COTTONWOOD DAM MANUAL FOR OPERATION AND MAINTENANCE DOCUMENfS eOtLICTlON STATE ^ ZQ81 I KiONTANA STArE LIiRARY 1515 E. 6th AVE- MONTANA 59620 HELENA, State Water Projects Bureau Water Resources Division Department of Natural Resources and Conservation 48 North Last Chance Gulch Box 201601 P. O. MX Helena, 59620-1601 Originally Published June, 1995 Revised July 2001 MONTANA STATE LIBRARY 3 0864 0015 5124 4 COTTONWOOD DAM MANUAL FOR OPERATION AND MAINTENANCE State Water Projects Bureau Water Resources Division Department of Natural Resources and Conservation 48 North Last Chance Gulch Box 201601 P. O. MX Helena, 59620-1601 Originally Published June, 1995 Revised July 2001 Digitized by the Internet Archive 2015 in https://archive.org/details/cottonwooddamman2001mont TABLE OF CONTENTS Page OVERVIEW 1 Map General Location (Figure 3 1) Project Area Map (Figure 2) 4 Dam General Layout Map (Figure 3) ^ 5 Monitoring Wells Map (Figure 4) !;T. .T. 6 . STATISTICAL INFORMATION 7 OPERATING PROCEDURES 11 Method and Schedule of Operation 11 Safe Drawdown 12 Limits of Appurtenances 12 Dam Operator 12 Storage Determination 13 Weather Monitoring 14 Interaction with Other Dams 14 Emergency 14 INSPECTION AND MONITORING 15 Structural Features Inspection 15 Riprap Inspection 16 Monitoring Wells 16 Seepage Monitoring 17 MAINTENANCE 19 Routine Maintenance 19 Annual Maintenance 20 Record Keeping 20 REFERENCES 23 APPENDICES 25 A. RATING CURVES AND TABLES Al Table SLOPE/ELEVATION/STORAGE TABLE A2 1. Table 2. ACTIVE STORAGE TABLE A3 Table 3. SPILLWAY RATING CURVE AND TABLE A4 Table 4. OUTFLOW RATING CURVE AND TABLE A5 B. INSPECTION REPORT FORM Bl C. O&M MANUAL DISTRIBUTION LIST CI D. MONITORING WELL LOGS Dl E. PROJECT DRAWINGS El 2001 1 2001 OVERVIEW Dam Cottonwood is located on Cottonwood Creek, approximately 3 miles northwest of town of Wilsall in Park County. Cottonwood Reservoir impounds runoff from a drainage area of 34 square miles located in Park and Gallatin Counties (See Figures 1 and Figure 3 provides a general layout of the dam, spUlway and 2). outlet works. Figure 4 shows the location of the monitoring wells. The dam is owned by the Montana Department of Natural Resources and Conservation (DNRC) and is managed by the State Water Projects Bureau (SWPB) of the DNRC. The Shields Canal Company (herein called the "association") operates and maintains the dam. The earthfill dam and dike were completed in 1953. The dam is 39-feet-high and 610-feet-long while the dike is up to 8- feet-high and 825-feet-long. In 1986 significant construction was completed to rehabUitate the spillway and riprap on the upstream face of the dam. Reports indicate the dam has historically received adequate maintenance. The dam's outlet works consist of a wet tower and a single 36-inch diameter slide gate with controls at the top of the tower. The low-level outlet conduit consists of 197 feet of 10 gauge, 36- inch diameter corrugated metal pipe double bituminous coated (inside and outside) and paved invert. The spillway is located in the right abutment. The spUlway is an uncontrolled concrete chute with 70-foot-wide guard dike and a 20-foot-wide ogee crest at the throat of a 20-foot-wide chute with concrete baffle blocks. The rehabilitation in 1986 added the 70- foot-wide guard dike at elevation 5,102.5, which was the elevation of the wooden flashboards (the flashboards were removed during 2001 1 . the rehabilitation work) Water from the reservoir is primarily used for irrigation. The reservoir is also used for water-based recreation. 2 2001 3 2001 4 2001