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Three corrugated metal half-pipes, each with an 8 -ft weir section , will provide the required 24 - ft total crest length . The three half- pipes connected by a common manifold will provide drainage from the containment basin via a single culvert under the dike . During dredging and dewatering operations , the return water pipeline will connect to this culvert and transport the clarified supernatant to the Indian River . Pipeline placement and retrieval is discussed in Section 3 . 1 . Removable flashboards will allow adjustment of weir heightover a range of 10 . 9 ft — from the initial elevation of ponded water within the basin following construction (estimated as + 1 . 8 ft NGVD) to a maximum elevation of + 12 . 7 ft NGVD . Setting the weirs at the minimum elevation permits the immediate release of ponded water at the start of dredging operations . The maximum elevation provides a 2 ft mean ponding depth and 2 ft of freeboard above the maximum deposition surface . The 5 . 5 in . x 5 . 5 in . flashboards (finished dimension) provide an adjustment increment roughly equivalent to the projected depth of flow (4 .2 in .) over the weir crest at the point the weir discharge approximately equals the liquid inflow to the containment basin , a balance reflected by the design weir loading, QB = 0 . 89 ft'/ft-sec . This design provides adequate adjustment resolution to maximize weir performance and effluent quality throughout the dredging operation and subsequent release of ponded water. The final weir design parameter considered is the location of the weirs within the containment basin . First, to reduce the likelihood of flow constriction , sediment resuspension, and dike instability the weir crests must be offset a minimum of 100 ft from the dike ' s inside toe . Second , the weirs must be placed to maximize their distance from the dredge pipe inlet and to minimize the return distance to the receiving waters . Providing the maximum inlet-weir separation also maximizes the basin ' s effective area and ensures that the effluent released from the basin meets the weirs ' performance criteria. Hydraulic analysis ( Section 2 . 3 . 3 ) indicates the 800-ft separation distance shown in Figure 2 . 1 to be adequate. In addition, locating the weirs to minimize the return distance from the weirs to 'the Indian River provides the most efficient effluent transport from the containment basin . Gravity flow will be used to the greatest extent possible. However, one or more dredging operations may be required to sufficiently raise the elevation of the basin interior such that all ponded water will drain by gravity flow . Until that time, auxiliary pumping may be required . Analysis of weir performance based on nomograms developed at the Waterways Experiment Station under the Dredged Material Research Program (Walski and Schroeder, 19 78) indicates that the weir design 15