Hydrology State of the Environment monitoring programme

Transcription

1 Hydrology State of the Environment monitoring programme Annual data report 3/4 M Harkness Environmental Science Department For more information, contact the Greater Wellington Regional Council: Wellington PO Box T F Masterton PO Box 4 T F GW/ESCI-T-4/7 ISBN: (online) December 4 info@gw.govt.nz

2 Report prepared by: M Harkness Senior Analyst, Hydrology Report reviewed by: N Boyens Team Leader, Hydrology Report approved for release by: G Sevicke-Jones Manager, Environmental Science Date: December 4 DISCLAIMER This report has been prepared by Environmental Science staff of Greater Wellington Regional Council (GWRC) and as such does not constitute Council policy. In preparing this report, the authors have used the best currently available data and have exercised all reasonable skill and care in presenting and interpreting these data. Nevertheless, GWRC does not accept any liability, whether direct, indirect, or consequential, arising out of the provision of the data and associated information within this report. Furthermore, as GWRC endeavours to continuously improve data quality, amendments to data included in, or used in the preparation of, this report may occur without notice at any time. GWRC requests that if excerpts or inferences are drawn from this report for further use, due care should be taken to ensure the appropriate context is preserved and is accurately reflected and referenced in subsequent written or verbal communications. Any use of the data and information enclosed in this report, for example, by inclusion in a subsequent report or media release, should be accompanied by an acknowledgement of the source. The report may be cited as: Harkness M. 4. Hydrology State of the Environment monitoring programme, Annual data report, 3/4. Greater Wellington Regional Council, Publication No. GW/ESCI-T-4/7, Wellington.

3 Contents. Introduction. Overview of Hydrology SoE monitoring programme. Monitoring objectives. Monitoring network 3.. Rainfall 3.. River levels and flow 3..3 Lake levels 4..4 Wetland levels 4..5 Tide levels 4..6 Soil moisture 4..7 Groundwater levels 5..8 Whaitua areas 5 3. Results 3. Rainfall 3. River flows Groundwater levels Lake and wetland levels Soil moisture 3 Acknowledgements 3 References 33

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5 Hydrology SoE monitoring programme: Annual data report, 3/4. Introduction Greater Wellington Regional Council (GWRC) operates a hydrometric network for measuring rainfall, river levels, lake levels, groundwater levels, tide levels and soil moisture. This report contains key results from the Hydrology State of Environment (SoE) monitoring programme for the period July 3 to 3 June 4 inclusive. Summaries of the recorded data are compared to long term averages, and any significant hydrological events are detailed. The Hydrology SoE programme is solely concerned with collecting data on the quantity of the region s water resources. GWRC operates other monitoring programmes which gather information on water quality and ecosystem health that are reported on separately. Refer to: Rivers State of the Environment Monitoring Programme: Annual Data Report 3/4 (Heath et al, 4) Groundwater Quality State of the Environment Monitoring Programme: Annual Data Report 3/4 (Tidswell, 4) V PAGE OF 33

6 Hydrology SoE monitoring programme: Annual data report, 3/4. Overview of Hydrology SoE monitoring programme Rainfall and river levels have been monitored for many years in the Wellington region. Some of the earliest rainfall records date back to 878 at the Karori Reservoir site and 89 at the Wainuiomata Reservoir site. Over the years the region s hydrometric network has evolved and grown and now comprises: 58 rainfall sites 6 river level/flow recording sites 6 lake level sites 5 wetland water level sites tide level sites 4 soil moisture sites 73 groundwater level sites (plus a further 7 manually monitored sites). All hydrological data are captured, processed and archived in accordance with national and international standards and quality assurance procedures. Telemetered rainfall, river, lake, groundwater and tide data are available at Monitoring objectives The information collected is used for: Providing information on the state of our water resources and the baseline quantity of water Detecting long and short term trends in climate and water resources Making informed decisions on the state of the region s freshwater resources and manage its sustainable allocation and use Informing whaitua committees to enable the creation of a unique vision and to prioritise objectives for land and water management Policy and Regional Plan development and review Providing flood and drought warnings Resource consent monitoring. PAGE OF V

7 Hydrology SoE monitoring programme: Annual data report, 3/4. Monitoring network.. Rainfall Figure. shows the distribution of the 58 rainfall sites maintained by GWRC. There is good coverage across much of the region with the exception of the Eastern Wairarapa hill country where the distribution of sites is sparse. All rainfall sites are automatic and typically record rainfall amounts at five minute intervals into a data logger on site. The majority of sites are telemetered back to the GWRC database to allow real time monitoring. There are two measuring devices at each site; an automatic tipping-bucket rain gauge that records rainfall amounts in.5mm or.mm increments and a check/storage gauge that collects and stores all rainfall between site visits by the monitoring team when it is measured and emptied. A number of rainfall sites have alarm levels that are automatically triggered if a high intensity rainfall above a certain threshold occurs. Alarms are received by flood-warning staff and a flood event will be monitored at any time of the day with warnings issued to relevant authorities and landowners if dangerous flood levels are predicted... River levels and flow River levels are recorded at 6 sites across the region. The distribution of the sites is shown in Figure. and is similar to the rainfall network. During the 3/4 year four of the sites were operated solely by NIWA and another four were jointly maintained by NIWA and GWRC. River level sites were originally installed for a number of reasons including flood warning, public water supply and water resource monitoring. As such the network tends to concentrate on the larger rivers and the upper parts of catchments. This has been changing over time as GWRC undertakes more monitoring in agricultural and urban areas and in the lower reaches of the catchments to manage abstractions, maintain environmental flows and ensure regional plan rules are being met. All river sites are automatic and typically record river levels every five to 5 minutes. Data are stored on loggers at the site, as well as being sent back to the GWRC database via telemetry to allow for real time monitoring. GWRC staff also physically measure the amount of flow in rivers and streams by completing a flow gauging using specialised equipment, and can measure from a trickle in a ditch to a major flood in the Ruamahanga River. The gauged flow and the water level at the time of the flow gauging are used to build up a flow-rating relationship that is used to convert the continuously measured river water levels into flow values. The flow-rating relationships at each site change often due to events such as a flood which might alter the river bed level, therefore gaugings are undertaken regularly to ensure the correct flows are being calculated from the recorded water levels V PAGE 3 OF 33

8 Hydrology SoE monitoring programme: Annual data report, 3/4 Most river sites have flood alarm levels that are automatically triggered if a river level rises above a certain threshold. Alarms are received by floodwarning staff and a flood event will be monitored at any time of the day with warnings to relevant authorities and landowners issued if dangerous flood levels are predicted...3 Lake levels The location of the six lake sites are shown in Figure.3. Three are situated on Lake Wairarapa to monitor compliance with minimum water levels (as set out in the Lake Wairarapa Wetlands Management Guidelines 99 and the Regional Freshwater Plan 999) and to monitor lake levels for flood control. The site at Lake Onoke is monitored for flood control purposes, particularly if the lake opening to the sea becomes blocked. The other two lake sites have been operating since 7 and monitor the levels of Lake Kohangapiripiri and Lake Kohangatera (collectively known as the Parangarahu Lakes). These lakes are part of East Harbour Regional Park and are of national significance...4 Wetland levels Wetland monitoring is a relatively recent development in GWRC s hydrological network. GWRC currently operate five continuous water level recorders on two wetland areas. Four of those are sited in the Te Hapua wetland complex near Te Horo on the Kapiti Coast. The remaining site is situated on the Taumata Lagoon near the confluence of the Waiohine and Ruamahanga rivers in the Wairarapa. The locations of these sites are shown in Figure Tide levels Tide levels are monitored at two sites; Wellington Harbour at Queens Wharf and Porirua Harbour at the Mana Cruising Club. The locations of these sites are shown in Figure.3. Two other sites (Hutt River at Estuary Bridge and Lake Onoke at Lake Ferry) can also be used to infer tide levels as they are situated at the mouths of the Hutt and Ruamahanga rivers respectively...6 Soil moisture Soil moisture is monitored at four sites in the region. The locations of these sites are shown in Figure.3. Knowing the water content of soil is important for managing groundwater recharge, assessing agricultural irrigation needs and soil chemistry. It is also used for analysis of long-term climate trends, measuring how often plant growth is restricted by soil moisture and providing an indication for early intervention and drought management decisions. PAGE 4 OF V

9 Hydrology SoE monitoring programme: Annual data report, 3/4..7 Groundwater levels The groundwater monitoring network covers the three principal groundwater areas in the region; Lower Hutt Valley, Kapiti Coast and Wairarapa Valley. The network utilises dedicated monitoring boreholes as well as privately owned boreholes, and the location of sites are shown in Figure.4. Note that some of the sites actually have two separate monitoring devices within a shallow bore and a deep bore. Continuous data on groundwater levels are collected at 73 sites. These are automatic sites where the groundwater level is recorded every five to 5 minutes and stored in a data logger at the site. The majority of sites are also linked to GWRC s database via telemetry. In addition to the automatic monitoring sites, GWRC also manually measures groundwater levels at a further 7 sites every four to seven weeks. Data from these manual sites can be compared to data from automatic sites to provide a fuller picture of the state of the region s groundwater resource. A number of these sites are also part of the groundwater quality network which is reported on separately (refer to the 3/4 Annual Data Report for Groundwater Quality State of the Environment monitoring programme)...8 Whaitua areas Managing the water resources of our region in a way that meets current needs and those of future generation s means that we need to understand what is important to people in their local area. GWRC has identified five areas that place different demands on land and water resources and is enlisting the support of community groups called whaitua committees to help understand local needs and make recommendations on how they are to be managed. The Māori word whaitua means a designated space or catchment. Whaitua committees will be established for the Wairarapa East Coast, Ruamāhanga Valley, Wellington/Hutt Valley, Porirua Harbour and Kāpiti Coast over the next few years. They will combine the knowledge and experience of the community who live in the catchment: iwi, householders, farmers, scientists, recreationalists and environmentalists. The Ruamāhanga Whaitua Committee and the Te Awarua o Porirua Whaitua Committee have been established to date. The whaitua areas are referenced throughout this report and in particular the areas are shown on the maps of the monitoring network in Figures. to V PAGE 5 OF 33

10 Hydrology SoE monitoring programme: Annual data report, 3/4 Figure.: Automatic rainfall monitoring sites 3/4 PAGE 6 OF V

11 Hydrology SoE monitoring programme: Annual data report, 3/4 Figure.: Automatic river level/flow monitoring sites 3/ V PAGE 7 OF 33

12 Hydrology SoE monitoring programme: Annual data report, 3/4 Figure.3: Automatic lake level, wetland level, tide level and soil moisture monitoring sites 3/4 PAGE 8 OF V

13 Hydrology SoE monitoring programme: Annual data report, 3/4 Figure.4: Groundwater level sites 3/ V PAGE 9 OF 33

14 Hydrology SoE monitoring programme: Annual data report, 3/4 3. Results 3. Rainfall Table 3. summarises the total annual rainfall for 3/4 at a range of monitoring sites across the region that are grouped by their whaitua area. Sites with greater than percent difference from their long term average are shaded orange (below average) and blue (above average). Table 3.: Annual rainfall totals (3/4) and percentage of long term average Site Catchment 3/4 total (mm) Average (mm) (Data period) % of long term average Kāpiti Coast whaitua Oriwa (Tararua) Otaki (99-3) 3 McIntosh (Tararua) Otaki (99-3) 5 Taungata (Tararua) Otaki (99-3) 98 Kapakapanui (Tararua) Otaki (99-3) 94 Transmission Lines Mangaone (99-3) 96 Otaki Depot Otaki (97-3) 86 Shoveler Lagoon Te Hapua Wetlands 873 NA Water Treatment Plant Waikanae 8 8 (969-3) 96 MacKays Crossing Whareroa (97-3) 85 Wellington Harbour and Hutt Valley whaitua Warwicks Akatarawa 3 7 (98-3) 9 Blue Gum Spur Whakatikei (98-3) 9 Kaitoke Headworks Hutt (95-3) 7 Te Marua Hutt 9 77 (993-3) 3 Centre Ridge Pakuratahi (984-3) 8 Tasman Vaccine Ltd Mangaroa (968-3) Cemetery Akatarawa (988-3) 98 Birch Lane/Mabey Rd Hutt 7 (995-3) 87 Shandon Golf Club Hutt 63 9 (-3) 4 Quartz Hill Makara 34 NA Khandallah at Library Wellington City 3 3 (996-3) 8 Karori Reservoir Kaiwharawhara (95-3) Regional Council Wellington City (996-3) 3 Hataitai Post Office Wellington City (997-3) 5 Newtown Mansfield Wellington City 3 44 (996-3) 8 Berhampore Wellington City 76 (996-3) 97 Miramar North Rd Wellington City 4 98 (4-3) 9 Orongo Swamp Orongorongo (98-3) 7 Wainuiomata Reservoir Wainuiomata (95-3) 99 Pencarrow Lakes Pencarrow Lakes 73 NA Insufficient number of years of data recorded to calculate average rainfall Some missing record during the 3/4 year and total derived using storage gauge data PAGE OF V

15 Hydrology SoE monitoring programme: Annual data report, 3/4 Table 3. (continued) Site Catchment 3/4 total (mm) Average (mm) (Data period) % of long term average Te Awarua o Porirua whaitua Battle Hill Horokiri NA Whenua Tapu Taupo 9 58 (99-3) 87 Tawa Pool Porirua 8 3 (996-3) 9 Seton Nossiter Park Porirua 4 95 (99-3) 94 Ruamāhanga whaitua Bannister (Tararua) Ruamahanga (974-3) 8 Carkeek (Tararua) Waiohine (976-3) Mt Bruce Ruamahanga 75 4 (997-3) Westons Waipoua 975 NA Angle Knob (Tararua) Waingawa (974-3) 4 Kaituna Waingawa (994-3) 6 Valley Hill Mangatarere (997-3) Bull Mound (Tararua) Tauherenikau (976-3) 9 Waiohine Gorge/Phelps Waiohine 66 (974-3) 8 Mauriceville Kopuaranga 59 NA Waihi Whangaehu 47 7 (-3) 3 Castlehill Tauweru (99-3) 8 Wairarapa College Ruamahanga (-3) Te Weraiti Tauweru (997-3) 96 Alloa/Racecourse Tauherenikau 73 7 (999-3) 5 Matthews Waiorongomai 56 NA Longbush Waikoukou (955-3) 4 Wairarapa Coast whaitua Tanawa Hut Whareama 63 3 (955-3) 4 Insufficient number of years of data recorded to calculate average rainfall V PAGE OF 33

16 Hydrology SoE monitoring programme: Annual data report, 3/4 Monthly rainfall totals at a number of rainfall monitoring sites across the region are shown in Figure 3.. The 3/4 totals are compared to the long term monthly average. 3/4 Monthly total Historical average rainfall total 5 Otaki Waikanae Rainfall (mm) 5 Rainfall (mm) Month Month 5 Porirua (Whenua Tapu) Karori Reservoir Rainfall (mm) 5 Rainfall (mm) Month Month 35 3 Wainuiomata Reservoir Lower Hutt Rainfall (mm) 5 Rainfall (mm) Month Month Figure 3.: Monthly rainfall totals (3/4) and long-term averages PAGE OF V

17 Hydrology SoE monitoring programme: Annual data report, 3/4 3/4 Monthly total Historical average rainfall total 5 Upper Hutt (Pinehaven) Tauherenikau Rainfall (mm) 5 Rainfall (mm) Month Month Masterton Tanawa Hut Rainfall (mm) Rainfall (mm) Month Month 5 Longbush (Waikoukou) Iraia Rainfall (mm) 5 Rainfall (mm) 5 Missing Data 5 5 Month Month Tararuas (Carkeek) Tararuas (McIntosh) Rainfall (mm) 6 4 Rainfall (mm) 6 4 Month Month Figure 3. (continued) V PAGE 3 OF 33

18 Hydrology SoE monitoring programme: Annual data report, 3/4 Seasonal rainfall totals for locations across the Greater Wellington region are presented in Table 3.. Sites that have a greater than percent difference from their long term seasonal average are shaded orange (below average) or blue (above average). Table 3.: Seasonal rainfall totals as percentage of long-term mean Whaitua area Rain gauge location Rainfall as a percentage of the long term average Winter 3 Spring 3 Summer 3/4 Autumn 4 Otaki 87% 5% 6% 7% Kāpiti Coast Waikanae 64% 87% 7% 5% McKays Crossing 86% 97% 57% 98% McIntosh (Tararuas) 88% 3% 97% 38% Te Awarua o Porirua Whenua Tapu % 9% 6% 9% Paparangi 9% 4% 8% % Kaitoke % 56% 73% 9% Lower Hutt % % 8% 89% Wellington Harbour and Hutt Valley Wainuiomata % 35% % 93% Berhampore 86% 98% % % Karori 33% 39% 95% 4% Makara 94% 6% 8% 93% Mt Bruce 5% % 97% 3% Waihi % 3% 7% 3% Castlehill 39% 34% 97% 36% Ruamāhanga Masterton 6% 85% 8% % Featherston 84% 6% 87% 43% Longbush % 8% 88% 3% Carkeek (Tararuas) 69% 8% 93% 9% Wairarapa Coast Tanawa Hut 38% 76% 78% 3% PAGE 4 OF V

19 Hydrology SoE monitoring programme: Annual data report, 3/4 An analysis of the maximum recorded rainfall totals during the 3/4 year for specific time periods of, 6 and hour durations is detailed in Table 3.3. Return periods have been estimated by frequency analysis. Values in blue shaded cells indicate a rainfall total with a 5-year return period or greater. Table 3.3: Maximum short duration rainfall totals during 3/4 hour 6 hours hours Site Rainfall Start date Return period (years) Rainfall Start date Return period (years) Rainfall Start date Water Treatment Plant.5mm 45mm 48mm (Waikanae) 8 Apr 4 8 Apr 4 8 Apr 4 QE Park.5mm 9.5mm 4mm (Paekakariki) 3 Jan 4 Nov 3 3 Oct 3 Warwicks 4mm 63.5mm 89mm (Akatarawa) 4 May 4 3 Oct 3 3 Oct 3 Te Marua 3mm 68.5mm 88mm 4 3 (Upper Hutt) 3 Jan 4 3 Oct 3 3 Oct 3 TVL 3mm 56.5mm 57mm 3 (Mangaroa) 3 Jan 4 3 Jan 4 3 Jan 4 Birch Lane.5mm 43mm 43mm (Lower Hutt) 3 Jan 4 3 Jan 4 3 Jan 4 Wainuiomata Reservoir 9.5mm 55.5mm 73mm (Wainuiomata) 3 Jan 4 4 Sep 4 4 Sep 3 Seton Nossiter Park 6mm 35.4mm 4mm (Porirua) Sep 3 6 Apr 4 6 Apr 4 Karori Reservoir.4mm 3.4mm 4mm (Wellington City) 9 Aug 3 6 Apr 4 8 Apr 4 McIntosh 35mm 6mm 83mm 8 5 (W Tararua Range) Sep 3 Sep 3 5 Jan 4 Bannister Basin 3mm 8mm 9mm 3 (E Tararua Range) 5 Jan 4 4 Jan 4 4 Jan 4 Waiohine Gorge mm 83mm 5mm (Waiohine) 4 Oct 3 4 Oct 3 7 Apr 4 Wairarapa College 4.4mm 4.6mm 39mm (Masterton) Apr 4 8 Nov 3 7 Nov 3 Racecourse.4mm 34.mm 5mm (Featherston) 3 7 Apr 4 Oct 3 Oct 3 Castlehill 9.5mm 6mm 89mm 8 (Tauweru) Jul 3 Jul 3 Jul 3 Tanawa Hut 7mm 83mm 6mm 7 6 (Whareama) Jul 3 Jul 3 Jul 3 Return periods estimated using HIRDS v3. (NIWA ). Return periods estimated using neighbouring Waiohine at Phelps site that was closed in January. 3 Return periods estimated using neighbouring Alloa site that was closed in November Return period (years) V PAGE 5 OF 33

20 Hydrology SoE monitoring programme: Annual data report, 3/4 An analysis of the maximum recorded rainfall totals during the 3/4 year for longer duration events of 4, 48 and 7 hour durations is detailed in Table 3.4. Return periods have been estimated by frequency analysis. Values in blue shaded cells indicate a rainfall total with a 5-year return period or greater. Table 3.4: Maximum long duration rainfall totals during 3/4 4 hour 48 hours 7 hours Site Rainfall Start date Return period (years) Rainfall Start date Return period (years) Rainfall Start date Water Treatment Plant 6mm 75mm 76mm (Waikanae) 3 Oct 3 3 Jan 4 Jan 4 QE Park 5mm 54mm 54mm (Paekakariki) 3 Oct 3 3 Jan 4 Jan 4 Warwicks 4mm 4mm 4mm (Akatarawa) 3 Oct 3 3 Jan 4 Jan 4 Te Marua mm mm mm (Upper Hutt) 3 Oct 3 3 Oct 3 9 Oct 3 TVL 75mm 94mm 95mm (Mangaroa) 3 Oct 3 3 Jan 4 Jan 4 Birch Lane 58mm 75mm 76mm (Lower Hutt) 3 Oct 3 3 Jan 4 Jan 4 Wainuiomata Reservoir 8mm 97mm 45mm (Wainuiomata) 4 Sep 3 Jul 3 9 Jul 3 Seton Nossiter Park 7mm 88mm 93mm (Porirua) 6 Apr 4 5 Apr 4 6 Apr 4 Karori Reservoir 68mm 99mm mm 3 (Wellington City) 6 Apr 4 5 Apr 4 5 Apr 4 McIntosh 3mm 9mm 99mm 3 3 (W Tararua Range) Sep 3 3 Jan 4 Jan 4 Bannister Basin 56mm 353mm 359mm 3 3 (E Tararua Range) 4 Jan 4 3 Jan 4 Jan 4 Waiohine Gorge 55mm 97mm mm 8 7 (Waiohine) 7 Apr 4 6 Apr 4 5 Apr 4 Wairarapa College 6mm 84mm mm (Masterton) 7 Nov 3 6 Nov 3 5 Nov 3 Racecourse 7mm 3mm 3mm 4 6 (Featherston) 3 7 Apr 4 6 Apr 4 5 Apr 4 Castlehill 7mm 3mm 44mm 3 4 (Tauweru) Jul 3 Jul 3 9 Jul 3 Tanawa Hut 7mm 6mm 79mm 6 4 (Whareama) Jul 3 Jul 3 Jul 3 Return periods estimated using HIRDS v3. (NIWA ). Return periods estimated using neighbouring Waiohine at Phelps site that was closed in January. 3 Return periods estimated using neighbouring Alloa site that was closed in November Return period (years) PAGE 6 OF V

21 Hydrology SoE monitoring programme: Annual data report, 3/4 The lowest recorded rainfall totals over periods of 4 days, 8 days and 3 months are detailed in Table 3.5 for sites across the region. Table 3.5: Lowest rainfall totals during 3/4 Site Rainfall (mm) 4 days 8 days 3 months Start Date Rainfall (mm) Start Date Rainfall (mm) Start Date Otaki Depot (Otaki) Water Treatment Plant (Waikanae) McKays Crossing (Paekakariki) -Feb-4, 8-Mar Feb Jan-4 4-Feb Jan Jan-4 -Feb-4 6-Jan Jan-4 Battle Hill (Horokiri) -Feb Jan-4 5-Jan-4 Tawa Pool -Feb Feb Jan-4 Karori Reservoir 3-Feb-4. 8-Nov Jan-4 Miramar North Rd -Feb Nov-3 5-Jan-4 Birch Lane (Lower Hutt) Wainuiomata Reservoir Savage Park (Upper Hutt) -Feb-4, 8-Dec-3, 6-Jul-3 -Feb-4, 6-Jul-3 8-Nov Jan Nov Jan-4 8-Nov Jan Jan-4 Kaitoke Headworks. 4-Feb Jan Jan-4 McIntosh (Tararuas - Penn Creek) Angle Knob (Tararuas - Waingawa River) 3.5 -Mar Feb Jan Jul Feb Jan-4 Waiohine River Gorge 3-Feb-4 5 -Jul Jan-4 Wairarapa College (Masterton) Tauherenikau Racecourse (Featherston) Tanawa Hut (E Wairarapa - Whareama) Longbush (E Wairarapa, Waikoukou) Iraia (SE Wairarapa, Ruakokoputuna) -Feb-4.6 -Feb Jan-4 -Feb-4, 8-Nov-3, 6-Jul-3 -Feb-4, 6-Jul-3 -Feb-4, 6-Jul Jul Jan-4 9-Nov Nov Nov Nov-3 -Feb Nov Nov V PAGE 7 OF 33

22 Hydrology SoE monitoring programme: Annual data report, 3/4 3. River flows Mean monthly river flows for selected monitoring sites are detailed in Figure 3.. The plots cover main rivers in the Kapiti Coast, Porirua, Hutt Valley, Wairarapa Valley and the Eastern Hills areas. Historical range of monthly mean flows Long-term Monthly Mean Flow /3 Monthly Mean Flow 3/4 Monthly Mean Flow Otaki River (98-4) 3 Waikanae River (974-4) 5 Monthly Mean Flow (m 3 /s) Wharemauku Stream (98-4) 4 Porirua Stream (965-4) Monthly Mean Flow (m 3 /s) Wainuiomata River (98-4) 8 Whakatikei River (976-4) Monthly Mean Flow (m 3 /s) Figure 3.: Mean monthly river flows (3/4) and long term averages PAGE 8 OF V

23 Hydrology SoE monitoring programme: Annual data report, 3/4 Historical range of monthly mean flows Long-term Monthly Mean Flow /3 Monthly Mean Flow 3/4 Monthly Mean Flow 35 Hutt River at Kaitoke (967-4) 4 Waingawa River (978-4) 3 35 Monthly Mean Flow (m 3 /s) Waiohine River (978-4) 3 Tauherenikau River (975-4) 8 5 Monthly Mean Flow (m3/s) Kopuaranga River (984-4) 35 Ruamahanga River at Waihenga (976-4) 3 Monthly Mean Flow (m 3 /s) Pahaoa River (986-4) 6 Whareama River (969-4) 5 Monthly Mean Flow (m 3 /s) Figure 3. (continued) V PAGE 9 OF 33

24 Hydrology SoE monitoring programme: Annual data report, 3/4 Maximum recorded river flows for a number of sites are detailed in Table 3.6. The two sites highlighted in blue shading indicate a flood flow in excess of a 5- year return period. The peak recorded flow for the 3/4 year for the Hutt River at Kaitoke is estimated at a 5-year return period. Table 3.6: Maximum river and stream flows during 3/4 Site 3/4 maximum flow (m 3 /s) Date occurred Estimated return period (years) Waitohu Stream at Water Supply Intake 8 -Sep-3 < Otaki River at Pukehinau 85 -Sep-3 < Mangaone Stream at Ratanui 3 -Sep-3 Waikanae River at Water Treatment Plant 5 5-Jan-4 < Hutt River at Kaitoke 45 4-May-4 5 Hutt River at Birchville Oct-3 Hutt River at Taita Gorge Oct-3 Pakuratahi River at Truss Bridge 95 -Sep-3 3 Mangaroa River at Te Marua 95 5-Sep-3 < Akatarawa River at Cemetery 68 3-Oct-3 < Whakatikei River at Dude Ranch 53 3-Oct-3 < Waiwhetu Stream at Whites Line East 3-Jan-4 < Wainuiomata River at Manuka Track 6 3-Jan-4 < Wainuiomata River at Leonard Wood Park 9 3-Jan-4 < Orongorongo River at Upper Dam Site 3 3-Jan-4 3 Taupo Stream at Flax Swamp 5-Oct-3 < Horokiri Stream at Snodgrass 7 3-Oct-3 < Porirua Stream at Town Centre 5 6-Apr-4 < Ruamahanga River at Mt Bruce 33 -Sep-3 Ruamahanga River at Wardells 47 -Sep-3 Ruamahanga River at Gladstone Bridge 843 -Sep-3 4 Ruamahanga River at Waihenga Bridge 9 -Jul-3 Waipoua River at Mikimiki Bridge 4 5-Oct-3 Waingawa River at Kaituna 34 -Sep-3 3 Mangatarere River at Gorge 7 8-Apr-4 Waiohine River at Gorge 943 -Sep-3 3 Tauherenikau at Gorge 36 5-Oct-3 4 Kopuaranga at Palmers Bridge 64 -Jul-3 3 Taueru River at Te Weraiti 359 -Jul-3 8 Huangarua at Hautotara 79 -Jul-3 Whareama River at Waiteko 437 -Jul-3 3 Pahaoa River at Hinakura 589 -Jul-3 3 Data provided by NIWA but frequency analysis performed by GWRC PAGE OF V

25 Hydrology SoE monitoring programme: Annual data report, 3/4 Minimum recorded river flows (averaged over 7 and 8 day periods) during the 3/4 year are detailed in Table 3.7 for the western part of the region, and Table 3.8 for the eastern part of the region. Significant low flow events (5-year return period or greater) are shaded orange. Table 3.7: Lowest 7-day and 8-day mean flows during 3/4 in the western Wellington region 7-day duration 8-day duration Site Waitohu Stream at WSI Otaki River at Pukehinau Mangaone Stream at Ratanui Waikanae River at WTP Hutt River at Kaitoke Hutt River at Birchville, Hutt River at Taita Gorge Pakuratahi River at Truss Bridge Mangaroa River at Te Marua Akatarawa River at Cemetery Whakatikei River at Dude Ranch Wainuiomata River at Manuka Track Orongorongo River at UDS Taupo Stream at Flax Swamp Horokiri Stream at Snodgrass Porirua Stream at Town Centre Data begins 3/4 lowest mean flow (m 3 /s) Start date Estimated return period (years) 3/4 lowest mean flow (m 3 /s) Start date Estimated return period (years) Apr 4.46 Apr Apr Mar Mar 4.77 Apr Apr Apr Apr 4.5 Mar Apr Mar Apr Mar Apr Feb Apr Mar Apr Feb Apr Apr Apr Mar Dec Dec Mar 4. Mar Apr 4. Mar Apr Mar 4 Low flow likely to have been significantly affected by upstream abstraction. Data provided by NIWA but frequency analysis performed by GWRC V PAGE OF 33

26 Hydrology SoE monitoring programme: Annual data report, 3/4 Table 3.8: Lowest 7-day and 8-day mean flows during 3/4 in the Wairarapa 7-day duration 8-day duration Site Ruamahanga River at Mt Bruce Ruamahanga River at Wardells Ruamahanga River at Waihenga Br Waipoua River at Mikimiki 3 Waingawa River at Kaituna Mangatarere Strm at Gorge Waiohine River at Gorge Tauherenikau River at Gorge Kopuaranga River at Palmers Otukura Stream at Weir Papawai Stream u/s Oxi Pond Pahaoa River at Hinakura Whareama River at Waiteko Data begins 3/4 lowest mean flow (m 3 /s) Start date Estimated return period (years) 3/4 lowest mean flow (m 3 /s) Start date Estimated return period (years) Apr Mar Apr Mar Apr Mar Mar Dec Mar Mar Feb Mar Apr Mar Apr Feb Apr Mar Feb Mar Mar 4.33 Mar Nov Jan Jan 4.79 Mar 4 Low flow likely to have been significantly affected by upstream abstraction. Data provided by NIWA but frequency analysis performed by GWRC. 3 Short data record at site. PAGE OF V

27 Hydrology SoE monitoring programme: Annual data report, 3/4 GWRC has defined low flow thresholds on a number of rivers and streams across the region to signify when restrictions on abstractions should begin (restriction thresholds) and when all abstractions shall stop (minimum flows). These are defined in the Regional Freshwater Plan. Table 3.9 summarises the number of instances that the first restriction threshold was reached during 3/4 for rivers and streams as specified in the Regional Freshwater Plan. Results from the previous three years are included for comparison. Table 3.9: Number of days where mean daily flow was below the first restriction threshold as specified in the Regional Freshwater Plan Area River or stream First restriction threshold (m 3 /s) Number of days below threshold 3/4 /3 / / Waitohu Stream Kapiti Coast Otaki River Mangaone Stream.45 Waikanae River.9 35 Ruamahanga River (Wardells) Ruamahanga River (Waihenga) Waiohine River 3.4 Wairarapa Tauherenikau River Waingawa River Kopuaranga River.7 34 Waipoua River Mangatarere Stream (Gorge) Wellington/Hutt Valley Hutt River (Birchville).45 Wainuiomata River Orongorongo River V PAGE 3 OF 33

28 Hydrology SoE monitoring programme: Annual data report, 3/4 As part of its floodwarning service, GWRC sets high river level alarms on many of its monitoring sites to provide early warning of rising river levels and possible flooding. Table 3. lists the rivers and sites where flood warning alarms were triggered during 3/4. Table 3.: Flood warning alarms triggered during 3/4 Event Date Sites where alarms were triggered Waipoua at Mikimiki Bridge Ruamahanga at Wardells July 3 Taueru at Te Weraiti Ruamahanga at Waihenga Huangarua at Hautotara 5 September 3 Orongorongo at Truss Bridge Orongorongo at Truss Bridge Hutt at Te Marua Hutt at Birchville Otaki at Pukehinau Akatarawa at Cemetery Mangaroa at Te Marua Waikanae at Water Treatment Plant - September 3 Ruamahanga at Mt Bruce Waiohine at Gorge Waipoua at Mikimiki Bridge Mangatarere at Gorge Waingawa at Kaituna Ruamahanga at Wardells Ruamahanga at Waihenga September 3 Porirua at Town Centre Hutt at Birchville Mangaroa at Te Marua 5 September 3 Hutt at Te Marua Ruamahanga at Waihenga Taueru at Te Weraiti Ruamahanga at Mt Bruce - October 3 Ruamahanga at Waihenga Waiohine at Gorge Waipoua at Mikimiki Bridge 4-4 October 3 Ruamahanga at Mt Bruce Ruamahanga at Wardells Ruamahanga at Waihenga PAGE 4 OF V

29 Hydrology SoE monitoring programme: Annual data report, 3/4 Table 3. (continued) Event Date 4-5 October 3 3 October - November 3 8 November 3 3 November 3 3 January 4 Sites where alarms were triggered Otaki at Pukehinau Hutt at Kaitoke Ruamahanga at Mt Bruce Waiohine at Gorge Ruamahanga at Wardells Ruamahanga at Waihenga Waipoua at Mikimiki Bridge Ruamahanga at Mt Bruce Waiohine at Gorge Ruamahanga at Waihenga Hutt at Kaitoke Akatarawa at Cemetery Hutt at Birchville Hutt at Te Marua Waikanae at Water Treatment Plant Hutt at Taita Gorge Orongorongo at Truss Bridge Waipoua at Mikimiki Bridge Ruamahanga at Wardells Ruamahanga at Waihenga Taueru at Te Weraiti Waiohine at Gorge Waipoua at Mikimiki Bridge Ruamahanga at Wardells Ruamahanga at Waihenga Porirua at Town Centre Waiwhetu at Whites Line East Wainuiomata at Manuka Track Hutt at Kaitoke Otaki at Pukehinau Waiohine at Gorge Ruamahanga at Mt Bruce Ruamahanga at Wardells V PAGE 5 OF 33

30 Hydrology SoE monitoring programme: Annual data report, 3/4 Table 3. (continued) Event Date 5 January 4 7 March April 4 5 May 4 6 May 4 Sites where alarms were triggered Otaki at Pukehinau Waikanae at Water Treatment Plant Hutt at Birchville Hutt at Kaitoke Akatarawa at Cemetery Ruamahanga at Mt Bruce Waiohine at Gorge Ruamahanga at Wardells Waipoua at Mikimiki Bridge Ruamahanga at Waihenga Hutt at Kaitoke Ruamahanga at Mt Bruce Waiohine at Gorge Ruamahanga at Waihenga Waipoua at Mikimiki Bridge Ruamahanga at Waihenga Waipoua at Mikimiki Bridge Ruamahanga at Mt Bruce Waiohine at Gorge Ruamahanga at Wardells Mangatarere at Gorge Taueru at Te Weraiti Hutt at Kaitoke Hutt at Te Marua Hutt at Birchville Waipoua at Mikimiki Bridge Ruamahanga at Mt Bruce Ruamahanga at Wardells Ruamahanga at Waihenga Waipoua at Mikimiki Bridge Ruamahanga at Mt Bruce Ruamahanga at Wardells June 4 Ruamahanga at Waihenga PAGE 6 OF V

31 Hydrology SoE monitoring programme: Annual data report, 3/4 3.3 Groundwater levels Figure 3.3 shows mean monthly groundwater levels for 3/4 (blue line) compared to historical mean monthly groundwater levels (dotted line) at selected monitoring bores in the Wairarapa Valley. The shaded areas represent the range of historic minimum and maximum mean monthly groundwater levels at each site. Historical Minimum and Maximum Levels Long-term Monthly Mean 3-4 Monthly Mean Groundwater Level -3 Monthly Mean Groundwater Level 66 Plot A: S6/743 (Baring) at Parkvale Confined aquifer - depth 33m Plot B: S6/738 (Towgood) at Parkvale Shallow unconfined aquifer - depth 5m Groundwater Level (m asml) Plot C: T6/494 (Oliver Deep) at Te Ore Ore Semi-confined aquifer - depth 3m Plot D: S6/49 (Perry) at Greytown Shallow unconfined aquifer - depth 5m 99-4 Groundwater Level (m asml) Groundwater Level (m asml) 5 3 Plot E: S7/57 (Martinborough Golf Club) at Martinborough Unconfined aquifer - depth 3m Plot F: S7/7 (Simmonds) at Kahutara Confined aquifer - depth 9m Figure 3.3: Mean monthly groundwater levels in the Wairarapa 3/ V PAGE 7 OF 33

32 Hydrology SoE monitoring programme: Annual data report, 3/4 Figure 3.4 shows mean monthly groundwater levels for 3/4 (blue line) compared to historical mean monthly groundwater levels (dotted line) at selected monitoring bores in the Hutt Valley and on the Kapiti Coast. The blue shaded areas represent the range of historic minimum and maximum mean monthly groundwater levels at each site. The bottom right graph shows alarm levels defined on the Waiwhetu Artesian Aquifer to manage the risk of saltwater intrusion. Historical Minimum and Maximum Levels Long-term Monthly Mean 3-4 Monthly Mean Groundwater Level -3 Monthly Mean Groundwater Level Groundwater Level (m asml) Plot A: R6/696 (CHP Shallow) at Waikanae Shallow semi-confined aquifer - depth m Plot B: R6/6594 (CHP Deep) at Waikanae Deep confined aquifer - depth 74m Plot C: R6/6886 (Te Harakeke) at Waikanae Shallow unconfined aquifer - depth 6m -4 Plot D: S5/58 (Centrepoint) at Te Horo Deep confined aquifer - depth 6m Groundwater Level (m asml) Groundwater Level (m asml) Plot E: R5/3 (Sims Rd South) at Te Horo Confined aquifer - depth 7m Plot F: R7/ (McEwan Park) at Lower Hutt Confined Waiwhetu aquifer - depth 6.m 97-4 Warning Level Critical Level Minimum Level.7 Figure 3.4: 3/4 mean monthly groundwater levels in the Hutt Valley and on the Kapiti Coast 3/4 PAGE 8 OF V

33 Hydrology SoE monitoring programme: Annual data report, 3/4 3.4 Lake and wetland levels Recorded lake levels at Lake Wairarapa and Lake Onoke are shown in Figure 3.5. The 3/4 data are presented as a daily mean level (thin blue trace) and a monthly mean level (bold blue trace). For comparison the long-term mean and historical range are also plotted. The minimum lake water level for Lake Wairarapa (as specified in the Regional Freshwater Plan) is shown by the red shaded area. Lake Wairarapa Seasonal Minimum Target Lake Levels 3-4 Daily Level 3-4 Mean Monthly Level Long-term Mean Lake Wairarapa (Burlings) Lake Level (m amsl) Month.8 Lake Onoke Lake Level (m amsl) Month Figure 3.5: Mean monthly lake levels 3/ V PAGE 9 OF 33

34 Hydrology SoE monitoring programme: Annual data report, 3/4 Water levels have been recorded at three monitoring sites within the Te Hapua wetland complex on the Kapiti Coast since 8. Figure 3.6 shows the 3/4 recorded daily mean water levels at each site in comparison to all previous years of record. 3.8 Te Hapua Wetland at Trotters 3.6 Water Level (metres above mean sea level) Te Hapua Wetland at Shoveler Water Level (metres above mean sea level) Te Hapua Wetland at Jill and Joys Water Level (metres above mean sea level) /9 9/.6 / / /3 3/4.4 Figure 3.6: Daily mean water levels in Te Hapua wetland complex (Kapiti Coast) PAGE 3 OF V

35 Hydrology SoE monitoring programme: Annual data report, 3/4 3.5 Soil moisture Monitoring results for soil moisture content are detailed in Figure 3.7 for the Tanawa Hut (near Tinui) and Longbush monitoring sites. The long-term mean and historical range of recorded values are also shown. Historical range of soil moisture content 3/4 Mean Daily Soil Moisture Content Long-term MeanDaily Soil Moisture Content 6 Tanawa Hut (NE Wairarapa, -4) Mean Daily Soil Moisture Content (%) Longbush (7-4) Mean Daily Soil Moisture Content (%) Month Figure 3.7: Mean daily soil moisture content 3/ V PAGE 3 OF 33

36 Hydrology SoE monitoring programme: Annual data report, 3/4 Acknowledgements Thanks to the hydrology team of GWRC for their assistance and contribution into putting this annual report together, and Nick Boyens, Lindsay Annear and Mike Gordon for reviewing the content. PAGE 3 OF V

37 Hydrology SoE monitoring programme: Annual data report, 3/4 References GWRC, 999. Regional Freshwater Plan for the Wellington Region. Updated July 4 Heath M.W, Perrie A, Morar S, 4. Rivers State of the Environment Monitoring Programme: Annual Data Report, 3/4. GWRC Publication No. GW/ESCI-T- 4/8 Lake Wairarapa Co-ordinating Committee, 99. Lake Wairarapa Wetlands Management Guidelines 99. Edited by Hugh A. Robertson. NIWA,. HIRDS.V3: High Intensity Rainfall Design System. Accessed from Tidswell S, 4. Groundwater Quality State of the Environment Monitoring Programme: Annual Data Report 3/4. GWRC Publication No. GW/ESCI-T- 4/ V PAGE 33 OF 33