HR: 15:10h
AN: H33G-07    [Abstracts]
TI: Using δ²H and δ¹⁸O data from precipitation and ground water to identify seasonality and zones of predominant recharge in arid and semiarid basins in north-central Arizona
AU: * Blasch, K W
EM: kblasch@usgs.gov
AF: U.S. Geological Suvey, 520 N. Park Ave., Suite 221, Tucson, AZ 85719 United States
AB: Stable isotope ratios of hydrogen (²H/¹H) and oxygen (¹⁸O/¹⁶O) were compared between precipitation and ground water to estimate the season and location of recharge in the basins of the Verde River Watershed in north-central Arizona. Stable-isotope data from precipitation were collected over a 2-year period. Values of δ²H and δ¹⁸O varied by elevation at a rate of -1.6 and -0.2 per mil per 100 meters of elevation increase, respectively. Summer precipitation is distinctly different from winter precipitation on the basis of stable isotope data. Ground-water δ²H and δ¹⁸O values varied from -92 to -66 per mil and -12.4 to -7.8 per mil, respectively, reflecting differences in the elevation of recharge, climate, and hydrogeology among basins. Ground-water values suggest that recharge consists mostly of winter precipitation (96-100 percent) with minimal contributions from summer and fall precipitation (0-4 percent). Among adjacent basins within the Verde River watershed, the percentage of land area contributing the majority of recharge varied from 8 to 76 percent on the basis of local precipitation-elevation relations. Data from basins having potentially large contributing areas indicate that contributions of recharge from mountain-block and mountain-front areas were similar in magnitude to channel-recharge contributions from lower elevations. Basins with small contributing areas typically had large proportions of recharge from precipitation at upper elevations and minimal recharge through basin channels. Commonly, the small contributing areas at upper elevations coincided with higher average annual precipitation rates and higher hydraulic conductivities of geologic units compared to the rest of the basin. The zones of predominant recharge will be used to represent zones of ground-water recharge in ground-water flow models.
DE: 1804 Catchment
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005