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-13- Ponds, Impoundments, Diversions Section 2.05.3(4) - pane 102 1. For all ponds, impoundments, and diversions located above any existing or proposed underground workings the Division requires that the applicant submit an analysis describing the potential effect on the structure in the event that subsidence of the subsurface strata would occur. This information, required by section 2.05.3(4)(a)(i)(D) should address the effects of worst case subsidence on the structure, the effect on the surface and ground water hydrology, and the environmental and health consequences of such an occurrence. This information will also be used in making our ~aritten findings. 2. Several impoundments, identified on ^1ap D-300, and D-301, will be left after reclamation. The Division requires the designs and purpose of these structures. Designs must comply with section 4.05.9. 3. The application should distinguish between existing and proposed sediment ponds, ditches, and culverts. The application should identify those structures that will need to be modified to comply with your submitted designs and our performance standards. 4.For the Division to verify that the concrete conduit of ~vorth Thompson Creek is in compliance with 4.05.4 the Division requires either a) Information on the past performance of the conduit including the maximum storm event that the conduit incured during its life and the performance of the structure during that event, or b) the design capacity of the conduit and the peak flow in IJorth Thompson for the,, 2.5-year, 24-hour event. ~:, i~ The following comments concern the adequacy of these structures in complying viith the performance standards of Rule 4. 1. Ditch D-1 that diverts area 10 was designed to divert 44 acres with a peak flow of 9 cfs but the 4Jash program indicated an area of 53 acres and 16.5 cfs. Since calculations on sheet 100-12 are abreviated,. it is not possible to determine if a slope adjustment factor and basin shape correction factor was used, lle are also unat~le to verify the unit of cfs/in runoff used. The applicant must address this concern and explain the discrepancy, of the design. 2. The design velocity of this ditch must be reported to verify compliance with section 4.05.3(6)(al. 3. The method used to size culvert C-1 must be submitted (i.e. headloss equations, Homographs etc.). Culverts must be designed to safely discharge the event without a head of water unless protection from fill saturation and erosion is provided (see section 4.03.2(4)(e)). Culvert sizing must include design for headloss at the inlet due to configuration and trash rack. 4. Design velocity of Ditch D-2 must be reported. Any change in grade that would alter the velocity should also be reported. Velocities must be low enough to prevent excessive erosion of the channel but high enough to minimize sediment deposition in the ditch from area 11. This information is required by section 4.05.3(6)(a).