83rd Annual

Tuesday, 11 February 2003
Precipitation induced isotopic variations in stream flow
Madhav V. Machavaram, LBNL, Berkeley, CA; and K. E. Bashford, M. E. Conrad, and N. L. Miller
Poster PDF (171.6 kB)
Understanding the pathways through which precipitation reaches streams and the response of streams to varying kinds of precipitation has been an important aspect of hydrogeological studies. These types of studies aid in the formulation of numerical models for the simulation of the catchment response, and also help in flood assessment and land-use management. Utilizing variations in the stable isotope compositions of hydrogen and oxygen in precipitation, stream waters and sub-surface waters is an effective way to estimate the response of various hydrologic compartments in a watershed during a precipitation event. As part of the DOE Water Cycle Pilot Study's Intensive Observation Period (IOP), measurements were made at Rock Creek, a 32 sq. km drainage in the Walnut River Watershed (WRW), Kansas. The Rock Creek is ~16 km long and drains into the Whitewater river.

During May 22-26 of 2002, two closely spaced convective precipitation events occurred over the Rock Creek drainage. Precipitation samples were collected from two sites in the catchment area to account for the spatial variations of both the volume and isotopic ratios of the rainfall. The isotopic composition of the precipitation was found to be different than the isotopic composition of the stream and surface waters. In addition, samples of surface water (streams and ponds), soil water and groundwater were collected before, during and after the precipitation events. A stock pond located upstream of the drainage influenced the stream flow at the headwater region in Rock Creek. Prior to the precipitation events, the water in the stock pond was characterized by higher isotopic ratios resulting from evaporation, making it an effective tracer for understanding the influence of the stock pond on the stream flow response to the precipitation. The response of the creek to intense precipitation events appears to be governed and altered by land management practices in the drainage area. Stable isotope analyses of various hydrologic components in the study area provided a better understanding of the influence of these components on the overall stream response.

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