FLOOD05850

• County: Montezuma
• Stream Name: Dolores River
• Basin: San Juan/Dolores
• Title: Field Report - The Dolores River
• Date: 11/1/2001
• Prepared By: CWCB, DNR
• Floodplain - Doc Type: Floodplain Report/Masterplan

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in the field. These control markers will allow interested parties to recheck the mapping
accuracy.

2. Hydrologic Analysis: The Corps of Engineers performed the original hydrologic
investigation for the 1978 floodplain study. The Dolores River has reliable stream flow
records, which date back to 1896, The Corps performed a statistical analysis of the
annual peak flow data for the computation of the 100- year peak discharge values for the
floodplain study. The statistical analysis was performed in accordance with standard
guidelines found in Bulletin 17B. A review of the available annual peak records for the
USGS stream station no. 09166500 (see appendix) was conducted. The flow records
indicate that from 1977 to the present time, no large flood events or rare discharges
occurred on the river. Therefore, it is not expected that the published 100-year peak flow
values for the Dolores River wOllld increase if a re-analysis is performed using the
additional 24 years of flow data fr()m the gaging station. The 10- and 100-year discharge
flood values are:

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Peak Di:schar es For Dolores River
.,... ;.....,? ',..... ,,'M"yeatfIo\V
'Giahlpii::Nhilibe~ ,/ cis
3 6,200
2 6,100
1 6,000

" ..., ~O():~1;f\QQ\V ..., ."'.'.
12,800
12,400
12,300

3. Hydraulic Aualysis: The Corps of Engineers performed the hydraulic analysis using
the standard step-backwater HEC-2 program. The HEC-2 program used in the 1977 study
is still acceptable in 2001. The C\VCB does acknowledge that there have been a number
of updates to the HEC-2prograrn over the years, however the basic methodologies,
routines, and assumptions developed for the HEC-2 program as used in 1977 are still
valid. Tl1e CWCB would not expect a significant change in the water surface elevations
for the floodplain study using the 2001 version of HEC-2 (now HEC-RAS). The flood
flow depths in the channel and floodplain areas can be determined from the peak flows
and stage table in the Corps report (see examples in the flood elevation table below) or
from the profiles in the Corps or FliMA Reports.

Flood Elevations For Dolores River
"'.". .;(;r~~#II'~t10~~~at,~sel,
· Number ," feet;triSl
3 7164.4
2 7213.7
1 7274.9

4. 100-year Floodplain DelineatiCln: The 100- year floodplain delineation was presented
on the detailed, large scale topography mapping that was prepared for the 1978 Corps'
study. Using the ground elevations and contour lines on the mapping ltlong with the
hydraulic determinations and flood profiles computed from the engineering analyses, the

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