Loading...
Chesterfield Rd MassDEP replacement xing worksheet march 2016.pdfMassDEP Wetlands Program: 310 CMR 10.24(10) and 10.53(8) Replacement Stream Crossing Evaluation Worksheet CHESTERFIELD ROAD CULVERT REPLACEMENT Page 1 of 3 Summary: Open-bottom concrete box or metal arch-type culverts that meet the Stream Crossing Standards are not feasible for this location due to the low road profile which does not allow enough depth of pavement and/or cover material to meet roadway load ratings and protect the pavement from heave. Although the twin 30” culvert replacement provides a feasible alternative to in-kind replacement, there are only marginal benefits including reducing scour pools and turbulence compared to the in-kind replacement. The twin culverts would not provide improved terrestrial or aquatic connectivity over the in-kind replacement. In addition to the marginal environmental improvements, the twin 30” culverts have potential issues with maintaining the pavement and drainage within the base course given the existing vertical alignment of the roadway. The City recommends the in-kind replacement given the marginal benefit to cost considerations. The following table details the environmental and engineering considerations for each alternative: Evaluation Criteria Alternative 1: Replace in-kind ____30” RCP___(dimensions) Alternative 2: Meet General Performance Standards for Bank and LUWW1 _Box or Arch Open-Bottom Culvert -- Span 7 feet__(dimensions) Alternative 3: Meet minimum applicable Stream Crossing Standards2 ___Twin 30” RCPs___(dimensions) Meets SCS (Except for Openness Ratio) Minimum Practicable, improved hydraulics to minimize turbulence and scour pools 1) potential for downstream flooding Currently no downstream flooding reported from DPW Highway Department or residents Would increase conveyance and peak flows downstream Would increase conveyance and peak flows downstream 2) upstream and downstream habitat Culvert is not perched, but terrestrial connectivity not available through the culvert Would provide connectivity Similar to existing conditions 3) potential for erosion and head- cutting Some scour in upstream and downstream pools No evidence of channel degradation or aggradation Would lessen stream velocities through culvert and decrease erosion/scour pools Would lessen the existing flow contraction and would result in less turbulence, although scour pools may persist MassDEP Wetlands Program: 310 CMR 10.24(10) and 10.53(8) Replacement Stream Crossing Evaluation Worksheet CHESTERFIELD ROAD CULVERT REPLACEMENT Page 2 of 3 Evaluation Criteria Alternative 1: Replace in-kind ____30” RCP___(dimensions) Alternative 2: Meet General Performance Standards for Bank and LUWW1 _Box or Arch Open-Bottom Culvert -- Span 7 feet__(dimensions) Alternative 3: Meet minimum applicable Stream Crossing Standards2 ___Twin 30” RCPs___(dimensions) 4) stream stability Upstream segment is stable, forested wetland, downstream is invasive knotweed, both no evidence of down-cutting or aggradation Increased peak flows downstream may increase erosion Similar to existing conditions, improved hydraulics may increase sediment movement upstream 5) habitat fragmentation caused by the crossing None. Downstream area does not have forested habitat. Upstream area is forested. Same as Alt. 1 Same as Alt. 1 6) amount of stream mileage made accessible Intermittent stream to wetland area upstream, unlikely fish habitat, terrestrial habitat is not accessible, although culvert is not perched and is embedded below the typical water level Would improve terrestrial connectivity Same as Alt. 1 7) storm flow conveyance Undersized culvert Improved conveyance for up to the 10-year storm Improved hydraulics would reduce turbulence and scour pools 8) engineering design constraints None Top of roadway at El. 312.99 ft to 313.05 ft Inverts at 309.54 ft to 308.66 ft Box culvert deck height is 10”, with a need for 8” minimum cover Metal arch culvert requires a minimum of 1.7 feet below the 4” pavement layer Larger than 30” pipes would require relocating the existing 5 foot deep water line deeper Pavement condition across the shallow 2 pipes would prove more difficult to maintain than a single 30” pipe 9) hydrologic constraints Does not convey the 10-year flow Conveys the 10-year flow Conveys the 10-year flow MassDEP Wetlands Program: 310 CMR 10.24(10) and 10.53(8) Replacement Stream Crossing Evaluation Worksheet CHESTERFIELD ROAD CULVERT REPLACEMENT Page 3 of 3 Evaluation Criteria Alternative 1: Replace in-kind ____30” RCP___(dimensions) Alternative 2: Meet General Performance Standards for Bank and LUWW1 _Box or Arch Open-Bottom Culvert -- Span 7 feet__(dimensions) Alternative 3: Meet minimum applicable Stream Crossing Standards2 ___Twin 30” RCPs___(dimensions) 10) impacts to wetlands that would occur Minor temporary impacts Less than 250 sf of BVW alteration and less than 500 sf of total wetland alteration Less than 25 sf of BVW alteration and less than 100 sf of total wetland alteration; some Bank alteration/movement 11) potential to affect property and infrastructure Remains undersized; however DPW Highway Dept. has not seen the roadway overtop Proper cover depth necessary to protect pavement Vertical alignment and drainage of roadway is more difficult to design and maintain than with single culvert given low profile 12) cost of replacement3 $21,000 $39,000 $28,000 1 Bank Standards at 310 CMR 10.54 and LUWW Standards at 310 CMR 10.56 (LUWW = Land Under Water Bodies & Waterways) 2 Per the Massachusetts River & Stream Crossing Standards (March 1, 2011, Revised March 8, 2012), Page 18, Item #2 - If it is not possible to meet all of the applicable standards, replacement crossings should be designed to avoid or mitigate the following problems: (1) Inlet drops; (2) Outlet drops; (3) Flow contraction that produces significant turbulence; (4) Tailwater armoring; (5) Tailwater scour pools; (6) Physical barriers to fish and wildlife passage. 3 Costs are installed costs including erosion control, demolition, water control/dewatering, excavation and pipe removal, pipe bedding, structural backfill, culvert, precast headwalls, mobilization and demobilization, rounded to the nearest $1,000.