Little Blue Run Impoundment History of Construction

Transcription

1 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station Beaver County, Pennsylvania October 2016 Prepared for: FirstEnergy Generation, LLC 800 Cabin Hill Drive Greensburg, Pennsylvania Prepared by: GAI Consultants, Inc. Murrysville Office 4200 Triangle Lane Export, Pennsylvania

2 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Page i Table of Contents 1.0 Purpose Introduction Construction Summary of Impoundment and Embankment References... 4 Table 1 Table 2 Figure 1 Appendix A Appendix B Appendix C Main Dam Core Material Engineering Properties Saddle Dam Material Engineering Properties Site Location Map Drawings Stage-Storage Curve Design Calculations for Spillways 2016 GAI CONSULTANTS C / October 2016

3 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Page Purpose This report, the Construction History of Bruce Mansfield Power Station Little Blue Run Impoundment, covers the following criteria listed in the Code of Federal Regulations (CFR) Coal Combustion Residuals (CCR) Rule 40 CFR (c)(1), to the extent feasible. Name and size of the watershed within which the CCR unit is located Location map Physical and engineering properties of materials used in embankment construction and the approximate dates of construction Site preparation and construction methods for each zone Detailed drawings Description of the existing instrumentation Area capacity curves Spillway and diversion features description, capacities, and calculations Construction specifications and provisions for surveillance, maintenance, and repair Any record or knowledge of structural instability 2.0 Introduction The Bruce Mansfield Power Station (Station) is a coal-fired electric generating station located in Shippingport, Beaver County, Pennsylvania (PA). The Station consists of three generating units, which are capable of producing 2,490 megawatts of electricity. CCRs generated at the Station are placed in the Little Blue Run CCR Surface Impoundment (Impoundment), which is located approximately 4.5 miles west of the Station. The location is shown on the USGS 7.5-minute topographic quadrangle map provided as Figure 1. According to the United States Geological Survey (USGS), the Impoundment is located in the Upper Ohio watershed (USGS Hydrologic Unit Code ). The Upper Ohio watershed area, according to the USGS, is 1,248,000 acres. The purpose of the Impoundment is to receive CCRs generated at the Station. The Impoundment is permitted under the following: National Pollutant Discharge Elimination System Permit No. PA Solid Waste Permit No PA Department of Environmental Protection (PADEP) Dam Permit I.D. D (Main Dam) PADEP Dam Permit I.D. D (Saddle Dam) PADEP Site I.D (Alternate I.D.) 3.0 Construction Summary of Impoundment and Embankment The Impoundment was constructed on the Allegheny and Conemaugh Formations. The Allegheny Formation consists primarily of sandstone, sandy shale, and shale with lesser amounts of claystone, limestone and coal. The Conemaugh Formation consists of shale, claystone, and sandy shale with lesser amounts of sandstone, limestone and coal. Little Blue Run has no stormwater diversion features; stormwater is regulated through the Secondary Spillway. The Operations and Maintenance Plan, developed for FirstEnergy Generation, LLC in February 2014, outlines the requirements for monitoring, inspection, and maintenance of the Impoundment. C / October 2016

4 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Page 2 Based on the information reviewed, there have been no identified safety issues at the Little Blue Run Dams. 3.1 Main Dam The Main Dam is a curved, rock fill embankment with a sloping impervious core on the upstream side. According to as-built drawings (see Appendix A), the core is trapezoidal and is approximately 13-feet thick near the embankment crest [approximately 1,094 feet above National Geodetic Vertical Datum (NGVD)] and 70-feet thick at the base (approximately 730 feet above NGVD) as measured perpendicular to seepage flow. The core is protected by thick filters and a shell of sound, durable sandstone. An impervious blanket and seepage collection system are installed under the dam. The physical and engineering properties of the materials used in construction of the Main Dam core are listed in Table 1. Construction of the Main Dam embankment began in June 1974 and was completed in May Table 1 lists the properties of the materials used in constructing each zone of the dam. Construction occurred continuously to the final embankment elevation (1,100 feet above NGVD) except for a major shutdown period due to extreme weather conditions, which occurred in January The Main Dam embankment was constructed in five zones according to construction specifications by Gibbs & Hill, Inc.: Zone 1: Impervious core material. Placed and spread in 10-inch uncompacted lifts; moisture was applied uniformly as needed, and each layer was compacted to 95 percent of maximum dry density as determined by ASTM International (ASTM) Specification D Zone 2: Random rock material. Zone 3: Resistant sandstone material. Placed and spread in lifts not exceeding three feet, and subjected to a vibratory roller for compaction. Zone 4: Resistant and semi-resistant rock material. Placed and spread in lifts not exceeding three feet, and subjected to a vibratory roller for compaction. Zone 5: Non-resistant rock transition material. Placed and spread in uncompacted lifts not exceeding 12-inches; moisture was applied uniformly as needed, and each layer was compacted to 95 percent of maximum dry density as determined by ASTM D Zones 2, 3 (downstream of embankment), and 4 are constructed on top of a filter blanket layer. Two perforated, one-foot diameter, poly vinyl chloride drain pipes, embedded within the foundation filter underdrain system, extend along the toe of the embankment on both abutments. Both pipes drain the foundation blanket underdrain by gravity to a concrete sump at the toe of the embankment. The sump drains into a toe drain pipe, which discharges into the Stilling Basin. The Main Dam was constructed with the following instrumentation: Upper Left Abutment Weir: measures flow from the spring on the left abutment. Lower Left Abutment Weir: measures flow from the spring on the left abutment. Right Abutment Weir: measures discharge flow from the secondary spillway. Right Abutment Flume 1: secondary monitoring station for secondary spillway discharge. Right Abutment Flume 2: measures flow that can be diverted to a nearby pilot plot of vegetation. Toe Drain Parshall Flume: measures seepage flow collected by the underdrain system of the embankment. Standpipe-type Piezometers (12): measure the water levels at locations indicated below. C / October 2016

5 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Page 3 Two piezometers are located in the filter blanket/underdrain system along the dam embankment. Two piezometers are located on the downstream edge of the crest of the dam embankment. Three piezometers are located on the ridge line between the dam and the emergency spillway on the left abutment. Five piezometers are located on the slope between the dam and the service spillway right-of-way on the left abutment. Surface monuments (22): measure the horizontal movement and settlement of the embankment. Nine monuments installed on the upstream surface of the embankment. Thirteen monuments installed on the downstream surface of the embankment. The Impoundment utilizes three spillways that could potentially discharge water: The Service Spillway, located on the left abutment ridge line, discharges through a 48-inch diameter concrete pipe into the Stilling Basin. Discharge up to 112 cubic feet per second (cfs) at 1,100 feet reservoir elevation. The Emergency Spillway, located on the left abutment ridge line, discharges through a 160-foot wide trapezoidal labyrinth weir into the Little Blue Run valley downstream of the Stilling Basin. Discharge up to 24,973 cfs at 1,100 feet reservoir elevation. The Secondary Spillway, located on the right abutment, discharges through an 18-inch diameter concrete pipe that regulates normal pool elevation. Discharge up to 26.5 cfs at 1,090 feet reservoir elevation. The spillway calculations are included as Appendix C. 3.2 Saddle Dam The Saddle Dam embankment was constructed with an internal core and a downstream embankment toe drainage system. The physical and engineering properties of the material used for the construction of the Saddle Dam are listed in Table 2. The Saddle Dam was constructed during the same period as the Main Dam. Construction occurred continuously to the final embankment elevation (1,100 feet above NGVD). The embankment is constructed of medium dense, sandy lean clay over very dense residual weathered shale. The rock underlying the embankment is silty to sandy shale with interbedded siltstone and claystone seams. The construction specifications used are the same as were used for the Main Dam. The Saddle Dam was constructed with the following instrumentation: Standpipe-type piezometers (2): measure the water levels at locations indicted below. One piezometer is located on the crest of the embankment. One piezometers is located on the downstream toe of the embankment. C / October 2016

6 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Page References GAI Consultants, Inc. Summary of Field Density Tests. Varies, GAI Consultants, Inc. Coal Combustion Residual Annual Report. January GAI Consultants, Inc. Little Blue Run - Dam Permit Application Impoundment Closure Plan - H&H Analyses. December GAI Consultants, Inc. Cumulative Pumping Record from 1975 to 1979, Sludge Drilling, Sampling and Testing Program, Little Blue Run Dam. Unknown date. GAI Consultants, Inc. Little Blue Run Dam, Existing Hydraulics May 2004, Secondary Spillway Discharge. May GAI Consultants, Inc. Inspection and Evaluation Report No. 15. February GAI Consultants, Inc. Inspection and Evaluation Report No. 20. June GAI Consultants, Inc. Inspection and Evaluation Report No. 21. August GAI Consultants, Inc. Inspection and Evaluation Report No. 22. December GAI Consultants, Inc. Inspection and Evaluation Report No. 28. July GAI Consultants, Inc. Inspection and Evaluation Report No. 81. January GAI Consultants, Inc. Inspection and Evaluation Report No. 85. September GAI Consultants, Inc. Inspection and Evaluation Report No December GAI Consultants, Inc. Dam Permit Application. February General Analytics, Inc. Preliminary Geologic Evaluation, Little Blue Run Sludge Disposal Area. July Gibbs & Hill, Inc. Little Blue Run, Impoundment Dam and Related Facilities, General Construction, Specification No S-4. April Gibbs & Hill, Inc. Plot Plan Impoundment Gibbs & Hill, Inc. Impoundment Dam, Typical Design Section of Embankment and Details. July Montana State University Environmental Statistics Group. Upper Ohio Cataloging Unit Retrieved June 7, C / October 2016

7 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania TABLES C / October 2016

8 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania Group A1 B2 Test Pit Number Test Type Sample Number Max. Dry Unit Weight Density (PCF) Modified Proctor Optimum Water Content (%) Table 1 Main Dam Core Material Engineering Properties Triaxial Consolidation Pressure (TSF) Dry Unit Weight Density (PCF) Tested Water Content (%) Permeability (cm/sec) Friction Angle φ or φ u (Degrees) Strength Cohesion C or C u (TSF) C C Consolidation 3 Permeability (constant head) Consolidation Triaxial Unconsolidated Undrained Triaxial Consolidated Undrained φ u 21.0 φ 27.1 C u 1.70 C 0.56 C F Void Ratio Permeability (constant head) Consolidation to Triaxial Unconsolidated Undrained Triaxial Consolidated Undrained φ u 13.5 φ 21.3 C u 1.60 C B1 5 Permeability < A2 30 Permeability Design Values Used φ u = 13.5 φ = 24.2 C u = 1.60 C = Notes: Table 2 Saddle Dam Material Engineering Properties Soil/Layer Number Description Total Unit Weight Saturated Unit Weight Cohesion Friction Angle (PCF) (PCF) (TSF) (Degrees) 1 Brown Sandy Lean Clay Brown Sandy Lean Clay Brown Sandy Lean Clay Brown Sandy Silt Decomposed Rock Bedrock PCF = Per Cubic Foot TSF = Tons per Square Foot CM/SEC = Centimeters per Second φ = Effective Angle of Internal Friction φ u = Angle of Internal Friction (Total Stress Analysis) C = Effective Cohesion C u = Cohesion (Total Stress Analysis) C C = Compression Index C F = Recompression Index C / October 2016

9 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania FIGURE C / October 2016

10 DRAWING TITLE DRAWN BY: HARRIWJ SITE LOCATION MAP PROJECT CLIENT LITTLE BLUE RUN FIRSTENERGY REVISION A/0 CHECKED BY: APPROVED BY: WALLAMJ SCALE: ISSUE DATE: AS SHOWN 06/13/2016 SHEET NO.: 1 OF 1 GAI FILE NUMBER: NO.: DATE: DWN: CHK: APV: DESCRIPTION: REVISION RECORD ISSUING OFFICE: Murrysville 4200 Triangle Lane, Export, PA HISTORY OF CONSTRUCTION GREENSBURG, PENNYLVANIA C C-B1-001 GAI DRAWING NUMBER: B2-001

11 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania APPENDIX A Drawings C / October 2016

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18 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania APPENDIX B Stage-Storage Curve C / October 2016

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21 Little Blue Run Impoundment History of Construction FirstEnergy Generation, LLC Bruce Mansfield Power Station, Beaver County, Pennsylvania APPENDIX C Design Calculations for Spillways C / October 2016

22 Murrysville Office T Triangle Lane F Export, Pennsylvania /15/2016 Project C Spillway Calculations Included in this calculations package are the calculations for the following spillways: Primary Spillway Secondary Spillway Emergency Spillway Hydrology and hydraulics (H&H) calculations were prepared for all spillways during closure conditions of the impoundment ( Little Blue Run Impoundment Closure H&H Analyses, Sheets 6, 9, 10, and 12-19). The proposed modifications to the secondary spillway listed in these calculations (Sheet 13) have not been constructed. The Little Blue Run Dam Existing Hydraulics: Secondary Spillway Discharge present the current operating conditions of the secondary spillway GAI CONSULTANTS

23 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 6 OF 19 RESERVOIR HYDROLOGY Modifications to the Little Blue Run Dam emergency spillway were designed and constructed between 2005 and At that time, the hydrologic parameters for the dam watershed were determined to be: Drainage Area = 1833 acres = 2.86 square miles Runoff Curve Number = 79 Lag Time = 1.64 hours - Reference, November 21, 2005 letter from GAI to Roger Adams of PaDEP, Division of Dam Safety The watershed boundary and time of concentration flow path worksheet are shown on the next 2 pages. The time of concentration calculation from 2005 is shown on sheet 9. Based on a comparison of the flow path worksheet from 2005 to closure plans used in this assessment, the time of concentration from 2005 can be considered appropriate for current use. Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

24 Little Blue Run Project By: KMB 13Oct2005 Checked by: Date: Time-of-concentration, t c Sheet Flow t c Estimate Shallow Concentrated Flow t c Estimate Slope Estimate Slope Estimate FLOWPATH Flowpath Surface Description Manning's n Flow Length (feet) 2-year, 24-hour Rainfall Upslope Elevation Downslope Elevation Slope tc (hour) Flowpath Surface Description Upslope Elevation Downslope Elevation Flow Length (feet) Slope Velocity (fps) tc (hour) 2 a-b grass b-c unpaved d-e unpaved f-g unpaved TOTALS Channel Flow t c Estimate Slope Estimate Flowpath B (feet) Side Slopes, z Assumed Flow Depth (feet) Flow Area (sq. feet) Wetted Perimeter (feet) Hydraulic Radius (feet) Length (feet) Upslope Elevation Downslope Elevation Slope Channel Lining Manning's n Velocity (fps) tc (hour) TOTAL (hours) c-d rock e-f grass LAG TIME = 0.6 * tc = 1.64 hours P:\1991\91511\D46\xls\tc revised path oct 05 kmb.xls, Tc (2010)

25 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 10 OF 19 The design storm event for both the Little Blue Run Dam and the Saddle Dam is the Probable Maximum Precipitation (PMP). The dam watershed, time of concentration, and PMP precipitation distribution will be constant over the closure period. Conditions within the watershed will vary as closure activities progress. The worst-case hydrology will be that which would show the largest runoff volume expected during the closure activities and will be the condition analyzed in these calculations. With the consideration that impounded water would produce the largest runoff, since there would be no infiltration, the material disposal plans (sheets 2-5) indicate that the worst-case hydrology would occur in the planned impoundment configuration for 2014 (sheet 2), which yields the largest acreage of impounded water. The area within the impoundment available for stormwater storage will be minimized after placement of cover soil (see the next page). Stage-storage data for the impoundment will therefore be determined with cover soil in place. Total watershed size = 2.86 square miles 1,830 acres Evaluate watershed conditions in 2014 Water acreage for 2014 is taken from the existing normal pool at elevation Area of terrain type (ac) Watershed Water FGD Mulched Revegetated Outside Pool Limits Total Weighted CN Water FGD Outside pool Total Use the following Curve Number Values: Water 100 FGD 90 Mulched 75 Revegetated with Cover Soil 72 Outside of Pool Limits 73 Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

26 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 12 OF 19 VERTICAL DATUM All references to the dam and its outlet devices are in the NGVD29 vertical datum. Contours within the reservoir and impoundment as shown on the phasing drawings represent NAVD datum. A 2011 study utilized VERTCON, a software program through the National Oceanic and Atmospheric Administration (NOAA), to provide for a conversion between the two datums at the project site: Results: Elev NAVD88 Elev NGVD29 = meters Elev NGVD29 = Elev NAVD meters = Elev NAVD feet Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

27 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 13 OF 19 RESERVOIR STAGE STORAGE As seen on the proposed modification to the secondary spillway, which controls normal pool elevation, the new normal pool in the Little Blue Run reservoir will be at elevation 1082: 1082 will be the starting water surface elevation for reservoir modeling. Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

28 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 14 OF 19 Based on the reservoir mapping, the following stage-storage relationship is determined, assuming 0 storage at elevation (just below normal pool): Stage-Storage above elevation 1081 NAVD88 NGVD 29 Avg Area Inc Vol Cum Vol Elev (ft) Elev (ft) Area (ac)* (ac) (ac-ft) (ac-ft) , , ,288 3,168 *Determined from the NAVD88 contours on the mapping Bold italic areas are interpolated Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

29 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 15 OF 19 DAM HYDRAULICS The Little Blue Run Dam contains three discharge mechanisms: A Secondary Spillway, installed in 2001 to maintain a normal pool in the reservoir around elevation The Service Spillway, used to convey discharge to the stilling basin downgradient of the dam The Emergency Spillway, reconstructed as a labyrinth in 2007 Secondary Spillway Given that the secondary spillway is used to control day-to-day pool levels in the impoundment, do not consider it as a discharge mechanism for PMP events. The proposed normal pool (elevation 1082) will be used as the starting water elevation in the impoundment for modeling. Service Spillways A 2003 calculation determined the stage-discharge rating curve for the service spillway. The rating curve is: Pool Elevation (feet) Discharge (cfs) source 2003 calculation Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

30 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 16 OF 19 The emergency spillway was re-designed as a labyrinth weir in Summarizing the design analyses, the emergency spillway stage discharge curve is: Pool Elevation (ft) Discharge (cfs) , , , , , , , ,973 The overall stage-storage-discharge rating curve for the dam is therefore: Service Spillway Emergency Spillway Net Elev (ft) Stor (ac-ft) Discharge (cfs) Discharge (cfs) Discharge (cfs) ,435 1, ,916 3, ,106 7, ,572 9, ,874 10, ,140 15, ,853 19, ,973 25,085 Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

31 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 17 OF 19 DESIGN STORM The design storm for the dam is the Probable Maximum Precipitation (PMP). Historically, the PMP distribution for the dam has been: Time (hr) Precipitation (in) To enable modeling in HEC-HMS, Figure 18 from the 1973 ed. of Design of Small Dams gives precipitation distributions for durations less than 6 hours: Ratio to 6-hour Time amount 15 minutes hour hours hours hours 1 Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

32 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 18 OF 19 The PMP precipitation distribution is therefore: Time (hr) Precipitation (in) Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

33 SUBJECT LITTLE BLUE RUN DAM PERMIT APPLICATION IMPOUNDMENT CLOSURE PLAN - H&H ANALYSES BY KMB DATE 12/13/2013 PROJ. NO.C CHKD. BY KMB2 DATE 01 /16 /2014 SHEET NO. 19 OF 19 PMP EVENT A potential PMP event was modeled in HEC-HMS for the conditions anticipated in 2014 (the worst hydrologic case). A 48-hour storm duration was used. Under this storm event, discharge through the secondary spillway was not considered. The model results are: The peak pool elevation = This produces 3.4 feet of freeboard and is acceptable. Z:\Energy\2013\C LBR Dam Permit App\Working Docs\H and H\LBR Closure H and H calcs.doc

34 GAI Project by KMB 09/17/2004 LITTLE BLUE RUN DAM EXISTING HYDRAULICS - MAY 2004 SECONDARY SPILLWAY DISCHARGE The design flow is based on an allowable discharge of 10 million gals. per day which is 6,944 gallons per minute = 15.5 cfs There are three components involved in getting flow into the riser: The secondary spillway discharges through the dam abutment into a concrete outlet structure. Based on the configuration of the outlet structure and the secondary spillway design hydraulics, it is apparent that inlet control will determine flow through the spillway pipe. 1. Estimate the range of flows for various pool elevations assuming free flow through the pipe (i.e. the flow control valve is fully open and does not throttle the flow). Assume square edge with headwall condition (most conservative results). Secondary Spillway invert elevation 1080 ft Secondary Spillway interior diameter 18 inches (pipe is 22" SDR 11 HDPE) Pipe length - use 510 ft Head loss coefficient for valves = S k v For the gate valve, use k v = 0.07 The flow control pinch valve will have very minor losses; use S k v = 0.2 Head loss coefficient for entrance (outlet control flow) k e 0.5 (from E&S Plan, 8/2001, pg 7 of calcs) Manning's n for HDPE pipe Use a tailwater elevation = 1061 ft The next page shows the inlet control chart from HDS-5 for concrete pipes (assume valid for HDPE) Outlet control will be computed by H = [ 1 + k e + k v + ( 29n 2 L / R 1.33 ) ] [ V 2 / 2g ] Elevation at pipe inlet (ft) HW (ft) HW/D Flow (cfs) Flow (gpm) A (sf) R (ft) V (ft/s) H (ft) Req'd HW elev. outlet control (ft) , , , , , , , , The inlet control elevations shown above control for all cases. Secondary Spillway Flows