178 CONSERVATION OF GROUND WATER 



portunity to study the operations of the hydrologic cycle 

 and particularly the relation of forests to stream flow and 

 ground-water storage. Located on the rugged east slope of 

 the Nantahala Range in southwestern North Carolina, the 

 headwaters of Coweeta Creek (in the Tennessee River drain- 

 age basin) has been used as a hydrologic laboratory by the 

 U.S. Forest Service since 1934. The experimental forest, 

 5,400 acres in extent, is underlain by gneiss and schist, 

 which has been fractured to a considerable but unknown 

 depth. The rocks have been deeply weathered, and the dis- 

 integrated rock is now covered by a clayey residual soil 

 ordinarily 2 to 4 feet deep on ridges and slopes. In valleys 

 and coves, and on benches, colluvium derived from these 

 residual soils is commonly 4 to 8 feet thick and may be as 

 much as 20 feet. 



The average annual precipitation on the experimental 

 forest ranges between 65 and 90 inches a year, depending 

 largely on the elevation, which varies from 2,200 to 5,200 

 feet above sea level. The precipitation, nearly all rain, is 

 uniformly distributed throughout the year, and at prac- 

 tically all times the soil moisture is adequate for the 

 luxuriant vegetation. Except for the 3 to 5 per cent that 

 falls directly in the stream channels, the water from pre- 

 cipitation infiltrates into the ground, and overland flow 

 is practically nil. About 15 per cent of the annual precipi- 

 tation is intercepted before it reaches the ground, 5 per cent 

 is returned to the atmosphere from the soil by evaporation 

 and 35 per cent by transpiration, and 45 per cent leaves the 

 area as stream flow. With practically all the water moving 

 beneath the surface to reach the streams, erosion in this 

 mountainous area is limited to the soil creep down steep 

 slopes, which is inevitable even with the best of vegetative 

 cover — an effect of gravitational pull operating with the as- 



Water Yields, Trans. Am. Geophys. Union, vol. 25, pp. 969- 

 977, 1944. 

 Dunford, E. G. r and P. W. Fletcher, Effect of Removal of 

 Streambank Vegetation upon Water Yields, Trans. Am. 

 Geophys. Union, vol. 28, pp. 105-110, 1947. 



