Sedimentation and Dredging (DM-26.3), Section 2: Coastal Sedimentation and Erosion

This section explains how sediment moves along a coast and why that matters when planning a harbor or shore protection. It begins with basic considerations: soil classification by grain size, from cobbles and gravel through sand to silt and clay; the principle of continuity, which says material going out of a control volume equals material coming in minus what is stored or plus what is eroded; and transport potential.

The idea of dynamic equilibrium is a useful one. A beach of constant width or a channel of constant cross section is stable only because as much material leaves as arrives. If more arrives than leaves, the beach builds or the channel shoals, and if less arrives, it erodes.

It then covers harbor siting, including littoral processes, gross and net longshore transport, and the seasonal summer and winter beach profiles, in which steep storm waves pull sand offshore into a bar and low swell brings it back. It discusses harbor entrances on open coasts, through natural inlets, and in estuaries. The section closes with shore protection, including shoreline armoring and beach preservation.

In this chapter

• Generalpage 125
• Basic Considerationspage 125
  • Soil classification
  • Continuity
  • Transport potential
• Harbor Sitingpage 128
  • Littoral processes
  • Harbor entrances on open coasts
  • Harbor entrances through natural inlets
  • Harbors in estuaries
• Shore Protectionpage 136
  • General
  • Shoreline armoring
  • Beach preservation