FLOOD02442

• County: Rio Grande
• Community: South Fork
• Stream Name: South Fork Rio Grande River
• Basin: Rio Grande
• Title: Flood Hazard Study
• Date: 10/1/1980
• Prepared For: South Fork
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Floodplain Report/Masterplan

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APP<:NDIX

The Rio Crande Re"er~oir Dorn was raioed in 1979 w,~\\ modificulons to
the emergency spillway. The current emergency sp;I1.."y capacity is 10,000
cIs. The eHimated IOO-year p"ak infl"" i. 5600 do, 'hich i"'pli... ~hat the
IOO-year frequcncy flood will not o""rtop the clam. For this reosons
b<eaohin~ analysis O/S8 not made.

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INVESTIGATIO~S, ANALYSES, AND TECHNICAL DATA

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Hydrology and Hydraulics
llydrology
Peak disehaq~,,-!requency data used In this study were developed from
(requeney analyses of peak discharges for selected streamgages. U.S. Waeer
ltesourees Council Guidelines for Dete>:1llining Flood Flow Frequency, "Bulletin
17-A",wereusedasamajorrefet'ence.

Peakdi8eharlles fortl1e 10-, SO-,IOO-andSOO-y"ar flood. ore
tabulated for each croSS .ection in'!:able 1 "Flood Frequency-Elevation and

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Discharge values for the South Fork segment of study were based on th e
,~uth Fork Streamgage No. 2195 "'1th 53 years of data. Adoptions for other
~~catlona along the stream ",ere based On procedures in Colorado Water
:onservatiouBoardTechnlcalManuaINo.l.

Oi.char'teData."
Ilydraulics
The hydraulic analy.is used in this study con.isted of computin" water
surface profiles using the Soil Conservation Service WSP-2 computer progra~.
11 description of thi.progra",is avsilahle in soilConaervstioo Ser vice
TechoicalReleaseNo. 6l "WSP-2Co",puterProllr81o." Basically the prograro.
uses a standard .tepOlethod for runnioghsckwliter profiles, and includes a
bridge los. analysis described in "Hydraulics of llridge Water..ay." by thO'
ll"re"u of Public Rond..
Cros.sectiondatli,andrench leoo;th infor..ationwereobtainedfroOl
photo"ralll!l\etricOlap. prepared especially for thi. study. Ilydraulic
roughness coefficienta ("n"vlilues) were dete"oined fro.. field inspection,

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The Del Nocte (62 years) and Wason (40 yeacs) streamgages were selected
;~: de,elo~ing discharge-frequency val~es for the Rio Crandc ~~in atem scg-
"""': of at~dy. A drainage area vs peak discharge retaHonsbip was estab-
:is"c~ for tbe main atcOl1Jsi"<l these two gages. D.1t" fcoc slI".,.."l other
.::eaag"ses in the region werll used foc checking and cocrelation purposes.

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Colorado Water Conservation Board Technicai Manual No. i.
U.S. Geological Survey regional CurVe~ in Water. Supply PapH 1682.
Hood Plain Inforlll3tion Report for the Rio Crlinde - M(>nte Vista,
Colorado, by tbeCorl's of Er>zlncers, U.s. Ar",y.

and docu",entedwith pl1otograph..
follow in" are a ubuhtion of hydraulic rou.."neu coefficient. for
various locIltionaalongthestudyarea.

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:t~er cefetences used for checking purposes inciude:

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~~~nr r~~~q',,!r ~O'l.~",.,etl"n ~nn~ "bop n" th~ Rf" r:r""~,, ~"dn~ th"

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Jc:LoJ 1910-1?lS. This had an affett on flo..." to the river, therefore only
:~ period 0' record follOWinG 1915 waS used in the study.

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;';>-2

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