A NATIONAL PLAN FOR AMERICAN FORESTRY 361 



Water supplies for domestic use and irrigation are reported to be 

 critically low in the arid portions of the basin. Irrigation is locally 

 important on the Nueces and Concho Rivers and to a minor extent 

 for rice growing near the mouth of the Sabine-Neches drainage. 



SILTING OF CHANNELS 



The streams of the west Gulf Basin are normally clear but during 

 periods of flood carry enormous quantities of soil eroded from the 

 watersheds. Ashe 33 states that the silt burden of the Colorado River 

 is roughly estimated at 1 percent of its volume or an average of 18,000 

 acre-feet a year; and that the Brazos River, above Waco, with a 

 drainage area of 30,000 square miles, carries more than 3,200,000 tons 

 of soil a year. Records of measurements made in the Brazos River 

 at Rosenberg over an 8-year period by the United States Bureau of 

 Agricultural Engineering, cooperating with the Texas Board of Water 

 Engineers, show that the maximum monthly silt load carried during 

 a flood period by this river was the 20,000 acre-feet carried in May 

 1930. 



Direct evidence of the economic significance of these silt loads are 

 cited by Ashe who states that the ill-fated Austin Dam on the Colorado 

 River, which broke after only 10 years of service, had its storage 

 capacity reduced 56 percent as a result of silting. The new reservoir 

 constructed in 1913 had by 1922 lost 84 percent of its capacity through 

 silting. 



Flood waters of the Trinity and Sabine Rivers are also quite muddy. 

 The Trinity River has overflows known locally as "black floods" and 

 "red floods", depending on whether the storm occurred in the black 

 waxy belt or in the regions of predominantly red soils. These heavy 

 soil loads are, however, considered by engineers to be much less than 

 the huge quantities transported by the Colorado and Brazos Rivers. 



EROSION PROBLEMS 



Extremely active erosion of the badlands type is occurring in a 

 region in northwestern Texas known as the "Breaks." This escarp- 

 ment, between the high plains on the west and the red prairies of 

 Edwards Plateau, varies in width from 1 to several miles and is intri- 

 cately dissected by the headwater streams of the Colorado and Brazos 

 Rivers with many steep and unstable slopes the zone of active 

 erosion extending out along the water courses into the red prairies. 



In central Texas, along the border of the Edwards Plateau, standing 

 400 to 1,000 feet above the coastal plain, the streams have cut deep 

 channels and have converted the original plateau edge into a ragged 

 escarpment of mesas, buttes, and rocky canyons. In many places 

 over an extensive area the relatively thin soil has been removed, 

 leaving the parent rock exposed. Moisture conditions are not particu- 

 larly favorable for tree growth, hence it is largely only where cool 

 exposures exist or when a deep soil occurs that the forest is able to 

 maintain itself. The stand is open and the woods frequently occur 

 as merely scattering patches interrupted by grassy openings. In such 

 locations, any marked disturbance to the cover results in erosion, 

 which when once under way progresses for a considerable period before 



33 Ashe, W. W. Financial Limitation in the Employment of Forest Cover in Protecting Reservoirs, 

 U.S.Dept.Agr.Bul. 1430, 1926. 



