HR: 0800h
AN: H51E-0405    [Abstracts]
TI: Detention Basins may Help Reduce Nutrient Loads to Lake Tahoe
AU: * Green, J M
EM: jmgreen@usgs.gov
AF: Jena M. Green, US Geological Survey 333 W. Nye Lane, Carson City, NV 89706
AB: Water clarity in Lake Tahoe has been declining at a rate of about one foot per year for more than 35 years. In an attempt to decrease sediment and associated nutrients from reaching the lake, many detention basins have been installed, although their efficiency was uncertain. Many basins were constructed near alpine streams. This setting effectively reduces sediments from reaching surface water, but may allow transport of nutrients by ground water beneath the detention basins possibly discharging to streams farther downgradient or directly to Lake Tahoe. Determining the effectiveness of detention basins in the Lake Tahoe area requires an understanding of the shallow subsurface environment in which nutrients travel. A study was carried out at Cattlemans detention basin, situated adjacent to Cold Creek, a tributary to Lake Tahoe. Ground-water and solute transport models were used to evaluate complex ground-water interactions with Cold Creek near Cattlemans detention basin. Based on observations that urban runoff entering the basin rarely exited as surface water, each model assumes all water entering the basin either infiltrates or is consumed by evapotranspiration. Modeling results indicated that the detention basin has altered the local ground-water flow system while efficiently reducing suspended sediments, although nutrients are not filtered out as readily. Nutrient discharge points were tracked by calculating ground-water flow paths and endpoints. Approximately 45 percent of ground water originating from the detention basin discharges to Cold Creek within the modeled area downstream of the detention basin. The remaining 55 percent of ground water could discharge to evapotranspiration, to Cold Creek farther downstream, or to Lake Tahoe.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005