River-stabilization structures are designed to protect the riverbanks and prevent lateral migration of alluvial channels through bank erosion. River-stabilization methods can be classified according to two different approaches: (1) strengthening the banks and (2) reducing hydrodynamic forces. This chapter first examines the bank stability of alluvial streams in Section 8.1. Bank-protection methods through strengthening the banks with riprap are discussed in Section 8.2, and other bank-strengthening methods are covered in Section 8.3. Flow-control structures offer an alternative approach by reducing the hydrodynamic forces applied against the riverbanks. The flow-control structures covered in Section 8.4 aim at gaining control over the flow depth and the direction and magnitude of flow velocity near the river banks. Some engineering considerations are discussed in Section 8.5.

Riverbank stability

Bank stability is examined in this section. First, the processes are reviewed in Subsection 8.1.1, followed by conceptual solutions for slope reduction in Subsection 8.1.2 and subsurface drainage in Subsection 8.1.3.

Bank-erosion processes

Processes of bank erosion are directly linked to the lateral migration of alluvial channels. Bank erosion is the result of flowing water that applies active forces met by the passive forces of the bank material to resist motion. As discussed in Chap. 6, the hydrodynamic forces in river bends induce secondary flow where the free-surface streamlines are deflected toward the outer bank and the near-bed streamlines are deflected toward the inner bank.