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<br />"
<br />
<br />"
<br />
<br />full during floods. Deftnitionoft.hesubcatchment.s455urnedaUrunotttrom
<br />tributary areas reached the main channel and ~a5 not diverted by ditches or
<br />tal10lo'''',
<br />
<br />"'able 1.
<br />
<br />~lnfall Distribution.
<br />
<br />Rainf..UDaU
<br />Rainfall depths tor the one-hour, 5-, 10-, 25-, 50-, and 100-year
<br />recurrence interval storms were obtained from the Precipitation Prequency
<br />~tlaB of the Western United States, ~tlaB 2, volume Ill, Colorado
<br />(reference 7). The SOO-year raInfall depth "'Sa estImated by extrapolation of
<br />the one-hour depths of the other recurrence intervals an ~extreme vslue~
<br />paper. ThedistributionofthepointrainfaUdoopthi""howninTabl"" The
<br />rainfall depthe used for each storm event are given in Table 2. ~infall
<br />intensities are given in Table 3.
<br />
<br /> EndotPeriod Percent of ene-Hour
<br /> (min\1tesl Rainfall Depth
<br />I , ,
<br />" ,
<br />,
<br />i " ,
<br />I
<br />i " ,
<br />, " ,
<br />i " "
<br />I " "
<br />" "
<br /> " ,
<br /> " ,
<br /> " .
<br /> '" ,
<br />
<br />Or~dnage IllIsin Parameters
<br />The parameters required to <letermine mnoff peaks and 'lOlWllM from SWMM
<br />are snbcatchment are.., width, percent impervious, infiltration rate,
<br />depression and detention storage, overland roughness ooefficient, channel
<br />geometry, cbannel alope, channel roughness coefficient, and storage-dischsrge
<br />Curve. for ponded areas. Thepercentsgeofimperviousares"ithinthestudy
<br />are.. "a. b1lsed on land use as definedbyth" land\lS""""p (figure3l. 'me
<br />hydroloyic "Jl..ly~ia fur this report ..~sumed futur" basi" condit lone only,
<br />because the future land use "ill be about the same as existing. It should be
<br />cmphasized that ainoc hydrologic analysi.. ..ssurned no significant future deve-
<br />lOP"'ent in the draina9<'ba"in above M.illiken, re"",,,,,,,endedde"igndiecharges
<br />for drain..ge improve",ents in to"" do not account for the increased ",noff that
<br />auchdevelopm..ntwouldproduce. 'meTownofMillikenshouldbeconsta"tly
<br />a"ar" of activity in the dralnaga basin so th..t the town can worl: with the
<br />
<br />T~bl.. ~.
<br />
<br />O,,~_>l""r ""I~f...ll n.-l,th~..
<br />
<br />Return Period
<br />(yearlll
<br />
<br />Rainfall Oepth
<br />(inchesl
<br />
<br />developer to 1"."'1""" ~~ 1~<:r""A" in p"'IIk "1"ch..r'J" "'1" otn,.,,'J'" "''''l"ir..",..nts
<br />
<br />,
<br />"
<br />"
<br />"
<br />'"
<br />",
<br />
<br />1.33
<br />
<br />1.60
<br />
<br />..bove the capacity of drainage structures built in Milliken i" accordance vith
<br />th.. resultll of analysi" pre"ented herein.
<br />I"tiltration rate.. for pervious areas were based on Boll types obtained
<br />frOM the "Weld County Soil SUrvey" (reference 8). Channel unit lenqths,
<br />elopes, and geom..triea were defined fro", field BUrveys and fr~ U.S.
<br />GeclogicaISurveyl:24,OOascaletopographicllldps. Manning'sroughn""aooet_
<br />ficienta were base" on tield lnvestigation and are summarized by reach in the
<br />
<br />1.95
<br />
<br />2.30
<br />2.56
<br />3.40
<br />
<br />.
<br />
<br />No aerial adjusem..nt.
<br />
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