HR: 0830h
AN: H51C-1075    [PDF]
TI: Effects of a Controlled Water Release on Water Quality in the Mokelumne River, California
AU: * Henson, S S
EM: sshenson@ucdavis.edu
AF: Dept. of Land, Air and Water Resources, University of California Davis, Davis, CA 95616 United States
AU: Ahearn, D S
EM: dsahearn@ucdavis.edu
AF: Dept. of Land, Air and Water Resources, University of California Davis, Davis, CA 95616 United States
AU: Dahlgren, R A
EM: radahlgren@ucdavis.edu
AF: Dept. of Land, Air and Water Resources, University of California Davis, Davis, CA 95616 United States
AU: Tate, K W
EM: kwtate@ucdavis.edu
AF: Dept. of Agronomy and Range Science, University of California Davis, Davis, CA 95616 United States
AU: Van Nieuwenhuyse, E
EM: evannieuwenhuyse@mp.usbr.gov
AF: U.S. Bureau of Reclamation, 2800 Cottage Way Sacramento, Sacramento, CA 95825-1898 United States
AB: Managed water releases from reservoirs (i.e., controlled flood events) help to restore impounded rivers to more "natural" ecological conditions. Periodic high discharge can remove fine sediments and algae from spawning gravels, mobilize gravel bars, and clear brush encroaching from the stream banks. The effects of a managed release event on water quality were investigated on the lower Mokelumne River in the western Sierra Nevada, central California. The managed release was characterized by an increase in flow over a three-day period (from 440 cfs to 2000 cfs) and then a gradual decrease to pre-flood conditions over the next nine days. In the two years preceding the controlled release, flows in the lower Mokelumne averaged 288 cfs and did not exceed 520 cfs. Four automatic pump samplers were placed along a 55 km stretch of the Mokelumne River below Camanche Dam: 0.7, 16.4, 37.4, 54.4 km below the dam. One sampling site was immediately below Lake Lodi, a small reservoir 36 km downstream of the dam. Water was collected over the 12 day release and was analyzed for total suspended solids (TSS), total nitrogen, ammonium (NH4-N), nitrate (NO3-N), total phosphorus, soluble reactive ortho-phosphate (PO4-P), DOC, chlorophyll, and selected pathogens. The chemograph of the rising limb exhibited spikes in TSS ($<$1.0 to 41 mg/L), total N (0.08 to 0.73 ppm), NH4-N +NO3-N (0.015 to 0.1 ppm), total P (0.02 to 0.13 ppm), PO4-P ($<$0.003 to 0.017 ppm), DOC (0.5 to 2.48 ppm), chlorophyll (0.7 to 6.4 ppb), fecal coliform (0-4326 cfu/100mL), and E. coli (0-2866 cfu/100mL). Due to the attenuation of the flood wave as it moved downstream similar trends with respect the upper site were observed at the lower sites but with less pronounced concentration spikes. Fluxes of TSS, total P and total N released over the 0.7 to 16.4 km reach were 300, 0.33 and 3.5 Mg, respectively. Lake Lodi acted as a sink for TSS, total N and total P retaining about 100 Mg of sediment, 0.2 Mg total P and 8.8 Mg of total N. The reservoir acted as a source of dissolved nutrients (NO3-N, NH4-N, and PO4-P). Unlike in rainfall generated storms, fluxes of each constituent were mobilized from the channel alone, with little terrestrial influence. This distinction creates an opportunity for differentiation between channel derived fluxes and landscape derived fluxes.
DE: 1803 Anthropogenic effects
DE: 1821 Floods
DE: 1857 Reservoirs (surface)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting