Project Background and Purpose:

• As a follow up to the completion of the Little Wekiva River Master Plan, SAI was contracted by Seminole County to design two erosion control countermeasures, Northwestern Avenue Bridge Area (NWBA) and Horse Lovers Lane (HLL) and a sedimentation basin along the river.

• SAI was also contracted by the City of Altamonte Springs to design an erosion control project in the vicinity of the Riverbend Apartments Area (RAA). Erosion in the river had resulted in property damage and condemnation of an apartment building.

 

 

Project Design / Implementation:

• The NWBA design included a 21 ft. high gabion wall (the highest in Seminole and Orange Counties) and the relocation of an adjacent gravity sewer. The gabion wall was designed to protect an existing wetland canopy. A wetland planting scheme and methodology was developed for the gabions as a pilot test.

• The HLL design included lowering the channel bottom of the Spring Lake tributary, replacement of a number of culverts, and reno mattress construction.

• The NWBA and HLL projects have been permitted through the SJRWMD and have been contracted for construction. The NWBA project is currently under construction with SAI providing construction administration.

• Two detailed sedimentation basin designs were provided to the County; one bermed and one vertical wall construction. Both involved a 30 ft. diversion weir in the river. The basin has been designed to remove approximately 25,000 tons of sediment per year.

• The RAA design is currently under construction and includes push-in sheet pile wall construction (new technology) and restoration of existing FDOT reno mattress failure.

• Design and coordination with utility company and their consultant.

 

Stormwater Modeling / Investigation:

• Water depths in the river fluctuate from 0 to 11 feet.

• Severe erosion was threatening to undermine the structural integrity of residential buildings and utilities.

• Erosion conditions at multiple locations were also creating sedimentation problems elsewhere in the river.

• The hydrodynamic model ICPR was used to design the countermeasures and demonstrate that no adverse hydraulic impacts would occur.

• The sedimentation basin was designed to minimize velocities through the basin and provide sufficient detention time for settling.

• Emergency authorization was obtained from the SJRWMD in order to construct the RAA project before receiving ERP and Sovereign Submerged Lands approval.