Effects of hydrograph characteristics on the hyporheic exchange in a pool-riffle stream

Hyporheic exchange (HE) is the exchange of water and substance between streamflow and sediment surrounding a stream and it is crucial to the riparian ecosystem. Effects of hydrograph characteristics on the HE in a pool-riffle stream will be investigated using tracer experiments and numerical simulations. Four flow regimes will be examined, including flat hydrographs of base flow and bankfull flow, and another two typical sharp peaked hydrographs that represent stream flooding before and after urbanization. Tracer experiments will be performed in a physical pool-riffle stream model built in a recirculating flume. Both surface flow and groundwater flow will be simulated, validated with laboratory data, and they are coupled using the water pressure along the water-sediment interface. Effects of different hydrological conditions on the HE characteristics, including flux, scale and residence time, will be quantified using numerical models. The study overall helps elucidate the basic HE processes in pool-riffle streams with changing discharge.