Presentation on theme: "Mordecai Lincoln Dam & Hunters Pond, Scituate, MA"— Presentation transcript:
1 Mordecai Lincoln Dam & Hunters Pond, Scituate, MA Bound BrookDam 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 site1969: Dam breached: Current dam constructed2013: Impoundment nearly full of sedimentOne 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 GrainedSediment DepositFine GrainedVegetationDamFLOWPROFILEVegetationSubmergedVegetationDamCoarse GrainedSediment DepositFine GrainedSediment DepositFLOWPROFILE
4 2013 GZA Dam Inspection & Repair Summary Dam Hazard Classification: SIGNIFICANT (class II)Dam Condition: POORGZA’s opinion of probable cost, for all recommended work:$450,000 - $750,000.SpillwayDam & BridgeBridgeCulvertAux. Weir - Culvert
5 Dam Removal Feasibility – Scope of Work 2013 Princeton HydroDam Removal Feasibility – Scope of WorkPreliminary Evaluation of Ex. Information & Site ConditionsDelineation of Regulated ResourcesSurvey and MappingPreliminary Hydrology & Hydraulics (with gage)Sediment Mapping, Characteristics, AnalysisHistoric ReviewPublic MeetingsPreliminary Design Plans for Dam Removal
6 Figure: Sediment Sample Locations ResultsRelatively small mobile sediment quantity and general lack of contamination.Mordecai Lincoln Road begins overtopping in flows in excess of the 100-year eventDam 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 flowsFlow 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 eventsDam removal will not change normal tidal influence on the former impoundment, which currently extends to base of both outletsFigure: Sediment Sample Locations
7 Dam Removal & Restore Channel/Floodplain Proposed Restoration Actions: for Removal:Full demolition and removal of dam’s spillway, concrete apron, & fishwaySlip-lining culvert under Mill building & reconfiguration of the upstream inletRe-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 $263,000Possible Additional Costs:Additional pipe under building ????Replacement of the bridge ????Sediment management $50,000 - $100,000Construction 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 & wildlifeAvenue for historical preservationJives with bike path and other recreational goalsNUMEROUS opportunities for funding assistance compared to other options.Source: BukatySource: BukatySource: 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 EXTRASTHIS is where we talk about the current NFWF/ USFWS funding opportunity.
12 Example of Dam Removal - Rakes Pond Dam Removal, PA 2012 – Post Dam Removal2011 – Rakes Pond
13 Example of Dam Removal - Millport Dam Removal, PA 1998 – Impoundment drawdown1998 – Millport Dam Impoundment1999 – Impoundment 1 growing season later2008 – Impoundment 10 yrs later
14 2013 GZA Dam Inspection & Repair Summary Dam Hazard Classification: SIGNIFICANT (class II)Dam Condition: POORProposed 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 1972199020052004200620082011
17 Infilling of a Man-made Impoundment Dam ConstructionWetland formationyears before present10080604020Source: TNCEven 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 wateremergent vegetationfloating-leaf vegetationfloodplain vegetation
18 Hunter’s Pond Impoundment IMPOUNDEDSEDIMENTDELTA4/17/2008 Pre growing season aerial of pond with impounded sediment delta submerged6/18/2010 summer aerial of impoundment with vegetated impounded sediment delta
19 Community Concerns Expressed at 1ST Neighborhood Discussion Existing WildlifeDam Alternatives & FundingAesthetics (i.e. mudflats)Dam SafetyRoad & Bridge SafetyFloodingSediment Infilling and Dredging
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