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• 52 6.3.4 Sediment Pond Adequacy The adequacy of existing and proposed sediment pond structures is determined by comparing the design storage wlume and spillway capacity to the required storage wlume and spillway capacity as presented in Table 13. Also given in Table 13 is the required storage wlume based on twice the 10-year, 24-hour runoff wlume. This value is used for comparison to account for the storage wlume being partially used before the occurrence of the design event. This condition is due to the nature of thunderstorms that occur within a few days time. Exiatinq Sediment Ponds "A", "C", and "T" and proposed Sediment Ponds "F" and "G" provide adequate storage volume for twice the 10-year, 24-hour runoff wlume plus the three-year sediment wlume. Existing Sediment Pond "e" provides ' for 1.4 times the 10-year, 24-hour runoff wlume plus the three-year sediment f wlume. No design data exists for the proposed relocation of Sediment Pond "E" or the two nlternatives for Sediment Pond "D". It is recommended that these two sediment pond structures be designed for a storage volume equal to twice • the 10-year, 24-hour runoff wlume plus the three-year sediment wlume as given in Table 13. Existing Sediment Ponds "A" and "C" and proposed Sediment Pond "F" provide adequate design capacities for the emergency spillway. Existing Sediment Ponds "B" and "T" will require modification of existing spillway dimensions to provide for the required spillway capacities. Proposed Sediment Pond "G' will require minor design modifications to provide for the required spillway capacity. Again, no design data exists for the proposed relocation of Sediment Pond "E" or the two alternatives for Sedis~ent Pond "D'. Recommended design capacities for emer- gency spillways on these sediment ponds are given in Table 13. Alternative two is recommneded for Sediment Pond "D'. This alternative requires design of diversion channel CH-15 as a permanent structure. This con- dition is assumed for the stability analysis and design of channel unit CH-15. 6.3.5 Reservoir Shape and Short Circuiting Generally, the shape of the existing and proposed sediment ponds is con- trolled by the land features. Sediment ponds which are located on the drainace . channel of a small subvatershed generally have no problems with short circuiting cue to the narrow, V-shaped drainages. Ponds located on side slopes of drainages