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Title: MULTIPLE APPROACHES TO ESTIMATING EPHEMERAL CHANNEL RECHARGE 1518

Author
item Goodrich, David - Dave
item WILLIAMS, D. - UNIVERSITY OF WYOMING
item Unkrich, Carl
item Scott, Russell - Russ
item HULTINE, K. - UNIVERSITY OF ARIZONA
item POOL, D. - USGS
item COES, A. - USGS
item HOGAN, J. - UNIVERSITY OF ARIZOAN

Submitted to: First Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 9/15/2003
Publication Date: 9/15/2003
Citation: Goodrich, D.C., Williams, D.G., Unkrich, C.L., Scott, R.L., Hultine, K., Pool, D.R., Coes, A., Hogan, J. 2003. Multiple approaches to estimating ephemeral channel recharge. Proceedings First Interagency Conference on Research in the Watersheds. Oct. 27-30, 2003. Benson, AZ., pp. 118-124.

Interpretive Summary: Arid and semi-arid regions account for approximately one-third of the land mass of earth. These regions are experiencing continued pressure from population growth in many parts of the world. Water is a critical resource in these regions and is often in short supply. Detailed study of water resources and the hydrology of semi-arid regions is important if we are to continue to populate and use these regions. An important part of the water supply for many semi-arid regions is groundwater. Understanding how rainfall soaks into the ground to become groundwater is not well understood. Observations from the Walnut Gulch Experimental Watershed, operated by the U.S. Dept. of Agriculture, Agricultural Research Service were used to estimate the amount of runoff water resulting from monsoon thunderstorms that becomes groundwater as it travels down dry channels. It was found that for the wet monsoon years of 1999 and 2000 runoff water soaking into the channels caused substantial changes in groundwater levels. When estimates of the volume of this runoff water are scaled up to the basin level it was concluded that groundwater recharge from runoff soaking into dry channels is an important groundwater source that can be subsequently pumped for agricultural and municipal water supplies.

Technical Abstract: Ephemeral channel transmission losses play an important role in ground water/surface water dynamics in arid and semi-arid basins in the Southwest. However, identification of the processes driving these dynamics is difficult. Specifically, data on the proportion of runoff transmission losses that escape from near-channel evapotranspiration (ET) and wetted channel evaporation to become deep ground water recharge are difficult to obtain. Quantifying recharge with greater certainty is a critical need required to manage basins whose primary source of water supply is derived from groundwater. This issue was addressed via coordinated field research within the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) located in southeastern Arizona. Groundwater, surface water, chemical, isotopic, tree sap flux, micrometeorological techniques, and changes in microgravity were used to independently estimate ephemeral channel recharge. Wet 1999 and 2000 monsoon seasons caused substantial changes in near-channel groundwater levels. Crudely scaled to the basin level, this recharge would constitute between 20 and 50% of basin recharge as estimated from a calibrated groundwater model.