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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SUMMARY

The following points summarize this study effort:

1. The construction of the Riverwood Estates Subdivision has resulted
in the placement of fill material within the FIS regulatory
floodway of the Rio Grande. This encroachment was completed prior
to the annexation of the subdivision by the City in 1983.

2. The encroachment into the floodway has been noted by FEMA to be in
confl i ct wi th the requi rements of the NFr P, whi ch requi rements
have been adopted by the City as a participant in the NFIP.

3. Maps, surveys and studies completed as a part of and following the
1976 FrS, clearly document the placement of fill and the resulting
floodway encroachment in the Riverwood Estates Subdivision area.

4. Hydraulically, the floodplain of the Rio Grande is very complex
and difficult to precisely represent using an acceptable computer
model of the river. The Corps of Engineers, through FEMA,
however, has calculated the base elevations and limits of the
100-year floodplain and floodway of the Rio Grande through
Riverwood Estates, which is documented in the 1976 FlS. Those
calculations are based upon estimates of flow splits between the
main channel and the left and right overbank areas.

5. This study developed a computer model of the FrS floodway, as of
1976 and 1986, to provide a relative comparison of the impact of
the fill encroachment at Riverwood Estates on the floodway
profile. The model did not re-estimate the base (100-year) flood
elevation but provided a comparison of the floodway profile before
and after encroachment. Thi s analytical model approach was
considered appropriate for this concern by FEMA.

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