Township of Manalapan
The Tepehemus Brook and Pine Brook are two significant watercourses within the Township of Manalapan. Both brooks are tributary to the South River watershed area and are important to the storm water management of this area. Over the years rainfall-induced erosion has caused slope failures and reduced the stream carrying capacity, resulting in problematic flooding and property loss for the residents in close proximity to the brooks.
Having become inundated with residential complaints and growing concern with the streams' reduced water volume capacity and increased siltation on downstream stormwater facilities, the Township of Manalapan directed CME Associates to evaluate the alternatives for stream embankment stabilization.
CME Associates evaluated and studied the surrounding communities to determine the best solutions for this problem. The most effective and cost-efficient solution appeared to be the use of an innovative vegetation slope stabilization. It was also recognized that slope stabilization with vegetation measures could not only aid in erosion control, it could also add considerably as an ecological and successional landscape amenity.
Several species of vegetational material were determined which would provide site aesthetics through flower displays. CME Associates suggested the use of coir fiber logs, a 16" diameter roll of coconut fiber encased in a coconut fiber netting, each 20 feet in length. This innovative approach utilizes coconut fiber, a byproduct of the coconut industry that has limited recycling capabilities; however, it provides an excellent growing medium due to its durability, biodegradability, water absorption, water retention and ability to trap waterborne sediments necessary for the re-establishment of the once lost stream banks.
In areas where steep cut back slopes existed, regrading was necessary along with another stabilization method employing a coir fiber blanket. This additional method of stabilization aided in lessening the water velocities resulting from the channelization of the streams.
Resting on the stream bed, where water is easily absorbed and retained, the coconut fiber logs were staked to ensure their stability. To ensure transplant success, CME Associates recommended that the plants behind the logs were of aquatic plant species native to the Manalapan soils. This not only promoted transplant success within the logs but also encouraged rooting into the existing stream bank to further promote natural erosion control. The added consideration was that the plant selection has a vast network of roots to hold the embankment soil in place.
As the project construction got under way, CME Associates was under a lot of pressure to complete the project during the spring and early summer growing season, therefore they were required to fast track the construction.
This added another element of constraints to the project because of the availability of the coconut fiber material with short notice and the scheduling of limited contractors with expertise in this unique type of construction. Even with limited time to order, ship, and deliver, CME Associates continuous correspondence with the manufacturer of the coconut fiber proved successful.
Through the innovative design of CME Associates, the Tepehemus Brook and the Pine Brook have been re-established and the property loss issues along with assistance to flooding concerns have been resolved in an aesthetically pleasing manner which partners its natural environment. Since the project's completion, the Mayor and Township Committee have received nothing but compliments from a community that has reclaimed their natural water courses.