Whately commission flags design shortfalls in Haydenville Road culvert plans, continues hearing

The Whately Conservation Commission on May 21 continued its public hearing on a Notice of Intent filed by the Town of Whately Highway Department for reconstruction of Haydenville Road after commissioners raised technical concerns about two stream crossings and a proposed replacement wetland.

Chair Scott Jackson reconvened the hearing at 7:10 p.m. and Kimberly Peace of Hoyle & Tanner presented new project information with assistance from Todd Clark (Hoyle & Tanner) and Erica Larner (MassDOT). Commissioners concentrated questioning on the design and aquatic-organism passage measures for two culvert replacements and on the plan to replicate Bordering Vegetated Wetland (BVW) lost to construction. With the applicant's permission, the Commission voted unanimously (5-0) to continue the hearing to Wednesday, June 18, 2025, at 7:10 p.m.

Why it matters: commissioners said the proposed crossings, as documented, may not satisfy hydraulic and ecological standards needed to maintain stream function and aquatic passage and could affect flood conveyance. Chair Scott Jackson's post-meeting notes state the project uses a baseline hydraulic design of a 25-year storm and that several required design details were missing from the submittal, most notably longitudinal profiles (only cross sections were provided) and storm-calculation outputs.

What the Commission flagged - Standards and data gaps: Jackson wrote that "the summary of stream crossing standards compliance is largely incorrect," noting the proposed structures are not open-bottom, are insufficiently embedded (one crossing has zero embedment, the other about one foot, versus a minimum of two feet recommended), and have culvert widths less than bankfull widths with no defined low-flow channel. He also reported the design's calculated "openness" (the recommended 0.82 ft / 0.25 m) is not met for a 60-inch pipe with the proposed configuration (openness ~0.654). - Station 40: Jackson asked where the calculations are that show the crossing will pass 10- and 25-year storms, suggested a corrugated culvert might be considered, and proposed a shallow rock weir to backwater outlets and prevent long-term outlet drops. He noted that construction-when-dry and dewatering methods could be required by condition in an Order of Conditions. - Station 84: Jackson repeated the request for storm-calculation documentation, expressed a preference for corrugated pipe instead of smooth plastic, and said internal baffles are not preferred. He recommended a 72-inch round pipe embedded at least 2 feet as an alternative. - Substrate and low-flow channel: the notes recommend a sub-armor layer of mixed sediment (including fines) with a stable rock surface layer and shaping of the substrate to form a low-flow channel that resists scour during significant storms. - BVW replication: Jackson warned that groundwater depth and soil-class conditions may vary across the proposed replacement area and may not match the existing wetland (Wetland F); he asked who will oversee construction of the replacement wetland and criticized equivocal wording in the BVW Replication Report that uses "should" instead of binding terms such as "will" or "shall." He recommended those points be addressed as conditions in the Order of Conditions.

What happens next The Commission continued the hearing to June 18 at 7:10 p.m. to allow the applicant and their engineers to provide additional hydraulic calculations, longitudinal profiles, clearer substrate and embedment specifications, and firm commitments for wetland replication oversight and required wording in replication documents. The hearing continuation was recorded as a unanimous vote (5-0).

At the meeting the Commission also accepted the minutes from its April 16 meeting (vote 5-0).