Metadata: Identification_Information: Citation: Citation_Information: Originator: Jim Wickham Publication_Date: 1998 Title: soil_loss Edition: 1 Geospatial_Data_Presentation_Form: Map Publication_Information: Publication_Place: Norris TN Publisher: Tennessee Valley Authority Description: Abstract: Important Note: Due to a computer failure, these data were re-created after the Mid-Atlantic Atlas was published. Since the "r factor" was created by interpolating off an erosivity isoline map, the data may vary from the original and therefore these results may be different from those published in the atlas. The Universal Soil Loss Equation (USLE) is designed to predict long-term average annual soil loss. It was developed primarily for agricultural situations, but has been more widely applied. The equation is based on the concept that rainfall patterns across a region set up characteristic erosion conditions that are mitigated or exacerbated by soil type, slope, and land cover conditions. The basic equation is: A = R * K * LS * C * P, where (1) A is long-term average annual soil loss (tons/acre/year), R is the rainfall erosivity factor, K is the soil erodibility factor, LS is the length-slope factor, C is cover and management factor, and P is the support management factor (e.g., strip cropping, buffer-strip cropping). Over the eastern U.S. R ranges between 75 and 450, and the other factors typically range between 0 and 1. Conceptually, USLE estimates soil erosion as a reduction in potential erosion from rainfall due to soil, slope, and land cover characteristics. For example, A for a corn-soybean rotation system in Indiana is: A = 200 * 0.37 * 0.93 * 0.12 * 0.5 = 4.1 (tons/acre/year). « (K) (LS) ¨ (P) Based on this example the rainfall erosion potential of 200 tons/acre/year is reduced to 4.1 because of the soil, slope, and cover and crop management characteristics. Purpose: These data were created as part of a regional assessment of landscape conditions in the mid-Atlantic region (SFR 3) (Jones et al., 1997). Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: Ending_Date: Currentness_Reference: Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -84 degrees West East_Bounding_Coordinate: -74 degrees West North_Bounding_Coordinate: 43 degrees North Keywords: Theme: Theme_Keyword_Thesaurus: None Theme_Keyword: USLE Theme_Keyword: Runoff Theme_Keyword: Landcover Theme_Keyword: sediment Theme_Keyword: Agriculture Theme_Keyword: erosion Place: Place_Keyword_Thesaurus: None Place_Keyword: United States Place_Keyword: Standard Federal Region III Access_Constraints: None Use_Constraints:None Point_of_Contact: Contact_Information: Contact_Person_Primary: Bruce Jones Contact_Person: Contact_Organization: EPA Landscape Ecology Division Contact_Address: Address_Type: mailing and physical address Address: U.S. Environmental Protection Agency, Box 93478 City: Las Vegas State_or_Province: Nevada Postal_Code: 89193-3478 Contact_Electronic_Mail_Address: jones.bruce@epamail.epa.gov Data_Set_Credit: MRLC Landcover: Native_Data_Set_Environment: These data are presently stored in ARC/INFO format. Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: none Logical_Consistency_Report: none Completeness_Report: Complete Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: None Source_Information: Source_Citation: Citation_Information: Other_Citation_Details: Jones, K.B., Riitters, K.H., Wickham, J.D., Tankersley, R.D., O'Neill, R.V., Chaloud, D.J., Smith, E.R., and Neale, A.C. 1997. An Ecological Assessment of the United States Mid-Atlantic Region: A Landscape Atlas. EPA/600/R97/130, U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. Source_Information: Source_Citation: Citation_Information: Other_Citation_Details: Process_Step: Process_Description: CALCULATION OF USLE FACTORS IN MID-ATLANTIC USING GIS Application of USLE is experiencing a resurgence because of the growth in Geographic Information Systems (GIS) and digital data. Length-slope factors (LS) can be estimated from Digital Elevation Model (DEM) data, soil erodibility factors (K) are estimated as part of the Soil Conservation Service (SCS) digital STATSGO soils data base, and cover factors ¨ can be estimated for land cover derived from satellite data. We used these data to estimate soil loss using USLE. C was estimated as the middle or average value from a range of values derived from different land cover types (see below). Land Cover Range of Values Value Pasture 0.003 0.36 0.40 0.42 0.45 0.22 Row Crops 0.06 0.07 0.18 0.19 0.26 0.29 0.69 0.78 0.31 Forest 0.0001 0.009 0.0045 Barren 0.66 1.30 0.98 LS was estimated using 90 meter DEM data according to the following equation: LS = (L/72.6) ^^ m * (65.41 sin^^2 A + 4.56 sin A + 0.65), where L is slope length in feet, m is an exponent factor based on percent slope (e.g., m = 0.5 if slope > 5%, 0.4 for slope 3.5-4.5%, . . .), and A is the slope in degrees. The following Arc AML was used to estimate LS from DEM data. K factors were taken from STATSGO soils data. The basic mapping unit of STATSGO soils is associated phases of soils series. Each soil series typically has a unique K factor. The K factor for each mapping was calculated as a weighted average. For example, the K factor for mapping unit VAO1O was calculated as (see table below): K = {(0.16 * 0.43) + (0.76 * 0.37) + (0.01 * .32) + (0.07 * 0.20)} = 0.396 MUID COMPNAME COMPPCT KFACTOR VAO1O Comus 4 0.43 VAO1O Kinkora 12 0.43 VAO1O Cordorus 60 0.37 VAO1O Lindside 1 0.32 VAO1O Hatboro 16 0.37 VAO1O Craigsville 7 0.20 The support management factor only applies to the land cover type, row crops. A constant management factor of contour strip cropping was assumed. Numbers ranged between 0.5 and 0.9 based on percent slope. R values are taken from the isoline map ("erosivity"). They vary some across the Mid-Atlantic Region. A table of R values by watershed would be used for the entire region. RESULTS AND CONSIDERATIONS Soils loss values for the example watershed range from 0 to 1130 (tons/acre/year). However, 68 percent of the pixels are either 0 or 1. Most of this watershed is forest, so the distribution of results is not surprising (i.e., 200 * .0045 = 0.9). Based on a very cursory look, most of the extremely high values seem to be associated with pasture and barren land cover categories. There is one important consideration. While the factors K, C, and P all reduce R because they are less than one, LS can amplify R when slopes are steep. For slope lengths of 300 feet (i.e., 90 meter pixels), LS becomes greater than 1.0 at a slope of 6 percent (1.17), and reaches 7.07 at a 20 percent slope. Thus, on a forested ridge at 20 percent slope, A could be nearly 6.4 (not accounting for K) (A = 200 * .7.07 * 0.0045 = 6.4). This is nearly equivalent to the amount of soil loss from an agricultural field on a 1 percent slope (without K) (A = 200 * .31 * .141 = 8.75). The impact of the LS factor in the Mid-Atlantic may be that forested ridges in the Ridge-and-Valley pop up as having a high erosion potential. This effect does turn up in the example watershed. Since USLE was originally calibrated for agricultural areas, it is probably best to restrict its application to pasture and row crop classes. Source_Used_Citation_Abbreviation: Source_Produced_Citation_Abbreviation: Process_Date: Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: raster Raster_Object_Information: Raster_Object_Type: Row_Count: Column_Count: Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Lambert_Azimuthal Lambert_Azimuthal: Radius of Sphere of Reference: 6370997 Longitude_of_Central_Meridian: -100 0 0 Latitude_of_Projection_Origin: 45 0 0 False_Easting: 0.0 False_Northing: 0.0 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: Row and column Coordinate_Representation: Abscissa_Resolution: Ordinate_Resolution: Planar_Distance_Units: meters Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: Entity_Type_Definition: Entity_Type_Definition_Source: ARC/INFO Attribute: Attribute_Label: Value Attribute_Definition: Soil loss in tons/acre/year Attribute_Definition_Source: ARC/INFO Attribute_Domain_Values: Range_Domain: Range_Domain_Maximum: Range_Domain_Minimum: Attribute_Measurement_Frequency: None planned Attribute: Attribute_Label: Attribute_Definition: Attribute_Definition_Source: ARC/INFO Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: Range_Domain_Maximum: Attribute_Measurement_Frequency: None planned Overview_Description: Entity_and_Attribute_Overview: Entity_and_Attribute_Detail_Citation: Not available Distribution_Information: Distributor: Contact_Information: Contact_Person_Primary: Contact_Person: Bruce Jones Contact_Organization: EPA Landscape Ecology Division Contact_Address: Address_Type: Address: U.S. Environmental Protection Agency, Box 93478 City: Las Vegas State_or_Province: Nevada Postal_Code: 89193-3478 Contact_Electronic_Mail_Address: jones.bruce@epamail.epa.gov Metadata_Reference_Information: Metadata_Date: 19980901 Metadata_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Jim Wickham Contact_Organization: U.S. Environmental Protection Agency Contact_Address: Address_Type: Address: U.S. Environmental Protection Agency Address: P. O. Box 93478 City: Las Vegas State_or_Province: Nevada Postal_Code: 89193-3478 Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata Metadata_Standard_Version: 19940608 Metadata_Security_Information: Metadata_Security_Classification_System: None Metadata_Security_Classification: Unclassified Metadata_Security_Handling_Description: None