Complete issue of the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / Flood flows and water quality in the Southwest are roust dramatically influenced by short, intense rainstorms. Runoff from these storms has been modeled with some success. One key element that has often been overlooked, however, is the importance of intra-storm rainfall distribution on runoff response. Actual storms were modeled for small experimental watersheds in the Southwest using different time increments of intra-storm rainfall. Increments of 5 minutes or less proven satisfactory for accurate hydrograph simulation. As increments became longer than 5 minutes, the ability to simulate actual hydrographs became increasingly difficult. Increments of 30 minutes or longer proved unacceptable for most storms. Hydrologic models must be sensitive to short time increments of intra-storm rainfall to accurately predict peak flows in the Southwest. Watershed treatments will be more cost-effective if their design considers intense bursts of intra-storm rainfall in addition to total storm volume.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / The Beaver Creek Watershed is located in southern Coconino and southeastern Yavapai Counties, Arizona. This 472 square mile watershed contributes to Beaver Creek which flows into the Verde River. The objectives of this study were: 1) to monitor a network of stock tanks in the watershed on a bi-weekly basis to document seasonal fluctuations in water levels over one year; 2) to investigate the impact of stock tanks on local hydrology by determining the number of times the tanks fill during one year; and 3) to determine a set of dependent variables which would quantify stock tank performance, and a set of independent variables representing characteristics of the tanks and their drainage basins which could affect the performance of the tanks. The relative importance of each of these independent variables in influencing tank performance was then determined through statistical analysis.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / Almost all runoff from small rangeland watersheds in the Southwest is the result of intense thunderstorm rainfall, and the variability of this rainfall is an important runoff-influencing factor in such areas where high intensity rainfall dominates watershed hydrology. Thunderstorm runoff estimates for small rangeland watersheds can be made using a multitude of estimating techniques ranging from simple table and graph procedures to utilizing high-speed computers, and even the most sophisticated models greatly simplify the rainfall input. In this paper, the combined effects of rainfall quantity and intensity, and the rainfall energy factor, EI, in the Universal Soil Loss Equation (USLE), were analyzed, and simple procedures for estimating semiarid rangeland runoff volumes were developed. Equally good correlations with runoff volumes were found for EI, and for total storm rainfall times maximum rainfall intensities for 5, 10, and 30 minutes and the square of the maximum 60-minute rainfall.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / Forest openings affect a snowpack during both accumulation and melt phases. At any point in time, a snowpack is the integrated result of all accumulation, redistribution, and melt processes that have taken place before the time of measurement. Since snowpacks do not always have distinct accumulation and melt phases, it is difficult to determine the effect that an opening will have on a snowpack regime. This paper describes an analysis of the effects of openings in Arizona ponderosa pine forests on snowpacks in and adjacent to the openings, using readily available input variables.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / A discrete form of the water balance equation is used to illustrate the interaction among precipitation, runoff, percolation below the root zone, bare soil evaporation, plant transpiration, and plant available soil moisture. Under rangeland conditions, water availability is often the limiting factor in plant survival and growth. Therefore, the water balance equation is used, together with soils data and water use efficiency factors, to estimate annual aboveground net primary production of perennial vegetation.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / Arizona's water resources system consists primarily of four active management areas (Tucson, Phoenix, Pinal and Prescott), the Central Arizona Project, and the Salt River Project. The problem of water allocation among user categories involves pumping from aquifers and diversions of surface flows. In systems less complex than Arizona, allocation policies may appear obvious. In this case, however, a two-level hierarchical management model is proposed to control water allocation to users: the active management areas as a lower echelon, and the Arizona Department of Water Resources at the higher level. A system theoretic approach combined with recent developments in the decentralized control theory are proposed to be included in the model. A significant characteristic of the proposed model is the ability to consider possible interactions among the active management areas as a result of policy decisions at the State level. A dynamic optimization model based on a state space formulation with total energy required as the objective function is solved for each of the subsystems. Detailed information thus generated at the regional level is then appropriately aggregated for statewide decision making. An iterative algorithm is suggested.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / Chlorine-36 is an important radioisotope with which to date old ground water. The initial chlorine-36 in ground water originates in the atmosphere by cosmic ray spallation of argon-40. Following precipitation and infiltration processes, the natural decay of this radioisotope is then used to date ground water. One must consider, however, the production of chlorine-36 in the subsurface. The production reaction of most interest is ³⁵C1 + neutron → ³⁶C1 + gamma. Buildup of chlorine-36 in the subsurface can result from cosmic ray secondary neutrons near the surface and natural radioactivity produced neutrons below the surface. These production mechanisms, if not taken into consideration, will contribute to the error in chlorine-36 age determinations. To predict subsurface production rates, field measurements were made of thermal neutron fluxes for various geologic materials and depths below the surface. Thermal neutron fluxes were found to vary by more than three orders of magnitude. Theoretical calculations of neutron flux were compared to filed measurements. Estimates of chlorine-36 production rates were then calculated and compared to measured values of chlorine-36 in very old ground water, where decay rates have been hypothesized to be equal to production rates.

From the Proceedings of the 1983 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona-Nevada Academy of Science - April 16, 1983, Flagstaff, Arizona / The relative importance of mountain front recharge as compared to total recharge was determined for a portion of the Tucson basin aquifer margin by interpretation of chemical and isotopic data. Concentrations of 180/160 lower than 6 -10.7 ⁰/00 as compared with a background of about 6 -9.3 ⁰/00 in ground water from the base of the mountains in the gneissic rock suggest the presence of recharge from significantly higher elevations. The trilinear diagram of major ions dissolved in ground water from 123 wells in the Santa Catalina foothills indicates three water types. Water from wells in gneissic rock is high in sodium and potassium content and low in calcium and magnesium. Wells in the gypsiferous Pantano Formation yield water high in sulfates. The majority of wells in the study area, which are along major streams and in the regional aquifer, have calcium carbonate type water. Their chemistry indicates only minor contributions from the gneissic mountain block and the underlying Pantano Formation. Funding for this project came from the Spanish Project Register T377017.