Climate change in arid and tropical humid regions
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Figure 25.11. Composite sketch, based on field sketches and photographs, showing the different varieties
of valley-floor gullies. Actively eroding scarps are indicated by darker shading. Discontinuous gullies (1)
form in tributary valleys. They will coalesce when the headcut at 6 reaches them. In this valley there are
two knickpoints (2, 3). The incision of the valley floor forms terraces (4, 5). Tributary gullies erode
alluvium that fills tributary valleys (7) and they will eventually integrate the drainage network (Brice,
1966, in Schumm et al. (1984), Figure 4.1).
Figure 25.12. Terrace trenched in a valley fill by incision of the Villafranca gully or Villafranca de Ebro,
Zaragoza province, Spain. Ebro Depression.