Figure - Dike


Dikes, sometimes referred to as wing dams or spur dikes, are structures placed in a river to redirect the river's own energy to provide a variety of effects. The structures are usually constructed out of stone, but other materials have been used for construction including but not limited to timber piles, concrete, and sand filled geotextile bags and tubes. On larger rivers, dikes are used to manage sediment response distribution within the channel to deepen the channel and provide adequate depth for navigation. On smaller rivers and tributaries, they have been used primarily to divert flow and stabilize eroding banks.

Dikes are usually built perpendicular to the river flow and vary considerably in height and length. On large rivers, they are built approximately at a height midway up the channel and lengths can vary depending upon a variety of factors.

  • Figure - Dikes 1
  • Figure - Dikes 2
  • Figure - Dikes 3

Notched Dikes

Rock dikes, running perpendicular to the shore, have long been used to guide the river and maintain the navigation channel. River engineers found that simply by adding notches, the dikes continue to create navigation dimensions as well as support diverse habitats. The river is allowed to move in and out between the notches creating all four of the primary river habitats. Sediment buildup forms small sandbars between each of the dikes. A variety of notch locations, sizes and widths were studied to create the optimum design. The overall result, however, is the creation of diverse environments by making a small but significant design modification. (Drawing illustrates environments)

  • Figure - Notched Dikes 1
  • Figure - Notched Dikes 2
  • Figure - Dike 3

Stepped-Up Dikes

Stepped-Up dike fields of various elevations were developed to provide an additional element of diversity. They counteract sediment deposition, thereby preventing the conversion of aquatic environment into terrestrial. In the stepped-up dike configuration, each dike in sequence rises two feet higher than the previous one. This approach utilizes the riverís energy to change the sediment deposits as the water level rises and falls. (Drawing illustrates environments)

  • Figure - Dike 4
  • Figure - Dike 5
  • Figure - Notched Dikes 3