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<br />DESCRIPTION OF TlIE STUDY AREA
<br />
<br />E l"y~~ i,,~. vary fr"""- .."" t"~n 13 ,1)00 feet ..Ion,;: ;:he dl "ide t" il, 130
<br />f""t (~"an Sea leYel elevacions) at the lower end of the study ..r"a ea"_ of
<br />the To~ of South Fork. Flowing 1" " general easterly direction, the Rio
<br />Gran<l.. i. fcd by scv".sl perennial nib";:..i,,. ""'iet! d.ain portion. of San
<br />Juan, Ilinsdale, Mineral, Saguach.e and Rio Gn"d.. Countie.. The Jugeet
<br />tdbutary, South Fork of the Rio Grande, flo..... in.. northeasterly direction
<br />~nd drains about 2l7.5 square ~ile. above the conftuence ..itlt tl,.. Rio Gund..
<br />located just co the north and east of the To"" of South Fork. The cocd
<br />drainage area,,! the Rio Gnnd" , indudingSoutll F,akRioGunde, ahove the
<br />10wet end of the study uoit i. 1,200.8 square ~ile..
<br />Cli..ate
<br />The neuest W<!4ther station is at OaI N"orte, 13..iles below tile lower
<br />study li~its on the Rio Grande. topography haa a significant effeot on the
<br />se~i-arid oli~ate and the sverage preoipitation varies fro.. 9.41 inohes at
<br />1><:1 Nurt" lo ov". 40 inches in the high,,>:, "",,,ncain ..Iev"tions wllere ..ost of
<br />the precipitation occurs oa anOw. Melling of the anovpack cauae. runoff
<br />during the "prinK .nd sustain"'! flow in the RioG.ande and ita tributariu.
<br />In Del Norte, the "un.,,1 ....lIn te..peratures range foOlll 21.4 degrees
<br />(Fahrenlleit) in J"nuary to63.5dellrees in July. The..e"nannual temperature
<br />ia 43.1 degrees.
<br />Study Limits
<br />Beginning at the confluence with tl,e Rio Grande. tile flood plain study
<br />area on the South Fork Rio Grande e><tends upstoeam along the river for a
<br />diatanoeof 3.S..iles. OnthpRioGrande, thc otudy are'l extends 4.5..ilei
<br />above and 2.9 ~ilcs below the confluencl' of the tWCI rive.... for a eombine~
<br />dut"nce nr I.~ m,le><. The u",ly ar..'I on both <Ivers eo".... a totJll di,t-
<br />;>.noeo!11.2",ile.. 'The To,"", of South Fo,k lies to the so"th "r th"Ri"
<br />
<br />;>'fe~s ~ere assistanoe lS needed bcfor~ Q full fl~od ~azard in(u.~at;on
<br />report e~n be prepared or Wh~re ~ full report is not sc~eduled.
<br />Authority for funding flood haurd .tudi~s is orovi:d~d by Seetioo 6 of
<br />Public Law 83~566, which authorises the U. S. Departrncnt of A~riculture to
<br />cooperllte with other fedeo~l, .t~te, aod looal a~encies to flI.1ke investi~a-
<br />tions and surveys of the wuersheds of rivers and oth",' w~ter ,uY' as a
<br />baaisforthedevelop",entofcoordinatedprollrsms. Incar"tyinsoutflood
<br />hazard studies, the Soil Conservation Service is beil\Jt responsiv" to Execu-
<br />ti"eOrder119SS,entitled"FloodPlainManagement",ondExecutiveOrder
<br />11990, entitled "Protection of Wetlands" (both effeceive May 24, 1911).
<br />
<br />Ursinalle Basin
<br />The South Fork Ri.o Grande is a ll\<ljor tributary to the Rio Crande in the
<br />upJ>Crheadwaters of the river basin. TheRioCrandeoriginatesinsouthnrn
<br />Colorado, flo...s throu~h New Mexico and becomes the boundary between the
<br />United States aodHexico at EI Paso, Tnxas. The study area is located
<br />within USCS Hydrolo~ic Unit Code 13010001.
<br />
<br />The upstre<lrll drainage area ori~inates in the San Juan mountains ot the
<br />top of. the Continent.~l Divide bet...cen the Rio Grnndc and San Juan River
<br />Basins.
<br />The San Juans ~r" a _ll-d"fin"d lire>> of rUllll"d ....."nt"ins rising above
<br />tbeSanLuisVatleyin the ltioGrand"llasin. Theyeonsist targcly nC vol-
<br />canicroc:ks in,,",reor lnsshorizont'lllayersoverlyingolderaediloentary
<br />focks. Soils are:ooderate!j' deep te..h3!lowwith rnekoatcrops;and
<br />pcr_abil ity and runoff cha'act'Hi~t ics are hi~hly variabt~.
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