Tuesday, June 5, 2007 - 11:30 AM
133

Impact of In-Stream Geomorphic Structures on Hyporheic Exchange of Water and Heat in Streams

Erich T. Hester, Curriculum in Ecology, University of North Carolina, 1412 Crestview Drive, Blacksburg, VA 24060 and Martin W. Doyle, Department of Geography, University of North Carolina, 205 Saunders Hall, CB# 3220, Chapel Hill, NC 27599-3220.

In-stream geomorphic structures such as debris dams and steps are common in undisturbed streams, are often installed as part of stream restoration projects, and can significantly enhance hyporheic exchange. This exchange is important ecologically for many reasons, including possible reduction of peak summer temperatures in streams that are impacted by loss of riparian shade and climate change. Despite this known importance, relationships between basic controlling factors and the magnitude of structure-induced water and heat exchange at the individual structure level (e.g., structure size and type) and at the stream reach or segment level (e.g., channel slope, background groundwater discharge, depth to bedrock) are relatively unknown. We combined surface and groundwater numerical hydraulic and heat flow models with field hydraulic and temperature measurements using a three-dimensional sensor network to quantify these relationships. Results indicate a number of nonlinear relationships between controlling factors and hydraulic and thermal response that have significant implications for both stream function and restoration design.  For example, under gaining conditions, hyporheic residence time generally peaks at relatively small structure sizes such that small structures may be the most effective for promoting hyporheic processes that need significant contact time with sediments.


Web Page: www.unc.edu/~ethester/