Stormwater treatment is extremely important to the overall health of streams, lakes, and other waterways, and our coastal communities must use especially prudent stormwater management to protect our oceans.
Recently, ESP partnered with the City of Sebastian to preserve its section of the Intracoastal Waterway while saving the city $60K and invaluable waterway real estate. In this case study, we describe how we performed the stormwater retrofit.
Sebastian’s Stormwater Problem
Collier Canal is the primary stormwater detention area for over 50 percent of the City of Sebastian (the City) along the east coast of Florida. The canal directly discharges into the Sebastian River, which flows into the Intracoastal Waterway, and subsequently into the Atlantic Ocean. Over the past decade, the service life of Sebastian’s Transite concrete seawalls reached a critical state and started to fail.
In order to preserve water quality, the City realized that they needed to take action. Many of the bulkhead sections along the 2.1 mile stretch of Collier Canal had failed, and concrete debris was falling into the canal. Silt had filled in the waterway, reduced water storage capacity, and compromised water quality.
After months of various design iterations, political protocols, and proposal reviews, and after rejecting the initial plan to use tons of riprap to build the wall, the City chose to rebuild with S.E. Cline Construction as General Contractor, with Everlast seawall engineering designs and vinyl sheet piling. Out of the five proposals provided to the City, the Cline/Everlast proposal was the only one to receive the highest marks from the evaluation committee in all categories.
The Collier Canal project was permitted through the St. Johns River Water Management District at the state level, and the U.S. Army Corps of Engineers at the federal level. Performance-based design criteria were established by the City’s consultant, requiring the wall design to be considered two ways:
- An extreme condition that contained a differential water level during a potential flood event.
- A common condition with a 250 psf surcharge.
Due to the confined space and location of pools, garages, and various other structures along the 11,100 LF of wall, traditional deadman systems were not a viable option. To overcome this challenge, we used 940 driven earth anchors. Each earth anchor was proof-loaded and documented to the specified minimum load of 9.9 kips. The anchors were connected to a reinforced concrete cap designed to support the top of the sheet pile and to span the distance between the tie-rod/earth anchor system.
The bridge along Fleming Street required special sheet pile and anchor designs to account for confined spacing and alignment of abutment end-bents. Design modifications were required in areas where soft soils were discovered by S.E. Cline’s crew. These modifications mandated the use of longer vinyl sheets and driven W-sections for deadmen. Unexpected drainage pipes and culverts required special sheet pile designs for the tie-in, as well. All of these unforeseen obstacles were successfully solved by the Cline/Everlast Team.
Installing the Vinyl Seawall
Using traditional materials, the 2.1 miles of canal bank stabilization would have required dumping 1,000 trailer loads of rock, but the vinyl sheet pile wall only required 10 flatbed loads. With most sheets weighing less than 50 pounds, Cline was able to use lighter and smaller equipment on the job. The sheets were easily offloaded and stored in designated staging areas.
Lighter materials and smaller equipment helped to alleviate the major concern that the 500 homes adjoining the project would be disturbed. The sheets were driven with a modified APE 6 vibratory hammer mounted to a excavator. Manta Ray Earth Anchors were driven using the same vibratory hammer, with a slight modification to the drive steel.
Areas near the Fleming Street Bridge required higher capacity anchors and tighter spacing to account for the larger load. Due to the skew of the abutment in relation to the wall alignment, Cline had to work with the pitch while driving the anchor at a horizontal angle. After installing Manta Ray Anchors and Everlast Vinyl Sheet Pile, the contractor secured tie-rods from the anchors to the tops of the sheet with two steel channels bolted on the front and rear of the vinyl sheets. This provided structural support as a temporary wale while the backfilling took place. Once fill was placed and compacted, minor alignment and adjustments were made just before the concrete cap was formed and poured.
Why Vinyl Sheet Pile?
S.E. Cline and Everlast met the City’s goal of improving water quality and increasing water storage capacities, and the construction caused minimal disruption to the 500 adjacent homes. Many of the community’s residents have commented on how much more aesthetically-pleasing Everlast Vinyl Sheet Piling looks in comparison to traditional materials.
Not only is a vinyl sheet pile bulkhead less expensive to build — it saved the city $60,000 while preserving homeowner real estate — but the life expectancy of vinyl is far greater than that of traditional materials. Nearly all of the work was performed by local personnel, which contributed to the economic benefit of the community.
The Collier Canal project was a dramatic success, and is an example of how communities can help to save the environment and their budgets by building with vinyl sheet pile.