Hydrologic, social and legal impacts of summary judgement of stockwatering ponds (stockponds) in the general stream adjudications in Arizona

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.hydrology collectio