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

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approximately the corporate limit line near river station 270+00 and
the State Street bridge. Also, the river was cleaned near Cole Park
and upstream and downstream of the rail road bri dge. The Ci ty is
committed to maintaining the channel in a vegetation free cOndition.

The HEC-2 model was rerun to measure the change from the regul atory
condition of 1976 and the encroached condition of 1986, usin9 the
favorable downstream hydraulic condition. The starting water surface
elevation of 7544.4 at Section 28.0 and channel roughness values of
0.03 were used.

Since this maintenance has been completed in 1985 and 1986 and a
commi tment is made to conti nue thi s effort, the downstream f1 oodway
profile is lower than that calculated in the FIS. The 1985
Reconnaissance Study calculated a water surface elevation at Section
28.0 of 7544.4, for the 10,900 cfs flow rate, using a roughness value
of 0.03, characteristic of the vegetation free river section. This
elevation is 0.4-feet lower than the FIS floodway elevation for that
section.

Figure 4 shows the calculated floodway profile (G) for this condition.
The profile is lower than the base condition profile (C), except at
Section 29.5 where the profiles are concurrent. Table 3 lists the
comparative elevations for. each section. Clearing and maintaining the
channel in a comparative clear condition, as the City has done, shows
a lower floodway profile of 0.0- to 0.4-feet to be characteristic of
the study reach.

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