Quantifying groundwater contribution to stream flow generation in a steep headwater catchment
Journal of Hydrology, Vol. 53 (1)
Barkle, G.F., Stenger, R., Burgess, C., Wall, A.
Silica (SiO2) concentration of water increases with contact time between the water and subsurface silica-bearing minerals. Consequently, SiO2 can be used as a tracer to investigate the water sources (reservoirs) and associated different flow paths through a catchment. By measuring flow and SiO2 concentration in a stream, and relating these data to the stream concentrations from near-surface (2.8 mg l-1 SiO2) and groundwater (23.0 mg l-1 SiO2), the contributions that each of these reservoirs make per rain event, on a monthly and annual basis can be estimated. Analysis of 23 rain events revealed an increase in stream flow (0.07 to 0.42 l s-1) can be explained by increase in groundwater discharge, without a contribution from ‘near-surface’ water. A regression equation that relates SiO2 concentrations to stream flow was used with a mixing model to determine the maximum groundwater discharge to stream flow (1.72 l s-1) occurs at 21.3 l/s which represents a contribution of 8.1% of the flow. On a monthly basis, the discharge from groundwater to stream flow is described by a logarithmic relationship, with maximum contribution of 1500 m3 month-1. Near-surface flow follows an exponential relationship and can reach 4000 m3 month-1. On an annual basis the contributions from both reservoirs are best described by linear models. Groundwater accounts for a minimum of 52 % of stream flow during the wettest of the nine years and a maximum of 74 % during the driest year. Concurrent measurements, suggests that SiO2 is better suited for separation of the sources of stream flow than 18O in this catchment.