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MISCELLANEOUS PUBLICATION NO. 1065, U.S. DEPARTMENT OF AGRICULTURE 



sheds; and development of methods and systems 

 for control of erosion and sediment problems. 



It has been clearly shown that rates of erosion 

 and resulting sediment delivery have been greatly 

 accelerated by man's use and management of 

 lands, vegetation, and stream channel systems. It 

 is also a well-accepted fact that stabilization of the 

 sediment source by proper erosion control meas- 

 ures is the most direct approach to solving most 

 sediment problems. Where the sediment is derived 

 from sheet and rill erosion on agricultural, forest, 

 or rangelands, certain agronomic and silvicultural 

 practices are known to effectively reduce sediment 

 yields. For instance, changing cultivated fields 

 from row crops to small grain may reduce soil loss 

 to sheet erosion by from 60 to 90 percent, depend- 

 ing on cover conditions, soils, and seasonal distri- 

 bution of rainfall. 



Rotation of crops to include meadow in the crop- 

 ping sequence may reduce average soil loss from 

 fields by 75 percent. Such practices as mulching 

 stripcropping, and contour cultivation have been 

 shown to be highly effective in reducing soil ero- 

 sion on farmlands. 



Graded cropland terraces may reduce erosion on 

 fields by 75 percent, and in combination with crop 

 rotations, mulching, minimum tillage, etc., can re- 

 duce to practically nothing soil loss from culti- 

 vated cropland fields. Converting croplands to 

 good grasslands, pasture, or woodlands can reduce 

 soil erosion by 90 percent or more. 



At Riesel, Tex., sediment yield from a 132-acre 

 watershed with good conservation practices (in- 

 cluding improved rotations, increase in acreage of 

 permanent grass, and graded cropland terraces) is 

 only 12 percent of that from an adjacent 176-acre 

 watershed without conservation practices. On 

 paired watersheds of 400 acres at Rosemont, Nebr., 

 land treatment measures started in 1957 have re- 

 duced sediment yield by about 50 percent. 



The effectiveness of watershed management 

 practices on National forest lands as stabilizers of 

 erosion and for control of floodborne sediment has 

 been clearly demonstrated. Improved grazing 

 practices, fire protection, contour trenches, and 

 seeding of perennial grasses have successfully pre- 

 vented debris-laden flows from the Wasatch Front 

 north of Salt Lake City, Utah. Adoption of re- 

 search-derived criteria for location and construc- 

 tion of logging roads and skid trails has mini- 



mized soil disturbance and sediment delivery from 

 timber harvest operations. Forestry research on 

 the abatement of wild fires has made a major con- 

 tribution in diminishing sediment delivery from 

 forested lands. 



Where the primary source of sediment is erosion 

 from gullies or stream channels, various types of 

 engineering works can effectively reduce the 

 amount of sediment delivery to downstream points. 

 On the 145-square-mile Buffalo Creek Watershed, 

 for instance, streambank erosion control measures 

 reduced sediment delivery by 40 percent. During 

 the same period, sediment delivery by other 

 streams tributary to the City Harbor of Buffalo, 

 N.Y., but without stream channel erosion control 

 practices, increased by about 10 percent. 



Mathematical equations of sediment-stream flow 

 relations, criteria for designing vegetation-lined 

 waterways and for streambank erosion control 

 measures, ratios between sediment delivery and 

 watershed erosion, and information about the 

 properties and distribution of sediment in reser- 

 voirs are also products of this research in the U.S. 

 Department of Agriculture. 



About 10 years ago, data from all of the coop- 

 erative soil erosion studies were brought together 

 at the Indiana Agricultural Experiment Station 

 where further cooperative research using a digital 

 computer reduced the data to a state permitting 

 meaningful evaluation of the key determinants in 

 soil loss, or sediment delivery. A "Soil Loss Equa- 

 tion" evolved from this comprehensive analysis of 

 the accrued data. 



The findings showed that erosion can be related 

 to the energy available for clislodgment and trans- 

 port of soil particles. The energy sources are (1) 

 falling raindrops and (2) the elevation differences 

 of sloping topography, which impart energy to 

 runoff water. Effective control measures include 

 using crop or residue covers to intercept the fall- 

 ing raindrops and promote water intake, planting 

 sod crops and crop row barriers to reduce runoff 

 velocity, and modifying the topography to reduce 

 slope steepness and length. 



The soil loss prediction handbook (136) , based 

 on the results from 35 locations in the United 

 States, has been used widely by the Soil Conserva- 

 tion Service and educational institutions in their 

 programs. 



