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Located in Memphis, Tenn.,on the Mississippi River, the new Beale Street Landing consists of a public park, passenger boat docking facility, and terminal building. A modern, world-class docking facility was needed to better accommodate passenger boat traffic up and down America's most used interior waterway. A secondary goal of the design was to create a unique public space and destination linking downtown Memphis to the riverfront and Tom Lee Park, Memphis's major event and festival venue.
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Memphis sits at the widest point on the Mississippi River and provides docking access for countless local excursion boats and approximately 50 stops from three major passenger vessels each year. To provide historical context, the adjacent Historic Cobblestone Landing is one of the nation's largest remaining cobblestone landings and is on the National Register of Historic Places. The landing was built in the second half of the 1800s to accommodate the heavy traffic of incoming ships that traded their cargo for loads of cotton, lumber, and other goods. This landing allowed Memphis to blossom as a major river port and still operates for leisure boat docking. However, the cobblestones are in need of repair, and the opening of Beale Street Landing will allow the city to divert traffic from the Historic Cobblestone Landing and begin restoration.
The yearly river stage cycle causes the project site to be submerged regularly, so the desired size and scope of this project presented several civil engineering challenges. In addition, the 600 feet of waterfront allocated for the landing required a highly orchestrated bank stabilization effort.
Project organization
The Beale Street Landing project was initiated in 2003 with an international design competition and subsequently divided into five phases. Phase 1 was the dredging of the Wolf River Harbor by the U.S. Army Corps of Engineers (Corps) to allow large river vessels greater maneuvering room for docking. The area of land dredged was relocated to the southern tip of Mud Island to satisfy Corps requirements to maintain wetland habitat. This work was performed in November 2006.
In Phase 2, the foundations for future phases were installed at the river's edge. A sheet pile retaining wall was constructed along 600 feet of the riverbank to form an edge to the park land that would be built in Phase 4b. Steel pipe piles also were driven and concrete pile caps installed for the foundations of the helical ramp and mooring arms. Work on Phase 2 was completed in September 2009.
In addition to constructing the helical ramp and mooring arms in Phase 3, the barge-like floating pontoons to which the boats will anchor were built offsite and floated into place. Phase 3 was substantially complete in the summer of 2012.
The terminal building and connecting bridge to the helical ramp were constructed in Phase 4a, beginning in the summer of 2010 and substantially completed at the end of 2012. Phase 4b, the terraced park with protruding islands, built on the riverbank bounded by the 600-foot sheet pile wall, is currently under construction. River boats are currently using the docking facility and the terminal building. The restaurant is expected to open in the spring of 2013, and the project will be 100 percent complete by the end of 2013.
Accommodating river elevation fluctuation
The banks of the Mississippi River are unlike most river waterfronts. Each spring, the river swells, conveying rains and snow melt from 40 percent of the continental United States, including 32 states and two Canadian provinces. Low river elevations typically occur in the fall and winter months, as most precipitation that falls in the northern states remains frozen. From May 2011 to September 2012, the river elevation fluctuated nearly 58 feet, representing a near record high and low. Average annual fluctuation is about 45 feet, with daily fluctuations of several feet. By all accounts, the Mississippi River will continue to fluctuate at even more dramatic rates. To accommodate this elevation change, boat landings on the Mississippi River are typically accomplished either by large vertical pilings, which are exposed and unsightly when the water is low, or sloped ramps that take up a large amount of space.
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To avoid vertical pilings and large ramps, the design team developed a solution involving river boats anchoring to and loading/unloading passengers with a 400-foot-long floating dock. This barge-like structure is anchored to the heads of two "mooring arms" that are pinned at their base elevation near river gauge zero. The heads of the mooring arms float up and down with the river level, hiding the mooring arm foundations and anchorage during higher river elevations. The mooring arm foundations are 5-foot-thick reinforced concrete pile caps over three 6-foot-diameter steel pipe piles. The pipe piles are filled with concrete down to the mudline. To prevent excessive lateral deformation of the foundation in the event of a boat or barge impact, steel plates extend out from the mooring arm pile caps, through the sheet pile wall to a 40-foot-long pile cap with 20 vertical and battered H-piles.
The south end of the floating dock is equipped with an adjustable hydraulic ramp that attaches to a five-level helical ramp. As the river rises and falls, the hydraulic ramp can be removed and re-attached to the required level of the helical ramp. Passengers exiting the boats will walk from the barges, up the hydraulic ramp, onto the helical ramp, then up the helical ramp to the top level, across a bridge and onto the plaza of the terminal building.
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The helical ramp is a 100-percent steel structure with braced tube column core and hollow structural section outriggers to support the walkway and cart ramp. All levels of the helical ramp are designed to be submerged in the river. To prevent water from becoming trapped in the structural steel framing and creating rust or freeze/thaw issues, all hollow steel members were filled with expansive foam. The five-level ramp was stick built in place, so after erection was completed, it was sand blasted and coated with a marine-grade epoxy to provide maximum corrosion protection.
The fluctuating river also impacts the usability of the riverfront recreational area that is being constructed in Phase 4b, so access at any river level was achieved by creating a terraced park with a paved, serpentine walkway to provide ADA accessibility. At high river levels, the sloping grass terraces will be submerged, but the park will remain usable with its two "islands." These guitar pick shaped structures appear to emerge out of the terraces as the grass slopes toward the river. The steel-framed walls slope out of the ground at a 60° angle, and are clad with the Brazillian hardwood Ipe to ensure longevity of the wood façade. The islands consist of two parts, with the higher west end built like a dock with 24-inch steel pipe piles extending up to the bottom of the 12-inch structural slab. The lower east end is a four-sided retaining wall which holds the earth fill used to raise the ground surface. Because of extreme settlement issues (up to 12 inches of settlement is expected in some locations), all concrete surfaces built on the sloping river bank are supported by HP12x53 piles driven as deep as 100 feet.
Green roof
In early designs, the terminal building was located much closer to the river. This building location allowed for ample green space between Tom Lee Park and the proposed park and existing cobblestones. Poor existing soils and budget constraints required the building to be located much closer to Riverside Drive, so the green space requirements were met by giving the building an arched, green roof.
The green roof greatly reduces the cooling load of the building, offsetting the inefficiency created by the glass-paneled east and west walls, which exist to create views of the river directly through open portions of the building. This reduction in energy requirement is essential in Memphis, where daily high temperatures exceed 95° F most of the summer.
The green roof also reduces stormwater runoff. The City of Memphis recently implemented a stormwater utility fee based on each property's contribution of runoff to the city's stormwater management system. In addition to being a best management practice, the green roof reduces that annual fee. The specified roof system was compatible with the sidewalks, patio, and elevator landing located on the roof, and coupled with a well-established lawn would hold up to extensive foot traffic. The installation of an irrigation system was necessary to keep the roof healthy.
The terminal building houses ticketing and baggage operations, a restaurant, small office space, storage for golf carts, and public restrooms. In some ways, its construction resembles a bridge more than a building. Founded on 50-foot-deep auger cast piles, angled end shear walls provide lateral resistance in both directions and effectively serve as abutments for the bridge-like roof. The building's roof is framed with large structural steel beams spanning more than 60 feet.
Bank stabilization
For the sloping terraces that are being constructed in Phase 4b, selecting a material to provide permanent bank stabilization that aligned with the sensitive aesthetics of the project was one of the greater challenges on the project. Beale Street Landing is situated at the site of the former confluence of the Mississippi and Wolf Rivers. In 1960, the Corps realigned the Wolf to enter the Mississippi further north, creating Wolf River Harbor. Creation of Wolf River Harbor greatly altered the flow conditions adjacent to the project site. During the course of the project, the design team noticed a strong eddy flow pattern at high river levels. The eddy causes erosion of the project bank in some areas and sediment deposition in others. Natural vegetation on the river bank near the project site is very sparse below the approximate elevation of 205 feet above sea level. Very few plant species will survive below that elevation because of the submersion frequency.
Due to large fluctuations of the Mississippi River level, backfill of the site required a material that would quickly relieve the saturated soils as the river level falls. Crushed stone originally was recommended as backfill, but most crushed stone is shipped into Memphis by way of barge and, consequently, has a much higher unit price than sand, which is readily dredged in the Memphis area. Washed sand was the only material that would make the project economically feasible.
However, river eddy patterns adjacent to the project site caused great concerns about erosion of the sand backfill material. Natural vegetation could not be used in the lower areas of the park because sparse growth would facilitate erosion. Any non-native plant species would most likely be suffocated by flooding or siltation. Rip rap could not be used because the client preferred something more visually pleasing that required little maintenance and would be less dangerous to the occasional park visitor who chose to ignore the serpentine walk and traverse the bank to reach the water's edge.
Ultimately, the design team proposed articulating concrete block (ACB) to meet client requirements. An open cell version of ArmorFlex, an ACB system produced by Contech Engineered Solutions, was chosen to stabilize the terrace slopes. The closed cell ArmorFlex FlatTop was selected for the bottom terrace level to provide a more negotiable path to park visitors wanting to enjoy the view of the river and harbor in lower river levels. The appearance of the ACB in the lower park creates a nice segue between the weathered cobblestones and the sleek terminal building.
Conclusion
As the planet experiences greater swings in weather patterns, ecological features such as rivers will behave more erratically. The Beale Street Landing design is sensitive to the river's changing nature – a sensitivity that works with the river rather than against it, promising longevity that will serve Memphis, its residents, and its visitors for many years.
Brett Dunagan, P.E., LEED AP, is a project manager and civil engineer at Smith Seckman Reid. He specializes in water modeling, grading and draining, and pavement design. He currently serves as a member of the City of Memphis Stormwater Review Board and acts as treasurer of the Memphis Professional Chapter of Engineers Without Borders. Andy Kizzee, EI, MS, is a structural engineer with Smith Seckman Reid. He specializes in seismic analysis and retrofit design of existing structures, is an active member of the Earthquake Engineering Research Institute, and is currently president of the Memphis Professional Chapter of Engineers Without Borders.
