1	REVISED UNIVERSAL SOIL LOSS EQUATION-Version 2 Predicting Soil Erosion By Water: A Guide to Conservation Planning
2	UNIT 1 Course Objectives and Topics
3	OBJECTIVES Understand erosion processes Learn RUSLE2 and its software Learn field office applications of RUSLE2
4	UNIT 2 Overview of Erosion
5	OVERVIEW OF EROSION Definition of erosion Erosion processes Types of erosion Why erosion is a concern Uses of erosion prediction tools
6	EROSION “Erosion is a process of detachment and transport of soil particles by erosive agents.” Ellison, 1944 Erosive Agents Raindrop impact Overland flow surface runoff from rainfall
7	DETACHMENT Removal of soil particles from soil surface Adds to the sediment load Sediment load: Rate sediment is transported downslope by runoff
8	DETACHMENT
9	DEPOSITION Reduces the sediment load Adds to the soil mass Local deposition Surface roughness depressions Row middles Remote deposition Concave slope Strips Terraces
10	DEPOSITION
11	TYPES OF EROSION Interrill and rill (sheet-rill) Ephemeral gully Permanent, incised (classical) gully Stream channel Mass movement Geologic
12	DEFINITIONS
13	DEFINITIONS
14	DEFINITIONS
15	DEFINITIONS
16	DEFINITIONS
17	LOCAL DEPOSITION
18	Credit for Deposition Local Deposition Full credit Remote Deposition Partial credit Amount Location Spacing of terraces
19	SEDIMENT CHARACTERISTICS Particle Classes Primary clay, primary silt, small aggregate, large aggregate, primary sand At Detachment Distribution of classes function of texture Diameter of small and large aggregates function of texture After Deposition Sediment enriched in fines
20	EROSION IS A CONCERN Degrades soil resource Reduces soil productivity Reduces soil organic matter Removes plant nutrients Causes downstream sedimentation Produces sediment which is a pollutant Produces sediment that carries pollutants
21	WHERE EROSION CAN BE A PROBLEM Low residue crops Conventional tillage Rows up/down steep slopes Low maintenance pasture Disturbed land with little cover
22	EROSION PREDICTION AS A TOOL Guide management decisions Evaluate impact of erosion Inventory soil erosion Conservation planning
23	EROSION PREDICTION AS A TOOL Concept: Estimate erosion rate Evaluate by ranking Evaluate against quality criteria Tool: RUSLE2 Quality Criteria: Soil loss tolerance
24	PLANNING VARIABLES Soil loss on eroding portions of hillslope Detachment (sediment production) on hillslope Conservation planning soil loss for hillslope Ratio of segment soil loss to soil tolerance adjusted for segment position Sediment yield from hillslope/terraces
25	UNIT 3 Overview of RUSLE2
26	OVERVIEW OF RUSLE2 (Revised Universal Soil Loss Equation-Version 2) Where RUSLE2 applies Major factors affecting erosion RUSLE2 factors RUSLE2 background
27	Landscape
28	FACTORS AFFECTING INTERILL-RILL EROSION Climate Soil Topography Land use Cultural practices Supporting practices
29	RUSLE2 FACTORS Daily Soil Loss a = r k l s c p r - Rainfall/Runoff k - Soil erodibility l - Slope length s - Slope steepness c - Cover-management p - Supporting practices
30	RUSLE FACTORS (Sediment Production) Climate r Soil k Topography ls Land Use and lscp Management
31	RUSLE FACTORS A = f (erodibility, erosivity) Erosivity – rklscp Erodibility - klc
32	RUSLE FACTORS Unit Plot Concept a = rk lscp rk - Unit plot soil loss (dimensions) lscp - Adjusts unit plot soil loss (dimensionless)
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35	How Deposition at a Grass Strip Affects Sediment Characteristics
36	RUSLE2 BACKGROUND Combines empirical field data-process based equations (natural runoff and rainfall simulator plots) Zingg’s equation (1940) Smith and Whit’s equation (1947) AH-282 (1965) “Undisturbed land” (1975) AH-537 (1978) Disturbed forestland (1980) RUSLE1 (1992) AH703 (1997) OSM Manual (mined, reclaimed land, construction sites) (1998) RUSLE2 (2001)
37	RUSLE2 APPLICATIONS Cropland Pastureland Rangeland Disturbed forest land Construction sites Surface mine reclamation Military training lands Parks Waste disposal/landfills
38	SUMMARY Factors affecting erosion RUSLE2 factors RUSLE2 background
39	Unit 4 RUSLE2 Factors
40	RUSLE2 Factors r- erosivity factor k- erodibility factor l- slope length factor s- slope steepness factor c- cover-management factor p- supporting practices factor
41	EROSIVITY Single storm Energy x 30 minute intensity Fundamentally product of rainfall amount x intensity Annual-sum of daily values Average annual-average of annual values Daily value=average annual x fraction that occurs on a given day
42	EROSIVITY - R Las Vegas, NV 8 Phoenix, AZ 22 Denver, CO 40 Syracuse, NY 80 Minneapolis, MN 110 Chicago, IL 140 Richmond, VA 200 St. Louis, MO 210 Dallas, TX 275 Birmingham, AL 350 Charleston, SC 400 New Orleans, LA 700
43	Erosivity Varies During Year
44	10 yr EI Reflects locations where intense, erosive storms occur that have a greater than proportional share of their effect on erosion Effectiveness and failure of contouring Effect of ponding on erosivity Sediment transport capacity
45	Reduction by Ponding Significant water depth reduces erosivity of raindrop impact Function of: 10 yr EI Landslope
46	SOIL ERODIBILITY - K Measure of soil erodibility under standard unit plot condition 72.6 ft long, 9% steep, tilled continuous fallow, up and down hill tillage Independent of management Major factors Texture, organic matter, structure, permeability
47	SOIL ERODIBILITY - K Effect of texture clay (0.1 - 0.2) resistant to detachment sand (0.05 - 0.15) easily detached, low runoff, large, dense particles not easily transported silt loam (0.25 - 0.35) moderately detachable, moderate to high runoff silt (0.4 -0.6) easily detached, high runoff, small, easily transported sediment
48	Time Variable K Varies during year High when rainfall is high Low when temperature is high Very low below about 25 °F
49	Time Variable K
50	TOPOGRAPHY Overland flow slope length Slope lengths for eroding portions of hillslopes Steepness Hillslope shape
51	Hillslope Shape
52	Overland Flow Slope Length Distance from the origin of overland flow to a concentrated flow area This slope length used when the analysis requires that the entire slope length be considered.
53	Slope Length for Eroding Portion of Slope Only works for simple slopes Traditional definition Distance from origin of overland flow to concentrated flow or to where deposition begins Definition is flawed for strips and concave:convex slopes Best approach: Use overland flow slope length and examine RUSLE2 slope segment soil loss values
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55	Slope Length for Concave Slope
56	Rule of Thumb for Deposition Beginning on Concave Slopes
57	Slope Length for Concave:Convex Slope
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59	Basic Principles Sediment load accumulates along the slope because of detachment Transport capacity function of distance along slope (runoff), steepness at slope location, cover-management, storm severity (10 yr EI) Deposition occurs where sediment load becomes greater than transport capacity
60	Detachment Proportional to Slope Length Factor Slope length effect l= (x/72.6)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
61	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
62	Detachment Proportional to Slope Steepness Factor
63	Effect of Slope Shape on Erosion
64	Land Use Cover-management Supporting practices
65	Cover-Management Vegetative community Crop Crop rotation Conservation tillage Application of surface and buried materials (mulch, manure) Increasing random roughness
66	Supporting Practices Contouring Strip systems Buffer, filter, strip cropping, barriers Terrace/Diversion Impoundments Tile drainage
67	Cover-Management Subfactors Canopy Ground cover Surface Roughness Ridges Below ground biomass Live roots, dead roots, buried residue Soil consolidation Antecedent soil moisture (NWRR only)
68	Cover-Management Effects
69	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
70	Effective Fall Height
71	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
72	Ground Cover Effect
73	Ground Cover Live cover depends on type of vegetation, production level, and stage Residue Amount added by senescence, flattening, and falling by decomposition at base Decomposition Rainfall amount Temperature
74	Interaction of Ground Cover and Canopy Canopy over ground cover is considered to be non-effective As fall height approaches zero, canopy behaves like ground cover
75	Random Roughness Creates depressions Usually creates erosion resistant clods Increases infiltration Increases hydraulic roughness that slows runoff, reducing detachment and transport capacity
76	Random Roughness Standard deviation of micro-elevations Roughness at tillage function of: Implement Roughness at time of disturbance and tillage intensity Soil texture Soil biomass Decays with: Rainfall amount Interrill erosion
77	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
78	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) Decomposition at base causes standing residue to fall
79	Decomposition of Dead Biomass Function of: Rainfall Temperature Type of material Standing residue decays much more slowly
80	Below ground biomass Live roots Distributed non-uniformly within soil Dead roots Buried residue Half of material decomposed on surface is added to upper 2 inches Incorporated biomass
81	Effect of Below Ground Biomass Roots mechanically hold the soil Add organic 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 (e.g. no-till)
82	Soil Consolidation Overall, freshly tilled soil is about twice as erodible as a fully consolidated soil Erodibility decreases with time Seven years in the Eastern US Depends on rainfall in Western US, up to 25 years
83	Width of Disturbance Width of disturbance taken into account in surface cover, random roughness, and soil consolidation
84	Antecedent Soil Moisture (NWRR) Soil loss depends on how much moisture previous cropping systems have removed from soil
85	Supporting Practices Contouring/Cross-slope farming Strips/barriers Rotational strip cropping, buffer strips, filter strips, grass hedges, filter fence, straw bales, gravel bags Terraces/diversions Impoundments
86	Contouring/Cross Slope Farming Redirects runoff Fail at long slope lengths Effectiveness depends on ridge height (no ridge height—no contouring effect)
87	Contouring/Cross Slope Farming (continued) Function of: Ridge height Row grade Cover-management Hydrologic soil group Storm severity (10 yr EI) Varies with time Tillage that form ridges Decay of ridges
88	Critical Slope Length If slope length longer than critical slope length, contouring fails allowing excessive rill erosion Function of: Storm severity, slope steepness, cover-management, EI distribution Critical slope length extensions below strips depend on degree that strip spreads runoff Terraces are used if changing cover-management or strips are not sufficient Soil disturbance required to restore failed contouring
89	Buffer/Filter Strips Narrow strips of dense vegetation (usually permanent grass) on contour Effective by inducing deposition (partial credit) and spreading runoff Most of deposition is in backwater above strip Buffer strips Multiple strips Either at bottom or not a strip at bottom Water quality-must have strip at bottom and this strip twice as wide as others Filter strip-single strip at bottom
90	Rotational Strip Cropping Equal width strips on contour Strips are rotated through a crop rotation cycle Offset starting dates among strips so that strips of close growing vegetation separate erodible strips Benefit: Deposition (full credit) Spreading runoff Reduced ephemeral gully erosion not credited in RUSLE2
91	Terraces Ridges and channels periodically placed along hillslope that divides hillslope into shorter slope lengths except for widely spaced parallel terraces that may have not effect on slope length Benefit: Shorten slope length and trap sediment Runoff management system Evenly spaced May or may have a terrace at bottom Maintenance required to deal with deposition
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93	Deposition in Terraces Deposition occurs when sediment load is greater than transport capacity Sediment load from sediment entering from overland area Transport capacity function of grade and storm erosivity Deposition depends on sediment characteristics Deposition enriches sediment in fines
94	Diversions Ridges and channels placed at strategic locations on hillslope to shorten slope length Reduce runoff rate and rill erosion Generally designed with a steepness sufficiently steep that no deposition occurs but not so steep that erosion occurs
95	Impoundments (Small sediment control basins) Deposition by settling process Function of: Sediment characteristic of sediment load reaching impoundment
96	Sequencing of Hydraulic Elements Hydraulic elements-channels and impoundments Can create a system Can put channels-impoundments in sequence Examples: Tile outlet terrace—channel:impoundment Impoundments in series—impoundment:impoundment
97	Benefit of Deposition Depends on type of deposition Local deposition gets full credit Remote deposition gets partial credit Credit for remote deposition Depends on location on hillslope Deposition at end gets almost no credit
98	Subsurface Drainage Systems Reflects effects of deep drainage systems Tile drainage systems Lateral, deep drainage ditches Describe by: Assigning hydrologic soil group for undrained and drained soil Fraction of area drained
99	Unit 5 Databases Worksheets Profiles Climate EI distribution Soil Management Operations Vegetation Residue Contouring Strips Diversion/terrace, sediment basin systems Sequence of hydraulic elements
100	Profiles Central part of a RUSLE2 soil loss estimate Profile is reference to a hillslope profile Six things describe a profile Location, soil, topography, management, supporting practice, hydraulic element system Topography described with profile Can specify segments by length and steepness for topography, segments by length for soil, segments by length for management Name and save with a name
101	Worksheets Three parts: Alternative managements, practices; Alternative profiles; Profiles for a field or watershed Alternative management, practices Compare alternatives for a single hillslope profile Alternative profiles Compare specific hillslope profiles Field/Watershed Compute average soil loss/sediment yield for a field or watershed Name and save worksheets
102	Concept of Core Database RUSLE2 has been calibrated to experimental erosion data using assumed data values for such things as cover-mass, residue at harvest, decomposition coefficient, root biomass, burial ratios, etc. The data used in this calibration are core calibration values Data used in RUSLE2 applications must be consistent with these values Core databases were set up for vegetation, residue, and operations NRCS data manager maintains these databases Working databases developed from the core databases
103	Critical RUSLE2 Rules RUSLE2 DEFINITIONS, RULES, PROCEDURES, and CORE DATA MUST BE FOLLOWED FOR GOOD RESULTS. Can’t independently change one set of data without recalibrating. Must let RUSLE2 factors and subfactors represent what they were intended to represent. For example, the K factor values are not to be modified to represent the effect of organic farming. The cover-management subfactors represent the effects of organic farming. Don’t like these rules—then don’t use RUSLE2 because results won’t be good.
104	Climate Input values for values used to described weather at a location, county, management zone Principal values Erosivity value, 10 yr EI value, EI distribution, monthly rainfall, monthly temperature Designate as Req zone and corresponding values Data available from NRCS National Weather and Climate Center Name and save by location
105	EI Distribution 24 values that describe distribution of erosivity R throughout year For a location, county, management zone, EI distribution zone Data available from NRCS Weather and Climate Center Name and save
106	Soil Data describes base soil conditions for unit plot conditions Data include erodibility value, soil texture, hydrologic soil group of undrained soil, efficient subsurface drainage, time to full soil consolidation, rock cover Erodibility nomograph available to estimate soil erodibility factor K Data available from NRCS soil survey database Name and same
107	Management Array of dates, operations, vegetations Specify if list of operations is a rotation Rotation is a cycle when operations begin to repeat Rotations used in cropping Rotations often not used immediately after land disturbances like construction and logging during recovery period Length of rotation Yield, depth, speeds of operations Added materials and amounts NRCS databases, Extension Service Name and save
108	Operations Operations describe events that change soil, vegetation, and residue conditions Mechanical soil disturbance, tillage, planting, seeding, frost, burning, harvest Describe using effects and the sequence of effects Speed and depth Source of data: Research core database, NRCS core database, working databases Name and save
109	Operation Effects No effect Begin growth Kill vegetation Flatten standing residue Disturb surface Live biomass removed Remove residue/other cover Add other cover
110	Operation Effects (cont) No effect Primarily used to obtain output at particular times or to add fallow years when not operation occurs in that year Begin growth Tells RUSLE2 to begin using data for particular vegetation starting at day zero Typically associated with planting and seeding operations Kill vegetation Transfers mass of above ground live vegetation into standing residue pool Transfers mass live roots into dead root pool Typically used in harvest and plant killing operations
111	Operation Effects (cont) Flatten standing residue Transfer residue mass from standing pool to flat, ground surface pool Based on a flattening ratio that is a function of residue type Used in harvest operations to determine fraction of residue left standing after harvest Used in tillage and other operations involving traffic to determine fraction of residue left standing after operation
112	Operation Effects (cont) Disturb surface For mechanical soil disturbance that loosens soil Tillage type (inversion, mixing+some inversion, mixing only, lifting fracturing, compression) determines where residue is placed in soil and how residue and roots are redistributed within soil Buries and resurfaces residue based on ratios that depend on residue type Tillage intensity (degree that existing roughness is obliterated) Recommended, minimum, maximum depths Initial ridge height Initial, final roughness (for the base condition) Fraction surface area disturbed (tilled strips)
113	Operation Effects (cont) Live biomass removed Fraction removed Fraction of that removed that is “lost” and left as ground cover (flat residue) Used with hay and silage harvest operations Remove residue/other cover All surface residues affected or only most recent one? Fraction of standing cover removed Fraction of flat cover removed Used in baling straw, burning operations
114	Operation Effects (cont) Add other cover Fraction added to surface versus fraction placed in soil Unless all mass added to surface, must be accompanied by disturbed soil effect (that is, mass can not be placed in soil without disturbance) Mass placed in soil is placed between ½ and maximum depth Used to add mulch and manure to surface, inject manure into soil
115	Vegetation Live plant material Static variables include: Residue name, yield, retardance, senescence, moisture depletion for NWRR Time varying variables Root biomass in upper 4 inches Canopy cover percent Fall height Live ground (surface) cover cover percent Source of data: Research core database, NRCS core database, working databases Name and save
116	Yield-Residue Relationship Residue at max canopy function of yield
117	Yield-Retardance Relationship Residence function of yield, on contour, and up and down hill
118	Retardance for Up and Downhill RUSLE2 chooses retardance based on row spacing and the retardance selected for a strip of the vegetation on the contour How does vegetation slow the runoff? Row spacing Vegetation on ridge-no retardance effect Wide row-no retardance effect (> 30 inches spacing) No rows, broadcast-same as strip on contour Narrow row-small grain in about 7 inch spacing Very narrow-same as narrow row except leaves lay in row middle to slow runoff Moderate-about 15 to 20 inches spacing
119	Residue Size, toughness 5 types: small, fragile (soybeans); moderate size, moderately fragile (wheat); large size, nonfragile (corn); large size, tough (woody debris); gravel, small stones Decomposition (coefficient, halflife) Mass-cover values Source: NRCS databases Name and save
120	Senescence Input the fraction of the biomass at max canopy that falls to soil surface when canopy decreases from its max value to its min value. Input the minimum canopy value that corresponds to fraction that experiences senescence Mass that falls is computed from difference in canopy percentages and nonlinear relationship between canopy percent and canopy mass
121	Contouring/Cross Slope Farming To have contouring, must have ridge heights To have ridge height, must have operation Ridge height assigned in operation Row grade Relative row grade (preferred) or absolute Create contouring practices based on relative row grade (row grade/land slope) Perfect (0%), exceeds NRCS specs (5%), meets specs (10%), Cross slope (25%), Cross slope (50%) Name and save contouring practice
122	Strips/Barriers Types Filter, buffer, rotational strip cropping Filter Specify width and management on strip Buffer Specify number, whether strip at bottom, for erosion or water quality control, width, strip management Rotational strip cropping Specify number, timing of rotation on each strip Name and save
123	Hydraulic Elements and Their Sequence Channels Specify grade Impoundments Nothing to specify Specific order of elements Name and save sequence
124	System of Hydraulic Elements System composed of named sequence of hydraulic elements Number of systems on hillslope Is the last one at the bottom of the slope? Name and save systems
125	Subsurface Drainage Systems Represented by: Hydrologic soil group for soil when it is well drained Entered in soil input Fraction of area that is drained Name and save
126	UNIT 6 Applicability
127	LIMITS OF APPLICABILITY How well does RUSLE apply to this situation? Erosion Processes Land Uses Geographic Regions Temporal Scale Uncertainty in computed values
128	APPLICABLE PROCESSES Yes: Interrill and rill erosion Yes: Sediment yield from overland flow slope length Yes: Sediment yield from terrace channels and simple sediment control basins No: Ephemeral or permanent incised gully erosion No: Stream channel erosion No: Mass wasting
129	Applicable Land Uses All land uses where overland flow and interrill-rill erosion occurs Land use independent Best: Cropland Moderate: Disturbed lands like military lands, construction sites, landfills, reclaimed lands Acceptable: Rangelands, disturbed forestlands, parks and recreational areas
130	Cropland Applications Best: Clean tilled corn, soybean, wheat crops Moderate: Conservation tillage, rotations involving hay Acceptable: Hay, pasture Most variable: Support practices, especially contouring
131	MOST APPLICABLE GEOGRAPHIC REGIONS Rainfall occurs regularly Rainfall predominant precipitation Rainfall exceeds 20 inches Northwest Wheat and Range Region (NWRR) special case West problem area because of infrequent storms
132	APPLICABLE SOILS Best: Medium Texture Moderate: Fine Texture Acceptable: Coarse Texture NO: Organic
133	APPLICABLE TOPOGRAPHY Slope Length Best: 50 - 300 feet Moderate: 0 - 50 ft , 300 - 600 ft. Acceptable: 600 - 1000 feet NO: >1000 feet
134	APPLICABLE TOPOGRAPHY Slope Steepness Best: 3 - 20% Moderate: 0 - 3%, 20 - 35% Acceptable: 35 - 100% NO: >100%
135	UNCERTAINTY Best (±25%): 4 < A < 30 t/ac/yr Moderate (±50%): 1 < A < 4 30 < A < 50 Least (>±100%): A < 1 (>±50%): A > 50
136	Significant Change Rule of thumb: A change in a RUSLE2 soil loss estimate by more than 10% is considered significant and meaningful in terms of representing main effect. An change less than 10% is not considered significant in general The accuracy for RUSLE2 representing how main effects affect soil loss is much better than the absolute accuracy for RUSLE2 estimating soil loss at any particular location and landscape condition.
137	TEMPORAL APPLICABILITY Best: Average annual, average annual season, average annual single day Least: Single storm provided great care used, generally not recommended
138	Sensitivity Change in soil loss per unit change in a particular variable Select a base condition Vary input values for a variables about base condition Sensitivity varies according to condition Variables with greatest sensitivity require greatest attention
139	Examples of Sensitivity Some variables have a linear effect Erosivity factor R Slope steepness Effect of most variables is nonlinear Ground cover Below ground biomass Roughness
140	Examples of Sensitivity (cont) Low sensitivity Slope length at flat slopes (0.5%) A= 4.6 t/a at k = 150 ft, 5.2 t/a at k = 500 ft, 5.5 t/a at k = 1000 ft Moderate sensitivity Slope length at steep slopes (20%) A = 129 t/a at k = 50 ft, A = 202 t/a at k = 100 ft, A = 317 t/a at k = 200 ft.
141	Examples of Sensitivity (cont) High sensitivity-Ground cover single most important Adding mulch Most variables interrelated Ground cover at planting not as much as expected Sequence of operations Effect of depth for a tandem disk Depends on whether proceeded by moldboard plow
142	SUMMARY RUSLE varies in its applicability Results from RUSLE must be judged Degree of confidence in results varies