• Hydrologic Aspects of Land-Use Planning at Tumamoc Hill, Tucson, Arizona

      Popkin, Barney Paul; Soils, Water and Engineering Department, The University of Arizona, Tucson (Arizona-Nevada Academy of Science, 1974-04-20)
      Tumamoc Hill, an 869-acre (352 ha) desert area near Tucson, Arizona, is being considered as a controlled- access environmental site. Water affects the site's geology, soils, vegetation, wildlife, and archaeology. The Hill is drained by three small watersheds. The largest is rapidly urbanizing upstream. Hydrologic aspects include potential flooding and erosion hazards. These may be reduced simply, economically, and wisely in a land-use plan. Upstream development increases storm runoff volumes, and flood peaks, and frequencies routed through the site, and threatens existing downstream urban development. Return periods of channel-overflow floods become shorter with urbanization. The region may be managed to reduce hydrologic hazards by three procedures: widen channels, install low checkdams, and vegetate drainageways. These methods will slow down runoff velocities, and increase cross -sectional area of flow and roughness coefficient. More water would also be available for vegetation and wildlife. The land-use plan should include environmental education programs. These would present important effects of water on the natural ecology, and hydrologic aspects of watershed urbanization.
    • Uncertainty in Sediment Yield from a Semi-Arid Watershed

      Smith, J. M.; Fogel, M.; Duckstein, L.; Systems & Industrial Engineering, University of Arizona, Tucson, Arizona 85721; Watershed Management and Systems & Industrial Engineering, University of Arizona, Tucson, Arizona 85721 (Arizona-Nevada Academy of Science, 1974-04-20)
      The paper presents a stochastic model for the prediction of sediment yield in a semi -arid watershed based on rainfall data and watershed characteristics. Uncertainty stems from each of the random variables used in the model, namely, rainfall amount, storm duration, runoff, and peak flow. Soil Conservation Service formulas are used to compute the runoff and peak flow components of the Universal Soil Loss Equation. A transformation of random variables is used to obtain the distribution function of sediment yield from the joint distribution of rainfall amount and storm duration. The model has applications in the planning of reservoirs and dams where the effective lifetime of the facility may be evaluated in terms of storage capacity as well as the effects of land management on the watershed. Experimental data from the Atterbury watershed is used to calibrate the model and to evaluate uncertainties associated with our uncertain knowledge of the parameters of the joint distribution of rainfall and storm duration.