2009-323A - Laserfiche WebLink

Home Browse Search

M • 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 - 11 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 IR44 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 I-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 -