Buttressed dams on rock foundations are subject to the same forces as other dams except that the downward component of the water pressure is greater and uplift is less. In fact, because of the easy lateral escape of pressure under the buttresses, uplift from headwater in the case of rock foundations is usually neglected. However, where the rock is liable to uplift pressures on horizontal seams, the foundation should be drilled for drainage. Full uplift from tailwater should always be included. Buttressed dams on previous foundations may require footing slabs designed to resist uplift loading. Wind pressure, which of hight velocity can reach the downstream side. On high thin buttresses, such pressures may increase the danger of buckling. Because the wind cannot strike the buttress face normally, a pressure of 10 lb per sq ft over a width not exceeding the clear distance between buttresses should be safe. Authoritative data are lacking. For well-braced or double-walled buttress, such pressures are of little importance.