Title

The Influence of Hyporheic Flow on the Temperature of a Riffle-Step-Pool Stream

Publication Date

7-2005

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geology

Department

Geosciences

Major Advisor

James McNamara

Abstract

The ability to predict stream temperature is important due to the many direct and indirect water use and watershed management effects on streams. The most rigorous physically based approach to evaluate stream temperature change is to use conservation of energy in a heat-energy budget. Failures of the energy budget approach to modeling stream temperature are often due to inadequate representation of all the processes that control stream temperature. Hyporheic flow, driven by gradient and controlled by morphology and substrate properties, influences stream temperature by temporarily removing water from the heating impact of solar radiation and other positive heat fluxes at the surface of the stream, heat conduction to the substrate, and mixing with groundwater, all resulting in flow returning from the substrate out of phase with stream temperature. The influence ofhyporheic flow is not often included in energy budget models to predict temperature change.

In this study stream temperature change is successfully modeled for a 400-meter long reach by using an energy budget temperature model and by including the often-neglected effects of advected water through the hyporheic zone as a major component of the energy budget. Predicting temperature change over a short reach by using an energy budget provides an understanding of the stream processes that influence stream temperature. The dominant energy fluxes into the stream during summer months are net radiation and sensible heat exchange with the atmosphere (61 and 36% respectively). The dominant heat energy flux out of the stream was from hyporheic flow, providing 36 to 75% of the energy sink.

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