| A unit of Lasting Forests
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A Total Forest Management Plan
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Gravity rules. The surface of every square meter of Earth is changing and one of the greatest changes is that of downward movement of soil and water. Erosion is the process by which Earth materials are worn away and moved from one spot to another by the action of water, wind, ice, frost action, plants and animals, and gravity.Whether called erosion, sediment, alluvium or colluvium, or particulate matter, there is a complex mixture of matter usually called "soil" that is being moved downward by one or more forces, generalized as water and wind but they also include mechanical effects and ground slippage and subsidence. 2.1 trillion pounds of suspended solids are discharged annually into US surface waters. Dissolved soil components of ionic" size" are of great concern but these are rarely discussed as erosion but as substances within "leachates", a minor distinction. Stall (1966) then estimated the value of soil nutrients removed by erosion was about $800 million. Wind and water may move a little soil "up" but the amount is insignificant. Over the globe, 20 billion cubic meters are transported into the ocean each year. McIntosh et al. (1989) note that erodability is a soil sample characteristic, unlike soil erosion which we view as the rate of soil loss per unit area. (It may simply be viewed as the process that includes detaching and transporting soil particles by wind or water.) "Prevent soil erosion" is a reasonable slogan but it matches people against nature, the natural geologic erosion and that which is allowed or produced by people.
The sources of eroded materials or" sediment" (typically into waters)(usually expressed as cubic meters per 100 km2) from various sources are:
Natural or geologic
Stream channel erosion (major storm-flow events)
Stream channel erosion (debris-slide effect)
Stream channel erosion (continual)
Management related
Mass failure of road fills
Mass failure (roads)
Mass failure (clearcuts)
Stream channel erosion
Pre-management erosion (all sources)
Sheet, rill, and gully erosion.
We call all of these moving entities "downward particles" or DP to avoid the debates about what they really are or ought to be called. As land managers, we believe that it is responsible to reduce the rate at which DP moves. We know that movement downward is normal, natural, and expected. We believe that all land managers should accept the constant fight of resisting or halting (temporarily) this movement.
We know what it does. It causes loss of organic matter, loss of soil minerals that contain plant nutrients, and exposure of subsoils that are often infertile or acidic. It decreases the water-holding capacity of the soil (by about 5% by volume) to supply water to growing plants during the critical period of the growing season when evapotranspiration exceeds rainfall. It degrades soil structure.
It rarely kills aquatic insects once it enters the waters. Suspended sediment is not intrinsically toxic to aquatic life but it can have sub-lethal effects. One such effect is to reduce insect feeding activity while the sediment is in the water column. It may cover spawning areas. A direct effect, rarely measured , is catastrophic drift of insects out of the stream reach. Drift can be continual - random and throughout the period, behavioral - related to genetically proscribed movements, and catastrophic - related to stream discharge change and response to soil (and related) inputs (called "sediment loading"). Gains as well as losses in algae can occur with sediment loading and it depends on season, temperature, surface area, and the nature of the sediment entering the water. Suspended sediments may cut out sunlight for growing aquatic plants. The sand and silt layers that form on the stream bottom can severely reduce colonization organisms and their populations. Such solids may carry fertilizers and cause aquatic plants to grow abundantly. Similarly, it can carry substances harmful to aquatic plants.
Sediment is fragmental material that originates from the chemical or physical disintigration of rocks. The disintegration products may have many different shapes and may range in sizr from large bolders to colloidal particles. In general they retain about the same mineral composition as the parent rocks.
In some cases, we think that movement of particles upward is responsible action, that is to dredge materials and move it for replacement in areas from which the material was gained. There is a snarled literature of sediment yields, surface mining restoration, effects of sediments on fish, surface runoff, mineral content of water, non-point pollution and, of course, land fertilization. Eroded soil becomes "sediment" in stream studies and a prominent factor in pond fishery work.
Non-Point Pollution
Sediment from agricultural fields and forests is considered a water pollutant ( as compared to point pollution (as from a factory waste disposal pipe into water). Studied by Seitz et al. (1982) and probably many time later there are many issues and it is very difficult to create policy, incentives, or penalties for non-point pollution. In The Trevey we work for the land and for profits. Profits are a net concept and minerals not lost or soil structure not lost can be a net gain in a calculus for the managed area. We do not buy soil, we prevent its loss. We do not need a social policy or financial award for doing so. We have a no-soil-loss policy. It is temporarily expensive but profitable given the expected production from the saved soil over the 150-year planning period. We will be temporarily out-competed by the land manager not doing soil erosion control but will win over the long run. We'll encourage investment by others. Often the costs of pollution control are minimum after structural changes (contouring, terracing, settling basins, etc.) have occurred. We support only source controls not instream water quality management. We know that some sediment will enter streams and believe that some communities within streams require a small annual sediment pulse. Our policy of trying to bring many areas under the Trevey influence with education on field trips and with financial awards from superior land management is the only policy that we now see that will achieve the longterm and lasting reductions in non-point pollution of Earth waters. While pesticides and fertilizers are also considered non-point pollution, we hold (at least temporarily) that they are strongly related to sediment in water and thus that our measure of control will be sediment in water. We''ll study "Toward Instream Water Quality Management" for specific actions to take (EPA's PB 83-110957 from the Env. Res Lab, EPA, College Station Road, Athens GA 30613). We think that sediment and managed vegetation in storm water basins will adequately reduce phosphorus contamination of stream waters.
In 2005 (and perhaps continuing) there was the EQIP (Environmental Quality Incentives Program) of the Natural Resources Conservation Service (NRCS). Voluntary, there may be assistance available. There are programs and evaluation periods. The objective is reducing non-point source pollution such as nurients, sediments, and pesticides. If needed information is not at the web site , contact NRCS at 540-382-3262, 540-745-2847, 540-921-1267 or 540-980-0170 use ext.#3.
Geologic Erosion
Frye(1985) noted that geologic erosion can be viewed as a beneficial process. Without it, half of the Earth's surface would be covered by a weathered-out mass of inert mineral matter instead of productive soils composed of weatherable materials, organic matter, and organisms. Human use of soils can speed up erosion. Western US areas are typically undergoing early stage geologic erosion; Appalachian areas are rounded and in advanced, nearly-stable state.
Over many years, we have become very aware of the variabilities in nature, especially in soils as related to plants and animals. They are difficult and costly to sample and samples are difficult to process consistently. For measuring sediment movement on hillslopes, vital to studies of soil erosion, no truly satisfactory measurement technique has been developed (Well and Wohlgemuth 1987). We use a modified form of collection employed by the BLM for verifying our GIS work. Estimates are strongly influenced by the amount and timing of rains before the estimates are made. Significant differences occur between plowed and unplowed soils. Silvicultural practices result in different erosion rates and compaction (higher bulk density) (Carter et al. 1997), clear cutting and deferrment-cut producing most disturbance. Presence and distribution of large rocks influences estimates. Uncertainty remains over the mathematical distribution of erosion events (e.g., Gausian?). Estimates have been made but they seem gross and if precise measurement is needed, new methods or vastly increased sampling will be needed. Roads (essential in most harvest operations) seem to produce the most sediment and thus raise debates about the sources of erosion ... the road, or the practice, or the whole operation. In some road work, wood excelsior erosion mats may be needed to produce the desired control (Grace et al. 1997). Most attention should be given to stabilizing fill slopes, especially within the first 6 months after road construction..
We do not believe that for practical, long-term land management, precise measurements are needed. (We may soon engage in detailed studies using modified soil traps within GIS-selected study sites.) We do, however, believe that the very best estimates of the relative differences among areas is needed. Stability can be observed; lack of major sediment movement can be observed, and such areas can be compared with other to assess relative DP. The concept that we propose using is simply to observe stable areas, then make others like them. We strive to minimize the difference between stable and unstable areas. We generally hold that any recent or easily seen erosion is undesirable. Accurately measuring differences denies the "integer-like" nature of erosion. It either exists or it does not; "a little" may quickly turn into "a lot". None is acceptable but the potential is lasting. We typically are striving to estimate how a change in land use (resulting from management decisions) would affect the DP at a site and throughout an area. Estimates should be gross for there are always four major factors or variables at work simultaneously:
The results of studies show that erosion does occur and even under the best conditions it enters into streams, ponds, or lakes. In the western US 66 to 90% of sediments come from streambeds and streambed erosion; of the rest (only about 17% of the total), 24% come from forested land, 22% from agricultural land, and 54 % from main channel banks. In the eastern US the land is generally more stable. Rational land owners paying taxes on land there know that the land surface, at least, is very important. Few people realize that one inch of soil over an acre weighs about 90 tons. When slight erosion occurs over a 1 acre garden on a hill side, (say 1/4 inch), then about 23 tons of soil are moved off of that garden. It goes somewhere! A point of view for the owner is that 23 tons of "anything" is probably worth something! It is at least worth the annual taxes paid per acre. It is worth much more in terms of crop production. Many statistics exist for the importance of topsoil in crop production (and obviously its loss). For example, erosion reduced corn production from 120 bushels per acre to 75 bushels following severe erosion. For the wildlands, few studies exist but one showed that for every ton of soil lost by erosion, timber production was reduced by approximately 3 cubic feet per acre at harvest.
Erosion is not very great in forests but it "does" occur and the total land base is critical to a smoothly functioning, stable land system. There is real loss of fertility (about $20 per acre per year per ton), loss of fertilizers and pesticides (estimated at $3 per acre per year) and, as if not enough, there is water pollution, stream sedimentation, and pond and reservoir filling ... all with high costs. See Table 1 and note that it takes a minimum of 30 years to create 1 inch of top soil (about 150 tons per acre) or 5 tons per year) while the maximum erosion policy of the US is 5 tons per acre in a year ... and in the US we now exceed that at 9 tons on farm land! Abiut forty million tons of silt and topsoil erode annually from the 25.5 million acres in Virginia.It is estimated that it takes about 32 years to remove the average inch of soil, 100 years to regenerate it. One half of the erosion occurs on 4% of the land. Major imporvements can be made by directing efforts to the worst problems.
| Table 1. Reported sediment losses from areas (Happ et al. 1940; Wharton et al 1982) | |
| Land Cover | Sediment loss (tons/acre/year) |
| Cotton field (downslope plowed) | 195.3 |
| Barren abandoned field | 160 |
| Cotton field (contour plowed) | 68.7 |
| Virginia average | 6.6 |
| National minimum (policy) | 5 (the national average is 9) |
| Bermuda grass field | 0.2 |
| Oak forest | 0.05 |
| 1 acre of dry soil, 1 inch deep, weighs about 90 tons. The weight is highly variable due to soil type, organic matter content, and bulk density. | |
| Table 2. Relative sediment losses from areas in different land uses, forests as the base. | |
| Land Use or Cover | Sediment loss factor |
| Forest | 1 |
| Grassland | 10 |
| Abandoned surface coal mine | 100 |
| Cropland | 200 |
| Harvested forest | 500 |
| Active surface mine | 2000 |
| Building construction | 2000 |
Lester Brown (Worldwatch Institute) said:
"In a world of continuously growing demand for food, land must be viewed as an irreplaceable resource ... In many countries, the stabilization of soils is such a vast undertaking that it will require a strong national political committment and a detailed plan of action ... Public support on the scale needed will not be forthcoming without a broader understanding of the costs to society of failing to act."
Allen (1982:3) observed that sediment in suspension is quite closely related to sediment in stream beds. He did not present the relationship but supplied tables from which a preliminary relationship could be devised. Grab samples from Virginia streams seem to us to be more stable and reflective of the watershed than sediment concentrations on a sampling day. Storm waters usually produce stream bank and channel sediments far in excess of overland sediments. Mass movements can take soils to bed rock and produce no sediments thereafter for many years (Helvey et al. 1985). We recommend grab-sample relationships be studied and used to characterize streams. Allen (1982:3) said that no one knows the absolute magnitude of errors to be expected for concentrations determined from suspended-sediment samples. Errors include those inherent to the sampler, the sampling conditions, the operator, and the laboratory analyses and the nature of mass movements after storms. Allen suggested, based on expected small increases in silt and clay in a vertical analysis, that the sediment data have "about two-place accuracy." In Illinois, observers found stream sediments were much greater when sampled in the rising part of a flow event than in the falling part.
Curtis observed that sediment in Kentucky streams influenced by mining increased sharply after mining. Half the total sediment yield occurred within the first 6 months, thereafter the yield had a "half-life" of about 6 months. Sediment concentrations are lower than when they are calculated as discharge-weighted averages. Sediment concentrations tend to increase faster than discharge.
Studies of soil erosion are abundant. Many have been concentrated on a universal soil loss equation, called the USLE (Wischmeier, W.H. C.B. Johnson, and B.V. Cross. 1971). It has been criticized and major revisions made to accommodate differences in rangeland, forest, and international soils. Mine soils (reconstructed), roadside soils, and organic soils have been especially difficult to model ( Rogowski et al. 1990). It is likely that work continues on its refinement.
The universal soil loss equation (USLE) is an estimator for the tons of soil eroding (sheet and rill only) annually off characterized agricultural fields. It has a long list of limitations but is the best tool available. A, soil loss, is estimated by RKLSCP, i.e., rainfall, soil, topography, vegetative cover, and management. R is the erosivity factor, K the soil erodibility factor, L is slope length, S is slope, C is cover, P a management factor index.
The USLE provides an opportunity to comment of several principles and concepts used within The Trevey. We believe that they are relevant throughout wildland management. The USLE has six components. If each were known fairly precisely, say a probability within 0.95 for each, then the probability of them all being correct is 0.73! Since 0.95 is absurdly high, consider some other probability, X, using the ralationship X6. For example, 0.76 is 0.12. This observation should create both new humility about mastering the ecosystem and thwart expectations for modeling accuracy beyond those that are reasonable.
We proposed studying GIS maps with transformations of single-factor pixel data based on the following (from Musgrave 1947 and later revisions from work with the USLE) suggesting that erosion is proportional to
The equation, quite sophisticated looking, has been criticized but it is all that is available. Each part has come at great cost. Imagine the cost of a nationwide network of rainfall measurement devices. Imagine the computer and staff costs of processing all records to get total annual precipitation and storm frequencies. The Rscore in the above equation for the area is drawn to an incredibly broad scale! Klopfer (1998) finally developed modeling for GIS applications to give precipitation estimates for 300-m square map grids. After all of the measurement to the tenth of an inch of rain and to the nearest large storm, the data are grossly grouped ... and a single value of R is used throughout each region. Some professionals may do more detailed local analyses, but I suspect that the majority is made from a general coefficient from a map. The opportunity for detailed, site-specific computation of R is now available in the modern geographic information system.
The R or Erosivity Factor Rainfall intensity data are difficult to collect and summarize. We use the modified Fournier's index(1960) which has been shown well correlated to R (0.89) within this region and others:
R = 6.86 
pi2 / p - 420
where monthly precipitation is squared and summed for all 12 months, then divided by P, the total annual precipitation.
There are some factors in the USLE over which the manager has control. R would not seem to be one. Using the general systems concepts, it is preferable to at least consider:
It is possible to determine experimentally the relative importance of variables. In a particular situation, (i.e., all inputs to the equation made) it would be possible to determine which is most important, a change of 1 percent in slope or a slope length of 10 percent. Those two options could be evaluated in terms of likely soil loss. While this can be determined algebraically here, the likely interactions in a larger system or just the size of most systems makes such a process inefficient. Several runs of a program can provide a site-specific answer.
Why not optimize? (in the case of erosion, the usual work is to find the minimum erosion for the least cost). In some cases, the designer can specify enough parts of a system (e.g., 4 of the 6 variables in the USLE), then do simple searching to pick the combination of variables that produce the lowest erosion (or within some proportion of the minimum, evidently zero). In most cases in a system with many variables, there are many ways to get the same answer or system performance. This end-combination is called equifinality. Understanding equifinality can:
Optimization in a dynamic system may be a big waste. For soil loss, many components are dynamic, especially C and P, but so too is S, and K may be changed in a short time. Because of the dynamics, the rates of change should be included for a planning period.
The variables for a map cell (an area for which erosion rates might be estimated) can be included within a GIS and soil loss estimated for large areas. The C value can be estimated from Landsat images Morton (1998). Where specific estimates cannot be made, a general value can be used (The Trevey is developed to receive continually the results of studies). One result is that relative values may be used (e.g., setting 1.0 as the cell with the maximum erosion and comparing all others to it), at least for mapping, developing planning aids, and assigning priorities. The maximums and minimums within an area are often all that are needed. For other purposes (e.g., estimating the rate at which a farm pond might fill with silt), detailed estimates are needed. Using gross estimates for an entire watershed has resulted in miscalculations of erosion, especially lake fill-in. More site-specific computation of A then summation, can lead to better estimates of area-wide soil losses and soil deposition.
The factor "soil loss", one item in an environmental information system is a multi-variable factor and requires six variables. Not "soil loss" but each of the factors plus one equation are what must be stored for ready-retrieval in a data base. When seen in this way, the data seem expanded, but in their more elemental form they can be used in many ways in many other models.
Should A be stored or just the equation? The GIS algorithms need A but only for study areas and temporary use. The answer is: A should be computed for each cell in a map, a file created, used, then erased. It can be re-created easily and after feedback applied. It should not become a permanent datum.
The K Factor
McIntosh et al. (1989) observed that the K factor of the equation, a measure of the ability of soil to withstand the destructive forces of rainfall and runoff, is perhaps the most important factor in designing practices to reduce erosion and yet is a factor very difficult to evaluate.
McIntosh et al. (1989) studied soils in Kentucky and found approximate K factors of topsoil 0.4, subsoil, 0.55 and mine spoil, 0.38. We have used these general factors in determining relative probable erosion along with the modified Fournier index.
Holzhey and Mausbach 1977 found that using descriptions in the soil classification system of the National Cooperative Soil Survey the variability in K is predicatble and thus soil taxonomy can be useful in estimating K.
Slope Classes
Actual slope percentage estimates were available in the GIS for all zeta units. Housana (1999) had previously computed slope effects for the GIS and his procedure was used. Average slope classes were studied using previously assigned values for the slope classes for the map of the world (Arnoldus 1977):
(We need to produce simple county level and project maps of slope, where slope is Slope1.3). This statistic needs to be studied separately from the USLE and its later revisions.
Slope Length
The maximum slope length was a standard 10 meters and assigned a value of xxxxx. For flat areas the loss is adjusted based on the equations of Murphree and Mutchler (1981).
P, The Management Factor P is taken as having the value of 1.0. Thus assigned, the index tends to suggest the potential erosion, thus a manager can evaluate or estimate the proportionate effect each (or any) suggested management or control practice might have on soil loss.
Foster and Wischmeier 1974 studied the LS or topographic factors of the USLE and suggested modifications for irregular slope surfaces.
Our work is grounded in past work on this equation. Rather than estimating the average tons of soil lost per year per acre (the typical output of the equation), we compute a relative amount of DP, a non-linear, relative index of DP in the watershed area. We use the alpha unit, 10 m x 10 m, as the size of the area for DP estimation. Definition of the boundary and conditions at the boundary can be useful in the future. The selected size and unit has roots in Landsat analyses and its size is justified elsewhere as the Alpha unit.. We create a dimemsionless number, the DPfor each alpha unit. The likely" erosion", the DP for every cell within the entire study area can be compared with reasonable precision and confidence to that in any other cell.
Curtis et al. 1977 used the following equation for estimating sheet-rill erosion (SD =sediment delivery ratio)on disturbed forest land
SD = 1 - (L / (50 + 4S)) Pwhere L is slope lenght from beginning of buffer strip to channel and S is percent slope of buffer strip
Herein, we are not discussing gully and rill erosion, only that called "sheet" erosion. We describe within a GIS region within each cell the general, perpetual, downward movement of particles. Rill and gully erosion are evident and need emergecy level attention. Knowledge of sheet erosion isolates potentials for massive rill and gully erosion, shows losses in tree and plant productivity, shows potential stream influences, suggests fossorial habitat change, and suggests forces in system dynamics" from the surface-geology-up "at least as influential as those "from the sun-down."
County or Large Area Erosion Score
See Gottschalk 1957 for estimating sediment yields from watersheds.
It may be possible to evaluate using GIS the Erosion potentials of a county, then to use this as the base and compare actual or on-going erosion based on the factors which people can manipulate (e.g., the covering of land with buildings, roads, etc.). The scoring can be based on averages or better, a summation of all alpha units
Sediments: The Results of Erosion
Meade (1969) said that modern sediment loads in the Atlantic-draining rivers are probably 4 to 5 times greater than they would be if the area had remained undisturbed by people.
Sediment yields are related to runoff in inches by the power curve
Y = 4.56 X 1.25 where Y is sediment yield in tons per acre and X is runoff in inches. (Lusby 1977)
Once most sediments or erosion products were caught behind large logs and in beaver dams. Both have disappeared and now sediments fill streams and ponds and harbors and of course the spaces behind peoples' dams. In one study, sediment storage behind obstacles can be 15 times more than that delivered to a stream point. Sediments are a major concern in streams for they influence fish spawning areas, reduce capacities of reservoirs, reduce nesting areas for fish, degrade wetlands, and, over time, simplify the bottom structure of ponds, lakes, and streams.
Perhaps more related to ponds and streams, it remains important to know the consequences of sediments to fish which are:
Specific effects:
Several procedures are used to estimate sediment delivered to streams and ponds. The typical one used is the USLE with an annual or seasonal delivery ratio. In 1979 it was found (Mildner and Boyce 1979) that there are big differences in seasonal patterns of sediment yield and erosion. Both the cover (C) and rainfall (R) factors in the USLE vary with season. Other factors are constant for an area. Either C or R or both together vary greatly in different areas. Mean monthly suspended sediments are likely to occur 8 to 10 months after the maximum predicted soil loss. This difference is due to overland sediment transport, blockages, and depositions. The USLE has no measure of upland deposition. Water available to move eroding particles plays a role in making a difference. Infiltration differs among areas affecting the amount of such water. If soils are "full of water" from previous rains, then rain events will make water available to move sediments. Effects of soil freezing and thawing are evident. In general, maximum water and sediment yield occurs in March and minimum sediment discharge in late summer and fall.
Sediment can be modified by the forestry practices selected. In one West Virginia study, the differences in Table 3 were observed and were largely related to skid road layout and construction. Surface erosion rates, highest immediately after harvest, decline rapidly.
| Logging Method | Maximum Turbidity (ppm) |
| Control watershed | 15 |
| Intensive "selection" harvest | 25 |
| Extensive"selection" harvest | 210 |
| Diameter limit harvest | 5200 |
| Commercial clearcut | 56,000 |
Precipitation
Barnett (1958) found that the maximum 60-minute intensity storm was the single factor (of many studied) that was most closely related to erosion. It accounted for 59.1 percent of the variation in erosion. Others have found the 30-minute maximum most highly correlated. No single factor adequately predicted erosion from variable intensity storms. The Fournier index uses the summation of the proportions of monthly precipitation to form an index of the K factor.
Stream Maps
We mapped the second-order and greater streams and assumed a small riparian sediment zone of 10 meters on each side of the stream. We believe this was conservative but saw no way to accommodate the extreme variability in stream sides (resistant rock walls to over-grazed pastures) over the xxx miles ( Km) of streams length within the area.) In Oregon, Anderson (1971) found that channel bank erosion contributed 54 to 55 percent of total sediment discharge from watersheds.
A Plan for Potential Soil Erosion Maps
Rural System Tracts maps and and individual county maps showing potential soil erosion are planned. The maps would show boundaries, major roads, and computed erosion potential based on best modified universal soil loss equations. That equation processes several variables including slope and slope length, land cover, precipitation and general soil characteristic.For special purposes (e.g., fishery interests) streams rather than roads will be displayed. Statistical summaries of the amounts of land (and proportions) in various categories of potential erosion may be more useful in some decisions than the maps.
Several zones (probably 3) will show relative risks of disturbance and costs of soil stabilization.
At cost, separate watersheds or small-area (approximately 500 acres) will be so mapped and analyzed.
The potential uses of such maps are:
References
Anderson, H.W. 1971. Relative contributions of sediment from source areas, and transport processes, p 55-63 in J. Morris, ed., Forest land uses and stream environment:proceedings of a symposium; 1970, Oregon State University, Corvallis, OR
Arnoldus, H.M.J. 1977. Methodology used to determine the maximum potential average annual soil loss due to sheet and rill erosion in Morocco. FAO Soils Bulletin 34, FAO of the UN, Rome.83pp.
Barnett, A. 1958. How intense rainfall affects runoff and soil erosion. Ag. Engr. 39(11):703-707
Bryan, R.B. 1968-1969. The development, use and efficiency of indices of soil erodibility Geoderma 2:5-26.
Carter, E., B. Rummer, and B. Stokes. 1997. Site disturbances associated with alternative prescriptions in an upland hardwood forest of Northern Alabama. Paper 975013, ASAE Annual International Meeting, Minneapolis, Mn.
Curtis, N.M. A.G. Darrach, and W.J. Sauerwein. 1977 Estimating sheet-rill erosion and sediment yield on disturbed western forests and woodlands. Woodland 10. USDA Soil Cons. Service, West Technical Service Center, Portland, Oregon 33p.
Furon, R. 1967. The problem of water. Faber and Faber Ltd, 180pp.
Foster, G.R. and W.H. Weischmeier. 1974. Evaluating irregular slopes for soil loss prediction. Trans. Amer. Soc of of Agricultural Engineers 17(2): 305-309.
Fournier, F. 1960. Climat et ´rosion. Presses Universitaires de France, Paris(Fournier, F. UNESCO, 7 Place Fontenoy, 75700 Paris, France)
Gottschalk, L.C. 1957. Problems of predicting sediment yields from watersheds. Trans Amer. Geophysical Union 38(6): 885-888
Grace, J.M. III, B. Rummer, and B.J. Stokes. 1997. Sediment production and runoff from forest road sideslopes. Paper 975019, ASAE Annual International Meeting, Minneapolis, Mn
Hassouna, K.M. 1997. Developing a natural resource database for geographic information system, Master of Forestry Thesis, Virginia Polytechnic Institute and State University, Blacksburg, Va. 81 pp.
Helvey, J. D., A.R. Tiedemann, and T.D. Anderson. 1985. Plant nutrient losses by soil erosion and mass movement after wildfire. J. Soil and Water Cons. 40(1):168-173.
Holzhey, C.S. and M.J. Mausbach, 1977. Uing soil taxonomy to estimate K values in the universal soil loss equation, in G.R. Foster ed. Soil erosion: prediction and control: proc. national conference on soil erosion; 1976 May 24-26 West Lafayette, IN Spec. Publ. 21 Ankeny, IA, Soil Conservation Soc. of America, 115-126.
Kochenderfer, J.N. 1970. Erosion control on logging roads in the Appalachians, USDA For. Serv. Res Paper NE-158, Upper Darby, Pa. 28pp.
Lull, H. and W.E. Sopper. 1969. Hydrologic effects from urbanization od forested watersheds in the Northeast. USDA For. Serv Res Paper NE-146, 31pp.
Lusby, G.C. 1977. Determination of runoff and sediment yield by rainfall simulation in T.J. Toy Erosion: research techniques, erodability and sediment delivery. Norwich England, Geo Abstracts Ltd 19-30.
McIntosh, J.E., R.I. Barnhisel, and J.L. Powell. 1989. Erodibility and sediment yield of reconstructed mine soil and spoil materials, Green Lands, 19(3) 24-27 (also Reclamation News and Views (Univ. Kentucky, Extension 7(2), 6pp.)
Morton, D. 1998. Landcover map of Virginia. M.S. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VA.
Murphree, C.E. and C.K. Mutchler. 1981. Verification of the slope factor in the univertsal soil loss equation for low slopes. J/ Soil and Water Cons.36(5):300-302
Musgrave, G.W. 1947. The quantitative evaluation of factors in water erosion -- a first approximation. J. Soil and Water Cons. 2(3):133-138
Reinhart, K.G., A.R. Eschner, and G.R. Trimble, Jr. 1963. Effects of streamflow of four forest practices in the mountains of West Virginia, USDA For. Serv. Res Paper NE-1, 79pp.
Rogowski, A.S. B>E> Weinrich, and R.M. Khanbilvardi. 1990. A nonparametric approach to potential erosion on mined and recalimed areas. J. Soil and Water Cons. 45(3):408-412
Stall, J.B. 1966. Man's role in affecting the sedimentation of streams and reservoirs, Proc. 2nd Annual Water Pes. Conf. 2:79-95.
Well and Wohlgemuth 1987. Sediment traps for measuring onslope surface sediment movement. PSW-393 USDA For. Serv. Pacific Southwest Forest and Range Exp. Sta, Berkeley, Calif. 6pp.
Wischeier, W.H. 1959. A rainfall erosion index for a universal soil loss eqquation. SSSA Proc. 23: 246-249.
Wischmeier, W.H. 1962. Rainfall erosion potential. Agr. Engr. 43: 212-215, 225.
Wischmeier, W.H. C.B. Johnson, and B.V. Cross. 1971. A soil erodability nomograph for farmland and conservation sites. J. Soil and Water Cons. 26:189-193.
Wischmeier, W.H. and D.D. Smith. 1978. Predicting railfall losses - a guide to conservation planning. USDA Agricultural Handbook No. 537.
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