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I I I I I I I SECTIONTWO ExISUng CondlUons 01 Stormwater Management Thl" <;cction di~cu..,...e\ the current operational condition... and financial mechani"ms and includes a general discussion of the hydrology and drainage 'ly"tem., in the Grand Valley. a.. well a... the problems and needs that have led [0 [hi... report. The problem... and need.. mclude the significant gap.. and overlaps of service... provided by the five entities. Ahcrnative method.. to address these gap" and overlaps were a primary focus of the Steering Committee. The concept of "Level of Service" (di,cus';'lxl in detail in Section -tAl for ..tormwater infra:>.truc{ure. defined as the rainfall event Ihat the system can accommodate without significant hazards or problem... i.., discus..ed in delail in Section -1.. In general. the Level of Service provided in Ihe valley wa... determined to be inadequate. There j.,;, a need to pro,'ide proteclion of property. Ihe safety of residenb. and to address federal regulation..... 2.1 HYDROLOGY AND DRAINAGE SYSTEM The Grand Valley conlain~ many basin... thai arc Iributaries 10 the Colorado River. and :!8 of the..;,e ba...in... effect the urban area..;, of Ihe valley. Although the area only gCb approximately eight inches of precipitation per year, Ilash llooding is common due to the melCorological and lopographical condilions. The basins on Ihe soulh side of the riwr experience Ihl' greate...1 flooding hecau...e they have relatively short ba..;,ins with headwater... in the Colorado ~alional ~1onllmcm with its Sleep cliffs and impef\'iolls ...lick rock. In addition. 95 percem of the storms in the Grand Valley comc from the southwest, and the slorms ,Iart at Ihe lOps of Ihe ba~ins and continue down into the valley. Then:fore, when the flows from rainfall at the headwaters reach Ihe lower ends of the basins. the storm i... over the lower end and peak 11m\"; arc ...ignificantly incre;:hed. I I I I I I I I I I Urban area... on the north side of the river ...ee less tlooding (han the ...outh ..;,ide due to Ihe distance ("If the BookCliffs and the storm pattern mentioned above: however. when they do flood. they affect a larger populalion base than south of the rJH:r. Becalhe the Grand Valley's land use was primanly agrirultural and progres,,"ed to urhan dnelopment, it relit'S on a system of agricuhural drains and nalural washes for a ~ignificalll percentage of it... stomlwater con\'eyall('e. The agricultural drains were constructed hy the Bureau of Reclamation 10 lowcr water lahles and are nO\~ owned. nlan3ged and opt"r~lIed hy (he Grand Junction Drainage D,slrict (the Dl...trictl. \\"hen the Grand Valley's land u...e changed from agricultural land 10 urhan land. the typical urhan drainage "..tem... of collection channels. conwyance pipc~ and defined outfall, w e\i...ting water hodie..;, were eilher not con~tructed at all t1r were L'\Jn~tnh.:ted in ;\ piece-meal fashilln without an o\er;\1I plan. IrrigaH0n ditches ~\cre relied upon ft1r a SIgnificant percentage llf the I I Sc'dimellt Laden Ff(JIl'from C(Jloradn XariO/llll .\f(llll/f/IOlf URS . ""';:;.'~C-S'=:l6..""'22_;:;"""'Ci_~'~..~V";;~'B_~ "<>O..'_C'~_'V'.~;....~ ".:>Q"-.~."'''''' "EP' "Ell 5 :!O:::-~~'.JUL-cJ 2-1