Riverbank Stabilization Techniques Workshop Merrimack River, Haverhill, MA

Transcription

1 Riverbank Stabilization Techniques Workshop Merrimack River, Haverhill, MA Dwight R. Dunk, PWS Association of Massachusetts Wetland Scientists September 30, 2011

2 Introduction Project History Design Development Environmental Permitting

3 Project History 1996 bank stabilization design was advanced Used coir fascines and bank planting Construction problems led to abandoning this effort 2001 City partnered with Corps of Engineers Design used rock rip rap slope to 10-year flood elevation Discretionary EIR required because of habitat loss Project abandoned

4 Project History (Continued) May 2006 Mother s Day Storm caused erosion on southern bank and broke sewer interceptor discharging raw sewage in to the Merrimack River Mother s Day Storm caused about 10 feet of erosion on Riverside Avenue northern bank Problem 54 inch sewer in Riverside Avenue Erosion at Coffin Ave observed Problem - sewer, sewage pump station and related infrastructure in Coffin Avenue

5 Project History (Continued) Riverside Ave. washout Coffin Ave. washout

6 Project History (Continued) City of Haverhill applied for and received MEMA Flood Hazard Mitigation Grant to stabilize up to 1,800 linear feet of Merrimack River bank to protect public infrastructure. Approval received in December 2006

7 Eroded Conditions

8 Existing Conditions Analysis Topographic survey Field inspection by design staff Assess causes of erosion

9 Existing Conditions Analysis

10 Design Development Site Constraints: 54-inch Sewer Interceptor Riverside Avenue

11 Design Development (Continued) Reviewed previous bank stabilization plan documents Assessed pros and cons of each design Entirely rip rap slope Entirely soft slope Identified ways to protect and enhance habitat Evaluated agency acceptance of each option Identified preferred option

12 Design Development (Continued) Developed conceptual bank profiles and treatments Pre-Application Meeting - Met and conferred with agency staff (Corps of Engineers, MEPA, MassDEP, NHESP, Haverhill Conservation Commission Agent) Revised drawings and advanced to +60% design stage and pursue required permits and approvals Incorporated permit conditions into contract drawings and specifications

13 ~ 30% Design Drawing

14 Aquatic Plantings Stumps & Logs Erosion Control Matting Temporary Portable Dam Coir Fascines & Live Stakes Stone Toe

15 Planting Schedule

16 Techniques & Function Design elements and purpose 1. Stone toe slope foundation, support, and debris protection 2. Coir fascines slope stabilization, plant media and debris protection 3. Live stakes toe of slope vegetation and bank stabilization 4. Turf reinforcement matting slope stabilization during plant grow-in 5. Coarse woody debris in-river wave breaks and fish habitat 6. Rooted aquatic vegetation fish habitat and sediment trap 7. Slope vegetation slope stabilizations and habitat 8. Drainage scuppers direct runoff to river in stabilized channels rather than over bank flow

17 Designer s Challenges Landscaping projects are as much an art as science (or engineering). Challenge is to prepare plans that convey design intent and still allow for field modifications. 1. Riverbank is a dynamic landform existing conditions can and will change from topographic survey to construction start 2. Public bid projects designer doesn t dictate means and methods, rather prepares performance specifications 3. Balance needed - to protect static, man-made infrastructure and incorporate natural bank characteristics

18 Environmental Permitting Approvals included: Massachusetts GP Category 2 Approval Corps of Engineers MEPA Certificate Section 401 Water Quality Certification MassDEP Chapter 91 License MassDEP Order of Conditions - Haverhill Conservation Commission

19 Environmental Permitting (Continued) Key success factors: Pre-Application meeting with concept plan Incorporate comments from pre-application meeting and advance design to preliminary design stage Pursue MEPA review with preliminary design Incorporate comments on ENF into permitting plans, +60% design stage Communicate with agency staff throughout process

20 Bank Construction SumCo Eco Contracting was selected contractor There were changes during construction Method work with tides and avoid using temporary portable dam Sub-soil type - slope angle and improved drainage Synthetic Turf Reinforcement Matting (TRM) seasonal adjustment

21 Acknowledgements CDM Team: Lisa Gove, PE Project Manager John Olcott, RLA Lead Designer Ron Strand, PE Lead Engineer Joe Coan and Josh Coroa Landscape Designers Andrew Poyant Environmental Scientist Eric Dahlgren Resident Engineer City of Haverhill Paul Jessel Conservation Commission MEMA