GLEAM

Great Lakes Environmental Assessment and Mapping Project

Shoreline hardening

The shoreline hardening stressor considers shoreline structures built parallel to shore, such as seawalls. These structures are constructed to protect and maintain human investments along the coast, but they can have a number of adverse impacts on nearshore ecosystems. In particular, artificial shoreline protective structures can:

  • Destroy local vegetation, often replacing it with impervious surface and impacting stormwater flow.
  • Cause local increases in water turbidity.
  • Alter nearshore sediment dynamics and accelerate lake bed erosion.
  • Facilitate the establishment of nuisance species like zebra and quagga mussels.

Mapping shoreline hardening as a Great Lakes stressor

The data source for the shoreline hardening stressor layer was the digital medium-resolution vector shoreline data set from the U.S. Army Corps. of Engineers and the Water Issues Division of Environment Canada, Ontario Division. In this dataset, the "shoreline protection" class represents the percentage to which individual shoreline segments are structurally protected. 

 

Amount of shoreline hardening for individual lakes.
 
Lake Percent shoreline with minimal hardening (<15%) Percent shoreline with excessive hardening (>70%)
Superior 89% 3%
Huron 92% 1%
Michigan 58% 9%
Erie 49% >20%
Ontario 57% 10%

 

Degree of shoreline protection (hardening) in the Great Lakes.

shoreline_hardening.jpg

We assumed that the influence of shoreline hardening did not extend beyond 1 km into the lakes. We assigned the value of each shoreline pixel to the adjacent water pixel.

 

Distribution of shoreline hardening as a stressor in the Laurentian Great Lakes (Inset: Western Lake Erie).

Web_06_ShorelineHardening_0.jpg