In the context of Project B2.4 "Hydrology and nutrient transport processes in surface water groundwater systems" of the CRC for Water Sensitive Cities, this paper presents an investigation of three case studies in Perth, Western Australia, where WSUD control elements have been implemented in urban areas with high watertables: a subsoil cut-off drain, a living stream and a reengineered compensation basin. Results from water balances at catchment scale, indicated that the shallow watertable contributed both flow and nutrients to drains irrespective of the catchment scale. Shallow groundwater discharge into drains made up from 60 % to 94 % of the total annual volume of the catchments and imposed its seasonal signal onto the drains' hydrological regimes and nutrient annual loading. The dominance of the subsurface pathways highlighted the importance of organic nutrients and suggested that under these conditions, the efficiencies of WSUD elements may be compromised. The results also highlighted gaps in our understanding of the impact of urbanization on urban hydrology and nutrient pathways in areas with shallow watertable; current understanding is based on predominantly end-of-pipe or catchment outlet monitoring data which may not be indicative of key processes. A framework to quantify and assess nutrient transformation along subsurface pathways is proposed, that will allow the formulation of new robust conceptual models for water and nutrients among WSUD and drainage elements in urban catchments, and to assist in the improvement of tools for better urban planning and development.
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