Abstract: Fluctuating pressure and its propagation within cracks under bed slabs in a plungepool downstream of a high dam are two main factors which cause destruction and scour of bed slabs in a plunge pool. The impingement by a free jet on the slabs in a plunge pool downstream of a large dam creates intense pressure flutuations within the cracks under slabs and causes the bed slabs to be unstable.The instantaneous differences of pressure on the upper and the lower surfaces of bed slabs can generate transient uplift ...