FLOOD04555

• County: Dolores
• County: Montezuma
• Stream Name: Dolores River
• Basin: San Juan/Dolores
• Title: Flood Hazard Information
• Date: 9/1/1978
• Prepared For: Dolores, Montezuma
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

o determine peak flows of the 100-year '
fl d, a fiow-frequency analysis of flows
re orded at the "below Rico" and "at Dolores"
str am gaging stations on the Dolores River'
w made according to the guidelines estab-
lis ed by the u.s. Water Resources Council.
Sn wmelt floods and rainfloods at the Dolores
ga e were separated and statistically analyzed
to etermine the type of event that would cause
th larger, less frequent floods. This type of
an lysis was not made for the Rico gage because
th period of record is too short.

nit hydrographs for the Dolores River were
de eloped by the Snyder, s-curve, and optimi-

Index Point

Drainage Are~
(Sq, Mi.)
270

Dolores River above'
the mouth of the
West Dolores River

West Dolores River
at mouth

Dolores River below
the mouth of Lost
Canyon Creek

Lost Canyon Creek
at mouth

167

567

72

As ndicated, peak flow information for floods
ot r than the 100-year flood was computed for
thi study. Peak flow-frequency values for 10-,
50- and 100-year floods (together with corres-
po ding water surface elevations) at each cross
sec ion used in the hydraulic analyses made for
thi study are shown in Appendix A.

ates 1-16 show the areas that would be
dated by the 100-year flood, The 10-year
flo would be contained within stream
cha nels, and the 50-year flood would closely
foil w the pattern of the 100-year flood,
The efore these floods have not been deli-
d. Delineating the 500-year flood was
nd the scope of the study authorization, As
n on plates 2, 5, 7-9, and 14-16, some areas
are subject to sheet flow. That is, broad,

zation techniques, and were based on the flows
of the September 1970 flood at the Rico and
Dolores gages. The October 13, 1941 storm and
flood were used to optimize the unit hydro-
graph for Lost Canyon Creek. Loss rates
developed for this study were compared to and
found basically the same as those from earlier
studies made by the Los Angeles District of the
Corps of Engineers and the u.S. Bureau of
Reclamation.

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Peak flow-frequency values fOund for the
10-, 50-, 100-, and 500-year floods at selected
index points are tabulated below.

Peak Flow (Cubic Feet per Second)

10-Year 50-Year l00-Year 500-Year
Flood Flood Flood Flood

3,700 6,000 7,500 20,000

2,300

3,800

4,800

11,500

6,800

11,500

14,500

36,000

600

1,700

2,500

4,500

overland flooding generally less than 2 feet
deep on the average and characterized by
unpredictable flow paths.

Water surface elevations of the 100-year
flood along the stream reaches studied are
shown on Plates 17-31. Flood elevations shown
were computed through use of the Corps of
Engineers' step-backwater program HEC-2.
Basic cross section input was from surveyed
cross section data furnished by the Colorado
Water Conservation Board, Depth of water in
the channel and adjacent flooded areas can be
determined from the profiles, Water surface
elevations in sheet flow areas are essentially
independent of those along adjacent stream-
ways and are affected principally by obstruc-
tions and local topography in the area flqoded,

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lPefl ds of record: 1914"15, 1919~21, and 1952wpresent, Rico gage; 1896w1903, 1911-12, and 1922-present, Dolores gage.

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