Watersheds and How to Care for Them 



Plants and the plant debris on the 

 ground surface protect the soil from 

 the direct impact of dashing raindrops. 

 Big drops are broken into little drops 

 that have less force. Tree trunks, the 

 stems of shrubs and herbs, and dead 

 twigs, leaves, and other trash on the 

 ground keep surface water spread out 

 and moving at low velocities, thus re- 

 ducing the capacity to erode the soil 

 and retarding movement toward chan- 

 nels. This favors infiltration of precipi- 

 tation into the soil and rock mantle, 

 and the subsequent yields of water as 

 seepage, rather than overland runoff. 



Roots of plants also help in the 

 process. They provide channels for the 

 percolation of water. They bind the 

 surface soil against the scouring effect 

 of storm runoff and anchor the soil 

 mantle on steep slopes to the bedrock. 



Vegetation lowers the air tempera- 

 ture near the ground surface and also 

 reduces wind velocity. These influences 

 are especially important in areas where 

 runoff is derived mainly from snow, 

 for they favor the accumulation of 

 snow in deep drifts and slow snow- 

 melting rates. It is not uncommon for 

 snow in the shelter of conifer trees to 

 remain a week or two longer than in 

 the open. This delay in snow melting 

 in turn means a slow and prolonged 

 yield of water. 



Also to be remembered is that plants, 

 while they produce good storage con- 

 ditions, use a great deal of water. An 

 ordinary elm tree of medium size will 

 get rid of 15,000 pounds of water on a 

 clear, dry, hot day. Losses of water by 

 evaporation and transpiration on well- 

 drained forested slopes are generally 

 not less than 15 inches a year and may 

 be twice that much on sites where rain- 

 fall is plentiful during the growing 

 season. Still greater volumes are lost 

 by plants along streams where roots 

 have continuous access to water. 



The ability of plants to withdraw 

 water from the soil may be bad or 

 good, depending upon the local water 

 problem. Where water is in high de- 

 mand and the supply is limited, high 

 losses from transpiration obviously ac- 



centuate problems of water shortage. 

 But where flood control is important, 

 the removal of water from the soil by 

 transpiration maintains a greater op- 

 portunity for storing storm water. 



AN EXAMINATION of the land, acre 

 by acre, will show whether watershed 

 conditions are satisfactory or unsatis- 

 factory. Water that is not getting into 

 the soil will accumulate and flow over 

 the surface. Such storm runoff will 

 leave its first traces in washed spots on 

 the soil surface, in little rills, and small 

 piles of leaves and debris. Later the 

 signs are more conspicuous severe 

 sheet erosion and large gullies. 



The management plan for the en- 

 tire watershed is based on the require- 

 ments of its independent parts. Some 

 soils can erode so easily that even the 

 slightest change in the natural vegeta- 

 tion results in disastrous erosion. On 

 them, it is good land management to 

 prevent any possible disturbance of 

 natural conditions ; if they already have 

 been disturbed, it is good land man- 

 agement to try to restore as much plant 

 cover as conditions will support and 

 as soon as possible. 



Failure to recognize watershed de- 

 terioration in its early stages and to 

 start remedial action toward the con- 

 trol of abnormal runoff and acceler- 

 ated erosion is almost certain to lead 

 to still greater deterioration and a 

 more difficult and costly restoration 

 job. This has happened in northern 

 Mississippi, where 60-foot gullies are 

 almost impossible to fill or stop. 



Examination of channels and stream 

 deposits is another approach toward 

 determining watershed condition. Un- 

 usual deposition, channel cutting, and 

 high watermarks may constitute direct 

 evidence of abnormal watershed con- 

 ditions. An accurate interpretation of 

 these downstream indicators is some- 

 times difficult because of complex 

 geologic and climatic factors. Even 

 under these circumstances, however, 

 the signs of flood runoff and siltation 

 are the best guide toward locating the 

 problem areas on the watershed. By 



