Tanyard Brook Watershed Study and Design

BETA  has been working with the Town of Bristol for many years on stormwater improvements, particularly in the residential area surrounding Tanyard Brook, where horrific flooding was frequently an issue with heavy rain events.

When the original 4,500-foot culvert was constructed, it consisted of an earthen bottom and dry-laid stone walls covered by concrete planks, which received stormwater runoff from a 500-acre watershed. As the town grew, buildings and concrete surfaces replaced woodlands that once helped minimize runoff. Unfortunately over time, due to a combination of increased storm intensity and impervious surface and the condition of the clogged and collapsed culvert, the surrounding areas became susceptible to flooding.

Our team conducted a hydraulic and hydrologic analysis of the brook and inspected the drainage networks contributing flow. We then incorporated the information into the Town-wide GIS network to construct a hydraulic model. BETA evaluated various alternatives to mitigate the problematic flooding within the low-lying areas adjacent to the brook, as well as the drainage system contributing to the brook.

It was found that the best solution was to replace the existing culvert with a new precast concrete box culvert and install new drain manholes and catch basins in a multi-phased approach. These measures have improved the culvert’s efficiency and increased its capacity.

The first phase incorporated green infrastructure design with an open channel culvert section area constructed through a wetland. The open channel allows the culvert to overflow into the adjacent wetland area during larger rain events or high tide. Once the storm subsides, the stormwater can then flow back into the culvert as the capacity becomes available. The temporary overflow helps mitigate potential surcharges and flooding in the upstream neighborhoods.

This ongoing project involved extensive environmental permitting through the Rhode Island Department of Environmental Management (RIDEM), coordination of temporary construction easements with private property owners, and utility relocations to accommodate the new culvert installation. BETA provided construction administration and resident inspection services for the Town.

BETA also worked with the Town to help secure a $1.8M grant from the Community Development Block Grant (CDBG) Disaster Relief Fund to support the project’s construction.

Following the last significant storm event, the Town Administrator was pleased to report that “In the parts of the Tanyard Brook project that are done, we saw none of the historic flooding we have seen from past storms in the area.”

Phase III, the final phase consisting of approximately 1,500 LF of culvert improvements, commenced construction in March 2022 and was completed in June 2023.