Keyline design

Valleys start or head where a portion of a slope near the top of a watershed or divide becomes steeper than the general slope on either side. Thus the first part of a valley formation is steeper than the ridges or shoulders on each side that form the valley. At some point down the valley--the Keypoint--the valley slope flattens to such an extent that it becomes flatter than the ridges or shoulders on each side in the same vertical interval.

Keyline development first controls the usual water run off into valleys from the higher land, by tremendously increasing the absorption capacity of this area and diffusing the excess water, thus greatly retarding and delaying its time of concentration.

The time needed for a drop of water to reach the outlet of a catchment from the most remote location within the catchment.