Introduction

The US Army Corps of Engineers (USACE) is in the process of preparing plans and specifications for the Miami River Maintenance Dredging project.  The USACE will issue a Request for Proposals rather than a Solicitation of Bids.  This means that the contractors will not only provide a price for the work but they will propose the method of dredging along with the proper handling and disposal of the dredged material.  The USACE will select the dredging contractor based upon “best value to the government” which may not be the lowest price.  Best value considers the dredging and disposal methodology, the environmental impacts, community impacts, etc., in addition to the cost.  Therefore, the dredge type will be determined during the selection process.  The work is expected to be completed by mechanical dredging. 

Disposal

Based upon extensive testing by federal, state, and local environmental agencies, the material to be dredged is considered contaminated but it is not hazardous.  The disposal or reuse of the dredged material will be required to meet applicable environmental standards.

Dredging

A dredge removes material from within the channel width, as shown in Figure 1.  The channel width is also the dredging limit.  As the dredge removes the material from the channel width, material adjacent to the channel will fall into the hole created as the dredge removes material.  The dredge will continue to remove material from the channel width until material ceases to fall into the channel.  This creates the channel slope.  The steepness of the channel slope depends upon the type of material.  The more unconsolidated and fine-grained the sediment, the flatter the slope and the farther outside of the channel material will be removed.  In the Miami River, the extent of the slope may also be influenced by rock and hard material that under lays the channel in many locations.  

Figure 1

Miami River Maintenance Dredging
Federal Channel Dredging Project

The Miami River is a federally authorized channel constructed in the 1930s.  The width of the channel varies from 150 feet wide at the mouth of the river, to 125 feet wide above the NW 17^th Avenue bridge, to 90 feet wide above the NW 27^th Avenue bridge.  The federally authorized channel depth is –15 feet mean low water (MLW).  The river has not been maintained since its construction.  The dredging will restore the original constructed channel depths and increase efficiency and safety of port operations.  The Miami River dredging project will remove accumulated infill; no blasting or removal of rock is included. 

Funding is in place for the federal channel dredging which is scheduled to begin in summer or fall of 2002.  The USACE is responsible for approximately 80% of the project costs and Miami-Dade County, as the Local Project Sponsor, is responsible for the remaining 20%.  A local funding partnership including Miami-Dade County, the City of Miami, the State of Florida, and the Florida Inland Navigation District has been formed to pay the local dredging share.   

Bank to Bank Option

The County is considering extending the federal dredging project beyond the limits of the federal channel, essentially bank to bank.  This would allow contaminated material outside the federal channel to be removed from the Miami River system.   Figure 2 shows the additional dredging for the bank-to-bank option.

 

Figure 2

The cost of this additional dredging would be the responsibility of the local funding partnership and it will have to be separately permitted from the federal project.  The federal government will not participate in the cost but it will include it in the scheduled contract.  The County is securing permits and pursuing funding options for this bank-to-bank option.

USACE Set-Back Policy

USACE policy is to maintain a minimum 25-foot distance between any structure and the dredging, unless the local sponsor requests a reduction in this distance.  Maintaining this 25-foot setback would result in significantly reducing width of the channel in some locations, as well as reducing the volume of contaminated sediment to be removed from the channel.   Miami-Dade County has requested that the USACE dredge to within 10 feet of structures along the Miami River, as the local sponsor. 

Dredging in the Vicinity of Waterfront Structures

If the waterfront structure is in poor or substandard condition, the shifting sediments associated with the dredging could negatively impact the stability of the structure.  Waterfront structures impacted by dredging fall into three general categories, based upon location, as shown in Figure 3 and discussed below. 

• Waterfront Structure 1:  If the waterfront structure is more than 10 feet from the federal navigation channel limits then the federal dredging project will be to the edge of the channel.  The bank-to-bank option will extend the dredging to 10 feet of the structure.

• Waterfront Structure 2:  If the waterfront structure is less than 10 feet from the federal navigation channel limits then the federal dredging project and the bank-to-bank option will also extend to within 10 feet from the structure.

• Waterfront Structure 3:  If the waterfront structure encroaches into the federal channel, federal regulations require that impediments to navigation be removed from the channel.  The dredging limits after the structure is modified to eliminate the encroachment will be the same as Structure 1 or 2 above depending upon the modified structure.

Figure 3

If you have any questions or would like additional information, call Nancy Case O’Bourke at 305/572-9960 or e-mail at nancy@caseobourke.com.