A procedure for estimating runoff from convective storms in the semiarid Southwest is needed for the design of small hydraulic structures. The aim of this study was to develop and test rainfall and runoff relationships based on the analysis of 12 years of hydrologic data for an 18-square mile experimental watershed. rhe experimental area is divided into four subwatersheds ranging in size from 0.5 to 7.8 square miles, Vegetation and soils are typical of what is encountered in the valley floors of southern Arizona. Rainfall is measured at 29 locations. Isohyetal maps were prepared for all of the storms which lead to the development of a rainfall model that describes the distribution of rainfall in space. An exponential relationship was found to adequately represent the spatial variation of each storm. A single equation for all storms was developed by using a parameter that is related to the storm center depth. The Kolmogorov-Smirnov procedure was used to test the hypothesis that storm center location is governed by chance in areas not influenced by topographic changes. It was found that the assumption which states that convective storm cells are randomly located within valley floors is acceptable. An equation was derived for calculating point rainfall probabilities from raingage network data, The results were based on the random location of storm centers and on an extremal distribution function fitted to storm center depths. The calculated probabilities were found to be significantly higher than the observed probabilities determined from a nearby, long-term U. S. Weather Bureau station. The volume of runoff from small, semiarid watersheds was found to be a function primarily of mean rainfall. In a multiple linear regression model, mean rainfall accounted for 67 to 82 percent of the variance. The use of a time distribution factor which includes the maximum 15-minute intensity reduced the unexplained variance to 11 to 16 percent. Inserting a space distribution variable into the model indicated that storm center location on the watershed was not a significant factor in predicting runoff. An antecedent rainfall index did not produce any significant correlation with runoff from convective storms. For winter frontal storms, however, a four-day antecedent rainfall index was found to be an important factor in oxplaining runoff. It appears that the commonly used Soil Conservation Service method underestimates convective storm runoff for most storm center depths below about three inches. A direct comparison with the multiple regression equation was not possible as this method does not take into account the variability of convective rainfall in time and space. As a means for estimating runoff volumes for ungaged watersheds, a runoff coefficient was defined as the ratio of runoff to effective rainfall (mean rainfall less initial abstractions). It appears that as a first approximation, the runoff coefficient can be considered as being equal to the coefficient in the well known rational formula. There is some evidence to the belief that the runoff coefficient is affected by a storm's time distribution factor. It was demonstrated that runoff volume recurrence intervals can be determined adequately from the rainfall and runoff relationships developed in this study.

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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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The main focus of the present study is to identify and integrate the factors affecting the degree of irregularity of five continental divide traces, as expressed by their fractal characteristics measured by the divider method. The factors studied are climate, relief and tectonic environment. The second objective of this study is to determine the relationship between uplift rates and divide trace fractal dimension. Analysis of the results suggests that the degree of irregularity of continental divide traces at fine scale (approximately 10-70 km of resolution) is strongly affected by both climate and tectonics. It is found that control of the factors is generally weaker at coarse scale (above approximately 70 km of resolution). Generic relief should be ranked below both climate and tectonic environment as a factor affecting the complexity of continental divide traces. In terms of the second objective, the fractal dimension at fine scales follows a weakly inverse relationship with uplift. At coarse scale, there is stronger inverse relationship between uplift rate and fractal dimension. / Introduction -- Methodology -- Geomorphic environment -- Evaluation of results -- Significance of control factors -- Conclusion. / Department of Geological Sciences

Previous works have applied the Divider Method to the shapes of drainage divides as measured from maps. This study focuses on the shapes of several drainage divides measured in the field at very fine scale. These divides, chosen for their sharp crests, include portions of the Continental Divide in Colorado and badlands-type divides in Arizona, Wyoming, South Dakota, and Texas. The badlands type divides were delineated using a laser theodolite to collect data at decimeter point spacing, and the Continental Divide segments were delineated using pace and bearing at a constant point spacing of 30 meters. A GIS was used to store and visualize the divide data, and an automated divider analysis was performed for each of the 16 drainage divides.The Richardson plots produced for each of the drainage divide datasets were visually inspected for portions of linearity. Fractal dimensions (D) were calculated using linear regression techniques for each of the linear segments identified in the Richardson plots. Six of the plots exhibited two distinct segments of linearity, nine plots exhibited one segment, and one plot exhibited no segments of linearity. Residual analyses of the trend lines show that about half of the Richardson plot segments used to calculate D exhibit slight curvature. While these segments are not strictly linear, linear models and associated D values may still serve well as approximations to describe degree of divide wandering.Most (20 out of 21) of the dimensions derived from the Richardson plots for the drainage divides fall within the range from 1.01-1.07. The D values calculated for the Continental Divide range from 1.02-1.07. The dimensions calculated for the badlandtype divides were distributed evenly across the range of 1.01-1.06, with a single exceptional D value at 1.12. Only four of the divide D values fall within a range of 1.06–1.12, the range for D established for drainage divides in published map-based studies, despite the apparent dominance of erosion processes on the measured divides. / Department of Geology

A simple model of surface and sub -surface soil temperature was developed at the watershed scale ( -100 km2) in a semi -arid rangeland environment. The model consisted of a linear combination of air temperature and net radiation and assumed: 1) topography controls the spatial distribution of net radiation, 2) near- surface air temperature and incoming solar radiation are relatively homogeneous at the watershed scale and are available from ground stations and 3) soil moisture dominates transient soil thermal property variability. Multiplicative constants were defined to account for clear sky diffuse radiation, soil thermal inertia, an initially fixed ratio between soil heat flux and net radiation and exponential attenuation of solar radiation through a partial canopy. The surface temperature can optionally be adjusted for temperature and emissivity differences between mixed hare soil and vegetation canopies. Model development stressed physical simplicity and commonly available spatial and temporal data sets. Slowly varying surface characteristics, such as albedo, vegetation density and topography were derived from a series of Landsat TM images and a 7.5" USGS digital elevation model at a spatial resolution of 30 m. Diurnally variable atmospheric parameters were derived from a pair of ground meteorological stations using 30 -60 min averages. One site was used to drive the model, the other served as a control to estimate model error. Data collected as part of the Monsoon '90 and WG '92 field experiments over the ARS Walnut Gulch Experimental. Watershed in SE Arizona were used to validate and test the model. Point, transect and spatially distributed values of modeled surface temperature were compared with synchronous ground, aircraft and satellite thermal measurements. There was little difference between ground and aircraft measurements of surface reflectance and temperature which makes aircraft transects the preferred method to "ground truth" satellite observations. Mid- morning modeled surface temperatures were within 2° C of observed values at all but satellite scales, where atmospheric water vapor corrections complicate the determination of accurate temperatures. The utility of satellite thermal measurements and models to study various ground phenomena (eg. soil thermal inertia and surface energy balance) were investigated. Soil moisture anomalies were detectable, but were more likely associated with average near -surface soil moisture levels than individual storm footprints.

A simple model of surface and sub-surface soil temperature was developed at the watershed scale (-100 km²) in a semi-arid rangeland environment. The model consisted of a linear combination of air temperature and net radiation and assumed: (1) topography controls the spatial distribution of net radiation, (2) near-surface air temperature and incoming solar radiation are relatively homogeneous at the watershed scale and are available from ground stations and (3) soil moisture dominates transient soil thermal property variability. Multiplicative constants were defined to account for clear sky diffuse radiation, soil thermal inertia, an initially fixed ratio between soil heat flux and net radiation and exponential attenuation of solar radiation through a partial canopy. The surface temperature can optionally be adjusted for temperature and emissivity differences between mixed bare soil and vegetation canopies. Model development stressed physical simplicity and commonly available spatial and temporal data sets. Slowly varying surface characteristics, such as albedo, vegetation density and topography were derived from a series of Landsat TM images and a 7.5" USGS digital elevation model at a spatial resolution of 30 m. Diurnally variable atmospheric parameters were derived from a pair of ground meteorological stations using 30-60 min averages. One site was used to drive the model, the other served as a control to estimate model error. Data collected as part of the Monsoon '90 and WG '92 field experiments over the ARS Walnut Gulch Experimental Watershed in SE Arizona were used to validate and test the model. Point, transect and spatially distributed values of modeled surface temperature were compared with synchronous ground, aircraft and satellite thermal measurements. There was little difference between ground and aircraft measurements of surface reflectance and temperature which makes aircraft transects the preferred method to "ground truth" satellite observations. Mid-morning modeled surface temperatures were within 2° C of observed values at all but satellite scales, where atmospheric water vapor corrections complicate the determination of accurate temperatures. The utility of satellite thermal measurements and models to study various ground phenomena (e.g. soil thermal inertia and surface energy balance) were investigated. Soil moisture anomalies were detectable, but were more likely associated with average near-surface soil moisture levels than individual storm footprints.