Drainage systems for the desert Southwest are currently designed without much consideration for the climatological or surficial conditions of the region. The "100 year" flood has become the design standard throughout the United States due to misunderstandings about requirements of the National Flood Insurance Program. The effect of larger floods is virtually ignored, seasonal variations of rainfall patterns and intensities are neglected, and hydrologic data collection is extremely limited in watersheds of the urbanizing Southwest. The laws of nature are obscured by the rules of man during the planning and design of desert drainageways. Procedures for extrapolating runoff records and estimating the magnitude of the 100-year flood, including the LP III probability density function, the NOAA Atlas, and HEC-1, have been widely adopted in the arid regions as part of local drainage regulations. Plans are normally not approved unless the basis of design complies with the regulations. Assumptions inherent in the methods are questionable and data to verify the assumptions are limited. Drainage design can be improved by using available field data and a simple method--based on the Rational Method--is developed. Benefit-cost analysis is a valuable tool for establishing project alternatives, project size, and cost/benefit allocation. An equitability index is defined for evaluating fairness, and it is combined with the benefit-cost ratio for refining and selecting project design. Estimates of flood peaks can be improved by considering channel abstractions as "negative base flow"; by recognizing the presence of the n-value paradox; by extending flood records through paleohydrologic study; by monitoring rainfall, runoff, and the effectiveness of design strategies in urban catchments; and by using more suitable rainfall estimates. Drainage design can be made more rational by also considering sediment transport; by including nonstructural design alternatives; and by evaluating a range of flood magnitudes, not just the 100-year flood. A conceptual drainage ordinance not based on the NFIP is presented.

A digitally simulated electronic watershed analog has been developed for the analysis of the hydrologic regime of a watershed. Individual electrical circuits were designed to synthesize the physical characteristics of the hydrologic components of a watershed: interception, surface storage, runoff, infiltration, and subsurface storage. These circuits were related to pertinent empirical studies of significance to each component. Electrical circuit analogies, despite advantages inherent in their direct physical correspondence to hydrologic systems, have fallen into disuse due to the inflexibility of fixed component networks. A digital simulation program developed by the electrical engineering profession to provide flexibility in the design of electronic circuitry has been adapted for the simulation of the electronic watershed analog. The typical digital circuit analysis program is "canned" and the user need not understand its intricacies. Input is in the form of circuit parameters on punched cards. The output is in numeric or graphic form. Using digital simulation methodology, the electronic watershed analog has been used to analyze a 1.63 acre forested watershed.

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Digitized by Kansas Correctional Industries

Runoff and rainfall data have been taken from three high mountain Utah watersheds and subjected to runoff to rainfall comparisons. The resulting Q./P ratios have been compared to the average volumes of runoff curve numbers (CN) computed from this data for each watershed. Runoff curve numbers were also estimated on the basis of the soils and vegetation data available for the watersheds. An attempt has been made t o estimate the watershed lag characteristics by computing synthetic hydrographs for successively larger values of time to peak estimates until the best fit comparison was achieved between the snythetic and the actual hydrographs. Time lag estimates were also made from the Kirpich method and the Mockus method.

Extreme value theory is used as a basis for deriving a distribution function for flood frequency analysis when runoff originates from nonhomogeneous sources. A modified least squares technique is used to estimate the parameters of the distribution function for eleven rivers. Goodness-of-fit statistics are computed and the distribution function is found to fit the data very well. The derived distribution function is recommended as a base method for flood frequency analysis for rivers exhibiting nonhomogeneous sources of runoff if further investigation also proves to be positive.

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No description available.