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

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e Table 10
" User Gage Weighting, 5-6 September 1970
"
, Most Upstream to McPhee Dam
Precipitation (inches)
Subbasin Drainage Area Depth
Name (sq mi) (inches)
West Fork Dolores 168 3.0
Dolores Headwaters 105 3.2
Dolores Upper Mid 65 2.2
Bear Creek 34 2.3
Dolores Mid 74 3.0
Dolores Lower 57 2.2
Dolores Out 1 2.2
Lost Canyon Creek 71 3.0 ,
"
Lost Canyon Creek Out 3 2.5
Dolores Lower Out 1 2.3
I
6.9 Model Validation for Flood Simulation. The validity of the upper Dolores River

basin HMS model developed for this flood insurance study was tested by using it to reproduce the

September 1970 high flow event on the watershed. The HMS model was run for the 1970 storm,

e

using the subbasins, unit hydro graphs, loss rates, baseflow, Muskingum routing parameters, 2-day

storm isohyetal map and hourly precipitation distribution discussed above. A comparison

between the output "computed hydro graph" and the observed hydro graph for the 1970 flood at

the Dolores gage is presented graphically on Plate 10. The two hydro graphs are tabulated in

Appendix A, Table 4. Since an observed hourly hydro graph for the East Fork below Rico gage

was not available for comparison, the peak flow and three-day volume were compared. Table 11

presents a comparison of computed and observed peak flows and volumes at the Rico and Dolores

gages. The September 1970 rainflood peak at Dolores was about a 4% event. The unit

hydro graph and streamflow routing parameters used for the 1970 flood calibration were not

changed for the 1 % rainflood simulation because a change in the results would be negligible. The

HMS model is assumed suitable for computing 1 % chance flood hydro graphs for this study.

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