Transient storage processes in a steep headwater stream

✍ Scribed by Elisa B. Scordo; R. Dan Moore

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 442 KB
• Volume: 23
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.7345

✦ Synopsis

Abstract

This study examined hyporheic exchange flow and transient storage processes within a steep headwater stream, using both hydrometric and tracer approaches. Vertical hydraulic gradients varied systematically with location within step‐pool units, with upwelling located in a relatively narrow zone immediately below the step. Downward hydraulic gradients were greatest immediately above channel steps, and in that zone, gradients were also correlated with step height. Hydraulic conductivity tended to be lower in downwelling zones than in upwelling and neutral locations. Transient storage areas determined from reach‐scale tracer tests tended to increase with discharge, whereas transient exchange coefficients were not correlated with discharge. Transient storage exchange fluxes estimated from the reach‐scale tracer tests were an order of magnitude greater than hyporheic exchange fluxes estimated by scaling up local estimates based on Darcy's Law and piezometer measurements. This difference could be explained by the presence of lateral hyporheic flow paths and/or the influences of transient storage in pools. Tracer injections into infiltrometers using Rhodamine WT and sodium chloride allowed visual determination of hyporheic discharge zones and calculation of residence times for hyporheic flow through the step (pool inflow) and transport through the downstream pool (pool outflow). These tests indicated that residence time in pools can be comparable to hyporheic residence times, although the lack of replication in time and space limits the drawing of strong inferences. Copyright © 2009 John Wiley & Sons, Ltd.