Stormwater Asset Management Plan

2009 - 2012

This Stormwater Asset Management Plan (AMP) produced for the public stormwater assets owned and managed by Nelson City Council provides a 12 year outlook starting in July 2009 and is updated every three years. The AMP demonstrates how Nelson City’s goal and delivering the agreed levels of service will be achieved through effective and sustainable management of the stormwater assets.

The replacement value of the stormwater infrastructural assets is $133M and accounts for 12% of the total Council infrastructural assets replacement value (2008).

Nelson’s stormwater system

Council’s stormwater and flood protection system includes urban rivers and streams and the urban stormwater reticulation system. The Council stormwater system can be categorized into two parts – a natural component and a constructed stormwater system.

Natural part

The natural part consists of rivers and streams that play an important role in the support of aquatic ecosystems, areas for recreation and public use and the channelling of stormwater flows in rainfall events.  During high rainfall events the rivers and streams transport large volumes of water and sediment with impressive levels of energy that are capable of causing significant damage to property adjoining these areas and within the flood path, should the flow escape the channel on the adjacent flood plains.

Constructed part

The constructed stormwater network provides water channels to drain stormwater and flows from roads and properties in the built up areas. The network includes pipes, channels, and overland flow paths which conveys stormwater to receiving water courses or the sea.  The stormwater system also incorporates pump stations, and some debris detainment devices. In a large part of the city a fully reticulated system is not provided.  Individual properties discharge stormwater to onsite soakage or to the road channel as part of the primary drainage system.

Goal of the stormwater activity

Council’s goal is to provide a stormwater system to Nelson City that is capable of accommodating stormwater from rainfall events in an efficient and sustainable way whilst ensuring that the cultural, economic, ecological, recreational values and natural structures of waterways are recognised and enhanced.

Rationale for Council’s involvement
Health and safety / property protection

Large parts of Nelson City occupy a narrow band of land wedged between the sea and low foothills, with the majority of development taking place in areas close to or influenced by rivers and streams.  The provision of a robust stormwater system allows people to carry out their day to day lives with minimal disruption or adverse health effects from rainfall events or ponding water.

Protection of environment and community well-being

The natural stormwater system comprises vegetation and ground soakage with overflow to rivers and streams in high rainfall events.  For the majority of time, rivers and streams sustain aquatic ecosystems and are increasingly linked to private properties and recreation activities, particularly for the larger rivers, by the residents of the City.  This system is also where the bulk of materials washed from roads and private properties in the City first contact the aquatic ecosystem.

As development in the city encroaches onto historical flood plains (those parts of the city where flood waters would have traditionally spread when the flow in the channel exceeds its capacity) the multiple demands on the remaining available river and stream channel areas of stormwater capacity and recreational use needs to be balanced to ensure the long term best possible outcome for the city.

Legislative requirements

Council has statutory obligations under the Local Government Act 2002 to continue to provide existing stormwater services and a general authority to construct public drains and undertake land drainage, recognising the requirement to take a sustainable development approach that takes into account:

  • the social, economic and cultural wellbeing of people and communities; and
  • the need to maintain and enhance the quality to the environment; and
  • the reasonably foreseeable needs of future generations

Download

Download the full Stormwater Asset Management Plan 2009-2012 (5.7MB PDF).

Download the 19 page Executive Summary of the Wastewater Asset Management Plan 2009-2012 (794KB PDF).