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Summary
The purpose of the Waimapu Watercourse Assessment is to provide a comprehensive environmental and stormwater infrastructure geodatabase to offer understanding of freshwater health at the catchment scale. This Assessment gives Council, hapū and the community insights as to the current state of freshwater bodies within the catchment. These insights can then be used to identify key environmental and infrastructure issues and their primary drivers, and potential opportunities for enhancement for statutory entities and hapū to consider as kaitiaki of the catchment.
A field survey was carried out by a team of environmental scientists and environmental engineers in October and November 2023. The survey area encapsulated a substantial urban zone with industrial areas and mixed residential housing, as well as rural land with a mixture of farms, native forest, forestry, horticulture and lifestyle blocks.
The data was combined to describe 38.1 km of assessed awa length within the surveyed area, with data pertaining to 632 stormwater pipes, culverts and associated assets, 400 miscellaneous points of interest, 21 bank or channel lining structures, 119 fish passage assessments, 6 eDNA test sites, 103 repo (wetland) and 30 puna wai (spring) environments.
Conclusion – For review
The Waimapu awa are most affected by the legacy of past urban development and ongoing urban landuse in the lower catchment area, and agricultural practises in the upper, rural catchment. Despite this, the main awa and its surrounding riparian zones are considered to be in relatively healthy condition with native flora, fauna and habitat found throughout.
In contrast, the side tributaries that join the Waimapu awa main stem were more often impacted by degradation via modification such as channel alterations and the introduction of fish passage barriers, particularly in the urban area. Several tributaries in the urban area were identified as ‘hot spots’ of industrial contamination and should be investigated for stormwater treatment opportunities (including improved source control practices). Invasive plants species have also invaded much of the riparian and in-stream habitats in the urban area, leading to habitat degradation and biodiversity loss as indigenous plant species are denied space to successfully re-establish.
In the rural catchment, a lack of stock fencing and run off of sediment and pastoral contaminants are key issues. Education and community engagement are a priority for improving the upper rural tributaries via the promotion of better environmental stewardship behaviour amongst landowners – an already emerging trend that can be leveraged further. Repo of natural, induced, and constructed origins were assessed, and determined to be in varying conditions. These ecosystems provide habitat, water treatment and amenity value, but were often subject to infestations of invasive pest plants that threaten native plant succession and habitat availability for native animals. Substantial potential for enhancement was identified, which will also provide for enhanced community connection to repo, enhanced carbon sequestration, and flood flow buffering and absorption.
Puna wai were mostly intact and exhibited healthy, clear flows. In the rural catchment area, some were located in unfenced pastures with stock access, however the majority were still in good condition with diverse indigenous riparian and in-stream vegetation present – fencing would further protect these precious ecosystems for the future. Puna wai in urban areas would benefit from ongoing care and protection from future impacts, given the likely loss of these ecosystems during past development.
Numerous opportunities to enhance freshwater health, as well as community connection to wai, and the provision of ecosystem services were identified. These range from operational infrastructure and parks maintenance tasks, through to major capital investment projects. Being a catchment on the urban fringes of a city, but which has also retained an extensive amount of its original freshwater ecosystems and ngahere, the Waimapu has both the possibility for substantial enhancement to thrive in the future, or further degradation from urban growth pressures – dependant on how these are managed. Upcoming environmental stewardship, management and investment decisions will determine the future trajectory of catchment health.