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decreasing the withdrawal depth should improve the basin ' s solids retention performance and improve effluent quality. Under most circumstances , maintaining the withdrawal depth less than the minimum ponding depth should help ensure that the weirs release only the clarified surface layer that contains relatively low concentrations of suspended sediment . The specified total weir crest length — 36 ft for the four weir stack design and 24 ft for the three weir stack option — derives from nomographs developed under the USACE ' s Waterways Experiment Station (WES) Dredged Material Research Program (e . g . , Walski and Schoeder, 1978) . Based on the discharge of the design dredge plant , the 36 -ft total length assumes the output characteristics of a 24 - in . dredge, while the 24 -ft length assumes an 18 -in. dredge. The preliminary design for the IR- 14 weir structure recommends the three weir stack option. This remainder of this chapter presents recommendations for minor design revisions to the weir system proposed for installation at the IR- 14 containment facility . As discussed above, the basic installation follows the predominant weir design now in use within the Jacksonville District, as well as the design installed at almost all FIND containment facilities . The proposed revisions do not require significant alteration of the weirs ' basic structure and can be installed as part of the dredging contractor' s site preparation responsibilities . 2 . 2 Deficiencies of the Predominant Weir Design As part of our investigations into possible deficiencies in the predominant weir design currently installed at existing FIND containment facilities , Taylor Engineering staff solicited information from two groups : ( 1 ) USACE personnel presently or recently engaged in planning, designing, contracting, or inspecting dredging/dredged material management operations at FIND dredged material containment facilities and (2) dredging contractors that have recently used or are familiar with existing FIND facilities . In addition to establishing typical weir operating procedures , these inquiries were intended to investigate perceived deficiencies in the design and construction of the weir systems presently installed in FIND dredged material containment facilities . The discussions with representatives of both the USACE and private dredging contractors focused on three basic concerns regarding present weir design : ( 1 ) the design ' s failure to adequately control leakage around the ends of the weir boards , where the boards key loosely into the vertical 1-beam channels; (2) its failure to adequately control leakage between the weir boards ; and (3 ) its failure to adequately provide a means to safely access the weirs as required to add or remove weir boards and to secure the boards in position. The discussions confirmed Taylor Engineering ' s own observations that - 3 -