Showing items related by title, author, creator and subject.

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  Land use and vegetation change in response to river basin development in the lower Tana Basin of Eastern Kenya

  Maingi, John Kaunda.; Marsh, Stuart E.; Hutchinson, Charles F.; Swetnam, Thomas W.; Huete, Alfredo R.; Reeves, Richard W. (The University of Arizona., 1998)

  This study describes the impacts of river development projects on land use and vegetation in a floodplain that includes old-growth forest and an important primate habitat located in eastern Kenya. River basin development activities include the construction of hydro-electric dams in the upper river basin, and an irrigation scheme, the Bura Irrigation and Settlement Project, in the lower basin. Through flood frequency analysis for both the pre- and post-dam period, I demonstrate that there has been a significant (p < 0.01) reduction in floods with a recurrence interval of 5 years or greater. A hydrological simulation model is used to estimate the frequency and duration of flooding of 73 vegetation sample plots for the pre- and post-dam period. Four of the plots, lying less than 1.25 m above dry season river level, show a slight increase in days flooded, whereas the rest show a significant decline in days flooded from the pre- to the post-dam period. Detailed descriptions of the structure and dynamics of the Tana riverine forest, and exploration into the influence of abiotic variables to species composition, are made using ordination and classification techniques. The three canopy levels examined, and the regeneration layer, had different species compositions. Many of the upper canopy species are not regenerating. Results of detailed land cover and change detection mapping using remotely sensed data reveal significant change. Forest cover declined slightly (about 2%) between 1975 and 1984. However, between 1989 and 1996, there was a 27% decline in riverine forest, while cultivated area within the forest increased by 45%. Over the same period, area of exposed soil increased by 112%. Several landscape measures are given and all indicate significant fragmentation of riverine forest. The extent of riverine forest along the active river channel declined by about 200 m between 1989 and 1996. Human disturbance now represents the greatest threat to continued survival of the forest. Results of a dendrochronologie investigation reveal that a number of species produce growth rings. Four species identified as offering the best chance for developing a ring-width chronology are; Acacia elatior, Acacia robusta, Tamarindus indica, and Newtonia hildebrandtii.
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  Factors affecting oxygen-18 concentrations in the Tucson basin and the Madrid basin

  Davis, Stanley N.; Gutierrez, Miguel Angel, 1948- (The University of Arizona., 1991)

  Two regional aquifers are analyzed based on their stable isotope and hydrochemical data. The Tucson basin (Arizona) and Madrid basin (Spain), present similarities in their geologic patterns. The ground-water flow regimens, however, are different. Madrid basin presents local, intermediate and regional flow. Rivers in the Madrid basin are perennial, while Tucson washes only drain surface run-off. The winter precipitation is the main source for recharge in both basins. This was deduced by the difference in oxygen-18 content between winter and summer precipitation over both basins. Madrid basin presents a continental effect occurring from west to east and an altitude effect from northeast to southwest. Tucson basin presents an altitude effect. The oxygen-18 content decreases toward the higher elevations. Mixing of waters in discharge areas in both basins due to anthropogenic activity masked relationships, if any, among the stable isotopes and hydrochemical species.
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  Chemical quality of water in relation to water use and basin characteristics, Tucson Basin, Arizona

  Feldman, Arlen.; Simpson, Eugene S.; Dutt, G. R.; Ferris, J. G. (The University of Arizona., 1966)

  The areal distribution of the chemical quality of the Tucson basin ground water has been mapped. The basin was divided into five study sections, according to the relative concentrations of the chemical ions studied, The five chemical quality sections are as follows: 1. Canada del Oro; Catalina, Tanque Verde, and Rincon Mountain foothills and extension into the northeast half of the basin low concentrations except for Tanque Verde anomaly. 2. Tucson-Benson Highway area extending from east of Vail northwest to the Santa Cruz Rivermoderately high concentrations. 3. Foothills of the Santa Rita and Sierrita Mountains extending to the Santa Cruz bottom land moderate concentrations. 4. The Santa Cruz bottom land from Arivaca to Rillito moderately high to high concentrations. 5. The Tucson Mountain foothills extending to the Santa Cruz bottom land low - moderate to moderately high cone entrations0 The water quality of these sections is correlated to the geology of the basin, according to the principles set forth in the section on the "Geochemistry of Ground Water." The effects of man's lowering of the water table are not as yet evidenced in the chemistry of the ground water In conclusion, the part of the Rillito Creek drainage basin in the northeast Tucson basin fill is found to have both the best water quality and the highest specific capacities of the entire basin. Subsurface storage and impermeable boundary limitations may restrict further development of this area, however. Artificial recharge into this aquifer, from Rillito Creek, could alleviate the quantity problems.