Excerpts from the report: Each year more than a million acres of land in the United States are converted from agricultural use to urban use. These changing acres are the sites for the new houses, shopping centers, schools, industrial parks, highways, and airports needed by our growing population. These changing acres also are the source of much of the sediment that pollutes streams and rivers and fills lakes and reservoirs. Studies show that erosion on land going into use for highways, houses, or shopping centers is about 10 times greater than on land in cultivated row crops, 200 times greater than on land in pasture, and 2,000 times greater than on land in timber.