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to life and p~operty. Wate~ flowing in excess of four feet per second is capable of t~ansporting sediment and causing severe erosion of streambanks and fill around bridge abutments. Where velocities drop below two feet per second, debris and silt deposits can build up, extending the flood damages and creating adverse health conditions. The saturation effects of prolonged flooding can weaken bridge abutments, levees and other embankment works so they fail as the floodwaters recede. Prope~ty damage f~om g~eat floods in developed areas Can be ove~whelming. The entire community suffe~s when streets, b~idges, sewers, and other public utilities are damaged or destroyed. Adding to the phySical haza~ds, a g~eat flood can unleash deadly epidemic diseases, Sanita~y Sewers become p~essure lines, blowing ~nhole cove~s to spew raw sewage into the floodwaters; sewage t~eatment plants and feeder lines can be washed out; stockyard waste Can add to the pollution and hazard of an epidemic disease. News~ papers sometime 'report a Hlighter side of the news" in picturing children at play in the mud and standing water left by a receding flood. Unfortunately, the contamination threat to domestic water supplies cannot be illustrated with similar aase. floodw~ters become isolated and entrapped in overbank areas resulting in depthS greater than thoee n~own on the ~iqh water prOfile". F~ Inter~tate 25 to t~e Mouth of Hospital Canyon, floodwater elevations for future floods may be expected to be greater in the overbank areas than along the ~ainstem because of the obstructive effects of bridge~, freeway aCCess ramps, and roadbed. In past floods, b.-idges "'ere washed out which increased channel conveyance and relieved overbank flooding. The areas i~ediately upstream from the mouth of Meores and Colorado Canyons are subject to severe flooding in case of floods of less magnitude tr4n the Intermediate Regional Flood. The stream channels arc insufficient to car.-y any but the snallest flow. The only major development on these flood plains is the trailer park in Moores Canyon. TheconduitsonfiehersPeakArroyOaooPinonCanyon will not convey floodwatern of Star.dard Project magnitude. Hshers Peak floodwater will leave the channel flowing through buildings and pri~arily do~~ Commercial Street. Floodwater on Pinon Canyon ",ill leave the chanr.elprior to the conduit at Colorado Avenue bccaus" of the ob~tructive effects of the willow Street bridge and insuffi~ cient channel capacity. Floodwaters of Standard Project and Inter~ mediate Region~l ~loods will leave the channel at Willow Street and imnlediately Lelow the Kansas Avenue conduit, respectively. Areal distributi~n for a given flood is non-uniforrr, and paths unprL~ictable. Depths of flow for any given stream location can be estirnated from the high water profiles shown on Plates 16 through 38. Plates 39 through 4S show selected cross sections of the streams that are typical of the approximately 145 sections surveyed in the study reaches; all cross section locations dre s'~wn on the profile plates. stream Flooded Areas and Flood Damage Trinidad Dam will effectively reduce the frequency of flooding ..long the Purgatoire .River in Trinidad from atorms occurring above the dam, but flood events may still inundate the historic flood plains. Should a severe storm occur over the study area, the trib- uta.-ies will sybject mdny areas to flooding, and the Purgatoire floodwaters will increase in intensity while proceeding downstre~~ and c:olleetinCJ frnm thp trihut:u,..". Pl..-rp?, '-'l ~n i"""1< n>'\!, fn,.- the succeeding Plates 3 through 15 which nbow the areas along the Purgatoire River and tributaries that will be flooded by the Stand- ard Project Flood, Ioterm~i~te PegionaL FLood, and the area flooded by the September 1904 flood of record. Floodwater elevations dete~ined in any particular ~rea are not always ir.dicative of the depths actually attained. Often characteristics d~tPrm'n~ f"-Qm tnP0~,.-~pnic md!,q, ~~,.-f~1 r~~nsr~rhq and valley cross sections were used to compute and define the flood situation. Velocities, Rates of Pise, and Duration The OCCurrenCe of the Intermediate Regional ~r Stand- ard Project flood would result in the flood characte.-istic$ "ho~~ in Table S. This data .-eflocts the avoraged maxi",,,,,, conditions ~.ith " "