FLOOD06561

• County: Montrose
• Basin: San Juan/Dolores
• Title: Hydrology Addendum Montrose County
• Date: 11/1/2000
• Prepared For: Montrose County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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ENGINEERING METHODS

Hvdrolol!ic Analvsis
The Montrose County PIS presents detailed and approximate floodplain delineations. Hydrologic
information used for the FEMA approximate floodplain delineations are not available or were
not documented by FEMA. The CWCB has developed acceptable hydrologic information for
undeveloped basins using regional regression methodologies for computing loo-year flood-flow
values.

The CWCB methodology is fully described in a publication by the CWCB entitled "Guidelines
for Determining IOO-year Flood Flows for Approximate Floodplains in Colorado". The Dolores
River Subregion (DLR-l) was used for streams in the Dolores River basin, while the Lower
Gunnison River Subregion (COL-3) was used for streams in the Gunnison River basin. The
CWCB equations are shown in Table 1.

Tabe . Re~iona el!reSSlOn ';quatIons or Montrose ountv
Sub-Region Discharge Equation Drainage Basin
10 Subregion Name (cfs) Limitations (sq.ml.)
DLR.l Dolores River Subregion 0'00 = 213.B(A)o.601 2 to 1,090
COL-3 Colorado River, Lower Gunnison River 0'00 = 1 BO.B(A)o.s7. 2 to B,Ooo
Subreoion

I 1

lR

E

~

c

For the equations shown in Table 1, the QlOO is the loo-year peak flow in cubic feet per second,
and A is the upstream (contributing) drainage area in square miles. The regression equations are
only valid for the range of drainage areas indicated.

The IOO-year discharge for approximate floodplains in Montrose County were estimated by
utilizing the regional regression equations shown above. The estimated loo-year peak
discharges are shown in Table 2.

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