The next section deals with groundwater sapping as a natural process and as a subject for simulation.  It is divided into two sections.  The first concerns groundwater sapping in cohesionless sediments, such as occurs on beach faces during falling tides, and on some river banks due to flow from the floodplain, often during receding floods.  The experiments were conducted in a narrow flume, shown in the next illustration.
	The relevant reference is:
	Howard, A.D. and McLane, C.F., 1988, Erosion of cohesionless sediment by groundwater seepage,  Water Resources Research, v. 24, p. 1659-1674.