Download - RUSLE2 Slide Set2
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REVISED UNIVERSAL SOIL LOSS EQUATION-Version 2
Predicting Soil Erosion By Water: A Guide to Conservation
Planning
RUSLE2
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UNIT 1
Course Objectives and Topics
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OBJECTIVES
Understand erosion processes Learn RUSLE2 and its software Learn field office applications of
RUSLE2
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UNIT 2
Overview of Erosion
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OVERVIEW OF EROSION
Definition of erosion Erosion processes Types of erosion Why erosion is a concern Uses of erosion prediction tools
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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
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DETACHMENT
Removal of soil particles from soil surface
Adds to the sediment load- Sediment load: Rate sediment is
transported downslope by runoff
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DETACHMENT
Soil
Sediment LoadSediment Transport
Detachment
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DEPOSITION
Reduces the sediment load Adds to the soil mass Local deposition
- Surface roughness depressions- Row middles
Remote deposition- Concave slope- Strips- Terraces
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DEPOSITION
Soil
Sediment LoadSediment Transport
Deposition
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TYPES OF EROSION
Interrill and rill (sheet-rill) Ephemeral gully Permanent, incised (classical) gully Stream channel Mass movement Geologic
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DEFINITIONS
SOIL LOSS
SEDIMENTYIELD
RUSLE2 ESTIMATES TO HERE
Simple Uniform Slope
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DEFINITIONS
Soil loss
Remote deposition
Sediment yield
Complex Slope
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DEFINITIONS
Soil loss
Remote deposition
Soil loss
Sediment yield
Complex Slope
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DEFINITIONS
Soil loss
Remote deposition Soil
loss
Sediment yield
Remote deposition
Soil loss
Strips
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DEFINITIONS
Soil loss
Remote deposition
Soil loss
Sediment yield
Remote deposition
Soil loss
Remote deposition
Terraces
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LOCAL DEPOSITION
Random Roughness
Ridges-Furrows
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Credit for Deposition
Local Deposition
Full credit
Remote Deposition
Partial credit
Amount
Location
Spacing of terraces
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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
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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
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WHERE EROSION CAN BE A PROBLEM
Low residue crops Conventional tillage Rows up/down steep slopes Low maintenance pasture Disturbed land with little cover
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EROSION PREDICTION AS A TOOL
Guide management decisions Evaluate impact of erosion Inventory soil erosion Conservation planning
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EROSION PREDICTION AS A TOOL
Concept:- Estimate erosion rate- Evaluate by ranking- Evaluate against quality criteria
Tool: RUSLE2 Quality Criteria: Soil loss tolerance
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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
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UNIT 3
Overview of RUSLE2
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OVERVIEW OF RUSLE2(Revised Universal Soil Loss Equation-
Version 2) Where RUSLE2 applies Major factors affecting erosion RUSLE2 factors RUSLE2 background
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LandscapeOverland flow
Interrill
Rill
EphemeralGully (Concentrated flow)
Erosion Types
RUSLE2 Area
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FACTORS AFFECTING INTERILL-RILL EROSION
Climate Soil Topography Land use
- Cultural practices- Supporting practices
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RUSLE2 FACTORSDaily 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
Daily Factors
Average annual soil loss = sum of daily soil loss values
Different formulation from USLE and RUSLE1
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RUSLE FACTORS(Sediment Production)
Climate r Soil k Topography ls Land Use and lscp
Management
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RUSLE FACTORS
A = f (erodibility, erosivity)
• Erosivity – rklscp
• Erodibility - klc
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RUSLE FACTORS
Unit Plot Concept
a = rk lscp
rk - Unit plot soil loss
(dimensions)
lscp - Adjusts unit plot soil loss
(dimensionless)
(Keep in mind that RUSLE2 operates on a daily basis)
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Deposition
Transport capacity = sediment load
Sediment production less than transport capacity
Deposition because sediment production exceeds transport capacity
Relation of deposition to transport capacity and sediment load on a complex slope
HillslopeTransport capacity
Sediment load
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Dense grass
Erodible soil surface
Deposition region
Deposition ends where transport capacity = sediment load
Transport capacity
Sediment load
Relationship of Deposition to Transport Capacity and Sediment Load for a Grass Strip
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How Deposition at a Grass Strip Affects Sediment Characteristics
Particle class Before (%) After (%)
Primary clay 5 22
Primary silt 24 58
Small aggreg. 36 14
Large aggreg. 24 5
Primary sand 7 1
SDR = 0.2
Note how deposition enriches sediment in fines
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RUSLE2 BACKGROUNDCombines 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)
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RUSLE2 APPLICATIONS Cropland Pastureland Rangeland Disturbed forest land Construction sites Surface mine reclamation Military training lands Parks Waste disposal/landfills
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SUMMARY
Factors affecting erosion
RUSLE2 factors
RUSLE2 background
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Unit 4
RUSLE2 Factors
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RUSLE2 Factors
r- erosivity factor k- erodibility factor l- slope length factor s- slope steepness factor c- cover-management factor p- supporting practices factor
(Keep in mind that factors are on a daily basis)
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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
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EROSIVITY - R
Las Vegas, NV 8Phoenix, AZ 22Denver, CO 40Syracuse, NY 80Minneapolis, MN 110Chicago, IL 140Richmond, VA 200St. Louis, MO 210Dallas, TX 275Birmingham, AL 350Charleston, SC 400New Orleans, LA 700
Measure of erosivity of climate at a location
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Erosivity Varies During Year
0
0.2
0.4
0.6
0.8
1
1.2
1
25
49
73
97
12
1
14
5
16
9
19
3
21
7
24
1
26
5
28
9
31
3
33
7
36
1Day in Year
% E
I on
Da
y CA
SD
MA
TN
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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
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Reduction by Ponding
Significant water depth reduces erosivity of raindrop impact
Function of:
- 10 yr EI
- Landslope
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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
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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
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Time Variable K
Varies during year High when rainfall is high Low when temperature is high Very low below about 25 oF
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Time Variable K
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.81
25
49
73
97
12
1
14
5
16
9
19
3
21
7
24
1
26
5
28
9
31
3
33
7
36
1
Day in Year
Da
ily S
oil
Ero
dib
ility
Va
lue
CA
SD
MA
TN
Base K value = 0.37
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TOPOGRAPHY
Overland flow slope length Slope lengths for eroding portions of
hillslopes Steepness Hillslope shape
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Hillslope Shape
Uniform
Convex
Concave Complex-Convex:concave
Complex-Concave:convex
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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.
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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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Soil loss
Remote deposition Soil
loss
Sediment yield
Remote deposition
Soil loss
Slope Lengths for Strips
Overland flow and eroding portion slope length
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Slope Length for Concave Slope
Deposition
Overland flow slope length
Eroding portion slope length
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Rule of Thumb for Deposition Beginning on Concave Slopes
Average steepness of concave portion
Deposition begins
Deposition begins at location where steepness = ½ average steepness of concave portion
Example:
Assume average slope of concave section = 10%
½ of 10% is 5%
Deposition begins at location where the steepness is 5%
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Slope Length for Concave:Convex Slope
Deposition
Overland flow slope length and slope length for lower eroding portion of slope
Slope length for upper eroding portion of slope
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Insert figures from AH703 to illustrate field slope lengths
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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
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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
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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
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Detachment Proportional to Slope Steepness Factor
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 5 10 15 20 25 30 35
Slope Steepness (%)
Fa
cto
r V
alu
e
Not affected by any other variable
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Effect of Slope Shape on Erosion
-100
-50
0
50
100
150
200
1 2 3 4 5 6 7 8 9 10
Segment Along Slope
So
il L
os
s (
t/a
c)
Concave
Convex
Uniform
100 ft long, 1% to 19% steepness range
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Land Use
Cover-management
Supporting practices
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Cover-Management
Vegetative community Crop Crop rotation Conservation tillage Application of surface and buried
materials (mulch, manure) Increasing random roughness
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Supporting Practices
Contouring Strip systems
- Buffer, filter, strip cropping, barriers Terrace/Diversion Impoundments Tile drainage
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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)
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Cover-Management EffectsRaindrops 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
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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
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Effective Fall Height
Effective fall height
Canopy height
Height to bottom of canopy
Gradient of canopy density Material
concentrated near top
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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
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Ground Cover Effect
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100 120
Ground Cover (%)
Gro
un
d C
ove
r E
ffe
ct
b=0.025
b=0.05
Eff = exp(-b x %grd cov)
b greater when rill erosion more dominant than interrill erosion
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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
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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
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Random Roughness
Creates depressions Usually creates erosion resistant clods Increases infiltration Increases hydraulic roughness that
slows runoff, reducing detachment and transport capacity
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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
0 12
0
2.5
Range (in)
Random Roughness (in)
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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
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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
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Decomposition of Dead Biomass
Function of:- Rainfall- Temperature- Type of material- Standing residue decays much more
slowly
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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
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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)
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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
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Width of Disturbance
Width of disturbance taken into account in surface cover, random roughness, and soil consolidation
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Antecedent Soil Moisture (NWRR)
Soil loss depends on how much moisture previous cropping systems have removed from soil
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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
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Contouring/Cross Slope Farming
Redirects runoff Fail at long slope lengths Effectiveness depends on ridge height
- (no ridge height—no contouring effect)
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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
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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
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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
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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
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Terraces
Ridges and channels periodically placed along hillslope that divides hillslope into shorter slope lengths except for widely spaced parallel terraces that may have no 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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Types of Terraces
Gradient terrace
Parallel terrace
Sediment basin into underground tile line
Grassed waterway
Contour line
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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
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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
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Impoundments (Small sediment control basins)
Deposition by settling process Function of:
- Sediment characteristic of sediment load reaching impoundment
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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
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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
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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
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Unit 5Databases
WorksheetsProfilesClimateEI distributionSoilManagementOperationsVegetationResidue
Contouring
Strips
Diversion/terrace, sediment basin systems
Sequence of hydraulic elements
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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Operation Effects
No effect Begin growth Kill vegetation Flatten standing residue Disturb surface Live biomass removed Remove residue/other cover Add other cover
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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
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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
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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)
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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
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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
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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
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Yield-Residue Relationship
Residue at max canopy function of yield
Yield 1 Yield 2
Yield
Residue at Max Canopy
Residue 1
Residue 2
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Yield-Retardance Relationship
Retardance function of yield, on contour, and up and down hill
Yield
No retardance at a significant yield (corn)
Retardance
No retardance at no yield (grass)
Significant retardance at no yield (wheat)
Retardance at a high yield
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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
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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
00
Mass per unit area
Enter 1 of 3 pts.
Mass @ 30, 60, or 90% cover
30%
60%
90%
% Cover
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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
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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
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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
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Hydraulic Elements and Their Sequence
Channels- Specify grade
Impoundments- Nothing to specify
Specific order of elements Name and save sequence
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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
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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
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UNIT 6
Applicability
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LIMITS OF APPLICABILITY
How well does RUSLE apply to this situation?- Erosion Processes- Land Uses- Geographic Regions- Temporal Scale- Uncertainty in computed values
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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
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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
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Cropland Applications
Best: Clean tilled corn, soybean, wheat crops
Moderate: Conservation tillage, rotations involving hay
Acceptable: Hay, pasture Most variable: Support practices,
especially contouring
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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
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APPLICABLE SOILS
Best: Medium Texture Moderate: Fine Texture Acceptable: Coarse Texture NO: Organic
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APPLICABLE TOPOGRAPHY
Slope Length- Best: 50 - 300 feet
- Moderate: 0 - 50 ft , 300 - 600 ft.
- Acceptable: 600 - 1000 feet
- NO: >1000 feet
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APPLICABLE TOPOGRAPHY
Slope Steepness- Best: 3 - 20%
- Moderate: 0 - 3%, 20 - 35%
- Acceptable: 35 - 100%
- NO: >100%
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UNCERTAINTY
Best (25%): 4 < A < 30 t/ac/yr Moderate (50%): 1 < A < 4
30 < A < 50 Least (>100%): A < 1
(>50%): A > 50
Confidence in Result
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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.
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TEMPORAL APPLICABILITY
Best: Average annual, average annual
season, average annual single day
Least: Single storm provided great care
used, generally not
recommended
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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
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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
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Examples of Sensitivity (cont)
Low sensitivity- Slope length at flat slopes (0.5%) A= 4.6
t/a at = 150 ft, 5.2 t/a at = 500 ft, 5.5 t/a at = 1000 ft
Moderate sensitivity- Slope length at steep slopes (20%) A =
129 t/a at = 50 ft, A = 202 t/a at = 100 ft, A = 317 t/a at = 200 ft.
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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
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SUMMARY
RUSLE varies in its applicability
Results from RUSLE must be judged
Degree of confidence in results varies