Marshfield-05A

Marshfield, South River

42.136226, -70.694155

Dimensions: 3.83ft diameter, 2.8ft height
Condition: Poor
Comments: There were two identical oval CMP culverts for each tide gate. Both culverts appeared to be in poor condition. The culverts were separating from the concrete headwall and significant deterioration and rust was observed. The northern culvert (downgradient of the inoperable tide gate) was approximately half full (21”) of sediment presumably since the tide gate was rusted shut; presumably not letting sediment from upstream stormwater flows out. Both the upstream and downstream headwalls were also in poor condition and deterioration / spalling was observed in multiple areas. Finally, it appeared that the downstream headwall's weep holes had been filled with concrete.

Comprehensive field assessment conducted in 2024

Upstream Invasive Species: Yes
Downstream Invasive Species: No
Invasive Species Notes: Phragmites limited to upland fringe.
Additional Comments (2024): Lack of low marsh community, channel erosion and plunge pool in front of tide gate indicate tide gate is not draining fast enough. Flappers are rusted shut and not opening but are corroded enough to allow some tidal exchange. Sediment build up in culverts may eventually clog pipes and needs maintenance anyways. Structural repairs and improved operation may promote improved tidal exchange, at least as an initial step.

Legacy data from previous surveys and documentation

Invasive Species: Yes
Restoration Status: Not Applicable
Invasive Comments: Abundant phragmites upstream.
Restoration Comments: No known restoration efforts or studies had been performed. Low lying properties including a dirt road and house were observed directly adjacent to the upstream impoundment.

General Comments: The site is accessible from Ferry Street at the intersection with Neptune Road.
Operation Plan: No
Operation Comments: It appeared that the principal purpose of the tide gates were for flood protection. An eye bolt was observed on the front face of the northern tide gate indicating that the tide gate was potentially periodically opened for maintenance or other reasons.
Gate Comments: There were two wooden flap gates at this location. Marshfield-05A was located to the north and Marshfield-05B was located to the south. The wood on both tide gates was heavily rotted and waterlogged with rusty wooden hinges. The northern tide gate was inoperable and was stuck shut; it appeared that the hinges were corroded shut. Additionally, the bolts securing the tide gate to the headwall were wearing through the wood. The southern tide gate was operable. Gaps were observed in the wooden backing behind each tide gate and it appeared that both tide gates did not create a watertight seal at high tide, thus enabling some level of upstream tidal flushing.

Elevation Comments: Staining was apparent on the upstream (U/S) and downstream (D/S) ends of the headwall (HW) so approximate extent of U/S and D/S tidal influence was able to be assessed in addition to tide gate (TG) invert elevations. The below lists measuredowns taken with a surveyors rod and corresponding top of headwall LiDAR elevations (NAVD88 datum). 1) TG Inv (D/S tide gate): Top of HW El (D/S) = 7.97’; Inv Measuredown = 11.70’; TG Inv = 7.97’ – 11.70 = -3.73’ 2) Upstream Tidal Influence: Top of headwall LiDAR Elevation = 8.16’; Staining Measuredown = 0.66’; U/S Tidal influence = 8.16 – 5.10 = 3.06’. 3) Downstream Tidal Influence: Top of headwall LiDAR elevation = 7.97’; Staining Measuredown = 3.80’; D/S Tidal Influence = 7.97’ – 3.80’ = 4.17’