Tweed Shire Demand Management Strategy & Water Supply Augmentation Options Study A Brief Technical Review

Transcription

1 Tweed Shire Demand Management Strategy & Water Supply Augmentation Options Study A Brief Technical Review quality solutions sustainable future

2 Tweed Shire Demand Management Strategy & Water Supply Augmentation Options Study A Brief Technical Review GeoLINK, 2011 PO Box 9 Lennox Head NSW 2478 T PO Box 1446 Coffs Harbour NSW 2450 T info@geolink.net.au

3 Version History UPR Description Date Issued Issued By Reviewed By 1 st issue 08/02/2011 Duncan Thomson Craig Zerk

4 Table of Contents 1 Background 1 2 General Comments Separation of the Studies Baseline Forecasts Tweed Shire s Future Water Supply The Challenge Note on Scenario 1 Assumptions Council's Current Favoured Options Potential Alternative Options Larger Rainwater Tanks Recycled Water combined with Rainwater Tanks Closing Remarks 9 i

5 Background The purpose of this document is to present the key issues identified as part of a brief technical review of various reports associated with the planning of the future water supply for Tweed Shire. These reports include: Tweed Shire Council: Demand Management Strategy Stage 1 (MWH, Rev. No. 3, 16/11/09) Tweed Shire Council: Demand Management Strategy Stage 2 (MWH, Rev. No. 2.1, 21/12/09) Tweed Shire Council: Demand Management Strategy (MWH, Rev. No. 1.1, 21/12/09) Tweed District Water Supply Augmentation Options Study: Stage 3 Fine Screen Assessment of Shortlisted Options (MWH, Rev. No. 3.0, 28/09/10) The review was carried out by engineers from GeoLINK, an environmental management and design consultancy that has been in operation on the north coast of NSW for twenty years. GeoLINK undertook the review at its own initiative and did not receive any payment for the work. The purpose of this review is to consider the water supply planning process with a 'fresh set of eyes'. The intention is to provide constructive suggestions that will assist Council in its quest to pursue the most appropriate and sustainable water supply strategy for Tweed Shire. This document constitutes a 'brief technical review'. It is not a comprehensive review of the aforementioned reports. It is understood that the water supply planning process has been ongoing for at least the past four years, involving the detailed analysis of options and collaboration with stakeholders. GeoLINK has not been involved in any aspect of this process and it has been a challenge to come 'up to speed' with the key issues in a short timeframe. Therefore, despite the fact that this document has been prepared in good faith, it is possible that some of the comments and assertions are inaccurate due to a lack of detailed understanding of the work. 1

6

7 General Comments 1.1 Separation of the Studies Undertaking the Demand Management Strategy and the Water Supply Augmentation Options Study as separate processes (as has been done in Tweed Shire) is unlikely to produce the best outcome. Both processes are a means to the same end i.e. ensuring there is sufficient water for the projected future population scenario. The required outcome can be achieved by numerous combinations of initiatives. Whether those initiatives are classified as 'loss reduction', 'demand management', 'water recycling' or 'supply augmentation' is inconsequential. The most appropriate and sustainable water supply strategy should be developed by considering all options in an integrated manner. The Water Supply Augmentation Options Study assessed nine options: Option 1 Raising Clarrie Hall Dam Option 2 New dam on Byrrill Creek Option 3 New dam on Oxley River Option 4 Pipeline to connect to Rous Water network Option 5 Pipeline to connect to SEQ network Option 6 Desalination Option 7 Groundwater supply Option 8 Indirect potable reuse Option 9 Direct potable reuse It would have been beneficial to include the options considered in the Demand Management Strategy (i.e. rainwater tanks and localised application of recycled water) in the same multi criteria assessment process to ensure the most appropriate integrated strategy was identified. It is acknowledged that these options on their own are unlikely to satisfy the required annual yield. However, this highlights a shortcoming of the Water Supply Augmentation Options Study, which is that combinations of options were not considered. Options 4 and 7 were automatically discarded because they didn't meet the minimum annual yield requirement. This ignores the possibility that they could have formed part of an integrated (and perhaps more flexible and resilient) solution that might have scored well in the multi criteria assessment. For example, what would have been the score for an option incorporating groundwater supply and recycled water for the greenfield major development areas? 1.2 Baseline Forecasts The NSW BASIX legislation and the federal WELS scheme are 'givens' they are not options that Council can decide to either pursue or abandon. All new residential buildings, as well as significant additions or alterations to existing residential buildings, must comply with the water saving requirements of BASIX. The WELS scheme has been in place for more than five years and it is reasonable to assume that it will not be abandoned. Therefore, the impact of BASIX and WELS should be included in any baseline forecasts of future water demand, because this essentially represents the 'do nothing' option from a Council perspective. It is considered unrealistic to present baseline forecasts that do not include the impact of these measures, as has been done in various reports, including Section of the Demand Management Strategy Stage 1 and Section of the Water Supply Augmentation Options Study. It is acknowledged that these unrealistic baseline forecasts have not been used to determine the required annual yield. However, the presentation of these forecasts in various tables and 3

8 charts is considered to be unhelpful to the process, because it provides a misleading impression of the Shire s future water demands. There is also concern that the baseline forecasts may have been unwittingly over-estimated because the numbers presented in Table 4-3 of the Demand Management Strategy Stage 1 are inconsistent with the numbers presented in the preceding Tables 4-1 and 4-2. If the numbers presented in Tables 4-1 and 4-2 are correct, then the average daily consumptions per account for 2004/05 and 2005/06 presented in Table 4-3 have been over-estimated by approximately 14%. If indeed there has been an unintentional over-estimation in Table 4-3, it appears as though this error has been carried through to Tables 4-4 and 4-5 and the subsequent baseline forecasts. 4

9 Tweed Shire s Future Water Supply 2.1 The Challenge According to Section of the Water Supply Augmentation Options Study, the current secure yield of 13,750 ML/yr will be exceeded in 2023 if Scenario 1 eventuates or 2031 if Scenario 4, which is Council's adopted 'demand management' scenario, eventuates. Given that Scenario 4 has been adopted by Council and presumably will be adequately funded and resourced, this scenario would seem to be a likely outcome. However, the study has adopted Scenario 1 for forecasting future water demands stating that it is a more conservative target and more readily achievable. Based on Scenario 1, future water demand is predicted to rise to 16,750 ML/yr by 2036, the end of the planning period. Therefore, the objective is to find an additional 3,000 ML/yr of secure yield compared to Scenario Note on Future Water Demand Forecasts The future water demand forecasts quoted above are taken from the Tweed District Water Supply Augmentation Options Study: Stage 3 Fine Screen Assessment of Shortlisted Options (MWH, Rev. No. 3.0, 28/09/10). However, a presentation to a Council workshop in late 2010 appears to indicate that the forecasts have been refined since the publication of this report and that under Scenario 1 the current secure yield of 13,750 ML/yr will not be exceeded until 2026 or possibly even Accordingly, the forecast water demand in 2036 has been revised down to 15,750 ML/yr or possibly even 14,750 ML/yr. If indeed the future water demand forecasts have been revised down, the water planning objective may be to find an additional 1,000 ML/yr or 2,000 ML/yr of secure yield compared to Scenario 1, rather than the 3,000 ML/yr quoted above Note on Scenario 1 Assumptions Scenario 1 is described as the implementation of BASIX in the five greenfield major development areas, with the achievement of BASIX compliance assumed to be through the incorporation of a 5,000 L rainwater tank connected to several household uses. It is unclear whether Scenario 1 also assumes the implementation of rainwater tanks in all other residential developments, including the greenfield developments that are outside the five major development areas and the infill developments. Scenario 1 needs to allow for this because all of these other residential developments will also need to comply with BASIX. If Scenario 1 does not assume rainwater tanks will be installed in all new residential developments, this is an oversight that should be corrected and the water demand forecasts should be updated accordingly. 2.2 Council's Current Favoured Options The Water Supply Augmentation Options Study recommended that Option 1 Raising Clarrie Hall Dam be pursued. Council has voted to instead pursue Option 2, which involves the construction of a new dam on Byrrill Creek. The option of raising Clarrie Hall Dam would provide an additional secure yield of 7,170 ML/yr, which is 2.4 times the required target of 3,000 ML/yr. The option of building a new dam on Byrrill Creek would provide 8,700 ML/yr, which is 2.9 times the required target. Bearing in mind that the 3,000 ML/yr target is considered to be 'conservative' and assumes that most of Council's adopted demand reduction initiatives will fail, both of these options seem to be out of proportion with the water supply challenge faced by the Shire in the current planning period (i.e. to 2036). 5

10 2.3 Potential Alternative Options Could the 3,000 ML/yr target be achieved by options, or combinations of options, other than those assessed in the Water Supply Augmentation Options Study? From a technical and cost perspective, there are benefits associated with options that can be implemented in a staged manner to match the gradual increase in demand over time. Examples include water supply options at the household scale (e.g. rainwater tanks, greywater treatment systems), decentralised water recycling schemes, and desalination. It is suggested that one option that could be investigated is making new residential developments more selfsufficient with regard to water. The Demand Management Strategy recommends that new residential dwellings should comply with the water saving requirements of BASIX and assumes that compliance will be achieved through the implementation of a 5,000 L rainwater tank (on average) for each dwelling, with the rainwater tank connected to external uses, toilets and the cold water supply to the washing machine. The study indicates that this scenario would lead to a reduction in town water use of approximately 36% (compared to the base case), which is equivalent to a reduction of 80 kl/yr or 219 L/d for the average household. Outlined below are two options that focus on making new residential developments more self-sufficient with respect to water. Each option would result in additional town water savings of approximately 1,000 ML/yr compared to the adopted Scenario 1. Therefore, either option would need to be part of a larger, integrated solution to achieve the 3,000 ML/yr target. However, if Council s overall demand management strategy proves to be more successful than has been assumed, either of these options may be sufficient to secure the Shire s water supply until 2036 and beyond. It is acknowledged that the unit rate cost of water (i.e. in $/ML) saved by either of these options is likely to be higher than the unit rate cost of water produced by the two dam options. However, they have significant environmental and sustainability benefits (reduced stormwater runoff impacts and reduced effluent discharges) and offer greater diversity and flexibility compared to the two dam options Larger Rainwater Tanks If town water use could be reduced by an additional 100 L/d for new detached houses and 50 L/d for new higher density residences, the additional reduction in town water demand would be approximately 1,000 ML/yr in This has been calculated as follows: 16,000 new detached houses x 100 L/d x 365 d/yr = 584 ML/yr + 23,000 new higher density dwellings x 50 L/d x 365 d/yr = 420 ML/yr 1,004 ML/yr One way to achieve this would be to increase the size of the rainwater tank and also increase the number of household uses that are supplied with the collected rainwater. NSW Health does not support the use of rainwater for drinking and cooking when a town water supply also exists. However, other uses that are acceptable include hot water supply, showering and bathing. A preliminary rainwater tank analysis has been undertaken and this suggests that for a typical detached house, additional water savings of 100 L/d could be achieved by increasing the rainwater tank size to 10,000 L and connecting the tank to external uses, toilets, laundry and the hot water supply. A similar analysis has not been completed for higher density residences, but it is expected that additional water savings of 50 L/d could be readily achieved with a similar approach. It is understood that there may be planning and legislative issues that would hamper the ability of Council to mandate the installation of rainwater tanks larger than those required to comply with BASIX. If this is the case, this issue should be resolved at the State level as a matter of priority because it directly contradicts the integrated water management outcomes that the State is trying to promote. Acknowledging that action on this issue at a State level may not happen quickly, a potential way around this is for Council to offer a financial incentive to homeowners and builders to install a tank of the size desired by Council. If an incentive of approximately $1,000 per dwelling was offered for the installation of a 10,000 L tank, this would be a cheaper 6

11 option for homeowners than installing a non-subsidised 5,000 L tank. To fund this incentive for all new residences would cost approximately $39M, which is comparable with the costs of the two dam options Recycled Water combined with Rainwater Tanks A recycled water scheme is likely to be most practical in the five greenfield major development areas (although it may also be a viable option in some of the smaller greenfield development areas). The Demand Management Strategy assessed Scenario 3, which involved the provision of recycled water to all residences in the major development areas, as well as 5,000 L rainwater tanks. The recycled water would be connected to external uses and toilets, while the rainwater tank would be connected to the cold water supply for the washing machine and showers. Table 5-11 of the Demand Management Strategy Stage 1 states that this scenario would result in additional water savings of 910 ML/yr compared to the adopted Scenario 1. If the uses of the rainwater were maximised to include all laundry uses and the hot water supply, it is likely that the additional water savings would be approximately 1,000 ML/yr compared to Scenario Decentralised Wastewater Recycling The wastewater recycling option assessed in the Demand Management Strategy comprised a centralised treatment approach, whereby wastewater from the five major development areas would be transferred to either the Banora Point Water Reclamation Plant (WRP) or the Kingscliff WRP for treatment. The recycled water would then be pumped from the WRPs back to the new subdivisions for supply to individual houses via a dedicated recycled water pipe system (i.e. dual reticulation). It is possible that the implementation of decentralised sewer mining schemes at each of the major development areas may be more cost-effective and it is suggested that this could be investigated further. The additional assessment of a new wastewater treatment plant at Cobaki Lakes, which is presented in the Demand Management Strategy, appears to support this assertion. Section of the Demand Management Strategy Stage 1 states that the implementation of a sewer mining scheme would not result in any savings in the sewage reticulation infrastructure because the wet weather flows would still need to pass through to the downstream WRP. However, it is noted that there would be operational cost savings associated with the fact that less wastewater would be transferred to the WRP and subsequently treated Community Acceptance In Section of the Demand Management Strategy Stage 1, it is stated that, with regard to the options for the five major development areas, Scenario 1 (rainwater tanks only) will have better community acceptance compared to Scenarios 2 and 3, which involve recycled water. Given the successful implementation of recycled water schemes in other regions of Australia in recent years, it is suggested that there are unlikely to be community acceptance issues that cannot be overcome with appropriate engagement and education Contingency Installation of Dual Reticulation Infrastructure If there is a possibility that recycled water may be supplied to a subdivision that is currently going through the design and approval process, it would be prudent to require the design of the subdivision to include dual reticulation. If the provision of recycled water to the subdivision is still undecided at the time of subdivision construction, key portions of the dual reticulation infrastructure (e.g. pipelines that run underneath roads) should be installed because it will be much cheaper than retrofitting at a later date. Council could consider covering the additional costs associated with this to ensure that the recycled water option remains available Stormwater as an Alternative Recycled Water Source The existing studies have generally focused on using wastewater (i.e. sewage) as the source of water for potential recycled water schemes, although a separate technical note on stormwater harvesting was prepared during the course of the Water Supply Augmentations Options Study. The use of stormwater as an alternative source of recycled water is certainly feasible and could be cost effective in locations with suitable topography. 7

12 As discussed in the stormwater harvesting technical note, stormwater requires treatment before it is suitable for use as recycled water. However, stormwater runoff from new subdivisions within the Shire will receive a substantial portion of the required treatment by default, in order to meet Council s stormwater quality management requirements. The additional treatment required to enable the stormwater to be used as recycled water is likely to include filtration and disinfection. A key challenge that needs to be addressed for successful stormwater harvesting schemes is the provision of adequate storage and this typically needs to be assessed and optimised on a site specific basis. 8

13 Closing Remarks Compared with some other areas of Australia, Tweed Shire is in the enviable position of having plenty of water to meet its current needs and the projected demands of at least the next twelve years. The Shire does not face an imminent water shortage crisis and, as such, there is no need to urgently pursue any major water supply augmentation works. A clear message of the various reports is that there is considerable uncertainty regarding the rate of future growth of water demand in the Shire. The date at which the current secure yield will be exceeded is heavily influenced by the success of Council s adopted Demand Management Strategy. If Council was to adequately fund and vigorously pursue the actions specified in the Demand Management Strategy, it is quite possible that no water supply augmentation would be required within the planning horizon to As stated in the Water Supply Augmentation Study, Council will be monitoring the success of the proposed demand management strategies over the coming years and the forecasts of future water demands will be continually refined. Given the need to upgrade the Clarrie Hall Dam spillway, there was an opportunity to expand the capacity of the dam at the same time. However, it is understood that the spillway upgrade will now proceed independently of any potential future works to increase the capacity of the dam. 9