FLOOD10104

• County: Alamosa
• Community: Alamosa
• Stream Name: Rio Grande
• Basin: Rio Grande
• Title: Riverwood Estates Subdivision Rio Grande Floodway Evaluation
• Date: 4/3/1987
• Prepared For: Alamosa
• Prepared By: Muller Engineering Company, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

River Channel Clearing and Maintenance

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The profile is not calculated to be lowered at Section 28.4, due
solely to the modeling process, the hydraulically flat river slope and
the backwater effects of the starting water surface elevation in the
downstream section. The excavation area shown on the map and the
cross sections depict a river section width of approximately 250 to
300-feet.

An approximation of the volume of material to be excavated indicates
the volume may be on the order of 50,000. cubic yards. Authorization
for excavation would need to be obtained from the property owner. The
excavated material could not be placed within the floodway or a
designated wetlands area, without a permit from the Corps of
Engineers.

The second mitigation measure is to consider the benefit of downstream
channel c1 eari ng of vegetati on and sandbars and conti nued regul ar
maintenance by the City.

In 1985, the real ization was made that the river channel had become
heavily congested with vegetation, including trees, willows and
sandbars. The vegetation had accumulated over years of no clearing
and maintenance of the river. The congested condition of the river
was typical of the condition the COE considered in the 1976 FIS. The
mature vegetation would hold the sandbars in place during high flows,
when the bars woul d otherwi se move with the flow, gi vi ng ri se to
lesser and lesser channel conveyance.

The high water of 1985 brought this consideration to the attention of
the communi ty. The 1985 Reconnai ssance Study identified the benefit
of removing the river vegetation and lowering the flood profiles.
Using emergency monies provided by the Colorado Department of Disaster
Emergency Servi ces, the Ci ty c1 eaned vegetati on, roots and sandbars
from the river. The river was cleaned in an area between

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