FLOOD06258

• Designation Number: 25
• County: Mesa
• Community: Grand Junction
• Basin: Colorado Mainstem
• Title: Floodplain Information Report - Colorado and Gunnison River, Grand Junction, Colorado
• Date: 3/1/1973
• Designation Date: 10/1/1973
• Floodplain - Doc Type: Floodplain Report/Masterplan

IrrrERMEDIATE REGIONAL FLOOD

The Intermediate Regional Flood is one that could occur about once

in 100 years on the average, although it may occur in any year. This

flood was determined by the use of flow-frequency curves derived

from streamflow records. Consideration was given to characteristic

climatic conditions as they relate to snowmelt, and to runoff

characteristics of the basin, taking Into account transmountaln and

Irrigation diversions, and the effect of Incidental storage provided

by upstream conservation reservoirs. Flows on the Gunnison River

were further modified to reflect flood control operations of Paonia

and Blue r4esa Reservoirs. Modification of floodflows on the Gunnison

River substantially reduces peak flows In the Colorado River down-

stream from the mouth of the Gunnison River.

The peak flows derived for the Intermediate Regional Flood on
the Colorado River above and below the mouth of the Gunnison River
and on the Gunnison River below Redlands Dam are shown In Table'2.
Stage hydrographs of flows In the Colorado and Gunnison Rivers, typical
of those to be expected for an Intermediate Regional Flood in the
study area are shown on Plate 3.

STANDARD PROJECT FLOOD

Standard Project Flood runoff Is that generated by the most severe

combination of meteorological conditions reasonably characteristic of

the hydrologic region, excluding extremely rare combinations. Peak

flows for the Standard Project Flood on the Colorado and Gunnison Rivers

were developed Tn the same manner as described for the Intermediate

Regional Flood. Peak flows for selected locations on the two rivers

are shown In Table 2.

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