Erosion; see, for example, Saynor et al. (2004) Geografiska A 86, 2 on scour holes and gullying. The depth of a scour hole in a river bed is strongly correlated with discharge, with scouring on the rising limb of the hydrograph, and filling as the rate of transport through the pool declines (Borg et al. (2007) Geomorph. 89, 1–2). See also Leopold in L. Leopold et al. (1964). Scour and fill is the erosion and subsequent filling of a channel; see Xu (2004) Geomorph. 57, 3–4, and Fuller and Hutchinson (2007) NZ Geogr. 63, 3 on measuring scour and fill. For river bed scours, see Eilertsen and Hansen (2008) Geomorph. 93, 3–4.