Water resources of Bannock Creek basin, southeastern Idaho

The potential for development of water resources in the Bannock Creek Basin is limited by water supply. Bannock Creek Basin covers 475 square miles in southeastern Idaho. Shoshone-Bannock tribal lands on the Fort Hall Indian Reservation occupy the northern part of the basin; the remainder of the basin is privately owned.

Only a small amount of information on the hydrologic and water-quality characteristics of Bannock Creek Basin is available, and two previous estimates of water yield from the basin ranged widely from 45,000 to 132,500 acre-feet per year. The Shoshone-Bannock Tribes need an accurate determination of water yield and baseline water-quality characteristics to plan and implement a sustainable level of water use in the basin.

Geologic setting, quantities of precipitation,
evapotranspiration, surface-water runoff, recharge,
and ground-water underflow were used to determine
water yield in the basin. Water yield is the
annual amount of surface and ground water available
in excess of evapotranspiration by crops and
native vegetation. Water yield from Bannock Creek
Basin was affected by completion of irrigation
projects in 1964. Average 1965-89 water yield
from five subbasins in Bannock Creek Basin determined
from water budgets was 60,600 acre-feet per
year. Water yield from the Fort Hall Indian Reservation
part of Bannock Creek Basin was estimated
to be 37,700 acre-feet per year.

Water from wells, springs, and streams is a
calcium bicarbonate type. Concentrations of dissolved
nitrite plus nitrate as nitrogen and fluoride
were less than Maximum Contaminant Levels for
public drinking-water supplies established by the
U.S. Environmental Protection Agency. Large concentrations
of chloride and nitrogen in water from
several wells, springs, and streams likely are due to
waste from septic tanks or stock animals. Estimated
suspended-sediment load near the mouth of
Bannock Creek was 13,300 tons from December
1988 through July 1989. Suspended-sediment discharge
was greatest during periods of high streamflow.