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<br />flooding of homes and businesses, the water-supply system, railroad bridges, and sewage disposal <br /> <br />plant were damaged. Railroad bridges and tracks bet\',:een Dolores and Rico were also damaged. <br /> <br />On 11 May 1941, high snowmelt runofT Hooded thc south portion of Dolores up to <br /> <br />Riverside A venue, washed out 20 dwellings along the river. and nooded the sewage disposal <br /> <br />plant. The peak flow was recorded at 8,070 ds. <br /> <br />An unusual combination of meteorological events early in September 1970 resulted in <br /> <br />flood-producing rains over the Four Comers area of Colorado. Utah. Arizona, and New Mexico. <br /> <br />This Labor Day stonn caused 23 deaths, and is the deadliest natural disaster in Arizona's history. <br /> <br />Flooding was not as much an issue in the upper Dolores River basin. However, the stonn. a <br /> <br />remnant of Tropical Stonn Nonna, spawned a tornado 12 miles west of Cortez on 5 September. <br /> <br />Precipitation recorded on 5 and 6 September was between 2 and 3 inches in and near upper <br /> <br />Dolores River basin. <br /> <br />6. lIistorical Flood Analysis and ,\Iodel Denlopmellt <br /> <br />6.1 Hydrologic Analysis - General. The most severe ilood in the city of Dolores resulted <br /> <br />from the general rainstonn of October 1911. A general rainstoml of this type, occurring in later <br /> <br />summer or early fall, produces widespread flooding of one 10 several days duration. The nlOolT <br /> <br />volume from a general rainstoml is relatively low when compared with snowmelt flood volumes. <br /> <br />but peak flows can be higher. The 1911 stann produced the peak flO\.... of record. higher than any <br /> <br />observed snowmelt flood. for the Dolores River at Dolores streamflow gage. In general tcmlS. <br /> <br />the I % chance flood hydrograph at Dolores was computed using a similar hypothetical general <br /> <br />rainslonn and a computer rainfa1l4runofTmodcl of the upper Dolores River basin. "Jl1e basin <br /> <br />parameters (subbasin unit hydrographs, loss rates, base flow and channel routing parameters) used <br /> <br />15 <br />