Spur Dikes Design for prevent the erosion of riverbanks
Spur dikes (or groynes) are structures constructed projecting from a bank to protect the bank from erosion. These are widely used for the purpose of river training and serve one or more of the following functions :
- Training the river along a desired course by attracting, deflecting (or repelling) and holding the flow in a channel. An attracting spur creates deep scour near the bank; a deflecting spur shifts deep scour away from the bank, and a holding spur maintains deep scour at the head of the spur.
- Creating a zone of slack flow with the object of silting up the spur.
- Protecting the river bank by keeping the flow away from it.
These structures may either be impermeable or permeable so as to allow some flow parallel to the bank but at a low enough velocity to prevent erosion and / or encourage sediment deposition. Care needs to be exercised in the use of spurs to ensure that they do not simply transfer erosion from one location to another, or initiate unforeseen changes in the general channel morphology.
The requirements of a spur are:
- Optimum alignment and angle consistent with the objective.
- Availability of a high river bank to anchor (or tie) the spur back, by extending it into the bank a sufficient distance to avoid it being outflanked.
- Sufficient freeboard provision (in case of non-submerged spurs).
- Adequate protection to nose/head against anticipated scour.
- Shank protection with stone pitching and stone apron for the length which is vulnerable to flow attack