Money Brook crosses VT-100 Bridge 108 one mile south of the VT-100A junction and enters the Black River just east of this point. Bridge 108 is situated at the base of a mountain with an approximate channel grade of 18%. Approximately 1/3 mile upstream from VT-100 there is a massive ongoing slope failure on the northern streambank that has existed for many years. The ongoing slope failure has resulted in an Alluvial fan of sediment deposits. Alluvial fans are natural phenomena, the geologic process of breaking down mountains over time, and they are extremely difficult areas to manage. The likelihood of impactful sediment deposition similar in magnitude to those shown in historical pictures of floods from the 1970s happening again is high. During heavy rainfall the Money Brook channel cuts the toe from the sediment source / slope thus creating an ongoing slope failure condition depositing large amounts of sediment/boulders downstream.

Scope of Resiliency Improvement:

• Armor the VT-100 fill slopes within the limits of the alluvial fan to minimize damage of VT-100 if overtopped by a flood.
• The extent of channel work will be determined during design in coordination with the permitting regulators, and the VTrans Hydraulics unit.
• Relief structures (culverts) will be included to prevent water from being trapped on the upstream side of VT-100. The risk of trapped water may result in a roadway breach. The size and locations of relief structures will be determined during design. Drainage structures may be sized such that equipment may operate within them for cleanup of sediment, or they could be sized with multiple smaller structures to minimize asset costs while satisfying the needs of this section of VT-100.     
• Pending further hydraulic analyis, to convey additional sediment transport, Bridge 108 may be supplemented with a multi-cell box culvert adjacent to the existing structure instead of several flood relief structures south of bridge 108.

Project Document Webpage:

https://outside.vermont.gov/agency/VTRANS/external/Projects/Structures/Forms/AllItems.aspx?id=%2Fagency%2FVTRANS%2Fexternal%2FProjects%2FStructures%2F23B746