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constable. It was made to give an approximate idea in terms of volume the Town might <br /> expect if a project like this moves forward. <br /> o The area of the channel is the shallowest,but the Bay itself is deeper. <br /> o Dredging here has been brought up at every for public meeting <br /> o "Mean Low Water"is the average of all the low water heights observed by NOAA at nearby <br /> tide stations over 19-year period (1983-2001) <br /> o Easiest way to think of this is:the average bottom in Ockway is 2.5 ft below the surface at <br /> low tide. <br /> Proposed Dredge Area v <br /> • Assumptions <br /> • Vertical channel walls <br /> • 453,290 sf(10.4 acres)total area for channel, Iq <br /> marina&mooring field <br /> • -6 ft NAVD88(includes 1 ft overdredge) <br /> • Total volume=58,390 cubic yards <br /> <r <br /> • 3 methods <br /> 1. Mechanical Dredging with upland disposal 0, al <br /> 2. Hydraulic dredging with upland disposal <br /> 3. Mechanical dredging with offshore <br /> disposal <br /> o Hydraulic dredging with beach nourishment is not suitable due to grain size <br /> o -6ft NAVD88 would essentially increase freeboard at low tide by —2 ft <br /> Preliminary cost estimates <br /> Estimated Method Estimated Minimum <br /> Volume(cy) Cost+30%Contingency <br /> 1.Mechanical dredging with upland disposal $6,299,839 <br /> 58,390 2.Hydraulic drefting with upland disposal 5 541 211 <br /> 3.Mechanical dredging with offshore disposal $13,879,190 <br /> Do not incorporate costs for engineering,permitting, monitoring,or mitigation. <br /> Dredging frequency:4-5 years. <br /> 1. These dredge costs must be considered planning level and should be reevaluated <br /> regularly. <br /> 2. Cost estimates are based on: <br /> a. Past dredging project costs and conversations with contractors, <br /> b. Have not been reviewed by an engineer <br /> 3. The 30%contingency is for all the unexpected things that can happen on a project of this <br /> size (equipment breakdown, weather delays, etc.) <br /> 4. Dredging costs are anticipated to increase annually,possibly exceeding annual inflation <br /> rates. <br /> 5. Competition for equipment between projects, cost of diesel, limited staffing, and few <br /> companies available has led to widely ranging bid estimates from recent projects. <br /> 6. Difference between 1 and 2 mainly due to scow mob/demob, which is required for <br /> mechanical dredging leading to a slightly higher$/cy for mechanical (77 vs 73) <br /> 7. Offshore requires larger lump sum for scow,greater distance of travel/time for dumping <br /> at approved offshore site, leading to an overall greater $/cy (170) <br />