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Del Norte is an older town with a minimum of recent construction. C0llr11ercia1 development is concentrated along a single main street with residential areas spreading beyond. The flood plains of all the flood sources considered in this study are essentially fully developed at present with si ng1 e famil y housi ng the predomi nant type. Therefore, increased encroachment is not anticipated in the future although the character of development may change with time. The climate of the study area includes low precipitation, low humidity, abundant sunshine, a wide daily temperature range, and generally low winds. The surrounding mountains act as a barrier preventing the northern cold air or eastern storms from penetrating the Upper Rio Grande Valley. Summers are cool in the study area wi th temperatures reaching into the 90' s a few times each SUl11l1er. Temperatures for the SUlTl11er nights usually drop below 50oF. Winter temperatures, particularly in the daytime, are usually warmer than those found at similar or lower elevations. Periods of extreme cold temperatures are of short duration. The e1 evation of the Rio Grande at Del Norte averages about 7,870 feet. The headwaters of the river originate in the San Juan Mountains at the Continental Divide among mountain peaks ranging in elevation from 12,000 to 14,000 feet. The Rio Grande main stem flows eastward from the San Juan Mountains to Gerrard, Colorado where it meets the South Fork Rio Grande. The South Fork drains the southern portion of the basin from the Wol f Creek Pass area. The upper Rio Grande and South Fork basins comprise the south- western portion of the Upper Rio Grande Valley in Mineral and Rio Grande counties. The valley occupies a narrow and long trough that was formed mainly by faulting. The main topographic features of this valley are the two great parallel north-south mountain ranges that border the valley, the San Juan and La Garita Mountains in the west and the Sangre De Cri sto Range on the east. The Sangre De Cri sto Range merges wi th a low range of hill s along the southern poriton of the valley. The larger tributaries of the Rio Grande River, originate in the San Juan Mountains. Vegetation varies considerably according to elevation in the basin. Vegetation below the 8,000 feet elevation consists of semi-arid growth such as pinion pine, juniper, and sage with sparse grass ground cover. Increased precipitation supports dense pine and aspen forests above thi s e1 evation to timberl ine. Rock outcrops and tundra grasses predominate on the high mountain peaks where climatic conditions are too severe for forest growth. A number of irrigation ditches; such as the Treasure Pass, Rober-Lohr and Fachs ditches convey water across natural drainage boundaries from the Colorado River Basin. A number of reservoirs 4