Removal of the Merrimack Village Dam

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1 University of Massachusetts - Amherst ScholarWorks@UMass Amherst International Conference on Engineering and Ecohydrology for Fish Passage International Conference on Engineering and Ecohydrology for Fish Passage 2012 Jun 6th, 4:25 PM - 6:00 PM Removal of the Merrimack Village Dam Mark Wamser Follow this and additional works at: Wamser, Mark, "Removal of the Merrimack Village Dam" (2012). International Conference on Engineering and Ecohydrology for Fish Passage This Event is brought to you for free and open access by the The Fish Passage Community at UMass Amherst at ScholarWorks@UMass Amherst. It has been accepted for inclusion in International Conference on Engineering and Ecohydrology for Fish Passage by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact scholarworks@library.umass.edu.

2 Removal of Merrimack Village Dam Presented by: Mark Wamser, PE

3 14 miles of free-flowing river between dams Merrimack Village Dam McLane Dam

4 Quick Facts Was lowermost dam on Souhegan River in Merrimack, NH Dam was ~20 feet high, 145 feet long Dam was owned by Pennichuck Water Works (PWW) since never used for water supply NH Dam Bureau identified several deficiencies Anadromous fish currently can migrate to base of dam- fish passage exists on Merrimack River

5 Major Issues Dam was highly visible from bridge; impoundment was isolated from public view, some townspeople had a sentimental and historic connection to the dam Obtaining permission to access dam from private property Sediment management Wetland issues

6 Location and Setting Subject to Backwater Merrimack Village Dam Wetland Sediment Deposition Free flowing

7 Chamberlain Bridge Apron Dam Wetland Private Property Road Runoff Location and Setting

8 Historic Use of Site 1734-ca 1800: Chamberlain Mills- Sawmill & Gristmill 1807-ca 1850: Riddle s Mills- Nail, Cotton & Wool s: Henderson Mill- Carpets & Flannels 1890 s-1900 s: Shoddy Hill, Table Factory & Merrimack Shoe Factory : W.H. McElwain and International Shoe- Shoe Factory World War II-2005: Chemical Factory 2005: Town of Merrimack 1934, Source: NHDES Shoe Factory Building 1934, Source: NHDES Source: Merrimack Historical Society Dam

9 Property Issues Access is limited to river right Land was privately owned Significant road runoff Land was all sand, highly erodable bank. Conducted borings to refusal- no bedrock Land access permissible so long as no erosion of river bank Land located on outside of river bend- higher velocities PWW and land owner reached agreement

10 Sediment Analysis Conducted: Bathymetric mapping Sediment probing to compute volume Sediment sampling for contaminants and grain size analysis Toxicity testing Sediment transport analysis Aquatic habitat evaluation below dam to Merrimack River confluence Water Sediment Refusal

11 Sediment Results Conducted: Sediment primarily sandheavy sediment load Total volume ~ 81,000 CY Sediment transport analysis indicated most sediment would mobilize upon dam removal Aquatic habitat conditions from dam to Merrimack River confluence was poor Due to high sediment volume and having clean sediment proposed allowing natural sediment transport Mark s Marker

12 Wetland An approximate 4-acre wetland was located behind fire department Wetland hydraulically connected to impoundment If not for the dam, no wetland would be present Wetland delineationcharacterized as palustrine open water and scrub-shrub Permitted to dewater wetland and no off-site mitigation- all parties understand wetland only present because of dam Fire Department Building Before After

13 Pre-Post Pictures

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16 Just Before Removal 7/15/2008, Flow= 50 cfs

17 ~ 1 year after removal 7/4/2009, Flow= 1250 cfs

18 ~ 2 years after removal 4/14/2011, Flow= 688 cfs

19 ~2.5 yrs after removal 11/8/2011, Flow= 614 cfs

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21 Final Thoughts Educate the public Removing dams does not dry up rivers Low head dams do not provide flood protection Extend the olive branch Meet with dam removal opponents Try to find common ground Foster a team approach Project Partners and consultant work collectively Keep Project Partners continually updated on work progress