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<br />general STorm condiTions withouT specific refere~e to lett-~ana <br />Creek. An Improved storm warning service should be avalla~le in <br />about two years since Boulder County is In the effective range of the <br />planned weather radar at Limon, Colorado. Even fhough this will pro- <br />vIdea better method of locatlngindlv1dual stormcells,ground <br />observers are needod fa indicate the progress and magnitude of flooding. <br />Consideration should be given to a local flash flood network wh1ch <br />can be effective wIth proper procedures and responsibilities. NormalLy, <br />thobasicforecastprocedure1sostabllshedbytheWeatherBurea\I as <br />part of their radar program. Local officials can then use these <br />techniques with supplemental information frorntheWeather Buroauas <br />the basis for local warnings. <br /> <br />GENERAL CONDITIONS <br /> <br />This section presents the general basin description and <br />a more detailed aescriptionof the stuovreach. <br /> <br />Stream and Valley CharecTeristics <br />Left-Hand Creek, a right bank tributary to St. Vrain <br />Crellk, li..s in north-central Colorado. The basin extends about <br />30 miles eash-ard from Its headwaters in the Roose~alt National <br />Forest to its junction with St. Vraln Creek at Longmont. Most of <br />thebasin,57,5squaramilas, lies In the RockyMQ.untalns and varies <br />in elevation from 11,000 to 5,600 feet. The remainder of the basin <br />Ilesinthehlghplainsandcontalnsanaddltlonal14.5squaremiles <br />between the mountains and the mouth. This lower basIn, with II stream <br />lengthofaboutl4mlles, Is the reach studied 1nthls report and the <br />remaining discussion refars only to this part. The Laft-Hand Creek <br />fiood plain ~arles from 500 to 1,000 feet ...tde except for the lower <br />two miles where 1t w1dens and merges with the St. Vraln flood plain. <br />Th"channcl bad slopes range from IS foot pcrmilaat the mouth to <br />120 foot per mila at the upper end of the study n.ach. The lowar <br />three miles of thastroamhavo been straightened and confined toa <br />"LJ" shaped channili, with farming axtandlng to the bank line. The <br /> <br />~ext ~i!e of ch~~nel shows evi~ence of sTra;g~tenlng ~UT is ~ore <br /> <br />typ ica Ily character; led by the unimproved channei. The un;mpro~ed <br />reaches ha~e a low flow channel approximately 15 feet wide, with the <br />r~ainder of the active channel sioping up to merge with the flood <br />plain, of tan with an Indistinct bank line. The following pictures <br />typify the channel throughout the study reach. <br /> <br />, <br /> <br />, <br />