Deposition is the transfer of sediment from the sediment load to the soil surface. Sediment can be deposited immediately near where it is detached.  This deposition is called local deposition.  Examples of local deposition include deposition in depressions and row middles. Sediment can also be deposited at some distance (10’s of feet) from where it was detached.  This deposition is known as remote deposition.  Examples of this deposition is deposition on concave slopes, at the upper edge of grass strips, and in terrace channels and impoundments.

Deposition is the transfer of sediment from the sediment load to the soil surface. Deposition causes sediment load to decreases and sediment to accumulate on the soil surface.

RUSLE2 estimates interrill and rill erosion, sometimes referred to as sheet-rill erosion.  Other procedures must be used to estimate the other types of erosion. Ephemeral gullies reoccur in the same location, rills are parallel and generally do not reoccur in the same location.

The simplest application of RUSLE2 is to assume a simple uniform slope.  RUSLE2 estimates the amount of sediment leaving the slope length assumed in the RUSLE2 computation. Soil loss is the net mass of sediment removed from a particular portion of the slope. In this simple uniform slope, sediment yield, which is the amount of sediment delivered to the end of the slope equals soil loss.  If deposition, like the deposition that occurs on concave slopes had occurred, sediment yield would have been less than soil loss. Soil loss is expressed in unit of mass divided by the area that produced the soil loss.

This complex slope has a concave section where deposition occurs.  The portion of the slope from the beginning of the slope to where deposition begins is the eroding portion of the slope. Soil loss occurs on the eroding portion of the slope.  It is this soil loss that would be used in conservation planning to protect this hillslope from excessive erosion. The deposition that occurs on this slope is remote deposition because it occurs some distance from where the sediment was detached.

Some times complex slopes have a flat section in the middle of them that causes deposition.  This deposition is also remote deposition because it occurs some distance from where the sediment was detached. Soil loss occurs at to two locations on the slope, one on the upper end of the slope and one on the lower portion of the slope. RUSLE2 can estimate soil on both sections of the slope and it computes the deposition that occurs in the middle of the slope. Applying RUSLE2 to compute soil loss on the upper of the slope is the same as applying RUSLE2 to a simple slope. Soil loss on the lower portion of the slope depends on runoff that originates over the entire slope length. Sediment yield (sediment delivery) for this slope is also less than soil loss because of deposition.

This slide illustrates the deposition that is caused by dense strips of grass.  This deposition is remote deposition because it occurs some distance from where the sediment was detached. Soil loss also occurs at several locations on the slope.  Even though deposition occurs, the surface runoff continue through the depositional area. Soil loss on the lower part of the slope depends on runoff that originated from the very upper end of the slope. A high soil loss occurs on the the “clean-tilled” area and a low soil loss occurs in the grass strips below where deposition ends within the strips.

This slide illustrates the remote deposition that occurs with a terrace system. Soil loss on the inter-terrace interval is less than soil loss without the terraces because terraces shorten up the slope length.  Runoff on the lower inter-terrace interval originates at the next terrace upslope, not from the very top of the hillslope. The deposition that occurs in the terrace channels is remote deposition because the location of the deposition is some distance from where the sediment was detached.  Also, the deposition is concentrated in a much smaller area than the area that produced the sediment. Sediment Yield = Soil Loss from Inter-terrace interval – Deposition in terrace

Deposition in depressions formed by random roughness and in furrows between ridges is local deposition. The deposition occurs very near to the location where the detachment occurred. The deposition is widespread over the entire slope rather than being concentrated in relatively small downslope areas. The detachment computed by RUSLE2 is actually the net of local detachment and local deposition.  That is, RUSLE2 does not explicitly compute local deposition, but RUSLE2 explicitly computes remote deposition.

Full credit as soil saved is give to local deposition because it is widely dispersed over the hillslope. Full credit is taken for local deposition even though it does enrich the soil surface in coarse particles. Only partial credit is taken for remote deposition because it is concentrated in relatively small areas away from the sediment source. Deposition at the lower end of a concave slope does nothing for maintaining the upper part of the slope.  Even though sediment is deposited at the lower end of the slope, the upper part of the slope is permanently degraded by erosion. When sediment is trapped up the slope, tillage tends to respread the deposited sediment some that benefit of this deposition is realized, especially for lower portions of the slope. Thus, the credit given for deposition depends on the amount and location of the deposition. In the case of terrace, the credit also depends on spacing of the terraces.  The credit is reduced as terrace spacing becomes wide.

Soil texture plays the major role in determining the sediment characteristics at the point of detachment.  The effect of soil texture on sediment characteristics at the point of detachment is considered by RUSLE2. High quality soil management that improves soil aggregates also affects sediment characteristics at the point of detachment, but that effect is not considered by RUSLE2.

Some of the reasons why we are concerned about erosion.

Situations where erosion is likely to be greatest.  In general, erosion is greatest is vegetative cover, including residue from last’s year crop, is low and where operations are directly up and down slope.

The principal use of erosion has been a tool to guide conservation planning. It has also been a major tool used to estimate soil loss in the USDA-NRI inventories. Erosion prediction tools have been used for Inventories i.e. NRI since 1967.

Generally for conservation planning the quality criteria is T (Tolerable Soil Loss) but other quality criteria may be used for planning due to offsite damages, or water quality concerns etc..

RUSLE2 computes values for several variables of use in conservation planning, depending on the planning objectives. Soil loss on the eroding portions of the hillslope provides soil loss values to compare to soil loss tolerance to select erosion control practices to protect the hillslope from degradation by excessive erosion. Detachment the average sediment production rate for the hillslope.  It is the average of the soil loss on the averages where soil loss is high along with the areas, like in grass strips, where sediment production is low. Conservation planning soil loss is the detachment for the slope less credit given for deposition, keeping mind that credit for deposition depends on amount, location, and spacing of terraces. Sediment yield is the amount of sediment that leaves the hillslope represented in RUSLE2. Because most hillslopes used in RUSLE2 do not go to the edge of the field, this value is generally not a sediment yield value to edge of field. RUSLE2 can compute soil loss, deposition, and sediment yield from irregular hillslopes by the hillslopes being divided into segments. The proper comparison of soil loss to soil loss tolerance for a hillslope segment requires that the soil loss tolerance value be adjusted based on position of the segment on the hillslope.  RUSLE2 makes that adjustment and computes the ratio of soil loss to adjusted T value by segment so that the proper mathematical comparison can be made.

This slide shows  the portion of the landscape where interrill-rill (sheet) erosion may occur.  The dashed lines on the left show the RUSLE area that is depicted in the upper right hand corner of the screen and the dashed line on the left side represents a subwatershed divide for a the two concentrated flow watersheds.

Steep and long slopes produce more erosion than do short and flat slopes. Land use has a huge effect on erosion.  Exposing the soil to raindrop and surface runoff dramatically increases erosion.

The USLE computed soil loss by A=RKLSCP, where an average annual value was computed for each factor.  With the exception of the interaction between the R factor and the C factor, not interaction between the USLE factors were considered.  The temporal scale used in computing the C factor was a crop stage period over which cover-management conditions were assumed to be represented by an average value for the period.  The length of crop stage periods typically ranged from a few days, like the rough plowed period in the spring, to a few months, like the after harvest period over the late fall, winter, and early spring. RUSLE1 considered additional interactions of the K and R factors and a partial interaction between P and R.  Also, the temporal time scale used in RUSLE1 was half month, and less if an operation occurred within a half month. This approach allowed a “paper version” of RUSLE1 to be used. However, while the mathematical techniques used in USLE and RUSLE1 were powerful and allowed paper versions, they were mathematically inaccurate by about 15 to 20% in several situations.  The proper mathematical procedure is to compute a daily value for each factor, compute a daily soil loss value, and add up the daily values to obtain a value for rotation.  RUSLE2 uses this mathematical procedure, which is a major change from both the USLE and RUSLE1. Although RUSLE2 computes an average annual value for the traditional USLE/RUSLE1 factors, those values are not used to compute soil loss.  In fact, multiplication of those values, as was done in the USLE and RUSLE1, will not give the RUSLE2 soil loss value.  The difference results from the far more proper mathematics in RUSLE2 than in the approximate mathematics in the USLE/RUSLE1. Small letters, rather than the traditional capitol letters, are used to distinguish the RUSLE2 approach from the USLE/RUSLE1 mathematical approach. The convention is that upper case letters in the USLE and RUSLE1 indicate average annual values while the lower case letters in RUSLE2 indicate daily values.

In agricultural situtations, climate, soil, and topography are determined by the location and are fixed.  However, ls can be changed by installing terraces. The most important consideration in conservation planning and the factor that has the single greatest effect on soil loss is land use, management, and the use of supporting practices like contouring. C also affects soil by changes in organic matter, random roughness and consolidation.

Erosivity is a measure of the forces actually applied to the soil by the erosive agents of raindrop impact, waterdrops falling from plant canopy, and surface runoff. Erosivity has two parts.  The inherent erosivity determined by the rainfall at a location and the infiltration of the soil based on inherent soil properties.  The other part of erosivity is the part that management can change such as changes in infiltration that affects rate and amount of runoff and the present of material that reduces the forces applied to the soil. Erodibility is a measure of the susceptibility(inverse of resistance) of the soil to erosion.  Erodibility has two parts, the inherent erodibility of the soil and the part of the erodibility that can be influenced by management. Notice that most RUSLE2 factors contain both an erosivity effect and an erodibility effect.

The unit plot provides a standard and reference condition to define and determine values for soil erodibility factor. The unit plot condition is a reference condition for all of the other RUSLE2 factors.  A value for another RUSLE2 factor besides r or k is the ratio of soil loss for the given condition to the soil loss from the reference condition of the unit plot. The starting in RUSLE2 is the product of rk, which gives a soil loss value for the reference unit plot condition.  The other factors adjust for the difference between field conditions and the reference unit plot condition.

This slide illustrates the interaction of transport capacity, sediment load, sediment production, and deposition on a complex slope. If transport capacity exceeds sediment load, sediment load will be determined by the amount of sediment made available by detachment. If sediment load exceeds the amount of sediment produced by detachment, deposition occurs. If the sediment load exceeds transport capacity because of a decrease in transport capacity, deposition occurs which reduces sediment load. When deposition occurs, sediment loads “lags” transport capacity depending on the fineness of the sediment. Deposition is a selective process where the coarse particles are deposited leaving the sediment load enriched in fines. In this illustration, local deposition occurs on the very flat portion of the hillslope because interrill erosion produces more sediment than the flow can transport. Deposition occurs on the lower end of the slope because of a decrease in transport capacity because of a flattening of the slope.  Deposition begins to occur where transport capacity equals sediment load.  Deposition does not necessarily begin to occur just where transport capacity begins to decease.

This slide illustrates how RUSLE2 computes deposition for a grass strip.  The strip causes an abrupt decrease in transports capacity at the upper edge of the strip. Deposition occurs because transport capacity drops to less than sediment load. If the strip is sufficiently wide, deposition will end within the strip where sediment load becomes equal to transport capacity.

The enrichment would have been greater if the sediment delivery ratio had been smaller.

RUSLE2 has evolved from a series of previous erosion prediction technologies.  The USLE was entirely an empirically based equation and was limited in its application to conditions where experimental data were available for deriving factor values. A major advancement in RUSLE1 was the use of subfactor relationships to compute C factor values from basis features of cover-management systems, which allowed RUSLE2 to be applied tofar more conditions than the USLE.  While RUSLE1 retained the basic structure of the USLE, process-based relationships were added where empirical data and relationships were inadequate, such as computing the effect of strip cropping for modern conservation tillage systems. RUSLE2 is another major advancement over RUSLE2.  While RUSLE2 uses the USLE basic formulation of the unit plot, the mathematics of RUSLE2 are on a daily basis.  Subfactor relationships are also used in RUSLE2 but these relationships have been improved from RUSLE1, a new ridge subfactor has been added, and the deposition equations have been extended to consider sediment characteristics and how deposition changes these characteristics.  It includes new relationships for handling residue, including resurfacing of residue by implements like field cultivators. The major change visible change in RUSLE2 is its new, modern graphical user interface that is easy to use, but is extremely powerful in the information that it displays and the types of situations that it can represent.  RUSLE2 is a vary powerful model yet it uses very simple, easy to obtain inputs. RUSLE2 computes both temporal and spatially variable effects such as the effect of soil and management varying along a hillslope. The RUSLE2 developers claim that it is the best available technology for conservation planning at the local field office level.  Its science is totally modern and is just as process-based as any other model and includes new science not available in any other model. RUSLE2 brings together of the empirically based models like the USLE/RUSLE1 and the process based models like WEPP. RUSLE2 does not compute ephemeral gully erosion at present, but capability is being planned for RUSLE2.  RUSLE2 will be the erosion prediction tool of choice for the next several years.

The core part of RUSLE2 is that it estimates soil loss from an individual storm. The linear relationship between erodibility and soil erodibility allow simple mathematical approaches to integrate the variables over time.

Erosivity varies greatly by location.  Climate is about 100 times more erosive in New Orleans than in Las Vegas.

The erosivity varies during the year, and the variation differs by location.

The important rainfall variable for the effect of cover-management practices is cumulative erosivity. The effect of supporting practices that are strongly influenced by runoff are much more dependent on the effects of a few, major intense storms. The effect of these few storms is captured in RUSLE2 by use of the10 Yr EI storm. For example, contouring is less effective in the Southern US than in the Northern US because of intensive storms.  Use of the 10 yr EI storm in computing the effectiveness of contouring allows RUSLE2 to capture that difference.

A build of water on the soil surface reduces the erosivity of raindrop impact. RUSLE2 captures this effect using the variables of 10 yr EI storm and the steepness of the land. The greatest reduction of ponding is for flat slopes where the 10 yr EI storm is large, like in the lower Mississippi Delta.

A key point is that soil erodibility is determined under the standard reference condition where management effects have been eliminated by maintaining the unit plots in a continuous tilled, fallow conditions for a number of years. The K value that is used if for the soil fines, but the influence of rock fragments in the soil profile should be considered in setting K values.  The effects of rock fragments on the soil surface is considered in the cover-management computations. Do not use a K value that has been adjusted for rock fragments on the soil surface because use of such an adjusted K value can cause a major mathematical error in RUSLE2. RUSLE2 computes a time varying K value as a function of monthly temperature and rainfall. In contrast to RUSLE1, the time varying K value can be used throughout the US except in the Northwest Wheat and Range Region (NWRR).

Values shown in parenthesis are typical K factors for those texture groups.

The K value is not a pure measure of soil erodibility as an intrinsic soil property. The K values also includes some erosivity effects by how soil properties affect runoff, which is a significant part of what the variable K is representing. The same storm occurring in August generally produces less runoff than the same storm occurring in April in a Midwestern location. The other part of what the variable K represents is that K values are typically high in the spring as and immediately after the soil thaws.

In particular the variation depends on the sequence of monthly temperature and precipitation at the location.

These are the main variables that determine how topography affects erosion.

Even though the hillslope is non-uniform, a uniform hillslope is often assumed in RUSLE2 to compute soil loss on the upper eroding portion of the hillslope. However, in some cases like concave:convex hillslope, the entire hillslope needs to be considered to obtain an accurate soil loss estimate.  Even though deposition occurs on the midpart of this hillslope, the entire hillslope length has to be considered because of the origin of the runoff that flows over the lower portion. RUSLE2 can be used to compute soil loss, deposition, and deposition for each of these slope shapes by dividing the slope into segments.

The entire slope length is used when the analysis requires that the entire slope length be used. Examples include computing sediment yield when deposition occurs on the slope or when deposition occurs on the midpart of the slope and the slope length is needed to compute soil loss on the lower part of the slope. See the next slide for determining slope length when the analysis deals with computing soil loss for the upper part of the slope.

This approach is the traditional way of applying erosion prediction for conservation planning. Sometimes determining where deposition begins is a problem on concave slopes. RUSLE2 determines that location. The location varies on a daily basis as conditions vary daily.

Even though deposition occurs on a slope with strips, the entire slope length is used because the runoff that flows over the lower portion of the slope originated at the top of the hillslope slope. Although deposition occurred, runoff flowed through the depositional area and through the strips to downslope areas. RUSLE2 computes how increased infiltration in the strips reduces runoff below the strips.

This slide illustrates the two major portions of a concave slope that include the upper eroding portion. A slope length to the upper edge of the deposition area can be used to compute soil loss on the eroding portion of the hillslope. The entire slope length can be used to compute erosion on the eroding portion, deposition on the depositional portion, and sediment yield and sediment characteristics for the sediment delivered from the slope.

This slide illustrates a way to estimate where deposition occurs.

The slope length to where deposition begins can be used to compute soil loss on the upper eroding portion of slope. However, the slope length for the lower eroding portion does not begin where deposition ends because of where runoff originates that flows across the lower portion. The entire slope length must be used to compute soil loss on the lower portion of slope.

Figures from AH703 will be added later.  In the meantime, refer to figure in the LS section of AH703.

One of the major changes from RUSLE1 was to eliminate the choice of an LS table in RUSLE1.04/1.05 or the choice of a land use in RUSLE1.06. The same fundamental approach is used where the slope length factor is a function of the rill to interrill erosion ratio. The rill to interrill erosion ratio is computed on a daily basis thus it changes on a daily basis as the factors, like ground cover, change on a daily basis.

The slope length factor represents the combination of erosion by surface runoff (rill erosion) and raindrop impact (interrill erosion). Thus, erosion increases most rapidly along those slopes where rill erosion is the dominant erosion process.

This figure shows the slope steepness factor relationship used in RUSLE2.  Detachment is proportional to the slope steepness factor.  It is not a function of anything in contrast to the slope length factor. However,in actuality the slope steepness is a function of the ratio of rill to interrill erosion but the science isn’t sufficient to develop a working relationship.

Note that maximum erosion rate on the concave slope is about the same for both the uniform and concave slope although sediment yield from the concave slope is much less than sediment yield from the uniform slope. Note that maximum erosion rate for the uniform and convex slope occurs at the end of the slope. Maximum erosion rate on the convex slope is much higher than maximum erosion rate on either the uniform or concave slopes.

Conservation practices  are based on either cover-management and/or supporting practices. Referring to supporting practices as conservation practices is improper.  No-till is a wonderful conservation practice that works entirely though cover-management effects.

Cover-management is used in a variety of ways for erosion control and conservation practices.b

Supporting practices are primarily related to practices that affect transport capacity of runoff.

RUSLE2 uses a set of subfactors to represent the effect of cover-management on erosion.

RUSLE2 uses equations to describe the effect of each subfactor and their interactions. The equations have parameter values that are functions of the properties of the cover-management system, such as percent canopy. Some of the effects of some subfactors are immediately obvious, while other effects are not. For example, roots hold the soil in place, die, and add biomass to the soil.  The effect that may not be obvious is that roots and their mass are an indirect indicator of plants removing soil moisture that in turn reduces runoff.

Canopy cover is cover above the soil surface that only affects rainfall and not surface runoff. Percent canopy and effective fall height are the two main variables used to describe canopy. Open space includes the open space between the outside perimeters of individual plant canopies as well as open space with the perimeter of the canopy of a particular plant.

Effective fall height is the single height that best represents the height from which reformed waterdrops fall from the canopy. Fall height depends on maximum height of canopy, height to the bottom of the canopy, shape of the canopy, and gradient of the canopy material within the canopy (is the material concentrated at the bottom of the canopy or at the top?)

If placed on a mechanically disturbed (tilled) soil before any rainfall after the disturbance, ground cover can maintain high infiltration rates, which contributes to reduced runoff.

Effectiveness of ground cover depends on the potential for rill erosion relative to interrill erosion. The equation Eff = exp(-b %grdcov) used to compute effect of ground cover. The b value in this equations represents the relative effectiveness of ground cover—increased effectiveness means an increased b values. Values for b range from 0.025 where interriill erosion is the dominant erosion to over 0.05 where rill erosion is dominant. Example, b value is higher for steep slopes where rill erosion predominates than for flat slopes where interrill erosion predominates. Value b is greater where increasing ground cover significantly increases infiltration. Effectiveness of residue depends on contact between soil and ground cover.  RUSLE2 assumes less effectiveness for conditions where soil loss biomass is low. Effectiveness of residue on steep slopes is a function of type of residue.  Rocks get more credit because of their contact with the soil than long pieces of mulch like un-chopped wheat straw.

Live ground cover is the the portion of the live aboveground plant material that is touching the soil surface. This percent cover is not double counted by also including it with canopy cover. It is a function of type of vegetation, production level, and stage of growth. Residue is dead plant material.  It is added to the soil surface by senescence, flattening by an operation like harvest or tillage, and falling as a result of decomposition at base. Residue on the soil surface decomposes as a function of daily rainfall amount and temperature. For example, the ground cover computed by RUSLE2 for no-till is significantly greater in Minnesota and than in Minnesota because of difference in rainfall and temperature, especially in the winter.

As canopy approaches the soil surface, its effect becomes the same as ground cover. Also, canopy above ground cover is given no credit.  Effective canopy percent is reduced in proportion to the ground cover percent.

Random roughness is the roughness associated with the random peaks and depressions formed by mechanical disturbance.

Random roughness values range from 0 inches to about 3 inches, which represents a very rough surface. Random roughness can be estimated by measuring the height from the bottom of the depressions to the top of the soil peaks. Random roughness can be estimated by comparing the roughness of the given surface to photographs of surfaces having a known roughness value.  See AH703 Random roughness can be measured by measuring micro-elevations with pins or with a laser. Roughness at the time of creation is function of implement, tillage intensity, soil texture, and soil biomass. Some implements create a rougher surface (moldboard plow versus a rototiller) Tillage intensity refers to the extent that the roughness following an implement is related to the roughness at the time of tillage.  A spike tooth harrow has a reduced tillage intensity (0.4) because it does not eliminate much roughness following a moldboard plow. A moldboard plow has a tillage intensity of 1 because it erases any sign of roughness existing at the time of tillage. Soils high in clay produce increased random roughness, medium textured soils produce moderate roughness, and soils high in sand produced reduced roughness. Increased roughness is computed for soils high in soil biomass, partly because of improved aggregation and stability.  Values derived empirically from erosion data in AH537.

The increase in soil loss begins to decrease as land slope becomes greater than 6% and disappears by a land slope of about 20%. Ridge height decays with rainfall and interrill erosion and thus the ridge effect decreases over time. Effect ranges from about 1.5 (ridges increase soil loss from unit plot condition) for high ridges to about 0.9 for a flat surface. Unit plot is assumed to have some ridge height, which is the reason for the 0.9 value. The effect of ridges increasing soil loss decreases as relative row grade decreases.

Operations shift dead biomass among pools (e.g. standing to flat, flat to buried, resurfacing of buried to flat) Operations with soil disturbing effects bury residue and resurface buried residue. Operations with soil disturbing effect redistributes residue and dead roots in soil. Decomposition causes standing residue to fall over and become flat residue.

Decomposition function of daily rainfall and temperature as driving mechanism. Decomposition half lives (decomposition coefficients) assigned based on type of vegetation.

Mass of roots per unit depth increases in first three inches to a maximum and then decreases over a depth of 15 inches regardless of stage of growth or plant type. A decrease of root biomass during year is assumed to be root sloughing and adds to the dead root pool. Root sloughing causes a build up of biomass in the soil that is a function of location, more where decomposition is less. A portion of the residue decomposed on the surface is arbitrarily added to soil biomass in upper 2 inches.

Below ground biomass has several effects, many of them interactive with other effects such as soil consolidation. The average amount of live and dead roots in 10 inches is the key variable for the effect of roots. The amount of buried residue in the upper three inches is the key variable for the effect of buried residue. The three inch depth is reduced as the soil consolidates to give greater credit to the build up of organic matter over time at the soil surface for no-till.

About seven years is the time assumed for soil to fully regain it resistance after tillage. RUSLE2 computes a long time in the Western US as a function of rainfall.

Width of disturbance is important for strip type operations like planting, fertilizer and manure injections, row cultivation and subsoil. The width is the width that the implement actually disturbs the soil, not the width that gets covered width “thrown” soil.

The effect of antecedent soil moisture is especially important in the region known as the Northwest Wheat and Range Region (NWRR). The effect is related to previous crops removing water from the soil resulting in higher infiltration rates and less runoff in subsequent periods. NWRR is unique with its high erosion rates in the winter, partly caused by freezing and thawing and light rain on thawing soil, and reduced infiltration rates.

Contouring relates to the direction of the tillage (ridges and furrows) with respect to the land slope. Traveling around the slope such that the ridges are on the contour can significantly reduce soil loss for moderate slopes. Cross slope farming is going at an angle to the direction of the land slope that is between being on the contour and up and down hill. Cross slope farming reduces soil loss some but not nearly as much as contouring. Strips and barriers slows runoff, reduce its transport capacity, and produce deposition. Terraces/diversions are ridges-channels placed on the hillslope to intercept runoff. Terraces are channels on such flat grades that deposition occurs in them because transport capacity is less than incoming sediment load, provided the grade of the terrace channel is sufficient flat. Diversions are design with a grade sufficiently steep that deposition doesn’t occur and with a grade sufficiently flat that erosion doesn’t occur. Impoundments trap and retain runoff, giving sediment time to settle and be deposited. Discharge for small basins can be discharged to an underground tile line thus eliminating concentrated flow at that point. Storage of runoff in impoundments reduce flow rate, and thus reduce concentrated flow erosion.

Contouring/cross slope farming redirects overland flow from a direct downhill path to a much less erodible one around the slope. Effectiveness of contouring directly tied to height of ridges and furrow grade.

Over factors such as cover-management, hydrologic soil group, and storm severity affect performance of contouring by affecting runoff. The effectiveness of contouring is almost entirely dependent on how it affects runoff. The effectiveness of contouring varies through time as ridges are formed by tillage and as ridges settle and are eroded after tillage.

If runoff becomes to great on a slope with a particular steepness and cover-management condition, contouring will fail at a particular location on the slope (critical slope length) and lose its effectiveness for the portion of slope beyond critical slope length. Erosion rates on this lower portion of the slope can be much greater than erosion rates on the remaining portion of the slope. Thus, a conservation objective is not allow critical slope length to be exceeded, at least not for substantial amount of time during the rotation. Critical slope can be increased by going to a cover-management system that leaves increased roughness and ground cover. If critical slope length can not be increased sufficiently with cover-management, it sometimes can be increased by buffer strips that spread the runoff. A soil disturbance (tillage operation) that forms ridges is required to restore lost contouring effectiveness lost by contour failure.

Should be placed as close to contour as possible for maximum effectiveness. If the last strip is at bottom of slope, it acts as a “filter” and significantly reduces sediment yield.

A rotational system that starts with a crop rotation like corn-corn-hay-hay-hay. Rotation is grown in strips so that the crops progress through the rotation on each strip. Strips are alternated so that the more erodible strips are placed between less erodible strips. Full credit is taken for deposition that occurs with rotational strip cropping.

Parallel terraces do not shorten slope length as much as gradient terrace. Special consideration should be given to how wide parallel terraces affect slope length. Parallel terraces usually include an impoundment placed in concentrated flow area that parallel terraces cross.

Spacing varies with gradient terraces because of nonuniform topography. Generally discharge into grassed waterway to get runoff down slope without causing ephemeral gully erosion Have to be careful to avoid grade along parallel terraces being too steep. Main purpose of both systems is runoff management to control excessive rill erosion and especially ephemeral gully erosion.

Deposition, including fraction of sediment load) in a terrace channel will be much less when little erosion occurs on inter-terrace interval. Transport capacity decreases with grade of terrace channel and runoff rate in channel. The amount of deposition depends on the fineness of sediment coming into terrace channel. For example, deposition will be less in a terrace where a grass strip immediately adjacent to the terraces induces significant deposition. Maintenance required because of deposition.  Otherwise terrace channels fill with sediment.

More effective at removing fines that other deposition on typical hillslope. Effectiveness highly dependent on the sediment distribution reaching basin. For example, basin at end of channel where much deposition occurs much less effective.

Impoundments in series on a construction site to remove as much sediment as possible from runoff.

Benefit of deposition depends on type, amount, and location of deposition.

Values are assigned based efficiency and effectiveness of drainage systems.

The information is typically placed in the databases before making a soil loss computation. Access to databases in terms of what can be seen and edited can be controlled. All of databases for RUSLE2 are housed in a single large database that be named and selected when RUSLE2 is being used. Data can be exported so that data can be shared among RUSLE2 users. Names used in databases are arbitrary and only serve as identifiers. When an identifier is selected, it brings the data associated with that identifier.

The profile is along the overland flow path when the surface is smooth without ridges affecting flow direction. Location, soil, topography, management, supporting practices, and hydraulic element system describe a profile. RUSLE2 represents a single, unique hillslope profile in each of its computations. Multiple RUSLE2 computations are made to represent to represent a complex area where values from each profile are weighted to obtain an estimate for the area. The profile describes the topographic shape along the overland flow path. Example: making multiple computations to evaluate alternative managements. First step in learning RUSLE2 should be in making soil loss computations with profiles.

Compute weighted values for a field, region, or watershed based on areas represented by each profile.

Must follow the rules of using core databases to get good results from RUSLE2. RUSLE2 has been calibrated to give good soil loss values based on research data assuming a certain set of input values. The input values used in application of RUSLE2 must be consistent with the calibration values. Core values have been set up to be consistent with the calibration values. A change away from the core values actually degrades the performance of RUSLE2 rather than improves it. RUSLE2 DEFINITIONS, RULES, PROCEDURES, and CORE DATA MUST BE FOLLOWED FOR GOOD RESULTS. 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.

The importance of the core database concept and following these rules is essential!

The climate database stores the weather data needed to make a RUSLE2 soil loss computations. Seek out their data and store only the data that will be used in RUSLE2 application.  No point having data in database that will never be used.

EI distributions that come with RUSLE2 are keyed to EI zone map in AH703.

Remember, data are for unit plot condition.  RUSLE2 cover-management factor takes into account differences between actual field condition and unit plot conditions.

Description of a management is a list of dates, operations that occur on each date, and the vegetations associated with an operation that has a “begin growth” effect and the residue associated with an operation that has an “adds other cover” effect. Specific operations, vegetations, and residues are selected from lists for those already in databases. If required information is not already in database, then a specific entry will have to be edited or a new entry made. Access to database may be limited and not available to particular users.  Check with your supplier of RUSLE2. In general, accept values in database because of the research and judgment gone into the preparation of databases by researchers, NRCS technical specialists, and technical specialists from other organizations. Be careful about trying to modify variables like yield, depth, and speed to exactly the field conditions. Changes in estimated soil loss may not be meaningful and significant for small changes. A management can include volunteer vegetation (weeds) in addition to planted crops. RUSLE2 is dumb.  Weeds must be in vegetation database and an operation must be present to get the weeds to grow, and then an operation must be present to stop weed growth.  The same applies to all vegetations. RUSLE2 only “sees” one vegetation at a time.  The information in a vegetation file must reflect the overall conditions at the time. For example, RUSLE2 can combine the information for small grain and a legume to know what is in the field.  The user must provide values for the combined condition and specifically name and save that vegetation. NRCS and Extension Service good source of information for cropland.  Consult other NRCS and other agencies like Bureau of Land Management for range for other land uses.

Typically human activity, but can animal, like grazing removing aboveground biomass, or natural like frost killing vegetation. If new new operations, must be created, follow the NRCS core database for cropland.  Consult with RUSLE2 developers for core data for other land uses.

These are effects used to describe operations.

No residue gets flattened unless it falls by decomposition at the base of the residue or an operation is used to flatten the residue. The flattening effect is used at harvest to determine how much of the aboveground biomass is left standing. Flattening ratio values are based on process used to flatten and the type of residue. Standing residue of some vegetations are more easily flattened than with other vegetations.

Critical effect for representing tillage and other soil disturbing operations. Burial and resurfacing ratio values function of implement and type of residue. Tillage intensity represents how much of the existing roughness at time of disturbance influences roughness after the disturbance.  A harrow does not eliminate all existing roughness (tillage intensity= 0.4).  The roughness left by a moldboard plow is independent of preexisting roughness (tillage intensity = 1.0).

Rock can be applied to soil surface and treated as a residue with essentially a zero decomposition coefficient. Refer to NRCS core database for properties of different types of manure.

Values in database must describe the conditions when this vegetation is present. RUSLE2 can not combine data from one vegetation and another vegetation to produce a composite vegetation. An example is intercropping and the understory of grass under shrubs on rangeland. Try to use time varying root biomass values to account for root sloughing so that RUSLE2 can compute a buildup of biomass in the soil. Use time varying canopy values where canopy values decrease to represent senescence and RUSLE2 can compute a litter layer on the soil surface. Review data from multiple studies and observations before selecting values.  Variability is large.  Don’t rely on data from a single source.  RUSLE2 is designed to represent main effects in a consistent way across applications.

RUSLE2 computes residue at maximum canopy as a linear function of yield.  The result is that the typical residue to yield ratio increases as yield decreases. Key point: It is the residue at maximum canopy that is described.  Not residue at harvest.  RUSLE2 computes residue at harvest.

Retardance refers to how vegetation and its standing residue slow runoff. Two data points are used to describe the curve.  One data is the retardance at a high yield. Condition 1: The vegetation has no effect at a low yield, which is the situation for the lowest curve in figure.  An example is that the retardance for corn is assumed to be zero at about 100 bu/ac. Condition 2: The vegetation has no retardance at a zero yield, which is the middle curve.  An example is grass. Condition 3: The vegetation has retardance at a zero yield, which is the upper curve.  An example is small grain like wheat. Retardance is described in two directions, on the contour and up and downhill.  The retardance relationship in the above figure is used to describe retardance on the contour.

Ask the question, to what degree does vegetation in rows up and downslope slow the runoff?

Decomposition is a function of distribution of stems, leaves, pods, roots, etc. but a single value is used. Also a single value is used for above ground and below ground decomposition. Mass-cover relationship.  Enter a data point on curve.  RUSLE2 self-calibrates. Stay with core values in core databases.  Interaction of mass-cover, residue at harvest and decomposition.  Change of one requires recalibration of RUSLE2.

Decrease in canopy percentage is used to compute amount of residue that falls to soil surface as a part of senescence. The input fraction is the fraction of the biomass existing at max canopy that will fall to the surface when the canopy cover decreases from its maximum value to a minimum value that is also input.

The other part of the contouring description is the ridge heights described in the soil disturbance effect used to describe operations. Remember: no ridges-no contouring effect.  To increase contouring effect, reduce row grade and increase ridge height.

For example, where strip width, spacing, and management vary by strips.

Channels (terraces and diversions) and impoundments (sediment control basins).

A simple system is a gradient terrace where a single channel is used.  Choose a channel with the appropriate grade and drains external to area. A simple sediment control basin is the combination of an impoundment that drains external. Sediment basins in series is an impoundment that drains to another impoundment. A simple PTO terrace is an overland area that drains to a channel that in turn drains to an impoundment.

The types of subsurface drainage that is represented are those that are deep drained by tiles or by deep lateral ditches. Main effect is how drainage system affects runoff, which is represented by inputting values for two hydrologic soil groups, one when no drainage system is present and the other is when the a highly efficient system is used. The fraction of the area relates to the fraction of the area where the soil loss is being computed that is treated with the drainage system. For example, a low value for the fraction drained would be entered where only wet spots are drained.

This section deals with general information about RUSLE2 that should be considered when RUSLE2 is being applied.

RUSLE2 is applied well beyond the central research data used to derive it.

RUSLE2 estimates sediment yield and sediment characteristics from overland slopes, low grade terrace type channels, and small sediment basins. RUSLE2 sediment yield estimates are not estimates of sediment yield from fields unless the slope length ends at the edge of field. RUSLE2 does not estimate ephemeral gully erosion.  While ephemeral gully erosion within field sized areas is a critical element in conservation planning, the benefits of controlling ephemeral gully erosion are not explicitly considered in RUSLE2. Also, runoff management and disposal from field-sized areas is critically important.  RUSLE2 is not designed to determine all of the benefits of runoff management in a field-sized area, even though it is a critically important part of conservation planning.

RUSLE2 estimates the erosion, deposition, and sediment transport associated with overland flow.  It does not, for example, estimate erosion by piping from flow internal in the soil. IT WORKS FOR ALL LANDUSE WHERE EROSION OCCURS IN ASSOCIATION WITH OVERLAND FLOW. RUSLE2 works better on some land uses than on other land uses because of the availability of data to derive parameter values.  Also, it does less on some land uses than other because of spatial variability of cover-management conditions, such as on some disturbed forestland.

RUSLE2 does least well for contouring that for any other factor because of variability with implement operation and with specific conditions at specific storms.

RUSLE2 works best for the eastern US because of the mass of data and the regularly occurring rainfall. RUSLE2 IS NOT A MIDWESTERN BASED EROSION PREDICTION TECHNOLOGY.  IT IS LOCATION INDEPENDENT EXCEPT FOR THE RELATIONSHIPS USED IN THE NWRR.

Works best for silt loam soils because of the large amount of empirical data. Works poorest for coarse textured soils because of the greater role of infiltration on runoff.

The range of applicability is determine by the availability of empirical data. RUSLE2 should not be applied to slope lengths longer than 1000 ft.  The longest slope length used derive RUSLE2 was about 650 ft.  Beyond 1000 ft is simply too much extrapolation.

RUSLE2 should not be applied to slopes greater than 100%.  Other processes like mass movement become a factor, something not represented by RUSLE2.

The range where soil erosion prediction technology needs to be accurate is from about 1 tons/acre to about 15 tons/acre for conservation planning for protecting the soil against excessive erosion. Anything less than 1 tons/acre is already below almost all soil loss tolerance values and thus erosion is problem. Anything greater than about 15 tons/acre (three times soil loss tolerance) is going to be recognized as being serious erosion problem regardless of the whether the estimate is 15, 25, or 40 tons/acre. The critical concern is does the technology accurately distinguish in recommending to a farmer that the proposed management practice will take soil loss from 10 tons/acre to 5 tons/acre. Accuracy for high soil loss estimates is important when sedimentation is important, such as the amount of sediment that will be trapped in sediment control basins, the amount of sediment that will be collected in roadside ditches, and the amount of sediment delivered to a stream. Accuracy of low soil loss estimates and sediment characteristics are important in water quality analysis. When all is said and done, no other erosion prediction has been demonstrated to perform better than RUSLE2 for day in and day out conservation planning at the field office level. Certain technologies are far more powerful than RUSLE2 for evaluating the performance of sediment control basin and erosion control structures used on severely disturbed land. Also, RUSLE2 does not apply to complex watershed for computing sediment delivery. However, when properly used, RUSLE2 is a proper (and best) tool for estimating interrill and rill erosion on large complex areas like in the USDA NRI.

Sensitivity analysis are very useful for understanding how RUSLE2 works. Sensitivity analysis have to be conducted with considerable care because the results depend on the situation. For example, depth of tillage with a tandem disk may be unimportant when it follows a moldboard plow but very important if it is the first operation after harvest. Another example, residue cover at planting, especially for clean-tilled and mulch till systems.  Varying residue cover at planting doesn’t always have as much effect as expected because of the effect of other variables over the course of the rotation. Many variables in RUSLE2 are interrelated, such as how yield affects soil loss. Nevertheless, the variables that have the greatest effect on soil loss should be considered most carefully.

Some variables like the erosivity factor and the steepness factor have a linear effect in RUSLE2.  Double the variable; double the effect. Most variables have a nonlinear effect such that doubling variable has more or less than a doubling effect on soil loss.

These results how sensitivity to a variable depends on the situation and illustrates how one need not be concerned with estimating a variable under one condition but give much greater care under another condition. For example, being off in slope length by 850 ft didn’t have much effect on a 0.5% slope, but being off just 50 ft had a tremendous effect on a 20% slope.