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.1 , I I I I I I I I I I I I I I I I I I PROBLEM IDENTIFICATION BASIN DESCRIPTION A description of the existing physical, environmental, social, economic, geotechnical, and cultural settings for the city of Rock Rapids, Iowa, follows below. PHYSICAL SETTING The Rock River is a left-bank tributary to the Big Sioux River and is about 120 miles in length, taking into consideration the channel sinuosity. The Rock River originates in southwestern Minnesota and flows south through Kinnesota and Iowa to where it joins the Big Sioux River at the Iowa-South Dakota State border. The Rock River drains approximately 1,688 square miles including about 851 square miles upstream from Rock Rapids. The total basin is about 75 miles in overall length (north to southl and 40 miles in width (east to westl. Approximately 45 percent of the total basin is located in Iowa and 60 percent is in Minnesota. The predominant land use in the Rock River basin is agricultural. The Rock River is generally a meandering river and could also be classified as a mature river by age. Keandering rivers are not subject to rapid movement, can be fairly predictable in behavior, and may be subject to bank erosion rather than extensive channel bottom erosion. The Rock River flood plain width varies from approximately 2 times to over 20 times the channel width. The sinuosity of the Rock River is likely to be in the range of 1.3 to 1.9. The banks of the Rock River through Rock Rapids are lined with trees, shrubs. and grasses. Two tributary streams join the Rock River within the city of Rock Rapids' corporate limits. Koon Creek, a right bank tributary, flows into the Rock River near the north end of the city and has a drainage area of about 11 square miles. Tom Creek. a left bank tributary, joins the Rock S