JAMES RIVER DAMS TECHNICAL REPORT. Prepared for : City of Richmond Department of Public Utilities

Transcription

1 ARCHITECTS ENGINEERS CONSULTANTS JAMES RIVER DAMS TECHNICAL REPORT Prepared for : City of Richmond Department of Public Utilities Manchester Dam Browns Island Dam Belle Isle & Belle Isle North Dams Hollywood Dam SUBMITTED BY: Dewberry 4805 Lake Brook Dr., Suite 200 Glen Allen, Virginia SUBMITTED TO: City of Richmond Department of Public Utilities 1400 Brander Street Richmond, VA 23224

2 TABLE OF CONTENTS FINAL ENGINEERING ASSESSMENT AND RECOMMENDATIONS... 2 Project Background... 2 Manchester Dam... 2 Browns Island Dam... 2 Belle Isle and Belle Isle North Dams... 4 Hollywood Dam... 5 Sunny Day Breach of Hollywood Dam... 6 Estimated Construction Cost Estimates... 7 Appendix A DCR Requirements... 8 Appendix B Dam Repair Cost Estimates... 9 Appendix C Inspection Reports and Site Photos

3 FINAL ENGINEERING ASSESSMENT AND RECOMMENDATIONS Project Background Dewberry inspected five (5) run of the river dams located on the James River in November of Dewberry prepared inspection reports for the five dams utilizing DCR Form This memorandum summarizes the condition of the dams, categorizes the dams in accordance with DCR regulations, assesses the stability and structural condition of the dams, and makes recommendations regarding repairs and improvements for the five dams. A dam shall be regulated by the state of Virginia if the dam is 25 feet or greater in height and creates an impoundment capacity of 15 acre feet or greater, or the dam is six feet or greater in height and creates an impoundment capacity of 50 acre feet or greater. Manchester Dam DCR Regulation The Manchester Dam is 2,220 feet long and varies in height. The dam is approximately four feet high on the north end of the dam. The height gradually increases to 6 feet where the dam ties into the south side of the river near the Army Corps Flood wall. There are three breaches in the dam where water can freely pass near the south bank of the James River. The dam has a 250 wide gap near the north bank of the James River. The breaches are used for fish passage and recreational boating. Per discussions with DCR, it was agreed that the Manchester Dam does not meet the state regulation criteria because the impoundment volume is roughly 30 acre feet and the maximum dam height is estimated at 6 feet. Final Assessment and Recommendations The majority of the Manchester Dam is a cast in place concrete, gravity dam. A short section of the dam, approximately 340 feet long, near the south bank of the James River is constructed of large stacked stones with a poured concrete cap. The concrete sections of the dam appear to have been poured directly on bedrock as no evidence of a mechanical anchor tying the dam to the bedrock was observed. Therefore, the dam is most likely relying on the weight of the concrete mass and friction at the interface of the bedrock and concrete to prevent it from overturning or sliding. Structural concerns for the Manchester Dam are limited to discrete, localized areas of concrete damage. The concrete cap along the top of dam exhibits signs of erosion in the form of the loss of the cement paste and exposed aggregate. During the inspection, water seepage through the vertical and horizontal cold joints between concrete pours was observed in several locations. Recommendations for the dam include resurfacing of the spalled and eroded areas (surficial) of the concrete dam using concrete repair materials. Eroded areas (cavities) at the base of the dam should be filled with lean concrete (flowable fill). In addition, debris and organic growth that has accumulated along the crest of the dam should be removed. Browns Island Dam DCR Regulation The Browns Island Dam (also known as the VEPCO Slot Dam) is 1,680 feet long and is divided into two distinct sections. The first section ties into the retaining wall on the north side of the river and runs for 2

4 1,250 feet. It is estimated that this portion of the dam varies in height between 3 and 6 feet. The dam acts as an inline weir with water constantly flowing overtop of the dam. There are 33 piers spaced at approximately 36 feet on center along this section of the dam. The piers support an iron catwalk which was part of a gated spillway system used to raise and lower the water level feeding the Haxall Canal. The second section of the Browns Island Dam is 430 feet long and is 6 feet higher than the top of section 1. This part of the dam has 11 large concrete piers located at approximately 36 feet on center. This section of the dam ties into the south side of the river and no water overtops this portion of the dam under normal flow conditions. A large amount of sediment and organic material has started to fill in the area on the upstream side of section 2 of the dam. Note that Dewberry cannot fully comment on the condition of the dam in the areas blocked from view by water or debris. Per discussions with DCR, the Browns Island Dam will be classified as a state regulated facility because the impoundment volume is roughly 214 acre feet and the maximum dam height is estimated at 12 feet. The dam should qualify as a special low hazard dam, subject to the criteria outlined in section 4VAC of the dam safety regulations (see Appendix A for a list of the criteria). There are numerous trees growing along the 430 foot section of the dam. Because the dam is state regulated, these trees will need to be removed where they are within 25 feet of the dam. Once the trees are removed, the dam is anticipated to meet DCR safety standards. The headgate for the Haxall Canal is located to the north of the Browns Island Dam. This headgate and the canal are owned and maintained by the City of Richmond. Per discussions with Steve Snell at DCR, the headgate should be considered part of the Browns Island Dam and it should be included in the dam inspection. Final Assessment and Recommendations The majority of the Browns Island Dam is a cast in place concrete, gravity dam. The piers associated with the dam are also cast in place concrete. The concrete inline weir sections of the Browns Island dam and the associated piers appear to have been poured directly on bedrock as no evidence of a mechanical anchor tying the two together was observed. Therefore, the dam is most likely relying on the weight of the concrete mass and friction at the interface of the bedrock and concrete to prevent it from overturning or sliding. In general, a majority of the piers have experienced significant section loss from their original construction thereby warranting further investigation for any future reuse of these piers to support overhead catwalk loading. The concrete piers exhibit signs of erosion and spalling, as evidenced by the loss of the cement paste and exposed aggregate. Each pier becomes narrower towards its base due the amount of section loss created by water rushing around the piers. The remaining exposed aggregate appears to be a mix of large river stone and brick. Organic growth (such as trees) has taken root in many of the piers, which accelerates the loss of concrete section. Horizontal cracking coinciding with cold joint locations was also observed on sections of the piers that were not eroded. Recommendations for the Browns Island Dam include removal of the trees within 25 feet of the dam along section 2 and removal of debris along the crest of the dam which has accumulated near the center of the river. Because the piers are slated for reuse as supports for a future overhead catwalk, it would be prudent to obtain strength information for the existing piers and concrete dam. Additional investigations should include collection of concrete core samples from the existing piers to verify the strength of the concrete. The core samples should be obtained from the piers located in the river 3

5 (section 1) and from the piers located in the river bank area (section 2). Due to the poor condition of the concrete and the large aggregates used in the concrete mix such as the brick and large river stone, taking concrete cores in the piers may prove difficult as the aggregate mix may disintegrate. Additionally, a petrographic analysis of the concrete may be performed to examine the extents of the aggregate cement paste breakdown. This analysis can be done on the concrete core samples taken from the piers. The bedrock foundation material (i.e. granite or shale) should be verified for the strength and bearing capacity for any future reuse. The dam should continue to be visually monitored for changes in the condition of the concrete. Belle Isle and Belle Isle North Dams Originally, these two dams functioned as one dam to impound water feeding the Belle Isle Power Plant, which is located on Belle Island. DCR Regulation The Belle Isle North Dam is approximately 1,650 feet long and runs from a rock outcropping in the James River to a point on the west end of Belle Island. The dam height varies between 4 and 6 feet. The dam has been breached in numerous locations and the dam no longer impounds any appreciable volume of water. Therefore, per discussions with DCR, it was agreed that the Belle Isle North Dam is not subject to state regulation. The Belle Isle Dam is 2,000 feet long and runs from the old power plant, located on the west end of Belle Island, to a point along the south side of the river. The dam is 16 feet high where it begins near the old power plant and gradually decreases in height to approximately 4 feet, where the dam ends on the south side of the James River. No flow overtops this dam under normal circumstances. A large amount of debris and sediment has accumulated in front of the higher portion (northern section) of the dam, making it more of an earth retaining wall than a dam. There are several concrete bridges and walkways near the old power plant, which are in poor condition, that are still being used by pedestrians. Under normal low flow conditions, the river flows around the north end of Belle Island, bypassing this dam. Per discussions with DCR, it was agreed that the Belle Isle Dam does not meet the state regulation criteria because the impoundment volume is roughly 28 acre feet and the dam height associated with the impoundment area is estimated at 5 feet. Final Assessment and Recommendations The Belle Isle Dam is constructed primarily of concrete with the exception of a short section of dam near the Belle Isle Power Plant that is constructed of a stone block wall with a concrete cap. A large debris field has formed on the upstream side of the Belle Isle dam which is preventing water from reaching the dam in this area. Organic material has filled the old Power Canal, causing the dam to act as a retaining wall holding back soil material. Typical structural damage to the dam near the Power Plant includes exposed rebar, concrete section loss, and concrete spalling on the downstream, angled side of the concrete cap above the stone wall. Cracking around the joint between the concrete cap and concrete buttress wall was observed in a majority of bays. Trees and other organic material were observed to be growing on and through the dam. The concrete buttress dam walls appear to be sound with the exception of minor spalling on some walls. 4

6 The Belle Isle North Dam is a cast in place concrete, gravity dam. In general, the concrete dam exhibits signs of erosion in the form of the loss of the cement paste and exposed aggregate. The breaches in Belle Isle North Dam are used for fish passage and recreational boating. The bases of both dams appear to be poured directly onto the bedrock along the riverbed. Therefore, the dams are most likely relying on the weight of the concrete mass and friction at the interface of the bedrock and concrete to prevent them from overturning or sliding. Recommendations for the Belle Isle dam include removal of the trees that are growing through the stacked block section of the dam (near the old Power Plant). In addition, the City should inspect the concrete footbridge and pipe bridge near the intake for the Power Canal. The presence of deteriorated concrete and the severed and exposed rebar warrants further investigation. In addition, debris that has accumulated along the crest of the dam should be removed. Recommendations for the Belle Isle North Dam include investigation of the stability of the 40 foot section of dam closest to Belle Isle. As an option to an investigation to analyze this section of the dam, consideration should be given to simply removing this section of the dam. Hollywood Dam DCR Regulation The Hollywood Dam is 2,315 feet long and ties into the north side of the river near the Dominion Virginia Power office building. The dam is 16 feet high where it ties into the north side of the river and gradually decreases in height to approximately 4 feet, where the dam ends at a point near a rock outcropping in the James River. There are two breaches in the Hollywood Dam where water can freely pass. The breaches in the dam are used for fish passage and recreational boating. Per discussions with DCR, the Hollywood Dam will be classified as a state regulated facility because the impoundment volume is roughly 91 acre feet and the maximum dam height is estimated at 16 feet. The dam should qualify as a special low hazard dam, subject to the criteria outlined in section 4VAC of the dam safety regulations (see Appendix A for a list of the criteria). Once the dam has been assessed for structural stability and a geotechnical investigation has been completed, the dam is anticipated to meet DCR safety standards. Per discussions with DCR, the Browns Island Dam will be classified as a state regulated facility because the impoundment volume is roughly 143 acre feet and the maximum dam height is estimated at 12 feet. The dam should qualify as a special low hazard dam, subject to the criteria outlined in section 4VAC of the dam safety regulations (see Appendix A for a list of the criteria). There are numerous trees growing along the 430 foot section of the dam. Because the dam is state regulated, these trees will need to be removed where they are within 25 feet of the dam. Once the trees are removed, the dam is anticipated to meet DCR safety standards. The headgate for the Hollywood Canal is adjacent to the main portion of the Hollywood Dam. This headgate and the island are owned and maintained by Dominion Virginia Power. Per discussions with Steve Snell at DCR, the headgate should be considered part of the Hollywood Dam and it should be included in the dam inspection. Richmond DPU staff is working with Dominion Virginia Power to determine the ownership and maintenance responsibilities for the dam and the headgates. 5

7 Final Assessment and Recommendations The concrete sections of the dam appear to have been poured directly on bedrock as no evidence of a mechanical anchor tying the dam to the bedrock was observed. It also appears that the concrete in the Hollywood Dam may have been placed in multiple layers over an unknown period of time in a possible attempt to adjust the water flow in the river. It appears that the later concrete pours were placed directly onto the original mass of concrete with no mechanical anchorage to the underlying concrete. Over time, the added concrete layers have become thin and broken away from the original section of the dams. In some locations, the uppermost concrete topping has broken away from the main section of the dams, causing a depression in the top of wall elevation. The concrete exhibits signs of erosion in the form of the loss of the cement paste and exposed aggregate. During the inspection, water seepage through the vertical and horizontal cold joints between concrete pours was also observed. Recommendations for dam repairs include patching of spalled concrete on the downstream face in numerous locations. There are also several locations where the top of the dam is in need of repair to prevent further deterioration. The portion of the dam near the Hollywood Canal appears to have experienced significant loss of section over the years and a stability analysis appears warranted. Recommendations for additional field testing include a field survey of the dam to determine its actual dimensions and verification of the material condition of the dam and foundation. This should include dam concrete and bedrock cores, concrete material testing, and an assessment of the bedrock to determine the underlying material. The foundation and underlying material should also be reviewed to determine the bearing capacity. A detailed stability analysis should also be conducted at the critical dam sections to assess the factors of safety associated with overturning/sliding of the gravity dam. The dam should also be visually monitored for changes in the condition of the concrete. Sunny Day Breach of Hollywood Dam An approximate sunny day breach analysis was performed on the Hollywood dam to assess the potential impacts to the area immediately downstream of the dam. The analysis was also done to access the potential for loss of life and economic damages resulting from failure of the dam. Dewberry reviewed the flows on the James River and determined that the 1 year storm event was equivalent to roughly 20,000 cfs. During the summer months, baseflow on the river is roughly 2,000 cfs. For the Sunny day breach analysis, a 16 high portion of the dam was analyzed for failure. A breach width was developed based on engineering criteria and the volume of water stored behind the dam was computed assuming a trapezoidal prism. Dam Breach formulas developed by Fread and Froelich were utilized to compute the breach flows. In addition, the weir equation was also reviewed to check the flows developed using the Fread and Froelich equations. FREAD EQUATION Q p = 5,442 cfs FROELICH EQUATION Q p = 5,137 cfs 6

8 DAM BREACH FLOWS USING WEIR EQUATION Q p = 7,680 cfs Q p =. Where: C = weir coefficient L = weir length H = height of water above breach bottom The empirical dam breach equations indicate that the potential sunny day breach flows are significantly less than the 1 year event along the river. It can be concluded that a sunny breach would have almost no impact on structures downstream of the dam. In addition, a sunny day breach would only cause an increase in flow depth of less than one foot at the Browns Island dam. Therefore, it is expected that there will be little or no loss of life resulting from a sunny day breach of the dam. Estimated Construction Cost Estimates Dewberry has completed a cost estimate to upgrade the four dams per DCR regulations. Note that the cost estimates do not include any upgrades that might be required as a result of the recommended field testing and evaluation. The cost breakdown for each dam is included in Appendix B. Manchester Dam See Appendix B Browns Island Dam See Appendix B Hollywood Dam See Appendix B Belle Isle and Belle Isle North Dams See Appendix B 7

9 Appendix A DCR Requirements 4VAC Special criteria for certain low hazard impounding structures. A. Notwithstanding the requirements of this chapter, should the failure of a low hazard potential impounding structure cause no expected loss of human life and no economic damage to any property except property owned by the impounding structure owner, then the owner may follow the below requirements instead of the requirements specified in this chapter: 1. No map required pursuant to 4VAC shall be required to be developed for the impounding structure should a licensed professional engineer certify that the impounding structure is a low hazard potential impounding structure and eligible to utilize the provisions of this section; 2. The spillway design flood for the impounding structure is recommended as a minimum 50 year flood; however, no specific spillway design flood shall be mandatory for an impounding structure found to qualify under the requirements of this section; 3. No emergency preparedness plan prepared pursuant to 4VAC shall be required. However, the impounding structure owner shall notify the local emergency services coordinator in the event of a failure or emergency condition at the impounding structure; 4. An owner shall perform inspections of the impounding structure annually in accordance with the requirements of 4VAC No inspection of the impounding structure by a licensed professional engineer shall be required, however, so long as the owner certifies at the time of operation and maintenance certificate renewal that conditions at the impounding structure and downstream are unchanged since the last inspection conducted by a licensed professional engineer; and 5. No certificate or permit fee established in this chapter shall be applicable to the impounding structure. B. Any owner of an impounding structure electing to utilize the requirements of subsection A of this section shall otherwise comply with all other requirements of this chapter applicable to low hazard impounding structures. C. The owner shall notify the department immediately of any change in circumstances that would cause the impounding structure to no longer qualify to utilize the provisions of this section. 8

10 Appendix B Dam Repair Cost Estimates Manchester Dam Cost Estimate Browns Island Dam Cost Estimate Belle Isle and Belle Isle North Dams Cost Estimate Hollywood Dam Cost Estimate 9

11 STATEMENT OF PROBABLE CONSTRUCTION COST MANCHESTER DAM - COST ESTIMATE Date: ITEM NO. 1 2 GENERAL CONDITIONS ITEM DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT SOURCE COMMENT A. GENERAL MOBILIZATION LS 1 7, , B. BARGE MOBILIZATION (WITH CONCRETE PUMPER) EA 1 8, , RS Means page 287 C. DAM ACCESS LS 1 5, , D. MIXING OF CONCRETE (3000 PSI) CY , RS Means page 74 E. RESURFACING OF SPALLED CONCRETE USING SHOTCRETE CY , RS Means page 78 F. FILLING OF CAVITIES WITH FLOWABLE FILL (PUMPED DIRECTLY INTO CY , RS Means page 75 THE WATER - NO COFFER DAM) 29, MISCELLANEOUS ITEMS A. CLEARING OF DEBRIS FROM DAM CY , Engineer's Estimate Hand clearing with chainsaws 2, NET 32, % FOR ENGINEERING: 5, % FOR CONTINGENCIES 3, , The Engineer s Statement of Probable Construction Costs is provided solely for the client's internal information and budgeting purposes. Engineer makes no representations or guarantee that the costs included in the estimate accurately predict the amount of Contractor s actual bids. Actual bids may be substantially higher or lower than the estimate. The estimate is prepared solely for the benefit of the client for the purpose stated above and no other parties may rely upon the estimate for any reason. Notes: 1. Volume of concrete required for repairs is a rough estimate. Actual amount of concrete will need to be verified in the field. 2. This estimate assumes that the work in the river will be covered under existing ACOE Nationwide Permits and nothing more than a PCN will be required. Page 1 of 1

12 STATEMENT OF PROBABLE CONSTRUCTION COST BROWNS ISLAND DAM - COST ESTIMATE Date: ITEM NO. 1 GENERAL CONDITIONS ITEM DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT SOURCE COMMENT A. GENERAL MOBILIZATION LS 1 10, , B. DAM ACCESS ROAD (12' WIDE x 600' LONG - 8" GRAVEL DEPTH) SY , RS Means page 21 C. REMOVAL OF TREES WITHIN 25' OF DAM - CUTTING AND HAUL AWAY EA , RS Means page 288 D. CHIPPING OF STUMPS ON SITE EA , RS Means page 287 E. SITE GRADING & CLEANUP LS 1 5, , , MISCELLANEOUS ITEMS A. CLEARING OF DEBRIS FROM DAM CY , Engineer's Estimate Hand clearing with chainsaws 7, NET 103, % FOR ENGINEERING: 15, % FOR CONTINGENCIES 10, , The Engineer s Statement of Probable Construction Costs is provided solely for the client's internal information and budgeting purposes. Engineer makes no representations or guarantee that the costs included di in the estimate accurately predict the amount of Contractor s actual bids. Actual bids may be substantially higher or lower than the estimate. The estimate is prepared solely for the benefit of the client for the purpose stated above and no other parties may rely upon the estimate for any reason. Notes: 1. Number of trees is a rough estimate. Actual number of trees will need to be verified in the field 2. Volume of the debris field is a rough estimate. Actual amount of debris will need to be verified in the field. 3. This estimate assumes that the work in the river will be covered under existing ACOE Nationwide Permits and nothing more than a PCN will be required. Page 1 of 1

13 STATEMENT OF PROBABLE CONSTRUCTION COST BELLE ISLE & BELLE ISLE NORTH DAMS - COST ESTIMATE Date: ITEM NO. 1 2 GENERAL CONDITIONS ITEM DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT SOURCE COMMENT A. GENERAL MOBILIZATION LS 1 10, , B. REMOVAL OF TREES WITHIN 25' OF DAM - CUTTING AND HAUL AWAY EA , RS Means page 288 C. CHIPPING OF STUMPS ON SITE EA , RS Means page 287 D. REPAIR OF CONCRETE FOOTBRIDGE LS 1 10, , Engineer's Estimate E. REMOVAL OF CONCRETE PIPE BRIDGE LS 1 5, , Engineer's Estimate 48, MISCELLANEOUS ITEMS A. CLEARING OF DEBRIS FROM DAM CY , Engineer's Estimate Hand clearing with chainsaws 10, NET 58, % FOR ENGINEERING: 9, % FOR CONTINGENCIES 6, , The Engineer s Statement of Probable Construction Costs is provided solely for the client's internal information and budgeting purposes. Engineer makes no representations or guarantee that the costs included in the estimate accurately predict the amount of Contractor s t actual lbid bids. At Actual lbid bids may be substantially bt till higher h or lower than the estimate. t The estimate t is prepared solely ll for the benefit of the client for the purpose stated above and no other parties may rely upon the estimate for any reason. Notes: 1. Number of trees is a rough estimate. Actual number of trees will need to be verified in the field 2. Volume of the debris field is a rough estimate. Actual amount of debris will need to be verified in the field. 3. This estimate assumes that the work in the river will be covered under existing ACOE Nationwide Permits and nothing more than a PCN will be required. Page 1 of 1

14 STATEMENT OF PROBABLE CONSTRUCTION COST HOLLYWOOD DAM - COST ESTIMATE Date: ITEM NO. 1 GENERAL CONDITIONS ITEM DESCRIPTION UNIT QUANTITY UNIT PRICE AMOUNT SOURCE COMMENT A. GENERAL MOBILIZATION LS 1 7, , B. BARGE MOBILIZATION (WITH CONCRETE PUMPER) EA 1 8, , RS Means page 287 C. DAM ACCESS LS 1 5, , D. MIXING OF CONCRETE (3000 PSI) CY , RS Means page 74 E. RESURFACING OF SPALLED CONCRETE USING SHOTCRETE CY , RS Means page 78 2 MISCELLANEOUS ITEMS A. 26, NET 27, % FOR ENGINEERING: 4, % FOR CONTINGENCIES 3, , The Engineer s Statement of Probable Construction Costs is provided solely for the client's internal information and budgeting purposes. Engineer makes no representations or guarantee that the costs included di in the estimate accurately predict the amount of Contractor s actual bids. Actual bids may be substantially higher or lower than the estimate. The estimate is prepared solely for the benefit of the client for the purpose stated above and no other parties may rely upon the estimate for any reason. Notes: 1. Volume of concrete required for repairs is a rough estimate. Actual amount of concrete will need to be verified in the field. 2. This estimate assumes that the work in the river will be covered under existing ACOE Nationwide Permits and nothing more than a PCN will be required. Page 1 of 1

15 Appendix C Inspection Reports and Site Photos Manchester Dam Inspection Report and Site Photos Browns Island Dam Inspection Report and Site Photos Belle Isle Dam Inspection Report and Site Photos Hollywood and Belle Isle North Dams Inspection Report and Site Photos 10