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<br />II. STULly,\REA
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<br />A. I.flCaliOll
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<br />The study area is apprQximately 17.3 sq mi, and is located within tha Town of Erie. Colorado. and Boulder
<br />andWcldCountie:;.Colorado,occupyingEY, Sections 3, 10, 15,22, 27, and 34, Sections 1,2, 11 through
<br />14,23 through 26, 35, and 36, TIN, R69W, and portion~ ofthewestcm part of Sections 7, 18, 19,30, and
<br />J I, TIN, R68\V, This study is principally concerned with rapidly developing properties within the
<br />jurisdiction or plannill,!:; area of the Town of erie. However, portions of the study area fall within the
<br />jurisdictions of Boulder County, Weld County, and the Cily of Lafayette. The study area is located within
<br />the South Platte River Basin. It is bounded by Colorado Highway 52 to the north, Coal Creek or
<br />Weld/Boulder County boundary tothe east, Baseline Road to the south (Highway 7), and U,S Highway 287
<br />to the west. Please refer to Loeation Map, Figure i,
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<br />B, Catchments
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<br />Portion~ of three important watersheds are located within the study area- Boulder Creek, Coal Creek, and
<br />Bullhead Gulch/prince Tributary (See Location [l,.lap, Figure I), Boulder Creek flows northeastwardly
<br />tllrough the study area and eventually join~ SI Vrain Creek downstream of tile study area, Coal Creek fluws
<br />northwardly along the eastern boundary of tile study area and joins Boulder Creek within the study area in
<br />Secti00 1, T1'1, R69W Bullllead Gulchiprince Tributary drains northwardly through the study area and
<br />joins Bouider Creek within tile study area in Section 10, Tl:-<, R60W
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<br />The B\lulder Count~' FIS (FEMA. 1995) repom the Boulder Creek drainage basin to he appro:<>imately 440
<br />square miles in area at ils cDntluence "ith Coal Creek and the Coal Creek basin to be approximately 79
<br />square miles io area at its confluence with Boulder Creek Bullhead GulchiPrince Tributary is
<br />approxImately 9,1 square miles in area at its Cl>ntluence witll Boulder Creek (Advanced Science" lnc,
<br />1992) Within th~ study area, appro;.:imalely 5,7 squarc miles is directly tributary to Boulder Creek.
<br />approximately S,Q square mile:; is dircctly tributary to Coal Creek, and appru",imately 3 6 square miles is
<br />located within Bullhead Gulcll/prince Tributary In addition to the on-site catchments, approximately 4.4
<br />>quarc miles of Bullhead GulchiPrince Tributary, twO off-site catchments tributary to eml Creek, and ooe
<br />otl:slle catchment tributar)' to Boulder Cr<'ek, were analyz<:d Oll-sitc catchments arc delmeated at! Figurcs
<br />2a, 2b,and 2c and otf-:;itc catchments are delineated on. Figure 3,
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<br />C. Flood Hislor)'
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<br />['he FlS for BOLtlder County (FE\IA, 19\)5) infers periodic i100ding ha, D<A:ul'led alOllg Boulder Creek and
<br />Coal Creek within thc study area There is t!o record of damage occllrring in tile study arca published in the
<br />F1S f]{lm these l1000 e'elllS. probabiydue :oth.c low populationden:;it'r' :11 the study area at the time l>fthe
<br />flo,,<.1 events Significant !lood evcnts alDng Boulder Creek have been reported in the City of Boulder
<br />occurring in 18<J4.1914.and 1938. The IS04 f100d is considered to ha,e approximatcdthe lOO-ycartlood
<br />f()fBnulder Crl'ck Floodevems aiong Coal Crni have r.een reported in 1876.18<)1. Junc _1,1921. \la\' 26.
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<br />1935, June 9, 1949, May 9,1957, and \lay 1969 The 1876 t10Dd peak discharge was estimated to be
<br />13,200 cf, near Erie and is believed to appro",imate the 100-year flood peak.
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<br />Significant floods have occurred along Bullhead Gulcll (Advanced Sciences, Inc, 199~) thrce times over tile
<br />pa:;t 70 years One storm in the mid-1940's produced flood depth~ estimated at thr'* feet near the
<br />inteN~<::tion oflsabdle Road and LS Highway 287, Bullhead Gulch reportedly had eroded to a depth of 15-
<br />to 20- feel between lsabclle Road and lhe Leyner-Cottonwood Ditch prior to the construction of the Leyner-
<br />COl!onwoodDitcll
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<br />Recently, Erie oilidals have observed periodic flooding at the Pre-School and High School near Old Town
<br />Erie just downstream of the Union Pacific Railroad (UPRR) tracks_ One photograph of flooding which
<br />occurred on April 30, 1999 and taken by Wendi Palmer of the Town of Erie is shown on page ES-l of the
<br />Executive Summary,
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<br />D. LandCharacteridics
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<br />Topographywithinthc study area is characterized by generally flat terrain aiong floodplains and moderate
<br />slopes adjaeent to floodplains, The sllldyarea currently includes significant amoumsofagricuhural1 ands,
<br />and many of the historic channcls in the study area Ilave been smoothed 0 raitereJoyagricultunllpractiees
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<br />Irrigation ditches have influenced historic surface drainage patterns and small reservoirs. development,
<br />railroad embankments, and gravel mining Few roadside ditches, culverts, or bridges operating
<br />independently of Irrigation dilch structures are lo;;ated in the smdy area Developmems have only ~lighlly
<br />influenccd drainage patterns Flow patterns have been allered by the Burlington Northern Railroad's
<br />(B'JRR) abandoned line which traverses the soutlleasl :;ection of the sludy area and the UPRR line which
<br />bisect~ the nonhero part of the sllldy area Gravcl1l1ining operatiDn" located primarily within the 100_year
<br />t100dplain of Boulder Creek, influence drainage patterns along BDulder Creek, The pOlential for stream
<br />capture by Ihese DpCJ1 pit areas along Boulder Creek wa, not evaluated, Abandoncd underground coal
<br />minesloemedthroughoutlhestudyareahaveapparentl)'notimpacted ,urface drainage patterns at thi:; !ime
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<br />Vegetation in the study arca consists of dry land and irrigated ClOpS in agricultural area" deciduou:;trces,
<br />evergreens, shrubs_and native gras>es along lloodplain:; and undi sturbed areas, and landscaping in
<br />residential areas Wetlands, which were delined conceptually by Boulder County and sh<)wn on Figure 4,
<br />are found through.outthe:;!lIdyarea,
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<br />Soils within the ,tudy area are primarily Hydrologic Soils Group B interspersed witll Hydrologic Soil,
<br />Group C and D. as shown on Figures Sa and Sb. Soil~ within and adjacent to tile study arca were obtained
<br />using soil maps developcd by the :\ational Rc,o\lrces C(ln~C'rvation Service (SCS, 1'175 and 1982)
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<br />Surfan> waTer 'l"ality in the study area ma~' bf cnhanced bv wctland:; which ha\'e b~come cstablished in
<br />:;ome of the new dNention facilities within the study area, induding Arapahoe Ridge Filinl! No I, Arapaho~
<br />Ridge Filing No 2, aml Orchard Glen No I lhe,e detention facilities were nOI miglllall, desigll"u to
<br />cnhance water qualitv, howewr the\' curremly '<)tVe that function
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