WSP05593 - Laserfiche WebLink

Home Browse Search

105CI OXd - oXs + RF + SP - CUc - CUp = dGWS where O~ = Oxford Farmers Ditch Company diversions; OXs = Oxford Farmers Ditch Company spillage; RF = Precipitation; SP Seepage to or from the Arkansas River; CUc Consumptive use of crops in the study area; CUp = Consumptive use of phreatophytes in the study area; and dGWS = Change in ground water storage. The precipitation term was computed by multiplying the monthly precip- itation from Fowler 1 SE Station (Table 5) times the total area of the system, 8,970 acres, which was determined by planiroetering the area shown on Plate 1. The determination of seepage, which can be either inflow or outflow, involved computation as stated by the following equation (see Sketch 1): SP = ~(AKn - OXd + CC + AP - NEV - OTd - AKcd) where AKn = Recorded flow at the state maintained gaging station, Arkansas River at Nepesta; AKcd = Recorded flow at the U.S.G.S. maintained gaging station, Arkansas River at Catlin Dam; AP = Recorded flow at the U.S.G.S. maintained gaging station, Apishapa River at Fowler; CC Recorded flow at the gaging station established on Chico sa Creek by the Water Conservation Board during September 1968; NEV = Evaporation less precipitation acting on the surface of the Arkansas River; and OTd = Headgate diversions of the Otero Canal. NEV was computed by subtracting the Fowler precipitation from seven- tenths of the Class A Pan evaporation observed at Pueblo City Reservoir or John Martin Reservoir for times observations weren't made at Pueblo City Reservoir and multiplying the difference times the surface area of the river, 541 acres, determined from Plate 1. The headgate diversions of the Otero Canal were obtained from the water commissioner's field books. Because seepage occurs along both banks it was necessary to divide the total in half according to the equation. Evapotranspiration or gross consumptive use, as it is used in this report, of the crops gro"~ in the Oxford Farmers system is a large part of the outflow. It is defined as the amount of water required, regardless of the source, to support optimum growth of the particular crop or crops under consideration and includes water evaporated from the fields as well as that transpired by the plants. Irrigation season total gross consumptive use was computed using the Lowry-Johnson method, and it was proportioned to the months of the irrigation season using the Thornthwaite distribution. The Lowry-Johnson method is based on experimental data determined from water-budget studies at several locations. It involves use of a relationship between gross consumptive use and an index computed - 15 -