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described above will produce an effluent suspended sediment concentration of less than 0 .45 g/l . Relating <br /> suspended solids concentration to Florida effluent quality standards — based on the turbidity of the effluent <br /> relative to the ambient turbidity of the receiving waters — is problematic since turbidity depends highly on <br /> the physical characteristics and concentration ofthe suspended material . However, WES guidelines (Palermo <br /> et al . , 1978 ; Walski and Schroeder, 1978) indicate that this 0 .45 g/1 falls well below typical standards for <br /> effluent discharged into estuarine waters . <br /> 2. 3. 3 Ponding Depth and Basin Performance <br /> Ponding depth refers to the height ofthe water column (with its suspended sediment load) maintained <br /> above the depositional surface during dredging operations . It is regulated by the height of the weir crest and, <br /> to a lesser extent, by dredge plant output. Given the initial slope of the basin interior (about 0 .2%), ponding <br /> depth will vary within the basin . The ponded water, most shallow nearest the inlet, will increase to its <br /> maximum depth nearest the weir. Conceptually, ponding depth is typically discussed in terms of its mean <br /> value over the entire basin interior. However, as a practical operational criterion , ponding depth is more <br /> usefully specified at the weir where it can be measured directly. At the weir, the excavated grade of the IR- <br /> I4 basin is 4 .2 ft NGVD, or 0. 8 ft below the average basin depth. Therefore, ponding depth at the weir <br /> exceeds the mean basin ponding depth by approximately 0. 8 ft. In the remainder of this report, ponding <br /> depth will be given in terms of the mean depth over the basin and, where appropriate, related to the <br /> corresponding depth at the weir. <br /> Ponding should be maintained at the greatest possible depth during dredging operations. Increased <br /> ponding depths produce increased retention times and decreased flow velocities through the containment <br /> basin and therefore improved solids retention and effluent quality. The limiting consideration for increased <br /> ponding depth is the amount of hydrostatic pressure the dike can withstand without loss ofstructural integrity. <br /> Analysis of sediment settling characteristics established whether the 2 .0=ft minimum mean ponding <br /> depth produces a basin retention time adequate for acceptable solids retention and effluent quality. The fine- <br /> grained sediment component, because it requires the longest time to settle out of suspension, determines the <br /> required basin retention time and therefore the required ponding depth . <br /> 16 <br />