SEDIMENT DAMAGES AND RECENT TRENDS IN THE UNITED STATES

Jerry M. Bernard[1] and Thomas A. Iivari²

ABSTRACT

  In the United States, cropland erosion has decreased by an estimated one billion tons or 42 percent for the period 1982 to 1997 (USDA NRCS, 1998) through erosion reduction provisions of the Food Security Act of 1985 and the ongoing soil conservation programs administered by the United States Department of Agriculture’s Soil Conservation Service (USDA-SCS), which became the Natural Resources Conservation Service (USDA-NRCS) in 1997.

  The U.S. Geological Survey has measured suspended sediment loads at stream gages from 1980 through 1989 and showed primarily decreases of from 1 to 12 percent for most regions and increases for only three regions, ranging from 2 to 12 percent.

  A Reservoir Sediment Information System (RESIS) was created so that decades of data on reservoir sediment deposits could be evaluated (Atwood, 1994; Steffen, 1994; Atwood and Steffen, 1994).  The results of analyses show a major increase in unit-area sediment deposition rates during the period 1970 through 1985, which may be attributable to increased cropland acreage, a switch from diversified farming to intensive monocultured crops, with widespread adoption of soybeans.  The most recent measured rates show that 25 percent of the United States reservoirs would be at least half-filled with sediment by 2018, although there is a significant data gap since 1985.  Relatively few reservoirs were surveyed since 1985 due to lack of funding priority and increased survey labor costs. 

Key Words: Cropland erosion, Soil conservation program, Suspended sediment, Reservoir sediment information system

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WINTER RUNOFF AND EROSION ON NORTHWESTERN USA CROPLAND

D.K. McCool[2], C.D. Pannkuk[3], K.E. Saxton[4], P.K. Kalita[5]

ABSTRACT

  Crop management is an important factor in preventing winter runoff and erosion on non-irrigated cropland of the Northwestern Wheat and Range Region of the U.S.  Much of the total annual runoff and soil loss from agricultural land in the region occurs as a result of rain and snowmelt on frozen and thawing soil.  Quantifying these effects is important for hydrologic model development and calibration, and for designing and selecting crop managements to prevent erosion.  An experimental setup with several runoff plots under a number of crop management systems was installed at the Palouse Conservation Field Station in the fall of 1978.  Data were collected from natural events on the replicated plots for 13 years.  Frost, thaw, and snow depths were measured on the plots regularly.  Runoff and sediment samples were obtained from collection tanks on a daily or event basis.  Data were analyzed and events were separated into frozen soil, thawing soil, and non-frozen soil.  Crop management had a substantial effect on infiltration and runoff, but an even more significant impact on soil erosion.

Key Words: Crop management, Erosion, Runoff, Winter hydrology, Frozen soil, Thawing soil

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RUNOFF-ENERGY FACTORS FOR

MUSLE SEDIMENT-YIELD MODEL FOR SURFACE MINES

James V. Bonta[6]

ABSTRACT

  The Modified Universal Soil Loss Equation (MUSLE) is often used for sediment-yield estimations in surface mines for design and impact evaluations.  However, it is not known if the widely-used runoff-energy factor of MUSLE is appropriate, or if its parameters are the same for surface mines as for agricultural watersheds from which MUSLE was developed.  Suspended-sediment data from three experimental watersheds in Ohio (approximately 10 - 20 ha), subjected to near complete disturbance due to mining and reclamation, were used to investigate five alternate runoff-energy factors in the MUSLE sediment-yield model for use in surface mines.  The evaluation led to the selection of the generalized model form, a (runoff volume x peak flow rate)b, as the best choice among models investigated.  Exponent b was greater than the widely-used value of 0.56, ranging from 0.68 to 1.10.  Parameter b was dependent on whether mining- or reclamation-related watershed activities were predominant.  The original Williams (1975) model fit the data least well of the five energy factors studied.

 Key Words: MUSLE, USLE, Surface mine, Hydrology, Sedimentation, Sediment yield, Erosion, Drastic land disturbance, Disturbed land, Curve number, Water quality

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SEDIMENT TRANSPORT PROCESSES IN AGRICULTURAL WATERSHEDS

Roger A. Kuhnle, Sean J. Bennett, Carlos V. Alonso, Ronald L. Bingner, and Eddy Langendoen[7]

ABSTRACT

  Determination of the total sediment load at selected points in agricultural watersheds is important for evaluating the status of a land area.  Total sediment load data allows the identification of problem areas where the land surface is eroding at rates too high to allow sustainable agriculture and/or is producing sediment at rates such that aquatic organisms in nearby streams will be adversely affected.  The development of effective sampling strategies and accurate computational models requires accurate information on the processes by which sediment is transported.  Researchers at the National Sedimentation Laboratory are developing and testing new methods to measure and predict sediment transport.  These new methods are providing an improved understanding of the processes involved in sediment transport and are leading to important advancements in the measurement and prediction of sediment transport.

Key Words: Total sediment load, Sediment transport, Sustainable agriculture, Water quality, Agricultural watershed

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EROSION RATES ON UPLAND AREAS IN THE MIDSOUTH USA

 K. C. McGregor, R. F. Cullum, and C. K. Mutchler[8]

ABSTRACT

  This study documents the erosivity of rainfall, the high erodibility of soils, and reduction in annual and storm soil loss rates by conservation tillage at Holly Springs, Mississippi. Holly Springs is in northern Mississippi in the Midsouth United States. Rainfall characteristic data and runoff data were examined for single storms and for cultivated fallow conditions for Loring (Typic Fragiudalfs) and Lexington (Typic Paleudalfs) soils during 1963 through 1968 using data from 135 single storm events. Rainfall erosion index (EI) was the best single estimator among those rainfall characteristics studied to estimate soil loss during the storms. Soil losses from a cultivated fallow plot were greater than 20 t/ha during each of 10 storms.  Average annual rainfall of 1314 mm and rainfall erosion index of 6315 MJ mm (ha h)-1 during 1958 to 1976 for the 303-square kilometer Pigeon Roost Watershed near Holly Springs, Mississippi illustrated the high erosivity of rainfall. Conservation tillage cropping systems for corn (grain and silage), soybean, cotton, and sorghum from 1974 to 1990 at Holly Springs effectively controlled erosion, especially as compared to conventional-till.  Soil losses from agricultural land previously under conventional-till were dramatically reduced. Cropping and management factor (SLR) values derived from selected large storms provided good estimates of annual SLR values for use in the universal soil loss equation.

Key Words: Erosivity, Conservation tillage, Rainfall characteristic data, Soil loss, Conventional till, Universal soil loss equation, Erosion index (EI)

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MANAGEMENT AND SUBSURFACE EFFECTS ON RUNOFF

AND SEDIMENT YIELD FROM SMALL WATERSHEDS

Dabney, S. M.[9], R. L. Raper[10], L. D. Meyer1 and C. E. Murphree1

ABSTRACT

  Research on erosion plots and small watersheds with upland loessal soils containing hydraulically-controlling subsurface horizons showed that as scale increases so does the amount of annual runoff.  The amount of runoff from 2 to 3 ha watersheds was twice that from 0.008 ha plots. However, the ratio of runoff from watersheds to plots was 3.0 from Dec through March, and only 1.7 during the rest of the year. Georeferenced penetrometer resistance measurements documented the presence of restrictive layers within 1 m of the soil surface.  Observation wells showed the presence of spatially varying perched water tables.  We propose that the runoff difference between plot and watershed scales was related to the increasing importance of hydraulically restrictive subsurface horizons, especially during the winter months. Water infiltrated into linear backslope areas that the plots represent may converge in concave toe slopes areas, creating wetter antecedent conditions and return flow contributions to surface runoff.  No-till management reduced sediment production by about 90% on plots and by at least 95% on watersheds; no-till reduced runoff about 10% from both plots and watersheds in this study.  Conservation management affected hydraulic resistance at the soil surface rather than the permeability of deep restrictive layers.

Key Words: Erosion plot, No-till management, Conservation management, Runoff, Sediment yield

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SEDIMENT TRAPPING BY VEGETATIVE FILTER STRIPS

 Chang-xing, Jin and M. J. M. Römkens[11]

ABSTRACT

  Sediment depositions in vegetative filter strips (VFS) were studied in a laboratory flume with simulated VFS. Results showed that VFS trapped sediment mainly through a reduction in the flow velocity and thus in the sediment transport capacity. Deposition in the VFS first took place at the entrance of the VFS, then extended down into the VFS and up to the approach channel above the VFS. The deposition rate decreased until a steady state was reached. Changing the flow rate or sediment concentration caused a new increase or decrease in the deposition rate. Deposition efficiency of the VFS decreased as sediment accumulated. Flume slope and sediment size composition greatly affected the deposition efficiency.  Flow rate had a minor effect on the deposition efficiency, while sediment concentration hardly affected the deposition efficiency. Most of the sediment deposited was larger than 150 mm in size. Over 80-90% of the sediment was deposited in the approach channel above the VFS and in the upper half of the VFS. Deposition moved downstream as the flow rate increased and the sediment size became smaller.

Key Words: Vegetative filter strips, Sediment deposition, Experimental study

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UNIQUE ASPECTS OF MODELING IRRIGATION-INDUCED SOIL EROSION

 .L. Bjorneberg[12], D.C. Kincaid¹, R.D. Lentz¹, R.E. Sojka¹ and T.J. Trout[13]

ABSTRACT

  The mechanics of soil erosion from irrigated and rainfed lands are similar. Soil particles are detached, transported and deposited. However, there are some systematic differences between irrigation and rainfall erosion. Electrolyte concentrations in irrigation water, for example, are almost always greater than in rain water. Differences between rainfall and irrigation are more prominent for surface irrigation than for sprinkler irrigation. For instance, rainfall wets the soil before runoff begins, but water initially flows onto dry soil in irrigation furrows. Furthermore, furrow flow rate decreases with distance and increases with time, while the opposite tends to occur with rainfall. For sprinkler systems, travel direction and slope aspect interact, so runoff can flow within the irrigated area or from the irrigated area onto dry or wet soil. Thus, a sprinkler-irrigation erosion model must consider both the rainfall-runoff situation and the furrow flow situation. These differences in soil and water interactions must be considered before computer models can accurately simulate irrigation-induced soil erosion.

 Key Words: Soil erosion, Irrigation, Electrolyte concentration, Furrow flow, Runoff, Modeling

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SEDIMENT YIELD AND HYDROLOGY IN NORTHWESTERN RANGELANDS

Charles W. Slaughter[14] and Frederick B. Pierson[15]

ABSTRACT

  Much of the rangeland of northwestern North America occupies highly variable, high-relief terrain with steep slopes, contrasting aspects, strong elevation gradients and diverse local climates. Rangeland erosion and sediment production are major concerns in northwestern natural resource management. Seasonal variability in precipitation, streamflow and energy available for sediment mobilization and transport is pronounced in northwestern rangeland catchments; thus,  runoff and sediment yield exhibit high spatial and temporal variability.  The sediment regime of such watersheds cannot be characterized by simple indices or short-term local measurements.  A long-term experimental rangeland watershed demonstrates the need for sustained measurement programs over a range of catchment scale and topographic position, to determine actual patterns and rates of runoff and sediment yield.  More research is needed to identify and quantify the pathways of sediment from initial detachment to temporary storage and subsequent remobilization and transport through the stream system.  The role of extreme hydrologic events in accelerated landscape erosion, remobilization of stored sediment, and interaction with dynamic channel-forming processes in rangeland streams remains inadequately defined.  It is necessary to better determine landscapes and channels susceptible to treatment to reduce stream sedimentation, and to populate and parameterize simulation models for rangeland catchment/stream systems.  Such information is required to address emerging issues of riparian zone and water quality management in northwestern rangelands.

Key Words: Sediment yield, Rangeland, High-relief terrain, Remobilization, Stream system, Water quality management, Riparian zone

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OPTIMAL MODE OF SEDIMENT TRANSPORT BY SHALLOW FLOWS IN UPLAND AREAS

D. PAL¹, S. N. PRASAD[16] and M. J. M. RÖMKENS[17]

ABSTRACT

  Soil erosion and sediment movement are serious problems of upland areas of a watershed. In these areas, most of the eroded sediment is transported in overland flows; either in shallow or in concentrated flow situations. These flows are usually associated with nonlinear waves, generally known as “roll waves” in the hydraulic engineering literature. Under suitable hydraulic conditions, these waves contain a significant fraction of the total kinetic energy of the flow regime. Hence, the waves act as the primary energy source in transporting eroded sediment in shallow flows on steep slopes. Our laboratory experiments under controlled condition suggest that modulation of the roll waves is effected by the addition of increasing amounts of sediment in the flow. The optimal condition in the sediment transport rate is reached when most of the available wave energy is consumed in carrying the sediment. A related set of experiments on gravitational flows of dry granular material show that the evolving scales of sediment waves are intrinsic to the transport mechanism of the solid phase.

Key Words: Upland areas, Sediment transport, Shallow flows, Wave modes, Granular organization.

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