|Benoit, George - RETIRED ARS EMPLOYEE|
Submitted to: Proceedings of Conference on Water Resources in Extreme Environments
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2000
Publication Date: N/A
Interpretive Summary: Groundwater recharge is vital to ensuring adequate water supplies in the northern plains. Recharge occurs during snowmelt in the spring, but little is known about the magnitude of recharge in spring as compared with other seasons of the year and the soil conditions under which recharge occurs in spring. We found that recharge is greatest at the time of snowmelt in the spring than at any other time of year. In addition, spring recharge occurs while the soil profile is frozen (as much as 1 m deep), apparently as a result of water flow through large, thawed cracks or pores in the soil profile. The importance of these cracks and pores in replenishing groundwater during snowmelt warrants further investigation by hydrologists into the size and occurrence of these thawed pores in the soil profile. This information will aid water resource managers in assessing water supplies as well as river forecast centers in predicting the potential for flooding in the spring.
Technical Abstract: Snowmelt is an important source for replenishing groundwater in cold regions. In the Prairie Pothole Region of North America, snowmelt collects in landscape depressions (forming temporary ponds) as a result of frozen soil impeding infiltration. These ponds drain and replenish groundwater during spring thaw. Little is known, however, about the dynamic changes in groundwater and the associated physical state of the soil that influences infiltration during snowmelt and spring thaw. The water table in a 2-ha landscape depression (prairie pothole) in west central Minnesota was monitored over three years. In addition, soil water content, snow cover, and soil frost depth were measured at 11equidistant locations that traversed the major and minor axis of the pothole. Temporal changes in the water table were more apparent in the spring than at any other time of the year. In the spring, recharge occurred while the soil was frozen across the elandscape depression. At locations in the bottom of the depression, an increase in water content throughout the soil profile occurred simultaneously with a rise in the water table. The rise in the water table appeared to expedite thawing from the bottom of the soil profile, but only at locations near the bottom of the depression. Recharge of groundwater within a prairie pothole during snowmelt is a seemingly localized process where surface water drains through thawed cracks or macropores located near the bottom of landscape depressions. The importance of these cracks and macropores in groundwater hydrology warrants further investigation into their abundance and formation.