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VTrans hydraulic study recommends larger structure, bank protection for culvert 375-28 on Winhall Hollow Road
Summary
A December 2025 VTrans hydraulics memo for Culvert 375-28 (Winhall TH-2) recommends replacing the existing 3-foot CMP with a minimum 4-foot CMP or a corrugated metal pipe arch (approx. 60" x 46") buried 1 foot below streambed, and advises coordination with VT ANR River Management for final sizing and permits.
A VTrans Hydraulics Unit memo dated Dec. 4, 2025 (Keith Friedland, Hydraulics Technician) provides hydrologic analysis and replacement recommendations for Culvert 375-28 on Winhall Hollow Road (TH-2). The memo lists a 37-acre drainage area and modeled design flows (Q2=16 cfs, Q10=23 cfs, Q25=28 cfs, Q50=31 cfs, Q100=35 cfs). It reports the existing 3-foot corrugated metal pipe is set at an adverse slope and yields headwater depths of ~3.4 ft (4% AEP) and ~3.6 ft (1% AEP), which do not meet current VTrans standards.
VTrans recommends a replacement such as a 4-foot CMP buried one foot below the streambed to provide about 10 sq ft of waterway area (estimated headwater 2.2 ft at 4% AEP), or a CMP arch with a 60-inch span and 46-inch height to provide ~11.4 sq ft (headwater 1.9 ft at 4% AEP). The memo also recommends stone protection (Type II) at banks, full-height headwalls and flared wingwalls, and cutoff walls or other undermining prevention for closed-bottom structures. The memo notes recommendations were made without a survey and that VT ANR River Management Engineer review is required before implementation.
