FLOOD10395 ‎(2)‎

• County: Montezuma
• Community: Dolores
• Stream Name: Dolores River
• Title: Dolores River near Dolores, Colorado, Flood Insurance Study
• Date: 5/1/2004
• Prepared For: Dolores
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

in a rainfall-runoff computer model (HEC-l or HEC-HMS) for the upper Dolores River basin

were developed based on analysis of an actual general rainflood event. The computer model used

observed rainfall to reconstitute the flood hydro graph ("computed flood hydro graph") compared

with the observed flood hydrograph. (See References 4-e and 4-h.)

6.2 Previous model development. An HEC-l rainfall-runoff computer model was

developed for the Dolores River at Dolores as part ofthe 1976 Flood Hazard Information Study

(see References 4-c and 4-h). The September 1970 general rain and flood event was analyzed to

develop the unit hydro graph and routing paramete:rs for the HEC-1 model. A 2-day storm

isohyetal map, hourly rainfall data from nearby precipitation stations, and the observed hourly

flow hydro graph for the Dolores River' at Dolores were available for the analysis. Unit

hydro graphs for upper mainstem Dolores River and West Dolores River in the model were based

on the S-clirve method developed by the Los Angeles District Corps of Engineers ("L.A.
Method"). The HEC-l model was used to compute a Standard Project Flood on the upper
Dolores River basin. The 1 % flood hydro graph on the upper Dolores River used in the 1976
study was a ratio ofthe Standard Project Flood hydrograph. Appendix A, Table 2 contains the
parameters used for development of the 1976 HEC-l model.
6.3 Current Flood Insurance Study model. An HEC-HMS computer model was used to
develop the 1 % chance flood hydro graphs used for this Flood Insurance Study (see Reference 4-

e). The HMS model is more detailed than the earlier HEC-l model, with more subbasins; it also

computes 15-minute flood hydro graphs. The HMS model was used to compute the 1 % chance

flood hydro graphs needed to develop the 1 % chance flood plain for the study area. Again, the

September 1970 general rainflood event was used to calibrate the new HMS model, with a

different division of subbasins. For the 1976 study, the "detailed study area" was divided into

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