CONTENTS 



Page 



INTRODUCTION 1 



STUDY AREA AND METHODS 3 



RESULTS . . 5 



Total Erosion 7 



Time Trends in Surface Erosion 8 



DISCUSSION AND CONCLUSIONS . 11 



REFERENCES 13 



ABSTRACT 



Effects of logging road construction on sediment production rates were 

 studied on small, ephemeral drainages in the Idaho Batholith, a large area of 

 granitic rock characterized by steep slopes and highly erodible soils. For 

 the 6-year study period, about 30 percent of the total accelerated sediment 

 production from roads was caused by surface erosion; the remainder resulted 

 from mass erosion. Surface erosion on roads decreased rapidly with time 

 after extremely high initial rates. A mass failure of a road fill slope oc- 

 curred about 4 years after construction, when surface erosion had fallen to a 

 low rate. The sediment production rate attributed to erosion within the area 

 disturbed by road construction averaged 770 times greater (220 because of 

 surface c rosion and 550 because of mass erosion) than that for similar, un- 

 disturbed lands in the vicinity. 



Results suggest three guides to use in the control of surface erosion on 

 roads and subsequent downslope sediment movement in the Idaho Batholith: 

 (a) Apply erosion control measures immediately after road construction for 

 maximum effectiveness; (b) ensure that treatments protect the soil surface 

 until vegetation becomes established; (c) take advantage of downslope barriers 

 (logs, branches, etc. ) to effectively delay and reduce the downslope movement 

 of sediment. 



