How does sediment affect a river

A fundamental approach to prediction is needed to further improve baseline erodibility estimation. Fundamental approaches are also needed to predict temporal changes in soil erodibility in response to climatic and cropping and management influences.

Our understanding of and ability to characterize temporal changes in soil properties needs much improvement. Two specific areas that deserve attention are surface roughness effects on erosion and the effects of surface sealing on infiltration Nearing et al. New process-based erosion prediction technology will require an extensive data base to be effective.

Innovative techniques for developing model parameters will be required, including expert systems. The new technology also opens new opportunities for refining existing and developing new erosion control practices. Methods for using the technology as an interactive tool for conservation systems design are needed. To apply the new process-based technology, we need additional research directed toward developing techniques for modeling natural resource systems. Validation and sensitivity analysis of the new erosion models must be done.

We know erosion is highly variable in time and space. With the new simulation models, we can begin to address more fully temporal and spatial distributions of soil loss and sediment yield, confidence limits for our erosion estimates, and probabilities of meeting conservation goals with given management systems.

Larson and colleagues discussed the tools for erosion control options available for conservation planning. Among other things, they discussed the following Larson et al. Parallel to the developments in computer hardware have been developments in computer software such as geographic information systems GIS , digital elevation models DEM , and expert systems ES. Combining digital elevation models with soil maps should permit 3-dimensional views of soils on landscapes and display wedges of soil that could be lost as predicted by WEPP and WEPS.

However, these software tools are stressing the attribute data of present digital databases such as the soil map which is the base from which all models run. More robust methods of representing the variability of soil properties within polygons delineations must be developed, perhaps to present a probabilistic representation of the properties. This same approach could then be extended to fields or watersheds.

Combined with climatic probabilities, systems could be developed according to erosion risks and systems designed to control the risks similar to flood control systems. The analytical tools and expert systems must be able to integrate all ramifications of a resource management system such as the effects of erosion control practices and crop management systems on water quality and the soil ecosystem. These ramifications are so extensive. Inadequate knowledge of the transport of sediments of specific particle size ranges is a major limitation in predicting the fate of adsorbed agricultural chemicals.

Furthermore, investigators must be aware of the temporal and spatial variabilities of absorbed chemicals in upland environments in contrast to those in gullies and channels. Concentrations of adsorbed chemicals in upland areas are presumably high, whereas the sediments originating in gullies and channel peripheries conceivably have lower amounts of adsorbed chemicals.

A major problem with modeling upland erosion and sediment transport where concentrated flow begins involves the hydraulic transport process. Most sediment transport processes for upland erosion models are taken from those developed for stream flows. The WEPP model uses a mathematical relationship described by Yalin , as modified by Foster and colleagues , for nonuniform sediments.

It is doubtful whether investigators can make significant progress in this area simply by using a different sediment transport formula. Theory must be developed and experiments specifically related to the development of new transport equations must be conducted for shallow rill- and interrill-type flows. Significant advances in characterizing turbulent flows have recently been made by using flow visualization and other techniques, but those studies have not been extended to the shallow flow conditions common to areas with rill and interrill erosion.

More important than which sediment transport equation should be used to predict soil erosion is the issue of what transport capacity means and how it is used. In basic terms, transport capacity is a balance between the entrainment and the deposition rates of the already detached sediment in the flow.

The description of the entrainment process does not include a factor for cohesive soil forces, but considers only the gravity forces of the sediment that must be overcome for the particle to be lifted into the flow. The implicit assumption, then, for erosion of cohesive soils is that cohesive forces are negligible once the soil has initially been detached from the in situ soil mass. The technology currently used to predict wind erosion in the United States is based on variations of the wind erosion equation WEQ.

The technology uses erosion loss estimates that are integrated over large areas and long time scales to produce average annual values. In order to increase the range of conditions to which WEQ technology can be applied in the short-term, a revised wind erosion equation RWEQ is under development. The RWEQ embodies improved values for the. WEQ factors and is designed to calculate erosion during periods as short as a month. As with water erosion, the widespread availability of personal computers and new research has led to results that can be used to adopt flexible, process-based technologies to assess and plan conservation practices for wind erosion control.

Thus the USDA also has a major program under way to develop new wind erosion prediction technologies. The wind erosion model development program has two stages. In this second stage, the submodels of WERM will be reorganized to increase computational speed, data bases will be expanded in size, and a user-friendly input-output section will be added to make the technology of greater utility to users.

WERM is modular and consists of a supervisory program and seven submodels weather, hydrology, decomposition, crop, management, soil, and erosion. Four databases are needed—soils, climate, crop growth and decomposition, and management.

The submodels permit easy testing and updating with new data during development of the technology. Finally, as in the WEPP technology, extensive experimental work is being carried out simultaneously with model development and is devoted to delineating parameter values that facilitate application of the algorithm to both measured and unmeasured processes Hagen, ; Hagen et al. As the new wind erosion prediction technology becomes operational, considerable work will need to be done to develop the data bases required for its implementation over the wide range of environmental conditions that occur in the United States and worldwide.

As with water erosion, wind erosion prediction technology will require development of associated technologies such as expert systems, digital elevation models, and geographic information systems. Despite the advances that have been made in estimating and predicting erosion by wind and water, many questions related to data sources, methods of data collection and extrapolation, and data accuracy and reliability remain unanswered. Soil erosion and sedimentation research is a capital-intensive and time-consuming exercise.

Furthermore, extrapolation to the global scale on the basis of the limited data collected by diverse and nonstandardized methods leads to gross approximations. There is an urgent need for methods that can be used to increase the.

Current data are often collected with equipment developed decades ago, and such equipment is incompatible with modern computer simulation technologies. Finally, the historical erosion data bases are often developed from data for agricultural crops varieties, row spacing, management practices that are different from those planted today. Significant investments in personnel and funds that are in excess of those currently available will be required to overcome such problems.

From a policy standpoint, land managers and conservationists need to be able to 1 target those lands that are most vulnerable to erosion, 2 develop and apply treatments to these vulnerable lands, and 3 predict how changing land uses and conservation practices have an impact on erosion from the new land uses and conservation practices.

Finally, the financial implications of those relationships need to be estimated. With the current state of technology, the objectives described above will be expedited with further development of 1 geographic information systems, to permit assembly and input of the data needed by the evolving models; 2 the data bases required by the new erosion and sedimentation models; 3 fundamental sediment transport relationships appropriate for use in upland farming areas where runoff occurs in small channels and where the hydraulic roughness is large relative to the flow depth; and 4 transport relations that address the particle size ranges of sediments so that assessments of adsorbed agricultural chemical transports can be made.

Technologies that can be used to reduce the amount of sediment in surface water focus on two objectives: 1 improving farming practices to reduce erosion and runoff, and 2 improving stream channels and riparian vegetation to reduce erosion of stream banks and streambeds.

The effects of different types of plant cover, tillage, and cropping systems have been evaluated on erosion plots and watersheds and by using rainfall simulators and wind tunnels. Various types of conservation tillage practices have been developed and evaluated. They have been found to reduce greatly both water and wind erosion from land during intensive cropping. Scientists have also identified and quantified those soil and sediment characteristics that affect erosion rates and sediment pollution potential.

Farming technologies, in an effort to meet producer needs to preserve soil quality, are designing equipment to meet changing farming systems. This no-till drill has an adjustable down-pressure system that applies constant force on the openers for consistent penetration in varying soil conditions. In most farming systems, the critical period for erosion is the time after harvest but before a new crop is established.

During this period, soil is most exposed to wind and water, and, therefore, is most vulnerable to erosion. Efforts have been and are being made to develop farming practices that increase soil cover during this noncrop period Mills et al. Much effort has gone into the development of reduced-tillage systems that increase the amounts of crop residues to provide soil cover after the crop is harvested.

Many different systems of conservation tillage have been developed for different farming systems in different regions. Mannering and colleagues described five kinds of conservation tillage systems in use in the United States, including no-till or slot planting, ridge-till, strip-till, mulch-till, and reduced-till systems Table All of these systems are designed to cover at least 30 percent of the soil at the time of planting.

The soil is left undisturbed prior to planting. Planting is completed in a narrow seedbed about 2- to 8-cm wide. Weed control is accomplished primarily with herbicides. About one-third of the soil surface is tilled with sweeps or row cleaners at planting time.

Planting is completed on ridges usually 10 to 15 cm higher than row middles. Weed control is usually accomplished with a combination of herbicides and cultivation. About one-third of the soil surface is tilled at planting time. Tillage in the row may be done by a rototiller, in-row chisel, row cleaners, and so on.

Weed control is accomplished with a combination of herbicides and cultivation. The total surface is disturbed prior to planting. Tillage tools such as chisels, field cultivators, disks, sweeps, or blades are used.

A combination of herbicides and cultivation is used to control weeds. This system consists of any other tillage and planting system not described above that produces 30 percent surface residue cover after planting. Mannering, D. Schertz, and B. Jump to Navigation Skip to main content.

When soils erode, sediments are washed into waterways. Causes of sedimentation. What are the potential sources of sediments from land use activities? Here are some simple steps to minimise the effects of sediment on water quality and mahinga kai. Related content. New weapon in fight against invasive aquatic weeds. Media Release. Information and reports collected from the department's extensive State-wide monitoring network, which are provided free for water management, state development and research purposes.

Erosion is the transport by wind, water and ice of soil, sediment and rock fragments produced by the weathering of geological features. Sedimentation occurs when eroded material that is being transported by water, settles out of the water column onto the surface, as the water flow slows.

The sediments that form a waterway's bed, banks and floodplain have been transported from higher in the catchment and deposited there by the flow of water.

Estuaries are shaped by the mixing of water and sediments from both a waterway and the ocean, creating complex sedimentary environments. Waterways, and their estuaries, are dynamic landforms and deposited sediments will be moved again under the right conditions.

The channel size, shape and bed material change, both over time and in response to changes in water flow and sediment load. A channel is considered to be relatively stable when its water flow and sediment flux are in balance over time.

If there is a change in either of these factors, then the channel will adjust its slope, depth, width, meander pattern, bed composition and vegetation density accordingly.

While erosion and sedimentation are natural processes, inappropriate land-use and management practices in the catchment and direct damage to a waterway's channels or banks can accelerate these processes and stimulate adjustments in the channel see River Restoration Manual No. Erosion is also caused by activities that interfere directly with waterways, such as straightening or deepening channels for flood control, building dams, bridges or crossings, uncontrolled livestock access and removing riparian fringing vegetation.

Riparian vegetation plays a critical role in stabilising the sediments that form waterways. Living plants and large woody debris, such as fallen logs, slow water flow and reduce its erosive power, while root networks hold the sediments in place. See also Water Note 9 The importance of large woody debris. When waterway banks are cleared of their vegetation, banks are more vulnerable to erosion. Floods are more likely to cause waterways to change their course and form new meanders or flood channels.

Topsoil can also be stripped from the floodplain leading to the loss of valuable agricultural land. Excess sediment can be damaging to the ecological health of waterways and reduce their environmental, social and cultural values.

Mobilised coarse sandy sediment tends to accumulate in areas of slow-flow and may smother bottom-dwelling organisms and their habitats. Deep permanent river pools, that are valuable habitats for aquatic fauna and refuges for wildlife during summer and drought, may become filled by course sediments.

Large sediment accumulations can cause upstream flooding, or deflect the flow into the adjacent stream bank or even onto adjacent land, causing further erosion. In addition sediment can fill the deep permanent pools of rivers to ruin this critical refuge habitat. Increased fine sediment suspended in the water column turbidity reduces the penetration of light and therefore the ability of algae and other aquatic plants to photosynthesize and clogs the gills of fish.

Updated: December 10, Sediment is made up of soil particles that have been detached from the land by a process called erosion. In Pennsylvania, water is the primary cause for erosion, and sediment is often dislodged by rainwater and transported by stormwater runoff. Sediment can range in size from small, pea-sized gravel to tiny soil particles, less than 2 millimeters in diameter, and is present in both native soil and some materials used for building unpaved roads, driveways, and farm lanes.

Consequently, the source of sediment can be from bare soil from construction sites or farm fields, poorly maintained dirt and gravel roads, or degrading stream banks.

Any soil that is not protected from rainfall or runoff may be vulnerable to erosion and become a source of sediment pollution. Raindrops that fall from the sky have enough force to dislodge soil particles from uncovered soil. Rain that is not absorbed into the ground becomes stormwater runoff and flows downhill, building momentum and picking up unprotected sediment until it reaches a waterway such as a stream, river, lake, or pond.

Initially the shallow flow of water over the land is spread out in a process called sheet flow. But as stormwater continues to flow downhill, it can concentrate and form small channels called rills, or larger channels called gullies, that intensifies the force of stormwater runoff that detaches and transports additional sediment. Eventually, this sediment laden stormwater will reach our waterways, turning the affected surface water a muddy brown color.

Sediment pollution can also originate within a stream channel itself.