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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 ICW W 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 R- 150 , produced the finest- grained sediment of the three locations within Reach 111 . 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