Determine the watershed area that drains Bell Valley, in Eastern San Diego County, with its mouth at the U.S.-Mexico border. The mouth is located approximately at 116o33'50" W. Longitude. The watershed crosses the U.S.-Mexico border from north to south, approximately 3.7 mi east of Tecate Road. Recommended procedure: Use TOPO! software (installed in only a few computers in PS231A, borrow disk from assistant) to determine watershed limits. Scan the delimited watershed (using the scanners in PS231B or E221). Take scanned image to CEE Computer Lab and import to AutoCAD. Adjust scale to measure the watershed area. Use TOPO! (installed in CEE Computer Lab) to measure the average slope along the principal stream. Measure average slope as: S1 Using USGS State equations practice (page 521 of text). Express slope in ft/mi and m/m.