Activity Group: Stormwater Drainage The quality of discharges from stormwater outfalls is regulated through resource Asset Description consents. There is a legacy of many old and outdated consents throughout The table below provides a summary of the scale of stormwater reticulation in Marlborough. A major project to consolidate, rationalise and update this each area. compliance framework is currently underway through the Blenheim Stormwater Strategy and is likely to be extended to other areas once it has been Reticulation length successfully implemented in Blenheim. Area (km) Reliable stormwater system — The efficacy of stormwater drainage can be Blenheim 125.5 difficult to assess as it is only required to perform at optimum capacity during Picton/Waikawa 28.7 relatively rare storm events. Mathematical models are used to model storms and Renwick 5.1 their outcomes. Okiwi Bay 0.8 The outcome of rainfall events is complicated by changing land use patterns and Riverlands 6.8 run-off characteristics from the land, weather patterns and the public’s changing expectations and living standards. Spring Creek 3.4 Provide a timely response — During severe storm events when flooding is Seddon/Grovetown/Anakiwa 1.6 predicted the Council will mobilise an Incident Management Centre to coordinate Rai Valley 0.3 the response to emergency calls. All calls are assessed and prioritised. Those Havelock 1.3 areas where there is a possibility of water entering either houses or commercial buildings are given the highest priority. Second priority is given to areas where Total 173.8 there is a possibility of water entering garages or outbuildings, followed by areas where water may pond on garden areas and roads. In the worst storms there The total asset value for the Stormwater Drainage Activity at 30 June 2017 was may be little that Council can do to manage the flood water as the infrastructure $73.1M. Depreciation is estimated as $1.4M per annum. Detailed information on and natural waterways are overloaded. In these circumstances the response is these assets, including information on levels of service performance, is provided to do whatever is possible to save life and reduce damage to property. in the Stormwater Asset Management Plan. During an emergency event Council maintains a log of customer service Urban populations are required to site their building platforms at an elevation requests to help prioritise and track the responses, identify clusters of particular that provides them with a level of flood protection whilst the stormwater concern and record events for debriefing and planning of future remedial works. infrastructure is designed and sized to drain the water to natural or man-made Sustainable stormwater — Responsible stewardship of major infrastructure water courses. Buried pipes and open channels are expensive to build and requires the Council to repair, renew and upgrade the assets in a timely fashion maintain and it is often expedient to use a combination of reticulation and road and avoid accumulating a legacy of decrepit assets. Decisions have to be made surfaces as secondary flow paths to divert high rain flows. As a result, as to when it is no longer cost-effective to continue to repair failing assets and to customers can become concerned about stormwater flows and ponding on local replace them instead. roads. The stormwater system is managed in close cooperation with the Rivers and Land Drainage networks. Planning of future stormwater infrastructure must ensure the downstream watercourse has sufficient capacity for the proposed development. 2018-2028 Long Term Plan Page 87