We were honored to have the opportunity to design a major water control structure serving the mid-region of Palm Coast, Fla., that is more cost effective and efficient and will save taxpayer dollars in the long run.
The control structure, located in the Lehigh Canal a half mile west of I-95, will replace an existing failed structure and help prevent flooding. It is an important structure because it has the largest drainage basin area – 10,676 acres – of all City control structures and controls the most amount of water in the entire city.
As hurricane season is underway in Florida, our design of the new L-4 surface water control structure in Palm Coast is under construction and nearing completion. The new structure will allow the city to draw down water levels quicker from its canal system ahead of a severe storm.
Contractors build a new weir structure designed by DRMP for the City of Palm Coast, Fla.
Our firm’s design of the new structure provides an upgraded water control system and keeps the public safer during a storm. It is more cost-effective, hydraulically efficient, and will have a longer service life than the City’s existing structure. It also will provide better access for maintenance and has a mechanical system for the weir gates, which allows the City to control it remotely.
Existing Structure Failures
The standard city water drawn down system is a single corrugated metal riser culvert with a 6-foot-long operable weir mounted to the front, such as the existing L-4 system. These structures control water levels, so when it storms, a basin has room to hold rainwater, preventing neighborhoods and commercial properties from flooding.
The existing structure over the years experienced several failures, which led the City to completely replace it, and later when it started to wash out, apply temporary fixes to it. On one occasion the city used 105 cubic yards of flowable fill to stabilize the washed-out structure. When the interior of the structure started to wash away, the city could not determine how seepage into the structure was occurring.
The old weir structure in the City of Palm Coast, Fla., pictured above has experienced many failures over the years.
Through drawn down analysis, DRMP determined increasing the operable weir gate setup from one 6-foot-wide gate to four 6-foot gates would achieve the city’s desired water level control of 4 feet of drawdown within 48 hours prior to a storm. The normal water level in the canal will be kept at elevation 18 (NAVD88 feet) on a regular basis and adjusted based on weather conditions.
In addition, between four separate metal risers and a single concrete riser with four gates, the City chose the concrete alternative instead of metal as this option provides improved access to the gates during high water/flow conditions and longer design service life. With the existing structure, there’s a space between the concrete pad and metal riser so field workers have to reach over and across the water to perform maintenance. The new structure allows safer and easier access.
New Design Capabilities
Our team designed the new L-4 control structure with a single box culvert barrel. We moved two of the weir openings to the sides of the structure and narrowed the width of the concrete overflow weir and sloped the top slab, which allows for a reduction in the footprint of the structure and has fewer environmental impacts. The sloped top slab pushes water away and keeps the concrete dry, so it doesn’t deteriorate.
The gate that allows the water to go in and out of the structure can be controlled remotely so city personnel do not have to go there in person. The existing structure does not have this capability or any mechanical aspect to it.
A contractor inspects sheet pile alignment during installation of a new weir structure in the City of Palm Coast, Fla.
Combining watershed-scale modeling capabilities with design of a major water control structure with remote control of automatic weir gates required a broad range of expertise from our firm. Our project team included experts in surface water modeling, structural design, geotechnical investigation, and construction, engineering, and inspection (CEI).
The project also required coordination and permitting with the St. Johns River Water Management District (SJRWMD) due to other surface waters (OSW) impacts.
Being located in a state frequently hit by hurricanes and thunderstorms, designing a more efficient and structurally sound water control structure for the City of Palm Coast makes this project even more critical and rewarding.
