Red River of the North Basin
National Water-Quality Assessment Program
Strobel, M.L., and Cowdery, T.K., 1994, Effects of the 1993 Flood on
Ground-Water Levels and Quality in the Sheyenne Delta Aquifer, Southeastern
North Dakota: Thirty-Ninth Annual Midwest Ground Water Conference,
October 16-18, 1994, Bismark, ND. p1-2.
Abstract
Unusually large amounts of rainfall in the Midwest during the summer of 1993
resulted in flooding and important changes in hydrologic conditions of many
shallow aquifers adjacent to rivers. Inundation of land by flood waters
changed ground-water gradients and increased recharge to ground water.
Increased recharge, coupled with decreased evapotranspiration because of
overcast conditions and decreased ground-water withdrawals, produced
higher-than-normal ground-water levels during the summer. Recharge may have
transported contaminants to aquifers that underlie areas that received large
amounts of rainfall.
The effects of flooding and large amounts of rainfall during the summer of
1993 on the Sheyenne Delta aquifer were examined. Water levels were measured
and water-quality samples were collected at 29 randomly distributed
observation wells in the aquifer during late summer 1993. Water levels in an
additional 30 wells also were measured every three weeks from November 1993
through May 1994. Additional water-quality samples were collected from 16 of
the original 29 wells in November 1993 and in March, April, and May 1994.
Ground-water levels in the Sheyenne Delta aquifer responded quickly to
rainfall and flooding. Ground-water levels rose more in areas away from the
river where gradients are small and flow toward the river is slower than in
areas near the river where gradients are large and flow toward the river is
faster. In areas very near the river, however, ground-water levels rose in
response to increased river stage caused by flooding, which decreased or
reversed the normal ground-water gradients.
Ground-water quality of the Sheyenne Delta aquifer possibly was affected
during the flood. Ground-water analyses showed low levels of ammonia and
nitrates in the aquifer. Following the flood, water samples from three wells
had detectable concentrations of picloram, indicating transport of pesticides
to the water table. In addition, almost all samples had detectable
concentrations of arsenic and selenium, and, in some cases, the concentrations
exceeded State and Federal drinking-water standards. The source of arsenic
and selenium to the aquifer is unclear, but potential sources include natural
and anthropogenic sources.
| 
U.S. Department of the Interior |
U.S. Geological Survey
