| Summary: | Bank storage is defined as a volume of water that periodically infiltrates a river's banks during increases in stream stage. It is a potentially critical variable for accurately modeling the water budget in semi-arid riparian systems, but is particularly difficult to assess and quantify. It is especially essential for understanding ground-water/surface-water interactions. In collaboration with other projects, a field-scale vadose monitoring effort took place in the San Pedro Riparian National Conservation Area (SPRNCA), Arizona. The San Pedro River flows north from Mexico into the United States, and SPRNCA is a 60 km stretch of U.S.-protected ecosystem north of the border. In addition to a progressive climate of ecological conservation, hydrological research that leads to an improved understanding of the water budget will ultimately improve the prospects for improved water policy decisions. Soil moisture, stream stage, and soil tension data were collected for over 8 consecutive months in both 1997 and 1998, and the data were used as input into a software program called HYDRUS-2D (§imiinek et al. 1996), which models two-dimensional, variably saturated flow. Field-collected data and subsequent modeling efforts suggest that the effects of bank storage were estimated to contribute approximately 8.5% of the river's total flow for 147 days in 1997. Accordingly, bank storage and its effects should be considered in future water-balance simulations of stream-aquifer interaction, and of the San Pedro River in particular. In addition, model estimates of root water uptake match favorably with other estimates of evapotranspiration in the cottonwood-willow forest gallery of the SPRNCA.
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