Dynamic analysis of groundwater discharge and partial-area contribution to Pukemanga Stream, New Zealand

摘要

The proportion and origin of groundwater contribution to streamflow fromagricultural catchments is relevant to estimation of the effects of nitrateleached from the soil on the quality of surface waters. This study addressesthe partitioning of streamflow contributions from near-surface runoff andfrom groundwater, each with different contributing land area, on a steeppastoral hillslope in a humid climate. The 3 ha headwater catchment of theperennial Pukemanga Stream, in the North Island of New Zealand, wasinstrumented for continuous observation of climatic data, streamflow andgroundwater level. The dynamics of groundwater levels and groundwatercontribution to streamflow were analysed by means of a one-parameter,eigenvalue-eigenfunction description of a 1-D aquifer model. Model resultsfor seven years of daily data predict that 36–44% of the topographicalcatchment contributes groundwater to the stream. The remaining groundwatergenerated within the catchment contributes to streamflow outside thecatchment. Groundwater was calculated to be 58–83% of observed annualstreamflow from the topographical catchment. When the smaller groundwatercatchment is taken into account, the groundwater contribution to streamflowis 78–93% on a unit area basis. Concurrent hourly data for streamflow andgroundwater levels at two sites indicate the dynamic behaviour of a localgroundwater system. Groundwater flow dynamics that support the perennialnature of this headwater stream are consistent with the size of thegroundwater body, porosity of the subsurface material, and hydraulicconductivity derived from partitioning of streamflow contributions.