Variation in hyporheic exchange with discharge and slope in a tropical mountain stream.

摘要

I assessed changes in hyporheic exchange flow (HEF) with discharge on Prieta Creek, Honduras. This cascade mountain stream was characterized by a distinct break in bed slope and dry to wet season flows (5 - 15 L·s -1), including dewatered conditions representing a community water supply. HEF was characterized by tracer transport, pressure, and biogeochemical observations, and mathematical transport and pressure models. Based on pressure data, observed downwelling significantly decreased (p 0.05) with decreasing streamflow. The MODFLOW pressure model estimates better matched observations in flatter sections, and Flow3D CFD model estimates were robust in all gradients. The STIR transport model estimated order of magnitude decreases in HEF with decreasing streamflow, allocating 95% of exchange to sub-channel storage, with 3 hour dewatered flow residence time. Nitrate and sulfate analyses suggest no significant loss of reducing zone during dewatering and fluoride monitoring supports potable use of water for a community water supply.