CLIENT BRIEF/PROJECT CHALLENGES
Nelson City Council (NCC) wanted to understand the impact of increasing planting along the Wakapuaka River on flooding in the catchment, as well as a range of other water-related ecosystem services, to help inform future land management planning. Prior to the start of the project, riparian planting along a portion of the Wakapuaka River had been carried out by Forest and Bird, with further riparian planting planned along an adjacent private property.
WSP used the innovative ecosystem services modelling tool LUCI (Land Utilisation and Capability Indicator) to assess the potential benefits of riparian planting along the Wakapuaka River, outside of Nelson CBD. WSP’s modelling demonstrated the improvements to flood risk, nutrient delivery and erosion that riparian planting could provide in the catchment, to inform land management decisions in the future. The project also identified areas where improvements across multiple different ecosystem services could be achieved, to inform targeted future land use changes within the catchment.
WSP used the innovative ecosystem services modelling tool LUCI (Land Utilisation and Capability Indicator) to highlight the potential for enhancing water-related ecosystem services in the Wakapuaka River catchment. LUCI is a holistic, spatially-explicit ecosystem services framework that uses soil, slope, landcover and climate information to model and map the impact of land management or land use change on ecosystem services within a catchment.
WSP used LUCI to model the ecosystem services provided by three different scenarios; no riparian planting, current (recently planted) riparian planting and future planned planting. Four services were investigated in particular: water quantity, water quality (nitrogen and phosphorus), erosion and sediment delivery, and agricultural productivity. The team also used trade-off analysis to identify areas within the Wakapuaka catchment where opportunities to enhance multiple ecosystem services were present. Considering multiple potential benefits that planting could have within the landscape allowed any opportunities for catchment improvement to be enhanced.
WSP demonstrated that the current and proposed riparian planting provides flood mitigation both along the Wakapuaka River and in the surrounding area. It was clear that nitrogen, phosphorus and sediment loads into the river were reduced by the planting scenarios. The trade-off analysis undertaken across the wider river catchment also identified areas that could be candidate sites for targeted future planting. The LUCI model results demonstrated that planting in these areas could reduce nutrient and/or sediment delivery to streams while having minimal impact on agricultural productivity.
The ecosystem services modelling has therefore added value to the conventional flood modelling approach by considering the other advantages of riparian planting. It provided NCC with evidence of the benefits of natural solutions within the catchment and could inform targeted land use change in the future, ultimately contributing to the improvement of freshwater issues in the Wakapuaka River catchment.
Different types of land cover provide different services to a water catchment, including flood mitigation, habitat for local species, water quality improvement, enhanced agricultural productivity or erosion prevention. The benefits that nature can provide are referred to as ecosystem services – which tend to be complex, interactive and therefore difficult to quantify. Land managers can be faced with trade-offs between different ecosystems services without being able to effectively measure their impact. Modelling is essential to inform land and catchment management decisions and quantify the various benefits or potentially adverse effects of land use change.
Trees, wetlands and deep permeable soils are examples of landscape features which can provide flood mitigation within a catchment. Phosphorus is transported bound to soil particles, unlike nitrogen which moves more freely through water. Therefore, areas which are more vulnerable to erosion can often have higher losses of phosphorus to waterways.