440 A NATIONAL PLAN FOB AMERICAN FORESTRY 



tracks, and to replace washed-out bridges, culverts, and parts of 

 highways and trackage. 



The 1929 floods, largely from the Rip Puerco and Rio Salado, 

 according to the report of the New Mexico State engineer caused a 

 loss of $950,000, excluding damage to roads and railroads. Thou- 

 sands of acres of farm land were buried under an almost worthless 

 layer of clay and sand, and the town of San Marcial was practically 

 wiped out by flood waters and by sand deposits as deep as 7 feet. 



Silt deposits resulting from erosion and floods have become so great 

 in the Rio Grande channel near Albuquerque that work has been 

 started on a drainage and flood-control project which the chief engineer 

 of the conservancy project estimates will cost $10,300,000 when com- 

 plete. In 17 years about 337,939 acre-feet of silt has been deposited 

 in the Elephant Butte Reservoir, the storage basin for the Rio Grande 

 project of New Mexico, Texas, and old Mexico, according to estimates 

 of the United States Reclamation Service, reducing its capacity by 

 nearly 13 percent. 



Since erosion, once started, accelerates and increases cumulatively 

 in seriousness until it is checked, it is reasonable to expect greater 

 flood damage and greater silting in the future unless corrective action 

 is taken. 



Erosion and flood problems exist on both the forest and the range 

 lands of the Rio Grande Basin. Although they are more serious on 

 the range lands which make up the larger part of the basin, this report 

 is concerned only with the situation on forest lands. 



Agriculture in the Rio Grande Basin is mainly dependent upon 

 irrigation. Irrigation developments in the small mountain valleys 

 aggregate several hundred thousand acres. The most extensive irri- 

 gation, accompanied by important urban developments occurs along 

 the Rio Grande and the Pecos Rivers and their main tributaries where 

 reservoirs have been established to impound flood waters and the 

 permanent run-off from the mountain forested areas. Existing 

 erosion conditions threaten the permanency of irrigation agriculture. 



EXISTING WATERSHED CONDITIONS BY FOREST TYPES 



Erosion and rainfall run-off conditions are in general more unsatis- 

 factory in the woodland type than in any other forest type in this 

 basin. The woodland type, the lowest type as to elevation, consists 

 of orchardlike, or occasionally rather dense, stands of jumper, pinon, 

 and oak with an understory of grasses, other herbs, and brush. 

 Originally such vegetation and the litter accompanying it covered up 

 to 50 percent, or occasionally more, of the soil surface. In open 

 stands of this type the litter cover is ordinarily slight and the under- 

 story vegetation is an important supplement to the trees in watershed 

 protection. Studies made by C. K. Cooperrider of the Southwestern 

 Forest and Range Experiment Station in Arizona, the semiarid climate 

 of which is comparable to that of the Rio Grande Basin, have shown that 

 the herbaceous vegetation of the woodland type varies in quantity as 

 between years of high rainfall and years of drought, but that a vigorous 

 vegetative stand covering as much as 35 percent of the soil surface 

 usually prevents excessive run-off and protects the soil against abnor- 

 mal erosion. With annual rainfall averaging only 14 to 20 inches, 

 normally dry springs, extreme droughts sometimes lasting several 



