URBAN STOCK WATER RACES AND THE DILEMMA OF OBLIGATIONS

S. Stern (AECOM)

ABSTRACT

Stock water races exist primarily to supply drinking water to stock as well as a secondary purpose of firefighting, irrigation and landscape. Urbanisation of towns around the Canterbury region is resulting in encroachment of these rural assets. Open water poses a drowning risk and pedestrian/road safety hazard but it also provides ecological, biodiversity and aesthetic values. Consideration of the piping of open water channels needs to be made on a case-by-case basis and can create a dilemma of meeting the hierarchy of obligations of Te Mana o te Wai.

This paper outlines the outcomes of the Waka Kotahi SH73 West Melton Improvements project in the Selwyn District which converted existing open stock water races to piped networks to address safety concerns and allow for associated traffic safety improvements. The paper focuses on stock water races, however, the philosophies are applicable to all open waterways. New Zealand has had tragedies and accidents involving open stock water races including the drowning of young children and car accidents. Piping stock water races eliminates the direct hazard to the community, however, there are pros and cons to converting to piped networks and it can create a dilemma of meeting the hierarchy of obligations of Te Mana o te Wai. Despite being artificial ecosystems, stock water races provide habitat for fish and macroinvertebrate. Riparian margins can be terrestrial habitats for lizards and birds. Piping stock water races disrupts these ecosystems, however, can create room within the road corridor for stormwater treatment swales/basins and landscaped areas to offset these impacts.

The SH73 West Melton Improvement Project converted approximately 1 km of existing open stock water race into a piped network. The site is surrounded by community facilities including a primary school, shopping centre, church, tavern and recreational reserve. This resulted in a direct interface with pedestrians and traffic with open water. The piping of the stock water races created space within the existing road reserve for traffic safety improvements (off-road shared user paths, road widening, kerbs, signalised intersections/crossings) as well as the construction 420 m of stormwater first-flush treatment swales and basins. The design improved the existing drainage regimes by removing untreated road runoff from soaking to ground or discharging to the open stock water race. The swales and basins were planted with Aposdasmia similis (Oioi) providing landscape, habitat and visual amenity whilst also reducing future maintenance. The projects achieved great safety outcomes for the community, eliminating the interface with open water and providing room in the road corridor for traffic safety improvements and stormwater treatment.

Community safety around infrastructure is a key issue for local authorities. Authorities should consider changes required associated with the development of previously rural or low-density areas. The decision to convert stock water races to a piped network should be made on a case-by-case basis and opportunities to retain open races should be adopted where possible to retain community connection with water and the surrounding environment.