Hydrologic Responses to Irrigation Management in the Wood River Basin, Klamath County, Oregon

The Wood River Basin (WRB) located upstream of Upper Klamath Lake (UKL) is the main reservoir of the USBR Klamath Irrigation Project. Water allocation became contentious in 2001 when drought led to curtailment of irrigation deliveries to the project to protect endangered fish species. After negotiations, the Klamath Basin Restoration Agreement in 2010 calls for flow increases of 30,000 ac-ft/yr into UKL from voluntary upstream sources. The WRB is a potential source of this water, but response to conservation strategies is uncertain due to the poorly understood hydrology of the basin. A physically-based hydrologic model for the basin was developed using the MIKE SHE/MIKE 11 model. The model was calibrated and validated using observed land use and hydrologic data between 2002 and 2009, a period when tracts of land in the basin were enrolled in land idling programs for water conservation. The calibrated model was used to simulate two end-member scenarios to determine the limits of water conservation strategies, basin-wide full-irrigation and non-irrigation. Two intermediate scenarios were also simulated, limiting irrigation only between June and July, and eliminating every other irrigation application. When compared to the full-irrigated scenario, the total increase of flow to UKL during the growing season was 60,000 acft/yr for the non-irrigated scenario; and 36,000 ac-ft/yr and 31,000 ac-ft/yr for the two intermediate scenarios, respectively. There is potential for water conservation strategies in the WRB to substantially increase water flow into UKL, but these strategies would have to be implemented extensively throughout the basin to reduce sub-irrigation contributions to consumptive use by neighboring irrigated lands.