Specifications include, but are not limited to: In sizing a new structure, we attempt to select structures that meet the hydraulic standards, fit the natural channel width, the roadway grade and other site conditions. At this time we recommended any of the following as a possible replacement: 1. A concrete box with a 6ft wide by 4ft high inside opening, with 3in high bed sills (baffles) in teh bottom. This will result in a 6ft wide by 3ft 9in high waterway opening above streambed, providing 22.5 sq. ft. of waterway area. Sills should be spaced no more than 8'-0" apart throughout the structure with one sill placed at the inled and one at the outlet. Sills should be cast horizontally across the width of the box. The sills add roughness to the bottom of the structure and will help reduce velocities through the box. This structure will result in a headwater depth at Q25 = 3.7ft (HW/D = 1.0), and at Q100 = 4.9ft (HW/D = 1/3). 2. Any similar structure with a minimum clear span of 6ft and at least 22.5 sq. ft. of waterway area, that fits the site conditions, could be considered. Any closed bottom structure should have corrugations or bed sills as described above. 3. The town may choose to examine the cost/benefit of replacing the culvert vs. removing the culvert and closing the road. The implications to be examined include capital and ongoing maintenance costs associated with a new crossing structure and inconvenience to local land and homeowners who need to negotiate alternative routes. There are consultant engineering firms who may be contracted to develop an analysis that considers public input and formulates recommendations based on a variety of conditions tailored to the needs of the community. A portion of any savings to FEMA using this approach may be made available for use elsewhere by the town. Town officials should contact FEMA for a determination.
