Section 7 Dredging Implementation Plan

Transcription

1 7.1 Overview Section 3 of this report presented level of service criteria to identify those areas where the existing system does not provide an acceptable level of service. Canals were selected for more detailed hydrographic survey and investigation based on the existing conditions level of service. Based on review of the sounding data collected in the SE Quadrant, 53 saltwater canals with C or D level of service were selected for detailed hydrographic/bathymetric survey (approximately miles of canals). Overall, there is approximately 42,868 cubic yards of volume quantified to be removed from the 53 saltwater canals with C or D level of service. Development of a dredging implementation plan is required in order to meet the desired level of service for the City managed canal system. 7.2 Prioritization of Dredging Projects In order to prioritize proposed projects for maintenance dredging, together with City staff, Gator Dredging personnel incorporated specific criteria to assist in measuring which projects would provide the greatest benefit. The prioritization criteria used for this plan are the following: 1. Stormwater Conveyance Level (Arterial, Collector or Local) 2. Existing Condition Level of Service (C or D) 3. Proximity to Other Dredge Locations The stormwater conveyance level criterion was given highest priority as it defines the level of the stormwater conveyance route or flowway through the City canal system. Arterial Canals are the highest level canals and/or main channels in the system. Arterial Canals are main channels delivering water from Collector Canals to open waters of the Caloosahatchee River and the Gulf of Mexico. Local Canals are lower level canals providing only local conveyance to the tributary systems. Local Canals connect to Collector Canals. Collector Canals are tributary canals serving several connecting local canal systems. The Collector Canals allow conveyance to larger, Arterial Canals. Since Arterial and Collector Canals also are used by more residents and visitors of the City to access properties and other canals, they also have been given priority over Local Canals affecting a smaller limited number of people. 7-1 February 2012

2 Existing condition level of service defines the existing depth of the canal system. The shallower the existing condition, the higher the priority to improve conveyance. The proximity of a proposed dredging project to other projects is also a major consideration in the prioritization plan. Keeping in mind dredging project costs, it is beneficial to consider grouping canals together that are adjacent or near each other to avoid returning to the same area. Economies of scale and efficiencies in construction can be created by reducing mobilization, pipe installation and dewatering costs. The next step in determining the prioritization was to assign point values to each of the above factors. The following are the point values assigned to prioritization criteria: 1. Stormwater Conveyance Level - Arterial Canal = 4 pts Collector Canal = 3 pts Local Canal = 0 pts 2. Existing Condition Level of Service (See Table 3-1) - Grade D = 4 pts Grade C = 2 pts 3. Proximity to Other Proposed Projects - Grouping of Canal Projects Available = 1 pt No Grouping = 0 pts Table 7-1 summarizes all of the above criteria and their point values into a matrix showing the prioritization of the canal dredging projects. Table 7-2 provides the prioritization summary sorted by total score. Canals receiving a score of 6 and above would have the highest priority. These canals are Collector or Arterial Canals and have a level of service grade of C or D. Canals receiving a score of 4 or 5 have the next highest priority since they are Local Canals with a D level of service grade. Canals receiving a 3 are given priority over a 2 because they are C level of service grade canals grouped with other potential canal projects. The remaining proposed projects with a scope of 2 are simply C level of service grade canals that are isolated from any other canals in this study. 7.3 Recommendations Along with the above prioritization, the size of the project, or volume to be removed, should also be taken into consideration when determining a final canal dredging implementation plan. Based 7-2 February 2012

3 Table 7 1 SE Quadrant Dredging Plan Prioritization Scoring by Canal Canal Unit Grade Grade Score Stormwater Conveyance Level Classification Score In a Grouping Y/N Grouping Score Total Score for Canal Alicante South 11 0 C 2 Local 0 YES 1 3 Antigua 15 0 C 2 Local 0 NO 0 2 Balboa 14 0 C* 2 Local 0 YES 1 3 Biarritz 21 0 D 4 Local 0 NO 0 4 Calabar North 21 0 C 2 Local 0 YES 1 3 Calabar West 21 0 C 2 Local 0 YES 1 3 Campo 21 0 C 2 Local 0 YES 1 3 Cat Cay Lake 89 0 C 2 Local 0 NO 0 2 Ceba 14 0 C* 2 Local 0 YES 1 3 Chantrey 18 1 D 4 Arterial 4 NO 0 8 Cologne 14 0 C 2 Local 0 YES 1 3 Croton 13 0 C 2 Local 0 NO 0 2 Darwin 19 0 C 2 Local 0 YES 1 3 Eliot 19 0 C 2 Local 0 NO 0 2 Everest West 21 0 D 4 Local 0 NO 0 4 Fermi 18 0 C 2 Local 0 NO 0 2 Genoa North 22 0 C 2 Local 0 YES 1 3 Genoa South 22 0 D 4 Local 0 YES 1 5 Genoa West 22 0 D 4 Local 0 YES 1 5 Glen Cove 11 0 D 4 Local 0 YES 1 5 Hogarth 19 0 C 2 Local 0 NO 0 2 Honolulu 22 0 C 2 Arterial 4 NO 0 6 Hudson 19 0 C 2 Local 0 YES 1 3 Little 89 0 D 4 Local 0 NO 0 4 Mackinac 23 0 D 4 Local 0 YES 1 5 Malaga 07 0 C 2 Collector 3 NO 0 5 Mango 14 0 C 2 Local 0 YES 1 3 Marlowe 19 0 C 2 Local 0 NO 0 2 Miramar 01 2 C 2 Collector 3 YES 1 6 Monteclaire 01 2 C 2 Local 0 YES 1 3 Monterey 01 2 C 2 Local 0 YES 1 3 Montevideo 22 0 D 4 Local 0 YES 1 5 Monticello 01 2 C 2 Local 0 YES 1 3 Nassau 06 3 D 4 Local 0 NO 0 4 Norfolk 06 4 D 4 Local 0 NO 0 4 Orange 21 0 C 2 Local 0 YES 1 3 Park 22 0 C 2 Local 0 YES 1 3 Riverhead North 21 0 C 2 Local 0 YES 1 3 Riverhead South 21 0 C 2 Local 0 YES 1 3 Riverhead West 21 0 C 2 Local 0 YES 1 3 Rondo 21 0 C 2 Local 0 YES 1 3 Saturn 07 0 C 2 Local 0 YES 1 3 Saxony 09 0 C 2 Local 0 YES 1 3 Sequoia 09 0 C 2 Local 0 YES 1 3 Sherwood 09 0 C 2 Local 0 YES 1 3 Shetland 08 0 C 2 Local 0 YES 1 3 Sierra South 11 0 C 2 Local 0 YES 1 3 Stokes 19 0 C 2 Collector 3 YES 1 6 Trinidad 09 0 C 2 Local 0 YES 1 3 Waikiki E/W 06 2 D 4 Local 0 YES 1 5 Waikiki N/S 06 2 D 4 Local 0 YES 1 5 Whippoorwill Sou 11 0 C 2 Local 0 YES February 2012

4 Canal Unit Grade Grade Score Stormwater Conveyance Level Classification Score In a Grouping Y/N Section 7 Table 7 2 SE Quadrant Dredging Plan Prioritization Scoring (Sorted by Total Score) Grouping Score Total Score for Canal Chantrey 18 1 D 4 Arterial 4 NO 0 8 Honolulu 22 0 C 2 Arterial 4 NO 0 6 Miramar 01 2 C 2 Collector 3 YES 1 6 Stokes 19 0 C 2 Collector 3 YES 1 6 Genoa South 22 0 D 4 Local 0 YES 1 5 Genoa West 22 0 D 4 Local 0 YES 1 5 Glen Cove 11 0 D 4 Local 0 YES 1 5 Mackinac 23 0 D 4 Local 0 YES 1 5 Malaga 07 0 C 2 Collector 3 NO 0 5 Montevideo 22 0 D 4 Local 0 YES 1 5 Waikiki E/W 06 2 D 4 Local 0 YES 1 5 Waikiki N/S 06 2 D 4 Local 0 YES 1 5 Biarritz 21 0 D 4 Local 0 NO 0 4 Everest West 21 0 D 4 Local 0 NO 0 4 Little 89 0 D 4 Local 0 NO 0 4 Nassau 06 3 D 4 Local 0 NO 0 4 Norfolk 06 4 D 4 Local 0 NO 0 4 Alicante South 11 0 C 2 Local 0 YES 1 3 Balboa 14 0 C* 2 Local 0 YES 1 3 Calabar North 21 0 C 2 Local 0 YES 1 3 Calabar West 21 0 C 2 Local 0 YES 1 3 Campo 21 0 C 2 Local 0 YES 1 3 Ceba 14 0 C* 2 Local 0 YES 1 3 Cologne 14 0 C 2 Local 0 YES 1 3 Darwin 19 0 C 2 Local 0 YES 1 3 Genoa North 22 0 C 2 Local 0 YES 1 3 Hudson 19 0 C 2 Local 0 YES 1 3 Mango 14 0 C 2 Local 0 YES 1 3 Monteclaire 01 2 C 2 Local 0 YES 1 3 Monterey 01 2 C 2 Local 0 YES 1 3 Monticello 01 2 C 2 Local 0 YES 1 3 Orange 21 0 C 2 Local 0 YES 1 3 Park 22 0 C 2 Local 0 YES 1 3 Riverhead North 21 0 C 2 Local 0 YES 1 3 Riverhead South 21 0 C 2 Local 0 YES 1 3 Riverhead West 21 0 C 2 Local 0 YES 1 3 Rondo 21 0 C 2 Local 0 YES 1 3 Saturn 07 0 C 2 Local 0 YES 1 3 Saxony 09 0 C 2 Local 0 YES 1 3 Sequoia 09 0 C 2 Local 0 YES 1 3 Sherwood 09 0 C 2 Local 0 YES 1 3 Shetland 08 0 C 2 Local 0 YES 1 3 Sierra South 11 0 C 2 Local 0 YES 1 3 Trinidad 09 0 C 2 Local 0 YES 1 3 Whippoorwill Sou 11 0 C 2 Local 0 YES 1 3 Antigua 15 0 C 2 Local 0 NO 0 2 Cat Cay Lake 89 0 C 2 Local 0 NO 0 2 Croton 13 0 C 2 Local 0 NO 0 2 Eliot 19 0 C 2 Local 0 NO 0 2 Fermi 18 0 C 2 Local 0 NO 0 2 Hogarth 19 0 C 2 Local 0 NO 0 2 Marlowe 19 0 C 2 Local 0 NO February 2012

5 on the proposed budget for each year, the above scoring can be combined with the consideration of dredge volume to allow for the maximum overall progression towards completion of all dredging within three fiscal years. For greatest efficiency of construction cost, different approaches to dredging equipment and methodology can be utilized. Based on the amount of sediment to be removed, projects can be further defined as large, medium or small. A larger hydraulic dredge is appropriate for larger volume projects, however would be very costly to deploy and utilized for small projects. Therefore, the following means and methods for large, medium, and small canal dredging projects are recommended as described below. Large Dredge Projects (Projects > 1,200 CY) For large dredge projects, greater than 1,200 cubic yards (CY), an 8-12 inch diameter hydraulic dredge is recommended. This type of hydraulic dredge is an operator controlled, water-based steel barge (approximately 50 feet) with a mounted swinging ladder or stationary cutterhead and an 8-12 inch suction pump. The cutterhead of the dredge is in constant contact with the sediment during dredging operations. During transport or relocation, the dredge head sits at the water line with no suction. Behind the cutterhead is the hydraulic pump which pumps sediment and water to dewatering cell(s). The dredge slurry consists of approximately 80/20 ratio of water/sand and the dredge will only allow up to 3.5-inch diameter solids through the pump. Figure 7-1 provides some example photographs of the proposed large dredge project methodology. Medium Dredge Projects (1,200 CY > Project > 150 CY) Medium dredging projects are defined as projects less than 1,200 CY and greater than 150 CY. Medium dredging projects can be performed using a 6-inch diameter hydraulic dredge pump mounted on a floating barge. The hydraulic power unit can be staged on shore at various staging areas based on dredging locations. This pump is powered by a diesel motor and the hydraulic power is supplied using biodegradable hydraulic fluid. Hydraulic hoses will run along the canal edge from the barge with mechanical attachment to the dewatering cell. Figure 7-2 provides some example photographs of the proposed medium dredge project methodology. Small Dredge Projects (Projects > 150 CY) Small dredging projects are defined as projects less than 150 CY. Dredging of small projects is proposed using a 4-6 inch diameter hydraulic submersible dredge pump. The hydraulic power unit will be staged on shore at various staging areas based on dredging locations. This unit is powered by diesel and the hydraulic power is supplied using biodegradable hydraulic fluid. Hydraulic hoses will run along the canal edge to a floating pontoon where the submersible pump head will be mounted. Attached to the pump head will be a 25-foot long 4-inch diameter hand 7-5 February 2012

6 2011 Ellicott Swinging Dragon Large Scale Dewatering Cells FIGURE 7-1 City of Cape Coral SE Dredging Management Masterplan Methodology for Large Dredge Projects

7 Floating Barges with 6-Inch Hydraulic Pumps Dewatering Cells FIGURE 7 2 City of Cape Coral SE Dredging Management Masterplan Methodology for Medium Dredge Projects

8 held flexible hose. The sediment is pumped through a temporary 4-inch flexible pipeline into dewatering tanks located upland in road right of ways or vacant lots based on dredging locations. City drainage easements and right-of-ways should be utilized. The sediment will settle within the dewatering tanks (40 cubic yard roll-off tanks or 20 cubic yard dump trucks with seals) which are specially designed with interior baffles to slow the velocities allowing for maximum settling time. All sealed and self contained dewatering tanks or dump trucks will be located in the designated staging areas. The sediment will remain in the tank and the decant water which spills over the interior weirs will be directed back to the dredge area in flexible hoses via gravity. The return water location will be enclosed by the floating turbidity curtain surrounding the dredge area and will be re-cycled for the dredging process. Return water will not be allowed to enter unprotected surface waters, storm drainage facilities, or wetlands. Once the tanks reach the maximum 15 cubic yard sediment hauling capacity, the excess decant water will be removed and the tanks will be hauled to the permitted disposal site. This process will be repeated until the work is completed. Figure 7-3 provides some example photographs of the proposed small dredge project methodology. Citizen Complaint Action Plan Periodically, the City receives reports and complaint from citizens regarding potential problems within the canal systems. Subsequent to the development of this, the following process is recommended for managing future citizen canal complaints. Initial Complaint Collection 1. Call Taker Receives Message/Collects Information or Contacts Resident to Collect Information a. Time of ground impact if available i. Winter/summer : Spring and neap tide for tidal, low or high water for WICC ii. Time of day: tide elevation at that time b. Boat Type i. Sailboat or power boat ii. Draft if known Complaint Review/Analysis 2. Does Canal meet permit requirements? (-5 ft-mlw or -5 ft below Fixed Weir NGVD Elevation) a. Canal sounding data available i. If known, is it part of master plan for dredging? 7-6 February 2012

9 Hydraulic Micro - Dredging Low Impact Micro - Dredging Piping Small Crew Dewatering and Disposal Methodology FIGURE 7-3 City of Cape Coral SE Dredging Management Masterplan Methodology for Small Dredge Projects

10 1. If master planned, respond with forthcoming dredging plan b. If no sounding data is available, identify canal for next step (NE or NW Quadrants) i. Is it part of next sounding plan under contract ii. If not part of next plan, print aerial and have crew gather field data on complaint. Complaint Resolution/Action Plan 3. Review data with staff to determine action item a. Contract to remove abandon vessel b. Contract to remove rock c. Contract to remove partial piling d. Develop in-house dredging plan e. Contract to remove sediment 7.4 Conclusions Overall, there is approximately 42,868 cubic yards of volume to be removed from the 53 detail surveyed canals. Using the above methodologies and implementation prioritization, based on current funding, all saltwater canals within the SE Quadrant of the City s canal system can be maintained to permit conditions within three fiscal years (or sooner depending on funding availability). Dredging of fresh water canal systems were not considered for this implementation plan as they currently provide an acceptable level of service required as permitted drainage systems. The permitted fresh water canal systems are inspected by a professional engineer, at least once every two years, to certify the stormwater management systems function according to original design and permit conditions. Additionally, the fresh water canal systems only provide localized navigation for residents living on the waterbody. Recreational and navigational use by others not living on the fresh water canal system is limited. Future sounding and survey efforts are recommended to monitor that a maximum of 5 feet below fixed weir elevations for freshwater canals is maintained. In addition, updated canal sounding and/or detailed hydrographic survey is recommended to measure the sedimentation/accumulation rate in the canal systems. Future detailed survey efforts are particularly recommended in canals with B* level of service where isolated canal bottom elevations between 3-5 feet below mean low water (MLW) were found, but not frequently enough to warrant the lower C level of service. Sediment accumulation rates may be higher in the previously identified areas. 7-7 February 2012