Sediment from the Researcher Perspective (2-D Processes)
In InterWET, the sediment from the researcher perspective gives a two
dimensional view or process level view of groundwater using the USLE Method.
1. Erosion Calculator.
Click the button below to load the Erosion Calculator.
The calculator can be resized to fit your screen.
This calculator determines erosion or detached sediment for a single storm. There are many factors which impact erosion. The first factor is the size or area of the site of interest. The second factor involves the idea of raindrop impact energy. When a raindrop falls from the sky and hits the ground, the surface soil adsorbs the energy. Erosion occurs when the energy is powerful enough to detach soil. The amount of energy the rainfall of a particular storm has depends in the frequency of the storm and the location. Certain areas of the country frequently have higher energy storms than other areas. A third factor is the soil texture. Just as soil texture influence water infiltration, it also impacts how easily soil can be detached. A fourth factor is the influence of the arrangement of the land surface or the topography of the site of interest. The steepness and the length of distance down the slope both will affect erosion. The final factor is land cover. Erosion levels depend on how much of the bare soil is vulnerable to raindrop impact. The erosion calculator will show how each of these factors affect the erosion.
2.Effects of Area, Storm Frequency and Location
Set the Land Area to 100 acres, Storm Frequency to Frequent, Location to Central Lowlands, Soil Texture to Sandy Loam, Length along slope to Moderate, and Slope to Moderately Steep. For Land Use and Land Cover, first select Residential, and then go down in the Residential Box and select Established Grass. Then hit the calculate button.
The calculator predicts around 150 tons or 1.5 tons/acre of erosion or sediment detached for this one storm. This value only reflects how much sediment was detached from the land surface, not the amount delivered to the nearest stream. The amount of detached soil which is delivered to streams varies between 5% to 30%.
Now change the land area to 10 acres and recalculate. Notice the proportional relationship between land area and detached soil.
Now experiment with the storm frequency and location.
The more infrequent the storm, the higher the raindrop energy and the higher the erosion. However, not every infrequent storm is created equal. In the desert, a very infrequent storm causes less erosion any storm in all other locations except the Rocky Mountains. The worse storms are the very infrequent hurricanes that hit the Atlantic and Gulf Coasts.
3.Effects of Soil Texture
Select a set of values and experiment with different soil textures.
Notice the erosion reaches a peak for silty clay loam soils, but decreases for clays. Larger textured soils like sands are more difficult to erode, because of their large particles. Clays are also difficult to detach because these soil tend to form large clumps called aggregates. Silty clay loam soil does not have many large sand particle or aggregates, so it is easiest to detach.
4.Effects of Slope and Length along the Slope
One would expect steeper areas to have more erosion. Experiment with different slopes to confirm this.
The idea of length along the slope is harder to understand. First use the calculator to experiment with different lengths. Notice that there is more erosion for longer lengths. Image one is comparing two fields with the same area. One field has a short length along the slope (short and wide). The other field has a long length along the slope (tall and thin). Actual past experiments have found that the tall and thin field would tend to have more detached sediment than the short and wide field.
5.Effects of Land Use and Land Cover
Land cover can dramatically change the amount of erosion. First, select a set of values and a Residential Land Cover with Established Grass. Under the Residential Box, compare all four options.
Notice that over 10 times as much of erosion occurs from scraped bare on construction sites as established grass.
Now change the Land Cover to Agricultural, Row Crops, Conventional Tillage, and Up and Down Slope. This is considered the highest erosion producing combination from agriculture. Yet, the erosion is almost half of the scraped bare during construction erosion.
While still using Agriculture Land Cover, experiment with the different crop, tillage implement, and tillage direction options. Notice that the use of No-Till Plows and Tillage with the contour, also known as Best Management Practices, can greatly reduce the erosion.
Finally, experiment with the Wooded Land Covers. Notice how low the erosion values are from these land areas.
Summary
Erosion or Detached Sediment Increases:
1. In larger areas,
2. For more infrequent storms,
3. In areas of the country that receive "stronger" storms,
4. For soils with smaller textures, except for clays which form larger aggregates,
5. For areas with steeper slopes and longer lengths along the slope,
6. For land covers that provide less protection of bare soil or vegetation to hold the soil.
More Details?
Check out the on-line dissertation on InterWET for more information behind the theory and techniques used to make this calculator.
Questions or Problems? Let me know at parson@andassoc.com.
Last revision 9/9/01.
Created by Shane Parson, Copyright 1999.
