DRAINWISE STRATEGIC REVIEW. For Gisborne District Council Lifelines Department

Transcription

1 DRAINWISE STRATEGIC REVIEW For Gisborne District Council Lifelines Department September 2017

2 REPORT INFORMATION AND QUALITY CONTROL Prepared for: Carrie White Strategic Planning and Policy Gisborne District Council Author: Ian Mayhew Principal Planning and Policy Consultant Reviewer: Trent Sunich Senior Environmental Consultant Draft Approved for Release: Aaron Andrew Managing Director Document Name Version History: V Final 7 September 2017

3 CONTENTS Page EXECUTIVE SUMMARY INTRODUCTION Background What is the Problem? What Causes the Problem? STRATEGIC DOCUMENT REVIEW Approach Wastewater Discharges Reduction Plan Problem Definition Targets Levels of Service Key Actions and Guiding Principles Options and Responsibilities for Remediation Works Remediation Cost Estimates Actions Drainwise Plan Implementation Gisborne Wastewater Network Model Updates and Upgrades Report Kaiti Stormwater Model Wastewater Discharges Reduction Workshop One What is the Problem? DISCUSSION AND RECOMMENDATIONS Drainwise Plan Discussion Integrated Stormwater and Wastewater Management Stormwater Flooding Wastewater Network Maintenance Addressing Private Property Stormwater Drainage Problems Funding Options Regulatory Tool Box Development Standards Recommendations List of Tables Table 1: Overflow discharge frequency... 5 Table 2: Remediation options and cost burden... 8 Table 3: GIS Model results (10 year ARI storm) Table 4: Comparison of funding options List of Figures Figure 1: Gisborne wastewater network schematic (from Drainwise)... 4 Figure 2: Responsibility for remedial drainage works Figure 3: Reducing on-property flooding public/private responsibility List of Appendices Appendix A: Relevant Legislation i

4 EXECUTIVE SUMMARY 4Sight Consulting has been commissioned to undertake a review of the Gisborne District Council s (GDC) Drainwise Discharge Reduction Plan (Drainwise Plan). This programme is aimed at improving the performance of Gisborne s wastewater network and specifically to reduce discharges to the environment, primarily wet weather overflows. As is described below, these overflows occur due to excessive ingress (inflow and infiltration) of stormwater into the wastewater network to the extent that capacity of the wastewater network is exceeded in some locations. High, moderate and low impact stormwater sources that contribute to overflows have been identified in the Drainwise Plan as being: High Impact Property flooding causing water to flow over and into gully traps Property flooding causing water to enter the wastewater network via cracked and leaking gully traps Roof water being directed into the wastewater system through gully traps or lateral wastewater pipes Moderate Impact Infiltration via leaking private property lateral wastewater pipes (from houses to the main network) Low Impact Infiltration via Council s wastewater system through leaks at main wastewater pipes and access points While the focus of the review is the Drainwise Plan, a number of other documents were reviewed to understand the problem more comprehensively and to identify GDC s response to date. These reports and documents have provided a comprehensive picture of the problem, issues, and to a lesser extent, GDC s response. They typically deliver a consistent message about the problem and the actions that need to be taken to address them. In our opinion, the Drainwise Plan is generally a good document. It provides a clear and understandable identification of the problem and specific issues, target levels of service, and a list of actions to achieve the target levels of service - although we do have some concerns about how the Drainwise Plan costs are expressed and that network maintenance was not explicitly identified (although probably included as part of business as usual). From our review, the key drainage issues appear clear: Private property drainage needs to be connected to the stormwater network in problem areas; The wastewater network needs to be protected from inflow of stormwater; and Proactive maintenance of the existing wastewater network is required to ensure its capacity and performance are optimised. The first two points are identified in the Drainwise Plan, the primary issue appears to be largely one of implementation the priority that is given to each action and the challenging issue of how private property stormwater flooding and drainage issues are funded and resolved. 1

5 In respect of this latter issue, the Drainwise Plan anticipated that grant funding would be available to fund stormwater improvement works on private property. However, this funding did not eventuate and to date, it appears that little progress has been made on resolving this important issue. In our view, private property flooding is a significant issue both in terms of its significant contribution to overflows and in its own right in respect of the social and health issues associated with flooding and ponding in relatively frequent rainfall events. Resolving property flooding is a key component of reducing overflows and it does not appear to be being substantially addressed by the current programme. In our opinion, the focus of the Drainwise Plan should be on all three key drainage issues identified in the points above particularly the first which we have concluded is a primary contributor to wastewater overflows (and other problems). While there are regulatory options available under s 459 of the Local Government Act (1974) to require appropriate private drainage, in our opinion Council funded and cost sharing options should be put back onto the table and considered, discussed and ultimately determined with the community. We acknowledge the concerns of investing public funds into private drainage, but in our view the issue is complex. Those most affected by flooding are not necessarily the exacerbators of the problem, but rather they can be affected by poor drainage on other properties and past land zoning/development and drainage decisions. The information we have reviewed indicates that reducing private property flooding, albeit potentially costly, is likely to be the single most effective investment to reduce wastewater overflows and furthermore, has other social and health benefits. A flood reduction programme, based on differentiating between private and public responsibilities (and funding) including identifying shared responsibilities and funding where appropriate, will most likely result in better, quicker and more robust long-term outcomes. To move the Drainwise Plan forward, we recommend the following actions: 1. Don t make the problem worse a. Ensure that building and land use consent processes, development standards and certification /inspection are robust and that all new development, re-development, additions and alterations and associated drainage are set at the correct height relative to known and potential future flood/ponding levels. 2. Proactively maintain the existing network a. Review maintenance programmes in problem areas and systematically target proactive maintenance in high risk areas so that the capacity and conveyance performance of the existing wastewater network are optimised. b. Ensure sufficient, on-going budget is provided to continue this maintenance on an appropriate cycle. 3. Implement an integrated wastewater and stormwater management approach a. Re-frame the Drainwise Plan to give stormwater flooding reduction greater prominence and emphasis given its significant contribution to overflows and to reflect the wider issues and benefits associated with flood reduction. b. Integrate stormwater and wastewater priorities and solutions, and focus effort and investment on specific priority areas/sub-catchments to make a tangible difference. c. Take some easy wins : i. Continue to enforce remedying of illegal cross connections/fixing gulley trap cracks etc; ii. iii. Consider options such as increasing gulley trap heights in problem areas (although this should be viewed as a temporary measure and should be undertaken in conjunction with flood mitigation so as not to worsen existing ponding/flooding); Select key GDC stormwater and / or wastewater capital works projects that will contribute to flood reduction/overflow reduction in problem/high-risk areas and implement these as a priority. 2

6 d. Identify the further projects including the wastewater/stormwater network capacity upgrades that are required should the 85% private stormwater inflow/infiltration reduction target not be met. e. Clearly identify the costs associated with the integrated Drainwise Plan above business as usual asset maintenance, replacement and renewal. f. Establish necessary budgets, including alternative revenue streams and funding options for the Drainwise Plan. 4. Develop and implement an equitable and consistent approach to resolving on-property flooding a. Develop, in consultation with the community, an equitable approach to reducing private property flooding and focus this on identified priority areas based on existing modelling and information from GDC s inspection programme. This should incorporate both regulatory tools (see Drainage Bylaw below) and funding/costs sharing approaches. b. Develop guidance as to the circumstances where regulatory, cost sharing and public investment will be applied to ensure equitable and consistent implementation. In developing this guidance, consideration should be given to the factors that contribute to private property flooding. 5. Ensure Council has the appropriate design and regulatory tools in place to address drainage problems a. Finalise the draft Engineering Code of Practice. b. Develop a (stormwater and wastewater) Drainage Bylaw, that addresses (at a minimum) the following: i. Prohibiting the direct discharge of stormwater into the wastewater system. ii. iii. iv. Reinforcing the ability of Council under LGA 1974 Section 459 to require private drainage to be provided to the satisfaction of the council and maintain private drainage to be utilised alongside other flood mitigation options as circumstances dictate. Managing connections to the public stormwater and wastewater networks. Giving effect to the Engineer Code of Practice (once finalised) to ensure the appropriate sizing and design of new stormwater and wastewater infrastructure. v. The appropriate management of overland flow paths to protect downstream properties from inappropriate diversion of stormwater runoff. vi. Works on, or in the vicinity of, the public stormwater and wastewater networks to avoid damage to these networks. c. Obtain legal advice regarding the ability/mechanisms to recover the costs of undertaking work on private property, including via a bylaw. 6. Continue communication and education a. Ensure the public is aware of their stormwater and wastewater management responsibilities for connections into the public stormwater network, wastewater network, and cross-connections. b. Provide information resources to targeted communities / areas including continuing the current assessment programme. c. Ensure this is also provided to non-affected upstream property owners, who may be contributing to downstream problems. Clear timeframes for carrying out the above actions need to be set, with commensurate budgets to fund this work. 3

7 1 INTRODUCTION 4Sight Consulting has been commissioned to undertake a review of the Gisborne District Council s (GDC) Drainwise Discharge Reduction Plan 1 (Drainwise Plan). This programme is aimed at improving the performance of Gisborne s wastewater network, and specifically to reduce wet weather overflows to the environment and private property. As is described below, these overflows occur primarily due to excessive ingress (inflow/infiltration) of stormwater into the wastewater network to the extent that the capacity of the wastewater network is exceeded in some locations, requiring overflow valves to be opened and wastewater to be discharged to rivers within Gisborne. This review is an independent assessment of the Drainwise Plan and associated documents and reports to provide recommendations on options and priorities for achieving the desired overflow reduction and other outcomes. It is not an engineering assessment about the technical options and associated costs of reducing overflows. 1.1 Background The Gisborne city wastewater network services approximately 14,750 houses and businesses. An average of 13,000 cubic metres of wastewater per day goes through the network to the treatment plant. The network is a large system of pipes and access points (manholes) and comprises both private elements (wastewater gully traps and lateral pipes to the public system), and a Council (public) system that comprises wastewater main pipes, pump stations and other wastewater reticulation infrastructure as shown in Figure 1. As such, Council only owns and manages approximately 50% of the wastewater network with the remaining 50% owned and managed by individual landowners and businesses. This has significant implications for managing the wastewater network in an integrated way. Figure 1: Gisborne wastewater network schematic (from Drainwise) 1.2 What is the Problem? The Gisborne City wastewater network has been designed and built to manage the wastewater needs of Gisborne households and businesses for growth over the next 30+ years. The Gisborne public network is generally designed to accommodate approximately four to five times average dry weather flow. This is a common wastewater network 1 Drainwise Wastewater Discharge Reduction Plan. Gisborne District Council, December 2016, Version 4. 4

8 design parameter that means that the network has sufficient capacity to cater for four times normal wastewater flows to accommodate wastewater peaks and some inevitable stormwater ingress into the network over time. Approximately three to four times a year (on average), during heavy rainfall, GDC s wastewater network cannot cope with the amount of water going through it. The excessive stormwater flow into the wastewater network can cause the back up of wastewater in the pipes to the extent that it can discharge from gully traps onto private property, make toilets unusable and damage wastewater infrastructure. To minimise these risks, the network has a series of relief valves that can be opened to allow the wastewater to be discharged in a controlled manner to rivers and the stormwater network (and then to rivers) within the urban area. While the controlled discharge of untreated wastewater to Gisborne s rivers not desirable, it is preferable to the more significant effects and public health risks associated with uncontrolled discharges of wastewater onto private property. Controlled wet weather wastewater overflows do not occur regularly, but only in response to high and prolonged rainfall events. Table 1 tabulates the frequency of overflow events over the past nine years and indicates an average frequency of between two and three overflow events per year. Table 1: Overflow discharge frequency Reporting Year Frequency of discharges 2016/ / / / / / / / / /08 2 Prior to 2006/07 unknown The very wet start to the recent New Zealand winter, from April to the end of May 2017, has resulted in overflows on four separate occasions in an approximate two-month period. This has reiterated and highlighted the problems with the performance of the wastewater network. The community have many concerns around the public health, environmental and cultural impacts of wastewater flowing onto private property, and into rivers and then to harbours and beaches. Some individual landowners are not able to use toilets and showers during heavy rainfall, and have increasing dampness under houses due to stormwater ponding (which in some instances includes wastewater) What Causes the Problem? The overflow happens mainly because large volumes of stormwater get into the wastewater network. There are several entry points for stormwater to get into the wastewater network: Property flooding causing water to flow over and into gully traps; Property flooding causing water to enter the wastewater network via cracked and leaking gully traps; Roof water being directed into the wastewater system through gully traps or lateral wastewater pipes; Infiltration via leaking private property lateral wastewater pipes (from houses to the main network); Infiltration via Council s wastewater system through leaks at main wastewater pipes and access points. 5

9 The above sources are ranked, from high to low, in accordance with the amount of water that could enter the wastewater network during a rain event 2. The first three sources are identified as being high impact, the fourth source being of moderate impact and the last source low impact in the Drainwise Plan. Inflow enters the wastewater system directly, e.g. via illegally or misconnected stormwater drains and overtopping of gully traps. Infiltration typically has a longer response time than that of inflow, and infiltration sources can be due to either high groundwater or rainfall (although high groundwater is usually a result of prolonged rainfall and poor stormwater drainage). Council s response was initially focused on fixing its part of the wastewater network by 3 : Increasing the size of Council s wastewater pipes where they are under capacity. Upgrading the stormwater network to manage larger flood events. Replacing Council s leaking wastewater pipes and access points. More recently Council has started to roll out a programme of private property inspections to: Remove roof downpipes from gully traps. Check for and repair leaking gully traps. Check if gully trap heights are too low. Check for illegal cross connections of stormwater to wastewater. Check for some leaking lateral sewer pipes. Where issues have been identified, Council have asked landowners to fix them, although Council has yet to see the improvements it had expected 3. It is also understood that Council has also recently undertaken jet cleaning of key interceptor pipelines, to reduce fat or silt build-up that may affect conveyance capacities. 2 STRATEGIC DOCUMENT REVIEW 2.1 Approach While the focus of the review is the Drainwise Plan, a range of other documents were reviewed to understand the problem more comprehensively and to identify GDC s response to date. Documents reviewed include: The Drainwise Wastewater Overflow Reduction Plan (v and v4 2016); Gisborne Wastewater Network Model Updates and Upgrades Draft Report; CH2M Beca Ltd, 13 July 2017; Kaiti Stormwater Model Build Report; Opus International Consultants, February 2016; Draft Engineering Code of Practice (Wastewater and Stormwater); Tairāwhiti First, Long Term Plan; amended 19 November 2015; Infiltration and Inflow Control Manual Volume One; Water New Zealand, March 2015; Wastewater Discharges Reduction Workshop One What is the Problem? Report to Future Tairāwhiti Committee, 28 January 2016; and Various presentations and staff reports to Council, and associated responses, spanning the period 2003 to present day. These reports and documents have provided a comprehensive picture of the problem, issues and, to a lesser extent, GDC s response. They typically deliver a consistent message about the problem and the actions that need to be taken to address them. 2 Drainwise Wastewater Discharge Reduction Strategy 2015, version 2. 3 From the Drainwise Plan 6

10 To provide a context for our assessment in the following section, we have focussed on four main documents and present our conclusions below. These documents are: 1. The Drainwise Plan. This is the primary subject of the review. 2. The Wastewater Network Model report. This provides information on the performance of the wastewater network and its response to a reduction in inflow/infiltration. 3. The Kaiti Stormwater Model Report. The overflow problem is as much a stormwater problem as it is a wastewater one. This report provides an example of the stormwater issues associated with a catchment that is identified as contributing significant stormwater to the wastewater network. 4. Wastewater Discharges Reduction Workshop One What is the Problem? This document provides additional information on the problems and what has been done to date. We have also discussed the current implementation programme with GDC staff. 2.2 Wastewater Discharges Reduction Plan In our view, the Drainwise Plan is generally a good document. It provides a clear and understandable identification of the problem and specific issues, target levels of service, remediation options/costs and where the cost lies, and actions to achieve the target levels of service. As much of the information in the Drainwise Plan has informed this review, we have presented the key elements below Problem Definition The background discussion in Section 1 above was sourced from the Drainwise Plan and is not repeated here. However, as we discuss below, while the cause of the problem (excessive stormwater ingress into the wastewater network) is well known, the respective contributions of the various components is not as well documented Targets Levels of Service The Drainwise Plan has set the following medium and long-term outcomes: Medium term: Long term: To reduce the risks to public health, cultural values and the environment of wastewater overflows into rivers and streams and onto private property. A sustainable, efficient and cost-effective wastewater network. It includes the following target levels of service: Reduction of wastewater releases into rivers and streams from four times per year (average) to once every two years (average) by 2026/27. Reduction of wastewater discharged onto private property during heavy rain from four times per year (average) to once every two years (average) by 2026/27. Greatly reduce the number of times households can t use their toilets and wastewater system during a heavy rain event by 2036/37 (10-20% probability of occurring annually). Reduce ponded water on private properties causing dampness in households Key Actions and Guiding Principles Key areas of action identified in the Drainwise Plan are summarised below: Ensure there is enough capacity in the stormwater system to receive stormwater from private property for a rain event that has at least a 10% probability of occurring annually; Ensure the wastewater network has enough capacity - approximately 14km of main wastewater pipes out of 220km require upsizing; Reduce the amount of stormwater entering the wastewater network on a prioritised basis (reducing High Impact by 85%). 7

11 Incentivise/subsidise property owners to assist them with property improvements to reduce the risk of stormwater entering the wastewater network and to reduce dampness. Enforce compliance requirements for privately owned sewer and stormwater drainage as set out in the building code but allow flexibility with timeframes to achieve compliance. Ensure that gully traps are installed above flood levels, stormwater is discharged to an approved outlet and wastewater laterals are up to standard. Council to have a greater involvement in the ongoing management of stormwater on existing private property and new developments due to the high risks this poses to achieving target levels of service. Communicate with the community to raise awareness and ownership of the issues, how they can help and the collective benefits of doing so. Implement a Ten Year Programme of modelling, investigations and remedial work starting with Kaiti, then Whataupoko and finally Elgin/CBD. The following guiding principles were identified to help deal with uncertainty and risk and ensure actions are effective: Managing the wastewater network in an integrated way across Council and private landowner boundaries. Managing wastewater and stormwater together to avoid transferring issues between the two networks. Prioritising actions that address each of the entry points into the wastewater network based on the level of risk. Programming work so that it is affordable for Council and landowners. Playing a more extensive role in coordinating work on private property to ensure it happens so we see improvements. Managing risks by taking incremental steps and basing decisions on robust evidence Options and Responsibilities for Remediation Works Table 2 outlines where the burden of cost falls for each type of remediation work identified in the Drainwise Plan. Table 2: Remediation options and cost burden (from Table 2 of the Drainwise Plan) Remediation GDC Property Owner Grant/ Subsidy Drain property flooding to approved outlet Raise gully traps above 10-year flood level Divert roof water going to ground in flood area to approved outlet Prevent flooding getting to properties Fix leaking gully traps Roof water going directly to gully traps or wastewater Private property sewer laterals leaking Councils sewer mains, access points and laterals leaking Capacity upgrade of wastewater system Capacity Upgrade of stormwater system Ponded water under houses 8

12 From this, it appears that GDC was anticipating the funding of drainage work on-private property by way of grant/subsidy to assist in reducing the cost implications on private property owners. However, as discussed below this funding did not eventuate and the resolution of flooding on private property has generally not been progressed. In terms of the scale of the problem, based on initial assessments in Kaiti, the Drainwise Plan assesses that: 12 houses per hectare (Ha) are affected by property flooding; 33% of property laterals require replacement in the next 20 years; and 14 km of GDC sewer main upgrades are required. We note that this density of properties affected by flooding (12/Ha) is significant. Given a hectare of urban area (10,000m 2 ), approximately 15% (1,500 m 2 ) is taken up by roads/footpaths/parks etc leaving 8,500 m 2 for houses. For an average property size of 650 m 2 (selected from a sample of sites in Kaiti) this equates to a house density of 13/Ha of urban land. Accordingly, the assumption is that almost all properties in problem areas are affected by property flooding. This is a significant issue that needs to be clarified. Where flooding is extensive and affects multiple properties in an area, council intervention or assistance may be appropriate. However, if the problem relates to isolated properties, a different approach may be warranted Remediation Cost Estimates The Drainwise Plan presents three cost estimates (over a 10-year timeframe) for reducing wet-weather overflows: Low option $38,579,900 Medium option $49,997,400 High option $80,097,400 While these cost estimates are itemised, it is not apparent to us how these figures are derived and the extent to which they resolve the problem. The largest component of cost sits in the public realm for wastewater ($11M (low) to $38M (high) for wastewater renewals, $3M to 5M for (public) laterals renewal, $5M to $8M for network upgrades) and stormwater (renewals and upgrades $7M). Significant expenditure ($5M to $13M) is also targeted at works to drain private property. Accordingly, it appears that much of the identified GDC expenditure relates to wastewater asset renewals. Accelerating the renewals/improvement programme under the high cost option may provide greater capacity within the wastewater network and reduce overflows to some extent. However, it may not be the most cost-effective method of reducing overflows and will not resolve on-property flooding. Upgrades to the stormwater network may assist in reducing the latter, provided that the network capacity is a limiting factor. From our understanding of the problem, a primary issue is the draining of stormwater on private properties to the public stormwater network. The costing appears to apply $5.4M to addressing this under the lost cost option up to $13.2M under the higher cost option. Leaving aside the issue of whether it is appropriate for Council to spend money on draining private property 4, this would appear to be the most significant and greatest benefit works that could be undertaken that is, the biggest bang for buck and accordingly we would expect it to be the focus of the programme in the short to medium term. Overall, we are concerned that the costs that are presented are slightly misleading in that asset renewals dominate all three cost options, but it is unclear what outcomes will be achieved when compared to a greater focus on resolving on-property flooding. That is, what asset renewal/upgrade would be required if the high cost option of $13.2M was directed at resolving on-property flooding? Finally, the Drainwise Plan discusses the development and cost implications. Key matters identified are: Council may need to manage property flooding to a higher standard than required by the Building Act (raise the gully trap above the 10 year flood level). The default gully trap height has not provided a solution to reducing gully trap inundation. 4 We understand that this was intended to be funded by grant funding 9

13 Gully trap heights above the 10 year flood level can be specified, when the wastewater network is affected. Costs to private property owners to address private sewer issues could vary from a few hundred dollars to $5,000 to $6,000, these issues will not be subject to grant funding. Where localised stormwater improvements are required, rough order of costs is $10,000, which could be grant funded due to wider betterment Actions The Drainwise Plan includes a series of actions to address the priority issues: 1. Flood waters flowing over and into gully traps (High Impact): a. Drain property flooding to the Council system for 10 year flood level; b. Raise gully traps above the 10 year flood level; c. Divert roof water to Council system if required; d. Prevent flooding getting to the property. 2. Water getting into leaking gully traps (High Impact): a. Inspect and repair/replace broken leaking gully traps. 3. Roof water being piped directly to gully traps or lateral wastewater pipes (High Impact): a. Require downpipes to be connected directly to the Council system. 4. Lateral wastewater pipes from houses to the main network leaking (Medium Impact): a. Inspect, repair/replace, prioritise based on age and leakiness (range of timeframes to achieve compliance). 5. Council s wastewater system leaking at main and lateral wastewater pipes and access points (Low Impact): a. Continue annual renewal of mains, manhole and Council's portion of the sewer lateral. These actions appear comprehensive and appropriate. However in our view the key issue is the relative priority of the actions and the extent to which the highest priority actions, particularly the draining of private property, are being impelemented Drainwise Plan Implementation Information was sought from GDC as to the status of the various implementation actions. We understand the following: Rainfall quick response in heavy rain has a peaking factor of approximately 10 to 15 times average dry weather flow. A subsequent peak occurs, once the ground is saturated, and there is ponding and ingress into gully traps and private laterals. This confirms the significant contribution of stormwater, both direct inflow and infiltration, to wastewater overflows. Currently GDC has two technicians undertaking door to door property inspections to identify illegal connections, gully trap height, condition, lie of the land and discuss ponding issues with landowners (where possible). Approximately 1,000 property inspections in the Kaiti area have been completed to date. It is understood that this information is collected/mapped electronically in the field and should enable problem areas to be identified and mapped. A second, two-person crew is also being trialled. This crew water tests gully traps and do basic seals. Private laterals are also smoke tested or subject to CCTV surveying depending on the age of the house (>75 years) or assessed as being in poor condition. Where illegal drainage is identified, notices to remedy are served, under the Local Government Act (LGA) rather than the Building Act. Where works are not undertaken, Council can step in and undertake the works. However, experience to date is that it is difficult to recover the cost and action is required to do so. Costs cannot be recovered through mechanisms such as adding to rates etc. 10

14 It was confirmed that under the original Drainwise Plan, the intention was to apply to the Eastland Community Trust for the grant funding to assist in resolving on-property flooding. However, we understand that GDC was advised that this application would not be successful and it was not pursued. Therefore, no funding was directed to resolving private drainage/on-property flooding (other than rectifying illegal drainage problems and fixing leaking gully traps). 2.3 Gisborne Wastewater Network Model Updates and Upgrades Report The Gisborne Wastewater Network Model Updates and Upgrades Report (CH2M Beca, July 2017) (Wastewater Model Report) provides the most up to date assessment of the performance and capacity of the wastewater network, its response to high rainfall events, and the effect of removing stormwater from the network. Relevant findings identified in this report are: A large proportion of the Gisborne wastewater network, including interceptors, is very flat. Grades are typically less than 1:200 and a significant proportion are less than 1:300. Due to the low velocities in these pipes, deposition of solids is likely to be occurring in the network effectively reducing the capacity of these pipes. In many instances upgrading existing pipe sizes will not provide significantly more flow capacity, rather they will provide more storage within the network. No overflows are predicted to occur at four times average dry weather flow, and only two in six times dry weather flow. This indicates that the Gisborne wastewater network has been designed adequately to generally convey six times dry weather flow. During a two-year ARI 5 storm, with 85% of fast response stormwater and property flooding removed, overflows will be significantly reduced. To eliminate overflows entirely for the two-year ARI storm (once 85% of fast response stormwater and property flooding inflow has been removed) requires minimal network upgrades, with a cost estimate of $77,000 of capital investment. If only 65% of the fast response stormwater and property flooding is removed, then 38 potential overflow points totalling 5,660 m 3 of overflow remain in a two-year ARI storm. Significant network upgrades would be required to remove all overflow points. These have been indicated in the report. The asset renewal programme should be assessed against the identified upgrades. As asset renewal is undertaken, opportunities to upsize elements of the network should be taken. From this we conclude that targeted, proactive network maintenance should be a component of the Drainwise Plan, to ensure that the performance of the current system is optimised as far as possible. Loss of network flow and storage capacity may unnecessarily contribute to overflows in some areas. Additionally, the wastewater modelling indicates that a significant volume of stormwater (85%) needs to be removed from problem areas to achieve the target overflow containment performance (an average of no more than one overflow every two years). If this is achieved, then minimal upgrades to the wastewater network are required. However, if less than 85% stormwater removal is achieved, a significant number of wastewater network upgrades will likely be required to reduce overflows to the identified one in two years average overflow performance target. Given the multiple benefits associated with reducing on-property flooding, we conclude that this should be the initial focus of the overflow reduction programme. Priority renewals and upgrading can then be sequenced into the LTP in line with affordability. 5 Annual Recurrence Interval A two-year ARI storm is a rainfall event of a magnitude that will occur, on average, once every two years. 11

15 2.4 Kaiti Stormwater Model The Kaiti Stormwater Model 6 is a hydraulic model of the stormwater network for the approximately 1,420 hectare Kaiti area. The catchment is an urban area of predominantly residential housing, with an industrial port area at the mouth of the Waimata River and is identified as a high stormwater inflow area in the Wastewater Model Report. The Stormwater Model Report indicates that when Kaiti experiences heavy rainfall, some areas of the stormwater network are unable to drain the urban area and flooding occurs. Also, some private properties are located below the road and have no, or limited, stormwater drainage, and pond with water during prolonged periods of rainfall. Where stormwater drainage is limited, this standing water then either flows directly or infiltrates into the wastewater system which is subsequently overloaded. It is thought that while the stormwater system generally has sufficient capacity, it is the location and/or capacity of the inlets/sumps and lack of private drainage into the system that cause the majority of the flooding issues. A review of available mapping suggests that approximately 50% of the property area within the catchment is not connected to the public stormwater network The model has been used to assess stormwater flows and flooding for the 10 year ARI storm. The results of this assessment are provided in Table 3 and shows the number and percentage of properties that are estimated to be affected by flooding in the Kaiti catchment and whether there is sufficient head to drain property flooding, assuming all flow is directed to the stormwater network. The report indicates that if only 50% of the private stormwater connections are in place and operating correctly, flood extents are predicted to increase by 75%, while deep flooding (>200mm) is predicted to increase by approximately 58%. Table 3: GIS Model results (10 year ARI storm) (From Opus, 2015) GIS Grouping Number of Parcels % of Total Parcels Total Parcel Area (ha) Sufficient Head and No Flooding (best case) Sufficient Head and Flooding (potential quick wins) Insufficient Head and No Flooding (potential risk areas) Insufficient Head and Flooding (worst case) 2, Wastewater Discharges Reduction Workshop One What is the Problem? This document, dated January 2016, provides a further succinct summary of the problems and considerations. It provides more emphasis on the range of issues associated with the problem, in addition to wastewater overflows to rivers, including: There is a high frequency of uncontrolled wastewater overflows on to private property during wet weather. There is a reasonable number of properties who cannot use their toilets/showers during wet weather events. There are potentially significant health issues within the community due to property flooding which is also contributing to our discharges and overflows. Gisborne has not seen the level of discharge reduction that was expected for the level of investment and intervention/enforcement to date. 6 Kaiti Stormwater Model Build Report. Prepared for Gisborne District Council by Opus International consultants,

16 The report also discussed other options for reducing overflows including capture and containment of the overflow in storage tanks and pumping back into reticulation once rainfall and peak flows had subsided. However, the report concluded that this approach is not preferred as: While it will reduce point source discharges to rivers, it will not address wastewater overflows onto private property (unless storage is significantly dispersed around the city) It will not address property flooding and its contingent problems including rising damp and moisture issues under a home and potential effects on the health and wellbeing of the occupier, and also the use and enjoyment of their property. Treatment plant biological processes are able to function more effectively where the influent wastewater flow is not significantly diluted by stormwater. The report concluded that continuing with the Wastewater Discharges Reduction Programme provides multiple and more comprehensive benefits to the community and the environment and should be continued. 3 DISCUSSION AND RECOMMENDATIONS We have reviewed a number of reports and relevant documents, and have included the key elements of the Drainwise Plan at some length above as it is the primary summary of information of the cause of wastewater overflows and GDC s approach to addressing these. We have also provided a short summary of other selected documents that we consider also provide relevant pieces of the puzzle and assist in understanding the cause, consequences or solutions to the problems and informing the conclusions we have drawn. 3.1 Drainwise Plan As indicated previously in our view the Drainwise Plan is, for the most part, an informative and well written document. It is informed by robust information from stormwater and wastewater models (which continue to be refined and enhanced), together with extensive consideration of on-the-ground issues and experience certainly more than is available for this review. Also, the actions that are indicated in the plan appear comprehensive and relevant to addressing the identified problems. However, implementation of the plan is key and in this regard our questions are: Does implementation address the key problems? We conclude the main issue is stormwater flooding, primarily as a result of private properties that are not connected to the public stormwater network, with overflows and other consequences largely arising from this. While this is identified in the Drainwise Plan, it does not appear to be a current focus of implementation. This appears to be due to the challenge of addressing private drainage, particularly funding this work. Given this important source is not being addressed, it is not surprising that the expected level of overflow reduction has yet to be seen. Does the programme and associated costs align with the actions needed to address the problems? As we have indicated above, we consider the presented costs to be slightly misleading and appear not to be targeted to solving the problem. An example of this, is that the costs of resolving on-site flooding problems varies between $5M to $13M for the low to high options. However, in our view resolving property flooding in high inflow/infiltration areas is the priority and the high cost option for resolving private property flooding should form part of the core programme, possibly in preference to wastewater reticulation and renewal upgrades (which may not be required or can be deferred if stormwater inflows are significantly reduced). Is the implementation strategy clear and the mechanisms appropriate? In respect of implementation we acknowledge that this is very difficult. This is primarily because of the need to address on-property drainage issues and associated cost apportionment and equity issues (and enforcement). However, despite the comprehensive actions in the plan, not obtaining grant funding for private stormwater upgrade has undoubtedly significantly affected the implementation of the plan. 13

17 3.2 Discussion Integrated Stormwater and Wastewater Management An over-arching observation is that, in our view, the title of the Drainwise Wastewater Discharges Reduction Plan is somewhat of a misnomer. As is discussed in the Drainwise Plan and the Wastewater Reduction Workshop Report, the programme is (or should be) much more than that. While there is a focus on the reduction of overflows to rivers, the programme also seeks to reduce potentially significant effects on property and communities such as frequent property flooding, wastewater discharges on private property and the basic function/right to be able use house toilets during rainfall events. Our impression from the reviewed documents (and media reports) is that there is greater emphasis on, and community awareness of, the reduction of overflows to the river and less on the private property and community impacts of flooding. While we understand the drivers for this in our view the stormwater/wastewater flooding issues on private property, and associated social and health impacts, are at least as important and should be afforded greater recognition and emphasis. The implications of the discharge of significant wastewater overflows in events up to the two-year ARI event, with a primary cause being on-property flooding and inundation of gully traps (either overtopping or leaking), is that there is significant property flooding during relatively frequent rainfall events. In our experience, and in accordance with design under the Building Code, private drainage systems should be designed to cater for the ten-year ARI event. We would not normally expect significant and widespread ponding, flooding and overland flow in the two year ARI event and below and certainly not to the extent and depth that would overtop gully traps, even ones that are set relatively low. We accept that this flooding problem is recognised and programmes are in place to progressively reduce problems in flood areas. However, we did not see evidence of a consistent approach to resolving on-property flooding. The Drainwise Plan included funding to resolve on-property flooding (Table 5, page 13), but also indicated that this would be grant funded (which was subsequently not available). A summary of the 2015/25 annual plan expenditure for the wastewater and stormwater activities is provided in a presentation to the Wastewater Options Review Group (WORG) on 28 February 2017 and does not include any provision for addressing private property improvements to address stormwater flooding. Instead, the presentation indicates that this would be the responsibility of private property owners. Accordingly, there does not currently appear to be any coordinated approach to resolving onproperty flooding. In our opinion, the Drainwise Plan requires an integrated wastewater and stormwater management approach. The primary problem is stormwater management and, in particular, on-property flooding. To address the broad spectrum of problems that have been identified requires a focussed and comprehensive approach with greater emphasis on the social and health impacts of property flooding. This could include greater emphasis on, and acceleration of, the target associated with household use of toilets and the addition of a flood resolution target as part of the Drainwise Plan Stormwater Flooding We have discussed the importance of this contributing factor above. The Drainwise Plan example discussed above assumes 12 properties/ha (more than 80%) are affected by flooding in problem areas such as Kaiti. This appears to be supported by the Kaiti Stormwater Model Build Report, particularly when the assumption that only 50% of properties drained to the stormwater network was applied. Accordingly, we assume that the predominant source of inflow and infiltration to the wastewater network is property flooding firstly via overtopping of gully traps and subsequently through increased groundwater levels and infiltration into private lateral drains. Reducing flooding will assist in reducing both sources. As such, we consider that it is useful to better understand the relative contribution of sources and ensure that resources and effort are directed at solving the problem. That said, in our view, there is sufficient evidence that resolving or significantly reducing onproperty flooding is essential to reduce overflows and provide other benefits and should be a priority moving forward with an emphasis on problem areas identified through stormwater modelling and on-site survey work Wastewater Network Maintenance The Wastewater Modelling report highlighted the shallow grade of much of Gisborne s urban drainage network and the high potential for fat/solid deposition and loss of conveyance capacity and network storage. We note that while 14

18 maintenance of the public networks was touched on in some reports, it was not explicitly addressed in the Drainwise Plan although it is likely to be part of business as usual. We are not able to determine or advise on the effect that loss of in-pipe capacity has on overflow volumes and frequency and the backing up of wastewater/floodwater on private property. Anecdotally, we have been made aware of several instances where maintenance resulted in the removal of a significant blockages and fat deposits and that in the past, some maintenance has been deferred to reduce operational expenditure. We appreciate that inspection and maintenance is a routine component of wastewater (and stormwater) network management and hence possibly has been taken as read. However, we have been involved in other wastewater network management programmes where one of the most significant advancements in reducing overflow events was achieved by systematically target proactive maintenance at identified problem hot spots. While the incidence of low-grade pipes is high in Gisborne, we assume that there will still be critical elements of the network that are more susceptible to fat/solid build-up or critical if capacity is reduced. In our view, systematically targeting proactive maintenance at identified problem hot spots should be included in the Drainwise Plan and appropriately budgeted for on a cyclical basis Addressing Private Property Stormwater Drainage Problems Clearly resolving the issue of cross connections and flooding of private property is a priority and is a complex issue, particularly in respect of the apportionment of responsibility and hence cost. In this regard, we generally concur with Table 2 of the Drainwise Plan (presented as our Table 2 above) in that responsibility for addressing the identified problems is a continuum from private through to public, depending on the nature of the problem and the circumstances. We have reframed the Drainwise table and have presented it in Figure 2 below, together with the addition of network maintenance. Illegal/cross connections/leaking gully traps/incorrect gully trap height Stormwater discharged to ground (where drainage available) Private wastewater lateral maintenance Private On-property flooding/innundation fo gully traps Private Public Public wastewater reticulation renewals/upgrades Public stormwater reticulation renewal/upgrades Maintenance of the public wastewater and stormwater networks Public Figure 2: Responsibility for remedial drainage works Probably the most contentious and complex area of responsibility apportionment occurs in the middle zone as depicted above and relates to the issue of on-property flooding and inundation of gully traps. While the February 2017 presentation to WORG advises that this is a private responsibility, we are of the view that this is not black and white and we agree more with the apportionment approach advocated in the Drainwise Plan. On-property flooding, and associated effects, can occur through a range of mechanisms and are not necessarily the fault of the affected 15

19 property owner their problems may result from the lack of suitable stormwater drainage and/or poor overland flow management upstream of their site. Where it arises due to a property s stormwater not being drained to the public stormwater network, and ponds as a result, then this is a private drainage issue and should be addressed by the property owner. However, if on-site flooding occurs in a natural topographical depression, that receives stormwater runoff from surrounding properties (and possibly roads), then we consider that GDC has a role in ensuring that overland flow from upstream properties is appropriately managed and directed to avoid adversely affecting other properties, upstream properties are connected to the public stormwater system, or to ensure that there is a suitable public stormwater system in place to drain properties. An example of this is that in response to questions on the Wastewater Discharges Reduction Workshop One, GDC Officers advised that: 25% of Kaiti houses had been built by the Ministry of Works had open drains which had now been filled in resulting in ponding many of these were owned by Housing Corporation who diligently maintained the properties It appears that, over time, property owners have been allowed to fill drainage channels without providing a suitable equivalent drainage solution. As such ponding on properties may occur due to the actions of others, and the lack of a suitable drainage system. We are also of the same view in respect of gully trap height. Where development has been allowed and the specified development standards of the time have been met and subsequently found to be insufficient, this is not the fault of the landowner, but may be the result of additional development and overland flow that is outside of their control. We are not advising that the responsibility for resolving on-property flooding rests with Council; rather that it is a complex issue that should be reconsidered to ensure an equitable and effective approach to reducing on-property flooding is identified as a priority to achieve multiple community and health benefits. The affected parties are not necessarily the exacerbators of the problem and the complexity of the problem is such that a consolidated and coordinated approach is required. Public drainage solutions/cost sharing should be considered alongside regulatory mechanisms (see the bylaw below) depending on the specific circumstances and an approach or set of criteria should be established to guide decisions. As a guide, Figure 3 shows an indication of where public and private responsibility may fall for common stormwater drainage problems. Generally Public Public or Private Generally Private Insufficient capacity in the public network (storm/waste water) Lack of suitable public stormwater connection in vicinity Where development has been allowed in low topographic areas with no suitable drainage solution Lack of private stormwater drainage multiple sites in same area Gulley trap set at correct legal height, but subsequently found to be too low Inappropriate diversion of overland flow Illegal cross connections Stormwater discharged to ground and not stormwater drain Lack of private stormwater drainage - public network in vicinity (single house) Gulley trap set below legal height Figure 3: Reducing on-property flooding public/private responsibility 16

20 3.2.5 Funding Options Options for funding works on private property are not unique to Gisborne, but are faced by most Councils, and funding strategies are addressed in Water New Zealand s Infiltration and Inflow Control Manual 7. They identified three options, each with their own benefits and disadvantages as summarised in Table 4. Table 4: Comparison of funding options (from Water NZ, 2015) Option Advantages Disadvantages 1 Owner pays full cost Low funding commitment from agency Lower participation rates Long timeframe for complete rehabilitation Low-income owners are disadvantaged 2 Agency (Council) pays full cost 3 Agency (Council) pays partial cost Higher participation rates Relatively shorter timeframe for complete rehabilitation Higher participation rates than 1 More affordable than 2 Increased funding for low-income owners could create more equitable situation May be cost-prohibitive Legal issues with using public funding for private assets Legal issues with using public funding for private assets Lower participation rates than 2 Less affordable than 1 The Water NZ report addressed options for addressing options 1 and 3 above. For option 1 (in addition to requiring owners to undertake the work) Council could consider carrying out the repair on the property owner s behalf and charging them for this work by one of the following: A separate charge; A soft-loan incentive by the Council to the property owner, reimbursable to the water -authority by separate payment of an on-going levy on their water-wastewater bill or local government rates; or Where owners are unable/unwilling to pay, place a lien/caveat upon the property for the cost of the works, accruing interest at an agreed rate recoverable upon sale of the property. However, we understand that Council s experience to date is that it is difficult and time consuming to undertake the work and recoup the costs where there is an unwilling landowner. The Water NZ did not appear to advise what legal mechanism could be used to implement the second and third options above this should be considered in more detail. In respect of the cost sharing model, while this could provide a feasible compromise to funding the rehabilitation; implementing a cost-sharing scheme also introduces complexities and numerous parameters including: The percentage of the cost the agency will fund; The dollar amount of the financial incentives to be offered to each property; If different properties receive different amounts; If properties in critical project areas should be offered higher amounts; If the amount offered depends on the level of rehabilitation required; The capped dollar amount per property; If low-income homeowners receive a higher amount; and 7 Infiltration & Inflow Control Manual: Volume One - Overview, Background, Theory. Water New Zealand. 2nd Edition March

21 The maximum amount of funds that can be offered per annum. Again however, the same issues of equity and what to do will unwilling landowners, or those who cannot afford to have the work done, are relevant. We concur with statements in the Water NZ assessment presented in Table 3 above. Participation rate, certainty and quality of outcome and implementation timeframes improve for Council funded or assisted options. In our view, Council funded/assisted options should be put back on the table and re-considered alongside other options to accelerate and better ensure overflow reduction and other outcomes Regulatory Tool Box We expect that GDC is well appraised of the tool box that can be applied to address issues that arise as they are utilising them on a regular basis and will be familiar with their respective applicability and success rate. A range of applicable regulatory tools are provided in Appendix A. One regulatory tool that has not been adopted by GDC to date is a wastewater/stormwater bylaw under the Local Government Act (2002). As indicated in Appendix A, a bylaw can be made by a territorial authority for a range of purposes including for the management of wastewater, drainage, and sanitation and land drainage. Water NZ (2015) indicates that Nelson City Council has adopted bylaws to facilitate its inflow and infiltration works. This bylaw prohibits the discharge of stormwater into the wastewater system and provides the Council a legal basis for investigating and rehabilitating inflow and infiltration sources on private property. This could also be used to issue defect notices and require property owners to remediate issues on their property. We are also aware that the Auckland Council Stormwater Bylaw (2015) is very broad in its content and application and includes the management of overland flow paths and the maintenance and operation of private stormwater systems. The Auckland Council also has a Water Supply and Wastewater Network Bylaw (2015), which (similar to the Nelson City Council Bylaw) includes a clause that prohibits stormwater entering the wastewater network. In our view, GDC should develop and implement a stormwater and wastewater drainage bylaw to assist in giving effect to its powers under the LGA in respect of drainage. While we have not made an extensive consideration of what aspects of drainage management would be best served by a bylaw, at a minimum it could address the following: Prohibiting the discharge of stormwater into the wastewater system. Reinforcing the ability of Council under LGA 1974 Section 459 to require private drainage to be provided to the satisfaction of the council and maintain private drainage to be utilised alongside other flood mitigation options as circumstances dictate. Managing connections to the public stormwater and wastewater networks. Giving effect to the Engineer Code of Practice (once finalised) to ensure the appropriate sizing and design of new stormwater and wastewater infrastructure. The appropriate management of overland flow paths to protect downstream properties from inappropriate diversion of stormwater runoff. Works on, or in the vicinity of, the public stormwater and wastewater networks to avoid damage to these networks. We note that while a bylaw will provide an additional tool to assist in managing drainage problems, it may not fully address all drainage and on-property issues. Additionally, a bylaw cannot impose a performance requirement, for example the height of a gully trap, that is more stringent than that of the Building Act and code. Legal advice should also be obtained as to whether a bylaw can facilitate cost recovery for drainage works undertaken by Council on private property, particularly whether costs can be recouped over time via an on-going levy on water/wastewater bills or local government rates (consistent with the options presented in the Water NZ report discussed above). 18

22 3.2.7 Development Standards With improved flood height information, GDC is in a position to better ensure that new development, redevelopment and additions (and associated gully traps) occur above flood levels so that flooding and wastewater overflow problems are not increased. As we have indicated previously, we have some concerns about where the cost should fall for retrospectively applying new standards to existing development for example requiring existing gully traps to be re-set above newly identified flood heights. However, it is important that appropriate standards are set and enforced for new and re-development to protect the wastewater and stormwater networks. This include finalising the draft Engineering Code of Practice (wastewater and stormwater) and ensuring that Building Act/Code requirements are appropriately implemented and compliance enforced/certified. 3.3 Recommendations In our view, the actions in the Drainwise Plan are valid and comprehensive. The primary issue appears to be largely one of implementation the priority that is given to each action and in particular the challenging issue of how private property flooding is funded and resolved/reduced. To move the Drainwise Plan forward, we have the following recommendations and associated actions: 1. Don t make the problem worse a. Ensure that building and land use consent processes and development standards and certification/inspection are robust and that all new development, re-development, additions and alterations and associated drainage are set at the correct height relative to known and potential future flood/ponding levels. While we appreciate that these processes are likely to already be in place, we think it is important to ensure that flooding and overflow problems are not exacerbated by poorly designed/constructed private drainage systems. Opportunities to upgrade systems should also be taken where redevelopment/significant additions occur. 2. Proactively maintain the existing network a. Review maintenance programmes in problem areas and systematically target proactive maintenance in high risk areas so that the capacity and conveyance performance of the existing wastewater network are optimised. b. Ensure sufficient, on-going budget is provided to continue this maintenance on an appropriate cycle. As indicated in the Wastewater Model Report, Gisborne has a large number of pipes that have low grades, resulting in low flow velocities and a susceptibility for fat/solid build up. Ongoing targeted proactive maintenance programmes should be implemented in problem areas and for critical infrastructure to ensure that a loss of network capacity is not contributing to overflows and the backing up of wastewater onto private property. 3. Implement an integrated wastewater and stormwater management approach a. Re-frame the Drainwise Plan to give stormwater flooding reduction greater prominence and emphasis given its significant contribution to overflows and to reflect the wider issues and benefits associated with flood reduction. b. Integrate stormwater and wastewater priorities and solutions, and focus effort and investment on specific priority areas/sub-catchments to make a tangible difference. c. Take some easy wins : i. Continue to enforce remedying of illegal cross connections/fixing gulley trap cracks etc; 19

23 ii. iii. Consider options such as increasing gulley trap heights in problem areas (although this should be viewed as a temporary measure and should be undertaken in conjunction with flood mitigation so as not to worsen existing ponding/flooding); Select key GDC stormwater and / or wastewater capital works projects that will contribute to flood reduction/overflow reduction in problem/high-risk areas and implement these as a priority. d. Identify the further projects including the wastewater/stormwater network capacity upgrades that are required should the 85% private stormwater inflow/infiltration reduction target not be met. e. Clearly identify the costs associated with the integrated Drainwise Plan above business as usual asset maintenance, replacement and renewal. f. Establish necessary budgets, including alternative revenue streams and funding options for the Drainwise Plan. While we appreciate that flooding is identified in the Drainwise Plan and discussions with GDC staff as a key contributor to overflows, it appears that flood resolution is given less emphasis than overflow reduction. In our view, the social and health issues associated with relatively frequent flooding and ponding on private property should have equal prominence. This could include a specific target for reducing flooding/ponded water on private land and a more aggressive target for the number of/period of time properties are unable to use their sanitary facilities. To maximise improvements, we recommend focusing on an area at a time. From our initial review and other information, the identified drainage catchment priorities in the Drainwise Plan are appropriate particularly if resolving stormwater flooding is given greater prominence. A problem resolution approach should be undertaken to identify the best improvements to reduce or resolve the problems across public and private wastewater and stormwater networks. These will need to be supported by appropriate funding. In our discussion above, we have raised the concern that the Drainwise Plan costs are potentially misleading in that they are dominated by asset renewal/upgrade when this does not appear to be the primary method of reducing overflows. In our opinion, flood mitigation on private property should be a fundamental component of all options with low, medium and high cost options being primarily associated with the timing and rate at which asset renewal and upgrading is undertaken to address lower impact sources. 4. Develop and implement an equitable and consistent approach to resolving on-property flooding a. Develop, in consultation with the community, an equitable approach to reducing private property flooding and focus this on identified priority areas based on existing modelling and information from GDC s inspection programme. This should incorporate both regulatory tools (see Drainage Bylaw below) and funding/costs sharing approaches. b. Develop guidance as to the circumstances where regulatory, cost sharing and public investment will be applied to ensure equitable and consistent implementation. In developing this guidance, consideration should be given to the factors that contribute to private property flooding. This is a key component to reduce ponding and associated overflow issues and it is clear that it is not being addressed by the current programme. In our view, Council funded and cost sharing options should be put back onto the table and considered, discussed and ultimately determined with the community alongside regulatory options. While we appreciate the issue and ramifications of investing public funds into private infrastructure, we agree with the Drainwise Plan when it indicates that there are wider benefits associated with flood mitigation. Those most affected are not necessarily the exacerbators of the problem, but rather they receive the consequences of a history of land development and drainage decisions. Additionally, the information we have reviewed indicates that reducing private property flooding, albeit potentially costly, is likely to be the single best investment to reduce overflows and other social and health impacts. 20

24 A Council/shared funding model will most likely result in better, quicker and more robust long-term outcomes. 5. Ensure Council has the appropriate design and regulatory tools in place to address drainage problems a. Finalise the draft Engineering Code of Practice. b. Develop a (stormwater and wastewater) Drainage Bylaw, that addresses (at a minimum) the following: i. Prohibiting the direct discharge of stormwater into the wastewater system. ii. iii. iv. Reinforcing the ability of Council under LGA 1974 Section 459 to require private drainage to be provided to the satisfaction of the council and maintain private drainage to be utilised alongside other flood mitigation options as circumstances dictate. Managing connections to the public stormwater and wastewater networks. Giving effect to the Engineer Code of Practice (once finalised) to ensure the appropriate sizing and design of new stormwater and wastewater infrastructure. v. The appropriate management of overland flow paths to protect downstream properties from inappropriate diversion of stormwater runoff. vi. Works on, or in the vicinity of, the public stormwater and wastewater networks to avoid damage to these networks. c. Obtain legal advice regarding the ability/mechanisms to recover the costs of undertaking work on private property, including via a bylaw. Bylaws are utilised by other councils to assist in the management of stormwater and wastewater under the LGA. A bylaw provides an additional mechanism by which illegal drainage, or requirements to provide drainage (pursuant to s459 of the LGA 1974) can be addressed. Consideration should also be given to whether a bylaw can assist in providing mechanisms to assist private funding of drainage works, including those identified in the Water NZ report discussed above. 6. Continue communication and education a. Ensure the public is aware of their stormwater and wastewater management responsibilities for connections into the public stormwater network, wastewater network, and cross-connections. b. Provide information resources to targeted communities / areas including continuing the current assessment programme. c. Ensure this is also provided to non-affected upstream property owners, who may be contributing to downstream problems. We appreciate that this has been an aspect of the Drainwise Plan and recommend that it continues to be implemented, subject to the changes in approach discussed above, particularly a greater emphasis on resolving on-property flooding. Clear timeframes for carrying out the above actions need to be set, with commensurate budgets to fund the work. 21

25 Appendix A: Relevant Legislation

26 Legislation Tool/Section Trigger/Application Building Act 2004 Building Code Local Government Act 1974 Subpart 8 Notices to fix G13 Foul Water Section 459 Council may require owners of land in certain cases to provide private drains A notice to fix is a statutory notice requiring a person to remedy a breach of the Building Act 2004 or regulations under that Act. A notice to fix can be issued for all breaches of the Act, not just for building work. The responsible authority must issue a notice to fix if it considers on reasonable grounds that: a specified person is contravening the Building Act 2004 (for example, doing building work without a building consent, or doing work not in accordance with a building consent) a specified person is contravening any of the Building Regulations under the 2004 Act (including Building Regulations 1992, containing the Building Code) a building warrant of fitness is not correct the inspection, maintenance or reporting procedures stated in the compliance schedule are not being, or have not been, complied with. The objective of this provision is to: (a) safeguard people from illness due to infection or contamination resulting from personal hygiene activities, and (b) safeguard people from loss of amenity due to the presence of unpleasant odours or the accumulation of offensive matter resulting from foul water disposal Council can require the owner of any land or building to: to provide, construct, and lay a private drain from any land or building which is not drained by some drain to the satisfaction of the council, and to connect that private drain with any public drain or watercourse or the sea, as the council thinks fit: to cleanse and repair or to relay or alter the course, direction, and outfall of any existing private drain of or belonging to the premises: to connect any such existing private drain with any public drain or watercourse other than the public drain or watercourse with which the private drain was previously connected: to provide and affix in and to any such existing private drain, and in and to any such new private drain, all such traps, methods of ventilation, and other fittings whatever as the council directs: to connect or disconnect any existing or new private drain with or from any water closet, urinal, bath, sink, grease trap, or other sanitary appliance: to execute, provide, and do generally any works, materials, and things which in the opinion of the council are necessary or expedient for the efficient drainage of the premises and every part thereof. The foregoing powers shall, among other things, enable the council to require any owner of premises to cause any pollutant and any water that does not contain any pollutant to be drained respectively by sewerage drains and stormwater drains to separate outfalls: provided that the council shall not in any such notice require any pollutant to be drained into any open drain. If the owner fails to do any work specified as directed, the council may, if it thinks fit, cause the work to be done, and may recover from him the costs and expenses of the work together with 10% of those costs and expenses for supervision by the officers or agents of the council, and interest at a rate per annum, as fixed by the council and apportion costs between landowners.

27 Legislation Tool/Section Trigger/Application Local Government Act 2002 Health Act 1956 Including the Health (Drinking Water) Amendment Act 2007 AS/NZS :2015 Part 8 Bylaws 151 General provisions applying to bylaws made under this Act 152 Effect of Building Act 2004 on bylaws S163 Removal of works in breach of bylaws Subpart 3 s181 Powers in relation to private land S242 penalties for offences S64 Bylaws Plumbing and drainage standards Territorial authorities have the ability to make bylaws for 1 or more of the following purposes: protecting the public from nuisance: protecting, promoting, and maintaining public health and safety: minimising the potential for offensive behaviour in public places. The Act specifies that (without limiting) a bylaw may be made for the purposes of regulating on-site wastewater disposal systems, waste management, trade waste and solid waste; and of managing, regulating against, or protecting from, damage, misuse, or loss, or for preventing the use of, the land, structures, or infrastructure associated with wastewater, drainage, and sanitation and land drainage. A bylaw may require anything to be done in any manner, or within any time, that is required by the local authority or by a person referred to in the bylaw. A bylaw may leave any matter or thing to be regulated, controlled, or prohibited by the local authority by resolution either generally, for any specified classes of case, or in a particular case. A council may not make a bylaw under this Act that purports to have the effect of requiring a building to achieve performance criteria additional to, or more restrictive than, those specified in the Building Act 2004 or the building code. If authorised by a bylaw to do so, a local authority may remove or alter a work or thing that is, or has been, constructed in breach of a bylaw; and recover the costs of removal or alteration from the person who committed the breach. A territorial authority may construct works on or under private land or under a building on private land that it considers necessary for sewage and stormwater drainage. This is subject to Schedule 12 if not consented to by the land owner. An enforcement officer may enter any land or building (but not a dwelling) to determine whether any drainage works on any land are being misused. Penalties for non-compliance with a Bylaw up to $20,000 ($200,000 for trade waste). Under this Act, bylaws can be made for: improving, promoting, or protecting public health, and preventing or abating nuisances: regulating drainage and the collection and disposal of sewage, and prescribing conditions to be observed in the construction of approved drains: Includes a number of standards relating to drainage design, drainage systems and general design requirements for sanitary plumbing.

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