Aug 07, 2019

Infestation to Restoration

Mosquito problem illuminates larger environmental issue in Augusta, Ga.

The outflow culvert suffered significant damage due to heavy rains and hillside collapse. This resulted in compromised water flow and stagnated water at the culvert mouth.
The outflow culvert suffered significant damage due to heavy rains and hillside collapse. This resulted in compromised water flow and stagnated water at the culvert mouth.

Swarms of mosquitoes near a retention pond adjacent to a big-box retail center were the first indication that the area was suffering from significant environmental damage. What started as a possible extermination project resulted in a major environmental initiative involving shoreline restoration and a range of related repairs.

 

Unwanted Visitors

When complaints of mosquito infestation surfaced in Augusta, Ga., last year, the owners of the retail center and city officials began the process of investigating the situation. There was some urgency since the retention pond was adjacent to a school. 

After closer analysis, it became clear that this mosquito breeding ground was the result of the certain dynamics on the property, including: 

  1. Collapsed shorelines along the retention pond caused by years of torrential rainfall;
  2. A compromised and damaged outflow culvert due to constant water pressure and collapsed shorelines;
  3. Accumulated sediment at the mouth of the culvert resulted in stagnant water, preventing water flow into the pond
  4. and causing invasive vegetation growth and algae; 
  5. A raised water level due to sediment accumulation resulting in reduced pond depth; and 
  6. Increased size of the pond’s surface area and water volume due to collapsed shorelines.

“These issues contributed to the mosquito infestation,” said Ryan G. Leeds, managing partner of Sox Erosion Solutions. “It quickly became clear that the increase of the mosquito population was the result of other environmental issues and structural problems that prevented the retention pond from doing its job of controlling flooding. One problem led to the next. What started out as an extermination issue cascaded into a total environmental hazard—collapsed land; build-up and accumulation of sediment in the pond; shallow pond; stagnating water; invasive plant species; and an increase in algae that compromised water quality.”

These challenges were the factors that created more breeding areas for mosquitoes and dangerous conditions for workers. In short, there was a domino effect that resulted in a number of problems, including the mosquito infestation.

Several tons of rocks were loaded onto the mesh to strengthen the pond bottom and enhance water flow out of the culvert.
Several tons of rocks were loaded onto the mesh to strengthen the pond bottom and enhance water flow out of the culvert.

Stabilizing the Shoreline

DGC Environmental Solutions, a storm water maintenance company, developed a comprehensive plan to not only reduce the mosquito population, but also solve other structural and environmental issues within the body of water.

“It would have been easy to take a short-term view and simply eliminate mosquitoes through extermination,” said Sidney Willis, CPESC & CESSWI, executive director of operations for DGC Environmental Solutions. “But that would have been short-sighted, resulting in the return of mosquitoes during the next mating season.”

DGC and Sox Erosion Solutions realized that corrective issues could not simply be limited to spraying the area with chemicals to control mosquitoes; rather, it would require a comprehensive strategy that included repairing the culvert along with shoreline stabilization using a bio-engineered vegetated system.

DGC identified the collapsed shorelines and sediment build-up as the major culprits. The shoreline restoration started with the installation of DredgeSox, a long-lasting and eco-friendly erosion control technology. It also is an effective way to remove sediment from waterways and reclaim shorelines that complies with the best management practices of living shoreline restorations.

“In layman’s terms, we are filling a huge specialized mesh sheet with rich organic sediment dredged from lake bottoms,” said Leeds. “It is then secured to the shoreline, re-creating the original and now living lake bank. In addition, the dredging process improves water flow, reduces pollution and nutrient loading, and starts the process of re-building healthy wildlife habitats. It also removes years of accumulated leaves and grass clippings.”

Once filled with sediment, the material is secured to the shoreline. Sod and other landscaping is planted and roots grow through the knitted mesh, creating a long-lasting living shoreline. The installment process also cleared sediment from the mouth of the culvert and promoted healthy water flow. Stabilizing the collapsed shoreline also made it safer for crews to mow and perform other maintenance work.

The material stabilized the hillside adjacent to the culvert. This secured the land and prevented torrents of water from damaging the repaired cement culvert. The reinforcement mat also was installed under water at the mouth of the culvert to further stabilize the bottom. Several tons of rocks were loaded onto the mesh to strengthen the pond bottom and enhance water flow out of the culvert.  

 

Standing Up to the Test

The major test of the restoration was yet to come. The installation was completed in August 2018. During the next seven months, Augusta experienced significant rainfall and hurricane conditions. This included 42 in. of rain, meaning more than 28 million gal of water flowed through the outflow culvert during those seven months. 

The system survived these torrential rains and flooding. The material protected the outside edge of the culvert, and the underwater reinforcement mat remained stable, while the rocks were displaced, and water flow was maintained. The material also survived the rains and prevented further erosion of the shoreline. Overall, improved water flow reduced invasive plant species, larvae and mosquitoes, and the new system served as a filter, reducing phosphates, nitrates and other pollutants from entering the pond. Clean water was able to flow to other nearby bodies of water. In addition to reclaiming shorelines, the installation process increased water depth while decreasing the actual size and circumference of the pond. Finally, with the reduction of invasive plants and improved water flow, the area became a healthier habitat for wildlife.

The retention pond now functions as an effective and environmentally safe flood
The retention pond now functions as an effective and environmentally safe flood.

“The major advantage is that this innovative product allows us to promote nature’s natural ability to stabilize the shoreline by planting and/or sodding directly through the SOX and establishing healthy rooted vegetation,” Leeds said. 

The key to the success of the project was that the property owner and city officials realized that swarming mosquitoes could not be viewed as an isolated situation. Rather, they recognized that it was a symptom of a much larger problem caused by other environmental factors.

“The multi-tiered approach provided a long-lasting, environmentally sound solution,” Leeds said. “Everyone benefited by taking the long look. The mosquito population was reduced without the over-use of harmful chemicals. By re-establishing the shoreline and dredging, we improved water flow and created a healthy habitat for wildlife. The mesh continues to serve as a filter, preventing nutrient overload from entering the water system. Through these efforts, the retention pond was able to serve its original purpose of preventing flooding.”

About the author

Casey Cittadino is national sales director for Sox Erosion Solutions. Cittadino can be reached at [email protected] or 631.478.8567.

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