A Disaggregation model was tested for arid land stream flow generating. The test was performed on data from Black River, near Fort Apache, Arizona. The model was tested in terms of preserving the relevant historical statistics on both monthly and daily levels, the monthly time series were disaggregated to a random observation of their daily components and the daily components were then reaggregated to yield monthly values. A computer model (DSGN) was developed to perform the model implementation. The model was written and executed on the Macintosh plus personal computer Data from two months were studied; the October data represented the low flow season, while the April data represented the high flow season. Twenty five years of data for each month was used. The generated data for the two months was compared with the historical data.

A continuous simulation streamflow model (i.e., SSARR - an acronym for Streamflow Synthesis and Reservoir Regulation) was evaluated and used to study winter streamflow from the Salt River Basin. This 4,306 square mile basin, which ranges in elevation from 2,200 to 11,500 feet, is associated with a diversity of watershed, vegetation, climatic and hydrologic characteristics. Program modifications allowed computation of potential evapotranspiration within the model. This provided improved flexibility in delineating simulation units and reduced the necessary time-dependent data inputs to daily values of precipitation and temperature. Refinement of initial parameter estimates and relationships was accomplished by trial and error methods. Four years of hydrometeorological data were utilized for model calibration and an additional four years used to test the validity of parameter estimates. Simulated hydrographs generally underestimated peak flows and overestimated recession flows following major rainfall events. The standard error of the estimate for simulated winter flows (November through May) was only 30,000 acre-feet for the calibration period but increased to approximately 120,000 acre-feet for the validation period. Average winter flows during the calibration and validation periods were 840,000 and 690,000 acre-feet, respectively. Approximately 25 to 45 percent of the winter runoff occurring after February 1, March 1 and April 1 could be predicted from simulated snowpack water equivalent and soil moisture conditions on the prediction date. High elevation portions of the basin were more efficient at producing streamflow from a given precipitation input than were the lower elevations. Maximum daily watershed efficiencies (ratio of generated runoff to rain and snowmelt inputs) usually occurred on the date of snowpack disappearance for the relatively high elevation simulation units. Simulated runoff volumes increased exponentially with increased basin precipitation but decreased linearly with increased basin air temperatures. For a selected winter period, simulations indicated streamflow response to a one-inch change in winter precipitation would be approximately 100,000 acre-feet, or 3.4 times greater than expected from a one-degree change in winter temperature.

Southwestern mixed conifer forests cover approximately 2.5 million acres in Arizona and New Mexico, and provide a wide range of commercial and noncommercial products. The problem is to develop a management prescription which will benefit the greatest mix of resources. An alternatives analysis predicted that a prescription that included small patch clearcutting, in addition to other stand modifications, would meet this criteria. The two Thomas Creek watersheds, in eastern Arizona, were used to validate and test the responses of the forest resources to the preferred prescription, and to increase the understanding of the mixed conifer forest system. The actual harvest created 63 small patch clearcut and group selection openings, averaging 1-2 acres, over 13% of the South Fork watershed. Overall stand density was reduced 34% to 132 square feet per acre. The harvest resulted in significant hydrological changes. Average annual streamflow increased by about 45%, or 1.72 inches, mostly because of increased winter runoff. A greater proportion of the snowmelt generated streamflow occurred earlier in the spring, while annual peak flows were increased by an average of 66%, or about 2.60 cubic feet per second per square mile. The number of days without flow decreased. Average watershed maximum snow water equivalents remained unchanged. The primary causes of the increases were reduced evapotranspiration and increased snow accumulation in the openings; however, it appears that the partially cut stand also contributed to the increases. The treatment benefitted the timber resource. Diameter growth on the South Fork increased for most species compared to the unharvested stand on North Fork. Stand gross growth remained unchanged, but the same volume was being added to fewer trees. The stand, including most openings, is well stocked with adequate numbers of natural and advance regeneration. The Thomas Creek prescription, after 8 years of evaluation, has achieved its objectives of increasing water yields and stand growth while insuring adequate regeneration. It has also benefitted many wildlife species as well as livestock. A similar prescription should increase water yields, by about 15,000 acre-feet annually, from the Upper Black River Basin without adversely impacting other forest resources.

General water rights adjudications are now taking place in Arizona. The Gila River and Little Colorado River adjudications are among the largest court proceedings ever undertaken in the United States, involving more than 78,000 water rights claims scattered over 50,000,000 acres of land. The cost of individually proving such a number of individual claims in a formal trial setting would be enormous — often greater than the water's economic worth. Also, the time required to complete such a proceeding would take decades. Consequently, alternative procedures are needed to streamline the investigations and forestall a potentially serious water resource management problem. There are an estimated 22,800 stockwatering ponds (stockponds or stocktanks) in the Gila River Basin alone, and each potentially could be tried as an individual case. If small claims such as those for stockwatering could be considered de minimis in their impact on other higher priority uses, they might be adjudicated as one class of use, thereby fore-stalling a case-by-case trial of each individual water right claim. However, a major obstacle in granting special treatment to small claims lies in demonstrating to litigants that certain small water uses do not, in fact, have a discernible impact on other downstream water right holders. This study was undertaken to quantify the actual losses to a river system from stockwatering ponds, and to compare those losses to other naturally occurring impacts on the hydrologic system. Employing a watershed model, portions of the Walnut Gulch Experimental Watershed at Tombstone, Arizona, an area located within the San Pedro watershed, were analyzed. Storm runoff was simulated with and without the presence of stockponds. Different storm events and storage conditions were modeled in order to measure the impact of stockpond storage under a wide range of field circumstances. This study demonstrated that the hydrologic effects of stockwatering ponds are de minimis with respect to their impact on other water users many tens or hundreds of miles downstream on the river system. Stockpond numbers, capacities, volume/surface area relationships, quantification methods, and effective retention are also evaluated. Statutes in other states are reviewed for their approach to handling stockwatering uses.

Relationships between thunderstorm and watershed variables and runoff from or within semiarid watersheds at Walnut Gulch, Arizona were examined. Variables showing greater sensitivity to basin and storm size were better flow predictors. Stepwise regression with three increasingly nonlinear algebraic models showed mean storm depth was the best simple predictor of runoff. Predictions improved using storm volume, a product of storm depth and areal extent. Initial runoff to streams was best described as a highly nonlinear function of storm and watershed variables. Runoff from a basin was a more linearized function of similar variables. The above differences were ascribed to channel transmission losses, reductions in runoff moving down initially dry channels. For a given basin and small storms, loss to runoff ratios exceeded 10:1 and were highly variable. Ratios were similar and less than 0.5:1 for storms centrally located over a basin and generating sufficient initial runoff to minimize flow variation due to losses. Losses increased disproportionately with basin size. Antecedent rainfall and first summer flows also affected rainfall runoff relationships in a differential manner. Wet conditions enhanced runoff more from larger versus smaller storms. First summer flows were less than expected probably because of higher soil infiltration and channel losses at the onset of summer storms. Overall, as storm size decreased or basin area increased, initial runoff was more often a localized phenomenon and downstream flow more dependent on storm depth, extent, location, and seasonal timing and basin channel losses, but less dependent on antecedent rainfall. Consequently, storm depth accounted for only 60% to 70% of the variation in flows while storm volume, antecedent rainfall, channel losses, and first summer flows explained 80% to 90%. Finally, oversimplifying storm or watershed variables or analytical methods led to errors in assessing their affect on runoff. It was also determined that current arguments supporting a recommendation to delete smaller, frequent annual floods to better fit remaining data to flood frequency curves were oversimplified. Distributed rainfall - runoff models with channel losses and regional storm depth - area - frequency data may be the way to develope flood curves for semiarid basins with short runoff records.

Many hydrologic basins in the southwest have seen their perennial streamflows turn to ephemeral, their riparian communities disappear or be jeopardized, and their aquifers suffer from severe overdrafts. Under -management of ground -water exploitation and of conjunctive use of surface and ground waters are the main reasons for these events.

Arizona is presently in the midst of a general adjudication for the Gila River system -- the watershed which comprises the southern two- thirds of the state. The purpose of the adjudication is to prioritize all water claims in the river system: both state -established and federally reserved rights. Arizona adheres to a bifurcated (or divided) system of water law which only recognizes a component of ground water -- called subflow -- to be appropriable. Wells which pump non-appropriable water -- called tributary flow -- are not to be included in the adjudication. The problem is that federal laws do not recognize this artificial bifurcation. The challenge lies in identifying a subflow zone which satisfies the hydrologic fiction of existing state precedents and the hydrologic reality of federal statutes. At the core of the problem lies the fate of Arizona's perennial stream water and the fulfillment of federally reserved tribal water rights. Thus, larger questions loom: can Arizona law reconcile its glutinous past with a water -scarce future, will the adjudication ever reach a finality, and even if it does, will it be a finality that all sides can live with?