Soil Conservation for Watershed Protection and Flood Control

Abstract

Soil and water constitute the physical basis of agriculture and fore- stry. The top soil is the most vital part of the soil. Lying to an average depth usually 20-25 cm. over the underlying ground or rock, this up- per layer of the soil is the principal feeding zone of the plants which provide food for human or livestock, consumption, fibre for clothing and timber for shelter. Under many cir- cumstances, unfortunately, it is one of the most unstable of all major natural resources. Water or wind in moving across the ground surface picks up soil particles and carries them away. Under natural condi- tions dense vegetation retards this movement of soil to a pace so slow, generally, that new soils formed from the parent material beneath are more or less equal to the amount of soil carried by water. This is a sort of natural erosion which is actu- ally a beneficial process. It contri- butes material for the development of alluvial plains and aeolion plains. But where the land surface is bared of protective vegetation, the soil is exposed directly to the abrasive action of the elements. Thus strip- ed of cover that normally holds soil against the moving force of wind and water, soil material is frequently transported a thousand times faster than under natural conditions bring- ing in its wake the utter destruction of watershed and the floods of the severest type.