Table 2. --Mean weight diameters in miViimetevs for each of the pvetreatment soils and 



for splashed soil material by splash distances 



Splashed soil 



Percent 

 s lope 



'■ Soil • 

 type 



Pretreatment 

 soil 



Splash 



distance 



in centimeters 









'■ 11 • 



34 : 



57 : 



80 





High-elevation 

 granitic 



1. 254 



0.992 



0.614 



0.444 



0.404 





Low- elevation 

 granitic 



1. 164 



1 . 178 



. 694 



.495 



.410 





Wasatrh r 1 



' ■ o d k> 1 ^ X O- r 



. 317 



. 386 



.311 



.316 



.272 





High- elevation 

 granitic 



1 . 497 



.808 



.628 



.476 



. 384 





Low - e 1 evat i on 

 granitic 



on o 



Q C 

 . OD / 



C "7 Q 



.506 



.421 





Wasatch clay 



. DOO 



/I A 1 



. J 1 J 



.292 



.288 





High -elevation 

 granitic 



1 . 456 



n n Q 



^ O Q 

 . DOO 



.662 



.455 



32 



Low-elevation 

 granitic 



.951 



.875 



.719 



.510 



.460 





Wasatch clay 



.372 



.355 



.324 



.248 



.261 



ERODIBILITY RAMKING BY SOIL TYPE 



In order to rank these soils according to their relative erodibility, the regres- 

 sion models illustrated in figures 2 and 5 were solved by using values of the indepen- 

 dent variables chosen so as to either maximize or minimize erosion. Each of the soil 

 variables was set at either the maximum or minimum value observed within each soil 

 type (table 3). Soil erosion by overland flow varies directly with rainfall intensity 

 and slope and inversely with the percent of soil particles and aggregates greater than 

 2 mm.; consequently, the calculated erosion was maximized by using the greatest rainfall 

 intensity, the steepest slope, and the lowest percent of soil particles and aggregates 

 greater than 2 mm. Conversely, soil erosion by overland flow is minimized by using the 

 lowest rainfall intensity, the most shallow slope, and the greatest percent of particles 

 and aggregates greater than 2 mm. Soil erosion due to raindrop splash varies directly 

 with both the soil bulk density and the percent of particles and aggregates between 

 61 and 2,000 microns. Therefore, raindrop-splash erosion was maximized by using the 

 largest values of rainfall intensity, slope, bulk density, and percent soil material 

 between 61 and 2,000 microns, and minimized by using the smallest values of these 

 variables. The results of these calculations are presented in table 4. 



The high-elevation granitic soil appears to be the least erodible of these three 

 soil types. The low-elevation granitic and Wasatch clay types are about equally 

 erodible on a total weight basis; the Wasatch clay is more susceptible to soil loss by 

 overland flow than the low-elevation granitic, but less susceptible to erosion by 

 raindrop splash. 



11 



