Influence of stream-groundwater exchange on the spatial variations in streamflow in a steep headwater catchment

Abstract:

Understanding the spatial variations in streamflow in montane streams is important in clarifying the streamflow generation process and improving watershed model structure. However, there has been little exploration about the spatial variations in streamflow in steep headwater catchments and its relationship with stream-groundwater exchange. We investigated streamflow and stream-groundwater exchange in a 45 m reach in a small steep headwater catchment in western Japan to explore the effects of stream-groundwater exchange on the spatial variation in streamflow. The study reach had an incised channel with the substrate of cobbles and boulders, and the channel gradient was 0.5 m/m. The streamflow was gauged at both ends of the reach, and series of tracer injection experiments were conducted to quantify the water exchange between stream and groundwater. The differences between the two gauges (∆Q) was approximately 0.2 L/s (34% of downstream discharge) in low flow period in January-May and increased to 1.4 L/s (56% of downstream discharge) during high flow period in June-July. The relative flux of stream-groundwater exchange increased with streamflow, in contrast to previous findings. Thus, in the steep headwater stream studied, the spatial variation in streamflow was large, and the influence of stream-groundwater exchange on streamflow variation became larger in high flow period, suggesting the presence of additional flow paths during high flow period. The combination of spatial variations in streamflow and stream-groundwater exchange can help to clarify the unique streamflow generation process in steep headwater catchment.