HR: 0800h
AN: H51B-0464    [Abstracts]
TI: Trends and Sources of Low Stream Flow in the Merced River, Sierra Nevada, California
AU: * Conklin, M H
EM: mconklin@ucmerced.edu
AF: University of California, Merced, P.O. Box 2039, Merced, CA 95344, United States
AU: Liu, F
EM: fliu@ucmerced.edu
AF: University of California, Merced, P.O. Box 2039, Merced, CA 95344, United States
AU: Conrad, M E
EM: msconrad@lbl.gov
AF: Lawrence Berkeley National Laboratory, Mailstop 70A-4418 One Cyclotron Rd, Berkeley, CA 94720, United States
AB: Evaluation of Upper Merced River low stream flow (streamflow from August to October) trends shows mean flows have declined significantly since 1984. For two water years, 2006 and 2007, stable isotopes and specific conductance were used to determine primary sources of low flow. These are two years with significantly different snowpacks. The Merced River Basin snow water equivalent (SWE) on April 1, 2007 was 45% of the historical April 1 average (based on monthly snow course data), while the April 1, 2006 was 124% of the April 1 average. For 2006, it has been determined that the primary sources of low flow are mountain-block recharge, lateral subsurface flow and overland flow. The mean contribution of mountain-block recharge to low flow was greater than 25% of total streamflow. Overland flow accounted for less than 30% and was primarily derived from higher elevations (>2,800 m). The contribution of lateral subsurface flow and overland flow decreased over time and responded to the timing of snowmelt and snow water equivalent in spring. These data were fitted with an exponential function to determine time response parameters. The response of lateral subsurface flow to snowmelt lagged two months behind the peak snowmelt, indicating that the mean travel time was about two months. Lateral subsurface flow appears to be more sensitive to the changes in snowmelt timing at higher elevations than lower elevations. In contrast, in 2007, overland flow contributions are significantly less and that the response of lateral subsurface flow to snowmelt was significantly shorter. These changes are attributed to the difference in snowpack distribution, with much less volume of snow at lower (<1,800 m) elevations than for 2006.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1804 Catchment
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Hydrology [H]
MN: 2007 Fall Meeting