Tidal Restrictions "As settlements grew…roads and railways were built all along the coast to facilitate
 overland transport…" (Purinton & Mountain)   The progression of "civilization" resulted in the expansion of local roads and the construction of railroads. Often these throughways traveled over or through coastal salt marshes and, therefore, required that bridges and culverts be built over tidal creeks. Theoretically these "tidal crossings" were not going to restrict the natural flow of the tide, but often the bridges were too narrow and culverts only allowed water to flow through a very small space (Purinton & Mountain).
 


 
 

These two black and white photos are courtesy of the Parker River Clean Water Association (PRCWA). For more information on tidal restrictions check out their Tidal Crossings Handbook.
 
 
 
 
  As a result, tidal flows were restricted and the ecology of numerous salt marshes was significantly altered. Areas of the marsh that had once been frequenlty inundated with salt water became brackish or fresh since seawater was unable to reach many of the restricted areas. This change in marsh hydrology enabled plants less tolerant of salt water to successfully invade the marsh and out-compete plants that had dominated the original salt marsh. Many of these successful invaders included common plants such as the common reed Phragmites australis, purple loosestrife, cattails, and cedar trees.

  Tidal restrictions are common in many of Massachusetts’ salt marshes. Belle Isle marsh is the "largest remaining salt marsh in Boston proper" (Mass Audubon). In 1910 this marsh was believed to be in a relatively natural state; the plant life present was that characteristic of a healthy undisturbed salt marsh and Phragmites was not present. In the 1930’s approximately 25 acres of Belle Isle marsh were enclosed by the construction of a dike and the disposal of dredge material. This dike restricted tidal flow and created prime conditions for Phragmites to invade, take hold, and flourish. Since then, 4 breaches have been created in the dike and this has allowed the reclamation of approximately 10 acres of salt marsh.
 
 

This page was created by: Wendy Dalia
Last update: 5/26/98
Please note this page is under construction.

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