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Page I 1 Proactive By Design. Our Company Commitment COLUMBUS AVENUE SEAWALL PROJECT REVIEW - NEIGHBORHOOD SUBCOMMITTEE MEETING JULY 28, 2020 GZA GeoEnvironmental, Inc. ---PAGE BREAK--- Page I 2 Meeting Agenda ➢Introduction ➢Prior Columbus Ave Seawall Assessment Work ➢GZA’s Current Project Scope ➢Project Summary/Progress To Date ➢Anticipated Schedule ➢Design Questions ➢Discussion ---PAGE BREAK--- Page I 3 Columbus Avenue Seawall ---PAGE BREAK--- Page I 4 Columbus Avenue Seawall ➢No Historic Information Found (pre-1938) ➢Seawall is approximately 474 ft long ➢Stone/Masonry Construction ➢Elevation Varies from 10.1 to 8.5 in North American Vertical Datum 1988 (NAVD88) Good Condition, per Massachusetts Coastal Infrastructure Inventory and Assessment Project, by the Massachusetts Department of Conservation and Recreation, North Shore 2009 ---PAGE BREAK--- Page I 5 Columbus Avenue Seawall ➢Observed to be in overall FAIR to POOR Condition • Loose/missing stones, • Deteriorated and missing mortar/cracks ---PAGE BREAK--- Page I 6 Columbus Avenue Seawall ---PAGE BREAK--- Page I 7 Columbus Avenue Seawall Alt No. Repair Recommendation Wall Height Cost Estimate Alt No. 1 In-kind Repairs No Change $90k to $120k Alt No. 2A Reconstruct with Existing and Supplemental Stone +0.9-2.5 ft $550k to $700k Alt No. 2B Reconstruct with Large Cut Granite Stone +0.9-2.5 ft $750k to $900k Alt No. 3 Reconstruct with Reinforced Concrete Wall +0.9-2.5 ft $1.4m to $1.7m Alt No. 4 Reconstruct with Hybrid-Concrete and Stone Veneer Wall +0.9-2.5 ft $1.5m to $1.8m ---PAGE BREAK--- Page I 8 Columbus Avenue Seawall ➢Alt No. 2B – Reconstruct with Large Cut Granite Stone Pros • Medium upfront cost • Increased flood protection • Aesthetics- stone masonry Cons • Routine maintenance/upkeep • Material availability ---PAGE BREAK--- Page I 9 Columbus Avenue Seawall ➢EOEEA Dams and Seawall Grant submitted July 2019 ➢March 2018 Storm Damage Seawall Assessment Report Letter – Oct 2019 ➢Award Notice January 2020 ➢GZA’s Scope of Services/Task Order March 2020 ---PAGE BREAK--- Page I 10 Columbus Avenue Seawall GZA’s Scope of Services ➢Task 1 – Project Review ➢Task 2 – Survey/Ecological Work ➢Task 3 – Design Development ➢Task 4 – Permitting ➢Task 5 – Final Design/Bid Documents ➢Task 6 – Bid Phase Services ---PAGE BREAK--- Page I 11 Columbus Avenue Seawall GZA’s Scope of Services ➢Task 1 – Project Review ➢Task 2 – Survey/Ecological Work ➢Task 3 – Design Development ➢Task 4 – Permitting ➢Task 5 – Final Design/Bid Documents ➢Task 6 – Bid Phase Services ---PAGE BREAK--- Page I 12 Columbus Avenue Seawall Living Shoreline – Marsh Enhancement Area ---PAGE BREAK--- Page I 13 Columbus Avenue Seawall ---PAGE BREAK--- Page I 14 Columbus Avenue Seawall • Partly desiccated with “pockmark” voids throughout • Erosion and undermining along seaward edge ---PAGE BREAK--- Page I 15 Columbus Avenue Seawall Living Shoreline Design: • New seaward sill • Sand nourishment fill to raise grades and fill voids • New and supplemental salt marsh plantings (Spartina patens and Spartina alterniflora) ---PAGE BREAK--- Page I 16 Columbus Avenue Seawall ➢Toe Sill – Coir Roll Pros • Natural and biodegradable material • Promotes vegetation growth – plant directly into coir roll • Absorbs wave energy with minimal reflection • Easy installation Cons • Temporary protection (2-5 years) • Minimal protection against waves and ice impacts • Additional maintenance (resetting, anchoring, or replacement) ---PAGE BREAK--- Page I 17 Columbus Avenue Seawall ➢Toe Sill – Stone Sill Pros • Long-term protection • Increased protection against waves and ice impacts • Easy to moderate installation Cons • Less natural- hard armoring • Possible wave reflection and scour ---PAGE BREAK--- Page I 18 Columbus Avenue Seawall GZA’s Scope of Services ➢Task 1 – Project Review ➢Task 2 – Survey/Ecological Work ➢Task 3 – Design Development ➢Task 4 – Permitting ➢Task 5 – Final Design/Bid Documents ➢Task 6 – Bid Phase Services ---PAGE BREAK--- Page I 19 Columbus Avenue Seawall ---PAGE BREAK--- Page I 20 Columbus Avenue Seawall ---PAGE BREAK--- Page I 21 Columbus Avenue Seawall January 2018 ---PAGE BREAK--- Page I 22 Columbus Avenue Seawall 1. Wave heights in the Cove/at the Columbus Ave seawall 2. Wave effect/wave run-up at NE end of seawall 3. Wave overtopping at seawall 4. Effects of Breakwater COASTAL MODELING – INTENT ---PAGE BREAK--- Page I 23 Columbus Avenue Seawall COASTAL MODELING – PARAMETERS Time Water Level2 (ft, NAVD88) Storm Type 1/4/2018 9.7 Nor’Easter 2/7/1978 9.6 Nor’Easter 3/2/2018 9.1 Nor’Easter 1/2/1987 8.7 Nor’Easter 10/30/1991 8.6 Nor’Easter 1/25/1979 8.5 Nor’Easter 12/12/1992 8.5 Nor’Easter 12/29/1959 8.5 Nor’Easter 2/19/1972 8.4 Nor’Easter 1/3/2014 8.3 Nor’Easter Analysis Wind Speed (mph) Statistics 10-year 50-year 100-year 500-year ASCE 7-16 61 75 80 GZA Statistical Analysis 56 68 74 87 Return Period FEMA USACE3 Stillwater Elevation1 (ft, NAVD88) Base Flood Elevation2 (ft, NAVD88) Stillwater Elevation (ft, NAVD88) Wave Height (ft) #10709 #10710 #69 #10709 #10710 #69 1-year 6.1 6.1 6.1 8.7 7.0 9.7 2-year 6.7 6.7 6.7 12.8 9.8 13.8 5-year 7.3 7.4 7.3 14.4 11.3 15.3 10-year 8.4 7.7 7.8 7.7 15.0 11.8 15.8 50-year 9.4 8.7 8.7 8.6 15.6 12.6 16.4 100-year 10.0 11 9.1 9.1 9.0 15.8 12.8 16.5 500-year 11.4 9.9 9.9 9.8 15.9 13.2 16.7 Scenario 1 – Due East/Scenario 2 - NE ---PAGE BREAK--- Page I 24 Columbus Avenue Seawall COASTAL MODELING – WAVE HEIGHTS SCENERIO 1 ---PAGE BREAK--- Page I 25 Columbus Avenue Seawall SWAN Model Output4 of Significant Wave Height (ft) Stations Scenario 1 Scenario 2 Output Station 1 1.6 1.2 Output Station 2 2.3 1.8 Output Station 3 2.7 2.3 Output Station 4 2.9 3.2 Output Station 5 3.1 3.2 Output Station 6 4.4 4.2 Output Station 7 6.0 5.8 Output Station 8 7.4 7.1 Output Station 9 10.0 9.6 Output Station 10 1.4 1.2 Output Station 11 2.2 1.7 Output Station 12 2.6 2.2 Output Station 13 2.0 1.8 COASTAL MODELING – WAVE HEIGHTS SCENERIO 1 ---PAGE BREAK--- Page I 26 Columbus Avenue Seawall COASTAL MODELING – WAVE HEIGHT/WAVE RUNUP ---PAGE BREAK--- Page I 27 Columbus Avenue Seawall COASTAL MODELING – WAVE HEIGHT/WAVE RUNUP Output Station1 Wall Height (ft, NAVD88) Bed Condition Stillwater Condition Wave Condition Wave Runup2 Overtopping Flowrate2 Sand Removal Bed Level1 (ft, NAVD88) Stillwater Elevation (ft, NAVD88) Water Depth (ft) Freeboard (ft) Significant Wave Height1 (ft) Peak Wave Period1 Wave Crest Elevation3 (ft, NAVD88) Wave Breaking? Wave Runup on Seawall (ft) Wave Runup Height (ft, NAVD88) per linear foot (gallon/min) Northeast Corner 11 No Sand Removal 7 10 3 1 1.4 11.1 11.0 No 2.7 12.7 41 After Sand Removal 4 10 6 1 1.1 11.1 10.8 No 2.1 12.1 17 12 No Sand Removal 7 10 3 2 1.4 11.1 11.0 No 2.7 12.7 6 After Sand Removal 4 10 6 2 1.1 11.1 10.8 No 2.1 12.1 2 Station 11 11 N/A 2.7 10 7.3 1 2.2 11.1 11.5 No 4.2 14.2 157 12 N/A 2.7 10 7.3 2 2.2 11.1 11.5 No 4.2 14.2 48 Station 12 11 N/A 3.6 10 6.4 1 2.6 11.1 11.8 No 5.0 15.0 243 12 N/A 3.6 10 6.4 2 2.6 11.1 11.8 No 5.0 15.0 89 Station 13 11 N/A 8.3 10 1.7 1 2.0 11.1 11.4 Yes 3.9 13.9 121 12 N/A 8.3 10 1.7 2 2.0 11.1 11.4 Yes 3.9 13.9 33 ---PAGE BREAK--- Page I 28 Columbus Avenue Seawall COASTAL MODELING – BREAKWATER EFFECTS ---PAGE BREAK--- Page I 29 Columbus Avenue Seawall COASTAL MODELING – BREAKWATER EFFECTS Figure 8. Revetment height: El. 8’ – Scenario 1 ---PAGE BREAK--- Page I 30 Columbus Avenue Seawall COASTAL MODELING – BREAKWATER EFFECTS Output Stations Revetment Height based on LiDAR Revetment Height El. 0’ Revetment Height El. 5’ Revetment Height El. 8’ Revetment Height El. 10’ Scenario 1 Scenario 2 Scenario 1 Scenario 2 Scenario 1 Scenario 2 Scenario 1 Scenario 2 Scenario 1 Scenario 2 #1 1.6 1.2 1.7 1.3 1.7 1.1 1.5 0.7 1.4 0.6 #2 2.3 1.8 2.3 1.9 2.3 1.6 2.1 0.9 2.0 0.8 #3 2.7 2.3 2.7 2.4 2.5 2.0 2.1 1.1 2.1 1.1 #4 2.9 3.2 2.9 3.1 2.5 2.8 2.3 1.7 2.3 1.9 #5 3.1 3.2 3.1 3.2 2.6 2.6 2.7 1.9 2.8 2.1 #6 4.4 4.2 4.2 4.0 3.3 3.2 2.2 2.0 2.6 2.4 #7 6.0 5.8 6.2 6.0 6.7 6.4 3.0 3.0 N/A N/A #8 7.4 7.1 7.4 7.1 7.4 7.1 7.4 7.1 7.4 7.1 #9 10.0 9.6 10.0 9.6 10.0 9.6 10.0 9.6 10.0 9.6 #10 1.4 1.2 1.5 1.3 1.4 1.2 1.0 0.7 0.8 0.6 #11 2.2 1.7 2.3 1.8 2.2 1.6 1.8 0.8 1.7 0.7 #12 2.6 2.2 2.6 2.3 2.4 1.9 1.9 0.9 1.8 0.8 #13 2.0 1.8 1.9 1.8 1.6 1.5 1.3 1.2 1.4 1.3 ---PAGE BREAK--- Page I 31 Columbus Avenue Seawall COASTAL MODELING – SUMMARY 1. Wave heights at seawall generally range from 2’ to 2.4’ except at the NE corner at 1.5’. 2. Additional wave runup contributing to wall overtopping at NE corner with sand build-up, however ≤ 0.5’. 3. Overtopping of seawall at El. 11 and 12 due to wave runup. 4. Existing breakwater only minimally attenuates incoming waves. ---PAGE BREAK--- Page I 32 Columbus Avenue Seawall ---PAGE BREAK--- Page I 33 Columbus Avenue Seawall ---PAGE BREAK--- Page I 34 In Closing… ➢ ANTICIPATED SCHEDULE ➢ REVIEW WITH THE CITY ➢ PERMITTING/CONSTRUCTION IMPLICATIONS ➢ IDENTIFY FUNDING OPPORTUNITIES ---PAGE BREAK--- Page I 35 Questions/Discussion