Deviations from equilibrium conditions will trigger a dynamic response from the alluvial river system to restore the balance between inflowing and outflowing water and sediment discharges. Section 7.1 of this chapter deals with the dynamics of stream response to changes in water and sediment discharges. Sections 7.2 and 7.3 describe the dynamic response of alluvial systems to degradation and aggradation, respectively, particularly the effects on hydraulic geometry and channel morphology. Section 7.4 focuses on river confluences and branches. Finally, Section 7.5 provides guidelines on river databases, data sources, and field surveys.

River dynamics

Conceptually, the fluvial system of the watershed sketched in Fig. 7.1 can be divided into three main zones: (1) an erosional zone of runoff production and sediment source; (2) a transport zone of water and sediment conveyance; and (3) a depositional zone of runoff delivery and sedimentation. The second zone is characterized by near-equilibrium conditions between the inflow and the outflow of water and sediment. The bed elevation in this equilibrium zone is fairly constant and the hydraulic geometry is described in Chap. 6 and this section. The upper zone is characterized by net erosion of bed material and channel degradation. The dynamic response of degrading fluvial systems is discussed in Section 7.2. The lower zone is characterized by net sedimentation and channel aggradation. The dynamic response of aggrading fluvial systems is discussed in Section 7.3.