HR: 1340h
AN: H13B-1338    [Abstracts]
TI: Wintertime Warming of Hyporeic Water in an Exposed Gravel Bar, American River
AU: * Silver, M H
EM: msilver@csus.edu
AF: Department of Geology, California State University, Sacramento, 6000 J Street, Sacramento, CA 95819-6043 United States
AU: Horner, T C
EM: hornertc@csus.edu
AF: Department of Geology, California State University, Sacramento, 6000 J Street, Sacramento, CA 95819-6043 United States
AB: Measurements of intergravel temperature near an exposed gravel bar along the American River near Sacramento, California show warmer intergravel water on the downstream end of the gravel bar than on the upstream end. Temperature loggers were installed at depths of 1', 2', and 4' below the gravel surface and used to collect data during the fall and winter of 2004. Surface water flows around the bar, but measurements of hydraulic head indicate a downward hydraulic gradient at the upstream site and an upward hydraulic gradient at the downstream site, suggesting that water also flows underneath the gravel bar. Temperature profiles from August 2004 suggest the same interpretation: at the upstream site, a large (~4 ° C) diurnal temperature fluctuation was present at 1' depth and some diurnal fluctuation was present at 4' depth, while at the downstream site, the 4' temperature did not fluctuate, and diurnal temperature fluctuation at the 1' level was dampened. In the following winter months, a similar pattern is observed at the upstream site, although with less diurnal fluctuation in water temperature. However, at the downstream site, discharging water was warmer than recorded upstream, and the thermal profile was inverted: the 4' temperature was the highest and 1' temperature the lowest. Inversion began on October 20, 2004 and continued until March 5, 2005. During this period, 1' downstream temperatures were up to 1 ° C warmer than those recorded at the same depth upstream and 4' temperatures were up to 3.5 ° C warmer at the downstream end of the gravel bar. During the period of inversion, the gravel bar appears to contribute heat to the stream, as water flowing out from underneath the bar is warmer than when it entered. This may be due to a seasonal reversal in thermal gradient, where a constant temperature at some depth beneath the stream results in heat flow from the surface downward in the summer and from the sub-surface upward in the winter. In September 2005, we installed instruments to measure temperature at two additional sites in the American River where similar temperature inversion and warming of water that has flowed under a gravel bar may occur. Data will be collected in the fall of 2005 and will be used to determine if the observed warming and temperature inversion occurs as water flows under other gravel bars along the American River.
DE: 0481 Restoration
DE: 1830 Groundwater/surface water interaction
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: Fall Meeting 2005