GENERAL49925 - Laserfiche WebLink

Home Browse Search

There is no indication of past or current flood irrigation of these areas along Middle Creek and the geomorphic characteristics of this area would not lend themselves to the development of an irrigation system. Based on [he lack of flood irrigation potential, the narrow and incised nature of the valley bottom, and the lack of meaningful differences between the creekside and upland vegetative communities, the Division has determined that areas upstream of the Connel ditch lateral crossing of Middle Creek, as shown on Map I5, are not alluvial valley floors. In this case, the extent of farmable acreage would be 10 acres or less. The areas are not presently and have not historically been farmed and evidence presented indicates that farming is not typically practiced on similar parcels in the region. A previous negative determination had already been made for those lands along Middle Creek downstream from the Counry Road No. 33 in section 12 to the first irrigation ditch crossing (Connel ditch lateral). Effects ofMining_gn identified Alluvial Vallev Floors Due to elevated levels of salinity documented in current and future mine discharge water and potential inhibitory effects of increased soil and alluvial ground water salinity on flood irrigated and subitrigated crops, the potential for material damage caused by salt loading was a major concern which had to be evaluated for each of the AVF's identified above. Material damage projections were calculated in both asub-irrigation and a flood irrigation case analysis, using data obtained during low-flow-of-record years. The subirrigation scenario assumed that the stream would recharge the alluvial aquifer in the spring during peak flows. The flood irrigation case utilized the period between June 1 and August 3 ] . Assumptions and equations used in projecting water quality impacts are discussed in the Yampa River CHIA, which is on file at the Division office. Salt loading projections were arrived at by stream flow modeling and analysis of past monitoring results and projected dewatering activities. In the supplemental information package dated September 22, 1986, the applicant submitted information on vegetation cover and production by species for flood irrigated and sub-irrigated croplands on the affected alluvial valley floors. Alluvial bodies, irrigated fields and vegetation sample locations are depicted on supplemental Map No. 1 "Twentymile Park Salt Loading Study Land Use and Hydrologic -Boundaries." This and other information was used by the Division to make the required findings with regard to material damage. Required findings for identified alluvial valley floors on Fish Creek, Trout Creek, and Foidel Creek/Middle Creek confluence are presented separately below. Fish reek The boundaries of the f ish Creek alluvial valley floor are as delineated on Map No. I S of the Foidel Creek Life of Mine application and include all alluvial deposits within and downstream from the proposed permit area as delineated on supplemental Map No. I. Information discussed below has reaffirmed the Division's original determination that alluvial deposits on Fish Creek meet alluvial valley floor criteria based on existing flood irrigation, potential for flood irrigation and subirrigation. The existence of a currently Flood irrigated field on lower Fish Creek and the presence of diversion structures and irrigation ditches on various stream segments as delineated on Map 1 S document [he potential for flood irrigation. 21