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Water Resources Development Act of 1986. P.L. 99–662, Nov. 17, 1985, 100 Stat. 4082.

PRAIRIE POTHOLES

Donald Hey

Introduction

The geographical region referred to as the prairie potholes comprises 192 million acres (Leitch, 1989). This area traverses the provinces of Alberta, Saskatchewan, and Manitoba in Canada, and the states of Montana, North Dakota, South Dakota, Minnesota, and Iowa in the United States. Of this area, 40 percent falls in the United States and 60 percent in Canada. The region is characterized by flat to undulating glaciated topography with poorly defined natural drainage. Millions of potholes, remnant glacial depressions, are sprinkled across the landscape.

Starting in the middle of the nineteenth century, the potholes and their watersheds were altered by European settlers to facilitate farming. Engineered, agricultural drains converted the poorly defined drainage to a well-defined system. Seasonal or perennial inundation of potholes was eliminated by drain tiles and outlet ditches. From the 1870s to the 1970s, 20 million acres of wetlands were reduced to 10 million acres. The effects on wildlife and water resources were dramatic. Although early population estimates are not available, recent studies (Weller, 1982) show a direct relationship between wildlife populations and ponded areas. Given a 50 percent reduction in life populations and ponded areas. Given a 50 percent reduction in ponded areas, wildlife populations were likely cut in half. At the same time, flood storage may have been reduced by as much as 20 million to 30 million acre-feet. This loss, no doubt, contributed to increased flooding along regional streams and rivers. Also, without the long detention times provided by the storage, sediments and nutrients were flushed from and through these former wetlands to foul receiving waters (Gilliam, 1986). However, no quantitative measure of these effects has been made.



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