WSPC01704

• File Number: 5000.375
• Description: Flood Protection Section - Alamosa - Rio Grande Flood
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 8/8/1985
• Author: CWCB - DODES
• Title: Report on the Findings of a State Damage Survey Team on the Rio Grande Flood of June 8-14 1985 - Rio Grande and Alamosa Counties - Colorado - CWCB - DODES - Second Preliminary Draft
• Water Supply Pro - Doc Type: Report/Study

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The levee system in Alamosa was construct~in the early
______ 1940' s (by loca 1 j,nteL es-r-~protect the city. Unfortunately,
r- it has been known for some time that floods of approximately
the 25-year or greater magnitudes will out-flank the upper end
of the levees and become entrapped in the overbank areas.

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Both Alamosa County and the City of Alamosa are
currently in the regular phase of the National Flood Insurance
Program (NFIP). ~ Comprehensive floodplain management
regulations have been adopted in both communities, Thus, it is
alarming that subdivision of the land as shown on the' most
recent town plat has been allowed.

As of March 1985, there were only 51 flood insurance
policies in force in the unincorporated area of Alamosa County,
and there were 419 policies in force in the City of Alamosa.

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Repair of 'the "levee" in this reach will only provide
protection from low magnitude floods. It should be noted that
the differences in elevation between the 10- and 50-year, the
50- and the 100-year, and the 100- and 500-year flbods of
Alamosa are, on the average, only about 1.5, 0.5, and 1.2 feet,
respectively.

There are no flood control structures (large dams) on
the Rio Grande to protect Alamos a , Monte Vista, or Del'Norte.
No space has been reserved for flood control in the irrigation
reservoirs in the upper reaches of the basin, The only
protection is that offered by major diversions for irrigation
purposes primarily in Rio Grande County. ,"'

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The volume
about 1300 feet
estimated at:

of material needed to fill the gaps totaling
in the so called levee at Site No. 1 is

1300 x 2 x 26 = 2504 cubic yards
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The volume of riprap necessary to protect the embankment
from high velocity flood waters is:

3900 x 2 x 12 = 3467 cubic yards.
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Approximately 15,000 feet of new major levees would be
necessary to prevent floods larger than the 25-year magnitude
flopd from circumventing the existing levee system.

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