Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 4 2008 10.5194/hess-12-975-2008 http://www.hydrol-earth-syst-sci.net/12/975/2008/ http://www.hydrol-earth-syst-sci.net/12/975/2008/hess-12-975-2008.html http://www.hydrol-earth-syst-sci.net/12/975/2008/hess-12-975-2008.pdf 975 987 2008-07-28 Dynamic analysis of groundwater discharge and partial-area contribution to Pukemanga Stream, New Zealand V. J. Bidwell bidwellv@lvl.co.nz R. Stenger G. F. Barkle Lincoln Environmental Research, Lincoln Ventures Ltd, Christchurch, New Zealand Lincoln Environmental Research, Lincoln Ventures Ltd, Hamilton, New Zealand Aqualinc Research Ltd, Hamilton, New Zealand The proportion and origin of groundwater contribution to streamflow from agricultural catchments is relevant to estimation of the effects of nitrate leached from the soil on the quality of surface waters. This study addresses the partitioning of streamflow contributions from near-surface runoff and from groundwater, each with different contributing land area, on a steep pastoral hillslope in a humid climate. The 3 ha headwater catchment of the perennial Pukemanga Stream, in the North Island of New Zealand, was instrumented for continuous observation of climatic data, streamflow and groundwater level. The dynamics of groundwater levels and groundwater contribution to streamflow were analysed by means of a one-parameter, eigenvalue-eigenfunction description of a 1-D aquifer model. Model results for seven years of daily data predict that 36–44% of the topographical catchment contributes groundwater to the stream. The remaining groundwater generated within the catchment contributes to streamflow outside the catchment. Groundwater was calculated to be 58–83% of observed annual streamflow from the topographical catchment. 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