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Mordecai Lincoln Dam & Hunters Pond, Scituate, MA

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Presentation on theme: "Mordecai Lincoln Dam & Hunters Pond, Scituate, MA"— Presentation transcript:

1 Mordecai Lincoln Dam & Hunters Pond, Scituate, MA
Bound Brook Dam is owned by the Ladd family, according to ODS. The Town owns the road. Goals of the project are to eliminate the liability of owning a dam, allow for fish passage and other natural riverine functions, and to dovetail with historical preservation and recreation interests. The Town’s partners include: CZM, NOAA, Mass Bays Program, and DER

2 Hunter’s Pond Infilling
1690: First dam built on site 1969: Dam breached : Current dam constructed 2013: Impoundment nearly full of sediment One thing that many folks in town have likely noticed is that the Hunters Pond impoundmetn has changed a lot over time. Mainyl, that’s due to the accumulation of sediment that the Brook wouodl normally flush out to the bay. This is a natual process that dams disrupt. When a dam slows the flow of a river, the larger particles drop out first, and the finer particles get carried closer to the dam. Over time, the sediment vegetates. Coarse Grained Sediment Deposit Fine Grained Vegetation Dam FLOW PROFILE Vegetation Submerged Vegetation Dam Coarse Grained Sediment Deposit Fine Grained Sediment Deposit FLOW PROFILE

3 Hunter’s Pond Impoundment

4 2013 GZA Dam Inspection & Repair Summary
Dam Hazard Classification: SIGNIFICANT (class II) Dam Condition: POOR GZA’s opinion of probable cost, for all recommended work: $450,000 - $750,000. Spillway Dam & Bridge Bridge Culvert Aux. Weir - Culvert

5 Dam Removal Feasibility – Scope of Work
2013 Princeton Hydro Dam Removal Feasibility – Scope of Work Preliminary Evaluation of Ex. Information & Site Conditions Delineation of Regulated Resources Survey and Mapping Preliminary Hydrology & Hydraulics (with gage) Sediment Mapping, Characteristics, Analysis Historic Review Public Meetings Preliminary Design Plans for Dam Removal

6 Figure: Sediment Sample Locations
Results Relatively small mobile sediment quantity and general lack of contamination. Mordecai Lincoln Road begins overtopping in flows in excess of the 100-year event Dam removal has little effect on upstream water levels during the 100- and 500-year storm events, with the maximum effects (decrease in water level) during the lowest flows Flow must be maintained through both outlets so as not to increase water levels during the 100-ye regulatory event. It is recommended that flow not be increased through the auxiliary outlet during storm events Dam removal will not change normal tidal influence on the former impoundment, which currently extends to base of both outlets Figure: Sediment Sample Locations

7 Dam Removal & Restore Channel/Floodplain
Proposed Restoration Actions: for Removal: Full demolition and removal of dam’s spillway, concrete apron, & fishway Slip-lining culvert under Mill building & reconfiguration of the upstream inlet Re-creation of approximately 700 linear feet of bifurcated channel to follow the legacy flow paths ; Stabilization & conversion of impoundment to ~2 ac of naturalized vegetated floodplain. PH’s opinion of probable cost = $263,000

8 Cost Comparison Summary
Dam Repair Construction Estimate $450,000 - $750,000 (with permitting & engineering, without construction oversight) Preliminary Dam Repair Construction Estimate $263,000 Possible Additional Costs: Additional pipe under building ???? Replacement of the bridge ???? Sediment management $50,000 - $100,000 Construction Oversight by Engineer $25,000 - $35,000

9 Additional Benefits of Dam Removal
Eliminates a large part of O&M (dam, road, culvert, etc.) Exceptional benefit to river herring and other fish & wildlife Avenue for historical preservation Jives with bike path and other recreational goals NUMEROUS opportunities for funding assistance compared to other options. Source: Bukaty Source: Bukaty Source: Southerland

10 Next Steps Town approval to support project (2013)
Apply for NFWF grant opportunity (January 2014) Determine project role of Moredecai Lincoln barn (2014) Engage consultant for engineering design & permitting ( ) Engage next level review of historical resources (2014) Dam Removal bid solicitation (2015) Dam Removal (2015) Ecological Monitoring (2015…)

11 EXTRAS THIS is where we talk about the current NFWF/ USFWS funding opportunity.

12 Example of Dam Removal - Rakes Pond Dam Removal, PA
2012 – Post Dam Removal 2011 – Rakes Pond

13 Example of Dam Removal - Millport Dam Removal, PA
1998 – Impoundment drawdown 1998 – Millport Dam Impoundment 1999 – Impoundment 1 growing season later 2008 – Impoundment 10 yrs later

14 2013 GZA Dam Inspection & Repair Summary
Dam Hazard Classification: SIGNIFICANT (class II) Dam Condition: POOR Proposed Remedial Actions for Repair: Clear trees and woody vegetation from embankment and backfill with compacted sand and gravel. Repair and re-grade upstream slope and install riprap slope protection. Install a graded filter blanket to control seepage at downstream toe of dam. Repair and re-grade downstream slope using dumped riprap or rockfill. Rehabilitate outlet works (repair or replace conduit and slide gate). Repair concrete defects at spillway. GZA’s opinion of probable cost, for all recommended and potential work, was estimated to be $450,000 - $750,000.

15 Mordecai Lincoln Dam & Hunters Pond
Bound Brook

16 Example of a Mill Pond Infilling - Heminway Pond Transition From 1970 to 2011 Watertown, CT
1972 1990 2005 2004 2006 2008 2011

17 Infilling of a Man-made Impoundment
Dam Construction Wetland formation years before present 100 80 60 40 20 Source: TNC Even after the dam had been build, usually an open-water condition existed. Only after many years did the pond begin to fill with sediments and wetland begin to form First as floating leaved vegetation, then as emergent wetlands as area of open water decreases, then as floodplain habitat as sediments accumulate above the normal water level. Usually, wetlands associated with dams are relatively young, are still in a transitional phase of development. open water emergent vegetation floating-leaf vegetation floodplain vegetation

18 Hunter’s Pond Impoundment
IMPOUNDED SEDIMENT DELTA 4/17/2008 Pre growing season aerial of pond with impounded sediment delta submerged 6/18/2010 summer aerial of impoundment with vegetated impounded sediment delta

19 Community Concerns Expressed at 1ST Neighborhood Discussion
Existing Wildlife Dam Alternatives & Funding Aesthetics (i.e. mudflats) Dam Safety Road & Bridge Safety Flooding Sediment Infilling and Dredging

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