55. Other improvements. There are other minor protective works along Purgatoire River. They consist mostly of pile and wire baskets filled with rock, dumped riprap, and other minor works, which were installed by the city of Trinidad, various transportation companies, and individuals for the protection of public and private property and bridge approaches. The cost of these works is not available. 56. Improvements desired.-A joint public hearing was held by the District Engineer, United States Engineer Office, Little Rock, Ark., and a representative of the Department of Agriculture at Trinidad, Colo., on September 8, 1937. The hearing was well attended and included State, city, and county officials, merchants, bankers, educators, farmers, ranchers, representatives of the Trinidad Chamber of Commerce, the La Junta Chamber of Commerce, the United States Soil Conservation Service, the United States Bureau of Reclamation, the United States Forest Service, several irrigation organizations, the Atchison, Topeka & Santa Fe Railway, the Denver & Rio Grande Western Railroad, the Colorado & Southern Railway, the Missouri Pacific Railroad Cos., the Holly Sugar Corporation, and the Colorado Fuel & Iron Co. The local interests described the extensive damages caused by the great flood of September 1904, for which they claim that a half a million dollars is a conservative estimate for Trinidad. They called attention to the destruction of bridges which crippled transportation in that section of the country, as well as other extensive damages to the city. Those present indicated that they are fearful that another great flood might occur which may cause a large loss of life. Also, the local interests claim that a conconsiderable amount of water is lost during flood periods which, if regulated, could be used for augmenting the present inadequate supply to the lands now under ditch. Residents advise that the irrigation water now decreed is far in excess of that available. 57. Generally, flood protection, particularly at Trinidad, and the conservation of flood flows for irrigation are desired. Interested parties suggested that this could be accomplished by means of regultory dams, in Burro, Zarcillo, Lorencito, and Wet Canyons. It was also suggested that, by means of a small channel dam on Purgatoire River and a connecting canal, flood waters could be stored in a reservoir located in Long Canyon near its mouth to augment the present inadequate water supply for irrigation. A report on the proposed irrigation and flood-control dams and data obtained from surveys made by the Civil Works Administration and the Federal Emergency Relief Administration, dated January 1933, was submitted. It was pointed out that, owing to the decline in coal mining and its related industries in recent years, it has been necessary for many of those formerly engaged in these industries to become either agriculturists or leave the locality. Attention was invited to the fact that there had been an exodus from the watershed because of lack of suitable lands and water for profitable farming. The opinion was expressed that flood control improvements designed to capture floodwaters for irrigation needs would make more lands available for lucrative farming, thus tending to stabilize the population of the basin. Others who are primarily interested in agricultural pursuits desire flood protection to reduce the loss of farm lands occasioned by caving banks or shifting of the river channel, and also to reduce the damages to their irrigation systems and bridges which result from flood flows. The officials and organizations, in general, stated that they would participate in the construction cost to the extent of their ability if floodwaters were conserved for irrigation use. The 58. Surveys.-The investigations for this report included topographic and economic surveys, meteorological, hydrological, and hydraulic studies, and field inspections of the entire area. topographic surveys included stream and valley cross-sections, valley topography, location and elevation of high-water marks, and location and description of all streams crossing structures. The Department of Interior, Bureau of Reclamation, had previously made detailed topographic surveys of the Sopris Reservoir site and had obtained core borings at the dam site. These data were made available by that agency for use in the preparation of this report. The major portion of the irrigated land, as well as the urban and industrial property subject to inundation, lies between Long Canyon (mile 164) and mile 122, therefore a detailed topographic map was made of this area only. From mile 122 to the mouth of the river, stream alinement and stream and valley cross-sections only were obtained. The economic survey consisted of a gross appraisal of the area and an inventory of flood damages. The appraisal was made by direct in quiry and investigation in the field to determine land values, crop distribution and values, and urban property and public utility values. Immediately following the flood of April 1942, a survey of damages and crop distribution was made from Sopris Dam site to the mouth of the river. 59. Flood problems. In the Purgatoire River Basin, two areas, one the urban area in the city of Trinidad, the other the agricultural areas between Sopris Dam site and the head of the Canyon section, comprise the major flood problems in the drainage area. In the urban area of Trinidad, the alinement and gradient of the present channel are such that the wave trains produced overflow the banks at comparatively small discharges in comparison with the area of the existing channel. Also, due to the existing alinement and the resulting wave trains, excessive erosion or bank sloughing is produced at critical locations, endangering the Atchison, Topeka & Santa Fe Railway; the Colorado & Southern Railway; and the Denver & Rio Grande Western Railroad; as well as the bridges spanning the river within the city. Impairment of these facilities not only affects Trinidad and vicinity but is also reflected in other sections of the country if railway transportation is curtailed. Discharges exceeding bankfull stages result in damages to normal economic pursuits in the city, inconvenience to the population within, and interruption of traffic outside of the watershed. In the agricultural areas the major flood problems are damage to lands and crops by overflowing, erosion and deposition on existing developed acreage, damage to irrigation structures, and the loss of flood discharges above the diversion capacity of the irrigation headworks which might be conserved for additional water supply. 60. Investigations and studies for flood control. The plan for flood control suggested by certain local interests and all other plans recommended or suggested by the city officials of Trinidad, representatives of organizations, and other individuals, have been investigated. The possibilities of flood control by diversions, the use of channel rectification, levees, and reservoirs, alone and in combination with levees and channel rectification, have also been considered. 61. Local interests-Plans of improvement.-Plans of improvement suggested by certain local interests, at the hearing and subsequently thereto, include regulatory reservoirs in Wet, Lorencito, Zarcillo, and Burro Canyons, and a storage reservoir in Long Canyon, all of which are tributary to the main stem above Trinidad. A low channel dam across Purgatoire River would divert floodwaters into Long Canyon, through a connecting canal. The stored water would be used for irrigation purposes. The proposed Long Canyon Reservoir with a capacity of 4,700 acre-feet, would be almost double the aggregate capacity of the four regulatory reservoirs in other canyons. Pertinent data on the five reservoirs suggested by local interests are shown in table No. 8. TABLE NO. 8.-Pertinent data on the five reservoir plans suggested by local interests 1 Capacities and drainage area are given by local interests. The drainage area of the four regulatory flood-control reservoirs would be only 25 percent of the total drainage area upstream of Trinidad, and even this portion of the area would not be completely controlled owing to the small reservoir capacities involved. The Long Canyon site would be used principally for irrigation storage and would not be dependable for flood-control purposes. Because of their limited drainage areas and their small capacities, the reservoirs would not afford any appreciable flood control in the main valley, particularly at Trinidad and downstream therefrom, and their construction could not be economically justified for that purpose. Flood damages in the local valleys immediately downstream from the suggested sites are very small. The plan would have some merit for the conservation of a part of the floodwaters. The regulatory reservoirs, by retarding the flow of flash floods and prolonging the period of higher discharge, would permit the capture of more water by irrigators, and the storage of water in Long Canyon would be of benefit as a supplemental supply to the farms under irrigation. The total benefits which would accrue from the execution of the plan would not be great enough to warrant the construction of the five reservoirs suggested by local interests. 62. Reservoirs in lower Purgatoire Basin.-From time to time, several reservoir sites have been surveyed in the lower basin of Purgatoire River with the view to providing a supplementary regulated water supply to Arkansas River. The 3 sites of greatest merit are the Mammoth site, near the upper end of the lower basin; the Purgatoire No. 2 site, approximately 6 miles below Higbee, Colo.; and the I. S. site at the Highland (Carman) Dam, approximately 20 miles below Higbee. It was found that for the purpose of providing a supplementary water supply for Arkansas River, the Mammoth site, although an excellent one, would control insufficient watershed. Since the inflow downstream from the Mammoth Dam site constitutes the major portion of the unused water discharged from the basin, the project would not be feasible. The Purgatoire No. 2 site, appears to be more feasible than the I. S. site. 63. The Purgatoire No. 2 site was originally surveyed in 1909 with a view to providing water storage for the development of the land lying south of the present irrigation area in Arkansas Basin. In 1924, the State Engineering Department of Colorado made a detailed survey of the site and proposed a dam 113 feet high above the stream bed, which would provide a capacity of 123,000 acre-feet. The "308" studies conducted under the direction of the Corps of Engineers, United States Army, and published in House Document No. 308, Seventy-fourth Congress, first session, considered a dam 118 feet in height with a capacity of 145,000 acre-feet at the Purgatoire No. 2 site to give a supplementary supply of 48,500 acre-feet. 64. The "308" studies have indicated, and the present studies confirm, that the benefits to be gained in the lower Purgatoire River Basin from the development of supplementary water supply at the Mammoth, I. S., or Purgatoire No. 2 sites, are negligible and that developments at these sites would have value only in the Arkansas River Basin. 65. Channel rectification, levees, and bank stabilization for flood control.-Channel rectification, levees, and bank stabilization have been considered, alone and in combination, for the protection of the rural portions of the area and also, along streams tributary to Purgatoire River. Owing to the length of the valley and the distribution of the damages, works of this nature would be very extensive and their cost would exceed the benefits to be obtained. In the construction of levees or rectifying the channel in the narrow flood plain, it would be necessary to utilize some lands on which damages occur. The average annual preventable flood damages to crops and improvements are about $21 per mile of channel in the flood plain. Channel rectification, levees, and bank stabilization in the rural areas are not economically justified at this time, nor does any other type of works for the general prevention of overflow or bank recession appear to be warranted at present in the agricultural areas or along tributary streams. 66. Water power and municipal supply. The erratic stream flow of Purgatoire River and demand for all available water for other purposes precludes the development of hydroelectric power in this area. There is no need for further municipal water supply in the basin as existing reservoirs meet the present needs. The existing storage capacity for water supply exerts no significant regulatory effect on stream flow. 67. Sopris Reservoir for flood control and irrigation.-A dual-purpose flood control and irrigation reservoir at the Sopris site has been considered as a plan for providing flood protection in Purgatoire Valley. In order not to induce a sense of false security in people in the flood plain, it was considered that the structure should provide flood protection equal to that of the maximum flood of record (September 1904) if economically justified. 68. Studies by the United States Department of the Interior, Bureau of Reclamation, indicated that for a flood detention capacity of 5,200 acre-feet, an additional 5,540 acre-feet of water would be available to irrigators annually. 69. The structure for plan 1 would provide a concrete overflow section, concrete bulkhead sections, and an earth embankment section. The over-all length of the structure would be 2,545 feet and the top of the dam would be at elevation 6,262, which is 107 feet above the elevation of the stream bed. The concrete spillway section would be 398 feet in length with the crest at elevation 6,235, which is approximately 100 feet above the elevation of bedrock. The spillway would be controlled by seven 22- by 50-foot Tainter gates to maximum pool elevation at 6,257. Two concrete bulkhead sections, one 205 feet in length would concatenate the spillway with the left bank abutment, the other 258 feet in length would key the embankment section. The embankment section would be a pervious rolled fill with 3 on 1 slopes with a riprapped blanket on the upstream face and a graded gravel blanket on the downstream face. An impervious core extending up to elevation 6,170 would key the pervious section to bedrock. Five outlets, one ungated and four gated, would be provided. State Highway 12 would be relocated for approximately 1 mile. The Colorado & Wyoming Railway would be relocated for a distance of 2.16 miles. This relocation would require a tunnel through the embankment section of the dam. Utilities and a cemetery would also have to be relocated. 70. The estimated first costs were $3,641,100 and the average annual charges were $176,000 for this structure. 71. Investigations to determine the dual-purpose reservoir which would provide the greatest ratio of benefits to cost, indicated that a concrete overflow section and concrete bulkheads with the spillway crest at elevation 6,195 would meet these criteria. 72. Studies of run-off, during the period of record from 1922 through 1941, indicated that for a flood detention capacity of 3,180 acre-feet an additional 5,200 acre-feet of water would be available to irrigators annually. 73. The structure for plan 2 would provide a 1,000-foot overflow section with a spillway crest at elevation 6,195, flanked by 2 bulkhead sections 160 and 190 feet in length. The over-all length would be 1,350 feet. The top of the dam would be at elevation 6,210, which is about 55 feet above stream bed elevation and 75 feet above bedrock. Discharge would be uncontrolled by one outlet to the crest elevation 6,195. State Highway 12 would be relocated for approximately 0.73 mile. The Colorado & Wyoming Railway would be relocated for a distance of 1.44 miles. Utilities would also be relocated. 74. The estimated first costs of the structure were $1,174,800 and the annual charges $61,600. 75. Details for these structures are given in appendix D.! 76. Sopris Reservoir for flood control only.-No detailed investigations were made for this structure, as it was obvious from the investigations of the dual-purpose structures that the project could not be justified at this time. (See project justification, par. 92.) 77. Sopris Reservoir for flood control and irrigation-Channel improvement through Trinidad for flood control.-It is apparent from the 1Not printed. |