HR: 1340h
AN: H33D-1406    [Abstracts]
TI: Analysis of Evaporative Flux Over Irrigated and Unirrigated Pasture in the Wood River Basin
AU: * Cuenca, R H
EM: richard.cuenca@oregonstate.edu
AF: Oregon State University, Department of Bioengineering, Corvallis, OR 97331 United States
AU: Mahrt, L
EM: mahrt@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331 United States
AU: Hagimoto, Y
EM: yuta@engr.orst.edu
AF: Oregon State University, Department of Bioengineering, Corvallis, OR 97331 United States
AU: Peterson, S
EM: shannon.peterson@kbrt.org
AF: Oregon State University, Environmental Science Program, Corvallis, OR 97331 United States
AB: The reduction in evaporative fluxes due to withholding irrigation water for pasture in the Wood River subbasin of the Upper Klamath Basin was evaluated to estimate the potential benefit in subsequent streamflow. Two Campbell Scientific (CSI) Bowen ratio - energy balance systems were installed, one over a fully irrigated site and one over a non-irrigated site separated by approximately 11 km. The systems were comprised of an infrared gas analyzer for water vapor gradients, fine-wire thermocouples for temperature gradients, net radiometer and soil heat flux sensors. Additional micrometeorological sensors for precipitation, solar radiation, air temperature and relative humidity, wind speed and direction enabled calculation of a Penman-Monteith reference evapotranspiration. Both sites had uniform fetch conditions in excess of 1 km in the predominant upwind direction. Bowen ratio data were quality controlled using the Ohmura algorithm and energy balance components and fluxes computed every 20-min. Soil temperature and soil moisture profile sensors in six depth layers down to 80 cm were installed at the same sites and monitored every 15-min. High frequency (10-min) recording piezometers for water table monitoring were also installed. Both irrigated and unirrigated sites started the 2004 growing season with virtually the same soil moisture conditions due to over winter precipitation and melting of the snowpack. The evaporative flux rates from the two sites were nearly identical early in the season, and the repeatability of the diurnal fluxes at the two sites during this period is excellent. Towards the middle of the growing season, the evaporative flux rate at the irrigated site increased relative to the unirrigated site until at the end of the season there was approximately a 40 percent unbiased (dividing by the mean) difference between the two sites. The micrometeorological data indicate nearly uniform atmospheric conditions at the two sites due to turbulent mixing of the air mass within the valley. The persistence of the evaporative flux rate at the unirrigated site was probably due to contributions from the water table, as exhibited in the diurnal piezometer data. The difference in soil heat flux rates between the two sites after dry-down of the unirrigated site was relatively high and affected the difference in available energy (net radiation - soil heat flux). Initial application of LANDSAT data to integrate regional effects of unirrigated project lands over the basin is presented.
DE: 1814 Energy budgets
DE: 1818 Evapotranspiration
DE: 1840 Hydrometeorology
DE: 1842 Irrigation
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: Fall Meeting 2005