Little Washita River Experimental Watershed, Oklahoma (Flow)

Over the past five decades, the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) and the United States Geological Survey (USGS) have collected stream flow, reservoir, and groundwater data in the Fort Cobb Reservoir Experimental Watershed (FCREW) and Southern Great Plains Research Watershed (SGPRW), which includes the Little Washita River Experimental Watershed (LWREW) in central Oklahoma. The climate in these watersheds is subhumid, with average annual rainfall of 800 mm (1971-2000 average for Caddo County; Oklahoma Climatology Survey, 2005). The drainage area of the SGPRW is 2927 km2 and includes the LWREW. The LWREW covers an area of 610 km2 and consists of mixed agricultural land use, mainly pasture and rangeland that covers 68% of the total area. The topography is rolling with a maximum relief of 180 m and sandy to loamy soils. Of the 13 USGS stream gauges in the LWREW, two of them, ARS 522 and ARS 526, were initially managed by the USDA-ARS but decommissioned in 1985. Gauge ARS 522 was colocated with the USGS stream gauge ID 7327490, and data from this gauge were used when ARS 522 was discontinued. In 1992, the USGS installed the stream gauge ID 7327447 at the same location (Little Washita River near Cement, OK) where ARS 526 existed. For the stream gauges ID 522 and 526 installed by the ARS, stream stage data were obtained using a Hg manometer bubble gauge and a continuous stage recorder. Periodic stream discharge measurements were made during rain events and low-flow periods to define the relationship between flow discharge and stage. Discharge data by time increments were computed from the stage charts by the stage shift method (Corbett, 1943; Brakensiek et al., 1979). The directly measured data are the stage, which is then used to estimate discharge using stage-discharge relationships. All measurements made at USGS gaging stations are quality assured and quality controlled. The equipment used to make the measurements is securely housed and regularly checked for calibration and drift. Current meters are spin tested before use and checked after use if the measured value is deemed questionable.