This appendix describes the process and results of the quantitative analysis conducted by the Bureau of Land Management (BLM) using the Water Erosion Prediction Project (WEPP) model for the Bighorn Basin Resource Management Plan (RMP) revision. The WEPP model was used to predict how management under each alternative would impact erosion in the Planning Area. WEPP simulates the conditions that impact erosion, such as the amount of vegetation canopy and soil water content. Specifically, the BLM used the WEPP model to calculate runoff amounts and erosion rates which were based on a series of parameters designed to estimate conditions in the Planning Area and model the impacts of management actions. The results of the analysis are described in the Soil and Water section of Chapter 4 of the Draft RMP and Environmental Impact Statement.
The WEPP model used by the BLM is a web-based interface designed by the United States Forest Service. The WEPP model can be accessed at: http://forest.moscowfsl.wsu.edu/fswepp/. Erosion rates are inherently difficult to predict, and the rates of erosion predicted by WEPP are within +/-50 percent. Despite this lack of precision, these rates are appropriate for comparing and analyzing impacts of the alternatives on the soil resource. Erosion rates were calculated for different resource programs using surface disturbance acreage figures as projected in Appendix T.
Two modules available in the WEPP interface were used by the BLM to estimate erosion rates: WEPP Road and Disturbed WEPP. The WEPP Road module was used to predict erosion rates for new roads built in the Planning Area over the life of the plan. Disturbed WEPP was used to estimate runoff amounts and all other erosion rates as a result of surface-disturbing activity in the Planning Area. WEPP allows users to predict erosion rates for numerous forest and rangeland erosion conditions. In order to estimate these conditions, the BLM used certain assumptions and input parameters for the analysis.
Climate parameters used by the WEPP model were developed using Worland, Wyoming precipitation data at 5,000 feet of elevation in order to represent the entire Planning Area. Both the Disturbed WEPP and WEPP Road modules are limited to four soil textures (clay loam, silt loam, sandy loam, and loam); a loam soil texture was used for all erosion predictions.
All WEPP erosion analyses were conducted using a 50-year simulation to represent the return interval.
The following parameters were used to simulate conditions in the Planning Area:
Slopes used in Disturbed WEPP: Upper slope 0 to 25 percent; lower slope 5 to 25 percent
Slope lengths used in Disturbed WEPP: 300 feet (standard length used for environmental analysis in the Planning Area)
Gradients used in WEPP Road: Road gradient 4 percent; fill gradient 30 percent; buffer gradient 15 percent
Lengths used in WEPP Road: Road length 200 feet; fill length 15 feet; buffer length 130 feet
Width used in WEPP Road: Road width 12 feet
Rock cover used in Disturbed WEPP and WEPP Road: 5 percent
In addition to simulating conditions in the Planning Area the BLM needed to model the conditions for short-term and long-term surface disturbances. Disturbed WEPP has eight vegetative treatment options available: 20-year-old forest, 5-year-old forest, shrub-dominated rangeland, tall-grass prairie, short-grass prairie, low-severity fire, high-severity fire, and skid trail. By adjusting cover parameters, these vegetative treatment options can be applied to a wide variety of vegetative communities and land uses. In order to simulate short-term and long-term disturbances, the following vegetation treatment and cover parameters were used:
Short-term disturbance: high-severity fire with zero percent cover
Long-term disturbance: short-grass prairie with 40 percent cover
The WEPP model, using these input parameters, calculated an initial average erosion rate of 4.165 tons per acre per year for short-term disturbances and a rate of 1.602 tons per acre per year for post-reclamation disturbances in the long term. Runoff amounts were calculated using the same parameters. The WEPP model estimated that areas impacted by short-term surface disturbance would experience 0.34 inches of runoff per year, and in the long term, average runoff would drop to .19 inches per year. The WEPP model estimated that with no disturbance there would be only trace amounts of annual runoff.
The WEPP Road module simulates road conditions using options for road design, road surface, and traffic level. Road design has four options including insloped, bare ditch; insloped, vegetated or rocked ditch; outsloped, rutted; and outsloped, unrutted. WEPP Road module options for road surface include native, graveled, or paved, and traffic level can be represented by a high, low, or no traffic option. For this analysis, the insloped, bare ditch road design, native road surface, and high traffic level were used. Using these parameters, the BLM calculated the erosion rate associated with road development to be 292.4 pounds per year per 200 foot long, 12 foot wide stretch of road.
Using these average erosion rates and the surface disturbance acreage figures as projected in Appendix T, the BLM calculated the erosion figures displayed in Table V-1.
Table V.1. Summary of Projected Tons of Erosion by Resource from BLM Actions
| Type of Disturbance | Alternative A | Alternative B | Alternative C | Alternative D |
|---|---|---|---|---|
| Mineral Resources – Leasable Oil and Gas (includes CBNG) | ||||
| Tons of Erosion from Disturbance in Short Term | 14,119 | 6,360 | 15,706 | 12,895 |
| Tons of Erosion from Disturbance in Long Term | 2,193 | 988 | 2,435 | 1,996 |
| Mineral Resources – Locatable Minerals | ||||
| Tons of Erosion from Disturbance in Short Term | 83,300 | 62,475 | 83,300 | 83,300 |
| Tons of Erosion from Disturbance in Long Term | 16,020 | 8,010 | 16,020 | 16,020 |
| Mineral Resources – Salable Minerals | ||||
| Tons of Erosion from Disturbance in Short Term | 8,330 | 3,332 | 8,330 | 7,497 |
| Tons of Erosion from Disturbance in Long Term | 2,563 | 961 | 2,563 | 2,163 |
| Mineral Resources – Other Solid Leasables | ||||
| Tons of Erosion from Disturbance in Short Term | 0 | 0 | 0 | 0 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Mineral Resources – Leasable Geothermal | ||||
| Tons of Erosion from Disturbance in Short Term | 0 | 0 | 0 | 0 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Fire and Fuels Management1,2 | ||||
| Prescribed Fire | ||||
| Tons of Erosion from Disturbance in Short Term | 166,600 | 83,300 | 333,200 | 166,600 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Mechanical Fuels Treatment | ||||
| Tons of Erosion from Disturbance in Short Term | 124,950 | 20,825 | 249,900 | 124,950 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Forest, Woodlands, and Forest Products | ||||
| Tons of Erosion from Disturbance in Short Term | 124,950 | 83,300 | 166,600 | 124,950 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Invasive Species3 | ||||
| Tons of Erosion from Disturbance in Short Term | 8,330 | 417 | 16,660 | 8,330 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Fish and Wildlife Resources | ||||
| Fisheries and Stream Enhancement Activities | ||||
| Tons of Erosion from Disturbance in Short Term | 0 | 379 | 0 | 0 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Watershed Enhancement Projects | ||||
| Tons of Erosion from Disturbance in Short Term | 3,253 | 6,506 | 1,629 | 3,253 |
| Tons of Erosion from Disturbance in Long Term | 370 | 740 | 266 | 370 |
| Health and Safety – Abandoned Facilities and AML | ||||
| Abandoned Facilities | ||||
| Tons of Erosion from Disturbance in Short Term | 833 | 833 | 833 | 833 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Abandoned Mine Lands Restoration | ||||
| Tons of Erosion from Disturbance in Short Term | 0 | 0 | 0 | 0 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Paleontological | ||||
| Tons of Erosion from Disturbance in Short Term | 833 | 1,041 | 833 | 833 |
| Tons of Erosion from Disturbance in Long Term | 80 | 160 | 80 | 80 |
| Renewable Energy – Wind Energy Development | ||||
| Tons of Erosion from Disturbance in Short Term | 833 | 833 | 833 | 833 |
| Tons of Erosion from Disturbance in Long Term | 80 | 80 | 80 | 80 |
| Rights-of-Way (ROW) | ||||
| Telephone and Fiber Optics | ||||
| Tons of Erosion from Disturbance in Short Term | 908 | 900 | 908 | 908 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Pipelines (Mineral and Water)4 | ||||
| Tons of Erosion from Disturbance in Short Term | 12,283 | 9,146 | 12,916 | 12,283 |
| Tons of Erosion from Disturbance in Long Term | 0 | 0 | 0 | 0 |
| Roads5,6 | ||||
| Tons of Erosion from Disturbance in Short Term | 5,217 | 3,261 | 12,307 | 5,217 |
| Tons of Erosion from Disturbance in Long Term | 2,608 | 1,632 | 6,154 | 2,608 |
| Powerlines | ||||
| Tons of Erosion from Disturbance in Short Term | 1,408 | 954 | 1,495 | 1,408 |
| Tons of Erosion from Disturbance in Long Term | 2 | 2 | 2 | 2 |
| Communication Sites | ||||
| Tons of Erosion from Disturbance in Short Term | 42 | 42 | 42 | 42 |
| Tons of Erosion from Disturbance in Long Term | 16 | 16 | 16 | 16 |
| Other Facilities7 | ||||
| Tons of Erosion from Disturbance in Short Term | 875 | 396 | 970 | 875 |
| Tons of Erosion from Disturbance in Long Term | 336 | 152 | 373 | 336 |
| Comprehensive Trails and Travel Management | ||||
| Motorized Vehicle Use | ||||
| Tons of Erosion from Disturbance in Short Term | 5,135 | 11,562 | 53,758 | 24,240 |
| Tons of Erosion from Disturbance in Long Term | 1,338 | 1,711 | 20,401 | 6,313 |
| Recreation | ||||
| Recreational Site Development | ||||
| Tons of Erosion from Disturbance in Short Term | 1,456 | 9,384 | 53,374 | 1,456 |
| Tons of Erosion from Disturbance in Long Term | 560 | 3,609 | 20,530 | 560 |
| Livestock Grazing | ||||
| Spring Development | ||||
| Tons of Erosion from Disturbance in Short Term | 21 | 10 | 42 | 21 |
| Tons of Erosion from Disturbance in Long Term | 2 | 1 | 8 | 2 |
| Pipeline Development | ||||
| Tons of Erosion from Disturbance in Short Term | 250 | 125 | 500 | 250 |
| Tons of Erosion from Disturbance in Long Term | 4 | 2 | 8 | 4 |
| Reservoir/Pit Development | ||||
| Tons of Erosion from Disturbance in Short Term | 167 | 83 | 333 | 167 |
| Tons of Erosion from Disturbance in Long Term | 8 | 4 | 16 | 8 |
| Fence Development | ||||
| Tons of Erosion from Disturbance in Short Term | 1,041 | 521 | 2,083 | 1,041 |
| Tons of Erosion from Disturbance in Long Term | 16 | 8 | 32 | 16 |
| Well Development | ||||
| Tons of Erosion from Disturbance in Short Term | 21 | 10 | 42 | 21 |
| Tons of Erosion from Disturbance in Long Term | 2 | 1 | 3 | 2 |
| Reservoir Maintenance Development | ||||
| Tons of Erosion from Disturbance in Short Term | 42 | 21 | 83 | 42 |
| Tons of Erosion from Disturbance in Long Term | 3 | 2 | 6 | 3 |
| Cumulative Disturbance | ||||
| Total Tons of Erosion from Disturbance in Short Term | 568,166 | 307,873 | 1,023,686 | 585,214 |
| Total Tons of Erosion from Disturbance in Long Term | 25,167 | 17,432 | 66,555 | 29,546 |
| 1 Acres disturbed by mechanical fuels treatment and prescribed fire will naturally be reclaimed within 5 years. Therefore long-term erosion will be zero. 2 Includes range enhancements and other wildlife habitat restoration actions. 3 Surface disturbance activities resulting from invasive species projects will be naturally reclaimed within 5 years. Therefore long-term erosion will be zero. 4 Actions would likely be mostly oil and gas related, including carbon dioxide and energy pipeline. 5 Calculated using WEPP Road module and parameters. 6 Approximately 50 percent of roads would be oil and gas related, with the rest coming from local demand. 7 Actions would likely be mostly oil and gas related. AML Abandoned Mine Land BLM Bureau of Land Management CBNG coalbed natural gas WEPP Water Erosion Prediction Project | ||||