FLOOD07275 - Laserfiche WebLink

Home Browse Search

TABLE 8, Depths of Flooding Stredm Rio Grande Trinchera Creek Basin Trinchera Creek Sang.e de Cristo Creek Unnamed. tributary to Trlnchera Cr~ek BelOW Smlth Reservoir and Northern Rranch to that Trihutary All other tributary streams Culp-brd Creek Basin Culebra Creek Rito Seeo (East Basin) Rito Seco (East Basin) Rito Seco (North Basin) Rito Seco (North Basin) All other tributdry streams Costilla Creek Basin Costilla Creek Reach Description ~nt ire reach From confluence with Rio Grande to levees near that confluence Upstream of levees From Smith Reservoir to Brown Lane From B.own Lane to Highway 159 From Hlghway 159 to confluence with Wagon Creek From confluence with Wagon Creek to confluence with Placer Creek Upstream of confluence with Placer Creek Upstream of Confluence with Trinchera Creek All reaches From confluence with Rio G~ande to ~astdale Vitch Upstream of ~astdale DitCh Within San Luis detailed ~tudy drea All other reaches Within San Luis detailed study area All other reaches All reaches ~rom New Mexico State Line to road and ditch at ~astdal~ Upstream of road ;lnd dltch at Eii ~t".ii le -33- Depth See CSU Maps , 1/2 f~et , feet , feet , 1/2 teet 10 feet ., 1;2 feet , feet 2 1;2 feet 5 feet 2112 feet ., foet See San Luis Study S feet See Sant.ui.s Study 5 feet 5 feet 7. 1/7. f<>et 5 f.....t 5.0 INTERPRETATION AND USE OF REPORT The floodplain information contained in this report consists primarily of flood discharges and floodplain delineation maps. Both kinds Of intormation are useful for evaluating flOOd risks and for performing en'lineering analyses. They are also useful for guiding actions to reduce flood damages. This chapter discusses the use Of the floodplain intormation for each of those purposes. S.l Flood Disoharqes The lOO~year flood event was used as the flood frequency for this floodplain analysis. The lOO-year frequency has been selected by the State of Colorado and the Federal Emergency Management Agency as the frequency to be USed for floodplain delineation and re'lulation. A~ a result, the flood dischar'les listed in Table 7 should be used to regulate proposed development in the delineated flOOdplain. For points other than those listed in Table 7. the discharge-drainage area relationship shown on Figure 5 should be used to compute a discharge. There is one exception. From the gage that is furthest downstream on each of the three major tributaries downstream to the confluence of that tributary with the Rio Grande. the flow at that C}age should be used. The above flows should also be used to develop revised floodplain delineations for any portion of the study area , whether to illustrate the effects of proposed floodplain development or to take advantage Of topographic or hydraulic information that is more current or refined than the intormation that was used tor this study. Chan'les to rhe discharges in this report must be approved by the Colorado Water Conservation Board and the Costilla County Board of Commissioners. The same requirements apply to proposed discharges for stream reaches not included in this study. 5.2 Flooded Area Maps I I , , The Flooded Area Maps in this report (Plates 2_22) show the approximate boundary Of the IOO-year floodplain for the stream reaches studied. Upon official approval of this report by the COlorado Water Conservation Board the areas outlined by the lOO_year flood boundary will be desi~ndted as floodplains and may be regulated accordingly by Costilla County. Upon the adoption of flOOdplain regulations by the county, all develcpmcnt ~~thin the ~elineated lOC.yea~ floodplains ~ill require a flOOdplain d...velopment permit. Any engineering for ~uch p~rmits ~ill need to ~8 based ou tbe flood discbarqes contained in. or deriv",d from. this report. as described above. -34-