MATARAWA FLOOD CONTROL SCHEME EXTENSION (PRD 5 20)

Transcription

1 Report No Decision Required MATARAWA FLOOD CONTROL SCHEME EXTENSION (PRD 5 20) 1. PURPOSE 1.1. The purpose of this item is to seek the approval of the Committee (and ultimately Council) to include in the Draft Annual Plan (DAP) a proposal to amend the scope / extent of the Matarawa Scheme to address issues highlighted by the June 2015 flood event. 2. RECOMMENDATION That the Committee recommends that Council: a. receives the information contained in Report No and Annex; b. instructs the Group Manager River Management to include for consultation in Council s DAP the following detail: i. adding the Matarawa Stream through the urban part of Whanganui to the inspection and maintenance schedule for the Matarawa Scheme; ii. undertaking a two year programme of deferred maintenance work that would commence in the financial year; iii. funding that work programme by way of a loan; and iv. repaying that loan and covering ongoing operating costs primarily by extending the targeted rate classification for the scheme to encompass the primary benefit area within the urban part of Whanganui (defined as Option B in Annex A). 3. FINANCIAL IMPACT 3.1. If adopted as proposed, the work programme would require additional expenditure estimated at $338,000 over two years commencing in the financial year. It is intended to loan-fund this expenditure and provide for the repayment cost (and the additional ongoing inspection and maintenance expenditure) by increasing overall Matarawa Flood Control Scheme rate income. The amount required is $40,250 for the first year and $51,200 per year for the next nine years. This would be mainly sourced by extending targeted rate income to encompass the added benefit area; in accordance with Council s funding policy the increased targeted rate income would attract an additional general rate contribution to the scheme of approximately $90,000 over 10 years. 4. COMMUNITY ENGAGEMENT 4.1. Initial community engagement in relation to this matter took place in the form of public meetings arranged by the Whanganui District Council (WDC) following the extensive flooding in Whanganui East in June Consultation around the changes proposed for inclusion in the DAP is intended to have two main components to it; writing to every new ratepayer in the urban area outlining the rationale to the proposal, followed by a public meeting in Whanganui East. This meeting would form part of the Catchment Community meeting for the Matarawa Scheme and is scheduled to take place early in the period that the DAP is open for submissions. Matarawa Flood Control Scheme Extension (PRD 5 20) Page 1

2 5. SIGNIFICANT BUSINESS RISK IMPACT 5.1. As previously advised, the primary risk identified with this proposal is that it could trigger an amended Long Term Plan process. If this risk were realised the primary impact for Council would be one of cost. This risk could be avoided by proceeding with the work but not amending the rating classification but it would introduce other risks (committing to expenditure outside the present defined extents of the scheme without a funding mechanism in place) The work could also be deferred but that has its own risks (further deterioration in the condition of the channel with the low probability over that period of another weather event severe enough to result in flooding) The staff view is that the risk that the changes proposed to the scheme are sufficient to be construed as meeting the wider definition of significant is low. The treatment strategy as outlined in Section 4 is to engage with all of those proposed to be included as new Matarawa Scheme ratepayers and to time a public meeting to coincide with the DAP submission period. That is, place particular emphasis on informing those ratepayers around the changes and encouraging Annual Plan submissions. 6. BACKGROUND 6.1. The Matarawa Flood Control Scheme was established in 1981 to provide a level of control of flooding in the Matarawa, Kaukatea, Mangaone, and Mangamoku (Longacre) Valleys. Flood control was to be achieved through the construction of five detention dams, extensive channel clearance works and some minor stopbanking The scheme area was defined by catchment boundaries and by the then Whanganui County / Whanganui City boundary in the lower reaches of the Matarawa Stream. The WDC declined to participate in the new scheme, preferring to manage the section of Matarawa Stream within Whanganui East either itself or through enforcing landowner responsibilities, which in most cases extend to the centre of the stream The severe storm that struck much of the Region in June 2015 resulted in extensive flooding adjacent to the lower reaches of the Matarawa Stream. An original component of scheme construction, the Mateongaonga Diversion, lessened that impact by diverting the upper catchment flow away from the lower reaches but the intensity of the lower catchment rainfall was still sufficient for extensive flooding to occur A number of affected property owners who attended the public meetings that followed the June 2015 event were of the view that the congested state of the stream channel had contributed significantly to the flooding. There was a very clear desire for the channel to be cleared and regularly maintained and an expectation that such work would be undertaken by either the District Council or Regional Council. Reinforcing that sentiment, the WDC submitted on Horizons draft Annual Plan, requesting (among other things), that Horizons look to urgently add this reach of the Matarawa Stream to the operational responsibilities encompassed by the Matarawa Scheme. 7. DISCUSSION 7.1. A detailed survey of the lower reach of the Matarawa Stream was undertaken by River Management staff in January Observations matched the feedback provided by residents following the June 2015 event, with the channel highly congested / overgrown. Matarawa Flood Control Scheme Extension (PRD 5 20) Page 2

3 Figure1: Matarawa Scheme Study Reach 7.2. In determining the work required to address those issues and the consequent cost to the scheme, a number of factors need to be taken into account. The number of residential properties involved (115 in total) adds considerable complexity to the work; in many instances houses are close to the stream limiting site access. This will limit the ability to use large mechanical equipment in many locations, and as a result removal of vegetation for disposal will be particularly difficult. Those complexities are reflected in both the relatively high physical works cost estimate and the staff time cost associated with managing the works The inspection also confirmed the view of staff (and feedback from residents) that maintenance of the channel is beyond the resources of the majority of residential property owners. Those few owners who might be capable will receive little benefit from their efforts if adjoining sections of channel are left unattended to. The reality is, irrespective of any legal requirement, that such a major watercourse will not be properly maintained by adjoining owners and without intervention its condition will continue to deteriorate Given that there is an established scheme in the Matarawa catchment, the levels of service for which include maintenance of stream and diversion channels immediately upstream of the urban area, it is logical that the urban section of channel also be maintained by the scheme. While the initial channel clearance works will create some significant demands on staff and funding resources, the ongoing maintenance work should be reasonably easily accommodated within the wider scheme management programme. 8. PROPOSED WORKS 8.1. It is proposed to undertake the initial clearance works over a two year period, commencing in In order to avoid localised exacerbation of flood hazard while work is underway it would commence at the downstream (Anzac Parade) end of the Matarawa Stream. Matarawa Flood Control Scheme Extension (PRD 5 20) Page 3

4 8.2. Note that the level of service commitment to the community would mirror that adopted in other parts of the scheme. That is, it would relate to flood flow conveyance (general channel management) but would not extend to erosion control / bank protection. This may pose some difficulties for Council in two ways the initial clearance programme could well involve making rather vexed decisions in regard to disturbance of existing bank protection works and the potential that a more open, free-flowing channel might (at least initially) give rise to claims around creating bank erosion issues (or exacerbating existing issues). These are not new operating risks the treatment strategies will centre on using senior staff to coordinate and manage the work, developing a comprehensive communication strategy with those property owners and ensuring a complete before and after photographic record of the work It should also be noted that the clearance work will not address all the factors that influence flood hazard in that reach of the Matarawa Stream; the four Whanganui District Council culvert / bridge crossings are likely to limit (to varying degrees) high flow. A freer-flowing channel will however to some extent aid the scouring of sediment in the stream bed which at present is reducing the capacity of those culverts. It will also greatly reduce the risk of debris blockage during high flows The estimated cost of the work is $344,000 including staff time costs. It is proposed that the work be loan funded with a 10-year loan term; a longer term is not desirable given the nature of the work (essentially deferred maintenance). Regular inspection and maintenance of that reach of stream channel would commence from The cost of that work can be expected to vary from year to year, depending on the incidence and magnitude of higher flow events. Average annual expenditure for that work is estimated at $10, FUNDING Year Additional Funding Required Regional Contribution Rate Targeted Contribution $50, $10, $40, each year each year onwards Table1: Funding Model $64,000 $12,800 $51,200 $10,000 $2,000 $8,000 Rate 9.1. It is proposed that the funding model required to both repay the loan and cover ongoing operating costs follow Council s funding policy. That is, 80% of the income required is sourced from additional targeted rate revenue with 20% coming from general rates. The targeted rate classification for the Matarawa Scheme was last reviewed in 2006 and comprises a contributor category, an indirect benefit category and a direct benefit category, proportioned 20:20:60 respectively. As this reach of the Matarawa lies outside the current classification extents a new direct benefit category needs to be established The total impact of the proposed works on all rating categories, including the proposed new urban direct benefit category, is shown in the table below. The figures are relative to that collected in the current financial year and include GST. Matarawa Flood Control Scheme Extension (PRD 5 20) Page 4

5 Year Additional Targeted Rate Required Additional Rate per Category L1 - L3, M1, M3, M4 MW (WDC contribution) $40,250 Nil +4,709 (21%) $51,200 Nil +$5,990 (27%) UC IN (rural indirect benefit) +$24,150 +3,340 (64%) +$30,720 +$4,249 (82%) CN (contributor) +$8,050 (64%) +$10,240 (82%) onwards $8,000 Nil +$937 (4%) Table2: Funding Impact of Proposed Works +$4,800 +$664 (13%) +$1,600 (13%) 9.3. Note that a substantial portion of the land adjoining the lower reach of the Matarawa Stream is owned by either the Crown or the WDC, with that land managed by the WDC as reserve land. The targeted rate scenarios presented above do allow for an increased WDC scheme contribution as part of an adjustment pro rata of existing indirect benefit income; it does not allow for recognition through direct benefit income, reflecting Horizons limited ability to compel the WDC to contribute to scheme operating costs beyond that already agreed Should the WDC choose to acknowledge that situation, the direct benefit income required from private property would reduce by $6,230 in and $7,925 annually beyond that out to It is intended that this matter be included as part of Horizons submission on the WDC s draft Annual Plan Three options have been looked at for defining direct benefits extents, presented in Annex A. Inputs to those options include the extent of flooding recorded for the June 2015 event, the nature of the topography for this part of Whanganui East and the nature of the WDC stormwater network. Those scenarios also include a qualitative assessment of a conceivable worst case; the effect of a channel with essentially no conveyance in combination with an extreme weather event Option A could be regarded as an absolute minimum, high-benefit area. Option C arguably reflects the opposite end of the spectrum and starts to reflect indirect benefits which are already accounted for. Option B is considered to most fairly define the area of direct benefit. It is proposed that the direct benefit be reflected by a single differential (UC = Urban Channel) applied to all those properties that fall within the Option B area. The rate would be based on capital value. 10. CONSULTATION Subject to adoption of the recommendations contained in this item, the proposal will be included in the DAP. The changes proposed would be identified in the Annual Plan Summary document and included in the Whanganui edition of the Across the Region publication that will focus on the DAP However, the consultation focus will centre on writing to all new ratepayers advising of the proposal and how it would affect them. That would be followed by a public meeting timed to coincide with the DAP consultation period. 11. SIGNIFICANCE This is not a significant decision according to the Council s Policy on Significance and Engagement. Matarawa Flood Control Scheme Extension (PRD 5 20) Page 5

6 Allan Cook PROJECT ENGINEER Ramon Strong GROUP MANAGER RIVER MANAGEMENT ANNEXES A Three Rating Options Matarawa Flood Control Scheme Extension (PRD 5 20) Page 6