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Subirrigation was evaluated for these alluvial deposits by <br />examining vertical proximity to the stream and indicator <br />vegetation species. The stream has incised 20-30 feet in <br />some areas to liG feet in other areas into the deposits, so <br />roots would have to approach this depth to tap the water <br />table. Deep rooted phreatophytes, such as cottonwoods, are <br />present along the course of the stream. However, understory <br />vegetation was not characteristic of subirrigated areas. No <br />evidence of water movement from the water table into the <br />potential rooting zone of agricultural crops was found. <br />This lack of Subirrigation, together with the unfavorable <br />conditions for flood irrigation, result in a non-AVF <br />classification for the Harvey Gap stream system. <br />Alluvial Valley Floor - West Elk Creek. Unconsolidated <br />stream laid deposits adjacent the permit area, along West <br />Elk Creek, occur in a narrow band immediately adjacent to <br />the stream channel. Some of the area outside these deposits <br />is being sprinkler irrigated. Subirrigation near the channel <br />is also probable. Therefore, West Elk Creek is an AVF and <br />is shaded on Figure 16. <br />Although identified as an AVF in the adjacent area, no <br />further study of the AVF is necessary since no portion of <br />this watershed is planned for surface disturbance or surface <br />. discharge. Further, the formations to be mined do not <br />outcrop or subcrop within the AVF. Therefore, this adjacent <br />area AVF will not be distrubed by the Eastside Mine <br />operations. <br />Alluvial Valley Floor - Colorado River. The presence of <br />unconsolidated stream-laid deposits along the Colorado River <br />is shown on Figure 16. Whether this area is a fan deposit <br />upon an old terrace or is an unsorted terrce is not known, <br />but due to its current use, the distinction is immaterial. <br />Most of this area is being flood irrigated using water from <br />Grass Valley Reservoir. Subirrigation is unlikely in the <br />area of the mapping because of the depth of the water table <br />Csee Ground Water section). Due to the presence of flood <br />irrigation on alluvial deposits, this area is an AVF and is <br />shaded on Figure 16. <br />Though this AVF is present on the permit are, the <br />underground mine workings would be stratigraphically at <br />least 3,760 feet below the alluvial deposits which are <br />40-200 feet deep (Collins 1975q see Ground Water section>. <br />Due to the low transmissivity of the Mesa Verde group, <br />hydraulic connection between the alluvium and the mine <br />workings is imporbable and no impact is predicted. <br /> <br />68 Revised 5/8' <br />