Mill River Dams Feasibility Study River Restoration and Diadromous Fish Passage
January 31st, 2008
Prepared for:
Massachusetts Riverways Program Riverways Program, DFG 251 Causeway St., Suite 400 Boston, MA 02114
3602 Atwood Avenue Suite 3 Madison, WI 53714
TABLE OF CONTENTS 1. Executive Summary...... 5
1.1. State Hospital Dam ...... 5
1.2. West Britannia Dam...... 8
1.3. Whittenton Pond ...... 9
2. Introduction ...... 13
2.1. Project Team and Scope of Work ...... 15
2.2. Report Format...... 15
3. Data Collection...... 16
3.1. Existing data ...... 16
3.2. Field data...... 16
4. Background Information...... 20
4.1. Natural History ...... 20
4.2. Fisheries History...... 20
4.3. Cultural Resources...... 21
4.4. Geologic history...... 27
4.5. Geomorphic History ...... 28
5. Existing Conditions ...... 30
5.1. Modern landuse...... 30
5.2. Existing Geomorphology...... 31
5.3. Wetland Resources ...... 32
5.4. Basis for projecting wetland resource alterations ...... 35
6. Hydrologic and Hydraulic Analysis ...... 38
6.1. Hydrology ...... 38
6.2. Hydraulic Modeling and Flood Profile Analysis ...... 48
2008 Inter-Fluve Inc.
6.3. Fish Passage Hydraulic Design...... 58
7. Sediment Characterization...... 65
7.1. Sediment volume estimation...... 65
7.2. Sediment Grain Size Analysis ...... 65
7.3. Due diligence ...... 66
7.4. Sediment quality – background information...... 67
7.5. Sediment quality – State Hospital...... 69
7.6. Sediment quality – West Britannia ...... 70
7.7. Sediment quality – Whittenton Pond ...... 72
7.8. Regulatory Perspectives on Quality Testing Results in Relation to Project Implementation ...... 73
8. State Hospital Dam: Design Options...... 76
8.1. Existing Conditions (No action or minimal action alternative) ...... 76
8.2. Full removal...... 80
8.3. Fish passage bypass channel...... 84
8.4. Conceptual Cost Estimates – State Hospital Dam ...... 87
9. West Britannia Dam: Design Options ...... 89
9.1. Existing Conditions (Do Nothing Option)...... 89
9.2. Full removal...... 93
9.3. Rock ramp (with dam repair)...... 97
9.4. Fish bypass channel (with dam repair) ...... 98
9.5. Fish ladder (with dam repair)...... 99
9.6. Conceptual Cost Estimates – West Britannia Dam...... 101
10. Whittenton Pond Dam: Design Options ...... 102
10.1. Existing Conditions (No action or minimal action alternative) ...... 102
10.2. Full removal – Whittenton Dam ...... 107
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10.3. Fish ladder (with dam reconstruction) ...... 115
10.4. Fish bypass channel (with dam reconstruction)...... 116
10.5. Rock ramp (with dam reconstruction) ...... 116
10.6. Conceptual Cost Estimates – Whittenton Pond Dam...... 119
11. Morey’s Bridge Dam: Recommendations ...... 120
12. Citations...... 121
Appendices Appendix A – Detailed cost estimates Appendix B - Due diligence summary Appendix C – Natural resources report Appendix D – HEC-RAS modeling results/summary tables Appendix E – Geolabs Report Appendix F – Infrastructure notes Appendix G – Fish Passage computations
Principal authors: Martin Melchior, Michael Burke, and Michael Chelminski
2008 Inter-Fluve Inc.
1. Executive Summary
This study examined the feasibility of various fish passage and river restoration options for the three downstream impoundments on the Mill River in Taunton, Massachusetts (Figure 1-1). We conclude that fish passage and river restoration are feasible, and we offer concept level design options for alternatives at each dam.
1.1. State Hospital Dam
The State Hospital Dam is an earthen fill dam with a concrete spillway (8 ft head) impounding a pond area of approximately 5.2 acres. The impoundment contains a maximum of 30,000 cubic yards of deposited sediment consisting primarily of sand.
No Action Alternative – As part of the study, we examined the implications of no action at each structure. No action at the State Hospital Dam would result in continued riverine habitat degradation through sediment deposition, organic material buildup, invasive plant proliferation, thermal pollution, and concentration of nutrients and pollutants. These negative effects of dams are well documented in numerous studies (Baxter 1977, Dauta et al. 1999, Petts 1984, Poole and Berman 2001, Schuman 1995, Stanley et al. 2002, Ward and Stanford 1979, 1987). No action also results in continued selective removal of fine material from the downstream reach, resulting in over-widening of the channel and homogenization of in-stream habitats (Gray and Ward 1982, Ligon et al. 1995, Ward and Stanford 1983).
No action with regard to river restoration and fish passage will require continued dam inspection, maintenance and eventual repair or replacement to keep the dam in compliance with Massachusetts Department of Dam Safety standards. The cost of these activities is typically borne by the dam owner. All dams continue to degrade, and without regular maintenance and repair, the risk of flooding due to dam failure increases. No action results in continued liability risk to the dam owner and continued risk to public safety (Graber et al. 2001).
Dam Removal Alternative – Removal of the State Hospital Dam is feasible and would fulfill the goals of the project. Dam removal would result in passage for diadramous fish (alewife, blueback herring) and other species (eg. American eel, amphibians), free flowing conditions, restored riparian and in-stream habitat, lower water temperatures, increased dissolved oxygen concentrations and the reestablishment of river dependent fish and wildlife (Bednarek, A. 2001, Calabro 2007, Maclin and Sicchio 1999). These include lithophilic or gravel dependent spawning fish, mussels and other macroinvertebrates, as well as riparian birds, amphibians, reptiles and small mammals. Dam removal would also reconnect the nutrient flow of upstream and downstream reaches, allowing both fish and nutrients to pass from reach to reach. Migrating fish, including alewife, blueback herring, eel and other species, would be able to move daily
2007 Inter-Fluve Inc. 5 Mill River Concept Report Morey’s Bridge Dam
Whittenton Pond Dam
West Britannia Dam
State Hospital Dam
Figure 1-1. Mill River in Taunton, MA showing the location of the project dams and seasonally through the reach to ensure access to optimal feeding and spawning habitat. Removal of the State Hospital dam would also remove dam owner liability and public safety concerns by eliminating potential risk of flooding due to dam failure.
Fish Passage Alternatives – Both a fish ladder and a nature-like bypass channel (Figure 1-2) are feasible at the State Hospital site and both fulfill the fish passage goals of the project. Either approach does not remove the dam owner’s liability, and does not improve the degraded condition of the upstream channel. Affordable Denil and prefabricated Alaska steep pass fish ladders have been shown to be successful in facilitating the migration of diadramous migratory alosid species (eg. alewife, blueback herring, American shad) in the northeast (Haro et al. 1999, Kleinschmidt 2005, Quinn 1994). Such a ladder could be installed at the State Hospital site, but the degraded raceway would require stabilization or partial reconstruction to provide the structural support necessary for a ladder. At this site, fish may have a tendency to bypass the fish ladder inlet and occupy the 60 feet of rock riffle apron. It is possible to limit low flow over the main spillway and divert or interrupt Figure 1-2 – Example of a nature-like fishway or higher flows to create more attraction in the bypass channel (photo L. Aadland) preferred downstream location. Any fish ladder would require significant concrete work to repair the dam, stabilize the left bank raceway and manipulate spillway flow patterns to ensure attraction. This concrete work could increase the cost of a ladder project while not ensuring passage of all Mill River fish species.
Nature-like or natural bypass channels have been successful at allowing passage of a wide variety of species (Eberstaller et al. 1998, FAO/DVWK 2002, Jungwirth et al 1998, Aerestrup et al 2003, Mader et al. 1998). A natural bypass channel was deemed feasible given the existence of the left bank historic sluiceway which would allow for bypass channel construction with minimal excavation. The gentle slope afforded by this route allows for a cascading riffle and pool design that would mimic natural stream conditions and allow for passage of both migratory species (eg. alewife, herring, adult American eel) and resident species (pickerel, darters, elvers).
2007 Inter-Fluve Inc. 7 Mill River Concept Report 1.2. West Britannia Dam
The West Britannia (Reed and Barton) Dam is 85 feet long with a structural height of 8.0 feet and a hydraulic head of 4.0 feet. The dam is an earthen berm and masonry dam with a concrete cap masonry spillway formerly impounding a pond area of approximately 8.23 acres. The dam is currently drawn down and has no significant impounded water area. The impoundment contains a maximum range of 13,000 to 26,000 cubic yards of deposited sediment consisting primarily of sand.
No Action Alternative – Because of the lowered impoundment and current run-of-river condition at the West Britannia Dam, no action does not have the same type of impacts as predicted for the State Hospital Dam. No action at West Britannia will maintain the existing condition of the impoundment, and the river conditions will remain relatively static. The dam will continue to block fish passage and will continue to present a maintenance cost and liability due to the risk of flooding from dam failure. In addition, the existing raceway (right bank) is a continued risk to the Reed and Barton mill buildings under which it flows.
Structural repairs are recommended for the West Britannia Dam. No action will still require some maintenance and repair to be financed by the dam owner.
Dam Removal Alternative – Removal of the West Britannia Dam would result in free flowing conditions, restored riparian and in-stream habitat, increased dissolved oxygen concentrations and reestablishment of riffle and pool dependent fish and wildlife. The reach is currently a deep, rectangular wetland channel. Removal of the dam would result in a steeper channel slope and more natural geomorphic function, including sediment movement, bar formation and riffle and pool development. Free passage of migrating fish and wildlife would be assured. Removal of the West Britannia dam would remove dam owner liability and public safety concerns by eliminating flooding due to dam failure or water passing under the mill buildings.
Fish Passage Alternative – Three non-removal fish passage alternatives were considered at the West Britannia site, rock ramp, fish ladder, and natural bypass channel. A rock ramp was deemed infeasible due to the filling of the channel downstream of the dam and the potential hydraulic impacts to the downstream bridge crossing. The flood capacity of the West Britannia Street bridge could potentially be reduced as filling would need to extend under the bridge.
An Alaska steep-pass or Denil-type fish ladder is feasible at the site, and would accomplish diadromous fish passage goals. A fish ladder could be installed along the left bank retaining wall. Any fish ladder would require significant concrete and masonry work to repair the dam, stabilize the left bank
2007 Inter-Fluve Inc. 8 Mill River Concept Report retaining wall and manipulate spillway flow patterns to ensure attraction. We recommend that any fish ladder design at the West Britannia dam also consider specialized eel and elver passage ramps.
A natural bypass channel was also deemed feasible if it could be constructed on the left bank floodplain area. With either fish ladder or natural bypass channel, the degraded condition of the upstream river reach remains, as does the dam owner’s liability risk.
1.3. Whittenton Pond
The Whittenton Pond Dam is a 10 ft high concrete and timber structure temporarily stabilized by a riprap spillway. The dam currently impounds a pond area of approximately 9.5 acres. The impoundment is currently partially drawn down as a result of 2005 emergency repairs that lowered the head of the dam to approximately 8 feet (Belisle 2006). The impoundment contains a maximum range of 1400 to 4,000 cubic yards of deposited sediment consisting primarily of sand.
No Action Alternative – No action at the Whittenton Pond Dam will maintain the existing degraded river condition of the upstream reach, including continued sedimentation, littoral vegetation accumulation and expansion, thermal pollution and nutrient loading. The stabilization measures taken in 2005 were intended to be temporary, and movement of stones and degradation of the structure were noted in our field effort. The dam will need to either be removed or rebuilt in the near future. In the meantime, the dam will continue to block fish passage and will continue to present a maintenance cost and liability due to the risk of downstream flooding from dam failure.
Dam Removal Alternative – Removal of the Whittenton Pond Dam would result in free flowing conditions, restored fish passage, restored riparian and in-stream habitat, increased dissolved oxygen concentrations and the reestablishment of riffle and pool dependent fish and wildlife. Removal of the Whittenton Pond Dam would remove dam owner liability and public safety concerns related to flooding from dam failure. Removal would result in a conversion of general ecological condition from a lentic or lake environment to a lotic, or riverine environment. This would include a restored sinuous channel roughly 50 feet wide with a riparian zone managed with natural and private landowner aesthetics in mind.
Fish Passage Alternative – Three non-removal fish passage alternatives were considered at the Whittenton Pond site, including rock ramp, fish ladder, and natural bypass channel. A rock ramp was deemed infeasible given the high cost versus benefit and the potential change in hydraulics at the downstream bridge crossing. The fish ladder and natural bypass options are feasible at the site, but would require rebuilding of the dam. Of the two alternatives, a fish ladder would be the most economical, but a natural bypass channel would ensure passage of a wider variety of fish species. With any of these fish
2007 Inter-Fluve Inc. 9 Mill River Concept Report passage alternatives, the degraded condition of the upstream river reach remains, as does the dam owner’s liability risk.
Alternatives analysis tables
Full dam removal and alternative fish passage options were both found to be feasible at each of the three study dams, with a range of associated feasibility level cost estimates. The following tables show the alternatives considered at the three dams considered in the study, and the advantages and disadvantages of each option. A more detailed discussion of restoration options is given in subsequent sections of this document. Detailed cost estimates are included as Appendix A.
Table 1-1. State Hospital Dam – fish passage alternatives
Estimated costs* Advantages Disadvantages
Do Nothing • No immediate cost • Increased cost of repair with time • Maintain pond aesthetic • Persistent long-term risk/liability of Repair - $250,000 failure and subsequent flooding Long term maintenance costs • Continued riverine habitat degradation are variable • Continued water quality impacts - thermal pollution, dissolved oxygen • Continued degraded sediment quality
Full Dam Removal • Improved fish passage • Short term construction disturbance • Restored natural river processes • Cost of contaminated sediment requires RECOMMENDED • Reduced or stabilized contaminants additional grant funding effort $989,000 – assuming special • Restored floodplain wetlands • Removal of sediment adds substantial handling of sediments cost, particularly if special handling is • Improved water quality required $546,000 – assuming no • Increased property value special handling • Reduced public safety risk • Funding available for removal and sediment management • Improved park land opportunity
Dam repair with fish passage • Improved fish passage • Cost of repair is generally not funded by bypass channel • Maintained impoundment water outside sources (eg. State or Federal levels grants) $250,000 – repair • Reduced public safety risk • Short term construction disturbance $224,800 – fish bypass • Persistent long-term risk/liability of Total $474,000 failure and subsequent flooding • Continued riverine habitat degradation • Continued water quality impacts - thermal pollution, dissolved oxygen • Continued degraded sediment quality *Estimates are rounded to the nearest thousand and include construction, engineering and permitting. Estimates for engineering, permitting, dewatering, site repair and maintenance are shared by both dam repair and fish passage elements. Estimates are feasibility level. The actual cost of construction may vary depending on final project approach, heavy construction market cost fluctuations and other factors. Estimates do not include construction cost contingency..
2007 Inter-Fluve Inc. 10 Mill River Concept Report Table 1-2. West Britannia Dam – fish passage alternatives
Estimated costs* Advantages Disadvantages
Do Nothing • No immediate cost • Increased cost of repair with time • Maintain pond aesthetic • Persistent long-term risk/liability of failure Repair - $200,000 and subsequent flooding Long term maintenance costs • Continued riverine habitat degradation are variable • Continued water quality impacts - thermal pollution, dissolved oxygen • Continued degraded sediment quality
Full Dam Removal • Improved fish passage • Short term disturbance of the west end of the • Restored natural river processes parking lot area (left bank – Reed and RECOMMENDED Barton) • Reduced or stabilized contaminants • Cost of contaminated sediment remediation $694,000 – assuming special • Restored floodplain wetlands handling of sediments requires additional grant funding effort • Improved water quality $452,000 – assuming no • Increased property value special handling of sediments • Reduced public safety risk • Funding available for removal and sediment management
Dam repair with fish passage • Improved fish passage • Cost of repair is generally not funded by bypass channel • Maintained impoundment water outside sources (eg. State or Federal grants) levels • Short term construction disturbance $200,000 – repair • Reduced public safety risk • Persistent long-term risk/liability of failure $230,000 – fish bypass and subsequent flooding Total $430,000 • Continued riverine habitat degradation • Continued water quality impacts - thermal pollution, dissolved oxygen • Continued degraded sediment quality
Dam repair with fish ladder • Improved fish passage • Cost of repair is generally not funded by • Maintained impoundment water outside sources (eg. State or Federal grants) $200,000 – repair levels • Short term construction disturbance $61,000 – Alaska steep pass • Reduced public safety risk • Persistent long-term risk/liability of failure fish ladder • Fish passage funding for ladders is and subsequent flooding Total $261,000 potentially available • Continued riverine habitat degradation • Continued water quality impacts - thermal pollution, dissolved oxygen • Continued degraded sediment quality *Estimates are rounded to the nearest thousand and include construction, engineering and permitting. Estimates for engineering, permitting, dewatering, site repair and maintenance are shared by both dam repair and fish passage elements. Estimates are feasibility level. The actual cost of construction may vary depending on final project approach, heavy construction market cost fluctuations and other factors.. Estimates do not include construction cost contingency.
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Table 1-3. Whittenton Pond Dam – fish passage alternatives
Advantages Disadvantages
Do Nothing • No immediate cost • Not a practical option given that repairs • Impoundment maintained at current level must be made to address public safety restores some of the riparian zone • Wetlands filling over time Rebuild Dam • Short term construction disturbance $1.5 Million • Persistent long-term risk/liability of failure and subsequent flooding
• Continued riverine habitat degradation Long-term maintenance • Continued water quality impacts - thermal costs variable pollution, dissolved oxygen • Continued degraded sediment quality Full Dam Removal • Improved fish passage • Lowered water levels (change in • Restored natural river processes recreational and aesthetic features) RECOMMENDED • Reduced or stabilized contaminants • Requires alternate fire suppression for the Mill area $927,000 – assuming • Restored floodplain wetlands contaminant removal • Cost of contaminated sediment requires • Improved water quality additional grant funding effort $564,000 – assuming no • Increased property value contaminant removal • Reduced public safety risk • Funding available for removal and Includes $50K for fire sediment management suppression improvements • Potentially increased property frontage
Dam replacement with • Improved fish passage • Cost may be prohibitive fish bypass channel • Maintained impoundment water levels • May not be permittable $1,505,000 - dam • Reduced public safety risk • Long-term risk of failure and sudden reconstruction flooding remains • Wetlands filling over time $203,000 - bypass channel • Degraded habitat • Water quality impacts - thermal pollution, Total $1,708,000 dissolved oxygen • Slow release of contaminants
Dam replacement with • Improved fish passage • Cost may be prohibitive fish ladder • Maintained impoundment water levels • May not be permittable $1,505,000 - dam • Reduced public safety risk • Short term construction disturbance reconstruction • Persistent long-term risk/liability of failure and subsequent flooding $69,000 - fish ladder installation Total $1,574,000 *Estimates are rounded to the nearest thousand and include construction, engineering and permitting. Estimates for engineering, permitting, dewatering, site repair and maintenance are shared by both dam repair and fish passage elements. Estimates are feasibility level. The actual cost of construction may vary depending on final project approach, heavy construction market cost fluctuations and other factors. Estimates do not include construction cost contingency.
2007 Inter-Fluve Inc. 12 Mill River Concept Report Mill River Dam Removal Photosimulations State Hospital Dam, West Britannia Dam, and Whittenton Mill Pond Dam
Note: these photosimulations were created to give people an idea of what the Mill River could look like at the dam sites if the dams are removed. These are not designs or engineering plans; they are conceptual only. State Hospital Dam, Taunton, MA State Hospital Dam removal simulation, Taunton, MA West Britannia Dam, Taunton, MA West Britannia Dam removal simulation #1, Taunton, MA West Britannia Dam removal simulation #2, Taunton, MA Whittenton Mill Pond Dam, Taunton, MA Whittenton Mill Pond Dam removal simulation #1, Taunton, MA Whittenton Mill Pond Dam removal simulation #2, Taunton, MA 2. Introduction
The goal of this study is to assess the feasibility of restoring diadromous fish passage at three dams on the Mill River in Taunton, Massachusetts. The study examines river restoration and fish passage through dam removal or alternative fish passage methods at the State Hospital, West Britannia and Whittenton Pond dams (Figure 1-1). Alternative fish passage methods examined include fish ladders, natural bypass channels (or nature-like fishways), and rock ramps. At the time the scope of the study was developed, the Morey’s Bridge dam controlling Lake Sabbatia was under a repair order from the Massachusetts Department of Dam Safety and thus could not be included in the study. Because Lake Sabbatia is a high use, recreational resource for Taunton, the Morey’s Bridge dam is not a removal candidate. However, future study and implementation of fish passage options at the Morey’s Bridge dam is recommended to allow passage of the restored herring population into Lake Sabbatia.
Project origins - The Mill River-Taunton Habitat Restoration project addresses habitat restoration at three dams on the Mill River in Taunton, Massachusetts. The Massachusetts Riverways Program (Riverways) and the Southeastern Regional Planning and Economic Development District (SRPEDD) are leading a partnership among local, state, and federal organizations to restore river connectivity and improve public safety at the project dams (Taunton State Hospital, West Britannia, and Whittenton Pond). Early in the project, the project partners stated that the concept or feasibility study should include an alternatives analysis that examines the following at the three dams: Improved public safety Infrastructure protection (roads, bridges, buildings) Fish passage for river herring and American eel Restoration of the lands surrounding the river (riparian zone) Improved opportunities for river-based recreation This report summarizes data collection, analysis and design options for the three dams, and discusses potential project impacts on the Morey’s Bridge Dam. Project partners include Riverways, SRPEDD, the National Oceanic and Atmospheric Administration (NOAA), the Massachusetts Division of Marine Fisheries (DMF), American Rivers (AR), The Nature Conservancy (TNC), and the Taunton River Watershed Association (TRWA).
The Mill River watershed encompasses an area of approximately 45 square miles. The Mill River valley flows between narrow uplands that separate the stream from the Taunton River valley to the east and Three Mile River to the west. The stream historically wound through wetlands for much of its length, including forested swamp areas in the north and seasonally flooded wetlands in the Taunton area. From the time of the last glaciation to around 1640, the stream flowed freely, with no natural barriers to fish passage. Industrial and residential development along the river resulted in the construction of several
2007 Inter-Fluve Inc. 13 Mill River Concept Report dams. From Lake Sabbatia to the confluence with the Taunton, four of these dams remain. The State Hospital dam is the most downstream structure, followed by the West Britannia dam and the Whittenton Pond dam, which all once functioned as mill dams but are no longer serving their intended purposes. During a large flood event in 2005, the Whittenton Pond dam was at risk of failure resulting in the evacuation of downtown residents and businesses and subsequent economic loss for the City of Taunton. Temporary measures were taken to reduce the risk of dam failure, but these measures are also at risk of failure as they degrade in the coming years.
Performance criteria - A project kickoff meeting was held on April 17th, 2007 in Taunton. Project funding partners met with Interfluve team staff to review and clarify the goals for the concept design project and to examine ways to integrate public comment. Regarding the technical aspects of final project outcomes, the following performance criteria were developed as being overwhelmingly important: Fish passage improvement for a variety of species Flood risk reduction Removal of dam owner liability Sediment management Aquatic species habitat restoration Riparian zone restoration Infrastructure protection (roads, bridges and buildings) River restoration as a whole rather than piecemeal projects Regarding the socioeconomic aspects of the project, the following concerns and performance criteria for the Feasibility Study were commonly cited: Develop effective public outreach Develop permitting requirements Estimate costs Outline economic benefits Identify cultural resources (historical and archaeological values) Make the project web-accessible Include public education Public education and outreach comments were consistent throughout the process and among participants. Public participation in the concept design process has been important to the project partners. Interfluve recommended the formation of a Citizen Advisory Group (CAG) to be organized by SRPEDD and Riverways. The CAG was formed by inviting local residents and concerned landowners to participate in regularly scheduled meetings designed to solicit feedback and comments. A public meeting was held in mid-April of 2007 to inform landowners about the topographic survey scheduled for May 2007. Following development of concept level drawings, a public meeting was held to solicit opinions from the
2007 Inter-Fluve Inc. 14 Mill River Concept Report public regarding design options at the three dams. We have taken those opinions into consideration when discussing the design options presented herein.
2.1. Project Team and Scope of Work
The project team included the project partner, the consultant team, and stakeholders. The initial phase of work was initiated through a contract let by the Massachusetts Riverways Program. Subsequent work was performed through a contract let by SRPEDD. The consultant team was comprised of Inter-Fluve Inc., Stantec (formerly Woodlot Alternatives, Inc.), and the Turner Group. Stakeholders included the project partners, the Citizen Advisory Group, the dam owners, and members of the public. The Citizen Advisory Group is made up of landowners and representatives from various groups and neighborhoods around the Mill River/Taunton community.
The project scope of work was initially developed by the project proponents, and was subsequently modified based on stakeholder input, recommendations from the consultant team, and financial resources. The scope of work reflects the project objectives listed above and deliverables include a concept design report and associated concept drawings.
2.2. Report Format
This report first summarizes data collected. Also included is a significant amount of background information, as we feel that in order to frame the concept designs, it is important for readers to have an understanding of the ecological, human and geomorphic history of the watershed. The subsequent sections detail the design analysis tools used. The results of the study are included in the subsequent sections detailing design alternatives for each of the three study dams.
2007 Inter-Fluve Inc. 15 Mill River Concept Report 3. Data Collection
3.1. Existing data
Historic maps and photos are important in determining the age of the dams, previous iterations of the dams, other dam sites and historic wetland and stream geomorphic conditions. Historic dams, either buried by sediment or long ago removed, can have a dramatic impact on the appearance of the modern landscape (Walter and Merrits 2007). Historic conditions create a frame of reference for future restoration.
Available information about the Mill River watershed was evaluated, including historical data obtained from the State of Massachusetts, the USGS, Mass Historical Commission, the Wampanoag Tribal Historic Preservation Officer and the Old Colony Historical Society. Historic maps and photographs evaluated included topographic maps, aerial photographs, Sanborn Fire Insurance maps and older regional and local maps depicting property ownership and general boundaries, including: 2005 color orthophotographs, 1:5,000 1996 black and white orthophotographs, 1:5,000 Black and white orthophotographs, 1941, 1952, 1960, 1971, 1974, 1977, 1980 April 28, 1992 – April, 1995 black and white orthophotographs, 1:12000 USGS 15-minute quadrangle maps (1893) USGS 7.5-minute quadrangle maps (1944, reprinted in 1949) USGS 15-minute quadrangle maps (1987) USGS 7.5 minute quadrangle maps (2003) City of Taunton Map (1728) City of Taunton Map (1790) Bristol County Map (1883) Various Sanborn Fire Insurance maps Interfluve reviewed the Pare Engineering assessment reports for Morey’s Bridge Dam (Pare 2005a) and the Whittenton Pond Dam (Pare 2005b), and reviewed the preliminary assessment report completed by Milone and MacBroom (MacBroom 2006). Literature review included regional histories (Emery 1893, Hurd 1883, Weston 1906), Mass DFW fisheries reports and Plymouth General Court proceedings.
3.2. Field data
3.2.1. Survey Creating a detailed base map of topographic conditions is the first step in the design process. This base map, as well as cut and fill volumes, hydraulic modeling, design and cost estimates, all hinge upon an accurate survey of existing conditions.
2007 Inter-Fluve Inc. 16 Mill River Concept Report In April and May of 2007, Interfluve staff, with the help of project partners, conducted a topographic and bathymetric survey of the project reach from 100 ft upstream of the Morey’s Bridge Dam to 400 feet downstream of the State Hospital Dam. This topographic survey included cross sections through the floodplain and channel every 50-200 feet. Landowners were notified of the survey plan and schedule via letter and an informational public meeting held at the Old Colony Historical Society. All landowners along the stream were cooperative, and several landowners contacted SRPEDD and Interfluve regarding access routes and particular concerns. Photographs were taken of the dam sites and the stream channel during various stages of flow. The Interfluve topographic data was combined with existing 2-ft contour data for the City of Taunton (obtained from Applied Geographics, Boston, MA) to create an existing conditions basemap of upland and wetland features.
Bathymetric survey – We conducted a bathymetric survey of submerged areas using boat mounted, GPS-linked depth sounding equipment. These data were combined with the upland topography, additional bathymetric data collected via total station, and sediment depth measurements to complete the existing conditions basemap (See Concept Plans).
Sediment survey – Interfluve collected sediment depth measurements in all three impounded areas. These data were collected by pushing a sediment depth probe through the fine sediments until refusal. Depth of refusal probes were taken at regularly spaced intervals (20-40ft) across cross-sections spaced roughly every 50-100 feet. Notes regarding the general type of sediment were recorded at each location, and locations were marked by GPS waypoint. Depth of refusal was measured from the impoundment water surface, and impoundment water surface was measured either via total station that same day or via water surface benchmark stakes installed prior to survey. The waypoint data was then downloaded and converted into CAD data to be incorporated in restoration designs.
Infrastructure survey – Existing infrastructure reports were reviewed and engineers conducted site visits to evaluate each of the dams for the condition of the structure, embankment, spillway, masonry, and reservoir, along with potential access issues.
3.2.2. Sediment characterization Dams often contain sediment deposited in their impoundments. This sediment contains a historic accumulation of nutrients and chemicals bound to fine sediment such as silt and clay. Assessing sediment quality is critical in determining the methods used to manage the sediment while minimizing risk to public safety. The sediment characterization in this feasibility phase is referred to as screening. This level of analysis is intended to establish the presence or absence of contaminants and help guide future sediment management planning. Once a design plan is in place, further testing will commence.
2007 Inter-Fluve Inc. 17 Mill River Concept Report
Due diligence – In order to determine the appropriate sediment quality testing regime, a due diligence review of potential contaminant sources was completed. This review examined watershed landuses and potential point sources of contaminants such as large chemical users, historic spills, underground utilities and storage tanks. Due diligence review of potential contaminant sources was completed in the summer of 2007, and included research of potential contaminant sources using the archives of local and state agencies. The detailed results of the due diligence review are included in Appendix B.
Sediment sampling - Samples for sediment quality testing were obtained by Petite Ponar dredge dropped from a small boat, or by coring with a small hand corer. Because of the lack of fine sediment typically found in the channel thalweg areas, we sampled the submerged impoundment surface at the edge of the deep channel. Samples were processed and subsamples distributed into glass bottles according to laboratory instructions. Sample locations within the impoundments were stratified to obtain samples near the dam structure, in the middle of the impoundment, and in the upper impoundment. Three samples were taken in the Whittenton and State Hospital impoundments, and two samples were collected in the West Britannia impoundment. Samples were sent to Geolabs (Braintree, MA) for testing of chemicals suggested by landuse and results of the due diligence review. Sediment was tested for petroleum hydrocarbons, polychlorinated biphenyls (PCBs), metals, polyaromatic hydrocarbons, volatile organic compounds and total organic carbon content.
3.2.3. Wetland assessment A wetland assessment was completed as part of this Concept Study to predict potential effects of fish passage restoration projects, particularly dam removal and impoundment drawdown, on wetland resources. Wetlands were first identified using available data through the Mass GIS web site for the project area, as well as Natural Resources Conservation Service (NRCS) soils mapping and web-based soils survey data for the project area (SSURGO, 2006). An Area of Interest (AOI) was developed for the project area using the NRCS web site to secure the relevant soils information, particularly the presence of hydric soils that have been mapped by NRCS for lands bordering and/or draining to the project area impoundments and lands encompassing the dam structures and raceways. Soils data for the AOI are provided in subsequent sections of this document.
Once the desktop information was collected and reviewed, partial wetland delineation and field reconnaissance of the project area was completed by staff from the National Oceanic and Atmospheric Administration (NOAA) Restoration center (J. Turek, S. Block) to ground truth mapping information, classify project area wetland types, and assess potential changes to wetlands that would result with implementation of one of project alternatives. The NOAA wetland reconnaissance was completed on May
2007 Inter-Fluve Inc. 18 Mill River Concept Report 21, 2007, using both foot access and kayaks to ground truth wetlands in the project area. Wetlands were classified and defined according to the National Wetland Inventory classification system (Cowardin et al., 1979) as well as resources defined under the Massachusetts Wetlands Protection Act (MWPA – 310 CMR 10.00-10.99). Photographs were taken of representative wetland plant community types. This task was supplemented by a wetland delineation completed by Massachusetts Riverways Program biologists for those lands only in close proximity of the project dams and raceways.
3.2.4. Natural Resource Area assessment The project team conducted an analysis of available natural resources of the Mill River Restoration project area to develop a general understanding of the area’s potential to support wetland communities and other resource areas regulated by the Massachusetts Wetlands Protection Act. As part of this analysis, we reviewed existing digital natural resource maps and aerial photographs of the project area in a Geographic Information System (GIS) database. The GIS data was obtained from the Massachusetts Geographic Information System and included the following data layers (see: www.mass.gov/mgis/massgis.htm): o 0.5 meter resolution color ortho photo images (2005) 1:5,000 scale o U.S. Geologic Survey 7.5 minute topographic quad images (1987) 1:25,000 scale o Massachusetts Department of Conservation and Recreation (MA DCR) Areas of Critical Environmental Concern (2007) 1:25,000 o Massachusetts Department of Environmental Protection (MA DEP) Wetlands map images (2007) 1:12,000 scale o Natural Resource Conservation Service (NRCS) Soil Survey Geographic (SSURGO) map images (2006) 1:25,000 scale o Federal Emergency Management Agency (FEMA) Q3 Flood data (1997) 1:25,000 scale
The U.S. Fish and Wildlife Service’s National Wetlands Inventory (NWI) maps were not available for the project area at the time of the analysis. Woodlot also reviewed GIS data from the MA Natural Heritage and Endangered Species Program (NHESP), including the Priority Habitat, Estimated Habitat, and Certified Vernal Pool datalayers. The natural resource assessment report results are discussed in Section 5, and the full report is given by in Appendix C.
2007 Inter-Fluve Inc. 19 Mill River Concept Report 4. Background Information
4.1. Natural History
The Mill River is a tributary to the Taunton watershed. These rivers originated on glacial outwash soils and developed over a broad, flat valley leading to the formation of many riparian wetlands. Several riparian wetland types are found along the Mill River, including red and silver maple dominated floodplain forests, Atlantic white cedar swamps, and palustrine forests dominated by red maple, sphagnum mosses, pepperbush, ferns, swamp white oak, green ash and white pine. The potential ecological quality of the Mill River is found to some degree in its parent watershed. The Taunton River watershed is the second largest watershed in Massachusetts and is home to numerous tributaries and extensive wetlands, including the Assawompsett Ponds and the 16,800-acre Hockomock Swamp, the largest remaining wetland in Massachusetts. The Taunton and its tributaries support 29 species of native fish, including native brook trout and the rare Atlantic sturgeon. The Nemasket River has the state's largest alewife run, and the Winnetuxet River provides an abundant warmwater fishery. The Taunton River also has a diverse freshwater mussel population, with seven species of mussels and three on the state list of special concern species (Eastern Pondmussel, Tidewater Mucket, and the Triangle Floater). There are currently nine cold-water streams supporting native brook trout, a species extremely sensitive to watershed disturbance. The watershed supports hundreds of bird species, including forest interior, grassland, wetland, waterfowl and rare breeding species (Calabro 2007).
The surrounding tributaries and the main Taunton River demonstrate the ecological potential of the Mill River. Given proper management, the Mill River can contribute substantially to the health of the Taunton River system. In the following paragraphs, we outline the human and geomorphic history of the Mill River, which offer keys to restoring natural functions of the system.
4.2. Fisheries History
The Wampanoags of Cohannet relied heavily on migratory fish for protein. Communities and family groups designed their lifestyles to be mobile, setting up localized camps near streams like the Mill River to capture alewives and herring. They followed this pattern to other streams, catching sturgeon, brook trout, and salmon, and then to the sea in summer to supplement their agricultural diet on shellfish, lobster, crabs, cod and striped bass. In September, camps retreated inland to catch returning eels. The importance of fish passage was not lost on early European settlers either, but economic forces in Taunton eventually outweighed public concern over fisheries (see the following section). Based on the history of dam construction, it is estimated that herring became extirpated from the Mill River sometime in the mid to late 1700s. All tributaries of the Taunton River have had or currently have runs of alewives (Alosa
2007 Inter-Fluve Inc. 20 Mill River Concept Report pseudoharengus), blueback herring (Alosa aestivalis), American eel (Anguilla rostrata) and white perch (Morone americana). American shad (Alosa sapadissima) were once abundant in the Taunton River watershed but attempts to restore successfully reproducing populations have met with little success.
In the last 30 years, the State of Massachusetts and the Federal government have taken steps to quantify the oceanic and inland constraints to migratory alosid populations and to increase populations through fisheries regulation, water quality improvement and restoration (Atlantic States Marine Fisheries Commission 1999, Reback et al. 2004). At least since the middle of the last century, alewives have been documented on the Mill River up to the first dam (Brady 2007 – pers. comm.). Reback and DiCarlo (1972) report that the Mill River contained mostly warmwater out migrants from Lake Sabbatia, including large-mouth bass (Microperus salmoides), pickerel (Esox sp.), black crappie (Pomoxis nigromaculatus), white perch (Morone Americana), yellow perch (Perca flavescens), brown bullhead (Ameiurus nebulosus), golden shiner (Notemigonus crysoleucas) , bluegill (Leposmis macrochirus), and pumpkinseed (Lepomis gibbosus), but did include migratory species up to the first dam including American eel and white sucker. In late July 2007, Massachusetts Division of Fisheries and Wildlife personnel conducted a fisheries sampling just downstream of the Whittenton dam and also just downstream of the State Hospital dam. Seven species were captured at the Whittenton dam site, including American eel, bluegill, brown bullhead, redfin pickerel (Esox americanus), chain pickerel (Esox niger), largemouth bass and tessellated darter (Etheostoma olmstedi). Only American eel and tessellated darter were found at the State Hospital site (Hurley 2007).
4.3. Cultural Resources
Prior to European settlement, the rivers of southeastern Massachusetts, including the Mill, were inhabited by various native peoples throughout prehistory. Cohannet, as Taunton was known prior to 1640, was inhabited by the Wampanoag at the time the first Europeans began to settle the area. Taunton is the oldest European colonial settlement in Bristol County, established sometime in the 1630s and incorporated in 1639. Early maps show the location of grist mills and other industry along the river (Figure 4-1, 4-2).
2007 Inter-Fluve Inc. 21 Mill River Concept Report N
Approximate location of the original Whittenton Pond dam
Figure 4-1 — Map of the Mill River and Taunton ca. 1728 (courtesy Old Colony Historical Society)
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Figure 4-2 — Map of the Mill River project area (USGS 1893)
2007 Inter-Fluve Inc. 23 Mill River Concept Report The ability of the Mill River to provide mechanical water power was a major attraction for early settlers. The first grist mill dam was located on what is now called Mill River Place. According to records, the dam was constructed at a grade drop, likely a riffle, on the Mill River just upstream of Cohannet Street, near the current downtown area and downstream of the State Hospital Dam (Emery 1893, Hurd 1883). The original dam at this location was built around 1639-40, but both the dam and grist mill were rebuilt by Robert Crosman in 1698. The second mill, called Crosman Mill, was converted from a grist mill to a fulling mill and continued to operate until 1823, when it was either renamed or rebuilt. The Woolstock Mill operated on the site into the 1900s, but no buildings remain. The dam abutments and some mill foundation remnants are still visible on both banks, but the dam is gone.
As more dams were erected, fish passage became a growing concern among Taunton residents. Another dam was built downtown around 1664 to power a sawmill owned by Henry Andrews and John Macomber. This dam was allowed to be built with provisions for timber sale, non-interference with grist mill operation and fish passage (Emery 1893). Sometime during his ownership, Robert Crosman constructed a “trench or dike on the East Side of the Mill River for the free passage of herrings around his dam.” This is perhaps one of the earliest instances of bypass channel construction by colonial residents, although for centuries native tribes had been using constructed fish weirs and channels to facilitate capture of migratory fish. Several actions of the General Court required dam owners to construct free passage of fish. The History of Plymouth gives this example of legal action taken against James Walker and his associates in June 1664 (spelling preserved):
In reference to the complaint of sundry of the inhabitants of the towne of Taunton against James Walker and others, for the restraining of the alewives from going up according to thiere usuall manner by reason of a sawmill in thiere herrieng river, by which obstruction of the said fish the said towne hat and is in danger to suffer much damage, this Court hath ordered, that betwixt this date and the next season of the fishies goeing up, they, the said owners of the mill shall make or cause to be made a free full and sufficient passage for the goeing up of the said fish, or otherwise, upon the further complaint of the towne, the Court will take an effectuall course that the same shall be done (Plym. Col. Rec., vol.IV, p.66).
Several other dams and mills were constructed in the next three centuries. At some point the economic pressure of large mill operations outweighed the desire for fish passage, and migration was blocked.
State Hospital Dam – In 1735, Captain James Leonard purchased a sawmill dam, water rights and mill property from Jon and Joseph Barney, who had been operating the sawmill for some time. The mill was located just downstream of Danforth Street, according to Emery (1893) about “1/3 of a mile below the old sawmill (Britannia)”. This became a rolling and slitting mill until around 1818, when Richmond
2007 Inter-Fluve Inc. 24 Mill River Concept Report constructed a large dam, the Hopewell Factory Dam, downstream of the older dam. The new dam, approximately 10 feet high, flooded the upstream mill foundation to a depth of 8 feet. Richmond built a cotton mill on the east bank, and in 1821, built a second mill building and a rolling mill. Various owners continued to manufacture cotton fabrics at the site into the 20th century. The property eventually came under the control of the Massachusetts Department of Health, and the dam is now referred to as the State Hospital Dam. The main spillway of the Hopewell Factory Dam was covered or removed, and the Mill River now flows down what was the center flume (Figure 4-3). In 1991, a portion of this property was transferred to the Department of Fisheries, Wildlife and Environmental Law Enforcement.
Figure 4-3 State Hospital dam (Hopewell Mills) site circa 1893 (Sanborn)
West Britannia Dam – In 1800, Samuel Leonard and William Crocker built a dam and mill just upstream of Britannia Street. This rolling and slitting mill produced iron plates and nail rod until 1807, when Crocker, Bush and Richmond bought the property and converted it to the production of copper plating, cylinders, and shells, along with some zinc works. Shortly thereafter, the mill was converted to a
2007 Inter-Fluve Inc. 25 Mill River Concept Report small iron ware works. In 1830, various owners conspired to build a brick manufactory on the west side of the Mill River, and eventually Reed and Barton purchased mill space in what was to become the Reed and Barton manufacturing complex. The most recent iteration of the dam was constructed in 1857, according to historic records and the date on the stone face of the dam (Figure 4-4). The dam remains today, complete with downstream raceway and a side diversion channel that runs underneath one of the larger Reed and Barton factory buildings. The flashboards were removed sometime prior to 1941, and the impoundment has not changed appreciably since that time.
Whittington (Whittenton) Dam – In 1666, James Leonard, an experienced bloomer or iron worker, purchased property in Whittington near the current Whittenton Mills dam. By 1669 he had proposed dam construction Figure 4-4 West Britannia Dam. In this picture, the dated stone is just underneath the leftmost piling and entered a flooding easement with his supporting the walkway (photo Inter-Fluve) neighbor George Macy across the Mill River. It is unclear exactly when the dam was built, but by 1678 Leonard had opened a small working iron foundry. The Whittington Iron Works foundry operated under the Leonard family name until 1810 when Crocker, Bush and Richmond purchased the mill, dam and property. In 1811, the foundry and mill buildings were burned and a cotton mill was constructed. It is believed that sometime in the early 1800s, a new and larger dam was constructed that impounded Whittenton Pond nearly to the outlet of Lake Sabbatia, then called various names including Scuddings, Studdings or Scaddings Pond. In October 2005, the superstructure of the dam was removed, and the remaining dam structure was shored with large riprap and cobbles in response to concerns over imminent failure as a result of heavy rainfall (Bellisle 2006). Dry stream conditions in the summer of 2007 revealed the presence of at least one, and possibly two earlier iterations of the Whittenton Pond Dam. The first, a timber crib skeleton is located just upstream of the existing dam and may either be an artifact of construction of the existing dam, or could be the remnants of an earlier dam (Figure 4-4). The second is located approximately 400 feet upstream of the existing dam and is connected to the left bank via a gravel ramp that may be a remnant of an early road crossing, part of an older earthen embankment dam, or some artifact of dam construction (Figure 4-5).
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Figure 4-5 (left) - Exposed structure at the Whittenton Pond Dam, looking downstream at the dam. Water is flowing through the dam structure and not over the spillway (photo TRWA) Figure 4-6 (right) - Exposed structure 100 feet upstream of Whittenton Pond Dam, looking from left bank across the impoundment (photo SRPEDD)
4.4. Geologic history The Mill River is a post glacial river originating near East Foxborough, Massachusetts as the Canoe and Little Canoe Rivers. On the north end of Winnecunnet Pond, the system picks up additional flow from smaller tributaries and from Mulberry Meadow Brook, which is fed by Poquanticut Brook and Beaver Brook to the north. From Winnecunnet Pond through the southern tip of the Great Cedar Swamp and into Lake Sabbatia, the stream is named the Snake River. Downstream of Lake Sabbatia, the Mill River drains south and east through mostly developed land in the city of Taunton (Figure 1-1). The Mill River drains an area of 45 square miles, emptying into the Taunton River just east of Ingell Street and south of Summer Street in Taunton. Surficial geology - As it receded from its southern-most extent, the Narragansett Bay-Buzzards Bay lobe of the Wisconsinan glacial ice sheet deposited much of the surficial sediments found today in southeastern Massachusetts. As the ice sheet receded and meltwaters were trapped by glacial moraines and adjacent ice sheets, Glacial Lake Taunton grew to about 500 square miles. Sediment carried into the lake by glacial meltwater streams was deposited in the form of deltas or flat beds; deltas were deposited on horizontal layers of sand, gravel, or lake bottom sediments, which consisted of clays or fine silts (Skehan 2001). The surficial deposits of the Mill River watershed are primarily stratified glacial deposits consisting of gravel, sand, silt, and clay. These deposits may be over 100 feet thick in some locations. Glacial outwash streams deposited much of this stratified material as the sediments were carried into Glacial Lake Taunton, but the deposits also come in the form of kames, eskers, ice-contact deposits, and outwash deposits.
2007 Inter-Fluve Inc. 27 Mill River Concept Report Because the gradient of the Taunton River watershed is generally low, there are many swamps and wetland areas, many of which contain extensive peat beds. The Mill River, however, is the exception within the Taunton River watershed, and has a higher gradient with no extensive, natural, wetland or swamp areas south of Lake Sabbatia. Most of the swamp deposits are to the north and east of Lake Sabbatia and the Mill River, though there are a few small deposits to the west. These swamp deposits consist of plant material with sediment consisting of clay, silt, sand, and gravel. See the wetland section of this report for further detail on localized wetland areas. There are a few small till deposits west of the Mill River. These consist of poorly sorted, unstratified sediment of varied material ranging from boulders to fine silt and some clay. The closest drumlin appears to be north of Lake Sabbatia, so these till deposits are likely in the form of uneven deposits that vary in thickness. The final type of natural deposit within the Mill River watershed south of Lake Sabbatia is alluvium. This deposit is found in the Mill River alluvial valley from approximately the Whittenton Bridge to below the State Hospital Dam and consists of stream-deposited gravel, sand, silt, and some clay. Soils - The soils along the Mill River downstream of the Bay Street crossing (Morey’s Bridge) are classified by the NRCS as three types, Freetown Muck, Hinckley sandy loam and urban land, with the Hinckley sandy loam making up the large majority of the soils in the immediate riparian area and adjacent uplands. Freetown muck soils are poorly drained organic material whereas the Hinckley sandy loams are more well drained alluvial soils. In addition to natural glacial and alluvial deposits, there is also artificial fill, termed urban land, around the Whittenton and Britannia dams that generally consist of sand and gravel.
4.5. Geomorphic History
4.5.1. Historic geomorphology, forestry, wetlands and fisheries Prior to the construction of dams, the Mill River flowed freely and likely looked much like it does now in the reach between the State Hospital Dam and the Hopewell Park area (Figure 4-7). Baseflow hydrology historically dominated the watershed due to the presence of headwater lakes and wetlands, and highly permeable soils, which suggests that the channel was relatively small and the riparian area semi- perennially wet. At that time, the channel would likely have had a balance of active erosion and deposition, with point bars and overbank deposition of fines creating a wide, mature floodplain between the State Hospital and Whittenton Dam sites. In this reach, the channel migrated slowly across the floodplain thick with flood tolerant red maple, willow and alder trees. Upstream of the Whittenton Dam site, the channel had a relatively flatter gradient as the channel drops over the Taunton River valley wall near the Whittenton site. The Whittenton reach had a wider and flatter floodplain than the downstream
2007 Inter-Fluve Inc. 28 Mill River Concept Report reach, with gentle meanders cutting through a broad valley bounded by what is now the former edge of the impoundment. The headwaters of the Mill River (Canoe) are steep for the first five miles, and then the channel tapers off until it drops steeply through the downtown area. There is only mild topographic variation in valley profile through much of the Mill River watershed. From Massapoag Lake to the confluence with the Taunton River, the elevation of the channel drops a total of 246 feet. Figure 4-7 – A typical gravel and cobble riffle on the Mill River downstream of the State Hospital The channel drops roughly seven feet from Lake Dam (photo Inter-Fluve) Sabbatia to Whittenton Street, with a bedslope of 0.14%. Downstream of Whittenton Pond to Washington Street, the channel drops 34 feet and the slope averages 0.29% (Figure 4-8).
Whittenton Dam site
Figure 4-8 – Approximate longitudinal profile of the Mill River
Forests - Prior to European settlement, the woodlands of the Taunton area were a patchwork of various communities dominated by the oak-chestnut forest type. At this time, southeastern Massachusetts forests were primarily black, red and white oak, chestnut and hickory, with hemlock and white pine stands present throughout (Emery 1893, Cronon 1983, O’Keefe and Foster 1998). The variability in soils, climate, slope and fire created a patchwork of isolated ecosystems including pitch pine in the dry sandy hills, Atlantic white cedar along bog edges, oak-chestnut midlands, and thick riparian lowland swamps dominated by red maple, white oak, alder and willow. Taunton’s developed areas sit atop dry land surrounded by former forested wetlands of the Three Mile and Mill Rivers to the west, Taunton River to the east, and Pine swamp and Hockomock Swamp (Great Cedar Swamp) to the north.
2007 Inter-Fluve Inc. 29 Mill River Concept Report With the exception of fire protected wetland areas, native peoples cleared understory with low temperature fires that kept hunting areas open and kept canopy trees intact. In addition to maintaining this parklike forest environment, Indians also used fire to clear forests for agriculture, a practice common among southern New England tribes (Cronon 1983, Merchant 1989). By the late 1500s, it is estimated that grain constituted one half to two thirds of the southern New England Indian diet. This practice probably had a local influence on the hydrology of streams. However, because of the low impact practices and the transitory nature of Indian agriculture whereby fields were abandoned when deemed infertile, it is likely that pre-European agriculture had little effect on water quality. Flows in the Mill River likely increased in rate and volume during the peak agriculture period of 1780 to 1850. To some degree, the return of forest cover since that time has probably restored the infiltration properties of the upper watershed back toward its pre-settlement condition, somewhat mitigating impact of roads, housing developments, dams, cranberry operations and scattered farms (Foster 1998). It is likely however, that pre-settlement flow was groundwater dominated and the channel through Taunton would have been smaller with forested wetlands dominating the riparian zone.
5. Existing Conditions
5.1. Modern landuse
Urban landuse has had a significant impact on Mill River health, mainly due to the effect of past industry, discussed in the next sections, and the increase in impervious surfaces. Driveways, roads, rooftops and other hard structures prevent the infiltration of precipitation and cause the baseflow of streams to decrease (Klein 1979, Schueler 1995). Conversely, rainwater falling on these impervious surfaces travels quickly to catch basins, storm drains and pipes that eventually dump into waterways. This causes flows in the stream to increase rapidly with greater frequency, resulting in more frequent and relatively severe flooding. Most of the impervious cover in the Mill River watershed is concentrated near the lower reaches, resulting in the most significant impact for the reaches through downtown Taunton. Some additional land use changes of note include:
Whittenton Pond - A side channel was constructed along the left bank (east bank) at the Whittenton Mills complex and existed until sometime between 1960 and 1971, when the channel was filled in to create additional parking area.
West Britannia - Although the Reed and Barton plants have expanded, the area of the dam site has not changed appreciably since at least the 1930s and the impoundment has been maintained at the same elevation. The impoundment soils were exposed following removal of the
2007 Inter-Fluve Inc. 30 Mill River Concept Report flashboards sometime prior to 1940. The West Britannia impoundment has undergone increase in shrub and tree growth since the 1930s. Large tree growth is limited due to invasive grasses and wet conditions.
All dams - Starting in the 1950s, residential density increased significantly until the 1980s, particularly along the Whittenton Pond riparian area. Development has been limited due to the presence of wetlands throughout the area.
5.2. Existing Geomorphology The geomorphic conditions at each dam site are described in more detail in the recommendations section of this report. This section briefly describes the existing geomorphology of the Mill River and how that geomorphology affects conditions at each dam. The Mill River originates as the Canoe and Little Canoe Rivers, joining Mulberry Meadow Brook at Winnecunnet Pond. Then called the Snake River, the stream runs through wetlands into Lake Sabbatia. The low gradient of the tributaries, combined with the backwater effect of Winnecunnet Pond and Lake Sabbatia limit the amount of sediment eroded from streambanks and transported through the system to the downstream reaches. The limited sediment supply is the primary reason why the Whittenton Pond has a relatively small amount of impounded sediment upstream of the dam. The lakes and wetlands absorb water and hence slow the flow of water through the system, attenuating peak discharges. There are free flowing segments of the Mill River just downstream of the Whittenton Dam, in the walled channel between the West Britannia dam and the State Hospital Dam impoundment, and also in the Hopewell Park area through to the Taunton River confluence. These reaches are heavily impacted by fill in the riparian zone and also by historic impounded sediment. The reaches are also armored, a condition common in channels downstream of dams. With the exception of the walled reach in the Reed and Barton factory area, all three reaches are slightly overwidened due to excess bank erosion, and the reach immediately below Whittenton is channelized. Streams downstream of dams are often referred to as “sediment starved”, a condition whereby sediment drops out in the impoundment and clear water is discharged downstream. This energy is expended through erosion of bank soils and selective removal of finer sediment from the channel bed, resulting in the armoring of the downstream channel. The reaches downstream of dams on the Mill River exhibit some evidence of armoring, although no quantification of sediment gradation was performed. Significant armoring limits the geomorphic activity of streams, which translates into wider and shallower reaches with homogenous and degraded habitat.
The infrastructure of downtown Taunton has a major effect on the geomorphology and local hydraulics of the Mill River. Much of the riparian area and floodplain in the downtown area has been filled, and thus floods are confined to the narrow channel. This concentration of flood flow subjects the
2007 Inter-Fluve Inc. 31 Mill River Concept Report channel to higher energy than it would receive if floods were allowed to dissipate over the floodplain. Elevated energy conditions cause scour of fine sediment and armoring of the channel, which limits bedload movement and thus habitat formation. Contrasted to this, in natural streams banks erode and fresh sediment is deposited on bars or on the floodplain. These interactions, along with inputs of wood and other features, create complexity that is critical to quality habitat.
Bridge crossings at Spring Street and Weir Street, and possibly others downtown do not appear to be able to pass the 100-year flood without backing up or overtopping. During the approximate 5-year rainfall runoff event in mid-April 2007, we observed less than six inches of freeboard under the low chord of both the Spring Street and the Weir Street bridges. While we did not formally assess the capacity of these bridges, based on these observations, the bridges may play a significant role in local flooding.
5.3. Wetland Resources Understanding the wetland resources in and around the impoundments is important in determining the potential impact to those resources. Here we describe the Mill River riparian wetlands in a general sense. Wetlands associated with each impoundment and dam site are described in more detail in sections 8-10. Wetlands in the project area include seasonally to semi-permanently flooded palustrine deciduous forested (PFO1C, PFO1F) swamp, seasonally to semi-permanently flooded palustrine deciduous scrub- shrub (PSS1C, PSS1F) wetlands, and semi-permanently to seasonally flooded palustrine persistent emergent (PEM5F, PEM5C) wetlands. Most of these resources are considered as Bordering Vegetated Wetlands (BVW) bordering and draining to Land Under Waterway (LUWW), as defined by the Massachusetts Wetland Protection Act (MWPA). Inland Bank, as defined by the MWPA (310 CMR 10.54 (2)) also exists along the Mill River and its tributaries within the project area. The data from the NRCS Soil Survey – Bristol County, MA, Northern Part revealed that at least 18 mapped soils units are present in the project AOI. Hinckley sandy loams are the prevalent soils forming the uplands and slopes bordering the impoundments where highly altered conditions resulting in Udorthents (urban lands) have not been mapped. Most of the mapped Hinckley soil units are 0-8 percent slopes, although in localized areas, slopes may reach 35 percent. Windsor and Deerfield loamy sands, Charlton-Paxton fine loamy stony sands Whitman fine sandy loam and very stony, and Unadilla very fine sandy loam are other mapped upland units that form the slopes and watersheds draining to the project area wetlands. In general, these soils units have relatively high permeability rates, and in lower slope areas, runoff is more likely to percolate into the soils and allow for greater groundwater transport. Seasonal groundwater discharge is then expected near slope breaks, where mapped hydric soils units are found. The project Area of Interest (AOI) includes five mapped hydric soils units: Wareham, Scarboro, Swansea, Freetown, and Whitman. Table 5-1 is a summary description of these hydric soils, as provided
2007 Inter-Fluve Inc. 32 Mill River Concept Report by the NRCS survey information. Information on depth to water table and frequency of standing water (“ponding”) has been highlighted to help explain the wetland types present. Highly permeable Wareham loamy sands with a seasonal high water table at or near the surface are typically found on terrace landforms along the borders of the impoundments and comprise areas dominated by bordering forested and scrub-shrub wetlands. Scarboro mucky sandy loams are also found on terrace landform features, but are more likely to be ponded and thus seasonally to semi-permanently flooded and/or saturated forested and scrub-shrub wetlands. Swansea and Freetown mucks are less frequently found in the project area and occupy bog-like areas where deep (sometimes exceeding 2 feet) organic mucks overlying deep sands form and remain ponded for extended periods with semi- permanently to permanently saturated soils. These areas typically are dominated by emergent and scrub- shrub wetlands. Whitman sandy loams are situated in topographic depressions and overly dense till soils with very low permeability, and may be seasonally flooded and saturated forested, scrub-shrub, or emergent wetlands with a perched water table condition. Ponding is frequent in the Whitman soil units which are more localized and discharge to down-gradient terrace units.
5.3.1. Critical Natural Resources No Priority Habitat, Estimated Habitat, or Certified Vernal Pools occurred within or near the Mill River project area. The portion of the Mill River north of the Morey’s Bridge Dam is included within the 2,037 acre Canoe River Aquifer Area of Critical Environmental Concern. Any activity proposed within this area may require additional regulatory review, including review under the Massachusetts Environmental Protection Act.
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Table 5-1. Key NRCS Mapped Hydric Soils within the Project Area
32A—Wareham 43A—Scarboro 51A—Swansea muck, 0 to 1 52A—Freetown muck, 0 73A—Whitman fine loamy sand, 0 to 3% mucky loamy fine % slopes to 1 % slopes sandy loam, 0 to 3 % slopes sand, 0 to 3 % slopes, extremely stony slopes Landform: Terraces Bogs Bogs Depressions Landform position (two- Footslope Toeslope Toeslope Toeslope Toeslope dimensional): Landform position (three- Tread Tread Tread Tread Base slope dimensional): Down-slope shape: Concave Concave Concave Concave Concave Across-slope shape: Concave Concave Concave Concave Concave Parent material: Loose sandy Loose sandy Highly-decomposed organic Highly-decomposed Friable coarse-loamy glaciofluvial deposits glaciofluvial deposits over loose sandy deposits organic material aeolian deposits over and/or firm loamy basal till dense coarse-loamy derived from igneous and lodgment till derived metamorphic rock from granite and gneiss
Slope: 0 to 3 percent 0 to 3 percent 0 to 1 percent 0 to 1 percent 0 to 3 percent Depth to restrictive More than 80 inches More than 80 inches More than 80 inches More than 80 inches 15 to 25 inches to dense feature: material Drainage class: Poorly drained Poorly drained Very poorly drained Very poorly drained Very poorly drained Capacity of the most High to very high High to very high Moderately high to high (0.60 Moderately high to high Very low to moderately limiting layer to transmit (6.00 to 20.00 in/hr) (6.00 to 20.00 in/hr) to 6.00 in/hr) (0.60 to 6.00 in/hr) high (0.00 to 0.20 in/hr) water (Ksat): Depth to water table: About 0 to 6 inches About 0 to 12 inches About 0 inches About 0 inches About 0 inches Frequency of flooding: None None None None None Frequency of ponding: None occasional Frequent frequent frequent Available water capacity: Low (about 4.1 Low (about 5.4 High (about 9.0 inches) Very high (about 22.2 Very low (about 1.8 inches) inches) inches) inches) Typical profile 0 to 4 inches: Loamy sand Mucky loamy sand Muck Muck Fine sandy loam (0-8) 4 to 36 inches: Loamy coarse sand Loamy sand Muck Muck (5-60 inches) Gravelly sandy loam (8- 60) 36 to 60 inches: Coarse sand Sand Gravelly loamy coarse sand (26-60)
2007 Inter-Fluve Inc. 34 Mill River Concept Report 5.4. Basis for projecting wetland resource alterations
Sections 8-10 dealing with the specific dam sites describe the existing conditions and how they may change with project alternatives. To better understand these impacts, we have roughly calculated potential impact areas using some metrics commonly used by Massachusetts DEP. The subsections below describe those water resources metrics. Values for mean annual low flow, mean annual flow and bank alteration are listed in each of the sections 8-10.
5.4.1. Land under water bodies and waterways (LUWW) changes Change in LUWW (square feet) is calculated by subtracting the proposed Mean Annual Low Flow (MALFL) channel dimensions from the impoundment area under Mean Annual Flow.
Mean annual low flow (MALFL) – MALFL is one way to quantify baseflow in streams. The August Median Flow is commonly accepted.
Mean annual flow (MAFL) – Mean annual flow is defined as the average flow for the individual year or multi-year period of interest. Mean annual flow is often calculated as equal to the bankfull elevation, roughly the top of bank or “first observable break in slope”.
5.4.2. Bank alteration The stream bank is defined as the area between the MALFL and MAFL. Bank alteration is then calculated as linear feet of alteration.
5.4.3. Land subject to flooding Land Subject to Flooding, as defined in the Massachusetts Wetlands Protection Act, has been divided in the regulations into two different types of areas. Bordering Land Subject to Flooding includes areas which flood as a result of water rising from creeks, ponds, rivers, or lakes. The boundary of Bordering Land Subject to Flooding is the estimated maximum lateral extent of flood water which will theoretically result from the 100-year frequency storm. Isolated Land Subject to Flooding includes areas which flood due to ponding of run-off or high ground water.
5.4.4. Bordering vegetated wetlands (BVW) Existing wetlands boundaries from existing maps and from partial field delineation are shown in Figure 5-1a and 5-1b. Accurate determination of the estimated change in BVW will require a thorough wetland delineation in future project phases. Wetlands may undergo a change in type, but it is likely that much of the existing BVW area will remain as BVW. Information regarding the criteria for bordering vegetated wetlands can be found at the Mass DEP web page: http://www.mass.gov/dep/water/laws/bvw.htm
35 0
7
0 5 I
60 0
4
50
r
e
v
i
R
l 0 5 l 50
i
M a
50
5
0
50
3C29
3C28 3C23 3C22 3C25 3C24 5 0 3C27 3C21 3C26 3C20 3C19 3C18
3D2 3D3 3D1 3D4 3C17 3D5:END 3C16
3C15
50 3C14
3A19 3C13 3A15 3A18 3A16 State Hospital Dam 3A14 3A17 3A12 3A13 3C12 3A11
3C5
3C10 3C7 3C9 3C8
3B13 3B12 3A10 3A9 3A4 3C4 3A8 3B11 3A3 3A5 3C3 3B10 3A7 0 3B14 3 3A2 3B9 3A6 3B7 3B8 3B15 3B6 3B3 3C2 3A1 3B5 3B1 3B4 3B2
70
60
Legend
6 Bordering Land Subject to Flooding 0 Bordering Vegetated Wetland FEMA 100 Year Flood Zone 0 150 Feet MA DEP Wetland
Hydric Soil 0 NOTE: 3 MA DEP Wetland & Hydric Soil Wetlands delineated by Massachusetts Riverways.
0 Dam 6
Prepared By: Project: Sheet Title: Date: May 2007
Scale: 1" = 150' Mill River Dam Removal Proj. No.: 107148 State Hospital Dam Wetlands Taunton, Massachusetts Figure: 2 107148-F02-StateHospitalWet.mxd 7 0
8
0
9
0 70
7 0 I 70
6
0
60 9 0 0
8
0 Moreys Bridge Dam 7
80 60
80 70
8 0 70
90 8 0 M
6 i 0 l
8 l 0 9 0 R 90 i 8 6 0 v 0
e
r 90 a
0 7
0
7
0
6
60
0 8 0 7
60 0 7 8 0
0 8
90
60
0
6
0 90 6
7
0
80
60
70
0 6 3Pink No ID~4 60 80 3Flag Re-Fresh 3LEC-2 3Pink No ID~2a 3LEC-1
0 6 3Pink No ID~3
6 0 3Pink No ID~2 3TGG - L31(?) 3Pink No ID 3TGG - L29 7 3TGG - L20 0 3TGG - L21 3TGG - L27 0 3TGG - L28L243TGG - L30 6 3E19 0 3TGG - L22 7 3E173E18 70 3E16 3TGG - L23 3E15
0 60 7
3E14
0
6
3E13 70 3E11 6 0 60 0
6 3E10
3E9
3E7 3E7 Legend 3E6 3E5 3E4 3E3A Whittenton Pond 3F8 3E3 FEMA 100 Year Flood Zone 3F9 3F7 (Mill River) Dam 0 6 3F6 50 3E2 MA DEP Wetland 5 0 3F5 3E1(?) 3F4 3E1 6 0 060 300 Feet Hydric Soil 3F3 3F2 0
7 MA DEP Wetland & Hydric Soil 3F1 NOTE:
Bordering Vegetated Wetland 0 6 6 6 0 Wetlands0 delineated by Dam Massachusetts Riverways
6 0 6 and others. Stream 0
Prepared By: Project: Sheet Title: Date: May 2007
Scale: 1" = 300' Mill River Dam Removal Proj. No.: 107148 Whittenton Dam Wetlands Taunton, Massachusetts Figure: 1 107148-F01-WhittentonWet.mxd
6. Hydrologic and Hydraulic Analysis
6.1. Hydrology
Project hydrology included the development of flow duration and peak flow statistics. The relevance and methodologies used in the development of these statistics are presented below.
6.1.1. Project Area The study area for this hydrologic evaluation encompasses Mill River from its confluence with the Taunton River in Taunton, Massachusetts, to its headwaters in Easton and Mansfield, Massachusetts. The headwaters of the Mill River include rural and agricultural lands, wetland complexes, ponds, and impoundments of former wetlands. The lower reach of the Mill River flows through more developed areas of Taunton, Massachusetts.
Watershed information was obtained from the Massachusetts state geographic information systems website (MassGIS [http://www.mass.gov/mgis/]), including watershed boundaries, major stream networks, and soil surveys. U.S. Geological Survey (USGS) 1:24,000 scale quadrangle map images for Taunton, Norton, Easton, and Mansfield were obtained from MassGIS and used to delineate the Mill River watershed boundary. The tributary drainage area of Mill River at the confluence with the Taunton River was determined to be approximately 43.75 square miles. The delineation of the tributary drainage area is somewhat indeterminate in the headwater reaches due to perched wetlands that may discharge to other watersheds, including the Neponset River watershed.
6.1.2. Methodology – Flow duration statistics Flow duration statistics for an adult alewife migration window from March 15 through June 30 were used to determine fish passage parameters for the feasibility study. Because of their similarities with regard to swimming performance, restoration projects passable by alewife are assumed to be passable by blueback herring. Fish ladder alternatives may be passable by alosids, but as we will discuss later in the document, may not be fully passable by a wide variety of species. These statistics provide a range of values for use in the evaluation of upstream fish passage associated with the project alternatives.
The flow duration statistics were developed using daily average flow data from the U.S. Geological Survey (USGS) Wading River gauging station (USGS No. 01109000) that was obtained from the USGS National Water Information System website. This gauging station was selected for use in the development of relevant flow-duration statistics because of its proximity to the Mill River, the similar watershed size to that of the Mill River, and the length of the gauge record. The Wading River gauging station is particularly well suited as its drainage area is 43.3 square miles, only 0.45 square miles smaller than the
38
Mill River at its confluence with the Taunton River. The Wading River gauge was established in 1925, and therefore has a data record of 82 years. By comparison, the Mill River gauging station (USGS No. 01108410) was established in December 2006 following high flows in October 2005 and has a data record of less than two years. The short period-of-record for the Mill River gauging station is not suitable for the development of flow duration statistics when compared to available data from the Wading River gauging station.
The general suitability of the Wading River data for the development of flow-duration statistics for the Mill River was evaluated by comparing both daily-average and 15-minute flow data over a period when the respective gauging records coincide. The comparison of daily-average flow data suggests that both gauges have a similar hydrologic response (Figure 6-1). With flows in the Wading River increasing more rapidly than in the Mill River (Figure 6-2), however, the 15-minute data indicates greater variation in flow characteristics (i.e., hydrograph duration) between the two gauging stations.
Flow duration statistics were developed by ranking 6,227 daily average flows between March 15 and June 30 (inclusive) for the period from June 1, 1925, through April 24, 2007. Table 6-1 presents relevant flow-duration statistics and Figure 6-3 presents a flow-duration curve based on this analysis.
Figure 6-1: Comparison of Daily-Average Flows
900
800
700
600
500
400
300
200
100
0 1/3/06 2/22/06 4/13/06 6/2/06 7/22/06 9/10/06 10/30/06 12/19/06 2/7/07 3/29/07 Date
# USGS 01108410 MILL RIVER AT SPRING STREET AT TAUNTON, MA
# USGS 01109000 WADING RIVER NEAR NORTON, MA
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Figure 6-2: Comparison of 15-Minute Flows
800
700
600
500
400
300
200
100
0 1/0/00 5/14/01 9/26/02 2/8/04 6/22/05 11/4/06 3/18/08 7/31/09 Date
# USGS 01108410 MILL RIVER AT SPRING STREET AT TAUNTON, MA
# USGS 01109000 WADING RIVER NEAR NORTON, MA
Table 6-1: Flow-Duration Statistics Exceedance Percentile (%) Flow (CFS) 10 207 20 152 50 (median) 81 80 37 90 23
Figure 6-3: Flow-Duration Curve
Estimated Flow Duration Curve During Target Fish Migration Period
1000
River Herring Migration Window
100 Flow (cfs) 10
1 0 20406080100 Percentage of Time Indicated Value Was Equaled or Exceeded
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6.1.3. Peak Flow Hydrology
Peak flow hydrologic statistics (i.e., flood flows) were developed for the project reach of the Mill River in Taunton, Massachusetts. These statistics were developed using regional regression equations and peak flow data obtained by the U.S. Geological Survey (USGS) at three rivers adjacent to the Mill River, including the Three Mile and Segreganset Rivers in Dighton, Massachusetts, and the Wading River in Norton, Massachusetts.
The existing USGS stream gauging station (USGS No. 01108410) was established on the Mill River in Taunton during December 2006 following high flows in October 2005. Due to the short period-of- record for the Mill River USGS stream gauging station, this data record does not provide sufficient data for the evaluation of peak flows in the Mill River. An evaluation of peak flows was therefore performed using other sources of information, including surrogate information obtained from USGS stream gauging stations on adjacent rivers, including Three Mile River, Segreganset River, and Wading River. These rivers are all tributaries to the Taunton River and adjacent to the Mill River. Based on the proximity of these rivers to the Mill River, information on peak discharges in these rivers can be used in the development of peak flow criteria for the Mill River.
Peak flow data recorded at USGS gauging stations on the Three Mile (USGS No. 01109060), Segreganset (USGS No. 01109070), and Wading Rivers (USGS No. 01109000) was obtained from the USGS National Water Information System website. The peak flow data for each river was evaluated using the USGS PeakFQ computer program to provide statistics for the 1.05, 2, 5, 10, 50, 100, and 500- year return-interval hydrologic events (return interval values reflect the data available). The lower interval flow values (i.e., 1.05, 2 year) provide information relevant to “geomorphic” (i.e., bankfull) flows and the higher interval flow values provide information relevant to flooding.
The Federal Emergency Management Agency (FEMA) Flood Insurance Study (FIS) for the City of Taunton, Massachusetts, dated June 18, 1987, was referenced for previous information on peak flows in the Mill River and adjacent rivers listed above, excluding the Wading River, which was obtained from the FEMA FIS for the City of Norton, Massachusetts, dated June 18, 1987. Peak discharges for the Three Mile and Segreganset Rivers for the Taunton FIS were developed for the 10, 50, 100, and 500-year return interval hydrologic events from data obtained at the respective USGS stations and transferred to the downstream community boundary using the gauge transfer relationship shown in Equation 1.
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Equation 6-1. FEMA peak discharge relationship
n (Q1/Q2) = (A1/A2) Where: Q1 = discharge for watershed 1 Q2 = discharge for watershed 2 A1 = watershed 1 drainage area A2 = watershed 2 drainage area
Peak discharges for the Wading River were determined using USGS gauge flow and a log-Pearson Type III distribution, with a weighted skew coefficient. The peak discharges for the Mill River were computed using Wandle’s (1983) formula, which requires drainage area and main channel slope. The FEMA FIS provided peak discharges for the 10, 50, 100, and 500-year return interval hydrologic events based on this equation.
Additionally, peak discharges for the four rivers were calculated for the 2, 5, 10, 50, 100, and 500- year return-interval hydrologic events using National Flood Frequency (NFF) regression equations (Equations 2-6) developed for Eastern Massachusetts and obtained from the USGS website (http://water.usgs.gov/software/nff_manual/ma/index.html). Watershed areas for use with these equations were obtained from the respective USGS gauges. The watershed areas for each of the four rivers is within the defined range of 0.27 and 622 square miles for use of these equations.
Equations 6-2. Eastern Massachusetts Flood Frequency Equations
Q2 = 36.30A0.682 Q5 = 55.38A0.670 Q10 = 72.12A0.660
Q25 = 96.71A0.651 Q50 = 118.1A0.645 Q100 = 143.1A0.638
6.1.4. Hydrologic Analysis Results The results from the FEMA Study, NFF regression equations, and PeakFQ analysis are shown in Table 6-1 and Figures 6-1 through 6-5. It should be noted that the FEMA drainage area for the Wading River of 42.4 square miles differs from the USGS drainage area of 43.3 square miles that was used for NFF and PeakFQ. It has been assumed that FEMA used a prior delineation of the USGS gauge drainage area, and that the change in area followed an updated delineation. 42
Based on this analysis, comparing data from all four rivers, it was determined that the FEMA and NFF unit discharges for the Segreganset River are 24 to 69 percent greater, those of the Three Mile River are 17 to 35 percent lower, and those of the Wading River are 0 to 27 percent lower than those of the Mill River. It was further determined that the drainage area for the Segreganset River is larger, that of the Three Mile River is smaller, and that of the Wading River is the same size as the Mill River watershed (Table 6-4).
Therefore, the proximity, size, and general watershed characteristics of the Wading and Mill Rivers suggest that streamflow data obtained from the Wading River is reasonable for the development of recommended peak flow values for the Mill River. Of note is that the FEMA, NFF, and Peak FQ values for the Wading River vary no more than 9 percent for the respective return-interval hydrologic events. That the Peak FQ values, which are based on a long-term dataset, are consistent with the NFF and FEMA values suggests that these are reliable values to be used in further analyses.
A comparison of the FEMA 10, 50, 100, and 500-year discharge values for the Mill River against those of the Wading River shows that Mill River values are 37 percent to 50 percent higher than Wading River values. This suggests that the Mill River FEMA discharge values may be conservatively high. The FEMA peak discharges for the Mill River were determined using a formula requiring only drainage area and channel slope, which was developed for use on a regional scale and not specific to the Mill River. The FEMA peak discharges for the Wading River were determined from a statistical analysis of a multi- decade data set of discharge values measured on the Wading River. A comparison of the NFF 2, 5, 10, 50, 100, and 500-year discharge values for the Mill River against those of the Wading River shows that the latter are only 0.3 percent to 1.3 percent higher than the former. The similarity of the calculated peak flows for the Mill and Wading Rivers calculated using the NFF equations is a direct result of their similar drainage areas, as drainage area is the only variable in the NFF equations for this region of Massachusetts.
Based on the results of this analysis, it is recommended that the peak flows calculated for the Wading River using PeakFQ be used for subsequent analysis and design as part of this project (Table 6-2). For continuity with the previously-prepared FEMA study, however, it is recommended that the Mill River FEMA discharge values for the 100 and 500-year events be used to evaluate potential changes in the regulatory floodplain associated with the evaluated alternatives (Table 6-3).
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Table 6-2. Mill River Recommended Flow Values (cubic feet per second) for Analysis and Design Return 1.05 2 5 10 50 100 500 Interval Discharge 239 470 686 843 1232 1416 3100
Table 6-3. Mill River Recommended Flow Values (cubic feet per second) for Evaluation within the Regulatory Floodplain
Return Interval 100-yr 500-yr Discharge 2100 cfs 3100 cfs
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Table 6-4. Mill River, Three Mile River, Segreganset River, and Wading River Calculated Discharges
1.05 2 Year 5 Year 10 Year 50 Year 100 Year 500 Year Location Drainage Area (sq. mi.) River cubic feet per second cubic feet per second cubic feet per second cubic feet per second cubic feet per second cubic feet per second cubic feet per second FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ at corporate at USGS limits (? Near at USGS gage Segreganset gage 5.4 10.6 10.6 N/A N/A 149 N/A 182 364 N/A 269 522 415 343 614 610 541 788 700 645 851 935 950 979 confluence with #01109070 #01109070 Taunton?) at USGS at USGS gage Wading at USGS gage gage 42.4 43.3 43.3 N/A N/A 239 N/A 474 470 N/A 692 686 800 867 843 1230 1340 1232 1450 1580 1416 2070 2280 1889 #01109000 #01109000 at confluence at USGS gage Mill N/A* 43.8 43.5 N/A N/A N/A N/A N/A 476 N/A N/A 694 N/A 1100 874 N/A 1700 1350 N/A 2100 1600 N/A 3100 2300 N/A with Taunton # 01108410 at USGS at confluence at USGS gage Three Mile gage 84.6 84.3 84.3 N/A N/A 440 N/A 747 1047 N/A 1081 1548 1820 1350 1949 2710 2060 2563 3170 2420 2844 4440 3460 3474 with Taunton #01109060 #01109060
1.05 2 Year 5 Year 10 Year 50 Year 100 Year 500 Year Location Drainage Area (sq. mi.) River unit discharge unit discharge unit discharge unit dischargeunit discharge unit discharge unit discharge FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ FEMA NFF PeakFQ at corporate at USGS limits (? Near at USGS gage Segreganset gage 5.4 10.6 10.6 N/A N/A 14.1 N/A 17.2 34.3 N/A 25.4 49.2 39.2 32.4 57.9 57.5 51.0 74.3 66.0 60.8 80.3 88.2 89.6 92.4 confluence with #01109070 #01109070 Taunton?) at USGS at USGS gage Wading at USGS gage gage 42.4 43.3 43.3 N/A N/A 5.5 N/A 10.9 10.9 N/A 16.0 15.8 18.5 20.0 19.5 28.4 30.9 28.5 33.5 36.5 32.7 47.8 52.7 43.6 #01109000 #01109000 at confluence at USGS gage Mill N/A* 43.8 43.5 N/A N/A N/A N/A N/A 10.9 N/A N/A 16.0 N/A 25.3 20.1 N/A 39.1 31.0 N/A 48.3 36.8 N/A 71.3 52.9 N/A with Taunton # 01108410 at USGS at confluence at USGS gage Three Mile gage 84.6 84.3 84.3 N/A N/A 5.2 N/A 8.9 12.4 N/A 12.8 18.4 21.6 16.0 23.1 32.1 24.4 30.4 37.6 28.7 33.7 52.7 41.0 41.2 with Taunton #01109060 #01109060
* Due to the short period-or-record for the Mill River USGS stream gaging station, this data does not provide sufficient data to evaluate peak flows on the Mill River. NOTE: FEMA data only available for 10, 50, 100, and 500 year events NFF equations only availble for 2, 5, 10, 50, and 100 year events
45
Figure 6-4. Mill River Peak Discharge Comparison
Mill River
3500
3000
2500
2000
1500 second) 1000
Dischage (cubic feet per 500
0 10 yr 50 year 100 year 500 year Frequency
FEMA NFF
Figure 6-5. Wading River Peak Discharge Comparison
Wading River
2500
2000
1500
1000 second)
500 Discharge (cubic feet per per feet (cubic Discharge 0 10 yr 50 year 100 year 500 year Frequency
FEMA NFF PeakFQ
46
Figure 6-6. Segreganset River Peak Discharge Comparison
Segreganset River
1200
1000
800
600 second) 400
200 Discharge (cubic feet per per feet (cubic Discharge 0 10 yr 50 year 100 year 500 year Frequency
FEMA NFF PeakFQ
Figure 6-7. Three Mile River Peak Discharge Comparison
Three Mile River
5000 4500 4000 3500 3000 2500 2000 1500 1000 500 Dischage (cubic feet per second) feet Dischage (cubic 0 10 year 50 year 100 year 500 year Frequency
FEMA NFF PeakFQ
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6.2. Hydraulic Modeling and Flood Profile Analysis
The following section summarizes development of a preliminary project hydraulic model, and application of the hydraulic model to estimate the relative change in flood flow profiles resulting from implementation of dam removal alternatives.
6.2.1. Hydraulic Model Introduction The U.S. Army Corps of Engineers Hydraulic Engineering Center River Analysis System (HEC- RAS) was used to develop a preliminary project hydraulic model to simulate existing and proposed conditions. HEC-RAS is a computer program that models the hydraulics of water flow through natural rivers and other channels. The program is one-dimensional, meaning that there is no direct modeling of the hydraulic effect of cross section shape changes, bends, and other two- and three-dimensional aspects of flow. The hydraulic model calculates channel and floodplain water velocities, depths and shear stresses for various input flows. When developing this feasibility analysis, the preliminary model provided the basis for determining existing hydraulic conditions at each site and relative differences in water surface elevations under removal scenarios.
The preliminary model will be refined in future phases to provide a basis for detailed hydraulic analysis of restoration plans, including: Channel stability of proposed restoration approaches Potential sediment deposition or movement Relative differences in flood elevations pre and post project Material sizes for restoration elements (gravel, erosion control fabric etc.) The preliminary project model was initially developed using the HEC-GeoRAS Geographic Information System (GIS) extension. The model extends from Morey’s Bridge downstream through the Whittenton, West Brittanica and State Hospital impoundments, to a location approximately 350 feet downstream of State Hospital dam, which corresponds to the downstream limit of the feasibility study reach. Developed as the base model case, the existing conditions model has length of 2.0 river miles, and contains 120 river cross sections, 5 bridges and 3 dams.
6.2.2. Existing Conditions Hydraulic Model Development The model geometry was developed using bathymetric, topographic and bridge data obtained as part of this study, and topographic data developed from aerial photography by others. It was initially proposed to use geometric data used for the existing City of Taunton flood insurance study (Federal Emergency Management Agency 1987), but these data were determined to be of marginal value, based on the number
48
and resolution of the cross sections in the FEMA model and the relatively limited capabilities of the USGS E431 hydraulic model used for that study.
It should be noted that very limited survey data was available adjacent to the West Britannia Dam, within the West Brittania impoundment, and in the river reach between West Brittania and Danforth streets due to lack of permission to access private property. For these areas, model geometry was estimated to the extent possible from the available data (aerial mapping, limited survey data, ground-level photographs and limited hand measurements) in order to result in a model that is continuous through the study reach. The resulting model is of reasonable resolution for examination of relative trends between project scenarios for each of the impoundments. Additional data collection will be required in these areas to support refinement of the model to a design level of detail in future project phases.
Roughness coefficients (Manning’s n values) applied at each model cross section were estimated from field observations, aerial photography and published values. Summarized in Table 6-5, the roughness values utilized fall within the range of values used in the 1987 FEMA study (Federal Emergency Management Agency 1987)
Table 6-5. Roughness coefficients used in the preliminary project model Description Manning’s n values Channel/Impoundment, natural substrate 0.04 Channel/Flume, concrete lined 0.015 Floodplain, heavily vegetated 0.1 Floodplain, mixed residential/lawns/landscape 0.07-0.08 trees/minor structures Floodplain, parking lots and roads 0.04-0.05
Hydrologic parameters for the HEC-RAS model were obtained from the hydrologic analyses performed as part of this study and from the FEMA FIS. The flood events utilized in the model include the 1.05-, 2-, 5-, 10-, 50- and 100-year estimates recommended for project analysis and design, and the 100-year flood estimate from the effective FIS (see Section 6.1.4). Also simulated were a range of flows (55-100 cfs) occurring during the survey effort (May 2007) for comparison to observed water surface elevations. Consistent with the FEMA study, the simulations were executed for steady state flow conditions.
Model input parameters were adjusted so that simulated water surface elevations within each impoundment approximately match (+/-0.2 to 0.5 ft) observed water surface elevations measured during
49
the May 2007 survey. Discharge during the survey ranged from 57 to 112 cfs. These discharges bracket the estimated median flow during the identified fish migration period. As such, the model should be considered reasonably calibrated for low to moderate flows within the impoundments, with accuracy sufficient for relative comparisons of hydraulic trends between project scenarios. While the model was developed with similar assumptions as the FEMA modeling study, the preliminary model development conducted for this study was not accomplished to the same level of detail as a FEMA floodplain mapping analysis. As such, application of the preliminary project model should be limited to analysis of relative hydraulic trends between existing and proposed project conditions.
Figure 6-8 shows the simulated water surface profiles under existing conditions for the range of simulated flows. Existing conditions model output is included in Appendix D.
50
Morey’s Bridge
Whittenton Dam
W. Brittania Dam
State Hospital Dam
Figure 6-8. Simulated water surface profiles for existing conditions.
51
6.2.3. Flood Profile Analysis - Proposed Conditions Model Development In order to assess the relative impact of dam removal on river water surface profiles associated with flood events, a proposed conditions dam removal project model was developed for comparison with the existing conditions model. The original intent of the analysis was to simulate two proposed conditions model cases in order to isolate the impacts associated with removal of each of the three dams. However, during development of the existing conditions model it became clear that there is insignificant hydraulic influence between dam facilities, thus the impacts associated with removal of each dam could be isolated within a single model case. Therefore, a single proposed model case was developed which includes removal of all three dams. Flood profiles were compared between existing and proposed conditions cases for the 2-year, 10-year and 100-year return period floods. For the 100-year event, two values were compared. These include the estimate developed as a part of this study for analysis and design, and the estimate included in the 1987 FEMA study (see Section 6.1.4).
The proposed conditions model was developed by modifying existing conditions model cross sections to reflect the proposed channel alignment, geometry and floodplain configuration associated with full removal of each facility. The proposed channel alignments and configurations are discussed in more detail in Sections 8-10, but the simulated restored channel has bankfull capacity equal to the 1.5-year return period flood, with associated incipient floodplain corridor width of 75 to 200 feet depending on location within the project reach. Channel lengths in the model were updated to reflect the restored channel alignment, resulting in a total model length of 2.1 river miles, 0.1 river miles longer than the existing conditions model. The spatial extents associated with roughness values in overbank areas were adjusted to reflect the expansion of incipient floodplain vegetation and roughness conditions over former impoundment surfaces outside the limits of the bankfull channel.
6.2.4. Flood Profile Analysis Results The simulated flood water surface profiles for existing and proposed (dam removal) cases for State Hospital, West Brittania and Whittenton Dam are shown in Figures 6-9, 6-10, and 6-11 respectively. The relative differences in water surface elevation for each of the flood events are summarized for selected locations spaced over the study reach in Table 6-6. Hydraulic output tables for each of the model cases are found in Appendix D.
The estimated impact of dam removal on flood water surface elevation based on the preliminary modeling results varies within each impoundment and in the river reaches between the impoundments with flood event and distance upstream from each dam. In all cases, water surface elevations associated with 2-year, 10-year, 100-year (study estimate) and 100-year (FEMA estimate) floods are estimated to
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decrease as a result of dam removal. In the State Hospital impoundment, the estimated decrease ranges from 5.1 feet at the upstream end of the impoundment during the 2-year flood to 10.1 feet near the dam for the 100-year (FEMA estimate) flood. In the West Brittania impoundment, the estimated decrease ranges from 1.2 feet at the upstream end of the impoundment during the 100-year (FEMA estimate) flood to 7.0 feet near the dam for the 2-year flood. In the Whittenton impoundment, the estimated decrease ranges from 3 feet at the upstream end of the impoundment during the 100-year (FEMA estimate) flood to 7.8 feet near the dam for the 2-year flood. The magnitude of decrease in flood water surface profile tends to increase with greater flood magnitude in the State Hospital impoundment, while the opposite trend is true for the West Brittania and Whittenton impoundments. This difference in trends reflects the influence of hydraulic backwater due to bridges downstream of the West Brittania and Whittenton facilities. The results also indicate decreases in flood water surface profiles in the river reaches between Danforth and West Brittania streets (0 to 6.5 feet) and between the railroad bridge and Whittenton Dam (0 to 1.5 feet).
It should be noted that these estimates of change in water surface profiles are based on the preliminary project model that contains uncertainties as described earlier in this section, but provide reasonable estimates of the general magnitude of relative difference in water surface profiles associated with 2-year, 10-year, 100-year (study estimate) and 100-year (FEMA estimate) floods. It should also be noted that the model simulations were executed for steady state conditions, consistent with the assumptions of the FEMA study. The steady state modeling approach does not account for dynamic flood storage that may occur within the impoundments currently. However, the site characteristics suggest that dynamic flood storage within each impoundment is likely limited as the three dams are run of river facilities, and the incremental flood storage available in each impoundment above the elevation of the respective facility’s spillway crest is assumed to be minor relative to the flow volume associated with major floods in the Mill River system. Additionally, the restored channel and floodplain configuration associated with full dam removal provide an analogous configuration to current conditions during floods as discharges greater than that associated with the 1.5 year flood will spill onto the restored floodplain, which will store floodwater and reduce water velocities. However, the relative impact of dam removal on dynamic flood storage during floods of varying magnitude could be quantified by future analyses if desired by project stakeholders. This would require development of a flood inflow hydrograph for each flood event, and unsteady hydraulic simulation.
The preliminary results demonstrate the potential for moderate to significant flood water surface reduction benefits to be realized as a result of dam removal on the Mill River. This can be contrasted with the potential for instantaneous flood releases associated dam failure at each of the facilities. The severity of flooding hazard and public safety risk associated with dam failure on the Mill River has not been
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quantified to date, but has been shown to be a significant concern for the residents of Taunton during recent years.
Table 6-6. Relative differences (feet) in flood water surface profiles at selected study reach locations resulting from removal of State Hospital, West Brittania and Whittenton Dams Flood Event Location 2-year 10-year 100-year study estimate 100-year FEMA estimate (470 cfs) (843 cfs) (1416 cfs) (2100 cfs) 75’ upstream of State Hospital Dam -7.8 -8.2 -9.0 -10.1 Midpoint State Hospital Impoundment -5.4 -6.0 -6.9 -8.1 100’ downstream of Danforth Street (upstream end S. Hospital Impoundment) -5.1 -5.6 -6.5 -7.7 50’ upstream of Danforth Street -4.0 -4.5 -5.4 -6.5 80’ downstream of West Brittania Street -2.7 -2.8 -3.1 -3.4 100’ upstream of West Brittania Dam -7.0 -6.4 -5.4 -4.2 Midpoint West Brittania Impoundment -4.1 -4.1 -4.2 -4.0 80’ downstream of the railroad bridge (upstream end W. Brittania Impoundment) -1.4 -1.2 -1.2 -1.2 70’ downstream of Whittenton Street -1.5 -1.4 -1.5 -1.5 160’ downstream of Whittenton Dam -0.9 -1.1 -1.3 -1.4 130’ upstream of Whittenton Dam -7.8 -7.5 -7.2 -6.9 Midpoint Whittenton Impoundment -7.4 -7.3 -7.1 -6.8 150’ downstream of Morey’s Bridge Dam (upstream end Whittenton Impoundment) -3.6 -3.3 -3.1 -3.0
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Ground Legend WS Year 2 - existing WS Year 10 - existing WS Year 100 - existing WS Year 2 - PROCASE 2 WS Year 10 - PROCASE 2 WS Year 100 - PRO CASE 2 WS 100 year FEMA - existing WS 100 year FEMA - PRO CASE 2 CASE PRO year - FEMA100 WS
W. Brittania Dam 2500
W. Brittania St. Bridge 2000
Danforth St. Bridge 1500 Mill MillRiver Reach Main Channel MainDistance Channel (ft) Mill River Flood Model Plan: 2 Model PRO2) Flood CASE existing River 1) 5/28/2008 5/28/2008 Mill 1000 500
S. Hospital Dam Figure 6-9. Simulated flood water surface profiles for existing conditions (blue) and proposed conditions (red) associated with removal of State
Hospital Dam. 50 45 40 35 30 25 Elevation (ft) Elevation
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Ground Legend WS Year 2 - existing WS Year 10 - existing WS Year 100 - existing WS Year 2 - PROCASE 2 WS Year 10 - PROCASE 2 WS Year 100 - PRO CASE 2 WS 100 year FEMA - existingyear - FEMA100 WS WS 100 year FEMA - PRO CASE 2 CASE PRO year - FEMA100 WS
Whittenton Dam
Whittenton St. Bridge 5000
Railroad Bridge 4000 Mill River Mill Mill Reach River Main Channel MainDistance Channel (ft) Mill River Flood Model Plan: 2 Model PRO2) Flood CASE existing River 1) 5/28/2008 5/28/2008 Mill 3000
W. Brittania Dam
Figure 6-10. Simulated flood water surface profiles for existing conditions W. Brittania St. Bridge (blue) and proposed conditions (red) associated with removal of West
60 50 40 30 Brittania Dam.
(ft) Elevation
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Ground Legend Morey’s Bridge WS Year 2 - existing WS Year 10 - existing WS Year 100 - existing WS Year 2 - PROCASE 2 WS Year 10 - PROCASE 2 WS Year 100 - PRO CASE 2 WS 100 year FEMA - existing WS 100 year FEMA - PRO CASE 2 CASE PRO year - FEMA100 WS 10000 9000 8000 Mill Mill River Reach Main Channel MainDistance Channel (ft) Mill River Flood Model Plan: 2 Model PRO2) Flood CASE existing River 1) 5/28/2008 5/28/2008 Mill 7000
Whittenton Dam 6000
Figure 6-11. Simulated flood water surface profiles for existing conditions (blue) and proposed conditions (red) 70 60 50 40 associated with removal of Whittenton
Elevation (ft) Elevation Dam.
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6.3. Fish Passage Hydraulic Design
6.3.1. Target species considerations The main goals of this project are to evaluate the feasibility of restoring the Mill River and improving fish passage for diadromous species. Ideally, restoration projects implemented will restore passage for all species of fish. It is impractical to develop fish passage assessments for all species, and thus we focus our effort on key species representative of fish assemblages (eg. alewife for alosids) or those deemed important from ecological, recreational or other points of view. This section briefly examines some of the characteristics of key species in the Mill River and how those characteristics relate to design.
Alosids - The life histories and behavior of northeastern U.S. diadromous alosids have been studied in some detail (Bozeman and Van Den Avyle 1989, Loesch 1987). Alewife and blueback herring are often referred to collectively as river herring, but there are behavioral differences pertaining directly to fish passage. Alewives typically spawn 3-4 weeks earlier than bluebacks, and alewives begin migrating through the Taunton River watershed as early as mid-March. Adult alewives are known to negotiate rapids more readily and migrate upstream farther than American shad (Bell 1991). Alewives spawn in streams, larger rivers and ponds in a variety of substrates, but optimal spawning habitat is defined by slow moving water over silty deposits, detritus and submerged vegetation. Blueback herring typically spawn on hard substrates (gravel, cobble) in the faster moving water of streams and deep rivers (Pardue 1983). These are important habitat parameters that will help to guide hydraulic parameters for passage and channel restoration designs.
Ideal fish passage conditions for alosids would recreate the natural, pre-dam river environment free of barriers (dam removal). Fish passage standard design guidelines for migratory alosids do not exist, but researchers and regional agency scientists are in the process of developing standards (A. Haro – pers. Comm.). Habitat suitability index models for river herring do not list water depth or velocity as index variables, but focus on spawning substrate, water temperature, food density and salinity (Pardue 1983).
Ideal alosid passage conditions for natural bypass channels and rock ramps are also not yet quantified. Fish passage ramps or natural bypass channels would need to provide adequate attraction flow, resting pools and passable velocities. There are no standards for attraction flow, but successful fishway entrances should be located as close to the base of the dam spillway as possible. Hydraulic conditions in resting pools and natural fishways depend on gradient, cross-sectional area and roughness, all of which can be manipulated to result in average velocities below the design target swimming speed for alosids. Cruising
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and darting speeds established by Bell (1973, 1991) are commonly used, but much higher darting speeds have been recorded (Haro 2004). The table below summarizes passage velocity ranges considered in this feasibility study.
Table 6-7. Swimming speeds for migratory fish of the Mill River Relative Swimming Type Alewife Juv. Alewife Herring Eel (Elver) Sustained speed 3-5 ft/s 0.6-1.0 3-5 0.5 Passage depth 0.5 ft 0.8 ft <.1 ft Darting speed (max) 5-11 5-11 Values in ft/s, blanks indicate no consistent data
Some typical designs exist for smaller Denil and Alaska steeppass ladders preferred for alosids passage. Research by the Conte Laboratory (Turners Falls, MA) suggests slopes less than 1v:8h for these ladders, while the USFWS recommends a headpond depth of 61 cm for Alaska steeppass fishways (Haro et al. 1999).
American eel – The American eel (Anguilla rostrata) is also found in the Mill River, and is uniquely different from alosids in body form, swimming ability and life history (Dixon 2003). Eel prefer shallow eutrophic and warm water (70˚ F), emergent vegetative cover and abundant aquatic macroinvertebrates (Knights and White 1998). Eel are catadramous, with juvenile eel migrating from spawning areas in the open ocean to freshwater streams (Dixon 1983, Tesch 1977). Thus river barriers have also been shown to dramatically impact American eel populations (Machut et al. 2007). American eel have different passage behaviors, and are dependent on a combination of crawling and swimming (Solomon and Beach 2004a, Knights and White 1998, Dixon 2003).
Ideal fish passage conditions for eel would mimic the natural, pre-dam river environment (dam removal). Eel passage has been documented for natural fishways, although no specific design guidelines have been established (Trudgill et al. 2003). European monitoring studies have shown that natural bypass channels do provide passage for a wide variety of species (Eberstaller et al. 1998, FAO/DVWK 2002, Jungwirth et al 1998, Aerestrup et al 2003, Mader et al. 1998).
Although some eel passage has been observed through traditional fish ladders, presumably by eels exploiting the boundary layers available, the velocities and turbulence in these structures are not optimal for eel passage (Armstrong 1994, Solomon and Beach 2004). Young eels or elvers have very limited swimming speeds (<0.5 ft/s) and are much more able to pass barriers fitted with elver-specific passage designs (Bell 1991, Desrochers and Fluery 1999, Solomon and Beach 2004a). These include inclined
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ramps fitted with roughness elements such as bristles or plastic matrices. Elvers are able to swim and crawl up these ramps provide there is enough flow to maintain depths of a few millimeters, and adequate roughness to create a constant boundary layer of low velocity. Legault (1993) recommends brush ramp slopes no greater than 35 degrees. Alternative manufacturers of eel passage ramps offer guidelines for their specific products (eg. Fish Pass, Millieu, Akwadrain).
Warmwater resident species – Restoration of the Mill River through dam removal would create more lotic habitat and thus limit the production of pond-dependent fish species found in the impoundment. This includes largemouth bass, bluegill and brown bullhead, which would likely be limited to backwater wetland ponds, slow water areas and any remaining impoundments under alternative fish passage scenarios (ie. non-removal). Passage of centrarchids (bass) and esocid (pike) species through traditional fish ladders, rock ramps or natural bypass channels is not well documented. As mentioned above, studies have shown that natural bypass channels provide passage for a wide variety of species.
6.3.2. Passage analysis criteria Fish passage criteria are based on alewife data and include a minimum depth of 0.5 ft, a preferred flow speed of less than 3.0 feet-per-second (fps), and a maximum flow speed of 5.0 fps. These criteria were used for the analysis assuming adult alewife as the representative diadromous alosid species. Jumping criteria are not well established for alewife/herring, and these fish ar e not known to be consistent leapers. However, we have established 6.0 inches as our maximum drop height for design based on observations of herring at other structures including the weir and pool ladder on the nearby Nemasket River at Middleborough (Figure 6-12). Elver Figure 6-12 Fish ladder on the passage criteria were not generated specifically for this project, Nemasket River near Middleborough, but final designs should follow standard elver passage ramp MA (photo Interfluve) designs outlined in Solomon and Beach (2004).
All alternative fish passage must provide three critical elements: attraction, resting opportunities and suitable hydraulic conditions. First, fish must be attracted to the outflow, which can be difficult if flow patterns over the main spillway are more attractive, causing fish to congregate at the base of the dam and never enter the bypass channel, ladder or ramp. Next, fish must be allowed to either pass easily up the bypass channel or rest along the route. All fish are limited in the type of current they can navigate. Finally, water depth, velocity and vertical barriers must be below the threshold for the fish in question. If
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the flow is too shallow, large fish will not be able to pass. If water velocities are too great or barriers too high, weak swimming fish will not be able to pass.
Although feasibility level analysis does not investigate detailed channel hydraulic conditions for post removal, rock ramp, natural bypass or fish ladder scenarios, we have used the established swimming speeds, depths and fish ladder design guidelines to establish target conditions that best suit the widest variety of fish species and life histories.
6.3.3. Hydrology Hydrologic parameters for fish passage analysis were developed previously as part of this project, and consist of a flow-duration statistics developed using daily average flow data from the U.S. Geological Survey (USGS) Wading River gauging station (USGS No. 01109000). These flow-duration statistics are based on an adult alewife migration window from March 15 through June 30, and provide a range of values for use in the evaluation of upstream fish passage associated with the project alternatives. Development of a final design may necessitate development of additional statistics, such as magnitude, frequency and duration of higher-flow events during the migration window. The flow duration statistics used for this analysis are given in Table 6-1.
6.3.4. Dam removal hydraulic conditions To ensure that fish passage would be possible under post-dam removal conditions, basic calculations of channel depth and velocity were conducted. Assuming a channel that contains the 1.5 year flow, as modeled under the removal conditions established in sections 8-10, and based on documented cruising and darting swimming speeds (Bell 1991), the hydraulic conditions under the post-removal scenario for each dam will allow for passage of alosids and eels. Natural channel design assumes low velocity conditions in boundary layers, interstitial spaces and backwater areas to provide the hydraulic variety necessary for migration. Table 6-8 below shows the range of average channel velocity values from the preliminary model at the Q10% flow (high flow for required fish passage flow range) through each of the former impoundments. These velocities are within the range of passable velocities for river herring.
Table 6-8. Channel velocities predicted for Mill River dam sites Range of average channel velocity Dam (ft/s) for proposed 1.5-year channel State Hospital Dam 2.8-3.1 West Britannia Dam 1.1-3.2 Whittenton Dam 0.3-2.5
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6.3.5. Natural bypass hydraulics and design Natural (nature-like) bypass channels were evaluated for fish passage at each of the three project dams. Bypass channels were considered appropriate based on the following factors:
Potential to create riverine habitat for fish and benthic organisms General suitability for upstream and downstream passage Aesthetic values Available physical space Site-specific flow-duration statistics Fish passage criteria Site geometry (topography, slope) Dam and spillway characteristics (flow patterns, length, apron) The availability of real estate or easements for construction of bypass channels was not evaluated in this study, but considerations are made in the specific dam sections 8-10.
The proposed designs maintain flow in the bypassed reach of the channel between the dam and the downstream end of each bypass channel. This approach is used to limit the flow in, and therefore cross- section size of, each bypass channel and reduce potential ecological impacts associated with dewatering of the bypassed reaches.
Hydraulics - To provide for effective fish passage, the proposed flow through each bypass channel was initially established as approximately half of the 90th percentile exceedence flow, or approximately 10 cubic feet per second (cfs). Based on this criterion, the upstream invert of the bypass channel at each dam would be established to route half of the 20 cfs flow over the spillway and half into the bypass channel. This value depends upon the spillway geometry at each site and the final design of the bypass channel, including any inlet works, but is in the approximate range of 0.25 to 1.0 ft below the spillway invert. At higher flows the fraction of the flow over the spillways will increase, thereby moderating the flow into the respective bypass channels. Inlet works may be required at the upstream terminus of each bypass channel to limit potentially-damaging flows into the bypass channels during peak-flow events.
In lieu of developing site-specific designs at this preliminary phase, a general set of design guidelines was developed using the project flow-duration statistics and target fish criteria. These design guidelines evaluated flow conditions for bypass channels with slopes of 1v:33h, 1:40, and 1:50 over a range of flows from 5 to 50 cfs in 5-cfs increments and varying roughness values. Side slopes for each channel were set at 3:1 for all cases, as this slope can be reasonably achieved with rock. Based on the results of a preliminary analysis for suitability, bottom widths of 4, 6, 8 and 10 feet (ft) were evaluated. A total of 12 general design geometries were evaluated (i.e., three channel slopes for each of the four bottom widths).
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Each of the design geometries includes the range of flows from 5 to 50 cfs. Normal-depth calculations were performed to determine representative depths for each of the geometries presented above, and are given in the top table of the Appendix G.
The last chart on each table of Appendix G presents an evaluation of potential upstream fish passage performance for the target fish species. Fish passage criteria include a minimum depth of 0.5 ft, a preferred flow speed of less than 3.0 feet-per-second (fps), and a maximum flow speed of 5.0 fps. Values of 1.0 (no shading) are considered passable based on depth, velocity and turbulence. Values of 0.5 are considered marginally-passable, while values of 0.0 (dark-shaded) are not passable. Suggested channel sizes and slopes for each dam are discussed below and again included in the dam site-specific sections 8- 10.
Design dimensions - The information presented in the Appendix G indicates that achieving fish passage criteria is very dependent upon a high effective roughness value (i.e., tending towards 0.060). The development of a bypass channel requiring Manning’s “n” values of this magnitude therefore necessitate a careful evaluation of hydraulic conditions at the final design phase. Based on these data, it is recommended that the preliminary design consider a trapezoidal channel with a bottom width (B) of approximately 6 ft, as the wider channels evaluated here resulted in depths of less than 0.5 ft at a flow of 10 cfs. Channel slopes of approximately 0.025 (2.5%) or less are recommended. Performance at increasing flows would require a detailed analysis of flow partitioning between the adjacent spillway and the associated bypass channel, and was not performed as part of this study. It is important to remember that these estimates are conceptual, and that further analysis would be required during future design stages.
Sizing of stable substrate material (i.e., rock) for construction of a bypass channel is largely dependent upon the maximum flows that are likely to occur in the channel. While it may be appropriate to construct the bed of the trapezoidal channel using rounded “river” rock, the banks should be constructed of angular material with a higher angle of repose. Bypass channels represent potentially-feasible alternatives for providing fish passage and riverine habitat adjacent to the three project dams.
6.3.6. Fish ladder hydraulics and design As stated above, small Denil and Alaska steeppass fish ladders are preferred for alosids passage. Design of fish ladders at the Mill River dams follows commonly used dimensions for ladder type, size, slope, entrance and exit configuration. In general, we recommend pre-fabricated Alaska steep pass ladders for cost efficiency and ease of installation. We recommend that any steep pass ladders be installed at
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slopes less than 8:1with a 60 cm headpond elevation and adequate attraction flow. Site-specific design parameters are discussed in Section 8-10.
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7. Sediment Characterization
7.1. Sediment volume estimation
One of the important steps in evaluating dam removal feasibility is quantification of impoundment sediment volume at each dam. Any project that may disturb this sediment will require a sediment management plan, which requires an estimate of how much sediment is present. Removal of sediment can be the most expensive item in fish passage projects, simply due to the potential for large volumes. Impoundment sediment volumes calculated for the Mill River dams are shown in the table below. The data are presented as ranges of potential volumes. Because the volume estimates are based on depth of refusal measurements, they do not quantify the patterns of deposition or distinguish between historic floodplains and deposited sediment as a result of dam construction. Future project phases will examine deep cores to differentiate between impoundment deposition and pre-dam floodplain surfaces. Sediment management strategies are included in each of the existing conditions summaries for the individual dams (See Section 8-10).
Table 7-1. Sediment volume estimates for Mill River dams Estimated impoundment sediment Dam volume (CY) State Hospital Dam 30,000 (max) West Britannia Dam 13,000 – 26,000 Whittenton Dam 1,400 – 4,000
7.2. Sediment Grain Size Analysis
The particle size of impoundment sediment is a measure of its potential to move through the system and also it’s potential to adsorb and retain contaminants. Sediment size therefore is important in determining the need for further sediment quality testing and predicting the consequences of removal actions. One standard way of measuring sediment grain size for fine sediment is to pass the material through a series of graded sieves, and express the amount of material passing each standard sieve size as a percentage (percent passing by weight). The State of Massachusetts requires analysis of the percentage of sediment passing the No. 200 US Standard Series Testing Sieve (nominal opening 0.074 mm = coarse silt). The following table shows a summary of the amount of silt in the samples for the three impoundments. Detailed sieve analysis results for all samples can be found in the sediment testing results of Appendix E.
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Table 7-2. Sieve analysis results Percent passing the No. Impoundment 200 Sieve (coarse silt) Whittenton 2, 3, 2% West Britannia 0, 5% State Hospital 3, 6, 0%
Generally no chemical testing is required if the sediment to be dredged contains less than 10% coarse silt and the due diligence results show no expected contamination. However, since the due diligence review (see next subsection) for the Mill River project area suggested the potential for contamination, testing was required.
Other observed trends in Mill River sediment gradation include the following:
• 95-100% of the sediment from the three dams is smaller than pea gravel (#3.5 sieve = 6 mm) • 20-40% of the sediment from the three dams is smaller than fine sand (#80 sieve = .178 mm) • 2-7% of the sediment from the three dams is smaller than coarse silt – see Table 7-2 (#200 sieve = .074 mm) • Samples SED2 and SED6 are well sorted sand, while the other samples are poorly sorted with sizes ranging from fine to coarse sand These results indicate that the sediment samples from all three impoundments are primarily composed of coarse and fine sand. This is advantageous in three ways. First, sand has a lower capacity to bind contaminants than do silt or clay dominated fines. Second, sand is much easier and cheaper to remove from impoundments than silt or clay fines, making potential restoration projects less costly. Thirdly, sand is less prone to mobility than silt, and thus is easier to control and manage during restoration activities.
In future phases, project partners will consult with Massachusetts DEP staff to consider the amount and size of sediment at each dam, and what steps must be taken to manage sediment quantity and quality during restoration. Understanding the mobility of the accumulated sediment in each restoration scenario will guide project design and construction materials and methods. More detailed discussions of how grain size results relate to restoration alternatives are included in Sections 8-10.
It is important to note that this is a screening level analysis. Future project phases will require deeper sediment coring and vertical stratification of samples to determine sediment sizes throughout their depth.
7.3. Due diligence
A due diligence study was performed with the goal of identifying potential contaminant sources in the watershed. For this and future phases, due diligence results help to select laboratory tests that target the
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most likely chemicals. This analysis included a review of the industrial history of the watershed summarized in the previous sections. From the historical review, it was clear that heavy metals and hydrocarbons could be possible contaminants, and that pesticides and herbicides were less likely to be present.
Due diligence review of current potential contaminant sources revealed the following: • One site assessed by the Massachusetts DEP Source Water Assessment Program with the potential for leaks if improperly managed. • Seven sites flagged in the Massachusetts Environmental Database review/MEPA project information system. • No USEPA Comprehensive Environmental Response, Compensation, and Liability Information System (CERCLIS) or No Further Remedial Action Planned (NFRAP) sites were found. • Of the 18 SQG sites found under the Resource Conservation & Recovery Act of 1976 (RCRA), six had past violations, but all of these have been corrected. • Our search found data for 13 leaky underground storage tank (LUST) sites and 14 Underground storage tank (UST) sites, nine of which have USTs currently in use. • There were no Superfund sites on National Priorities List (NPL). • Regarding the Environmental Site Assessments, ASTM E-1527-00, Section 7.2.1.1: we searched the EPA’s Waste Site Cleanup and Reuse listing for Massachusetts and found that of 356 sites in MA, only a few are in Taunton, and none are located on Mill River above State Hospital Dam. A summary of the industrial history of the project reach is given in Section 4.3. A detailed summary of due diligence results is found in Appendix B. The due diligence results, particularly the history of industrial use in the watershed, indicates a probability of contamination from heavy metals and aromatic hydrocarbons. The sediment screening testing included these chemical groups.
7.4. Sediment quality – background information
The following segment summarizes the sediment quality testing and discusses the results at each dam site. It is important to note that sediment quality information in the feasibility phase is intended only to determine the potential presence of contaminants. No conclusions should be made regarding concentrations of contaminants until more detailed testing is completed in future phases. All of the sediment samples tested revealed the presence of heavy metals and hydrocarbons. Heavy metals were selected for testing based on due diligence review. The metals tested are commonly found in impoundments of the northeast U.S., and could come from forge operation, cotton milling and dyeing, road runoff, plating operations and many other historical industrial sources along the Mill River. The samples tested did not reveal the presence of polychlorinated biphenyls (PCBs), once used in paper production and electrical transformers.
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Screening for hydrocarbons included a summary test for all hydrocarbons called Total petroleum hydrocarbons (TPH), Volatile organic compounds (VOC), and Polyaromatic hydrocarbons (PAH). These hydrocarbons are found in rivers and impoundments throughout the U.S. TPH is a measure of the presence of petroleum oil or fuel in the sample, but does not give any indication of type or chemical signature. VOCs tend to evaporate quickly but can persist in soils. Of the 66 volatile organic compounds tested, only methylene chloride was found in the Mill River. Methylene chloride is widely used as an industrial solvent and paint stripper found in aerosol and pesticide products, photographic film, spray paints, automotive cleaners and other household products.
PAHs are a group of about 100 chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, such as tobacco and charbroiled meat. Coal tar is the major source of naphthalene and its derivatives that make up all polyaromatic hydrocarbons. The tables in the following sections show the PAH compounds present in the Mill River impoundments.
The total organic carbon value refers to the concentration of organic material in the sample. Samples with more decomposing plant matter such as leaves and other detritus will have higher organic carbon concentrations. These values are expressed as mass densities, and demonstrate the relative mass of sediment versus organic material in a sample. For example, sample SED1 below contains 53,700 mg/Kg or .0537 kilograms per Kg (5.4%) of organic material. The table below shows the number of compounds tested for in the laboratory, while the columns under each dam show the number of compounds found in each dam site for each tested category. For instance, of the 13 heavy metals examined, Whittenton yielded positive results for two metals, West Britannia five, and State Hospital seven.
Table 7-3. Distribution of contaminants found in the Mill River impoundments
Total number of compounds tested Whittenton W. Brit. St. Hosp. PCBs 8 ND ND ND Metals 13 2 5 7 Petroleum Total Present present present hydrocarbons PAH 17 11 11 13 VOC 66 1 ND 1 ND = non-detect (no compounds found above the lowest detectable testing limit)
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7.5. Sediment quality – State Hospital Three contaminant screening samples were taken in the State Hospital impoundment, one approximately 20 feet upstream of the center of the dam (SED4), one in the middle of the impoundment (SED5), and one at the upper end of the impoundment (SED6 - see table below).
Table 7-4. State Hospital sediment sample locations
Sample ID Station Description Latitude/Longitude Grab sample - Just upstream and to the right N 41deg 54'53.8" SED 4 14000 of the spillway W 071 deg 05'49.1" Grab sample - Right of center, middle of the N 41deg 54'56.0" SED 5 14200 impoundment W 071 deg 05'53.7" Grab sample - Head of the impoundment, N 41deg 54'58.6" SED 6 14550 where stream enters the impoundment. W 071 deg 05'56.2"
Samples were taken with a mini-Ponar grab sampler. Samples were taken roughly along the edge of the thalweg. Table 7-5 below shows the results of the screening. As with the screening samples from the other dams, sediments tested positive for total petroleum hydrocarbons (TPH), PAHs, and metals. Methylene chloride was found in the State Hospital sediments, but PCBs were not found. Threshold values - The following Table 7-5 and similar tables for the other two dams show contaminant concentrations in the samples taken. Values shown in blue italics indicate concentrations exceeding the Freshwater Sediment Benchmark (FSB) threshold, while values in red italics indicate concentrations exceeding both the FSB and the Massachusetts Contingency Plan (MCP) S1-GW1 threshold. Freshwater Sediment Benchmarks are typically used in screening level surveys, and are thresholds developed as part of the MCP intended to provide guidance for determining the ecological risk of contaminated soil disposal. The FSB values refer to threshold effects concentrations (TEC), or the concentrations below which harmful effects are unlikely to be observed in benthic organisms. There are many other similar sets of threshold values used by various agencies across the country. The MCP S1- GW1 threshold values are generally higher than the ecological thresholds, and refer to the risk of harm to humans from exposure to the chemicals in the soil and the potential impacts to groundwater.
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Table 7-5. Concentrations of contaminants in State Hospital samples (concentrations given in mg/Kg-dry except PAHs given as μg/Kg-dry) TEC MCP S1-GW1 SED 4 SED 5 SED 6 Threshold Threshold Total Petroleum Hydrocarbons 604 449 108 1610 200 Total Metals by ICP Chromium 195 206 ND 43.4 1,000 Copper 189 331 20.6 31.6 30 Lead 239 420 28.8 35.8 300 Nickel 239 53 ND 22.7 20 Zinc 250 475 64.6 121 2,500 Total Silver 87 209 4.39 NL 100 Mercury 0.578 0.987 ND 0.2 20 Polyaromatic Hydrocarbons Acenaphthylene 612 ND 323 NL NL Anthracene 578 ND 362 57.2 1,000,000 Benz(a)Anthracene 1670 971 933 108 7,000 Benz(a)Pyrene 1790 856 780 150 2,000 Benzo(b)Flouranthene 1870 1050 643 27.2 7,000 Benzo(g,h,i)Perylene 1360 962 644 NL NL Benzo(k)Flouranthene 1110 897 689 NL 70,000 Chrysene 1990 1400 1010 166 7,000 Dibenz(a,h)Anthracene ND ND 40.8 NL 700 Flouranthene 3440 2180 1860 423 1,000,000 Indeno(1,2,3-cd)Pyrene 1260 874 630 NL NL Phenanthrene 2110 1090 903 204 1,000,000 Pyrene 3750 2410 1740 195 1,000,000 Volatile Organic Compounds Methylene Chloride 2010 3440 576 NL NL Total Organic Carbon 91,700 115,000 10,200 NA NA Values in the table shown in blue italics indicate values exceeding the Freshwater Sediment Benchmark TEC (MacDonald et al 2000) threshold, while values both red italics indicate concentrations exceeding the TEC and the Massachusetts Contingency Plan (MCP) S1- GW1 threshold. ND = Non-detect (no chemicals found above the threshold detection limit) NL = Not listed in Merrill (2003) or MacDonald et al. (2000) references. NA = Not applicable.
7.6. Sediment quality – West Britannia Two contaminant screening samples were taken in the West Britannia impoundment, one approximately 100 feet upstream of the dam (SED8) and one at the upper end of the impoundment (SED7) (see table below).
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Table 7-6. West Britannia sediment sample locations Sample ID Station Description Latitude/Longitude Core sample of the bank adjacent to a N 41deg 55'09.5" SED 7 16250 vegetated left bank deposit. W 071 deg 06'07.2" Core sample of the bank adjacent to a N 41deg 55'14.83" W SED 8 16870 vegetated right bank deposit. 071 deg 06'11.21"
Sampling using a mini-ponar grab sampler was not possible at these sites given the lack of fine sediment in the channel, and so core samples were taken from sediments on the edge of the historic channel bank. Core samples were taken from the upper six inches of sediment and generally consisted of sandy silt loam. Table 7-7 below shows the results of the screening. As with the other screening samples from the other dams, sediments tested positive for total petroleum hydrocarbons (TPH), PAHs, and metals.
Table 7-7. Concentrations of contaminants in West Britannia samples (concentrations given in mg/Kg-dry except PAHs given as μg/Kg-dry) TEC MCP S1-GW1 SED 7 SED 8 Threshold Threshold Total Petroleum Hydrocarbons 135 216 1610 200 Total Metals Chromium 59.5 81.9 43.4 1,000 Copper 24.3 88 31.6 30 Lead 109 345 35.8 300 Zinc 55.6 287 121 2,500 Total Silver 4.28 5.47 NL 100 Mercury ND 0.417 0.2 20 Polyaromatic Hydrocarbons Anthracene ND 327 57.2 1,000,000 Benz(a)Anthracene 508 1170 108 7,000 Benz(a)Pyrene 439 1150 150 2,000 Benzo(b)Flouranthene 388 1120 27.2 7,000 Benzo(g,h,i)Perylene 433 731 NL NL Benzo(k)Flouranthene 392 1020 NL 70,000 Chrysene 674 1470 166 7,000 Flouranthene 909 2260 423 1,000,000 Indeno(1,2,3-cd)Pyrene 373 661 NL NL Phenanthrene 502 1270 204 1,000,000 Pyrene 1020 2670 195 1,000,000
NA NA Total Organic Carbon 36,300 61,300 Values in the table shown in blue italics indicate values exceeding the Freshwater Sediment Benchmark TEC (MacDonald et al 2000) threshold, while values both red italics indicate concentrations exceeding the TEC and the Massachusetts Contingency Plan (MCP) S1-GW1 threshold. ND = Non-detect (no chemicals found above the threshold detection limit) NL = Not listed in Merrill (2003) or MacDonald et al. (2000) references. NA = Not applicable.
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The results are in mg/Kg rather than ug/Kg for PAH values, and thus differ by a factor of 1000. Methylene chloride was not found in the West Britannia sediments, nor were PCBs. Values in the table shown in blue italics indicate values exceeding the Freshwater Sediment Benchmark threshold, while values in red italics indicate concentrations exceeding the Massachusetts Contingency Plan (MCP) S1- GW1 threshold. One sample (SED 8) slightly exceeded the MCP S1-GW1 threshold for lead at West Britannia. See section 7.5 for description of FSB and MCP S1-GW1 thresholds.
7.7. Sediment quality – Whittenton Pond
Three sediment quality screening samples were taken in the Whittenton impoundment, one near the dam (SED3), one in the middle of the impoundment (SED2), and one at the upper end of the impoundment (SED1) (see table below and plans for sample locations).
Table 7-8. Whittenton Pond sediment sample locations Sample ID Station Description Latitude/Longitude SED 1 22900 Channel thalweg - grab sample on the tail of N 41deg 55'56.4" the right bank sand bar W 071 deg 06'27.3" SED 2 21040 Core sample of the left bank sand bar - N 41deg 55'41.1" excavated down approx. 0.5 feet W 071 deg 06'22.0" SED 3 19600 Core sample upstream of dam on riverside N 41deg 55'31.1" edge of the left bank bar W 071 deg 06'25.2"
Sampling using a mini-ponar grab sampler was not possible at sites 2 and 3 given the lack of fine sediment in the channel, and so core samples were taken from sediments on the edge of the historic channel bank. Core samples were taken from the upper six inches of sediment and generally consisted of sandy silt loam. Table 7-9 below shows the results of the screening. Values in the table shown in italics indicate values exceeding the Freshwater Sediment Benchmark threshold, while values both bold and italic indicate concentrations exceeding the Massachusetts Contingency Plan (MCP) S1-GW1 threshold. One sample (SED1) exceeded the S1-GW1 threshold for total petroleum hydrocarbons in Whittenton Pond.
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Table 7-9. Concentration s of contaminants in Whittenton Pond samples (concentrations given in mg/Kg-dry except PAHs given as μg/Kg-dry) TEC MCP S1-GW1 SED1 SED2 SED3 Threshold Threshold Total Petroleum Hydrocarbons 205 40.7 85.3 1610 200 Total Metals Lead 96.2 ND 30.5 35.8 300 Zinc 188 14.4 63.9 121 2,500 Silver 4.01 6.35 2.68 NL 100 Mercury ND 0.168 ND 0.2 20 Polyaromatic Hydrocarbons Anthracene ND ND 194 57.2 1,000,000 Benz(a)Anthracene ND 98.4 425 108 7,000 Benz(a)Pyrene ND ND 402 150 2,000 Benzo(b)Flouranthene ND ND 405 27.2 7,000 Benzo(g,h,i)Perylene ND ND 370 NL NL Benzo(k)Flouranthene ND ND 405 NL 70,000 Chrysene ND ND 635 166 7,000 Flouranthene ND 243 1290 423 1,000,000 Indeno(1,2,3-cd)Pyrene ND ND 326 NL NL Phenanthrene ND 298 1210 204 1,000,000 Pyrene ND 207 1190 195 1,000,000 Volatile Organic Compounds Methylene Chloride ND 827 935 NL NL Total Organic Carbon 53,700 18,800 28,400 NA NA Values in the table shown in blue italics indicate values exceeding the Freshwater Sediment Benchmark TEC (MacDonald et al 2000) threshold, while values both red italics indicate concentrations exceeding the TEC and the Massachusetts Contingency Plan (MCP) S1- GW1 threshold. ND = Non-detect (no chemicals found above the threshold detection limit) NL = Not listed in Merrill (2003) or MacDonald et al. (2000) references. NA = Not applicable.
7.8. Regulatory Perspectives on Quality Testing Results in Relation to Project Implementation
The following is a summary of regulatory requirements that may apply to sediment removal at the dam sites:
What regulatory laws govern contaminated sediment treatment or removal in the study impoundments? The amount of sediment proposed to be removed at each of the dams is over 100 cubic yards, triggering the required submittal of a 401 Water Quality Certification Dredge Permit Form. Because due diligence review of the Whittenton area revealed potential anthropogenic contaminant sources, performance standards, chemical and physical testing must meet the requirements of 310 CRM 9.07 (2)(b).
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The project must demonstrate that disposal of dredged sediment is managed in accordance with 314 CMR 9.07 (9), (10), and (11).
The primary law governing contaminated sites is the Massachusetts Contingency Plan (MCP), but applies only to soils (upland or exposed impoundments) and not sediment (lakes, ponds, rivers and water bodies). Any contaminated sediment not excavated from the impoundment area would fall under these regulations.
In-stream management (allowing the sediment to erode naturally without intervention) still technically involves the movement of sediment and is considered dredging under Mass DEP’s 401 Water Quality Certification Regulations (314 CMR 9.00). Sediment management under this scenario must minimize exposure and disturbance to downstream organisms. To view these regulations, go to www.mass.gov/dep/service/regulations/314cmr09.pdf
What additional testing would be needed for sediment removal on the Mill RIver? The Mass DEP guidelines for conducting environmental risk assessments are intended to be flexible, to “allow the scope and level of effort of an assessment to be commensurate with the nature and complexity of the risks posed by the site.”
The need for further sediment testing under dredging regulations is determined by due diligence review and sieve analysis, both of which were completed as part of this project.
The amount of additional sediment samples needed is based in part on the total cubic yardage of material to be removed.
A sediment sampling plan would be developed in close consultation with Mass DEP. We recommend that cores be separated by depth to evaluate both sedimentation rates and the depth of contamination.
Some of the contaminants found are in excess of the established Freshwater Sediment Benchmark values. Above what contaminant concentration does dredged sediment need to go to an approved or specialized disposal facility? There are no clear standards or triggering thresholds that answer this question. The process is designed to be flexible, to allow for input from the stakeholders and regulators so that a reasonable program can be implemented.
During the Section 401 Water Quality Certification process, the levels of contaminants in the dredged material are compared to ecological and human health screening values. Project regulatory staff (MADEP) work with the project partners to evaluate risk and options for
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management. For nearby projects in Plymouth, the State has used Threshold Effects Concentration (TEC) and Probable Effects Concentration (PEC) ecological screening values from MacDonald et al (2000) and the NOAA Screening Quick Reference Tables (SQRTs). According to Section 401 Water Quality Certification regulations, human health risk is evaluated by comparison of contaminant values to Method 1 cleanup standards in the Massachusetts Contingency Plan (MCP). The MCP has Reportable Concentrations (RCs), which if exceeded may trigger a reporting requirement and entry into the regulatory system. Together, the comparisons listed above are used to evaluate management options. The required chemical analyses spelled out in the 401 WQ Cert regulations coincide with an interim DEP policy (http://www.mass.gov/dep/recycle/laws/dredge.pdf) that helps determine whether landfill disposal is an option or if sediments can be reused on site. A final design testing plan should include all of the above analyses, incorporating due diligence results. Contaminant levels found above these values may be deemed inappropriate for landfill disposal, and may require incineration or other treatment.
When do soils need to be stabilized in place to prevent natural erosion of sediment? Any stabilization of contaminated soils (soil by MCP definition) requires an assessment of the possibility of direct human exposure or contaminants entering the food web. If it is concluded that the ecological risks are manageable through bioengineering or other bank stabilization, and do not increase the amount of pollution already in the system, then design alternatives that embrace natural meandering of the stream including adjustments through time through natural erosional and depositional processes may be feasible. This may be the case if the concentrations are below MCP Method 1 standards, for which human health risks are minimal. If values are above MCP Method 1 standards, then risk must be evaluated more thoroughly with a formal risk assessment according to the MCP (310 CMR 40.0900). The results of the risk assessment would then determine if a proposed management scenario is feasible. This also assumes that contamination is consistent through depth, which may not be the case. If the sediment is not confined to certain layers or only to the upper layers, then full removal of the sediment may provide the best sediment management option. The converse may also be true however, and more contamination may be present in lower (older) sediment layers. Depending on the action taken, subsequent design steps will need to include more detailed sediment sampling stratified by depth.
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8. State Hospital Dam: Design Options
8.1. Existing Conditions (No action or minimal action alternative)
8.1.1. Dam structure The State Hospital Dam is located just upstream of the Hopewell Park area and downstream of Danforth Street on the Taunton State Hospital grounds. There has been a dam at this location since the Hopewell Factory Dam was constructed in the early 1800s. The earthen berm dam is over 350 feet long with a hydraulic head, including the ramped tailrace, of approximately 8.0 feet. Flow passes through a 38- foot wide concrete ogee spillway and down a steep 100 foot long tailrace with several small vertical drops (Figure 8-1). A gated turbine inlet on the face of the dam just to the right of the spillway discharges 50 feet downstream of the crest, within the raceway. The uncontrolled primary spillway is in good condition, with no major cracks or structural problems observed.
The primary spillway is actually the secondary spillway of the original dam configuration. The main spillway was located approximately 200 feet to the west (right) of the existing spillway edge. Sanborn Fire Insurance maps of the site from 1893 show the main spillway and flumes, as well as Figure 8-1. State Hospital Dam spillway the former mill buildings (Figure 4-3). It is unknown whether the main spillway was removed or simply buried. Any project should include soil borings in this area to confirm.
The right abutment wall is concrete with flatstone masonry approximately 100 feet long and 18 inches thick. The wall is in fair condition, with several large surface cracks, some missing stones and minor erosion areas behind the wall. The left abutment wall is approximately 130 feet of concrete and 65 feet of stone wall. The wall is in fair condition but less stable than the right wall, with a one inch shift at a major vertical crack near the spillway crest. The wall has several other large vertical cracks and severe erosion and piped soil loss behind the wall.
The earthen embankment is in good condition, with some minor foot traffic causing erosion of soils along the abutment walls. The downstream slope is approximately 10:1 and covered with tree and shrub growth. No stability issues were observed on the earthen embankment. Remnants of old mill buildings are
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visible on both sides of the raceway, particularly on the left embankment downstream of the crest. A remnant raceway runs east parallel to the spillway crest and then bends south around the structure, reentering the Mill River downstream of the raceway. This channel holds periodic high flows and some headcutting and erosion are noted. Access and staging are good at the dam site, with both available on either the left or right bank areas. No overhead infrastructure was visible near the dam, but overhead lines are present along Hamilton Street. Some trees would likely need to be removed to construct access roads from either side. If nothing is done to repair the structural issues with the State Hospital Dam, the abutment walls and the dam spillway will continue to degrade. Cracks will widen on the left abutment wall, and leaks will encourage seepage loss of fines from the bank. Once the wall has failed to the point where flood flows can go behind the wall, rapid soil loss and structural failure could occur. If headcutting continues to erode up the eastern raceway (during large magnitude runoff events), the earthen berm could fail catastrophically, releasing all of the impoundment water in a large flood wave. If the dam is maintained or repaired in its current state, the existing seasonal pool elevations will persist.
8.1.2. Impoundment Sediment Upstream sediment supply is limited by Winnecunnet Pond, Lake Sabbatia, the Whittenton impoundment and the West Britannia impoundment. Sediments found in the depth of refusal study included fine sand, silt and gravel. Grab samples for contaminant screening yielded fine to coarse sand with a high organic content. Assuming the entire depth of refusal area to be deposited sediment as a result of dam construction, the total amount of deposited sediment would be over 30,000 cubic yards. Like Whittenton Pond, depth of refusal data shows saturated fine sandy silt deposits varying in depth from 0 – 8 feet. Final design involving floodplain manipulation should include deep core samples to 10 - 15 feet to more accurately determine the pattern of deposition in the impoundment area. For this assessment, we are basing the amount of sediment accumulated on depth of refusal data, local topographic trends and cross-section shape upstream and downstream of the impoundment.
8.1.2.1. Contaminated sediment If nothing is done to treat the contaminants, most will eventually breakdown. PAH compounds can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks. PAHs do not dissolve easily in water and they adhere to soil particles where microorganisms will eventually break them down. Most volatile organic compounds have a short life span once exposed to the air. Methylene chloride, the only VOC found at the dam sites, reacts with photochemically produced compounds and decomposes within 130 days. Heavy metals could remain in the soil indefinitely unless
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natural forces remove the dams and the channel resumes migration whereby sediments would be moved downstream over hundreds of years.
8.1.2.2. Fish passage There is currently no fish passage at the State Hospital dam. If the dam remains in place, passage of migratory fish from downstream reaches would remain blocked.
8.1.3. Aquatic habitat conditions With no action, the habitat in the State Hospital impoundment will remain degraded and lentic, benefiting only warmwater emigrants from Lake Sabbatia that cannot travel upstream back into the lake. The pond will harbor tolerant organisms and continue to warm stream water through solar exposure. Increased temperatures, algae and vegetative growth will limit oxygen levels in the impoundment. Normal river geomorphic function will remain depressed without moving water, and the impoundment will remain much the same over time, slowly accumulating organic matter. As more organic sediment deposits, the shallow littoral zones will become increasingly more shallow and fully vegetated with emergent wetland vegetation. Sediment will continue to accumulate, minimizing quality habitat for fish dependent on faster moving water. Upstream and downstream migration will remain limited, and diadromous fish migration will remain completely blocked.
8.1.4. Wetlands –State Hospital Impoundment and Dam Non-persistent and persistent emergent wetlands dominate a significant portion of the upper impoundment where deltaic deposits predominate. Arrow arum (Peltandra virginica) and water willow (Decodon verticillatus) are co-dominants in the shallow water areas where water depths <1.5 feet were noted during the May 2007 reconnaissance (See Figure 8-2). This emergent community extends out up to 70 feet from the swamp-dominated shoreline. Other persistent emergent wetland vegetation in the impoundment includes broad-leaved cattail (Typha latifolia) and purple loosestrife (Lythrum salicaria). Although not emerged during the May site visit, it appeared that spatterdock (Nuphar sp.) and/or fragrant water lily (Nymphaea spp.) also inhabits a substantial portion of the shallow water, non-central channel areas of the upper basin. Along the shoreline of the impoundment, silver maple (Acer saccharinum), red maple (A. rubrum) and black willow (Salix nigra) are dominant canopy species in the forested swamp on the northeast side of the impoundment. Silky dogwood (Cornus amomum) is the dominant shrub in this forested swamp. Scarboro soils are the mapped hydric soil unit for this area. Water level signatures on emergent plants and tree trunks suggest that water levels often reach heights of more than 1-foot greater than the conditions noted during the May 2007 site visit. The main channel depths in the upper basin were <5 feet deep during the visit.
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Wetland vegetation is less prevalent along the steeper-sloped western and southwestern portion of the basin. Here, silky dogwood, water willow, purple loosestrife, buttonbush (Cephalanthus occidentalis), and northern arrowwood (Viburnum recognitum) are present in a wetland band generally less than 20-feet wide. Cottonwood, silver maple, green ash (Fraxinus pennsylvanica), and red maple are present in the seasonally-flooded, narrow forested swamp canopy. Along the Hospital facility banks, only steep upland banks (inland bank resource) are present, with impoundment waters of 5-6 foot depth present immediately off the banks.
Figure 8-2. State Hospital Dam impoundment Peltandra and Decodon-dominated emergent wetlands (foreground) and Acer-dominated forested swamp (background), May 2007
Immediately upstream of the impoundment but downstream of the road bridge crossing, a forested floodplain swamp is dominated by red maple and cottonwood (Populus deltoides) in the canopy and silky dogwood and elderberry (Sambucus canadensis) in the shrub layer. There is minimal wetland vegetation upstream of the bridge, as dry-stone rock walls form the riverbanks in this area downstream of the Reed and Barton factory plant.
In vicinity of the Hospital dam along the southwestern portion of the impoundment, seasonally flooded silky dogwood dominates a 5-10-foot wide shrub wetland for an 80-foot long section of the shoreline. Along the southeastern portion of the shoreline, silky dogwood also extends for approximately 60 feet north from the dam as a 12-ft wide shrub wetland fringe. Seasonally flooded maple and water willow also form a narrow fringe in this area.
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Freetown mucks have been mapped for the floodplain area downstream of the State Hospital Dam, although the mapped hydric soil areas near the earthen berm have been filled by the past construction of the dam, raceway, and other associated structures. This wetland is dominated by seasonally flooded red maple and silky dogwood.
8.1.5. Riparian habitat conditions The riparian zone is limited due to encroachment of infrastructure. The pond does have a forested buffer between 50 – 100 feet in width. There are three private residences at the north end of the impoundment, and one light industrial lot on the eastern edge. The rest of the property is owned by the Commonwealth of Massachusetts/Taunton State Hospital.
8.2. Full removal Full removal of the State Hospital dam would restore free flow and fish passage from the Taunton River confluence upstream to the West Britannia dam, and would dramatically improve the habitat quality of the Mill River in this reach. From a cost versus benefit perspective, this option is the most economical for the benefit achieved. Removal of the dam structure would require the excavation of the concrete and stone spillway, partial removal of the earthen berm and removal of contaminated sediment, which may require either on site treatment or disposal at an approved facility. Restoration of the area could include partial excavation and historic preservation of the Hopewell Mill buildings, combined with creation of a natural community park area where residents could learn about the natural and industrial history of the area. Stormwater detention and infiltration of residential and parking lot runoff could be incorporated into the eastern riparian area. Removal sequencing would likely proceed as follows: • Initial mobilization and staging – The project could use the flats to the west or a cleared area to the east for access to the dam site. A large sycamore tree is located near the old eastern raceway and would need to be well protected from construction disturbance. Access to the north end of the impoundment can be made from the public access spur off of Danforth on the east side of the river. • Dewatering – The eastern raceway could be used as a gravity flow channel to partially dewater the site and allow for embankment excavation and removal of the abutment walls and raceway. Removal of the spillway would likely require pumping of water around the site. • Structure removal – Most of the dam is earthen berm, but the spillway would require demolition using hydraulic jack and a medium sized excavator. Soil borings may confirm the presence of the buried main spillway, which will influence removal costs.
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• Sediment removal – We recommend partial drawdown and allowing time for the impoundment to dry out prior to major floodplain excavation. Once the sediments are dry (6- 12 months), they can be removed by mechanical means. Special permitting, handling and disposal may be required due to the contaminants present. • Stream restoration - Once the structure is removed some bank construction and stabilization would take place upstream. Bank stabilization would include simple staking of bioengineering fabric and trenching of transition areas to prevent blanket from washing away. Some banks would likely need to be constructed by shaping or encapsulation of compacted soils (Figure 8-3 through 8-6).
Figure 8-3 through 8-6. Dam removal typically involves four major stages shown clockwise from top left: Structure demolition, sediment management or removal, impoundment stream restoration and planting maintenance such as watering and weed control (photo Inter-Fluve).
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• Habitat restoration - Following sediment removal and bank stabilization, tree and shrub planting and exotic species treatment should follow a 3-5 year maintenance schedule to ensure success. Passive versus active sediment management - If the dam was removed without intervention upstream, and sediment was allowed to erode, a channel would quickly headcut through the thalweg sediments. Flood flows would begin to erode the banks, creating a new floodplain similar in cross-section to the old. The resulting channel in the State Hospital impoundment would have a bankfull width similar, but probably slightly narrower than currently downstream of the dam. A stable channel in this reach would be a gently winding riffle and pool channel, with gravel and small cobbles making up riffles. This would potentially introduce 10,000 - 15,000 cubic yards of sediment downstream, and we do not recommend this method of removal, particularly due to the potential of contaminants in the impoundment sediment. We have designed our concepts based on mechanical removal of impoundment sediments. The amount of sediment removed depends in part on the expected future development and stormwater management, desired channel conditions, wetland and riparian conditions and cost. Once these criteria are established, then a stable channel can be designed that approaches the desired function. As previously stated however, one cannot design any sized channel desired. If a channel is built to steep or too narrow, it will degrade and erode. Conversely, if a channel is sized too wide or with too much sinuosity (low slope), it may aggrade with deposited sediment.
Floodplain and channel restoration – We follow a design approach that examines the creation of a regularly inundated floodplain forest, with banks overtopping frequently. We have also considered construction of a larger capacity channel. We calculated the amount of channel and floodplain excavation needed to construct a stable channel under three scenarios:
A wide and shallow channel with a narrow floodplain A wide and shallow channel with a wide floodplain A deeper channel with reduced floodplain excavation
This design plan either excavates the impounded sediment so that the floodplain is accessible during regular floods, or floods less frequently but is still in equilibrium with existing hydrologic conditions. We examined two types of stable channel cross-sections, a moderately wide channel designed to overtop its banks roughly once every 1.5 years (Q1.5), and a larger channel designed to overtop every five years (Q5). To derive the 200 foot wide floodplain width (wide floodplain option), we projected the obvious valley wall slopes through the impounded sediment to the approximate design floodplain grades at the dam location, and checked this width at the other locations in the impoundment.
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We developed alternative conceptual channel designs for the restored channel and floodplain through the State Hospital impoundment. The conceptual designs for the State Hospital impoundment are summarized in Table 8-1 below. Table 8-1. Proposed conceptual design parameters and preliminary excavation volumes – State Hospital Bankfull channel capacity 365 cfs ≈ 1.5 yr 365 cfs ≈ 1.5 yr 686 cfs ≈ 5 yr 686 cfs ≈ 5 yr frequency event frequency event frequency event frequency event Average channel slope (%) 0.32 0.32 0.32 0.32 Topwidth or bankfull width 50 50 55 55 (ft) Mean bankfull depth (ft) 2.5 2.5 3.6 3.6 Maximum shear stress at 0.5 0.5 0.72 0.72 bankfull flow (lb/ft2) Target Floodplain width (ft) 100 200 100 200 Floodplain flow depth at 4.3 2.9 3.5 2.3 Q100 (ft) Velocity on floodplain at 1.6 2.3 1.8 2.0 Q100 (ft/s) Shear stress on floodplain at 0.52 2 0.99 0.65 0.81 Q100 (lb/ft ) Total volume of sediment 16500 27500 15000 22000 removal required (CY) Fraction as dredged (channel) 11500 11500 11500 11500 (CY) Fraction as soil (bank and 5000 16000 3500 10500 floodplain) (CY)
We estimated the potential excavation required to implement the alternative conceptual designs by comparing the conceptual design cross sections to cross sections taken through the existing reservoir bathymetry and topography. The 14 cross sections were spaced through the reservoir and the reach through the embankment to capture the variability of the impoundment shape. The general approach involved estimating the area of excavation at each cross section and then converting this to an excavation volume for the entire impoundment using the average-end area method. When comparing the conceptual channel design cross sections to the existing bathymetry, we found that the existing channel grades and capacity differed to the extent that excavation would be required. In particular, excavation is required in reaches where the proposed alignment differs from the existing alignment (See Concept Plans sheet 7), and where the channel cuts through the dam embankment at the location of the backfilled spillway (Stations 163+50 to 165+50). We employed the same method to determine potential floodplain excavation requirements. In general, we found that the existing impoundment submerged floodplain grades differed moderately (significantly
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where the channel cuts through the embankment) from the conceptual design floodplain grades, indicating that excavation is required to attain the conceptual floodplain grades. It should be noted that restoration of the floodplain surface in the State Hospital impoundment and through the embankment would result in a contiguous floodplain corridor from Danforth Street downstream to Washington Street. The larger capacity (Q5) bankfull channel alternative results in a typical channel cross section that has the same bottom width and sideslopes as that of the channel with approximate Q1.5 capacity, but is approximately 1.1’ deeper. The use of this channel alternative has little effect on the required channel excavation volume. This relatively deeper cross section does reduce the volume of excavation in the floodplain as described above. While based on preliminary survey data, and hydraulic and design analyses, these results indicate that an ‘active’ channel restoration approaches is feasible for restoration of the State Hospital impoundment. In this case, restoration will require excavation of sediment from the reservoir and excavation of the dam structure itself, accompanied by stabilization of the banks and bed of the channel. It should be noted that the above volumes do not include subgrade excavation that may be required for installation of bank and bed stabilization measures. It should also be noted that the above volume estimates are based on survey of the impoundment sediments in a saturated condition. Following drawdown of the impoundment, a certain degree of sediment consolidation may occur initially due to drainage of pore water from the soil matrix, and over time due to decomposition of organic materials. This may reduce the overall volume of excavation required if the impoundment is drawn down for a period of time before excavation commences. Additionally, the hydraulic results reported above are based on preliminary, at-a-station calculations but are adequate for the purposes of this study. These preliminary results can be confirmed during detailed design through development of a detailed hydraulic model for the selected alternative. Finally, increased bank stabilization measures may be required throughout the reservoir if subsequent assessment concludes mobilization of the sediment in the impoundment poses an unacceptable risk of contaminant pollution. These aspects of the design can be evaluated in more detail during the final design phase of the project.
8.3. Fish passage bypass channel A second practical option at the State Hospital dam is to construct a natural fish bypass channel in the footprint of the eastern raceway channel (See Concept Plans sheet 6). This would potentially cause the normal pool elevation to be slightly lower, as water would be diverted over the fish bypass during certain flows. A fish bypass channel in this footprint would have a cascading boulder and cobble riffle configuration with a 1.8% slope and an average top width of 6 ft. The benefits of this channel would be to maintain the pond aesthetic condition, provide passage for a wide variety of fish species and create
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additional riverine habitat. A feasible fish bypass channel, as discussed in Section 6 would be constructed of rounded stone and would have a cascading riffle configuration. If six inch small boulder steps or short relatively steeper riffles are added, intervening velocity, shear and incipient motion values will drop. If this option were pursued in subsequent design phases, the design of this bypass channel can be optimized to provide conservative passage conditions over a mixed boulder/cobble/gravel bed. The channel can either be designed to withstand larger flood events, or flood flows can be limited. To limit the amount of flood water entering the fish passage channel, a rectangular opening/water control structure can be installed that allows for upstream fish passage but places a maximum cap on the amount of flow entering the channel. This could be created by a three sided metal structure with a foot bridge over the top to improve the aesthetics and facilitate viewing. Because the property required for this passage option is already publicly owned, there are no outstanding real estate or construction easement issues. The abandoned sluiceway is still partially in place, which minimizes the cost of excavation. The main drawback of this approach is that the pond conditions that degrade the water quality in the Mill River will still remain. Some river habitat can be regained through a fish bypass channel, but this will be limited to the short channel length. The dam also remains in place with this option. It will continue to degrade over time and will eventually need repairs. Some repair of the abutment walls should be included in this option, and we have included this repair in the cost estimate.
8.3.1. Anticipated Wetland Impacts The extent of wetland alteration with project implementation will be dependent on the type of project selected for the site. Full dam removal would potentially result in the greatest change in wetland type, but would result in a more long term stable riparian wetland ecosystem. Keeping and repairing the dam and installing a structural fishway (e.g., fish bypass channel) at the dam would likely result in the least amount of short term construction and drawdown related wetland disturbance but existing conditions would remain.
Dam removal impacts - Direct impacts to bordering vegetated wetlands in close proximity to the dam would be temporary. Disturbance caused by construction equipment would be required, but all disturbed areas would be restored. Temporary impacts may include equipment access roads for water diversion and channel installation. Proper erosion and sediment controls would be needed to ensure minimal potential for sediment release to the river or nearby wetlands. Disturbed areas can be easily restored through grading, soil amendment and planting of native species.
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With the dam removal and floodplain restoration options described above, permanent impoundment drawdown would occur. For the smaller channel (Q1.5), areas currently deep water habitat (>3 feet) will see a conversion a conversion of open water submerged and floating emergent wetland vegetation (e.g., water lily, spatterdock) to more persistent emergent (e.g., cattail, cutgrass) and shrub (e.g., water willow, buttonbush) species tolerant of prolonged flooding. Eventually, proper forest management will convert develop a succession plan that will result in seasonally-flooded to semi-permanently-flooded wooded swamp wetlands. The spatial extent of this conversion depends mainly on the width of the floodplain determined in the final design process. Design of a deeper channel will result in less frequently inundated floodplain conditions and establishment of a small river floodplain forest community type. Prolonged flood-tolerant species (e.g., black willow, black gum, buttonbush) may become less dominant with more drought-tolerant species (e.g., silver maple, green ash) expanding in area, although this plant species succession would not necessarily be considered a negative ecological change. Active planting of desired native species can help guide the succession toward an ecologically sustainable forest community.
Less change would likely occur where depressional topography and deep Freetown, Scarboro and/or Swansea mucks are present. These deep muck sites would be expected to retain substantial groundwater at or very near the surface during much of the growing season, and in some locations would sustain ponded waters throughout the season. Where less ponded water could result, one might expect wildlife species that use these standing water habitats (e.g., black and wood duck, muskrat) to seek nearby areas of the restored river with more favorable conditions. Substantial carrying capacity is available in these impoundments to help sustain wildlife populations that are present, and with restored riverine conditions, there should be an increase in populations of freshwater mussels, other aquatic macro-invertebrates, and riverine fishes, including river herring, to help contribute to the restored river ecology.
In other projects, we have successfully created backwater channels, side channels, vernal pools and oxbow depressions simulating natural floodplain complexity. Any and all of these options can be incorporated during final design and construction for little or no extra cost. These designs are usually incorporated as mitigating amenities to improve wetland ecological function. We also frequently install floodplain woody debris elements to increase roughness and provide additional wildlife habitat.
The 100 and 200 foot wide floodplain excavation options will cause some marginal or fringe areas to become dryer riparian forest habitats. Exact wetland impact areas would depend on the final channel bed elevation and the amount and depth of floodplain excavation planned. Table 8-2 shows the predicted change in Land Under Waterbody parameters and bank alteration. It should be noted that these are approximate values based on feasibility level estimates.
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Table 8-2. State Hospital impacted resource areas resulting from dam removal Measure Existing Full Removal Mean Annual Low Flow 4.9 acres 1.24 acres (MALFL) Mean Annual Flow (MAFL) 6.9 acres 1.7 acres Bank alteration 2,850 ft 3,600 ft We recommend active planting and exotic species control to the extent practical to prevent establishment by non-native plants such as reed canary grass (Phalaris arundinacea), purple loosestrife and Japanese knotweed.
Fish passage channel impacts – In the fish passage channel scenario, the State Hospital impoundment will not change appreciably. Some loss of water level will occur as a result of natural bypass construction. This may result in a narrow band (<10 feet wide) of littoral zone becoming dominated by more emergent species (cattail, cutgrass). Approximately 400 feet of channel habitat will be created, with streambank habitat along the entire length.
8.4. Conceptual Cost Estimates – State Hospital Dam The table below gives ballpark cost estimates for the State Hospital Dam fish passage alternatives, and are meant for the purposes of relative cost comparison between project altternatives. The actual cost of project implementation may vary from these estimates dependant on the final project approach, heavy construction market cost fluctuations and other factors. Note that a construction cost contingency has not been added to the estimated costs summarized below. Application of a typical concept-level construction cost contingency would result in adjustment of the estimated costs by up to 30%. Detailed cost estimates are given in Appendix A.
Table 8-3. Conceptual cost estimates for State Hospital Dam Options Full removal (special Full removal (no Repair and natural fish
handling of sediments) special handling) bypass channel Construction $ 834,350 $ 390,950 $ 293,725 Engineering Design $ 90,000 $ 90,000 $ 125,000
Permitting $ 65,000 $ 65,000 $ 55,000
Total cost $ 989,350 $ 545,950 $ 473,725
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The costs associated with full dam removal assume a 1.5-year channel with a 100 ft wide floodplain and special handling of sediments, representing the moderate approach. Channel size, floodplain shape, and sediment quality will have a significant impact on restoration costs. Although called the “do nothing” or “no action” option, the dam must still be repaired and maintained. The liability and long term maintenance costs of dam ownership are hard to quantify, but the cost of repair continues to increase as the dam degrades.
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9. West Britannia Dam: Design Options
9.1. Existing Conditions (Do Nothing Option)
9.1.1. Dam structure The West Britannia Dam is located just upstream of West Britannia Street on the northern end of the Reed and Barton property. The dam is 85 feet long with a structural height of 8.0 feet and a hydraulic head of 4.0 feet (Figure 9-1, 9-2). The dam is comprised of stone masonry with an 83 ft long concrete cap primary and auxiliary spillway. The West Britannia street wall forms the right abutment and the parking lot wall is connected to the left abutment. The dam itself is in poor condition and in need of repair, with several missing stones from the flat and angular stone masonry making up the structure. Joints are open and in mostly poor condition, with two leakage areas noted at the toe of the dam below the auxiliary spillway. The primary spillway is a broad-crested concrete cap 28 feet in length, while the auxiliary spillway is 55 feet in length. Both are in fair condition with minor cracks and some missing stone on the downstream side. The approach area is a heavily vegetated and tree covered wetland, while the discharge area is a cobble lined channel. At the time of inspection (June 15, 2007), there was 1-2 inches of water flowing over the spillway crest. Project engineers recommend repair of the spillway. The dam’s left embankment is a grass and tree covered earthen embankment in generally good condition but with several small holes about 4 inches in diameter, and two minor areas of erosion in need of repair.
Figure 9-1 (left) – West Britannia Dam (looking southeast) during spring runoff, April 2007 Figure 9-2 (right) – West Britannia Dam (looking north) during summer flow, June 2007
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The left downstream abutment is a mortared flat stone masonry wall plumb vertically with a uniform top elevation. The wall is in good condition with a few missing stones and minor toe erosion. Abutment contacts are good with no sinkholes or erosion noted behind the abutment. The north parking lot for Reed and Barton is paved to the edge of the wall. The right abutment is a concrete panel roadway embankment in good condition, with a Reno stone mattress for toe protection. The dam is approximately 100 feet upstream of the West Britannia Street bridge built in 2005. There are underground gas, sewer and water pipes in the street embankment next to the dam and under the bridge deck. On overhead electrical pone line runs along the right downstream wall of the dam. Access and staging are good at the dam site, particularly in the parking lot on the left bank. Access would require a construction easement with private landowners. If nothing is done to repair the structural issues with the West Britannia dam, the dam will continue to degrade. Stones will continue to loosen, cracks will widen and leaks will encourage structural degradation. If the dam is maintained or repaired in its current state, the existing seasonal pool elevations will persist. Base flow and water elevations slightly below those of the 5-year event are contained within the existing stream channel. The bathymetry data and depth of refusal probing suggest that the existing cross-section is deeper than that prior to the dam construction.
9.1.2. Impoundment sediment Upstream sediment supply is limited by Winnecunnet Pond, Lake Sabbatia and the Whittenton impoundment, but the West Britannia impoundment appears to have a significant amount of impoundment sediment. Like Whittenton, the impoundment is dissected by a channel likely similar in bankfull width to the pre-dam channel. The West Britannia channel is less sinuous, however, suggesting some floodplain deposition of sediment. We estimate the total amount of impounded sediment upstream of the dam to be approximately 13,000 – 26,000 cubic yards. From the collected field information, determining the extent of recent sediment deposition is difficult. Like Whittenton Pond, depth of refusal data shows saturated fine sandy silt deposits varying in depth from 0 – 9 feet. Depth of refusal also reveals the presence of gravel riffles along the deepest sections of the impoundment. There have been unconfirmed reports of a drawdown of the Whittenton impoundment that resulted in large pulse sediment deposition in the West Britannia impoundment, but we saw no obvious evidence of this. Analysis of historic aerial photographs show that the dam has had the same planform and exposed floodplain configuration at least since 1941. The date shown on the face of the dam indicates construction of the present form in 1857. Assuming the entire depth of refusal area to be deposited sediment as a result of dam construction, and assuming that all of the sediment deposition took place after this date until the flashboards were removed (assume 1940), the sediment then accumulated an
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average of 1.1 inches per year. Assuming sediment accumulation beginning in 1800, sediment would have accumulated at an average rate of 0.68 inches per year. It is unlikely that the entire depth of the impoundment sediment has accumulated since dam construction, and much of this is likely historic floodplain wetland soil. Based on our calculations of channel size and probable floodplain elevation, we estimate that the current floodplain is variably 1-2 feet higher than the pre-dam floodplain. Assuming an impoundment area of 358,000 ft2, this means a total volume of impounded sediment between 13,000 and 26,000 CY. Final design involving floodplain manipulation should include deep core samples (12-15 feet) to more accurately determine the historic floodplain elevation and the pattern of deposition in the impoundment area. For this assessment, we are basing the amount of sediment accumulated on depth of refusal data, local topographic trends and cross-section shape upstream and downstream of the impoundment. Regardless of project type, fish passage restoration, removal, repair or replacement, sediment will need to be removed. The amount of sediment removed will depend on the construction methods used and the final configuration of the project.
9.1.2.1. Contaminated sediment If nothing is done to treat the contaminants, most will eventually breakdown. PAH compounds can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks. PAHs do not dissolve easily in water and they adhere to soil particles where microorganisms will eventually break them down. Most volatile organic compounds have a short life span once exposed to the air. Methylene chloride, the only VOC found at the dam sites, reacts with photochemically produced compounds and decomposes within 130 days. Heavy metals could remain in the sediments indefinitely.
9.1.2.2. Fish passage There is currently no fish passage at the West Britannia dam. If the dam remains in place, passage of migratory fish from downstream reaches would remain blocked. Wildlife passage is also limited given the West Britannia road crossing on the right bank and the paved parking lot on the walled left bank.
9.1.3. Aquatic habitat conditions The reach through the West Britannia impoundment is characterized by steep banks, undercuts, deep runs and overhanging grasses and shrubs. Partial drawdown of the dam (removal of flashboards) has caused a straight, uniform channel to stabilize through the reach. Gravel was encountered in the thalweg during depth of refusal cross-sections. The river has established wetland stream ecological properties, and the dam is currently impounding an area only slightly wider than the adjacent free flowing stream reaches. Upstream supply of sediment is limited, and soundings near the dam indicate that what little sediment is input is passing through the reach. As with the Whittenton channel, however, normal river
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geomorphology (channel migration, erosion, riffle formation, and deposition of bars and floodplain surfaces) cannot function without moving water, and so the impoundment will remain much the same over time. Some deep water and undercut habitat is present, but velocities are slowed and the existing habitat is homogenous. The exposed floodplain areas within the impoundment have revegetated, with grasses and dogwood dominating the near bank areas. A more detailed discussion of riparian vegetation is given in the wetland resources section of this report.
9.1.4. Wetlands –West Britannia Impoundment and Dam The West Britannia impoundment is relatively limited in area, as extensive infilling of the impoundment has occurred. The impounded river in this reach appears to average 25-28 feet in width. The impoundment infilling is dominated primarily by seasonally-flooded forested and scrub-shrub floodplain. Red maple is the dominant canopy species with green ash less frequent and black willow also present. Silky dogwood and smooth alder are dominant shrub species. Persistent emergent wetland vegetation exists as a denser cover in the lower 2/3 of the basin, and is dominated by tussock sedge, royal fern (Osmunda regalis), sensitive fern (Onoclea sensibilis) and manna grass (Glyceria canadensis) (See Figure 9-3). In some locations, the bordering vegetated wetland extends for more than 125 feet on each side of the impounded river. Freetown mucks underlie these broader depressional floodplain areas upstream of the West Britannia Dam. The uppermost third of the basin, forested and shrub swamp dominates a narrower bordering vegetated wetland.
Figure 9-3. Wooded swamp and persistent emergent wetlands, West Britannia impoundment, May 2007
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9.1.5. Riparian habitat conditions The riparian zone is in good condition given its proximity to an urban center, with open canopy wetlands and second growth forest comprising a vegetated buffer up to 200 feet in width. There are 18 separate lots on the left terrace, with houses set back 20-200 feet from the current edge of bank. There are only 4 residential lots on the left bank, with considerably more greenspace away from the former impoundment edge. Because the normal pool elevation has dropped, this wooded riparian zone will slowly expand toward the narrow impoundment edge. If no action is taken, impoundment will maintain its current appearance, with more flood tolerant trees (willow) colonizing over time.
9.2. Full removal Full removal of the West Britannia dam would restore fish passage from the State Hospital dam up to the Whittenton Dam, and would improve the riverine habitat quality of the Mill River in this reach. Removal of the dam structure would require the excavation of roughly 150-200 cubic yards of concrete and stone. Because the right abutment is actually part of West Britannia Street, and the left abutment joins the parking lot to the east, stabilization of this dam site would require either concrete or masonry work to ensure infrastructure stability. The channel could be moved to the north and east slightly to allow for a small floodplain bench and integration of bioengineering with the road infrastructure. A gently sloping natural gravel and cobble riffle would likely be designed at or upstream of the current dam site, to control final grade through the reach. Removal sequencing would likely proceed as follows: • Initial mobilization and staging – The project could use the parking lot to the east for access to the dam site. Access through private lands would need to be arranged for easy access to the upper impoundment. • Dewatering – Partial removal of the dam could be accomplished by piping the flow through the center of the dam. Staged drawdown is not necessary at this site due to the lack of fine sediment in the channel. Isolation of the work area and in-situ dewatering of the work area may be the only dewatering necessary for structure removal. Restoring the impoundment area would require damming and pumping of water around the work area. • Structure removal – Road infrastructure (pipes, cable) would need to be isolated and rerouted if necessary. Given its age, the dam structure will likely dismantle easily with a hydraulic jack and a medium sized excavator. • Sediment removal – We recommend isolation of spring flows and allowing time for the impoundment to dry out prior to major floodplain excavation. Once the sediments are dry (6- 12 months), they can be removed by mechanical means without specialized wetland
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construction equipment. Drying can also be accomplished through staged drawdown if soil loss is a concern. • Habitat restoration - Following sediment removal and bank stabilization, tree and shrub planting and exotic species treatment should follow a 3-5 year maintenance schedule to ensure success. The resulting channel in the West Britannia impoundment would have a bankfull width similar to what has been in place for the past 70 years, but whereas the bank height is currently 6-7 feet above the channel bottom, a stable post-removal bank would be lower in some areas. A stable channel in this reach would be a gently winding riffle and pool channel, with gravel and small cobbles making up riffles. The channel would likely be slightly narrower and deeper than that currently observed downstream of the State Hospital Dam, but with similar riparian character (Figure 4-7). The amount of sediment removed depends in part on the expected future development and stormwater management, desired channel conditions, wetland and riparian conditions and cost. Once these criteria are established, then a stable channel can be designed that approaches the desired function. As stated above however, one cannot design any sized channel desired. If a channel is built to steep or too narrow, it will degrade and erode. Conversely, if a channel is sized too wide or with too much sinuosity (low slope), it may aggrade with deposited sediment. Passive versus active sediment management – Because the existing impoundment channel is at approximately the same bed elevation as the historic channel bed, removal of the West Britannia dam would not result in major sediment loss downstream due to headcutting. Potential sediment loss in this case would result from exposing high banks with inadequate soil stabilizing vegetation and changing moisture conditions. Sloughing and loss of soil would continue until the channel widened and formed an incipient floodplain. A stable channel in this reach would be a gently winding riffle and pool channel, with gravel and small cobbles making up riffles. This would potentially introduce 5,000 - 9,000 cubic yards of sandy loam sediment downstream, and we do not recommend this method of removal exclusively. As discussed below, a mixure of active and passive sediment management may be prudent for this dam removal. Floodplain and channel restoration – Based on field observation during the spring of 2007, the Mill River channel in the West Britannia impoundment reaches bankfull between the 2 and the 5-year flood event. The river in the West Britannia area is slightly steeper than that in the Whittenton area, and the surrounding riparian area was more likely dryer but still a regularly inundated floodplain forest.
We again calculated the amount of channel and floodplain excavation needed to construct a stable channel under three scenarios:
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A wide and shallow channel with a narrow floodplain A wide and shallow channel with a wide floodplain A deeper channel with reduced floodplain excavation
This design plan either excavates the impounded sediment so that the floodplain is accessible during regular floods, or one that floods less frequently but is still in equilibrium with existing hydrologic conditions. We again examined two types of stable channel cross-sections, both a moderately wide channel designed to overtop its banks roughly once every 1.5 years (Q1.5), and a larger channel designed to overtop every five years (Q5). We initially examined alternative conceptual channel designs for the restored channel and floodplain through the West Britannia impoundment.. The alternative conceptual channel designs included cross sections with capacity equal to approximately to the 1.5-year return period peak flood (Q1.5) and the 5- year return period peak flood (Q5). In addition to conceptual channel designs based on the proposed channel planform (See concept plans), we prepared a second set of conceptual channel designs based on the existing channel planform through the impoundment. We estimated the potential excavation required to implement the alternative conceptual designs for the West Britannia impoundment. Cross sections were spaced through the reservoir to capture the variability of the impoundment shape. The general approach involved estimating the area of excavation at each cross section and then converting this to an excavation volume for the entire impoundment using the average-end area method. When comparing the conceptual channel design cross sections to the existing bathymetry in the impoundment, we found that the existing channel capacity was approximately equal to the Q1.5 conceptual channel design at the upstream end of the impoundment (approximate stations 119+50 to 122+00) suggesting that negligible channel excavation would be required in this reach. In this reach, the existing channel profile grades were also approximately similar to the design channel profile grades. In the remainder of the impoundment (approximate stations 122+00 to 141+00), we found that the existing channel profile grades were similar to the proposed profile grades, but that existing channel capacity differed by approximately 50% from the Q1.5 conceptual channel design, thus excavation would be required. In addition, where the proposed channel alignment diverges from the existing channel alignment, excavation would be required. We employed similar methods to determine potential floodplain excavation requirements. In general, we found that the existing impoundment submerged floodplain grades approximately matched or were lower than the conceptual design floodplain grades, with the capacity of the existing floodplain exceeding that of the conceptual design in most locations. This suggests that minimal excavation of the submerged floodplain would be required to meet the conceptual design. Given this, the smaller capacity floodplain
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alternative (100 ft) has been discarded and the larger capacity floodplain alternative (200 ft) has been assumed in Table 9-1 below. It should be noted that of the three impoundments, the ground survey/bathymetric survey coverage of the West Britannia impoundment is the sparsest due to access restrictions. Additional survey will be required during detailed design if removal is selected for this impoundment.
Since the floodplain surface generally agrees with the Q1.5 bankfull elevation, the conceptual channel design would have to increase in width to provide capacity equal to the Q5 flood, which would increase excavation requirements and decrease habitat quality over the range of flows due to an overwidened condition. For these reasons, the larger capacity conceptual channel design was discarded for the West Britannia impoundment. While based on preliminary survey data, and hydraulic and design analyses, these results indicate that a mix of ‘passive’ and ‘active’ channel restoration approaches may be feasible for restoration of the West Britannia impoundment. An active restoration approach will be required in the reach between approximate stations 122+00 and 141+00 to achieve the conceptual channel and floodplain designs and grades. In this case, restoration will require excavation of sediment from the reservoir and excavation of the dam structure itself, accompanied by stabilization of the banks and bed of the channel. It should be noted that the above volumes do not include sub-grade excavation that may be required for installation of bank and bed stabilization measures. The above volume estimates are based on survey of the impoundment sediments in a saturated condition, and following drawdown of the impoundment, a certain degree of sediment consolidation may occur initially due to drainage of pore water from the soil matrix, and over time due to decomposition of organic materials. This may reduce the overall volume of excavation required if the impoundment is drawn down for a period of time before excavation commences. Increased bank stabilization measures may be required throughout the reservoir if subsequent assessment concludes mobilization of the sediment in the impoundment poses an unacceptable risk of contaminant pollution. These aspects of the design can be evaluated in more detail during the final design phase of the project.
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Table 9-1. Proposed conceptual design parameters and preliminary excavation volumes – West Britannia Bankfull channel capacity 365 cfs ≈ 1.5 year 365 cfs ≈ 1.5 year frequency event frequency event (proposed alignment) (existing alignment) Average channel slope (%) 0.15 0.18 Topwidth or bankfull width (ft) 45 45 Mean bankfull depth (ft) 4 4 Maximum shear stress at bankfull 0.4 0.43 flow (lb/ft2) Target Floodplain width (ft) 200 200 Floodplain flow depth at Q100 (ft) 3.3 3.3 Velocity on floodplain at Q100 (ft/s) 1.5 1.5 Shear stress on floodplain at Q100 0.46 0.46 (lb/ft2) Total volume of sediment removal 9000 5500 required (CY) Fraction as dredged (channel) (CY) 9000 5500 Fraction as soil (bank and floodplain) 0 0 (CY)
There is currently an old millrace that flows underneath the Reed and Barton building on the right bank downstream of West Britannia Street. Any project at this site should consider the option of filling this channel in to remove liability and provide added structural stability to the complex. This channel may be important in passing flood flows backwatered at the West Britannia Street bridge crossing, and so may play a role in permitting the project. Typically, water projects are not allowed to cause a significant rise in the 100-year flood elevation upstream. Filling the raceway may have an affect on the 100-year flood elevation, and a detailed hydraulic study should be part of any project.
9.3. Rock ramp (with dam repair) Rock ramp - An apparently significant constraint on the construction and function of a rock ramp at the West Britannia site is presented by the downstream road bridge, which is 120 feet downstream of the dam and has limited hydraulic capacity. Construction of a rock ramp at a typical slope of 20:1 (h:v) to 40:1 would likely require the placement of fill under the bridge, further reducing its hydraulic conveyance capacity. Accounting for approximately 1 ft of drop in the channel between the dam and the channel, a rock ramp with a slope of 20:1 (H:V) would terminate at the upstream face of the dam. A ramp with a slope of 20:1 is marginally passable, and the use of a rock ramp is therefore considered marginally feasible at this site. Because of the apparently limited conveyance capacity of the existing bridge, a ramp with a shallower slope passing under the bridge is not considered acceptable.
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9.4. Fish bypass channel (with dam repair) Natural bypass - The existing vertical-walled channel through the Reed and Barton complex to the right of the main channel may be suitable for creating a bypass channel for upstream fish passage. This channel is approximately 400 ft long and has an approximate width of 15 ft. The length of this channel could facilitate construction of a relatively low-gradient bypass channel (approximately 50:1 or 2%). Use of this channel would apparently require construction of an inlet structure where it diverges from the Mill River immediately upstream from the dam. Installation of weirs within the channel may be appropriate for this alignment, as their use would limit the need for fill placement and potentially provide a means to improve the stability of the existing vertical walls. Apparent disadvantages of this alignment include 1) that the fishpass inlet (downstream end) would be located well downstream from the dam, and 2) the likely need to provide for flow in both the main channel and the bypass under most flow conditions. A fish bypass channel could also be constructed along the left bank, provided construction easements can be obtained. A feasible fish bypass channel would be constructed of rounded stone and would have a cascading riffle configuration. We recommend the bypass channel (upstream) inlet be configured to constrain the amount of water flowing down the channel at flows above the 50% exceedence flow to limit damaging flood flow in the constructed channel. The balance of the flow will be passed over the dam itself. In this way, the estimated hydraulic conditions for the 50% exceedence flow would apply up to the 10% exceedence flow, which is the typical upper end of the flow range considered in fish passage evaluations. As with the right bank channel option, the left bank channel would be approximately 400 ft long with a 15 ft top width and 2% slope. This channel would be a combination of cascading pools and resting areas, with riffle drops of ~ 1-ft between pools. A high degree of roughness could be incorporated by designing the bed based on high flow stability and setting the rock with protruding elements. This would require a poorly-graded rock comprised of 18" material with 24" to 30" outliers installed to increase roughness above the surface. A sinuous velocity profile could be designed with skimming flow during high flow events. Formal sizing of material would require final design information. A particular strength of this alignment is that the fish passage inlet could be located close to the downstream face of the dam, which would limit problems associated with fish moving upstream beyond the fish passage inlet and potential diversion of water around the downstream channel of the river. A natural fish bypass channel would require temporary disturbance of the western end of the parking lot area, and may require permanent easement of 20-30 feet of the lot depending on the design used. Amenities such as walkways and viewing areas could be designed to encourage viewing of passing fish during migration periods.
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9.5. Fish ladder (with dam repair) Installation of a small fish passage ladder is feasible at the West Britannia site. A steep pass ladder could be fitted to the left abutment and training wall. Observations at spring runoff and at low flow indicate that slightly more flow passes over the left half of the dam, and that the right side of the channel downstream of the dam is dry during low flow or low velocity during moderate flows. Thus attraction to a fish ladder would be best installed along the left bank near the dam. The left bank training wall is curved, which may require either modification of the wall or a custom designed fish ladder. A 1v:10h sloped ladder could be constructed along 40 feet of the left abutment or along a shorter distance with a switchback design. An additional constraining factor is flow through the Reed and Barton raceway. During spring runoff, flow frequently passes through this raceway, in which an internal dam also blocks fish passage. This flow may distract migrating fish and would need to be limited. The hydraulic effect of this action on the West Britannia crossing would need to be determined through detailed hydraulic modeling of the crossing.
9.5.1. Dam repair Alternative fish passage, in this case a bypass channel or ladder, will require some dam repair to bring the dam up to safety standards according to Massachusetts Department of Dam Safety regulations. A ballpark cost estimate is included for dam repairs. A formal preliminary structural engineering design (30%) should be conducted prior to any consideration of detailed costs for repair. As part of the final design process, preliminary engineering would examine the dam more closely during low flow, and make detailed measurements of structural elements in need of repair. A dam remains in place with this option. Despite any new repairs, the dam will continue to degrade and will eventually need further repairs. The logistics and cost of yearly maintenance of the dam and bypass channel will need to be considered.
9.5.2. Anticipated Wetland Impacts The extent of wetland alteration with project implementation will be dependent on the type of project selected for the site. Full dam removal would result in the greatest change in wetland type, whereas a fish ladder or bypass channel would not cause appreciable short term wetland changes.
Dam removal impacts - Temporary impacts to bordering vegetated wetlands during dam removal would include equipment access during water diversion, dam removal and restoration. Removal plans will include an erosion and sediment control plan to ensure minimal sediment release to the river or nearby wetlands. Disturbed areas would be restored through grading, soil amendment and planting of native species.
With the West Britannia dam removal and floodplain restoration options described above, bank height during low flow would drop, and further impoundment drawdown would occur. For the smaller
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channel (Q1.5), areas currently grass and dogwood dominated floodplain wetlands will see a conversion a conversion to of seasonally-flooded to semi-permanently-flooded wooded swamp wetlands. The spatial extent of this conversion depends mainly on the width of the floodplain determined in the final design process. Design of a deeper channel would result in less frequently inundated floodplain conditions and establishment of a small river floodplain forest community type (e.g., silver maple, green ash dominant forest). Active planting of desired native species can help guide the succession toward an ecologically sustainable forest community. This type of conversion is likely what is naturally occurring downstream of the State Hospital dam after removal of the Woolstock Dam.
As with the State Hospital impoundment, deep muck sites would be expected to retain substantial groundwater at or very near the surface during much of the growing season, and in some locations would sustain ponded waters throughout the season. Restored riparian forest conditions combined with restored flowing river in-stream conditions will improve habitat for riparian zone dependent wildlife that feed on aquatic species. Examples of such riparian wildlife include herons, wood duck, great horned owl, flycatchers, kingfishers, vireos, weasels, mink, muskrats, turtles, salamanders, frogs and reptiles (Small and Johnson 1986, Wigley and Melchiors 1994). Backwater channels, side channels, vernal pools, floodplain woody debris and oxbow depressions simulating natural floodplain complexity can be incorporated during final design and construction for little or no extra cost.
The 100 and 200 foot wide floodplain excavation options will cause some marginal areas to become dryer upland habitats. Exact impact areas would depend on the final channel bed elevation and the amount and depth of floodplain excavation planned. Table 9-2 shows the predicted change in Land Under Waterbody parameters and bank alteration. It should be noted that these are approximate values based on feasibility level estimates.
Table 9-2. West Britannia impacted resource areas resulting from dam removal Measure Existing Full Removal Mean Annual Low Flow 6.6 acres 1.5 acres (MALFL) Mean Annual Flow (MAFL) 9.6 acres 1.9 acres Bank alteration 3,800 ft 4,300 ft
Construction disturbance and a drop in groundwater levels could make the restored floodplain susceptible to invasion by aggressive exotic species. We recommend active planting and exotic species control to the extent practical to prevent establishment by non-native plants such as reed canary grass (Phalaris arundinacea), purple loosestrife and Japanese knotweed.
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Fish passage channel impacts – In the fish passage channel scenario, the West Britannia impoundment wetlands will not change appreciably. Some loss of water level will occur as a result of natural bypass construction. This may result in a slight lowering of riparian groundwater levels resulting in more flood tolerant tree establishment (eg. Red maple). Approximately 400 feet of bypass channel habitat will be created, with streambank habitat along the entire length.
9.6. Conceptual Cost Estimates – West Britannia Dam The table below gives ballpark cost estimates for the Whittenton Pond Dam fish passage alternatives, and are meant for the purposes of relative cost comparison between project altternatives. The actual cost of project implementation may vary from these estimates dependant on the final project approach, heavy construction market cost fluctuations and other factors. Note that a construction cost contingency has not been added to the estimated costs summarized below. Application of a typical concept-level construction cost contingency would result in adjustment of the estimated costs by up to 30%. Detailed cost estimates are given in Appendix A.
Table 9-2. Conceptual cost estimates for West Britannia Options Full removal Full removal (no Repair and fish Repair and natural (special handling of special handling) ladder fish bypass channel sediments) Construction $ 546,750 $ 304,950 $ 249,600 $ 157,025
Engineering $ 82,000 $ 82,000 $ 125,000 $ 68,000
Permitting $ 65,000 $ 65,000 $ 55,000 $ 35,000
Total cost $ 693,750 $ 451,950 $ 429,600 $ 260,025
These costs are conceptual and assume a mixture of active and passive planting approaches. The cost estimates in the table reflect the most active floodplain management scenario (removal of the most sediment). Channel and floodplain shape and sediment quality will have a significant impact on restoration costs. Although called the “do nothing” or “no action” option, the dam must still be repaired and maintained. The liability and long term maintenance costs of dam ownership are hard to quantify, but the cost of repair continues to increase as the dam degrades.
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10. Whittenton Pond Dam: Design Options
10.1. Existing Conditions (No action or minimal action alternative)
10.1.1. Dam structure A detailed account of the structural makeup of the dam is found in Pare (2005b) and USACE (1979) and is not repeated here. To summarize, the Whittenton Pond Dam consists of a 120 foot long spillway with vertical masonry abutments. The crest of the dam is a 2 foot wide concrete cap, and the base of the original spillway is a rockfill apron with large cut stone blocks. During the temporary repair activity in 2005, the wooden walkway and guideposts were removed and the downstream face of the dam was shored with various sizes of riprap (Figure 10-1, 10-2). Two trapezoidal spillways were constructed over the surface of the rock fill. Pare reported that the current structure is classified as a High Hazard dam, has a hydraulic head of 12 feet and impounds 160 acre-feet at maximum pool elevation.
Figure 10-1 (left) – Whittenton Dam prior to emergency spillway repair, Spring 2005 (photo NRCS) Figure 10-2 (right) – Emergency spillway repair under construction, Spring 2005 (photo NRCS)
At low flow during the late fall of 2007, no water was flowing over the spillway crest, and all flow was diffusing through the dam structure (Figure 4-5). Our team engineers were in general concurrence with the 2005 Pare inspection, but the June 2007 inspection found some leakage at the left and right abutment walls, and portions of the downstream riprap fill had moved, exposing aggregate in spots. At the time of survey, approximately 1-3 gallons per minute (gpm) were seeping from the right abutment, and 10-30 gpm from the left abutment. If the dam is maintained, the we recommend the following repair actions:
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• Repair or replace mobile riprap fill • Repair rutting in rockfill dam • Remove trees on the right abutment area and stabilize rockfill • Repair leakage/seeping of abutment walls • Replace rockfill at the downstream toe • Repair or replace damaged areas on the left masonry wall • Repair undermining of abutment walls • Repair abutment rock contacts and subsidence of fill at masonry wall • Repair heaving of masonry wall sections • Remove vegetation in masonry walls Because of the changes that have occurred since the 2005 work, we also recommend regular monitoring of general dam structural integrity. Detailed survey notes are included in the Appendix F.
If the dam is maintained or repaired in its current state, the existing seasonal pool elevations will persist, with much of the low flow being lost through the structure, resulting in a lower pool elevation during dry periods. Because the impoundment surface area is decreased, water exiting the dam will be slightly cooler than prior to 2005. The bathymetry data and recent exposure of the floodplain during low flow reveals a relatively intact river channel with frequent gravel riffles observed throughout. In the fall of 2007, the stream upstream of the dam adopted a width similar to what would be there if the dam was fully removed.
10.1.2. Impoundment sediment Upstream sediment supply is limited in the Whittenton impoundment, but the impoundment will continue to accumulate silt and organic material from decaying littoral zone vegetation. Depth of refusal data shows saturated fine sandy silt deposits varying in depth from 0 – 7 feet, but analysis of downstream cross-section data suggests that some or all of this sediment is former floodplain material. We estimate the total amount of impounded sediment upstream of the Whittenton dam to be approximately 1400 to 4,000 cubic yards. Although a rebar rod can penetrate these sediments, they easily support walking without sinking. Depth of refusal also reveals the presence of gravel riffles along the deepest sections of the Whittenton impoundment. Drawdown of the impoundment following the 2005 emergency repairs revealed the presence of tree stumps along the entire edge of the thalweg at what appears to the be the top of the historic channel bank (Figure 10-3). Given
Figure 10-3 – Historic stumps lining the 103 former Mill River bank within the Whittenton impoundment (photo Interfluve)
the size of the stumps and the history of dam construction in the Whittenton Mills area, it is probable that these trees were not pre-settlement but were secondary growth that was flooded sometime after Crocker, Bush and Richmond constructed their larger cotton mill dam after 1811. Thus the tree stumps correlate well with the bathymetric and topographic data suggesting that in the upper and middle impoundment area, the pre-dam channel cross-section and profile have remained relatively unchanged since construction of the most recent dam. In the lower impoundment area, the existing floodplain grades suggest some deposition or floodplain filling. Coring and dating of floodplain sediments is suggested to more accurately date the sediment deposition. Accumulated sediment is present upstream of the dam, along with imported gravel fill near the dam site. If the dam is to be replaced, sediment impacting the construction area would need to be removed. The amount of sediment removed will depend on the construction methods used and the final configuration of the new dam. We estimate from depth of refusal data that there is approximately 1400 cubic yards of fine sediment and gravel within 100 feet of the dam structure.
10.1.3. Contaminated sediment If nothing is done to treat the contaminants, most will eventually breakdown. PAH compounds can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks. PAHs do not dissolve easily in water and they adhere to soil particles where microorganisms will eventually break them down. Most volatile organic compounds have a short life span once exposed to the air. Methylene chloride, the only VOC found at the dam sites, reacts with photochemically produced compounds and decomposes within 130 days. Heavy metals could remain in the soil indefinitely unless natural forces remove the dams and the channel resumes migration whereby sediments would be moved downstream over hundreds of years.
10.1.4. Fish passage There is currently no fish passage at the Whittenton Pond dam. Although some flow passes through the dam, it is unlikely that small fish would use this route due to high velocities and depth restrictions. If the dam remains in place, passage of migratory fish from downstream reaches would remain blocked.
Recent observations of the dam during low flow have shown that fish are being trapped in the rip-rap emergency spillway (SRPEDD, Riverways personal comm..2007). Water passes over the dam and also through openings in the structure, allowing fish to pass downstream into the riprap where they are then trapped.
10.1.5. Aquatic habitat conditions The habitat in the river will remain degraded and lentic, benefiting only warmwater emigrants from Lake Sabbatia that cannot travel upstream back into the lake. Lentic habit is also limited due to the
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prevalence of macrophytes, which decreases available fish habitat except on the margins of the main channel. Normal river geomorphology cannot function without moving water, and so the impoundment will remain much the same over time. The exposed floodplain areas within the impoundment have already begun to revegetate, with tolerant weedy species dominating. Some red maple seedlings were observed throughout the impoundment, and these will continue to thrive as long as the soils remain moist. Other less aggressive shrub and tree species may begin to colonize the fringe of the impoundment, but it is likely that aggressive exotic grasses will take over the exposed flats, preventing native species from establishing. This pattern of revegetation following drawdown is common when no active planting plan is implemented (Lenhart 2000). These monocultures are marginal habitat for bird species, and provide a food supply only to those organisms tolerant of a limited diet.
10.1.6. Wetlands – Whittenton Pond and Dam At the remnant dam site, much of this area has been altered by the placement of riprap to address the dam breaching that occurred in October 2005. Minimal bordering vegetation exists in the temporary stone dam area.
With the partial breach conditions present in Whittenton Pond during the May 2007 site visit, water level signatures appear to be ~1.6-1.75-feet higher than the water levels observed in the lower basin during the wetland reconnaissance. In the lower basin, purple loosestrife and water willow were co- dominants in the persistent emergent wetlands, with red maple and sweet pepperbush (Clethra alnifolia) forming fringe forested and scrub-shrub swamp along the impoundment, and bordered by upslope upland lawns, particularly on the western shore. In some flooded and poorly-drained impoundment shoreline areas, tussock sedge (Carex stricta) forms a mosaic of tussocks and shallow standing water. A broader forested swamp dominated by red maple and smooth alder (Alnus serrulata) and pepperbush exists on the west side of the basin, providing a dense cover on the point bar of the flooded river meander in this location. Other sedges (Carex spp.), blue flag (Iris versicolor), rush (Juncus spp.), and swamp rose (Rosa palustris) form an emergent and low-shrub cover along the shoreline of the central pond basin (Figure 10- 4). Approximately 2/3 the way up the impoundment, the bordering vegetated is ~40-feet wide and dominated by water willow and tussock sedge. Fragrant water lily is a dominant floating emergent of the deeper pond waters, peripheral to the central flow channel.
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Figure 10-4. Backwater emergent and scrub-shrub wetlands, upper Whittenton Pond, east side, May 2007
Near the head of the impoundment, water willow typically forms a narrow fringe along the steeper upland banks. Downstream of the Bay Street (Route 138), Morey’s Bridge crossing, broad back eddies exist on each side of the river inlet, and deltaic deposits exist and are dominated by water willow with patchy broad-leaved cattail. A depression marsh and shrub wetland complex that is hydrologically connected to Whittenton Pond is situated on the east side of the pond and south and west of Route 138, and is dominated by tussock sedge and water willow. Deeper Freetown and/or Scarboro mucks underlie this bordering vegetated wetland.
10.1.7. Riparian habitat conditions The riparian zone is in good condition given its proximity to an urban center, with secondary growth trees making up a forested buffer between 50 – 200 feet in width. Some low density residential developments line the impoundment, but structures are generally set back from the edge of the impoundment. Because the normal pool elevation has dropped, this wooded riparian zone will slowly expand toward the narrow impoundment edge. The impoundment will look similar to that upstream of the West Britannia dam, with wet areas dominated by reed canarygrass, alder and dogwood. More upland or dryer areas of the exposed floodplain will likely be subject to invasion by exotic Japanese knotweed, a highly fecund annual plant that quickly colonizes disturbed areas. If no action is taken, the wetlands will continue to degrade. Decaying vegetation will accumulate as organic matter and the water depth in the impoundment will continue to decrease until the littoral vegetation takes over all but a narrow channel of moving water similar in width to the unrestricted stream. As water depth decreases, invasive plants such as reed canarygrass and purple loosestrife will proliferate, choking out native vegetation. When the dam fails, the channel will erode and incise through the
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impoundment, possibly perching and drying out many of the wetland areas. For this reason the wetlands in the impoundment are entirely dependent on maintenance of water levels in perpetuity.
10.2. Full removal – Whittenton Dam
10.2.1. Description of alternative
Full removal of the Whittenton Pond dam would restore fish passage from the West Britannia dam up to Bay Street, and would dramatically improve the habitat quality of the Mill River in this reach. From a cost versus benefit perspective, this option is the most economical for the benefit achieved and also the easiest to engineer and permit. Removal of the dam would require the excavation of roughly 1300 cubic yards of riprap and concrete. Failing abutments would be removed and the streambanks stabilized with bioengineering. A gently sloping natural gravel and cobble riffle would likely be designed at the dam site, to control final grade through the reach. Removal sequencing would likely proceed as follows: • Initial mobilization and staging – The project could use the same access route as was used in the 2005 emergency stabilization, and could also use the property along the Whittenton Mills area. Access to the upper reservoir may potentially be gained at the Morey’s Bridge crossing (Bay Street) or from cooperating landowners. • Dewatering – Partial removal of the dam could be accomplished by piping the flow through the center of the dam. Staged drawdown may be necessary at this site to minimize the movement of fine sediment upstream of the dam. Full dewatering of the site is recommended via gravity flow or by piping the stream around the work area during low-flow. A logical location to begin dewatering is approximately 800 feet upstream of the dam at station 200+00 where the channel narrows considerably. • Following dewatering, removal and disposal of sediment would commence. At the same time, the structure would be removed using large track excavators and probably a machine mounted hydraulic jackhammer. • Sediment removal – The bulk of sediment to be removed at Whittenton is within 100 feet of the existing dam structure. This sediment could be removed by mechanical means with wide track, low pressure wetland construction equipment. Drying of sediments could be used to minimize the total volume excavated and reduce costs. Drying can be accomplished through staged drawdown and dewatering to minimize soil loss. At this time, we do not recommend major sediment excavation upstream of the immediate dam area.
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• Once the structure is removed some bank construction and stabilization would take place upstream. Bank stabilization would include simple staking of bioengineering fabric and trenching of transition areas to prevent blanket from washing away. Some banks would likely need to be constructed by shaping or encapsulation of compacted soils (Figure 8-3 through 8- 6).
• Habitat restoration - Following sediment removal and bank stabilization, tree and shrub planting and exotic species treatment in the riparian area should follow a 3-5 year maintenance schedule to ensure success. Interfluve recommends aggressive treatment of Japanese knotweed in the area to ensure the establishment of woody bank stabilizing vegetation. Habitat restoration activities could be performed, including riffle and pool construction and wood placement (Figure 8-5, 8-6). The resulting channel would have a bankfull width similar to that observed at the site currently, and low flows would be slightly narrower, with a normal wetted width of roughly 15-20 feet. As mentioned earlier, the channel would look similar to that downstream of the State Hospital Dam (Figure 4-7). The amount of sediment removed depends in part on the expected future development and stormwater management, desired channel conditions, wetland and riparian conditions and cost. Once these criteria are established, then a stable channel can be designed that approaches the desired function. However, channel size and planform must be in equilibrium with the forces that move water and sediment, or the project will fail. Because only certain patterns in geomorphology are dynamically stable, there are limitations to design regarding planform, slope and channel size. Passive versus active sediment management – According to our initial investigation, the Whittenton Pond impoundment does not contain a large volume of mobile sediment. This may allow for more passive restoration approaches that focus mainly on vegetation restoration and less on excavation and streambank stabilization. A detailed discussion of floodplain and channel restoration options follows. Floodplain and channel restoration – Streams dissipate flood energy by overtopping banks and flowing over floodplains. Historically, the Whittenton impoundment likely flooded regularly once or twice per year. If a wide and shallow channel is designed so that more frequent floods occur, then enough floodplain needs to be excavated to create this floodplain bench. This design essentially excavates the impounded sediment so that the floodplain is returned to its pre-dam state, or one that is in equilibrium with existing hydrologic conditions. As with the other dam removal options, a second alternative is to design a deeper channel. If the river is designed to be deep, more flood flows can be contained within the channel and the floodplain would
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get inundated less frequently. This would result in an entirely different set of appropriate vegetation, as the floodplain would be dryer. Sediment excavation in dam removals can be the biggest cost component. In order to consider the impact of sediment excavation on restoration, we examined two types of stable channel cross-sections, both a moderately wide channel designed to overtop its banks roughly once every 1.5 years (Q1.5), and a larger channel designed to overtop every five years (Q5). We developed alternative conceptual channel designs for the restored channel through the Whittenton impoundment. These conceptual designs were based on the estimated peak flow hydrology for the Mill River at the site (Section 6) and the proposed channel profile, which was determined by 1) the proposed alignment for the restored channel (see plansheets) and 2) the existing channel bed elevations at the upstream and downstream transitions between the existing and proposed alignments. The alternative conceptual channel designs included cross sections with capacity approximately equal to the 1.5-year return period peak flood (Q1.5) and the 5-year return period peak flood (Q5). These alternative channel and floodplain designs balanced several channel design criteria, including estimated velocities and shear stresses over the floodplain during large floods, the estimated width of the pre-disturbance floodplain based on inspection of the bathymetric and topographic data observations of the existing relatively intact channel below State Hospital Dam, typical bankfull channel width to depth relationships, flow capacity, and channel competence, which refers to the ability of flood flows to mobilize sediment on the channel bed. The conceptual channel and floodplain designs for the Whittenton impoundment are summarized in Table 10-1 below. We estimated the potential excavation required to implement the alternative conceptual designs by comparing the conceptual design cross sections to cross sections taken through the existing reservoir bathymetry and topography. The cross sections were spaced through the reservoir to capture the variability of the impoundment shape. The general approach involved estimating the area of excavation at each cross section and then converting this to an excavation volume for the entire impoundment using the average-end area method. Channel form - When comparing the conceptual channel design cross sections to the existing bathymetry in the upper portion of the impoundment (approximate stations 58+00 to 93+00 – see existing topography in plansheets), we found that the existing channel capacity was typically similar to or greater than either the 1.5 or 5 year flood design channel capacity, suggesting that negligible channel excavation would be required in this reach. In this reach, the existing channel profile grades were also approximately similar to the design channel profile grades. In subsequent design phases, selective reuse of excavated material should be considered to proactively define the restored channel in the reach below Morey’s Bridge Dam, from approximate station 58+00 to 76+00.
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In the lower portion of the reservoir (approximate stations 93+00 to 107+00), we found that the existing channel geometry grades and capacity differed (relatively smaller capacity and relatively higher elevations) to the extent that excavation would be required. In this case, since the amount of sediment required is minimal, we recommend construction of a channel to contain the 1.5 year event. At its deepest points, this channel would have the energy to move fines, sand and small gravels under 1.2 inches in diameter at the bankfull event, but would not have enough energy to move large gravels. In this case, shear stresses below 1 lb/ft2 can be resisted adequately with well designed bioengineering using biodegradable fabrics. Simple bioengineering could be used to design any bank stabilization in this environment. This channel size would allow for frequent inundation of the floodplain, thus preserving floodplain wetlands and more closely mimicking historic conditions, and would actually require less excavation than a channel designed to contain a larger event. This is because the historic channel and floodplain remains largely intact. Although depth of refusal data suggest that the floodplain contains roughly 5-6 feet of saturated fine sediment, the bathymetry data and the consistent presence of historic tree stumps suggests that the material is not impounded sediment but is former floodplain wetland sediment. Further coring and sampling should be completed to confirm this assumption. Floodplain excavation - We employed the same method to determine potential floodplain excavation requirements. In general, we found that the existing impoundment submerged floodplain grades approximately matched or were lower than the conceptual design floodplain grades, with the capacity of the existing floodplain exceeding that of the conceptual design in many locations. The exception to this is in the right overbank between approximate stations 87+00 and 99+50. It should be noted that at several locations along the reservoir (approximate stations 72+00, 89+00 and 93+00), the valley width is naturally constrained to less than the wider of the two floodplain width alternatives. In these locations, the valley width governs the concept design and excavation volume estimates.
The larger capacity (Q5) bankfull channel alternative results in a typical channel cross section that has the same bottom width and sideslopes as that of the channel with approximate Q1.5 capacity, but is approximately 1’ deeper. The use of this channel alternative has little effect on the required channel excavation volume. This relatively deeper cross section does reduce the volume of excavation in the floodplain as described above. The primary hydraulic effect of the use of this design would be to create a flow constriction in the reach upstream of the dam (stations 87+00 to 107+00) up to the Q5 flow level, which would result in increased shear stresses in the reach, and would tend to create additional backwater in the upper impoundment between the Q1.5 and Q5 flow levels. While based on preliminary survey data, and hydraulic and design analyses, these results indicate that a mix of ‘passive’ and ‘active’ channel and floodplain restoration approaches may be feasible for
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restoration of the Whittenton impoundment. The relationship of the existing and proposed channel geometries and channel profiles between approximate stations 58+00 to 93+00 suggest that a passive approach may be feasible here, whereby the channel would generally be allowed to evolve following drawdown of the impoundment, with minimal stabilization effort. Over this same reach selected grading (excavation between stations 87+00 to 93+00, select reuse of excavated material as fill in upstream portion of the reservoir) and revegetation of the floodplain would be required to attain the conceptual design grades. An active floodplain restoration approach will be required in the reach between approximate stations 93+00 and 107+00 to achieve the conceptual channel and floodplain designs and grades. In this case, restoration will require excavation of sediment from the reservoir and excavation of the dam structure itself, accompanied by stabilization of the banks and bed of the channel.
Table 10-1. Proposed conceptual design parameters and preliminary excavation volumes – Whittenton Pond Bankfull channel capacity 365 cfs ≈ 1.5 365 cfs ≈ 1.5 686 cfs ≈ 5 686 cfs ≈ 5 year year frequency year frequency year frequency frequency event event event event Average channel slope (%) 0.12 0.12 0.12 0.12 Topwidth or bankfull width 49 49 49 49 (ft) Mean bankfull depth (ft) 4 4 5 5 Maximum shear stress at 0.3 0.3 0.4 0.4 bankfull flow (lb/ft2) Target Floodplain width (ft) 100 200 100 200 Floodplain flow depth at 5.4 3.6 4.4 2.9 Q100 (ft) Velocity on floodplain at 1.8 1.4 1.5 1.2 Q100 (ft/s) Shear stress on floodplain at 0.51 0.37 0.42 0.30 Q100 (lb/ft2) Total volume of sediment 13500 20000 11200 16000 removal required (CY) Fraction as dredged 8000 8000 8000 8000 (channel) (CY) Fraction as soil (bank and 5500 12000 3200 8000 floodplain) (CY)
It should be noted that the above volumes do not include subgrade excavation that may be required for installation of bank and bed stabilization measures. It should also be noted that the above volume estimates are based on survey of the impoundment sediments in a saturated condition. Following
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drawdown of the impoundment, a certain degree of sediment consolidation may occur initially due to drainage of pore water from the soil matrix, and over time due to decomposition of organic materials. This may reduce the overall volume of excavation required if the impoundment is drawn down for a period of time before excavation commences. Additionally, the hydraulic results reported above are based on preliminary, at-a-station calculations but are adequate for the purposes of this study. These preliminary results can be confirmed during detailed design through development of a detailed hydraulic model for the selected alternative. Finally, increased bank stabilization measures may be required throughout the reservoir if subsequent assessment concludes mobilization of the sediment in the impoundment poses an unacceptable risk of contaminant pollution. These aspects of the design can be evaluated in more detail during the final design phase of the project.
10.2.2. Sediment Removal In a full removal scenario, the maximum amount of sediment proposed to be dredged from the channel at Whittenton is over 1,000 cubic yards but under 10,000 cubic yards (Table 10-1). In this scenario, Mass DEP regulations call for one sediment core for every 1000 cubic yards of dredged material, with some composite sampling allowed. Other options would require less sediment testing commensurate with the design. We recommend that cores be subsampled by depth to analyze sedimentation and to evaluate vertical zones of contamination. The table above reflects mechanical removal of the sediment within 800 feet upstream of the dam (straight line distance, 1400 feet along thalweg), and then allowing natural sediment movement (in-stream management) upstream of that location, if permitting allows. We recommend bioengineering bank stabilization of soils throughout the project area, to minimize soil loss over time. Given the low gradient of the reach, sediment loss should be minimal if proper bank stabilization is completed.
10.2.3. Ecological impact As stated in the previous sections, full removal would result in the restoration of riverine conditions throughout the impoundment reach. Gravel riffles would be exposed and 2-3 foot deep pools would occupy the outside of meander bends. Water quality would improve, including lowered average and peak water temperatures, decreased nutrient levels, increased dissolved oxygen levels and free upstream and downstream exchange of nutrients and carbon. These improved water quality conditions would favor fish and macroinvertebrate populations adapted to moving water. Generalist species tolerant of poor water quality would be replaced by more specialized river species. Increased stream velocities would keep spawning gravel clean and oxygenated, favoring reproduction of riverine fish such as herring.
Any exposed impoundment sediment not stabilized will erode and move downstream during high water. This sediment will deposit rapidly, typically in the first low energy areas encountered, such as the
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inside of meander bends, wide sections or backwater channels. If the entire sediment load just upstream of the dam (1400 CY) was allowed to erode without intervention some adverse deposition would occur downstream, but the affect would be temporary. The following generalization illustrates the potential effect of sediment delivery downstream: 1400 cubic yards of material is equal to roughly 93 medium sized dump trucks, and spread over a channel width of 30 feet, could cover a mile of downstream channel bottom with 3.0 inches sediment. This is a generalization, and patterns of sediment deposition would vary with time and distance.
10.2.4. Fire suppression In discussions with the Taunton Deputy Fire Chief, project engineers have the following understanding. The Mill complex needs 26 inches of water depth over the fire supply intake for the intake to function, this equates to 2.0-2.5 feet below the dam crest. Removal would thus require some alternative fire suppression. The Quarry upstream of the dam discharges 50,000 gallons per minute (gpm) continuously into the river and this water could be piped into the Mill complex to augment fire water supply.
The Mill area needs approximately 1000 gpm running constantly for 30 minutes. Three additional options could also provide this level of fire suppression flow:
Drill a well and install a header for connection to a fire pumper at a cost of $20K - $25K
Install fiberglass cistern tanks under the mill area parking lot at a cost of $25K - $35K.
There is currently a quarry water discharge into the river is just below the Whittenton Street Bridge, 500 feet below the dam and the mill complex. One way of utilizing this water for additional fire water supply for the mill would be to connect the existing discharge outfall to a new gravity pipeline, constructed as a siphon under the river and connected to a fiberglass or concrete vault with a dry hydrant header connection. The vault would also be fitted with an outlet weir such that water, under normal conditions, will continue to discharge freely to the river. When needed for fire flow, weir boards would be added to close flow from going to the river, and create a sump from which water would be pumped via the dry hydrant header to the mill area. The cost for this installation would vary from $50,000 to $75,000 depending upon the construction difficulty of the siphon crossing.
10.2.5. Remnant structures There appear to be at least two other remnant dam structures buried beneath the impounded sediments. The first is a remnant of a timber crib, either part of the current dam’s original construction or an earlier version of the dam (4-5). A second structure protrudes from the impoundment sediments
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approximately 300 feet upstream of the existing dam (Figure 4-6). This appears to be another crib like structure with an attached gravel access road or crossing. Both of these structures would need to be removed in order to restore the stream bed and banks in the lower impoundment.
10.2.6. Effects of Whittenton Dam alteration on Morey’s Bridge Dam Potential effects on backwater impacts at Morey’s Bridge Dam associated with the removal of Whittenton Pond Dam were evaluated. This analysis was performed using the project HEC-RAS hydraulic model with the dam in place (“Dam In”) and with the dam removed (“Dam Out”). The Dam Out scenario included removal of the dam and re-grading of the upstream cross sections. The re-grading of the upstream cross sections was performed to account for the likely removal of sediments that have accumulated immediately upstream from Whittenton Pond Dam. This analysis was performed for using the hydrologic data presented in Section 6.
Table 10-2. Calculated Change in Water-Surface Elevation Downstream from Morey’s Bridge Dam Based on Removal of Whittenton Dam and flow estimates developed for analysis and design in this study.
Return Interval 1.05 2 5 10 50 100 500 (years) Discharge (cfs) 239 470 686 843 1232 1416 3100 Whittenton Dam In 57.87 58.43 58.87 59.14 59.75 59.99 61.75 (WSEL* [ft]) Whittenton Dam Out 55.14 56.41 57.21 57.7 58.65 59.02 61.14 (WSEL [ft]) Difference (ft) 2.73 2.02 1.66 1.44 1.1 0.97 0.61 *Note: “Water Surface Elevation”
Table 10-3. Calculated Change in Water-Surface Elevation Downstream from Morey’s Bridge Dam Based on Removal of Whittenton Dam the FEMA flow estimates.
Return Interval (years) 100 500 Discharge (cfs) 2100 cfs 3100 cfs Dam In (WSEL [ft]) 60.8 61.75 Dam Out (WSEL [ft]) 60.06 61.14 Difference (ft) 0.74 0.61
The results of this analysis indicate that the hydraulic backwater at Morey’s Bridge Dam is dependent upon the prevailing flow regime. At low flows, the difference in the backwater between the Dam In and Dam Out conditions is relatively large (e.g., 2.73 ft during the 1.05 year return-interval hydrologic event). The difference in the backwater diminishes with higher flows, and is approximately 1 ft for hydrologic
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events with return intervals in excess of 50-years. This result is consistent with one-dimensional hydraulic theory.
Changes in the boundaries of the channel between Whittenton Pond Dam and Morey’s Bridge Dam following removal of Whittenton Pond Dam could increase the difference in the calculated water surface elevations, however. Such changes would be related to increased scour and degradation of the channel, thereby increasing its conveyance capacity resulting in lower water surface elevations.
10.2.7. Access With the exception of the Mill fire supply intake, there are no recorded overhead or underground utilities at the dam site. Access to the dam and site storage areas are available, but on private property. These were used recently for the Whittenton Street Bridge replacement in 2007. The most convenient access to the dam site is the left bank and floodplain in the mill complex, which has potentially large storage and staging areas. Access to the lower impoundment can be gained on gravel roads on the north side of the mill complex. Access to the upper impoundment is more difficult, and would need to be from the Whittenton Mills area, the Morey’s Bridge area or from private properties on either side of the impoundment.
10.3. Fish ladder (with dam reconstruction) A Denil or Alaska steeppass ladder could be installed at the Whittenton Dam site to meet diadromous fish passage goals, provided the dam is reconstructed to meet Massachusetts Department of Dam Safety standards. We recommend the installation of a combination steep pass and elver ramp to accommodate both alosid and elver migration. An Alaska steep pass ladder could be added at a small fraction of the total project cost. At a slope of 1v:8h, a steep pass ladder scaling 10 feet of head would need to be 80 feet in length. Based on available cost estimates for northeast fish passage projects (Turek et al. 2007), such a ladder would cost approximately $250,000. We cannot make recommendations for the location of a ladder given that the dam will need to be rebuilt. No plans for such a dam are in place at this time. A Denil type ladder or a pool and weir ladder could also be constructed. These projects would vary in cost between $350,000 and $400,000 due to the amount of concrete work involved in installation. A Denil or weir and pool ladder would require significant concrete and earth work, and would also require easement acquisition or land purchase for construction along the bank. Any fish ladder solution requires the dam to be rebuilt. This option therefore does not restore the natural riverine function of the stream or riparian area, and dam owner liability remains.
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10.4. Fish bypass channel (with dam reconstruction)
A nature-like or natural fish bypass channel that meets the diadromous fish passage goals of the project could be constructed along either the left or right bank, provided construction easements can be obtained. A feasible fish bypass channel at the Whittenton Dam site would be constructed of rounded stone and would have a cascading riffle configuration. Preliminary estimates of the hydraulic conditions at various flows in Appendix G indicate that passage would be possible through a cobble and boulder step:pool channel with a slope of 2.5%. It is assumed that the bypass channel (upstream) inlet will be configured to constrain the amount of water flowing down the channel at high flows in order to promote channel stability. The balance of the flow will be passed over the dam itself.
The right bank offers slightly more working area for construction of a natural bypass channel. Retaining wall construction would increase the available working area along either bank and allow for construction of the channel closer to the bank, thus minimizing intrusion into private property. The space between the building and the left bank would require some infrastructure protection that could be built into the system with construction of the new dam. The natural bypass channel approach would need to consider the purchase of privately held real estate or easements for construction and maintenance of the channel. A right bank channel could be constructed to drop 10 feet over approximately 420-450 feet (2.2 – 2.3 %) and would require acquisition or easement of approximately 0.7-1.0 acres of private property. A left bank channel would be slightly steeper, dropping the head over 330 – 380 feet (2.6 – 3.0 %) and would require acquisition or easement of approximately 0.5-0.7 acres.
Any fish bypass solution requires the dam to be rebuilt in accordance with Massachusetts Department of Dam Safety regulations. This option therefore does not restore the natural riverine function of the stream or riparian area, and dam owner liability remains.
10.5. Rock ramp (with dam reconstruction)
A rock ramp alternative was examined at the Whittenton Dam site, and is considered marginally feasible. Assuming a head drop from a 10-foot high reconstructed dam, a 5% slope ramp would be approximately 200 feet long. A ramp of these dimensions would require approximately 3,400 cubic yards of installed rock. The Whittenton Street crossing is 370 feet downstream of the current dam. This type of ramp may impact flooding at the crossing by decreasing channel capacity upstream of the crossing. A ramp with a slope of 1v:20h would provide restored fish passage, and therefore considered marginally feasible at this site provided bridge hydraulics are not impacted. As with the West Britannia dam, because of the apparently limited conveyance capacity of the downstream bridge, a ramp with a shallower slope passing under the bridge is not considered acceptable.
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A rock ramp fish passage solution does not restore the natural riverine function of the stream or riparian area, and even with dam reconstruction, dam owner liability remains. Because rock ramp passage may influence flooding at the downstream bridge, and requires reconstruction of the dam, this option is not preferred and was not evaluated further.
10.5.1. Dam reconstruction Evaluation of dam reconstruction is beyond the scope of this study and was not evaluated in detail. A dam remains in place with this option. As with the many previous Mill River dams, any new dam will immediately begin to degrade and will eventually need repairs. The logistics and cost of yearly maintenance of the dam and bypass channel will need to be considered. Some repair of the downstream abutment walls should be included in this option, and we have included this repair in the cost estimate.
New dam construction may not be permittable, no matter what the design, and the feasibility of permitting and construction should be examined in detail before this type of major project is attempted.
10.5.2. Anticipated Wetland Impacts Recent drawdown due to the 2005 emergency spillway modifications have changed the Whittenton impoundment. Lowered water levels have exposed the floodplain and historic tree stumps lining the banks. Seed banks have sprouted, and in some areas, red maple and other hardwoods are taking root. Full dam removal would result in the greatest change in wetland type and quality, depending on riparian zone management. Replacing the dam and installing a structural fishway (e.g., fish bypass channel or ladder) would result either in maintenance of existing pond levels or an increase in pond levels.
Dam removal impacts - Removal of the Whittenton Pond Dam would lower the water additionally, but because the channel banks are steep, the wetted width of the channel would be only slightly less than what is currently observed during summer flows. The greatest change in depth would occur within close proximity to the dam. As with the other proposed removal scenarios, the extent of wetland alteration at Whittenton varies with the manner of floodplain restoration. No major excavation would be required for floodplain restoration, and so floodplain wetland condition would depend primarily on the planting approach.
Construction activity near the dam would result in temporary impacts to bordering vegetated wetlands. These disturbed areas would be restored through fine grading, soil amendment, stabilization and planting of native species.
With the dam removal and floodplain restoration options described above, permanent impoundment drawdown would occur. For the smaller channel (Q1.5), areas currently deep water habitat (>3 feet) will be converted from open water submerged and floating emergent wetland vegetation (e.g., water lily,
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spatterdock) to more persistent emergent (e.g., cattail, cutgrass) and shrub (e.g., water willow, buttonbush) species tolerant of prolonged flooding. Riparian forests will eventually establish, or could be managed toward seasonally-flooded wooded swamp wetlands. Design of a deeper channel will result in less frequently inundated floodplain conditions and establishment of a small river floodplain forest community type. Prolonged flood-tolerant species (e.g., black willow, black gum, buttonbush) may become less dominant with more drought-tolerant species (e.g., silver maple, green ash) expanding in area. Less change would likely occur where depressional topography and muck soils are present, such as the backwater wetlands along the left bank at Station 230+00 and the right bank along station 220+00. These sites have active groundwater seepage and would be expected to retain their current groundwater levels.
Active planting of desired native species can help guide the succession toward an ecologically sustainable forest community. This can be accomplished through potted stock, wetland plugs, seeding or a combination of approaches. Any planting plan must consider invasive species management. Newly exposed floodplain areas are very susceptible to invasion by Japanese knotweed, reed canarygrass, garlic mustard and other invasive plants.
Because of the wide floodplain in the Whittenton impoundment, there are good spatial opportunities for the creation of backwater channels, side channels, vernal pools, large wood habitat and oxbow depressions. Such features would add to the habitat quality of the riparian zone and would promote a more diverse flora and fauna.
The 100 and 200 foot wide floodplain excavation options will cause some marginal areas to become dryer riparian forest habitats. Exact impact areas would depend on the final channel bed elevation and the amount and depth of floodplain excavation planned. Table 10-5 shows the predicted change in Land Under Waterbody parameters and bank alteration. It should be noted that these are approximate values based on feasibility level estimates.
Table 10-5. Whittenton Pond impacted resource areas resulting from dam removal Measure Existing Full Removal Mean Annual Low Flow 13.4 acres 3.4 acres (MALFL) Mean Annual Flow (MAFL) 27 acres 5.6 acres Bank alteration 10,800 ft 9,700 ft
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Fish passage channel or fish ladder impacts – Wetland impacts due to the fish passage channel or fish ladder alternatives depend heavily on whether or not the reconstructed dam would be built to the existing pond level or to the former pond level. If built to the existing pond level, the exposed floodplain could be managed for invasives and native species could be encouraged through plantings. The soils would remain saturated and will become dominated by persistent emergent wetland plants. If built to the former pond level, water would inundate to the former pond edge and submergent and emergent wetland plant species would dominate the littoral zone.
10.6. Conceptual Cost Estimates – Whittenton Pond Dam The table below gives ballpark cost estimates for the Whittenton Pond Dam fish passage alternatives, and are meant for the purposes of relative cost comparison between project altternatives. The actual cost of project implementation may vary from these estimates dependant on the final project approach, heavy construction market cost fluctuations and other factors. Note that a construction cost contingency has not been added to the estimated costs summarized below. Application of a typical concept-level construction cost contingency would result in adjustment of the estimated costs by up to 30%. Detailed cost estimates are given in Appendix A.
Table 10-6. Conceptual cost estimates for Whittenton Pond Options Full removal Full removal (special handling of (no special Repair and bypass Repair and fish sediment) handling) channel ladder Construction $ 779,650 $ 416,850 $ 1,452,800 $ 1,369,300 Engineering $ 82,000 $ 82,000 $ 165,000 $ 115,000 Permitting $ 65,000 $ 65,000 $ 90,000 $ 90,000 Total cost $ 926,650 $ 563,850 $ 1,707,800 $ 1,574,300
These costs are general and assume a mixture of active and passive planting approaches. The cost estimates in the table reflect establishment of a Q1.5 capacity channel with minimum target floodplain width of 100 feet in areas slated for active restoration. The “no action” option is not a feasible option given that the emergency spillway repairs were designed to be temporary and are already beginning to degrade. The dam must either be removed or must undergo major repair or rebuild. The liability and long term maintenance costs of dam ownership are hard to quantify, but the cost of repair only continues to increase as the dam degrades.
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11. Morey’s Bridge Dam: Recommendations The Morey’s Bridge dam is being considered for repair and the Bay Street crossing may also be renovated as part of or in conjunction with this effort. Although analysis of fish passage alternatives at Morey’s Bridge is beyond the scope of this study, we recommend that any dam repair or rebuild include consideration of fish passage. Neither the old spillway or the temporary coffer dam currently allows for fish passage. Permitting of a new permanent dam or repaired structure will require hydraulic engineering analysis that includes analysis of spillway capacity and fish passage options. Ideally, improvements to the existing condition would provide for fish passage while also meeting regulatory hydraulic requirements and maintaining perennial minimum instream flows (e.g., by way of a water level management/release program) sufficient to sustain downstream fish and wildlife. If consensus can be achieved, the Taunton community has an excellent opportunity to achieve its lake recreational, ecological and transportation safety goals all at the same time.
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12. Citations
Aarestrup, K., Lucas, M.C., and Hansen, J.A. 2003. Efficiency of a nature-like bypass channel for sea trout (Salmo trutta) ascending a small Danish stream studied by PIT telemetry. Ecology of Freshwater Fish 12: 160-168. Armstrong G. 1994. NRA experience with freshwater fish passes. In: Fish passes in Barrage and Weir Design. Hydraulics Research, Wallingford, Report MIS3. Atlantic States Marine Fisheries Commission. 1999. Amendment 1 to the Interstate Fishery Management Plan for shad and river herring. Fishery Management Report No. 35. Baxter, R.M. 1977. Environmental effects of dams and impoundments. Ann. Rev. of Ecol. and Systematics 8:255-283. Bednarek, A. 2001. Undamming rivers: A review of the ecological impacts of dam removal. Envir. Mgmt. 27(6): 803-814. Belding, David L. 1920. A Report Upon the Alewife Fisheries of Massachusetts. 1-135. Boston, MA. The Commonwealth of Massachusetts Division of Fisheries and Game, Department of Conservation. Bell, M.C. 1973. Fisheries handbook of engineering requirements and biological criteria. US Army Corps of Engineers. Fish Passage Development and Evaluation Program, North Pacific Division, Portland, Oregon. Contract DACW57-68-0086. Bell, M.C. 1991. Fisheries Handbook of Engineering Requirements and Biological Criteria. US Army Corps of Engineers, North Pacific Division, Portland, OR Bellisle, M.J. 2006. Emergency response at the Whittenton Mill Dam. Journal of Dam Safety, Summer 2006. Bozeman, E. L., Jr., Van Den Avyle, M. J. 1989. Species profiles: Life histories and environmental requirements of coastal fishes and invertebrates (South Atlantic)--Alewife and Blueback herring. U.S.Fish and Wildlife Service Biological Report 82(11.111)[TR EL 82-4], 1-12. United States Fish and Wildlife Service. Calabro, R. 2007. Taunton Wild and Scenic River Study; draft report and environmental assessment. National Park Service Report, Boston, MA. Cowardin, L.M, Carter, V., Golet, F.C., and E.T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. FWS/OBS-79/31, US Fish and Wildlife Service, Washington, DC. 103 pp. Cronon, William. 1983. Changes in the Land: Indians, Colonists, and the Ecology of New England. Farrar, Strauss, and Giroux, New York, New York. Dauta, A. , Lapaquellerie, Y. and N. Maillet. 1999. Role of the dams on the River Lot on two types of pollution: Point sources (cadmium) and non-point sources (phosphorous). Hydrobiologia 410:307- 314. Dixon, D.A. (Ed.). 2003. Biology, management and protection of catadromous eels; 1st International Anguillid Symposium. American Fisheries Society, Bethesda. Desrochers, D. and C. Fluery. 1999. Operation of an eel ladder at the Chambly Dam and study of the St. Lawrence River juvenile eel upstream migration. Milieu Inc. pour Hydraulique et Environment Group Production, Hydro Quebec. 166pp.
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Eberstaller, J., Hinterhofer, M., Parasiewicz, P. 1998. The effectiveness of two nature-like bypass channels in an upland Austrian river. Pages 363-383 in: Jungwirth, M., S. Schmutz, and S. Weiss, eds. Fish Migration and Fish Bypasses. Fishing News Books, Oxford. Emery, S.H. 1893. History of Taunton, Massachusetts from its settlement to the present time. D. Mason and Co. Publishers, Syracuse, NY. FAO/DVWK. 2002. Fish passes – design, dimensions, and monitoring. FAO, Rome. 119 pp. Federal Emergency Management Agency. 1987. Flood Insurance Study, City of Taunton, MA, Bristol County. June 18, 1987. Community number 250066. Foster, C.H.W. (ed.) 1998. Stepping back to look forward; A history of the Massachusetts Forest. Harvard University. 339 pp. Graber, B., Yap, C., and S. Johnson. 2001. Small dam removal; a review of potential economic benefits. Trout Unlimited, Arlington, VA. 48pp. Gray, L. J. and J. V. Ward. 1982. Effects of releases of sediment from reservoirs on stream biota. Colorado Water Resources Research Institute Completion Report No. 116, Colorado State University, Fort Collins. Haro, A. 2002. Passage of American shad through natural and experimental high velocity flow environments. Report to American Rivers, Washington DC. 17 pp. Haro, A., M. Odeh, T. Castro-Santos, and J. Noreika. 1999. Effect of Slope and Headpond on Passage of American Shad and Blueback Herring through Simple Denil and Deepened Alaska Steeppass Fishways. North American Journal of Fisheries Management 19(1): 51–58. Hurd, D.H. 1883. History of Bristol County Massachusetts with Biographical Sketches of many of its Pioneers and Prominent Men. Compiled under the supervision of Duane Hamilton Hurd. Illustrated. J.W. Lewis and Co., Philadelphia. Hurley, S. 2007. Draft fisheries sampling report, Mill River, Taunton. Mass. Div. Fish. Wild. Report. Jungwirth, M., Schmutz, S., and Weiss, S. 1998. Fish migration and fish bypasses. Fishing News Books, Oxford. Klein, R.D. 1979. Urbanization and stream quality impairment. Wat. Res. Bull. 15:948-963. Kleinschmidt 2005. South Berwick hydroelectric project (FERC No. 11163-ME); Report on 2004 fish passage evaluation studies. Report to Consolidated Hydro New Hampshire, Inc. Knights, B. and E.M. White. 1998. Enhancing immigration and recruitment of eels; the use of passes and associated trapping systems. Fish. Mgmt. and Ecol. 5:459-471. Legault A. 1993. Eel: Management of obstacles to migration. Publication No. 37, Ministry of Agriculture and Rural Development. 33pp. Lenhart C.F. 2000. The vegetation and hydrology of impoundments after dam removal in southern Wisconsin. Ms. Thesis, Department of Landscape Architecture, University of Wisconsin, Madison. Leopold, L.B., 1994. A View of the River. Harvard University Press, Cambridge, MA. 298 pp. Ligon, F.K., Dietrich, W.E., and W.J. Trush. 1995. Downstream ecological effects of dams: a geomorphic perspective. Bioscience 45(3) 183-192. Loesch, Joseph, G. 1987. Overview of Life History of Anadromous Alewife and Blueback Herring in Freshwater Habitats in Dadswell, Michael J. et al. Common Strategies of Anadromous and Catadromous Fishes. 89-103. Bethesda, Maryland, American Fisheries Society. American Fisheries Society Symposium.
122
MacBroom, J. 2006. Mill River Dams - Preliminary survey report. Massachusetts Riverways, Boston, MA. MacDonald, D.D., C.G. Ingersoll, and T.A. Berger. 2000. Development and Evaluation of Consensus- based Sediment Quality Guidelines for Freshwater Ecosystems. Archives of Environmental Contamination and Toxicology, 39 20-31. Machut, L.S., Limburg, K.E., Schmidt, R.E., and D. Ditman. 2007. Anthropgenic impacts on American eel populations in Hudson River tributaries, New York. Trans. Am. Fish. Soc. 136: 1699-1713. Maclin, E. and M. Sicchio, eds. 1999. Dam removal success stories. American Rivers, Friends of the Earth, and Trout Unlimited. Washington, DC. Mader, H., Unfer, G., Schmutz, S. 1998. The effectiveness of Nature-like bypass channels in a lowland river, the Marchfeldkanal. Pages 384-402 in: Jungwirth, M. , S. Schmutz, and S. Weiss, eds. Fish Migration and Fish Bypasses. Fishing News Books, Oxford. Merchant, C. 1989. Ecological revolutions: nature, gender, and science in New England. University of North Carolina Press, Chapel Hill. Merrill, M.D. 2003. Impoundment sediment and dam removal in Massachusetts; A decision making framework regarding dam removal and sediment management options. Mass. Dept. Fish, Wildlife and Env. Law Enf., Riverways Programs, Boston, MA. O’Keefe, J.F. and D.R. Foster. 1998. The ecological history of Massachusetts forests. In C.H.W. Foster ed. Stepping back to look forward, A history of the Massachusetts forest, Harvard University Press, Harvard. Pardue, G.B. 1983. Habitat suitability index models: Alewife and blueback herring. FWS/OBS-82/10.58, September 1983. US Fish and Wildlife Service, Washington, DC. Pare Engineering. 2005a. Morey’s Bridge Dam, inspection/evaluation report. Pare Engineering Corporation. November 10th, 2005. Pare Engineering. 2005b. Mill River Dam (Whittenton Pond Dam), inspection/evaluation report. Pare Engineering Corporation. November 10th, 2005. Petts, G.E., 1984. Impounded rivers, perspectives for ecological management, John Wiley and Sons, New York, NY, 326p. Poole, G.C. and C. H. Berman. 2001. An ecological perspective on in-stream temperature: natural heat dynamics and mechanisms of human-caused thermal degradation. Envir. Mgmt. 27(6): 787 – 802. Provencher, B., Sarakinos, H. and T. Meyer. 2006. Does small dam removal affect local property values? An empirical analysis. University of Wisconsin-Madison Department of Ag. And Appl. Econ. Staff Paper No. 501. Quinn, R.F. 1994. Fish passage facilities for Alosa. Pp. 119-127 in J.E. Cooper, R.T. Eades, R.J. Klauda, and J.G. Loesch (eds.). Anadromous Alosa symposium, Tidewater Chapter, American Fisheries Society, Bethesda, MD. Reback, K.E. and J.S. DiCarlo, 1972. Completion Report on the Anadromous Fish Project. Publication #6496, Massachusetts Division of Marine Fisheries, Commonwealth of MA, Boston, MA, 113 pp. Reback, K.E., Brady, P.D, McLaughlin, K.D., and C.G. Miliken. 2004. A survey of anadromous fish passage in coastal Massachusetts, Part 1. Southeastern Massachusetts. Massachusetts Division of Marine Fisheries Technical Report TR-15. Schuman, J.R. 1995. Environmental considerations for assessing dam removal alternatives for river restoration. Reg. Riv. Res. Mgmt. 11:240-261.
123
Small, M.F., and W.N. Johnson, Jr. 1986. Wildlife management in riparian habitats. Pages 69-79 in J.A. Bissonette, ed. Is good forestry good wildlife management? Maine Agric. Exp. Sta. Misc. Publ. No. 689. Solomon, D.J. and M.H. Beach. 2004a. Fish pass design for eel and elver (Anguilla anguilla). R&D Technical Report W2-070/TR1. Environment Agency, Bristol UK. 92pp. Solomon, D.J. and M.H. Beach. 2004b. Manual of provision of upstream migration facilities for eel and elver. Science Report SC020075/SR2. Environment Agency, Bristol UK. 63pp. SSURGO. 2006. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Soil Survey Geographic (SSURGO) Database for Taunton, Massachusetts. Available online at http://soildatamart.nrcs.usda.gov accessed July 2006. Stanley, E.H., Luebke, M.A., Doyle, M.W., and D.W. Marshall. 2002. Short-term changes in channel form and macroinvertebrate communities following low head dam removal. J. N. Am. Benthol. Soc. 21(1): 172-187. Tesch, F.W. 1977. The Eel – biology and management of anguillid eels. Chapman and Hall, London. Trudgill, N., Atkinson, R. Mischenko, P., Mullinger, A., Firth, C, and P. O’Brien. 2003. Ridingsare River Report 2003. Environment Agency, 16pp. Turek, J., Cavallaro, L. and C. Linder. 2007. Economic costs of diadromous fish passage in the northeast. Presentation to the American Fisheries Society Annual Meeting. San Francisco, CA. USACE. 1979. Mill River Dam MA00813 Phase I Inspection National Dam Inspection Program, ACOE – Metcalf and Eddy, Waltham, MA, April 1979. Walter, R.C., and D.J. Merrits. 2007. Natural streams and the legacy of water powered mills. Science 319: 299-304. Wandle, S. W. 1983. Estimating Peak Discharges of Small, Rural Streams in Massachusetts. U.S.Department of the Interior, Geological Survey, Water Supply Paper 2214, Washington, D.C.. Ward, J. V. and J.S. Stanford. 1983. The serial discontinuity concept of lotic ecosystems. Ch. 2 in T.D. Fontaine and S.M. Bartell (editors), Dynamics of lotic ecosystems. Ann Arbor Science Publishers. Ward, J.V., and J.A. Stanford. 1979. Ecological factors controlling stream zoobenthos with emphasis on thermal modifications of regulated streams. Pages 35-55 in J.V. Ward and J. A. Stanford (eds) The Ecology of Regulated Streams. Plenum Press, New York. Ward, J.V., and J.A. Stanford. 1989. Riverine ecosystems: the influence of man on catchment dynamics and fish ecology in Dodge, D/P. (Ed), Proceedings of the International Large River Symposium. Can Spec. Publ. Fish Aquat. Sci., 106:56-64. Weston, T. 1906. History of the Town of Middleboro, Massachusetts. Houghton, Mifflin, and Company, Boston. Wigley, T.B., and M.A. Melchiors. 1994. Wildlife habitat and communities in streamside management zones: a literature review for the eastern United States. Pages 100- 121 in Riparian ecosystems in the humid U.S.: functions, values, and management. Natl. Assoc. Conserv. Dist., Washington, D.C. Wolman, M.G., and J.P. Miller. 1960. Magnitude and frequency of forces in geomorphic processes. Journal of Geology 68 (1), 54-74.
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