7. Gully Control Structures

Gully control structures, i.e., the check dams, have been used since the twelfth century for soil and water conservation and more frequently over the past 150 years. These are employed in severely eroded gullies that cannot be managed with biological or vegetative erosion control measures. The temporary or permanent structures are constructed across the gully to reduce the channel gradient and stabilise the gully to prevent further erosion. This chapter presents the design principles used in designing temporary gully control structures, i.e., different check dams, preferred in areas where labour is inexpensive and the appropriate construction materials are readily available. The design includes the number of structures, spacing between structures and a spillway to handle the peak runoff due to a 10-year return period storm. Subsequently, the chapter introduces three established permanent gully control structures, i.e., the drop spillway, drop-inlet spillway and chute spillway, preferred in medium to large gullies with significantly high flows that the temporary structures cannot handle. The hydrologic, hydraulic and structural design principles of the permanent structures are introduced. The chapter also includes the prerequisites, viz., the specific energy considerations, critical flow characteristics and hydraulic jump, for designing permanent structures.