From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona / The University of Arizona Atterbury Experimental Watershed, located southeast of Tucson, Arizona has been instrumented for precipitation and runoff measurements since 1956. Early on the afternoon of July 16, 1975 an intense convective thunderstorm produced more than three inches of rainfall in less than 50 minutes as recorded in several rain gages located in the middle of one 8.1 square-mile desert subwatershed. Storm runoff from this rural subwatershed and an adjacent recently urbanized subwatershed filled the newly finished Lakeside Reservoir and topped the concrete flood spillway with a peak of greater than 3000 cfs, the greatest flow since monitoring began. An analysis of storm characteristics, along with previously available data from local urbanized watersheds, allows speculation on the effect of such an intensive storm in a highly urbanized area.

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona / The geomorphic threshold concept of landform evolution and its effect on hydrologic performance of drainage systems was investigated on small semiarid watersheds in Southeastern Arizona. Thresholds develop within a geomorphic system with time and can, when exceeded, cause drastic changes in the geomorphic features and in the hydrologic performance of the watershed. The slow continuous evolution of drainage characteristics can be suddenly altered with major readjustment of the landscape taking place. A new state of dynamic equilibrium will then prevail until the drainage system is again subjected to conditions which cause some geomorphic threshold to be exceeded. Areas of potential geomorphic readjustment can be identified from parameters such as channel slope, average land surface slope, drainage density, and mean length of first order streams and these data can be used as components in a calibrated kinematic-cascade model to determine the effects of various degrees of drainage system alteration. The influence on runoff from exceeding various geomorphic thresholds is tested and the resulting hydrologic modifications are simulated and discussed.

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona / In the absence of pure piston flow, the carbon-14 ages of ground-water can be related to groundwater residence times only in the context of a flow model. To do this, a three-dimensional digital computer model of a portion of the Tucson Basin Aquifer was constructed using the theory of finite-state mixing cell models. The model was calibrated against the spatial distribution of adjusted carbon-14 ground-water ages, and once a reasonable fit was obtained, the ground-water residence times were calculated. The model also provides a first approximation to three-dimensional flow in the aquifer as well as an estimate of the long-term average annual recharge to the aquifer.

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona / A conventional water balance method, employing long-term average values of rainfall, runoff and evapotranspiration yields near-zero recharge values for the Empire and the Sonoita basins. These results, however, are not in agreement with those obtained from an analysis of the local ground water regimes. A different approach for calculating recharge, based on the typical characteristics of these arid basins, is proposed. In particular, both basins are characterized by intense thunderstorms of short duration in the summer which occur usually towards the evening, and shallow, sandy-gravelly soils with a relatively high permeability overlying fractured rocks in the elevated mountain regions. These factors may cause a considerable amount of water to infiltrate through the soil profile, thereby escaping evapotranspiration during the following day. The proposed model deals with separate thunderstorm events using mean values of rainfall intensity and frequency corresponding to elevation. This model was coupled with a numerical solution of the flow equation which was used to solve the one dimensional water flow through a soil profile. The solution includes sink terms and was solved for the simultaneous processes of infiltration, moisture redistribution and evapotranspiration. The results obtained show almost no recharge in the low valleys, but significant recharge in the mountains. The amount of recharge increases with elevation and decreases with the depth of the soil profile.

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona

From the Proceedings of the 1976 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 29-May 1, 1976, Tucson, Arizona / Construction of a hydraulic monolith weighing lysimeter was undertaken, however, due to inherent design and/or construction errors this proved to be an inadequate device for the accurate determination of evapotranspiration from Larrea divaricatta (creosote bush). Prior inability to stabilize the lysimeter with respect to barometric and temperature fluctuations, and eventual failure within the hydraulic transducer package led to the eventual abandonment of the hydraulic load cell design, and adoption of an electronic strain gage transducer package. This paper deals with the detailed design and construction phases of the original lysimeter, the inherent difficulties encountered, and with the modification and conversion of the lysimeter to the electronic transducer assembly. Accompanying test data with respect to sensitivity, response time and differential loading characteristics support the premise that the electronic load cell design has inherent maintenance and operational advantages over the hydraulic transducer lysimeter.

From the Proceedings of the 1977 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 15-16, 1977, Las Vegas, Nevada / During a standard bioassay using fish and the antitranspirant Folicote, a significant deoxygenation of the water was observed. Oxygen demand tests without fish using distilled water indicated that at 25 °C Folicote reduced D.O. from saturation (8 ppm) to 0.1 ppm within 60 hrs. Oxygen consumptive qualities of Folicote should be taken under consideration during actual field applications.

From the Proceedings of the 1977 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 15-16, 1977, Las Vegas, Nevada / Factors controlling transpiration and photosynthesis of saltcedar were investigated in the field near Bernardo, New Mexico. Transpiration rates were similar to those for several herbaceous species, but photosynthesis and water use efficiency were significantly lower in saltcedar. Photosynthesis was light saturated at an irradiance equal to 44% of full sunlight, while the stomata were apparently fully open at light levels greater than one-third full sunlight. Optimum leaf temperatures for photosynthesis were between 23° and 28 °C, considerably lower than typical daytime ambient temperatures. Photosynthesis was reduced about 20% at 35 °C. Stomatal resistance increased linearly with increases in leaf temperature between 14° and 50 °C, with relative humidity held constant. The increase in stomatal resistance could have been caused by direct effects of temperature on the stomata, by increases in the absolute humidity gradient from leaf to air, or by both. Increased stomatal resistance at high temperatures and low relative humidities would account for observed afternoon depressions in transpiration and photosynthesis and increases in canopy resistance. Estimates of stomatal resistance for twigs in full sunlight ranged from 2 to 6 sec cm⁻¹, with most values falling between 3 and 5 sec cm-, when leaves were at 30 °C.