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I • <br />shed inventories (erosion). New guidance replaces previous <br />policy on erosion inventories provided in Phase 1, Watershed <br />Conservation and Development System, Manual Section 7322.1, and <br />Instruction Memorandum No. 79-665. The erosion inventory may be <br />applied to landforms which represent areas of a few acres to <br />several hundred acres. <br />As part of the inventory plan based on guidance from the preplan- <br />ning analysis, team members need to decide what is to be sampled. <br />As mentioned in SVIM, BLM Manual, Section 4412.14D1, it is <br />necessary to stratify the inventory area into homogeneous <br />units--called site writeup areas-the basic unit for collecting <br />data on the vegetation and soil resources. Stratification is <br />necessary since it is beyond manpower and funding capability to <br />sample all mapping units. <br />Caution: The stratified SWA (site writeup area) sampling <br />technique may not be adequate to provide for sampling of all <br />degrees of erosion that are occurring in the inventory area. <br />Example: Inclusions of more than one soil-vegetation units <br />within a SWA may not be sampled. Data on inclusions is necessary <br />for subsequent data analysis and interpretations. <br />Therefore, at the mapping stage, all mapping units should have a <br />SSF completed and recorded on Form 4412-26. If time precludes <br />the SSF determination of all mapping units, complete SSF on at <br />least one vegetation-soil unit (including inclusions) in each <br />• erosion condition class, if this exists in the inventory area. A <br />icey then must be developed for which the data will be interpo- <br />lated for unsampled vegetation-soil units in each respective <br />erosion condition class. <br />2. In the second step, the technician should observe the total <br />sample area and determine an average condition for each of the <br />seven items considered in the procedure. These are shown on <br />Table 1, along with weighted value assigned to each item. <br />The degree of erosion, as manifested by each of the seven erosion <br />features, is assigned a numerical score ranging between 0 and 14 <br />for all features, except rills and gullies, which have a range of <br />0 to 15. Two of the features were assigned a maximum score of 15 <br />simply to give a maximum composite score of 100 for all seven <br />features. These numerical scores are called soil surface factor <br />(SSF) values. When used for all the erosional features evaluated <br />together for a sample site, they are called composite SSF values. <br />• <br />6 <br /> <br />