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e e e flooding of homes and businesses, the water-supply system, railroad bridges, and sewage disposal plant were damaged. Railroad bridges and tracks between Dolores and Rico were also damaged. On 11 May 1941, high snowmelt runoff flooded the south portion of Dolores up to Riverside Avenue, washed out 20 dwellings along the river, and flooded the sewage disposal plant. The peak flow was recorded at 8,070 cfs. An unusual combination of meteorological events early in September 1970 resulted in flood-producing rains over the Four Corners area of Colorado, Utah, Arizona, and New Mexico. This Labor Day storm caused 23 deaths, and is the deadliest natural disaster in Arizona's history. Flooding was not as much an issue in the upper Dolores River basin. However, the storm, a remnant of Tropical Storm Norma, spawned a tornado 12 miles west of Cortez on 5 September. Precipitation recorded on 5 and 6 September was between 2 and 3 inches in and near upper Dolores River basin. 6. Historical Flood Analysis and Model Development 6.1 Hydrologic Analysis - General. The most severe flood in the city of Dolores resulted from the general rainstorm of October 1911. A general rainstorm of this type, occurring in later summer or early fall, produces widespread flooding of one to several days duration. The runoff volume from a general rainstorm is relatively low when compared with snowmelt flood volumes, but peak flows can be higher. The 1911 storm produced the peak flow of record, higher than any observed snowmelt flood, for the Dolores River at Dolores streamflow gage. In general terms, the 1 % chance flood hydro graph at Dolores was computed using a similar hypothetical general rainstorm and a computer rainfall-runoff model of the upper Dolores River basin. The basin parameters (subbasin unit hydrographs, loss rates, base flow and channel routing parameters) used 15