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Fish Creek Like Foidel and Middle Creeks, Fish Creek flows in a generally northerly direction through the. Northem Mining District. The overburden depth varies from 1,0~ feet to 1,400 feet through the panels. The {ocatian of the creek is shown on Map 23B, Structures and Renewable Resources. The projected impacts to the creek are presented in Exhibii 4e-3, Northem Mining bistrict Subsidence, prepared by Sub Terra, Inc. As noted in the exhibit, subsidence varies from 0 to 67 inches over the panels. Based upon the data presented in Exhibit 4e3, the maximum increase in the stream gradient of 0.025 (2.5°k). It is not anticipated this will cause significant changes to the creek's profile and resultant erosion should not be a concern. TCC has experienced similar changes in gradient in the EMD without resultant erosional problems in either Foidel or Middle creeks. The same type of subsidence features will occur along Fish Creek, i.e. traugh-shaped, ponding will occur over the panels. The ponds mitigate any change in gradient as the velocity of the water diminishes as it passes through he ponded areas. The extent of ponding, i.e. flooding of AVF, is presented in Exhibit 4e-3. As stated in the exhibit approximately 210 acres will be flooded by the mining of panels 13 Right through 16 Right.. Prior to full extraction under the creek, a channel survey will be completed to enhance the information used in the preparation of the probable hydrologic consequences section of this application. It should be noted that full extraction under Fish Creek will occur in pa~tei 13 flight, which is not anticipated until 2001. Fish Creek Alluvial Valley Floor The Fish Creek alluvial valley floor will be undermined and subsided during the mining of panels 13 Right through I6 Right. The subsidence for the AVF will mirror that projected for the creek. The impacts anticipated for the valley floor would be pooling of water in the subsidence troughs created in panels 13 Right [hrough 16 Right presently, there are no irrigation headgates Located within the panels. This demonstrates that flood irrigation of these bottom lands is not practical and that any enhancement of vegetative growth results from subirrigation. The subsiding of the valley floor will increase the potential for subirtigation to occur. This results from the establishment of the flow point out of the trough at the gateroad. This controls the elevation of the water in the stream in relation to the area of the subsidence trough. As can be visualized, this leads to increasing the area of potential subimga[ion. In addition to the ponding that will result from subsiding the AVF, there will be aeeas within the AVF where the water level will be immediately below the surface, i.e. saturated soil conditions. The impacts of this will be limited due to the fact that the majourity of the AVF will be flooded. The overall impact may be a change in vegetation, water tolerant species taking over areas of saturated soils. This will only serve [o increase the size of the riparian area, which is not considered a negative impact. Ashley Impoundments and Ditch The Ashley impoundments and ditch will be undermined and subsided during mining of panels 12 and 13 Right. The location of the impoundments and ditch is shown on Map 23B, Structures and Renewable Resources. The impoundments are in a general state of disrepair. The impoundments are of earthen construction and in need of repair. Twentymile will document the condition of the impoundments prior to subsiding them and then evaluate them after subsidence is completed. Any necessary repairs will be done after the evaluation, In reference to the ditch, it traverses portions of panels 12 Right, 13 Right, and 14 Right. will require regrading or selective placement of a culvert to reestablish flow in the ditch. of these s[tvctures will be presented in the following section. APPROVED JUN 2 8 2000 Subsidence of the ditch The control plan for both pR 99-OS 2.05-181.8 03/28!00