FLOOD07458 - Laserfiche WebLink

Home Browse Search

shown by a reference pOint on the flooded Area Maps, Plates 3~7, and the FloodProfiJeS,PlatesS.14. Thereferencepoints,floodelevatiOl1sand discharges are tabulated in Tables 4 and 5, Flood Frequency, Elevation and Discharge Data for the Mancos River dnd Chicken Cree~, respectively. the areas north of the Grand/Montezuma intersection, between Grand and Main, and the school area west of Mesa. Near the downstream study area, the floodplain widens and the channel flow velocities generally decrease. Upon reachil1g the Spruce Street Bridge, the flow splits, with approximately Floodplain roughness factors (Manning's "n") used in thesecomp utations were selected based on field inspection of the actual floodplain conditions. The roughness factors used in this study are listed as follows: 60 percent of the flow under the bridge and 40 percent of the flow over the road in the left overbank. TABLE 3 FLOODPLAIN ROUGHNESS FACTORS MilncosRiver I , , Reach Left Overbank Channel Right Overbank I I Station 0+00 to 34+00 0.070 0.045 0.070 , Station 34+00 to 50+00 0.100 0.040 0.070 Station 50+{l0 " 65+00 0.060 0.035 0.060 Sections ,,& 35 0.060 0.040 0.060 Stations 65+00 " 90+00 0.080 0.045 0.080 Section 46 0.080 0.045 0.050 Average IOO-year flow velocities in the river channel range from 5- to g-feet per second and through the bridges, 8- to 14-feet per second. Flow depths range from approximately 3~ to 7-feet along the study reach. The Chicken Creek floodplain similar1y is confined to thechanne 1 section. Channel velocities range from 2- to g.feet per second and depths vary from 3-to8-feet. Fiowvelocities upstrearnof the U.S. 160 crossing range between 1- to 3.feet per second while velocities through the rest of the ~tudy r€d(h ronge from 4- to q-feet per ~econd. Station 0+00 to 17+00 Station 17~00 to 67+00 Station 57+00 to 79+GO 0.050 0.070 0.040 0.030 0.040 0.050 0.050 0.070 0.040 A detailed description of the hydraulic analyses completed as a part of this study is included in the Technical Addendum on file with theColorad o Water Chicken Creek Conser~<1 t ion Board. Through the Town of Mancos. the Mancos River 100-year floodplain is generally confil1edwithin the channel banks, except certain locationswh ere shallow flooding velocities of 1- to 3-feet per second occur in the channel overbanks. Overban~ flood depths range up to I ~ to 2 -feet. Sha 11 ow flood i ng occu rs in ~I7~ -18-