【正文】 lope length and slope length for lower eroding portion of slope Slope length for upper eroding portion of slope Insert figures from AH703 to illustrate field slope lengths Basic Principles ? Sediment load accumulates along the slope because of detachment ? Transport capacity function of distance along slope (runoff), steepness at slope location, covermanagement, storm severity (10 yr EI) ? Deposition occurs where sediment load bees greater than transport capacity Detachment Proportional to Slope Length Factor ? Slope length effect l= (x/)n x = location on slope n = slope length exponent ? Slope length exponent Related to rill:interrill ratio Slope steepness, rill:interrill erodibility, ground cover, soil biomass, soil consolidation ? Slope length factor varies on a daily basis Slope Length Effects ? Slope length effect is greater on slopes where rill erosion is greater relative to interrill erosion ? Examples: Steep slopes Soils susceptible to rill erosion Soils recently tilled Low soil biomass Detachment Proportional to Slope Steepness Factor 00 . 511 . 522 . 533 . 544 . 50 5 10 15 20 25 30 35S l o p e S t e e p n e s s ( % )Factor ValueNot affected by any other variable Effect of Slope Shape on Erosion 1 0 0 5 00501001502001 2 3 4 5 6 7 8 9 10S e g m e n t A l o n g S l o p eSoil Loss (t/ac)C o n ca v eC o n v e xU n i f o r m100 ft long, 1% to 19% steepness range Land Use ? Covermanagement ? Supporting practices CoverManagement ? Vegetative munity ? Crop ? Crop rotation ? Conservation tillage ? Application of surface and buried materials (mulch, manure) ? Increasing random roughness Supporting Practices ? Contouring ? Strip systems Buffer, filter, strip cropping, barriers ? Terrace/Diversion ? Impoundments ? Tile drainage CoverManagement Subfactors ? Canopy ? Ground cover ? Surface Roughness ? Ridges ? Below ground biomass Live roots, dead roots, buried residue ? Soil consolidation ? Antecedent soil moisture (NWRR only) CoverManagement Effects Raindrops intercepted by canopy cover Raindrops not intercepted by canopy cover Intercepted rainfall falling from canopy cover Canopy cover Ground cover Ridges Buried residue Dead roots Live roots Antecedent soil moisture (NWRR) Soil consolidation Random roughness Canopy ? Cover above soil surface that intercepts rainfall but does not touch soil surface to affect surface flow ? Main variables Percent of surface covered by canopy Effective fall height Effective Fall Height Effective fall height Canopy height Height to bottom of canopy Gradient of canopy density Material concentrated near top Ground Cover ? Cover directly in contact with soil surface that intercepts raindrops, slows runoff, increases infiltration ? Examples Live plant material Plant residue and litter Applied mulch Stones Ground Cover Effect 00 . 20 . 40 . 60 . 811 . 20 20 40 60 80 100 120G r o u n d C o v e r ( % )Ground Cover Effectb = 0 . 0 2 5b = 0 . 0 5Eff = exp(b x %grd cov) b greater when rill erosion more dominant than interrill erosion Ground Cover ? Live cover depends on type of vegetation, production level, and stage ? Residue Amount added by senescence, flattening, and falling by deposition at base Deposition ? Rainfall amount ? Temperature Interaction of Ground Cover and Canopy ? Canopy over ground cover is considered to be noneffective ? As fall height approaches zero, canopy behaves like ground cover Random Roughness ? Creates depressions ? Usually creates erosion resistant clods ? Increases infiltration ? Increases hydraulic roughness that slows runoff, reducing detachment and transport capacity Random Roughness ? Standard deviation of microelevations ? Roughness at tillage function of: Implement Roughness at time of disturbance and tillage intensity Soil texture Soil biomass ? Decays with: Rainfall amount Interrill erosion 0 12 0 Range (in) Random Roughness (in) Ridges ? Ridges up and downhill increase soil loss by increasing interrill erosion ? Function of: Effect increases with ridge height Effect decreases with slope steepness above 6% ? Ridge height decays with rainfall amount and interrill erosion ? Effect shifts from increasing soil loss when up and downhill to decreasing soil loss when on the contour Dead Biomass Pools ? Killing vegetation converts live standing to dead standing and live roots to dead roots ? Operations Flatten standing residue to flat residue (ground cover) Bury flat residue Resurface buried residue Redistribute dead roots in soil Material spread on surface Material incorporated (lower one half of depth of disturbance) ? Deposition at base causes standing residue to fall Deposition of Dead Biomass ? Function of: Rainfall Temperature Type of material Standing residue decays much more slowly Below ground biomass ? Live roots Distributed nonuniformly within soil ? Dead roots ? Buried residue Half of material deposed on surface is added to upper 2 inches Incorporated biomass Effect of Below Ground Biomass ? Roots mechanically hold the soil ? Add anic matter that improves soil quality, reduces erodibility, increases infiltration ? Affect rill erosion more than interrill erosion ? Effect of roots considered over upper 10 inches ? Effect of buried residue over upper 3 inches, but depth decreases to 1 inch as soil consolidates (. notill) Soil Consolidation ? Ove