WSP04799

• File Number: 8281.960
• Description: Colorado River Studies and Investigations -- Lower Colorado Comprehensive Framework Study
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1971
• Title: Lower Colorado Region Comprehensive Framework Study -- Appendix IX - Flood Control
• Water Supply Pro - Doc Type: Report/Study

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1

SUMMARY

Major fload prablems exist in urban and in highly develaped agricul-
tural areas thraughaut the Lower Calarada Reglan. Flaods along the majar
streams cause recurrent damage af major propartians by cutting streambanks,
changing the shape and lacatian of channels, and erading farmlands; inundating
farmlands and urban areas; and damaging and destraying irrigatian, cammunica-
tian, utility, and transportation facilities.

initially, flaad plain lands in the Regian were develaped for agriculture
because they were near a saurce of water that was required for irrigatian.
However, law rainfall and infrequent flaad accurrence have encauraged the
expansian af urban growth into. the flaod plains af majar streams, which
are dry most af the time, and anta alluvial fans where stream channels
are Inadequate to. accommadate even minar flaws and where flaedflows may
take any'ene ef a number ef paths.

Estimated average annual flaed damages for the LOWer Celarada Reglen
were abeut $41 million in 1965. The papulatien and econemic projectiens
(MODIFIED OBERS) fer the Regien indicate that without any further fleed
centrel measures damages weuld increase to. $310 millien by 2020. Future
damages were determined by prejecting 1965 damages by using growth factars.
Prejections used in this appendix were based en the Department ef Cemmerce
Office of Ousiness Ecenemics and the Department of Agriculture Econemic
Research Service prajectiens, which were modified in the Regien. Detailed
informatien en the pepulatien and econamlc growth prejectiens is cantalned
in Appendix IV, Ecenemic Base and Project lens.

Fleo.d plain management is a cemprehensive term that embraces the range
ef alternatives, including fleed centrol structures, that can be employed
to. realize an apprepriate use ef flood plains. Praper floed plain management
combines appropriate use with reduced risk, giving at the same time consider-
atien to. envlrenmental, secial, and economic aspects. Flaod damage reductien
may be accempl ished by cantrell ing the flew of water or by placing contrels
en the use and develapment ef the fload plains. Altheugh it is unrealistic
to. expect'preventien ef all flaed damages, the prajects in the fleod contro.l
program sheuld prevlde a minimum standard ef pretectien. In agricultural
areas, protectien frem the 10-year fleed should be previded, and in urban
areas, pretectlen from the 100-year flood should be provided.

Implementation ef the flood control program of structural and nen-
structural measures would effect damage preventien so. that remaining damages
ef $68 mi 11ion are estimated by the year 2020. The 1966-2020floed central
program would cest about $944 millien. Incremental cests are estimated
at abeut $359 mi 11 ion, $337 mi II ien, and $248 mi 11 ien, in the time frames
ef 1966-1980, 1981-2000, and 2001-2020, respectively.

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