Availability of ground water for irrigation from glacial outwash in the Perham area, Otter Tail County, Minnesota

The Perham study area includes about 350 square miles of surficial deposits of glacial outwash in the central part of Otter Tail County in westcentral Minnesota. The aquifer characteristics have a wide range, as follows: Transmissivity values range from nearly 0 along the perimeter of the area to more than 100,000 gallons per day per foot in the central parts of the area; storage coefficient values range from 0.1 to 0.2; and the saturated thickness of the upper outwash material ranges from nearly 0 to more than 100 feet. Most of the aquifer material is fairly well scrted and is in the particle-size range of fine to coarse sand. Wells penetrating the full thickness of the aquifer and developed to 100percent efficiency can be expected to yield 1,200 gallons per minute for 30 days and to have drawdowns of less than two-thirds the aquifer thickness in much of the area; however, well yields vary widely within short distances. Yields of 300 gallons per minute or less can be expected from wells drilled near the edges of the area and in the general area east and southeast of Otter Tail Lake. Results from the mathematical analyses show that the amount of streamflow leaving the area will not be depleted within the 10-year analysis period, if not more than 6 inches of water per year is used on all the irrigable land in the outwash area. If pumpage and its effects on the streams is assumed to be prorated proportionately along the full length of the streams within the area, then the levels of lakes along these streams generally will not be lowered appreciably. However, owing to the heterogeneity of the aquifer and the other variable factors involved, some reaches of the streams may cease to flow when full ground-water development is approached, which, in turn, would result in a decline in some lake levels. Lakes and ponds not connected to streams in the area are expected to be lowered considerably or to be dried up completely as pumping becomes more extensive in years to come. If irrigation wells and other large-yield wells in the study area are spaced 1 mile or more away from streams and lakes, the effect of ground-water pumping on the streams will be small, and the lake levels will be affected very little. However, the lakes and ponds are expected to approach normal levels during periods of above-normal precipitation and during periods of no pumping. 1 2 GROUND WATER FOR IRRIGATION, PERHAM AREA, FINN. INTRODUCTION The present study of ground water in the Perham area was made by the U.S. Geological Survey in cooperation with the WestCentral Minnesota Resource Conservation and Development Committee and the Division of Waters, Soils, and Minerals of the Minnesota Department of Conservation. PURPOSE OF INVESTIGATION This investigation was one of several studies made primarily to obtain information on the water resources of sandy soil areas in Minnesota, where irrigation might be feasible by using ground water from surficial aquifers to supplement precipitation. Crop yields in unirrigated areas are generally poor because tl x e normal rainfall is insufficient to supply crops during the main part of the growing season and because the sandy soils have a low waterholding capacity. The purpose of the study was to investigate the adequacy of both the quantity and the quality of ground water in the upper sand-and-gravel aquifer for irrigation, to determine the areal extent and thickness of these deposits; to determine the potential yield that can be anticipated from ground-water development for irrigation on a long-range basis; to predict the effects of this development on the local water system; and to provide guidelines to local planners and irrigators in the development of the water resources in the area. LOCATION AND EXTENT OF AREA The study area includes about 350 square miles in the central part of Otter Tail County in west-central Minnesota (fig. 1). The boundary of the study area is based primarily on the type of soil and on the extent of the surficial deposits of glacial outwash sand. The major towns in the area are shown in figure 1. About 90 lakes, each having a surface area of 10 acres or mere (Minnesota Division of Waters, Soils, and Minerals, 1969, p. 306-327), lie within the study area and cover about 24 percent (84 square miles) of the area. The largest lakes, in square miles, are Otter Tail, 21.7; West Battle, 8.9; Rush, 8.3; and Big Pine, 7.5. Also, swamps cover an additional 10 to 15 percent of the study area. Most of the study area is in the Otter Tail River watershed, but a small part southeast of Otter Tail Lake is in the Crow Wing River watershed (fig. 1), as outlined in the Hydrologic Atlas of Minnesota (Minnesota Division of Waters, 1959, Units VIII and XVI).