A NATIONAL PLAN FOR AMERICAN FORESTRY 427 



Fire danger is extreme on the steep mountain slopes. In summer 

 the chaparral becomes almost tinder dry and fires run rapidly, as 

 much as 12 miles in an hour, and are difficult to control. Summer 

 fires ordinarily consume the chaparral cover entirely, leaving the 

 steep slopes bare and exposed to rapid run-off and abnormal erosion. 

 As previously mentioned, in experiments conducted by the California 

 Forest Experiment Station surface run-off from soils burned clean of 

 vegetation and litter exceeded that from similar soils with a Litter 

 cover in ratios up to 66 to 1 . Erosion was about 400 times as great 

 on the denuded soils. 



The results of these studies partially explain the heavy run-off from 

 recently burned canyons in southern California which valley residents 

 often attribute to "cloudbursts." The Burbank flood of 1928, for 

 example, followed a fire of 1927 which burned over 704 acres of the 

 watershed above this town. With only 1.07 inches of rain in 3 hours, 

 but with a maximum intensity of 1.70 inches per hour for about 10 

 minutes, surface run-off was three times as great as on adjacent 

 unburned canyons. Between 25,000 and 50,000 cubic yards of 

 eroded material was swept off the burned watershed, while no notice- 

 able erosion took place on adjacent unburned canyons. 



Chief Engineer E. C. Eaton of the Los Angeles County Flood Con- 

 trol District is quoted in the bulletin Forestry in the State- Wide 

 Water Plan as follows : 



Intense rains falling on a brush-covered watershed washed down only 400 cubic 

 yards of debris per square mile, while the corresponding amount on adjacent 

 burned-over areas rose to 12,000 cubic yards. 



Even with the controlling influence of 300 check dams per square mile on the 

 burned area, the detrital material still amounted to 7,000 cubic yards. It is 

 further important to note that the brush cover not only proved to be a strong 

 check on the debris movement, but that it also effectually functioned in reducing 

 the surface run-off. With 1.36 inches of rain per hour the burned-over area gave 

 1.01 inches in surface run-off while the area covered with brush produced only 

 0.42 inches. It follows that on the burned-off area only 0.35 inches of water 

 were available for percolation * * * in contrast to 0.94 inches of water on 

 the unburned area. 



Such erosion debris rapidly impairs the permanency of flood-control 

 ind other reservoirs. Eaton, in discussing the Los Angeles flood- 

 control district in the bulletin South Coastal Basin, points out that 

 mountain fault lines limit the number of available reservoir sites and 

 that construction on these sites would be costly. 



While expenditures for fire control are heavy, practically nothing 

 is being spent for restoration of cover. Intensive studies are war- 

 ranted to determine economical means of rapidly reestablishing a 

 vegetative cover and possibilities of replacing some of the highly 

 inflammable species of chaparral with species more resistant to fire. 

 The California Forest Experiment Station has made an important 

 start in studying methods of revegetating the great cuts and fills of 

 mountain highways in southern California. Autumn sowing of 

 winter wheat and of seed of sunflower and native shrubs in contour 

 furrows reinforced by cuttings of willows and elder, although rather 

 costly, has proved very effective. This mixed vegetation, developing 

 rapidly, maintained the treated slopes practically intact, while adja- 

 cent untreated slopes gullied at the rate of 800 cubic yards per acre 

 during one winter and required heavy filling to restore them to safe 

 grade. 



