CERRO RESERVOIR DRAWDOWN PLAN

Transcription

1 GEOTECHNICAL AND WATER RESOURCES ENGINEERING CERRO RESERVOIR DRAWDOWN PLAN CERRO RESERVOIR OUTLET WORKS REPLACEMENT PROJECT MONTROSE COUNTY, COLORADO Submitted to City of Montrose 433 South First Street Montrose, Colorado Submitted by RJH Consultants, Inc Mt. Pyramid Court, Suite 330 Englewood, Colorado May 2018 Project Michael L. Graber, P.E. Project Manager

2 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 TABLE OF CONTENTS TABLE OF CONTENTS... I SECTION 1 - INTRODUCTION PURPOSE GENERAL DESCRIPTION OF THE SITE DAM CONSTRUCTION AND MODIFICATION HISTORY Western Dam Southern Dam Eastern Dam SUBSURFACE DATA AND EXISTING SEEPAGE CONDITIONS Presently Available Geologic and Geotechnical Information Seepage Conditions... 4 SECTION 2 - RESERVOIR DRAWDOWN PLAN GENERAL COORDINATION SCHEDULE... 5 SECTION 3 - DRAWDOWN BY SIPHON GENERAL SIPHON DESIGN ACTIVATING AND DEACTIVATING THE SIPHON AND MAINTENANCE... 8 SECTION 4 - DRAWDOWN BY PUMP GENERAL SYSTEM COMPONENTS SECTION 5 - EMBANKMENT MONITORING DURING DRAWDOWN RAPID DRAWDOWN FAILURE MODE GENERAL EMBANKMENT MONITORING RESERVOIR LEVEL MONITORING EMBANKMENT INSPECTION i Cerro Reservoir Drawdown Plan

3 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May REPORTING SECTION 6 - CONTINGENCY PLAN SECTION 7 - REFERENCES LIST OF FIGURES Figure 2.1 Elevation-Area-Capacity Curve Figure 3.1 Siphon Approximate Rating Curve APPENDICES Appendix A Appendix B Appendix C Appendix D Tentative Schedule and Discharge Rates Inspection Forms Siphon Design Drawings Existing Construction Information ii Cerro Reservoir Drawdown Plan

4 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 1 - INTRODUCTION 1.1 Purpose The purpose of this Reservoir Drawdown Plan (Plan) is to provide recommendations for drawdown of Cerro Reservoir (aka Montrose Reservoir) (DAMID ) located in Montrose County, Colorado. The reservoir will be lowered from the approximate maximum normal water surface elevation to the reservoir bottom, effectively draining the reservoir. The reservoir is being drained to facilitate construction of The Cerro Outlet Works Replacement Project (Project), which requires excavation and replacement of a portion of the western embankment. This Plan includes a schedule for reservoir drawdown, reservoir elevation-capacity data, siphon construction and operation details, pump operation details, recommendations for monitoring and inspection during drawdown, and contingency plans. 1.2 General Description of the Site Cerro Reservoir Dam is a high hazard dam owned and operated by the City of Montrose (City) located approximately 14 miles east of Montrose, Colorado along Highway 50. The dam impounds a 720 acre-foot (ac-ft) reservoir at the maximum normal water level (NWL) elevation (El.) Based on survey data from April 2018, the reservoir is at or below El The reservoir is impounded by three earthen embankment dams: a western embankment, a southern embankment, and an eastern embankment. The outlet works is located through the western embankment and the spillway is located on the left abutment of the eastern embankment. The invert of the auxiliary spillway is at El The reservoir is filled by a 24-inch-diameter diversion pipeline that discharges into the reservoir at the left abutment of the southern embankment at El The Vernal Mesa Canal (aka Cimarron Canal) (Canal) traverses the Site from south to north and is generally located west of the western embankment. The Vernal Mesa Canal Company (Canal Company) owns and operates the Canal and maintains a residence and appurtenances downstream of the western embankment. A map of the Site location and plan of the Reservoir are presented on the construction drawings in Appendix C. 1.3 Dam Construction and Modification History The west and south embankments were constructed prior to 1953 and original construction records are not available. The reservoir was enlarged in 1953 and the outlet Cerro Reservoir Drawdown Plan

5 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 works was modified in conjunction with the enlargement (C-644, 1953). It is our understanding that the 1953 modifications included the following components: A 10-foot vertical raise to the west and south earth embankments. Construction of the east embankment. An enlarged auxiliary spillway at the left abutment with a loose-placed riprap control section and earthen channel. Abandonment of the existing auxiliary spillway located at the right abutment of the west embankment. Additional upstream slope protection. Modifications to the outlet works. In 1966, the reservoir basin was enlarged by excavating material located in the northeast portion of the reservoir basin (C-644A, 1966). Excavated material was designed to be stockpiled north and west of the west dam embankment. Drawings from the original enlargement are included in Appendix D. The Project drawings appear to be as-builts and, based on RJH field observations and discussions with the City, the drawings do not completely reflect as-constructed conditions at the dam. A summary of the embankments is provided below. Embankment dimensions were generalized from embankment enlargement drawings (C-644, 1953) and Survey data (Del-Mont, 2017) Western Dam The original western dam was approximately 370 feet long and 16 feet tall. Following the 1954 enlargement, the dam was approximately 520 feet long and 26 feet tall with a 15-foot-wide crest, and 2 horizontal to 1 vertical (2H:1V) upstream and downstream slopes. The upstream slope is approximately 3H:1V below the maximum NWL. New fill was designed to be keyed into the existing dam crest with a 4-foot-deep by 6- foot-wide core trench. Between Station 1+25 and Station 4+50, new fill was also designed to be keyed into the existing foundation with a 4-foot-deep (minimum) by 10- foot-wide core trench Cerro Reservoir Drawdown Plan

6 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May Southern Dam The original southern dam was approximately 520 feet long and 38 feet tall. Following the 1954 enlargement, the dam was approximately 800 feet long and 53 feet tall with a 16-foot-wide crest and 2H:1V upstream and downstream slopes. The upstream slope is approximately 3H:1V below the maximum NWL. A core trench was not designed to be constructed at the south dam but a requirement was included to remove vegetation and corrugate the downstream slope prior to placing new fill. An aggregate toe drain is located at the maximum embankment section, which was designed to be connected to a granular drain trench that discharges downstream of the dam. The granular trench drain was designed to consist of a layer of well graded gravel around select rubble material. As shown on the drawings in Appendix D, the select rubble is in contact with foundation soils. Gradations are not available for these materials and the outfall location of the drain is unknown Eastern Dam The eastern dam was constructed in 1953 and consists of an approximate 280-foot-long, 10-foot-tall embankment with an 11-foot-wide crest and 2H:1V upstream and downstream slopes. New fill at the eastern dam was designed to be keyed into foundation soils with a 4-footdeep (minimum) by 10-foot-wide core trench. 1.4 Subsurface Data and Existing Seepage Conditions Presently Available Geologic and Geotechnical Information According to published maps (Steven and Hail, 1989; Dickinson, 1963), the Project site consists of Quaternary-age (less than 2.6 million years old) landslide soil deposits overlying Upper Cretaceous aged Mancos Shale (between 99.6 and 65.5 million years ago). Landslide deposits are expected to consist of heterogeneous deposits of material formed largely by repeated complex slump, mudflow, earthflow, and rockfall movements. The thickness of the landslide deposits are currently unknown. Mancos Shale typically consists of dark-gray to black, sandy, silty, and calcareous shale Cerro Reservoir Drawdown Plan

7 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 In 2017, RJH collected soil samples from the eastern dam and the western dam in the vicinity of existing point source seepages. Recovered material consisted of mostly medium to high plasticity fines with between 4 and 21 percent sand. In 2018, RJH excavated test pits around the reservoir basin and advanced borings at and downstream of the western embankment. The data report summarizing these efforts is ongoing but embankment and foundation materials typically consisted of medium to high plasticity fines with minimal sand-sized particles Seepage Conditions Based on the 2017 Engineer s Inspection Report (SEO, 2017), active seepage was identified at the toe of the western dam and eastern dam, and active seepage was not identified downstream of the southern dam. Seepage conditions generally consist of relatively low gradient point source seepage flowing at a trickle. Additionally, boggy conditions typically persist downstream of the eastern dam Cerro Reservoir Drawdown Plan

8 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 2 - RESERVOIR DRAWDOWN PLAN 2.1 General The drawdown plan consists of slowly lowering the reservoir according to the drawdown schedule in this Plan and monitoring the slopes of the reservoir for signs of displacement or instability. Approximately the top 20.5 feet of the reservoir (El to El ) will be lowered using a siphon and the remaining 18.0 feet (El to El ) will be lowered using one or more centrifugal-type pumps (aka trash pump). Water removed from the reservoir will be discharged into the Canal downstream of the western embankment. Prior to beginning reservoir drawdown, City staff and RJH should review this Plan and the anticipated schedule. City personnel or subcontractors to the City who will be directly involved with dam and reservoir operations, monitoring, or surveillance activities should be familiar with this Plan. An initial inspection of the embankment and reservoir area prior to beginning the drawdown should be performed and documented. 2.2 Coordination The Canal Company has agreed to allow discharge of stored reservoir water to the Canal prior to September 15, During drawdown, discharge rates may need to be increased, if deemed safe with respect to slope stability, to meet this delivery schedule. Alert the SEO prior to initiating drawdown or making significant changes to the drawdown schedule. Alert RJH if slope instability or other dam safety problems arise. Alert the local emergency manager (Greg Fisher (970) ) of work being performed at the dam. 2.3 Schedule The drawdown schedule was developed based on our experience and is expected to change as drawdown progresses based on the performance of the embankment dams. The drawdown schedule generally consists of the following: Cerro Reservoir Drawdown Plan

9 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 Between El and El (top 22.5 feet) Lower the water surface 3 vertical feet at 0.5 vertical feet/day (6 days); hold for minimum 2 days at each 3- vertical-foot increment. Between El and El (bottom 16 feet) Lower the water surface 3 vertical feet at 1.0 vertical foot/day (3 days); hold for 2 days at each 3-verticalfoot increment. Monitor the embankment once a day during drawdown and once every 2 days during each hold period. An acceptable tolerance is ±2 vertical inches for any 1 day (total of 4 to 8 inches of vertical drop after 1 day) and 0 to -2 vertical inches between hold periods (total of 34 to 36 inches of vertical drop). The reservoir area-volume capacity curve is presented on Figure 2.1. A table of the drawdown schedule is provided in Appendix A. These schedules are only tentative because unforeseen circumstances (i.e., embankment stability, pumping or siphoning issues, etc.) could require reduced release rates Cerro Reservoir Drawdown Plan

10 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 3 - DRAWDOWN BY SIPHON 3.1 General The siphon consists of a pipe extended over the dam that, when filled (primed) with water, uses atmospheric pressure to force water through the pipe and over and downstream of the dam. The siphon is designed to operate continuously (24 hours a day). 3.2 Siphon Design The siphon consists of a 12-inch-diameter American Water Works Association (AWWA) C-900 poly vinyl chloride (PVC) pressure pipe with restrained bell and spigot gasket joints. The wall thickness is approximately 0.73 inch, which corresponds to dimension ratio 18 (DR-18). The siphon was located approximately 50 feet north of the existing outlet works on the western embankment because, at this location, the siphon will be within the excavation limits planned for the outlet works replacement but will not influence the existing outlet. The siphon will be notched approximately 6 feet into the embankment to maximize the operating range of the siphon. The notch will not introduce potential defects into the embankment dam because this material will be removed and replaced as part of the outlet works replacement. A plan and profile of the siphon is presented in Appendix C. Components illustrated on the schematic perform the following functions: Anti-vortex plate Prevents a whirlpool effect which could introduce air into the siphon and either reduce capacity or stop the siphon. Upstream and downstream gate valves Allows the system to be primed without the use of a vacuum pump, maintains prime when siphon is not operating, and allows the flow rate to be throttled. Priming port The priming port is used to prime the siphon. The ball valve can be used to seal the siphon after it has been primed. Air release standpipe The ball valves and standpipe can be used to periodically purge air that accumulates in the system. The siphon was designed to operate between El and approximately El A rating curve of the hydraulic capacity is presented on Figure 3.1. At El we expect the siphon to approximate the maximum lift limitation. Since siphon discharge is driven by atmospheric pressure the maximum lift of the siphon is limited by atmospheric Cerro Reservoir Drawdown Plan

11 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 pressure at the Site, and by friction and minor losses (i.e., bends, valves, etc.) in the siphon. At this Site, the available atmospheric pressure is approximately 22 inches of mercury (Hg) which corresponds to a 24.5-foot column of water. At El the siphon is predicted to lose approximately 1.1 feet of pressure head between the water surface and the invert of the siphon at the dam crest and the velocity head is expected to be approximately 0.4 foot. This leaves approximately = 23.0 feet of lift for the siphon. From the invert of the siphon at the dam crest (approximately El ) the lowest water level that the siphon will likely operate is El El Additionally, the level of the canal could be too high relative to the reservoir to provide sufficient differential head to drive the siphon. If the canal is at El and the reservoir is at El the expected volumetric flow rate is approximately 4 cubic feet per second (cfs), which is less than the required discharge at this elevation. Both of these alternatives are expected to reduce the feasibility of continued siphon use below El ; however, during operation, it is possible that the siphon elevation could be lowered a couple of feet. 3.3 Activating and Deactivating the Siphon and Maintenance Siphon operation is expected to be a dynamic process and the operational scenario is expected to evolve as drawdown progresses. General operation is expected to be achieved as summarized below. The siphon is activated as follows: Close the gate valves on the downstream and upstream ends of the siphon. Fill the upstream and downstream legs of the siphon with water by filling at the priming port and allowing air to escape from the vent. Close the ball valve on the priming port and the upper ball valve on the air release standpipe. Leave the lower ball valve on the air release standpipe open. Open the gate valves simultaneously. The siphon is deactivated as follows: Slowly close the gate valves on the upstream and downstream ends of the siphon. Slowly open the ball valve on the priming port. If siphon use is to be discontinued, open the gate valves to remove water from the upstream and downstream legs Cerro Reservoir Drawdown Plan

12 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 During operation air is expected to accumulate in the siphon which could deactivate the siphon. Sources of air include: air entrained in the reservoir water, air which enters at the downstream end, air which enters through fittings, and air which results from water vaporization at low pressures (cavitation). The system is designed with an air release standpipe for air removal. We expect that air can be removed using a combination of one of the following methods: 1. Bleed air from the system by slowly opening the air release standpipe ball valve. This may not be practical depending on minimum system pressure achieved. 2. Remove air as follows: a. Close bottom ball valve on air release standpipe. b. Open upper ball valve on air release standpipe. c. Fill air release standpipe with water and close upper ball valve on air release standpipe. d. Open bottom ball valve on air release standpipe. 3. Removed from the system using negative pressure generated by a vacuum pump connected directly to the air release standpipe. If the siphon periodically deactivates due to excessive air confirm the following: PVC pipe joints, fittings, valves, etc. are seated and air tight. Joints are not deflected in excess of manufacturer recommendations. Siphon outlet is adequately submerged in the Canal. Siphon intake is adequately submerged in the reservoir. Anti-vortex plate is functioning properly. If insufficient flow is present in the Canal to submerge the siphon outlet, additional fittings may need to be added in the field to prevent air from entering the siphon Cerro Reservoir Drawdown Plan

13 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 4 - DRAWDOWN BY PUMP 4.1 General Reservoir drawdown by pump consists of using a centrifugal pump to move water over and downstream of the dam. The selected pump will need to operate continuously (24 hours a day). 4.2 System Components We expect that the siphon pipe will be used as the discharge pipe to convey water over the dam and into the canal. As the reservoir is lowered the pump may need to be relocated toward the water surface to avoid causing cavitation in the pumping equipment. The pump will likely operate at the following head and discharge rates: 7.5 cfs, 3,400 gpm, 24.5 foot static head, 75 feet of total pumping head (TPH) 4 cfs, 1,800 gpm, 40.5 foot static head, 55 feet of TPH Pumping may need to be initiated near the bottom operational limits of the siphon to supplement discharge capacity and maintain the tentative release schedule presented in Section Cerro Reservoir Drawdown Plan

14 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 5 - EMBANKMENT MONITORING DURING DRAWDOWN 5.1 Rapid Drawdown Failure Mode Lowering the reservoir level has the potential to cause a rapid drawdown upstream slope failure in the embankment dams. This failure mode develops when the stabilizing buttress of reservoir water is removed faster than water can drain out of the embankment fill. Embankment fill at this Site is particularly susceptible to this failure mode because of the lack of granular free draining material and relatively high plasticity (relatively high plasticity material will tend to retain water longer than lower plasticity material). A rapid drawdown failure would manifest as a displaced wedge or block and would generally resemble a landslide. If the landslide is large enough it could potentially capture the dam crest and create an uncontrolled release of the reservoir potentially causing substantial damage to property and loss of life. Within the reservoir basin a rapid drawdown failure could cause a large block or wedge of upstream slope embankment to rotate into the reservoir basin. To mitigate this potential failure mode we have set limitations on the drawdown rate (vertical feet per day) and have required hold periods to evaluate embankment drainage and allow excess porewater additional time to partially drain. 5.2 General Embankment Monitoring Monitoring the upstream slope for a rapid drawdown failure consists of methodically and consistently observing the slope and halting the drawdown if a change in conditions is observed. During a day when a release is made the embankment should be monitored once daily. During a day when the reservoir level is held constant the embankment should be monitored at least every other day. Monitoring shall include the following activities: Measure the reservoir water level drop in elevation. Using this change in elevation and the reservoir stage/area/capacity table, estimate the discharge flow rate from the siphon and pumps. Adjust flow rate as necessary to hit target drawdown elevations. Embankment Inspection Observe the upstream embankment slope, crest, and downstream slope; take photographs at defined locations and areas of concern; stake areas of potential changing conditions for additional monitoring; and fill out on observation form Cerro Reservoir Drawdown Plan

15 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 If there are indications of developing slope instability (cracks, embankment displacement, scarps or slides), stop reservoir drawdown and contact RJH for further evaluation. Monitoring activities are described in the following sections. 5.3 Reservoir Level Monitoring Careful monitoring of the reservoir level is critical for embankment stability as well as maintaining the drawdown schedule. To measure the elevation change in the reservoir we recommend staking a temporary control point near the edge of the water surface along the left abutment of the western embankment and sighting to this control point with an Engineer s hand level or a self-leveling level during drawdown. At each 3-foot drop additional temporary control points should be installed to track progress of the drawdown and provide redundant control points. The temporary control points should be adequately embedded in the subgrade to prevent displacement or vandalism during drawdown. 5.4 Embankment Inspection Embankment inspection consists of walking the length of each embankment (total of three embankments) and sighting the slopes and crest from various angles to detect development of a rapid drawdown slope instability. We have the following recommendations regarding routine inspections of an embankment dam: Maintain Consistent Personnel Personnel responsible for inspection should be consistent throughout the drawdown to maintain continuity and increase their ability to identify changing conditions. Inspection Direction Reverse the direction of the inspection every other day because some features may be more apparent from a different angle. Inspection Time Maintain a consistent inspection time to provide a consistent comparison between photographs. Inspection Photographs Take photographs of areas where potentially changing conditions are occurring and at consistent locations along each embankment slope and crest. Consistent photographs can be used to identify changing conditions. Inspection Forms A Site-specific inspection form has been created for this drawdown and is provided in Appendix B. A plan of the dams to assist in spatially locating concerning features is provided as Figure B.1 in Appendix B Cerro Reservoir Drawdown Plan

16 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 Inspection Equipment Engineer s hand level, tape measure, hiking staff, camera, adequate supply of lath and flagging, felt-tipped marker, cellular phone, Emergency Action Plan (EAP), this Plan, and safety equipment. A rapid drawdown failure will likely display the following characteristics prior to and following movement of a large wedge or block: Concentrated Seepage This feature will consist of water flowing out of a single location or a series of locations in the upstream slope riprap or earthen slope above the reservoir water surface. Shallow Depression or Bulge in the Slope This feature can be identified as a subtle change from a continuous slope and could indicate the initiation of a rotational slope failure. To identify a depression or bulge sight along the slope to observe for slight changes in slope grade (slope angle). Cracking This feature generally consists of unexplained separation between two materials or within a single material. A crack is an initial sign of a mass movement and could be present along the upstream slope, crest, or even the downstream slope if the displaced wedge is large enough. Mass Movement, Scarp, and Debris Pile This feature consists of a slope failure where the scarp is a distinct near-vertical step along the upslope edge and the debris pile is the mass of material which has slid off the slope toward the toe of the slope. If any of these conditions are observed, except consistent concentrated seepage, perform the following: Stake the vertical and horizontal limits of the observed feature. Measure pertinent dimensions including the width, length, approximate elevation, and height of the scarp, bulge, and crack width (if applicable). Take lots of photographs. Observe the feature closely and document seepage, cracking, or soft material. Contact RJH immediately for further evaluation and to determine necessary remedial measures. 5.5 Reporting At the conclusion of each day send an electronic copy of reports and photographs to RJH for review Cerro Reservoir Drawdown Plan

17 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 6 - CONTINGENCY PLAN Below is a list of potential issues that could occur during the drawdown and the suggested mitigation plan to respond to the issue. Based on observed conditions, more aggressive actions may be required than those listed below. Potential Issue: Concentrated seepage observed Description: Water is observed flowing out of a single location or a series of locations in the riprap or earthen slope into the reservoir. Actions: If concentrated seep is within 1 vertical foot of the water surface continue to monitor. If concentrated seep is greater than 1 vertical foot of the water surface stop the reservoir release and hold the water level constant until the concentrated seep dissipates. Notifications: RJH. Potential Issue: Shallow depression or bulge is observed Description: A shallow depression or bulge is observed along a reach of embankment where the slope was previously consistent. Actions: Continue to draw down and monitor the feature. If the feature progresses halt the reservoir drawdown and monitor. Notifications: RJH. Potential Issue: Mass movement, scarp, or debris pile Description: A mass movement is observed along a reach of embankment where the slope was previously consistent. Actions: Stop the reservoir drawdown. Notifications: RJH Cerro Reservoir Drawdown Plan

18 Cerro Reservoir Drawdown Plan Cerro Reservoir Outlet Works Replacement Project May 2018 SECTION 7 - REFERENCES Colorado Office of the State Engineer (SEO, 2017). Engineer s 2017 Inspection Report. Cerro Dam, Dam ID (620105). Construction File Number C-644 (C-644, 1953). Enlargement Plans for Cerro Reservoir Dam. Construction File Number C-644A (C-644A, 1966). Cerro Reservoir Enlargement. Del-Mont Construction Surveyors (Del-Mont, 2017). Existing Site Survey for Cerro Reservoir, Montrose County, CO. Job No Dickinson, Robert G. (Dickinson, 1963). U.S. Geological Survey (USGS), Geologic Map of the Cerro Summit Quandrangle, Montrose County, Colorado. GQ-486 Steven, T.A. and Hail, W.J. Jr. (Steven and Hail, 1989). U.S. Geological Survey (USGS), Geologic Map of the Montrose 30 x60 Quadrangle, Southwestern Colorado. MAP I Cerro Reservoir Drawdown Plan

19 APPENDIX A TENTATIVE SCHEDULE AND DISCHARGE RATES

20 6/1/2018 Start Date 0.5 Release Rate (ft/day) 7980 Low Elevation (feet) 1 Low Elevation Release Rate (ft/day) Tentative Release Schedule Day Date Week Day Target Elevation Drop Water Surface Elevation Storage (acrefeet) Released Volume (acreft) Release Rate (cfs) (24 hours per day) 0 6/1/2018 Monday /2/2018 Tuesday /3/2018 Wednesday /4/2018 Thursday /5/2018 Friday /6/2018 Saturday /7/2018 Sunday /8/2018 Monday /9/2018 Tuesday /10/2018 Wednesday /11/2018 Thursday /12/2018 Friday /13/2018 Saturday /14/2018 Sunday /15/2018 Monday /16/2018 Tuesday /17/2018 Wednesday /18/2018 Thursday /19/2018 Friday /20/2018 Saturday /21/2018 Sunday /22/2018 Monday /23/2018 Tuesday /24/2018 Wednesday /25/2018 Thursday /26/2018 Friday /27/2018 Saturday /28/2018 Sunday /29/2018 Monday /30/2018 Tuesday /1/2018 Wednesday /2/2018 Thursday /3/2018 Friday /4/2018 Saturday /5/2018 Sunday /6/2018 Monday /7/2018 Tuesday /8/2018 Wednesday /9/2018 Thursday /10/2018 Friday /11/2018 Saturday /12/2018 Sunday /13/2018 Monday /14/2018 Tuesday /15/2018 Wednesday /16/2018 Thursday /17/2018 Friday /18/2018 Saturday /19/2018 Sunday /20/2018 Monday /21/2018 Tuesday /22/2018 Wednesday /23/2018 Thursday Approx elevation to start pumping. P:\ Cerro Outlet Works Replacement\Engineering\Task Reservoir Drain Plan\Drain Plan\Attachment A - Release Schedule.xlsx Sheet1 1/2

21 6/1/2018 Start Date 0.5 Release Rate (ft/day) 7980 Low Elevation (feet) 1 Low Elevation Release Rate (ft/day) Tentative Release Schedule Day Date Week Day Target Elevation Drop Water Surface Elevation Storage (acrefeet) Released Volume (acreft) Release Rate (cfs) (24 hours per day) 53 7/24/2018 Friday /25/2018 Saturday /26/2018 Sunday /27/2018 Monday /28/2018 Tuesday /29/2018 Wednesday /30/2018 Thursday /31/2018 Friday /1/2018 Saturday /2/2018 Sunday /3/2018 Monday /4/2018 Tuesday /5/2018 Wednesday /6/2018 Thursday /7/2018 Friday /8/2018 Saturday /9/2018 Sunday /10/2018 Monday /11/2018 Tuesday /12/2018 Wednesday /13/2018 Thursday /14/2018 Friday /15/2018 Saturday /16/2018 Sunday /17/2018 Monday /18/2018 Tuesday /19/2018 Wednesday /20/2018 Thursday /21/2018 Friday /22/2018 Saturday /23/2018 Sunday /24/2018 Monday P:\ Cerro Outlet Works Replacement\Engineering\Task Reservoir Drain Plan\Drain Plan\Attachment A - Release Schedule.xlsx Sheet1 2/2

22 APPENDIX B INSPECTION FORMS

23 Date and Time: Inspector: Weather: Reservoir Elevation (1) Hold Period Yes No CERRO RESERVOIR DRAWDOWN MONITORING REPORT Observation Steps 1. Fill out paperwork for every inspection, whether or not concerning features are observed. 2. If concerning features are observed perform the following: a. Stake vertical and horizontal limits. b. Measure pertinent dimensions (refer to table below). c. Observe feature closely and document seepage, cracking, and soft material. d. Take photographs of the entire feature and close-ups of unique features. Include scale (tape measure, etc.) in photograph, as appropriate. e. Contact RJH (Mike Graber ), as appropriate, (303) (RJH Office). Feature Number (2) Existing Feature (3) Feature (4) Starting Station (5) Length (5) (ft) Elevation (5) (ft) Offset (5)(6) (ft) Notes (7) Western Embankment Southern Embankment Eastern Embankment 1. Water Surface Vertical Distance Below Spillway Flowline: 2. Example W-001 for the first observation at the western embankment. 3. Mark X if the observation was observed on a previous day. 4. Example: Concentrated Seepage (Conc Seep), Depression (Dep) or Bulge, Cracking (crack), Mass Movement (slide) 5. Dimensions are approximate. 6. Width of crack or height of scarp at location of mass movement. 7. If feature has not changed for six days, consider closing out observation point

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25 APPENDIX C SIPHON DESIGN DRAWINGS

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32 SEE BID PACKET FOR DETAIL REGARDING MATERIALS AND WORK PERFORMED BY OTHERS

33 APPENDIX D EXISTING CONSTRUCTION INFORMATION

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