which is approximately three times the magnitude of the 100 year return period flood in the case of the Lee Dam (refer paragraph 6.7 of this evidence), will cause much damage on its own without the dam failing The incremental damages from a sunny day failure are typically significantly greater than from failure caused by an extreme hydrological event, and this is also the case for the Lee Dam. In addition, there are extenuating circumstances which reduce the incremental damage in a flood-related dam failure, particularly with regard to potential loss-of-life. That is, while there may be little warning of an impending sunny day failure (e.g. from an earthquake rupture), a flood (rainy day) failure occurs in the context of a major hydrological event which may take days to develop with consequently more warning and heightened awareness of potential risk. The high flows in the river during a significant flood would also tend to deter use of the river and its margins for recreational or other purposes Furthermore, as Mr Croft presents in his evidence, the dam has been designed so that sufficient freeboard will be provided to the dam crest to accommodate the inflow from the PMF (i.e. the flood that can be expected from the most severe combination of critical meteorological and hydrological conditions that are reasonably possible in a region).

38 37 Therefore, the probability of a rapid dam failure from overtopping caused by an extreme flood event is effectively nil Based on the above considerations, my opinion is that the PIC of the Lee Dam should be based on the potential downstream hazard identified from a sunny day dam failure Sunny day failure modes include earthquake-induced failures, piping (internal erosion), and the potential for landslide induced waves failure under normal operating conditions. Mr Croft presents evidence on these possible failure mechanisms and the design responses to defend against each potential risk involved. Dam breach parameters For a given failure scenario, a dam break analysis entails the following workflow: (a) (b) (c) (d) (e) Selecting the breach location (or locations, if the embankment is particularly long) and failure mechanism at the dam that would result in the maximum downstream damage typically, the worst-case scenario is for a breach through the tallest part of the dam which would allow the entire reservoir storage to discharge. Estimating parameters for the dam breach, such as the final breach dimensions and geometry and the breach progression rate. Modelling of the rate of outflow (hydrograph) from the breach. Applying this breach outflow hydrograph in a computer hydraulic model to determine the extent of the dam break flood path and its hydraulic characteristics such as the flow depth, direction and velocity. Assessing the likely damage and the population-at-risk caused by the dam break flood To estimate the appropriate breach parameters, I refer to a report by the USBR 18, which provides a comprehensive summary of the methods developed by various researchers for predicting breach parameters for embankment dams. The predictive formulae are empirical to a large extent and developed from world-wide case studies of historical dam failures. Exhibit DL20 shows the breach geometry I assessed for the Lee Dam based on these empirical relationships and topographical features at the dam site Of the several parameters required to define a failure scenario, the parameter which has the most impact on the magnitude of the peak outflow, but which is also subject to a higher level of uncertainty, is the 18 Wahl, T. L Prediction of Embankment Dam Breach Parameters: A Literature Review and Needs Assessment. Water Resources Research Laboratory, Dam Safety Office, U.S. Bureau of Reclamation, Report DSO , July 1998

39 38 breach formation time. The shorter the breach formation time, the higher the peak outflow and therefore the more severe the downstream impacts. The breach formation time was determined from empirical formulae to range from approximately 0.5 hours to 1.5 hours. From this range, three breach durations were chosen for modelling, being 0.5 hours for a fast failure case (worst-case), and 0.9 hours (mid-range) and 1.5 hours (slow failure) Exhibit DL21 shows the discharge hydrographs computed using a HEC-HMS 19 model of the dam and reservoir based on the adopted breach parameters. For the worst-case scenario (0.5 hour failure), the simulated peak outflow from a sunny day failure was approximately 13,600m 3 /s, which compares with a peak discharge of approximately 5,000m 3 /s for the 1.5 hour failure case. All three scenarios were carried through to dynamic hydraulic modelling, which I will describe next, and to the hazard and PIC assessments, to test if the PIC rating was sensitive to the assumed failure duration. Hydraulic modelling of flood wave from dam break The Danish Hydraulic Institute s (DHI) Mike Flood modelling suite was used to represent the river channel and floodplain from the proposed dam site on the Lee River to the mouth of the Waimea River at Rabbit Island in Tasman Bay, a distance of about 27km. The modelling approach combined a 1 dimensional representation (Mike 11) of the river channel and confined steep-sided valley regions with a 2 dimensional representation (Mike 21) of the floodplain downstream from the Wairoa Gorge. This ensured optimal representation of the channel geometry and floodplain topography. A key component of the model is the ground elevation, which was based on LiDAR information provided by Tasman District Council Details of the model build and its output, including boundary conditions, floodplain hydraulic roughness assumptions, and simulation results for the modelled scenarios, are provided in the Phase 2 Feasibility Report 20. The modelled dam break hydrographs from the HEC-HMS model (Exhibit DL21) were used as an upstream inflow boundary in the hydraulic model. Exhibit DL22 provides an overall pictorial summary of the inundation extents for a worst-case sunny day failure corresponding with a 0.5 hour breach formation time Exhibits DL23 and DL24 show the progression of the flow and flood depth hydrographs for the 0.5 hour dam failure case for a number of discrete locations along the river. The flood depth relates to water depth in the river, and therefore does not reflect the water depth in the floodplain. Table 7 provides a description of the river locations for which these hydrographs have been generated. 19 HEC-HMS: Hydrologic Engineering Center Hydrologic Modelling System, U.S. Army Corps of Engineers. 20 Tonkin & Taylor (2009). Lee Valley Storage Dam Engineering Feasibility Report, December Refer to Appendix E.

40 39 Table 7 Model chainages and locations Lee / Wairoa / Waimea River Chainage (m) Location River 0 Lee Dam (Waimea Community Dam) Lee River 2910 Lucy Creek confluence 8220 Fairdale 8970 Upstream extent of Mike 21 model Wairoa River confluence Wairoa River State Highway 6 bridge Wai-iti River confluence Waimea River Coastal Highway Bridge (SH60) The results show that there is minimal attenuation in the flood wave in the first 10km downstream of the dam site. Peak flows in this narrow and confined upper reach are roughly similar to the peak flows at the dam site. By the time the floodwave reaches SH6 near Brightwater the peak flow is significantly lower as a result of flood storage and attenuation on the floodplain. Comparison of the three modelled scenarios indicate that the peak dam break flow adjacent to Brightwater is not significantly affected by the choice of breach formation time The lowest flood water depth occurs at around chainage 16,720m and this is related to the flow breakout from the river channel that occurs upstream. The water depth downstream increases again as flow is returned to the Waimea River via the Wai-iti River. At chainage 23,500m (confluence with Wai-iti River) the peak flow ranges from 2,415m 3 /s, corresponding with the 1.5 hour failure scenario, to 2,590m 3 /s, corresponding with the 0.5 hour failure scenario. This difference of 175m 3 /s (7%) is relatively small. A similar trend is observed for water depth, where the maximum water depth at chainage 23,500m varies by only about 0.17m across the three modelled scenarios. Assessment of potential hazard from dam break I now describe the downstream hazard potential if the proposed dam failed. To put this discussion into proper context, it is essential to draw the distinction between hazard potential, that is, the effects of the dam breach were it to occur, and the risk or probability of the dam breach actually occurring. The risk of failure occurring for a dam engineered, built, maintained and monitored to appropriate standards, as would be the case for the Waimea Community Dam, would be extremely low The hydraulic modelling results show that the dam break flow would first overtop the river banks approximately 5km south-east of Brightwater, near Leedale and Max s Bush. In the area between Leedale and the SH6 Bridge there would be significant break out flows in excess of 3m deep along the true left bank, and to a lesser extent

41 40 along the right bank. The flow velocity at the break out flow along the left bank is likely to be in excess of 4m/s in isolated places for short periods of time. The flood wave would affect eastern and northern extents of Brightwater, as shown in Exhibit DL The Building (Dam Safety) Regulations 2008 necessitates identification of the population at risk, or PAR. The PAR is defined as the number of people likely to be affected by inundation greater than 0.5m in depth. Hydraulic modelling results, such as shown in Exhibit DL22, have been used to determine the extent of inundation with a maximum flooding depth of greater than 0.5m The numbers of properties at risk in each of the three modelled dam break scenarios are summarised in Table 8. As noted earlier, three breach scenarios have been evaluated because of the uncertainty in the breach formation time. Aerial photography and land boundary information has primarily been used to identify buildings that may be flooded as a result of a dam break. The estimated number of residential properties that would be inundated is likely to be an overestimate since it was not possible to ascertain building use from aerial photography in all cases. However, to avoid being overly conservative, the assumption was made that there would be only one residential property per building lot In order to assess the PAR for each scenario, information from Statistics New Zealand has been used to provide an estimate of the average number of people per dwelling. For the Tasman region, the 2006 Census indicates that there are approximately 2.55 persons per occupied dwelling. On this basis, the PAR is between 700 and 800 persons depending on the assumed dam failure duration. Table 8 Properties at Risk from Inundation Location Scenario hr breach progression time Number of flooded residential properties downstream of Wairoa Gorge (>0.5m flood depth) Number of flooded residential properties upstream of Wairoa Gorge (>0.5m flood depth) Scenario hr breach progression time Scenario hr breach progression time Approximately 300 Approximately 290 Approximately 260 (Approximately 2/3 of the flooded properties are located in Brightwater) Additional facilities of interest that would be flooded to greater than 0.5m ( =flooded, x = no flooding, or less than 0.5m): Brightwater School Ellis Street Saint Peter & Paul Catholic Church at Waimea West Road, Richmond Speedway grounds at 122 Lansdowne Road Marginal Marginal X Marginal X X

42 41 Location Scenario hr breach progression time (marginal) Appleby School - 19 Moutere Highway (marginal) Girl Guide regional camp at Paretai, 129 Lee Valley Road Scenario hr breach progression time Scenario hr breach progression time Marginal Marginal X Other potential environmental and economic damages arising from a dam break event include the following: (a) (b) (c) (d) (e) (f) (g) Destruction or damage of some vineyards and orchards located within the inundation area. Livestock losses and loss of topsoil. Damage to road infrastructure including potential damage to the SH6 Bridge. Deposition of silt in downstream areas as the flood recedes derived from the dam embankment material eroded and entrained into the dam breach outflow. Economic loss to the dam owner, including loss of the asset and operating revenue. Damage to existing river protection/training works/stopbanks. Other potential environmental and economic damages arising from a dam break event. Potential Impact Classification of the Lee Dam (PIC) The Building (Dam Safety) Regulations (2008), which becomes operative on 1 July 2015, adopts a classification system that assigns a PIC of High, Medium or Low to all large dams in New Zealand. The PIC is used to determine the appropriate design standards, e.g. for earthquake loading and safe flood passage, as well as the level of rigour that needs to be applied to site investigations, construction, commissioning and on-going maintenance and surveillance. The consequences of failure, specifically the downstream harm and damage potential, are the main determinants for assessing the dam s PIC Table 1 from Schedule 1 of the Regulations is reproduced as Table 9. This shows the Regulation s interpretation of catastrophic, major, moderate and minimal damages. The circled cells of the table shaded in grey indicate my assessment of damages from dam break of the Lee Dam.

43 42 Table 9 Determination of Assessed Damage Level (Table 1 of Schedule 1 of the Building (Dam Safety) regulations 2008) Damage level Catastrophic More than 50 houses destroyed Major Moderate Specified Categories Residential houses 1 Critical or major infrastructure 2 Damage Time to Natural environment restore to operation houses destroyed and a number of houses damaged 1-3 houses destroyed and some damaged Extensive and widespread destruction of and damage to several major infrastructure components Extensive destruction of and damage to more than 1 major infrastructure component Significant damage to at least 1 major infrastructure component Minimal Minor damage Minor damage to major infrastructure components More than 1 year Up to 12 months Up to 3 months Up to 1 week Extensive and widespread damage Heavy damage and costly restoration Significant but recoverable damage Short-term damage Community recovery time Many years Years Months Days to weeks Notes: 1. In relation to residential houses, destroyed means rendered uninhabitable. 2. Critical or major infrastructure includes: a) lifelines (power supply, water supply, gas supply, transportations systems, wastewater treatment, telecommunications (network mains and nodes rather than local connections)); b) emergency facilities e.g. hospitals, police, fire services; c) large industrial, commercial, or community facilities, the loss of which would have a significant impact on the community; and d) the dam, if the service the dam provides is critical to the community and that service cannot be provided by alternative means. 3. The estimated time required to repair the damage sufficiently to return the critical or major infrastructure to normal operation That is, excluding the economic losses suffered by the dam owner, the following damage descriptors are indicated: (a) (b) (c) (d) Catastrophic for the number of residential houses that would be destroyed. Major for damage to critical or major infrastructure and the time to restore to operation. Major for Natural Environment damage. Major for community recovery time (years) Table 2 from Schedule 1 of the Regulations, which shows the determination of the PIC for a dam, is reproduced as Table 10. The cells of the table shaded in grey indicate my assessment of the PIC for the Waimea Community Dam. Because the PAR (700 to 800) is significantly greater than 100, and the assessed damage level is either Major or Catastrophic it is clear that the appropriate classification for the dam is High PIC. The assessment of the High PIC rating is not sensitive to the uncertainty in the selection of the dam breach formation time nor to the precise assessed damage level.

44 43 Table 10 Determination of Dam Classification (Table 2 of Schedule 1 of the Building (Dam Safety) regulations 2008) Assessed damage level Population at risk (PAR) Catastrophic High PIC High PIC High PIC High PIC Major Medium PIC Med/High PIC (see note 4) Moderate Low PIC Low/Med/High PIC (see notes 3 and 4) Minimal Low PIC Low/Med/High PIC (see notes 1, 3 and 4) High PIC Med/High PIC (see note 4) Low/Med/High PIC (see notes 1, 3 and 4) High PIC Med/High PIC (see notes 2 and 4) Low/Med/High PIC (see notes 1, 3 and 4) Notes: 1. With a PAR of 5 or more people, it is unlikely that the potential impact will be low 2. With a PAR of more than 100 people, it is unlikely that the potential impact will be medium 3. Use a medium classification if it is highly likely that a life will be lost 4. Use a high classification if it is highly likely that 2 or more lives will be lost This is the highest classification in the New Zealand Dam Safety Scheme, corresponding with the highest design standards for the dam (e.g. for earthquake loading and safe flood passage) and the highest level of rigour for site investigations, construction, commissioning and on-going maintenance and surveillance. These high standards, which are described by Mr Croft in his evidence, are required to ensure that the probability of failure will indeed be extremely low commensurate with the degree to which the potential impact of dam failure is high Nevertheless, as is standard practice in the industry, and also a requirement of the Dam Safety Scheme for all Medium and High PIC dams, an EAP will be prepared for the dam in accordance with the requirements set out in the New Zealand Dam Safety Guidelines (NZSOLD 2000). The EAP will describe the actions to be taken by the dam owner and operators and relevant agencies such as Civil Defence, Police and territorial local authorities, if there is an imminent threat to the safety of the dam. A draft EAP for the Waimea Community Dam is included as Appendix F in the Assessment of Environmental Effects (AEE, T&T, July 2014) accompanying the application.

45 SUBMISSIONS DAM BREAK HAZARD 11.1 I have been provided with a copy of the submissions received on the Lee Dam resource consent applications. A number of submitters have expressed concern regarding the possibility and consequences of dam break, especially in the context of the seismic risk at the dam site, including questioning the selection of the site close to faults. The relevant submissions are summarised in Table 11. Table 11 Issues on Dam Safety Raised by Submitters Submitter No. Submitter (a) Proximity to faults, dam failure from earthquake Issue (b) Brightwater, etc. at risk from dam failure 7 Cecilia Higgins 8 Susan Mary Challies 1 17 Gordon Hugh Challies 19 Catherin Gale Hughson 20 Robert & Patricia Todd 25 F & C Bacon Family Trust 2 29 Brightwater Community Association Inc. 30 John Martin Todd 34 Victoria Davis 39 Waimea Irrigators and Water Users Ltd 41 J D & L M Russ Ltd 42 F J & E A O Connor 48 Mary Elllen O Connor 50 R B & M J Wagner 52 Redwood Valley Irrigators 57 Patricia Ann Palmer 58 Jonathan Norman Harrey 59 Matthew Anthony Kenneth Stuart 60 David Leigh Irvine 61 Stanley Mitchell Irvine 67 Pearl Creek Farm Partnership 83 Ian Paterson 87 Margaret Mary O Connor 88 William Hill 89 Lars Jensen 90 Trevor Hugh Riley 91 Joanne L F Westbrooke 92 Brownlow J Westbrooke 93 Maxwell Clark & Shona McBride 95 Kevin D Ford & Glenys A Busch Note: 1 2 Additional concern includes inability to evacuate in time Additional concern includes reduced property values

46 I note that Mr Foley and Mr Croft also address these concerns in their evidence, especially with regard to seismic risk and dam safety. My response to all these and similar submissions is that, in recognition of the severe downstream consequences of dam failure, the dam is assigned a High PIC rating which attracts the highest design standards for the dam, which will ensure that the probability of catastrophic failure is extremely remote, and that if there is a threat of failure, there is an appropriate emergency response. 12. OFFICER'S REPORT 12.1 I have read the Officer's Report and comment below, and elsewhere in my evidence, on issues relevant to my area of expertise. I have also provided input where appropriate into the recommended consent conditions which are being produced in an amended form by the applicant Paragraphs and of the Officer's Report considers and questions the operation of the dam and reservoir under severe (low probability) drought events approaching and exceeding the 60-year return period drought. The first part of paragraph relates to the flow releases from the dam once the reservoir level drops to RL 166.5m, which is its nominal minimum operating level. As Mr Croft explains in his evidence, water is able to be released from the dam in accordance with proposed consent condition 59 subject to the amended wording proposed by Mr Croft In practice, and presuming a drought management plan which I outlined earlier in paragraphs 8.8 to 8.11 is implemented, it would be very rare for the reservoir to be drawn down to the minimum operating level during flow augmentation operation. Droughts more severe than the 60 year return period drought, as assessed against historical flow records and climate data (i.e. not under future climate conditions), should be manageable with modest to moderate restrictions on abstractive take (depending on the severity of the drought), without the reservoir level going below RL 166.5m. Under such severe drought conditions, the dam would continue to provide environmental flow augmentation while the natural flow in the other tributaries of the Waimea River decline to very low flows or cease to flow Paragraph of the Officer's Report requests further information in relation to the apparent inconsistency between the TRMP, specifically Table 1A Schedule 31C which specifies minimum flows for the Waimea River and triggers for water use rationing, and the proposed operating regime described in the AEE (T&T, July 2014). The operating regime presented in the AEE and which I described earlier in Section 7 of this statement is based on an idealised and

47 46 simplified operating basis, the primary purpose of which is to determine the storage capacity of the reservoir to fully meet downstream demands up to a particular (but nominal) drought reliability standard As noted earlier in paragraphs 8.8 to 8.11, the actual operation of the reservoir and dam releases would likely be guided by an operating system that would incorporate a contingency plan to manage drought conditions. It is my opinion that it would be possible to develop an operating system for the reservoir with a drought management plan that is consistent with the relevant parameters set out in the TRMP I note that Mr Foster, in Supplementary Report D, considered that it was not appropriate to leave the construction emergency action plan solely to the dam constructor, and that a dam breach assessment for a partially completed dam should be provided by the designer for inclusion in the construction emergency plan. I accept Mr Foster s point As part of the design of the river diversion works, a comprehensive range of coffer dam failure scenarios together with their downstream consequences was assessed. The modelled scenarios included dam breach at five partial completion levels (i.e. RL157.3m, RL165.0m, RL 175.0m, RL 185.0m and RL 194.0m) in addition to a no dam situation for a number of inflow flood events, ranging from the 2.3 year to 10,000-year ARI events Exhibit DL25 provides a map of the potential inundation area if the partially constructed dam were breached at a height of RL 175m, which is slightly higher, and therefore more conservative, than a breach at RL 173.4m requested by Mr Foster. As Mr Croft describes in his evidence, this level (RL 173.4m) corresponds with the critical downstream stage of the construction sequence for the embankment. Once the embankment reaches this level a flood between the 100-year ARI and 200-year ARI events can be passed through the diversion culverts without any overtopping. The flooding extents shown correspond with a 1,000-year ARI inflow flood, which is at the upper bound of international practice in terms of construction diversion flood capacity for a large dam. 13. CONCLUSIONS 13.1 It is my view that the reservoir capacity and thus dam height is appropriate for its intended flow augmentation purpose under current and anticipated future climate conditions. Both in-stream needs and consumptive demands have been appropriately considered for the Lee Dam. While principally for downstream flow augmentation to meet instream needs and consumptive uses, the dam also presents an opportunity for hydropower generation. The operation of the reservoir

48 47 and dam releases would also likely be guided by an operating system that would incorporate a contingency plan to manage drought conditions In terms of the effect on downstream river morphology from sediment retention in the reservoir, the removal of gravel supply to the lower river is not expected to have a significant effect in view of the relatively small amount of gravel supplied by the Lee River above the dam site compared with the remainder of the Waimea catchment The Lee Dam is assigned a High PIC rating which attracts the highest design standards for the dam, which will ensure that the probability of catastrophic failure is extremely remote, and that if there is a threat of failure, there is an appropriate emergency response. In my opinion, the risk of failure occurring for a dam engineered, built, maintained and monitored to appropriate standards would be extremely low David Leong 12 November 2014

49 EXHIBITS DL01 Design Irrigation Demand for the 1982/1983 Drought Year DL02 Annual Irrigation Demand Volumes from 1942 to 2007 (year ending 30 June) DL03 Projected Urban and Industrial Demand Pattern in 100 Years DL04 Comparison of Phase 1 and Phase 2 Water Demand Profiles for the 1982/1983 Water Year Based on Future Assumed Allocations DL05 Phase 2 flow augmentation functions: primary function based on 1-day demand and supplementary function based on 4-day demand DL06 Location of flow and rainfall gauges in relation to the catchment above the proposed dam site on the Lee River DL07 Lee at Waterfall Creek flows (red) plotted against Wairoa at Irvines flows factored downwards by 0.2 (blue) from April 2007 to April All flows in m 3 /s DL08 Wairoa at Gorge/Irvines flood frequency analysis peak instantaneous flow DL09 Synthetic design flood hydrographs for Lee Dam adjusted for climate change for A1B emission scenario to year 2090 DL10 Simulated reservoir storage behaviour with no hydro generation DL11 Simulated reservoir level behaviour with no hydro generation DL12 Storage drawdown frequency analysis for the Lee Dam DL13 Lee Dam Storage Elevation Curve, showing NTWL at RL m DL14 Lee Dam at Chainage Storage Drawdown Versus Duration DL15 Comparison of simulated flow hydrographs at Lee Dam site before and after dam construction DL16 Comparison of flow hydrographs at Wairoa Gorge before and after (simulated) dam construction DL 17 Simulated reservoir levels at Lee River dam site - comparison of without hydro and with hydro scenarios for the period July 1981 to June 1983 DL18 Comparison of simulated dam outflows (July1981 June 1983) for without hydro power and with hydro power scenarios DL19 Flow duration curves for simulated dam inflows (green line) and outflows (blue = without hydro power, red = with hydro power) for DL20 Assumed breach location and geometry of fully formed breach DL21 Dam breach hydrograph for three breach formation times DL22 Maximum flood extent (>0.5m depth) for 0.5 hour breach formation time in a sunny day dam failure DL23 Flow hydrograph at selected river locations for 0.5 hour breach formation time DL24 Water depth at selected river locations for 0.5 hour breach formation time DL25 Maximum flood extent in a 1000 year ARI flood for failure of a partially built dam completed to RL 175 m

50 DL01 Design Irrigation Demand for the 1982/1983 Drought Year 250, ,000 Total Irrigation Demand (m 3 /day) 150, ,000 50, Jul82 1Aug82 1Sep82 1Oct82 1Nov82 1Dec82 1Jan83 1Feb83 1Mar83 1Apr83 1May83 1Jun83 DL02 Annual Irrigation Demand Volumes from 1942 to 2007 (year ending 30 June) Annual Irrigation Demand (million m 3 ) Year Ending 30 June

51 DL03 Projected Urban and Industrial Demand Pattern in 100 Years Time 70,000 60,000 Urban and Industrial Demand in 100 Years (m 3 /day) 50,000 40,000 30,000 20,000 10, Jul 1Aug 1Sep 1Oct 1Nov 1Dec 1Jan 1Feb 1Mar 1Apr 1May 1Jun DL04 Comparison of Phase 1 and Phase 2 Water Demand Profiles for the 1982/1983 Water Year Based on Future Assumed Allocations Phase 1 - Groundwater take Phase 2 - Groundwater take Phase 1 - Surface water take Phase 2 - Surface water take Demand Pattern 1982 / 83 Water Year Jul Jul Jul Aug Aug 82 9 Sep Sep 82 7 Oct Oct 82 4 Nov Nov 82 2 Dec Dec Dec Jan Jan Feb Feb Mar Mar 83 7 Apr Apr 83 5 May May 83 2 Jun Jun Jun 83 Take Rate (l/s)

52 DL05 Phase 2 flow augmentation functions: primary function based on 1-day demand and supplementary function based on 4-day demand 1800 Flow Augmentation Vs Net Wairoa at Irvines Primary (1-day) and Supplemntary (4-day) Functions Flow Augmentation (l/s) augmentation 2001 augmnetation Funtion for g/w take = 2500 l/s 4-day function for g/w take = 2500 l/s Function for g/w take = 1500 l/s 4-day function for g/w take = 1500 l/s Function for g/w take = 500 l/s 4-day function for g/w take = 500 l/s Wairoa at Irvines (l/s)

53 DL06 Location of flow and rainfall gauges in relation to the catchment above the proposed dam site on the Lee River

54 DL07 Lee at Waterfall Creek flows (red) plotted against Wairoa at Irvines flows factored downwards by 0.2 (blue) from April 2007 to April All flows in m 3 /s 30 Lee at Waterfall Apr :30 Jun-07 Jul-07 Aug-07 Sep-07 Oct Nov-07 Dec-07 Jan-08 Feb-08 Mar-08 Apr-08 site (Item 1R )/1000 site (Flow l/s)/ DL08 Wairoa at Gorge/Irvines flood frequency analysis peak instantaneous flow 2000 Wairoa River at Gorge / Irvines : / Flood Frequency : 1958 to 2008 Annual Peaks (PWM fit) Annual Maximum Flow (m 3 /s) Return Period EV1 68.3% Gumbel Variate -ln{-ln(1-1/t)}

55 DL09 Synthetic design flood hydrographs for Lee Dam adjusted for climate change for A1B emission scenario to year 2090

56 DL10 Simulated reservoir storage behaviour with no hydro generation 14,000,000 Lee River Dam at Ch12430 Simulated Storage Behaviour 1100 l/s Appleby residual flow, MALF dam residual, Future Regional Supply Full Supply Level m (13.0 million m 3 ) 12,000,000 10,000,000 Storage (m 3 ) 8,000,000 6,000,000 4,000,000 2,000,000 0

57 DL11 Simulated reservoir level behaviour with no hydro generation 200 Lee River Dam at Chainage 12430: Simulated Reservoir Level Behaviour 1100 l/s Appleby residual flow, MALF dam residual, Future Regional Supply Full Supply Level RL m (13.0 million m 3 ) Reservoir Level (RL m)

58 DL12 Storage drawdown frequency analysis for the Lee Dam 14,000,000 Lee River Dam above Anslow Creek at Chainage (77.5 km 2 ) Storage Drawdown Frequency Analysis : 1958 to 2008 Annual Series ,000, Annual Maximum Drawdown (m 3 ) 10,000,000 8,000,000 6,000,000 4,000,000 2,000,000 Return Period Gumbel Variate -ln{-ln(1-1/t)} DL13 Lee Dam Storage Elevation Curve, showing NTWL at RL m

59 DL14 Lee Dam at Chainage Storage Drawdown Versus Duration 10 Lee River Dam at Chainage Drawdown Duration Curve 9 8 Drawdown From Full (m) % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent Time Drawdown Is Exceeded

60 DL15 Comparison of simulated flow hydrographs at Lee Dam site before and after dam construction ,000 10,000 Flow (litres/second) 8,000 6,000 4,000 Dam Inflow 2, Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1983 Dam Outflow

61 DL16 Comparison of flow hydrographs at Wairoa Gorge before and after (simulated) dam construction ,000 1 July 1981 to 30 June ,000 16,000 Natural Flow Augmented Flow 14,000 12,000 10,000 8,000 6,000 4,000 2, Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1983 Flow (litres/second)

62 DL17 Simulated reservoir levels at Lee River dam site - comparison of without hydro and with hydro scenarios for the period July 1981 to June Comparison of "No Hydro" and "With Hydro" Dam Levels 195 Reservoir Level (RL m) Jul-81 1-Aug-81 1-Sep-81 1-Oct-81 1-Nov-81 1-Dec-81 1-Jan-82 1-Feb-82 1-Mar-82 1-Apr-82 1-May-82 1-Jun-82 1-Jul-82 1-Aug-82 1-Sep-82 1-Oct-82 1-Nov-82 1-Dec-82 1-Jan-83 1-Feb-83 1-Mar-83 1-Apr-83 1-May-83 1-Jun-83 Levels - with hydro Levels - no hydro

63 DL18 Comparison of simulated dam outflows (July1981 June 1983) for without hydro power and with hydro power scenarios Comparison of "No Hydro" and "With Hydro" Dam Outflows Outflow - with hydro Outflow - no hydro Jul-81 1-Aug-81 1-Sep-81 1-Oct-81 1-Nov-81 1-Dec-81 1-Jan-82 1-Feb-82 1-Mar-82 1-Apr-82 1-May-82 1-Jun-82 1-Jul-82 1-Aug-82 1-Sep-82 1-Oct-82 1-Nov-82 1-Dec-82 1-Jan-83 1-Feb-83 1-Mar-83 1-Apr-83 1-May-83 1-Jun-83 Total outflow from dam (l/s)

64 DL19 Flow duration curves for simulated dam inflows (green line) and outflows (blue = without hydro power, red = with hydro power) for All flows in m 3 /s

65 DL20 Assumed breach location and geometry of fully formed breach DL21 Dam breach hydrograph for three breach formation times

66 DL22 Maximum flood extent (>0.5m depth) for 0.5 hour breach formation time in a sunny day dam failure

67 DL23 Flow hydrograph at selected river locations for 0.5 hour breach formation time DL24 Water depth at selected river locations for 0.5 hour breach formation time

68 DL25 Maximum flood extent in a 1000 year ARI flood for failure of a partially built dam completed to RL 175 m