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Data characterizing channel sediments in Reach III were obtained in a program of sampling and analysis conducted during the plan development phase . As documented in the Phase I report (Taylor et al . , 1997 ), sediment samples were taken at nine locations within the Indian River segment of the ICWW channel including three locations within Reach III . In an effort to sample worst case conditions, each sampling station was located near a potential source of fine sediment. Analysis determined that sampling location IR-3 -2, located at ICWW mile 213 .93 (Cut IR-30 , station 14+25 ) south of Vero Beach and opposite Prang Island near channel marker R450 , produced the finest- grained sediment ofthe three locations within Reach III . Silt and clay-sized particles (particles passing a #200 sieve, or with diameters less than 0 .074 mm ) comprised 80% of the sample (Figure 2 . 4) . Based on this conservative design criterion, an associated zone settling velocity was then determined from an empirical relationship between the percentage of fine-grained material and settling behavior. This relationship was developed from U . S. Army Corps of Engineers (COE) sediment data characterizing the silt content of a variety of ICWW channel sediments and the corresponding settling behavior of slurry concentrations similar to those typically encountered in dredging operations (Figure 2 . 5 , Taylor and McFetridge, 1989). From these data the characteristic zone settling velocity for the sediment to be placed in Site IR- 14 was determined to be 0. 25 cm/min, or 0.49 ft/hr. This settling velocity was then used to determine the retention time needed to provide adequate sedimentation within the containment basin . Retention time relates directly to the depth of ponded water maintained within the basin . The preliminary design of the containment basin provides a minimum 2 .0-ft mean ponding depth above the deposition surface. Analysis of the hydraulic characteristics of the proposed containment basin (Gallagher and Company, 1978) indicates that a 2 . 0-ft mean ponding depth will provide a maximum retention time of 6 . 19 hours during which the flow over the weir balances the liquid discharge of the dredge. In comparison, the time required for the sediment to settle out of the"2 .0-ft mean ponding depth is less than 4. 13 hours based on the projected zone settling velocity of the Station IR-3 -2 material . However, research (Shields, Thackston and Schroeder, 1987) by the WES under the DMRP indicates that the predicted settling time of the dredged material should be multiplied by a correction factor of 2 .25 to account for field conditions . This yields an adjusted required settling time of 9 .28 hours, a time which exceeds the maximum retention time of 6 . 19 hrs produced by a 2 .0-ft mean ponding depth . Increasing the mean ponding depth to 4. 0 ft provides a maximum retention time 12 .38 hrs, which exceeds the adjusted settling time required to maintain acceptable effluent 17