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a relatively narrow (200 feet or less) river channel, the most severe channel restriction being the Commercial Street Bridge, a massive double arch concrete structure crossing the narrowest section of the river channel. Five other bridges cross th~ river in the business area, creating lesser degrees of constriction. Floodwater leaving the channel at the Commercial Street Bridge enters primarily into the l~ft overbank flood plain, following the Atchison, Topeka, and Santa Fe Railway tracks eastward, to the city limits. Depths of flooding are generally shallow, and the areal distribution is non-uniform with unpredictable flow paths. . Tributary streams within th~ city limits are generally narrow and deep in their upper reaches. Overbank flood- ing occurs along Prospect Canyon and the lower reaches of Portland Avenue Canyon. The pinon Canyon channel capacity between Nevada Avenue and Arizona Avenue is insufficient to convey floods of 100-year magnitude or greater; floodwater flows in an easterly and southerly direction through the business district to the Purgatoire River. A closed' conduit on Fishers Peak Arroyo that runs under the business district is inade- quate for floods in excess of the 100-year discharge, and is also subject to clogging problems. Flood flows leave the channel below Second Street, flow through buildings built over the channel, and then continue down Commercial Street at a shallow depth and through unpredictable flow paths. . 2.4 Flood Protection Measures Following the destructive S~ptember 1904 flood, the city and concerned railroad comp~nies cooperated in a project involving channel straightening and construction of concrete retaining walls along the Purgatoire River through the city's more congested urban area. In 1936 and 1938, the Works Progres~ Administration did addi- tional bank protection work!, including repairs to sec- tions that had suffered,dam~ge. , . The U. S. Army Corps of Engineers' Trinidad Lake Project, located on the Purgatoire R~ver about 4 miles south- west of Trinidad, will prov~de a high degree of flood protection to Trinidad. It'will effectively reduce the frequency of flooding along: the Purgatoire piver in Trinidad from storms occurr~ng above the dam. The reservoir, which is complete for flood control purposes, will retain floods with a r!:ocurrence interval greater than 100 years. Flows from! the reservoir will be released to limit downstrea~ flows to non-damaging rates, insofar as possible. This Flood Insurance Study assumes that the project is! in full operation. . 6