PROBLEMS FROM LAND OCCUPANCY 179 



sistance of frost action, water lubrication, or other factors. 



An important development of research at Coweeta has 

 been the concept of "subsurface storm flow." In many ob- 

 servation wells, particularly where the water table is within 

 10 feet of the surface, the water levels rise sharply in re- 

 sponse to infiltration from major storms. There is a cor- 

 relative rise in stream discharge, closely resembling the 

 pattern of storm flow in streams of other areas. Water must 

 move rapidly underground to reach the stream so quickly. 

 This movement is partly by turbulent flow, for trickling 

 water can be heard underground after storms at Coweeta. 

 Such rapid movement occurs especially in the porous soil 

 with its litter, decayed root openings, animal tunnels, and 

 the like. It is completely foreign to the capabilities of the 

 mineral matter, for the gneiss and schist weather ultimately 

 to a relatively impermeable clayey mass. Thus the vegeta- 

 tion has developed within the soil zone a permeability 

 that permits detention storage for hours and even days. 

 This detention storage reduces the crest of flood peaks in 

 the streams and enables a greater portion of water to perco- 

 late into the less permeable rock materials below. The 

 underlying less permeable material, rather than the sur- 

 ficial organic material, probably provides the retention 

 storage that sustains the minimum flow of the streams over 

 periods of several months. 



The Coweeta Forest offers the benefits of clear, perennial 

 supplies at a formidable cost in water. More than 40 inches 

 of water is returned annually to the atmosphere from the 

 experimental area, a quantity that exceeds the total precipi- 

 tation in most of the country. One phase of research has 

 been directed toward increasing water yield with minimum 

 sacrifice of the benefits of the permeable forest soil. On one 

 small watershed all vegetation has been cut periodically for 

 nine years (leaving the cuttings in place so as not to disturb 

 the soil) and the annual yield of water to streams has been 

 increased about 65 per cent; the yield during the hottest 

 summer months has been doubled because of the reduction 



