' ' t UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE Bureau of Sport Fisheries and Wilflife Southwestern Region Albuquerque, New Mexico A REPORT ON FISH AND WILDLIFE RESOURCES CURECANTI UNIT COLORADO RIVER STORAGE PROJECT, COLORADO Prepared in Cooperation with the Colorado Game and Fish Department September 1957 PREFACE This report contains a detailed analysis of the effect of Curecanti unit, Colorado River Storage project, upon fish and wildlife resources in the Gunnison River Valley, Colorado. The information in it is intended for consideration by the Secretary of the Interior in determining whether or not the project is economically justified, as required under the provision in Section 1, Public Law 485, 84th Con­ gress, 2nd Session, which authorized the Colorado River Storage Proj­ ect April 11, 1956. As planned by the Bureau of Reclamation, Curecanti unit will consist of 4 dams and reservoirs. The area influenced by these faci­ lities will begin at the headwaters of Curecanti Reservoir on the Gunnision River near the mouth of North Beaver Creek, 6 miles west of Gunnison, Colorado. It will extend down the river through Narrow Gauge, Morrow Point, and Crystal Reservoir sites. From Crystal Dam, 37.5 miles downstream from the mouth of North Beaver Creek, effects of the project will extend another 33 miles to the mouth of the North Fork of the Gunnison River. The current plan has been prepared for consideration by the Secretary of the Interior in accord with the above-mentioned provision of Public Law 485. Project data were fur­ nished this Service by the Bureau of Reclamation in letters dated December 1, 1954, June 9, 1955, and May 19, 1957, and by copy of the status report, Curecanti unit, dated February 1956. By preliminary report dated January 18, 1955, contained in a letter to Regional Director Larson, Bureau of Reclamation, Bureau 4, the Fish and Wildlife Service, with the concurrence of the Colo­ rado Game and Fish Department, cited reasons for opposing construction of reservoirs on the Gunnison River above the confluence of the North Fork of the Gunnison River. The adoption of an alternate plan using reservoirs located elsewhere was recommended. In addition to the foregoing report, the U.S. Fish and Wildlife Service has prepared other reports on the Colorado River Storage project and participating projects that refer to the Curecanti (Cottonwood Gulch) Reservoir at the Blue Mesa (Cottonwood Gulch) Dam site. Included in this group ar~ the following:(1) A Preliminary Report on Fish and Wildlife Resources in Relation to the Colorado River Storage project, Colorado River and Tributaries above Lees Ferry, Arizona, January 10, 1949, and (2) A Preliminary Report on Fish and Wildlife Resources in Relation to the Colorado River Stor­ age Project and Participating Projects, January 1951. Personnel of the Colorado Game and Fish Department assisted in field investigations and in providing from departmental files data essential to preparation of this report. BUREAU OF SPORT FISHERIES AND WILDLIFE DESCRIPTION OF THE PROPOSED PROJECT Project Status 1. The Curecanti unit, consisting of 4 dams and reservoirs on the Gunnison River below the town of Gunnison, Colorado, was provi­ sionally authorized by Congress as a part of the Colorado River -Stor­ age project, April 1956. Provisions limit Curecanti Reservoir to not less than 940,000 acre-feet capacity, or more than a maximum water surface elevation of 7,520 feet 1/. Provisions further stipulate that construction of Curecanti unit shall not be undertaken until the Sec­ retary of Interior has re-examined the economic justification and certified to Congress and the President that, in his judgment, the benefits from such unit will exceed its costs. Purposes 2. The primary purpose of Curecanti unit is to provide hydro­ electric power. According to the Bureau of Reclamation's Status Re­ port on this unit, dated February 1956, "Benefits to downstream water users from river regulation .•. would not be significant in deter­ mining the unit's economic justification". Location 3. Curecanti Reservoir will be impounded by Blue Mesa Dam, the site of which is on the Gunnison River in Gunnison County, Colorado, about 26 miles by road southwest of the town of Gunnison. The reser­ voir will extend upstream to a point approximately 6 miles from the Gunnison city limit. The other 3 proposed reservoirs will be located along a 15-mile reach of deep canyon section of the Gunnison River above Black Canyon of the Gunnison National Monument and above the existing Gunnison Tunnel that diverts from the river to the Uncompahgre reclamation project. Crystal Dam will be located farthest downstream, 4 miles upstream from the east portal of Gunnison Tunnel:; Morrow Point Dam will be located on the Gunnison River about 1 mile downstream from the mouth of Cimarron Creek; and Narrow Gauge Dam will be located 7 miles downstream from the town of Sapinero, Colorado, and 3.5 miles downstream from the proposed Curecanti (Blue .Mesa) Dam site. lf All elevations in this report refer to mean sea level datum. BUREAU OF SPORT FISHERIES AND WILDLIFE Proiect Features Engineering data 4. To date no detailed design for the proposed Blue Mesa Dam has been developed. It has not been decided whether earthfill and rock­ fill or concrete-arch construction will be utilized. A tentative plan provides for an earthfill and rockfill structure with a crest length of 820 feet, 350 feet above streambed. There will be a free-overflow­ type spillway with a crest of 187 feet in length, with a capacity of 31,000 second-feet. Reservoir releases will be accomplished by a pen­ stock outlet, capacity 2,100 second-feet, leading to a powerplant at the base of the dam. The powerplant will consist of 2 generators having a combined capacity of 51,000 kilowatts. 5. Data available ort the other 3 sites are quite limited. They are summarized in table 1, together with similar data for Blue Mesa Dam. Table 1-'."'Pertinent Enqi,neering Data, Cur.e,canti Unit. , Crest Installed Height of dam length generating Type of above streambed of dam capacity Dam §tructure . (feet) (feet) . -~<kilgwa.ttsl Blue Mesa Undetermined 350 820 --5I, 000 Narrow Gauge Concrete gravity 135 465 18,000 Morrow Point Concrete gravity 260 310 60,000 Crvstal Concrete qravitv 155 360 23 QDO Operation 6. Curecanti Reservoir will be operated to facilitate a firm power output from the hydroelectric plant at the base of Blue Mesa Dam. An operation study based upon the period 1931-1945 indicated that reservoir outflow, including releases through the powerplant and spills, will average 1,325 second-feet. 7. At capacity, Curecanti Reservoir will contain not less than 940,000 acre-feet of water with a surface area of 9,240 acres. The high water line, by law, cannot be above elevation 7,520 feet. The operation study indicates, however, that the reservoir will not fill to capacity in some years and that the average annual maximum pool will have a surface are of 8,970 acres. The average annual minimum pool will have a surface area of 6,490 acres. In some years the surface area will be reduced to a minimum of 2,990 acres. The annual draw­ down will vary from 23 feet to 99 feet and will average 47 feet. Data pertaining to Curecanti Reservoir operating levels are summarized in table 2. 2 BUREAU OF SPORT FISHERIES AND WILDLIFE Taple 2~-0perating levelsL Curecanti Reservoix Surface Elevation Content area Waj:e_r surf ace (feet) (acre-feet) (acres) Extreme high pool 7~516 17 940,000 9,240 Average annual maximum pool 7,509 876,000 8,970 Average annual minimum pool 7,462 516,000 6,490 · Extreme low pool 7,398 213,000 2,990 Dead storage pool 7,393 200,000 2,850 Sir~ambed 7 183 8. Releases from Curecanti Reservoir and minor inflows from local tributaries will be regulated largely on a daily basis at the Narrow Gauge Reservoir. Water from the reservoir will be released for power production at the Narrow Gauge Powerplant at Narrow Gauge Dam. 9. T~ilwater from the Narrow Gauge Powerplant and a moderate amount of total tributary inflow will be controlled by the Morrow Point Reservoir. The reservoir will provide regulation largely on a daily and seasonal basis. Release s from the reservoir will be made for power production at the Morrow Point Powerplant, located at Morrow Point Dam. 10. Tailwater from the Morrow Point Powerplant will be regulated on a daily basis at Crystal Reservoir. Releases from Crystal Reser­ voir will be made on a relatively uniform basis, particularly during the irrigation season, · and will be utilized for power production at the Crystal Powerplant, located at Crystal Dam. Releases from Crys­ tal Reservoir will be maintained at rates in excess of diversions to the Uncompahgre project and other presently irrigated lands downstream. 11, A comparison of streamflow on a monthly basis as it would be with the unit in operation as it existed histotically is shown in table 3. In the absence of information concerning rate or frequency of daily streamflow fluctuations with the unit, only the apparent gross effects may be noted. These will be a reduction in volume of high flows and a corresponding increase in volume at times of histori­ cal low flow. Monthly data do not provide the information necessary for adequate analysis and firm conclusions as to conditions with the unit as compared to those without. Modification of streamflow, how­ ever, will have considerable effect upon Gunnison River as far down­ stream as the mouth of N0 rth Fork, and this will be considered the lower limit of project influence.