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excavated and area ranchers were interviewed to assess the importance of subirrigation to • ranching operations. Asa result of these water availability investigations, the essential hydrologic functions of designated AVF's may be identified. Based on the geomorphic and water availability criteria discussed above, the regulations of the Colorado Mined Land Reclamation Board, and OSM's AVF Identification and Study Guidelines, AVF determinations were msde for valleys in [he study area associated with P&M's proposed Fislt Creek Mine. In addition, an assessment was made for the designated AVF as to the importance (or significance) of that AVF (or portion of AVF) to specific local ranching operations. The outline for the balance of this report follows the major elements of the AVF protection requirements of the regulations and guidelines. Therefore, the report first presents basic data related to the identification of AVF's (i.e. geomorphic and water availability data) and then evaluates this data in order to make determinations relative to the existence of AVFs in the study area. Following these determinations, the report addresses the significance of designated AVFs to local ranching operations and also makes recommendations with respect to AVF monitoring. SECTION II GEOMORPHIC CHARACTERISTICS In order to assess the geomorphic characteristics of the Fislt Creek valley within the study area, • alluvial deposits are mapped using field observations, backhoe pits, interpretation of aerial photographs, and reference to previous investigations Water Waste and Land, 1981 and Walsh, 1980). The results of this mapping are shown on Map 1. (It should be pointed out that [his ,.~~~ -~-~' ~ ` mapping was done at a large scale to allow detailed mapping of individual terraces in order to ~1,~ ~;-"' =.~,-• ~'~ Pn delineate [lie outside boundary of potential alluvial valley floors (AVFs). Map 2 provides a more general description of geomorphic characteristics of the study area considering geomorphic ' sizing criteria for AVFs, as discussed below. 1[ is considered that Map 2 generally represents a more convenient reference (in terms of scale) for this AVF evaluation.) Terraces along the stream channel in the study area were identified on the basis of landform and difference in elevation. The extent of each terrace level along Fish Creek indicates that each level is a consistent landform along the creek. Designations of terrace levels were made, with Tl indicating the lowest level and higher numbers indicating higher, older terraces. The purpose of mapping the alluvial terraces was to delineate [he outside limit of valley bottom areas that may be AVFs (see Map 2~. Geomorphic criteria given in OSM's AVF identification and Study Guidelines, specify that unconsolidated streamlaid deposits greater than 50 feet and_ greater (Ilan 10 acres in size in isolated valley area should be included for further evaluation as AVFs. In addition, as specified in the definition of "unconsolidated streamlaid deposits holding streams: (Section 1.04 (142)), the size of the active stream channel also represents a geomorphic criteria for AVFs. More specifically, the definition requires that streams which may qualify for AVF designation must leave channels that are greater [Ilan three (3) feet in bankfull width and greater [Iran 0.5 fee[ in bankfull depth. I[ should be noted that the drainage of Fish Creek leas an active channel of !~ ;.=a~i1~1~ JUP~ 2 8 2000 I:environ\tracy\docuntenUExhibTA 2 01/IG/98