HR: 0800h
AN: H51B-0355    [Abstracts]
TI: Lessons Learned from Predicting the Poorly Gauged Sweetwater Creek Basin, in Central Idaho
AU: * Morehead, M D
EM: morehead@uidaho.edu
AF: Center for Ecohydraulics Research, University of Idaho, Idaho Water Center 322 E. Front St, Suite 340, Boise, ID 83702 United States
AU: Peckham, S
EM: peckhams@Colorado.EDU
AF: Institute of Arctic and Alpine Research, University of Colorado, Campus Box 450, Boulder, CO 80309 United States
AU: Muskatirovic, J
EM: muski@uidaho.edu
AF: Center for Ecohydraulics Research, University of Idaho, Idaho Water Center 322 E. Front St, Suite 340, Boise, ID 83702 United States
AB: The flow regime of a poorly gauged basin in central Idaho was modeled in response to Agency, Tribal and Irrigation District needs to provide water for irrigation while still providing flows for a healthy ecosystem in Sweetwater Creek. This modeling effort shows some strengths and weakness of our present state of knowledge in simulating the hydrology of a basin. The spring freshet of a normal and a high flow year were simulated relatively successfully. However, the low flow year and summer thunderstorm events were not simulated as well, with the model over simulating the flow rates for these events. Improvements in a number of areas would increase the accuracy of the modeled flows. Improved meteorological data collection may help considerably. It is known that storm systems are funneled up the valley of Clearwater River where the present meteorological gauging sites are. Having meteorological gauging sites further into Sweetwater Creek Basin and away from the effects of the Clearwater River would improve the input conditions. Additionally, this semi-arid watershed commonly breaks the assumption of a moist soil profile. When these soils are dry, a wetting front must establish and propagate its way through the soil before a shallow groundwater flow system can be set up. Much of the precipitation input from the intermittent summer rainstorms can be absorbed into the soil profile and evaporated without having a significant discharge signal. An improved, semiarid groundwater model is needed for this type of environment. An irrigation project exists on Sweetwater Creek near Lewiston Idaho that decreases the flows on the creek, particularly during low flow periods, including late summer and early fall. There are concerns over the effects of the operation of the irrigation system on in-stream habitat. Limited data have been collected, which would allow an evaluation of the natural flow regime of Sweetwater Creek. Due to the lack of natural flow data, a numerical model was used to simulate the natural flow regime of Sweetwater Creek. This study provided information on the natural flow regime that is being used in the decision making process to balance ecosystem health with irrigation demands by determining the volumes of flows needed to provide for a healthy river system with high-quality physical conditions. A spatially distributed river basin simulation model TopoFlow was used to generate stream flows under a variety of meteorological conditions. In order to capture the range of variability present in flows of Sweetwater Creek, three years were modeled representing high (1996), low (1992) and near average (1986) modern flow conditions. The model results show that the low flow conditions during the late summer and fall months and during dry years are controlled from falling below certain levels by the Twenty One Ranch springs. These springs are feed through a groundwater flow system from Lake Waha. Lake Waha is a naturally dammed lake created by a very large landslide and has no surface flow outlet. The low flows are naturally controlled by this spring system and the magnitude of the flows depend on the lake level and the efficiency of the groundwater flow system. The modeling effort shows that the higher winter and spring flows are controlled by the weather during the immediate time period and the snow accumulations and fast reacting ground water pool levels controlled by previous weather and hydrologic conditions.
DE: 1805 Computational hydrology
DE: 1860 Streamflow
DE: 1874 Ungaged basins
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: Fall Meeting 2005