The Role of Channel Bar Influences on Groundwater / Surface Water Interactions
Abstract
Channel bars are dominant in-stream geomorphic island features present in a large range of river classes throughout the world, particularly in the arid western United States. A quantitative understanding of groundwater and surface water exchange through channel bar features is necessary to understand near-stream hyporheic flow patterns. The Truckee River in northwestern Nevada was used as a research site to quantitatively examine the influence of channel bars on near-stream water fluxes using heat as a tracer. This study provided the near-stream hydraulic physical framework for current and future research on nutrient cycling and biogeochemical impacts of near-stream exchange and can be used for assessing critical water quality impacts. Field activities included the installation and development of monitoring wells and piezometers, instrumentation of the piezometers with pressure transducers and temperature thermistors, and slug tests to estimate hydraulic conductivity. The potentiometric surface throughout the study site was monitored over time and the temperature thermistors were used to estimate transport using heat as a tracer. Horizontal and vertical Darcian water fluxes were estimated from field observations. To increase confidence in the hydraulic conductivity values for water flux estimates, heat-based numerical simulations were completed. Three-dimensional models of the channel bar study area were constructed and hydraulic conductivity was inversely estimated by minimizing the difference between observed and simulated head and temperature measurements. Numerical simulations indicated that lateral water fluxes between the channel bar and the stream were an order of magnitude greater than between the adjacent streambank and the stream. The fluxes at the downstream end of the channel bar were an order of magnitude greater than upstream fluxes. Net groundwater and surface water fluxes at the channel bar and stream interface were at least 2 times greater than fluxes within the channel bar. Overall, results indicate significantly increased groundwater and surface water exchange between the stream and channel bar compared to stream exchanges with streambed or streambank. The presence of the channel bar increased the local exchange 6 times relative to only vertical streambed exchange estimates during the study period. Results suggest the increase in groundwater and stream exchange from the channel bar enhanced near stream biogeochemical reactions, as well as vegetation, and habitat structure relative to stream reaches without channel bars.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H21B1040S
- Keywords:
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- 1805 HYDROLOGY / Computational hydrology;
- 1830 HYDROLOGY / Groundwater/surface water interaction;
- 1894 HYDROLOGY / Instruments and techniques: modeling;
- 1895 HYDROLOGY / Instruments and techniques: monitoring