Experiences with Bed Sills in Stream Stabilization

Bed sills have proven to be effective in controlling stream channel degradation resulting from meander loop cutoff. Design of bed sills horizontal spacing and vertical drop distance is controlled by: (1) the water surface profile; (2) longitudinal variation of the erosive forces; and (3) resistive capabilities of channel material. Location of maximum scour does not coincide with the location of maximum bed shear stress. The ratio of the maximum to minimum bed shear is equal to the two-thirds power of the ratio of bed slopes. Spacing of sills for subcritical flow is nonuniform if local scour drop is to be constant. For a bed slope ratio k = 2 the maximum erosive ability of the flow in the cutoff is approximately 3-1/2 times the initial value.