Pipes Replace Canal
Severe erosion and sedimentation also plagued the Park Manor Canal system, home to several other safety hazards due to the proximity of houses to its banks and steep side slopes.
The project area had construction accessibility problems because the right of way wasn't wide enough in most areas to properly maintain the condition of the ditches or regrade them to more stable side slopes. Additionally, the canal, which was burdened by flooding and dense vegitation, had meandered over time to several areas outside of the county's right of way and onto private property.
The division decided to replace the canal with a concrete pipe system, which would eliminate the bank stabilization and erosion issues and return the system to within the county right of way.
Because it posed hydraulic limitations due to the reduction in canal conveyance cross section, the system was designed to be fairly oversized to compensate for some loss of storage in moving from the open canal to the closed pipe system. Thus, the new storm-sewer system would feature ditch bottom inlets in place of the canals.
The new system offers several benefits, including no significant change in water quality treatment and no significant increase in the peak rate of flow or velocities from the canal system.
Rip-Rap Stabilizes Banks
- Construction: $998,000
- Design: $96,500
The hurricanes caused severe bank erosion to both Little Wekiva River North and Little Wekiva River South.
The north branch, with its rapidly rising stages during the wet season, had severe sedimentation. The channel geometry and flow velocities along the river bend at the project location also made it conducive to rapid erosion. It needed immediate attention.
The county and WMD implemented several stabilization and improvement projects upstream and downstream of the location. Located just downstream of a previous river stabilization project, this particular project was an emergency design-build effort to replace a failed arch culvert that had collapsed and damaged numerous homes. The county bought and removed more than 30 properties to replace the culvert with an open river channel.
The division decided to stabilize the banks with rip-rap, which also would be used to regrade the bottom of the river. This would provide a more consistent river profile and match a bank stabilization and bottom regrading project that was already under way downstream.
Rip-rap was chosen because it's economical to build, installation is straightforward, and it doesn't reduce the river's water flow. Long-term maintenance is lower than other alternatives, and, like the concrete mats used to shore up the outfall at Eastbrook canal, rip-rap is pervious.
Little Wekiva River South suffered from severe bank erosion as well. A section of the river bank failed and encroached upon private property.
Located between residential lots with very high and steep banks adjacent to the river, this section posed other hazards as well: a bridge with numerous utility crossings, rapidly rising waters during the wet season, and severe sedimentation and excessive vegetation, which reduced conveyance.
Like Little Wekiva River North, stabilization was accomplished using rubble rip-rap.
- Little Wekiva River North
- Construction: $619,000
- Design: $35,000
- Little Wekiva River South
- Construction: $314,000
- Design: $31,000