Cape Cod Water Resources Restoration Project: Restoring salt marshes at Red River Beach in Harwich

Making room for the new culvert under Deep Hole Road

by Lindsay Cook, Cape Cod Conservation District intern

If you've been to Red River Beach in Harwich lately you might have noticed that construction is underway. So often, the sound of construction equipment means bad news for the environment, but not this time! This construction was planned as a part of the Cape Cod Water Resources Restoration Project (CCWRRP) and, when completed, will help restore and protect the native salt marsh communities behind Red River Beach.

Historically, there were three healthy salt marshes behind Red River Beach: the upper marsh, middle marsh, and lower marsh. As the tide came in, it moved up Red River and pushed tidal waters down a tributary to feed the marshes. However, when Uncle Venies Road and Deep Hole Road were extended to provide access to the beach, tidal waters were restricted.

A culvert was put under each road to allow tidal flow to enter both the middle and upper marsh, but they were too small. At 24 inches in diameter, only limited tidal waters made it to the middle marsh and even less made it to the upper marsh. Salt marshes like these that do not receive a natural amount of tidal water are termed “tidally restricted.”

Map of the site showing the three marsh areas

After years of being tidally restricted, the upper and middle marshes began to show clear signs of stress, including the establishment of invasive species such as common reed (a.k.a. Phragmites australis) and poor water quality.

Tidal flow restricted by undersized culvert

With funding from the CCWRRP, the Town of Harwich will restore the marshes to their former healthy state.

To do this, the Town will replace the undersized culverts with much larger box culverts (4ft x 8ft under Uncle Venies Road and 3ft x 4ft under Deep Hole Road) that will allow adequate tidal flow to come in to both marshes and, in time, restore the natural salt marsh habitat and improve water quality.