Imaging hyporheic exchange



The dynamics of flow through the subterranean area at the base and along the sides of streambeds, known as the hyporheic zone, affect stream ecosystem dynamics, but researchers do not have a solid understanding of what controls the amount of hyporheic exchange.Ward et al. injected tracers into a stream in the H.J. Andrews Experimental Forest in Oregon and used electrical resistivity imaging to quantify the shape and size of the hyporheic zone. Repeated experiments quantify changes from spring high to summer low flows in the stream. The researchers studied how valley morphology and hydraulic gradients between the stream and surrounding landscape affected hyporheic exchange. Contrary to their expectations based on commonly accepted conceptual models, the scientists found that increasing hydraulic gradients from catchment to stream did not always lead to smaller hyporheic zones. They conclude that hydraulic gradients were not the dominant control on hyporheic exchange in the setting they studied. (Water Resources Research, doi:10.1029/2011WR011461, 2012)