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the cost of local side drainage inlets and of revision of irrigation diversion facilities within the project limits; and (e) maintain and operate all the works after completion in accordance with regulations prescribed by the Secretary of War. However, as no conservation is provided and in view of the national interest in the benefits provided to important transportation facilities, no participation in direct construction costs other than (d) above, should be required of local interests. The city of Trinidad, by resolution, has agreed to meet the requirements for local cooperation outlined above.

113. Conclusions.--A serious flood problem exists in the Purgatoire River Basin at Trinidad, Colo., which not only affects the welfare of the community, but also involves national interests, in that vital transportation facilities, both rail and highway, are subject to extensive culo flood damage and attendant interruption. Flood damages are sustained also by the agricultural areas in the Purgatoire River Basin on nyt and by the irrigation diversion structures along the main channel. There is a demand for the conservation of floodwaters for irrigation TON

Provision of food protection to both the Trinidad urban area and the agricultural areas subject to damage in the Purgatoire River do Basin, by means of flood control or dual-purpose reservoirs with conservation features, is not economically feasible. A combination reservoir and channel-improvement project cannot be justified. The most economical method of providing flood-control benefits to the Trinidad urban area and for the protection of vulnerable transportation facilities located therein, is the construction of a channel improvement within Trinidad at an estimated first cost of $1,034,500 and annual charges of $42,200. The estimated monetary benefits accruing to the channel-improvement project closely approximate the estimated annual team costs, and in consideration of the important intangible benefits attended a bit ant, its construction is justified.

114. Recommendation.-It is recommended that the channel improvement project at Trinidad, Colo., be adopted as the most suitable plan for essential flood protection in Purgatoire River, Colo., and that Federal funds in the amount of $909,000 be appropriated for construction and none for annual maintenance, provided, local interests thrɔugh their responsible representative agency, furnish assurances satisfactory to the Secretary of War that they will: (a) Provide, without cost to the United States, all lands, easements, and rights-ofway necessary for the construction of the project; (6) hold and save the United States free from damages due to the construction works; (c) provide the costs of public utility and bridge revisions, relocations, or replacements; (d) provide the cost of local side-drainage inlets and of revision of irrigation diversion facilities within the project limits; and (e) maintain and operate all the works after completion in accordance with regulations prescribed by the Secretary of War.

It is further recommended that the first costs of the project be provided in a lump sum in order to secure economical and advantageous prosecution of the work.

L. ROSENBERG,
Colonel, Corps of Engineers,

District Engineer.

(First endorsement]
OFFICE, DIVISION ENGINEER,

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Dallas, Tex., March 15, 1943. To the Chief or ENGINEERS, UNITED States Army.

1. The Purgatoire (Picket Wire) River, with a watershed area of 3,390 square miles, is the most important tributary of the Arkansas River in the State of Colorado. Its topographic relief varies over 10,000 feet in elevation, ranging from the 14,000-foot peaks of the frontal ranges of the Rocky Mountains to the relatively flat, rolling prairies at an elevation of around 4,000 feet above sea level in southeastern Colorado. The climate is semiarid, but despite that fact the basin at times suffers severe flood damage especially in the spring months when the run-off from melting snow is augmented by general rainfall

. Other severe floods are also experienced as a result of precipitation of almost cloudburst proportions concentrated over comparatively small areas, which in conjunction with the extremely steep slopes readily produce "flash" floods with high peak rates of discharge but smali volume.

2. The principal area subject to overflow in this basin is a 35-mile alluvial reach that extends downstream from the mouth of Long Canyon, and includes not only several thousand acres of well-developed agricultural land that is under irrigation, but also includes a portion of Trinidad, the largest city in the basin (population 13,223). The urban area consists of about 370 acres of residential, business, and industrial property, as well as roads, railroads, and bridges, all with a total value of nearly $5,000,000. In the major flood of April 1942, which had a peak flow of approximately 36,000 cubic feet per second, the damages sustained by the city alone amounted to around $400,000, including the loss of two city bridges and the failure of the approach to a railroad bridge. The flood of September 1904 was of considerably greater magnitude (45,000 cubic feet per second) and estimates of the damage caused by that flood varied from $350,000 to $500,000, including the complete destruction of four bridges. It is believed without question that a repetition of that flood under present-day conditions would result in vastly increased losses, not only in the directly evaluable damages but also in other widespread although intangible losses.

3. Investigation was made of all possible means of providing flood protection, not only for Trinidad, but also for the agricultural areas and communities. The cost of construction of the desired improvements was, however, found in general to be prohibitive. Furthermore, even when consideration was given to the construction of dual-purpose works for the conservation of water for irrigation use in combination with flood protection it was found that the anticipated conservation benefits added to the prevented flood losses were wholly incommensurate with the estimated costs.

4. The most feasible plan of improvement was that for an unlined floodway, part leveed and part with reinforced concrete cantilever retaining walls, which was designed to insure safe passage through Trinidad of all flood flows up to the maximum of record, or 45,000 cubic feet per second. On the basis of the invoiceable benefits the

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justification for construction of this floodway is a border-line proposition, since the ratio of annual charges to annual benefits is 1:0.99; however, the district engineer, after giving due weight to the urban character and high property values in the areas that would be protected by the floodway, and also to all other benefits of an intangible nature, came to the conclusion that the project was justified and accordingly recommended its construction.

5. I concur in the findings of the district engineer both as to the effectiveness of the proposed floodway as a means of controlling floods in Trinidad and also as to his evaluation of the flood losses that will be prevented thereby. I further concur that the invoiceable benefits alone are not a true measure of the worth of the required improvements, since it is quite reasonable to expect that a considerable percentage of the direct flood damages will be missed or impractical to determine in a city of this size. Furthermore, it is almost impossible to evaluate in terms of dollars and cents the indirect effects of floods that cause suspension of normal business activities, or which interfere with interstate commerce of importance to the national welfare as a result of damage to transcontinental rail and road facilities. Consequently, when these intangible but nonetheless positive benefits are credited to the proposed floodway, and when in addition account is taken of the break-down of sanitary conditions and the possibility of loss of human life in a crowded urban area, the economic attractiveness of this projected channel improvement is very appreciably enhanced.

6. In view of the foregoing, I therefore recommend that the United States construct the floodway for the protection of Trinidad, Colo., at an estimated cost to the Federal Government of $909,000; provided that local interests shall not only meet the prescribed requirements of local cooperation, but shall also participate in the direct costs of construction, all substantially as set forth in the report of the district engineer; and provided further that the State of Colorado shall, through the enactment of appropriate legislation if necessary, insure that the construction of bridges or other works which might adversely

affect the flood-carrying capacity of the channel of the Purgatoire River through the city of Trinidad will not be permitted.

R. R. NEYLAND,
Colonel, Corps of Engineers,

Division Engineer.
O

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