If runoff becomes to great on a slope with a particular steepness and cover-management condition, contouring will fail at a particular location on the slope (critical slope length) and lose its effectiveness for the portion of slope beyond critical slope length.
	Erosion rates on this lower portion of the slope can be much greater than erosion rates on the remaining portion of the slope.
	Thus, a conservation objective is not allow critical slope length to be exceeded, at least not for substantial amount of time during the rotation.
	Critical slope can be increased by going to a cover-management system that leaves increased roughness and ground cover.
	If critical slope length can not be increased sufficiently with cover-management, it sometimes can be increased by buffer strips that spread the runoff.
	In difficult cases, terraces or a diversion are installed.
	A soil disturbance (tillage operation) that forms ridges is required to restore lost contouring effectiveness lost by contour failure.