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Article : Ewing Township Erosion Control

Residents Get Peace-of-Mind

Schoor DePalma

For decades, the residents of Ewing Township in Mercer County, NJ have dealt with flooding and bank erosion issues associated with the West Branch of the Shabakunk Creek. Numerous agencies have looked at the Creek to help alleviate the problems. Studies dating from 1973 to 1992 done by agencies such as the Soil Conservation Service, New Jersey Department of Transportation, and the Army Corps of Engineers all tried to address the problem.

On June 12, 1996, however, residents got much more than they had ever bargained for when a 100-year storm event brought over seven inches of rain in less than four hours to the town of 34,000. The torrential downpour resulted in over $10 million in damages. The Red Cross was called in to help the 176 impacted residents and 75 local businesses. Some businesses were closed for up to thirteen days, repairing damages and cleaning up the mess left by floodwaters. The Township sustained $24 million in municipal overtime costs resulting from efforts to help cleanup the devastated area. This one event cost Ewing Township more than $30 million. And, although this storm was extraordinary, the Shabakunk Creek would cause problems for the township with each passing shower in terms of property lost to erosion and comprised water quality.

A Permanent Solution

The Shabakunk Creek is classified as Trout Maintenance Water, dictating that all construction, begun in October, had to be completed by May 1. The project team was able to secure the 300 property owners' "sign-off" on agreements needed to begin work in time to accomodate the stringent construction schedule.

It was clear that a more permanent, regional solution was required to prevent further economic loss and personal hardship to both the residents and businesses of Ewing Township. The township commissioned Schoor DePalma, an engineering and design firm, to perform a study and make recommendations for a flood control project that would provide real relief for residents and business owners.

“I was losing a bit of my backyard every time we had a storm” said Tula Arland, a local resident. “I was concerned that one day the stream would be up to my back door."

The township wanted a program that would not only alleviate the flooding problem, but also address the erosion that resulted in compromised water quality and preserve as much property, public and private, as possible.

“They formed a team of their professionals to handle all aspects of the project, from stormwater management, hydraulic and hydrologic design, environmental and construction permitting, and construction management,” said Ewing Township Mayor Alfred Bridges.

Meeting the Challenge

Three sites along the stream were designated for stream detention basins. The basins provide areas for flood waters to collect, while increasing water quality by allowing pollutants to have a place to settle out of the creek.

Schoor DePalma faced numerous challenges as they studied the situation and prepared to implement a program. One challenge was that The Shabakunk Creek is classified as Trout Maintenance Water, dictating that all construction, begun in October, had to be completed by May 1. This left a mere five-month window of potentially harsh winter weather, to complete the project in order to avoid disturbing the delicate ecosystem and maintain a healthy habitat for the native fish.

The project team was able to secure the 300 property owners’ “sign-off” on agreements needed to begin work in time enough to accommodate the stringent construction schedule imposed by the creek’s Trout Maintenance Water status. Lou Cattuna, of the NJ Department of Environmental Protection noted: “The project team worked closely with the State to comply with the stringent permitting regulations.” Another challenge was that this was the first project of its kind in the State of New Jersey, so cooperation and coordination was needed from the NJ Department of Environmental Protection, which had never issued permits for a project of this type or magnitude.

Also, designing flexibility into the construction contract was imperative since so many private property owners would be impacted by the project. To ensure that the project would proceed in a manner sensitive to the needs of the private citizens, residents and business owners, the project team solicited ideas from prospective contractors to determine the best approach to result in the least disturbance to property owners.

The contractor that was eventually chosen to implement the project demonstrated flexibility during construction with individualized attention to property owners who had special conditions, such as existing trees, buildings and fences adjacent to the stream. Utmost concern was employed to preserve existing structures throughout the process. The contractor also took special care with extraordinary terrain features, such as steep slopes, difficult access, wet conditions, and strove to keep the stream clean throughout construction.

The West Branch of the Shabakunk Creek is over four miles long, originating at the Mercer County Airport, and terminating at the southern end of Towns at its confluence with the main branch of the Shabakunk Creek. The entire creek was walked and observation skills, engineering judgment and hydraulic modeling was used to prioritize areas that were experiencing the most severe bank erosion. This method also allowed the firm to determine and propose critical property purchases that would ultimately provide the maximum relief to land owners.

To stabilize the banks, it was determined that the best method would be an innovative one. Design and construction specifications provided for a new method of bank stabilization that employs interlocking concrete blocks to help control stream velocities and stabilize the banks. The interlocking blocks allow the efficient passage of flood flows in the creek while holding the underlying soil in place, protecting the banks from erosion and promoting better water quality. The spaces in the block have been filled with topsoil and seeded to give the final product a “green” look and provide vegetation along the stream banks, thus giving the stabilized areas along the Creek a more natural look. In the end, a total of two miles of the creek’s banks were stabilized through the use of this interlocking block method.

In areas of slower stream velocities (less than 6 feet-per-second), vegetative “biologs” were used to buffer the velocities and further stabilize the banks. The “biologs,” comprised of a geotextile material, and consisting of coconut grass matting, were staked in place along the banks and planted with a variety of wetland plant species. Coconut Fiber erosion control matting was used from the bottom of the banks to the top of the banks to stabilize these soils until the vegetation planted there could take root.

The biologs provide a supportive network in which the new plants can take root and mature. Within 10 years, the biologs and matting will naturally degrade and the new plants’ roots will take control, anchoring the soil and stabilizing the stream banks. This method of stabilization also serves to mitigate the wetlands disturbed by the project. In addition to the biologs, more than 400 new trees were planted throughout the affected area, providing overstory and shade for the stream biology, enhancing the project’s aesthetic qualities, further stabilizing stream banks and mitigating disturbed wetlands.

To further protect the town, it was determined that three water quality improvement basins should be included along a four-mile stretch of the creek. Strategically located upstream of residences and business sites to provide maximum flood relief, the basins provide a place for excess water to collect, rather than having it join the creek water and cause the water level to swell beyond what the banks can support.

In a highly developed township such as Ewing, finding land suitable for use as on stream detention basins was a challenge. Nine potential sites were identified, and the township chose three to be used for the project. The sites included an existing township park, an unused tract of land owned by the Incarnation Church, and a driving range. Each site was excavated and a weir was constructed across the creek to contain the flows. The basins now provide areas for flood waters to collect, while increasing water quality, by allowing pollutants to have a place to settle out of the Creek. The construction of these basins has provided immeasurable flood relief for a number of properties. A recent article in the local newspaper reported that the residents are very happy with the results of the work and that the potential for flooding of their homes and businesses has been greatly reduced.

Finally, the creek was desnagged and desilted. This work is a continuation and expansion of long and ongoing desnagging project that the township has undertaken. The stream now flows free from silt and debris and the public works department will use the new maintenance equipment purchased during the project (including sweepers, sewer cleaners, loaders and trucks) to ensure it will stay that way in the future.

The Funding Mechanism

Freshly laid interlocking blocks help to channel the flow of the Shabakunk.

The township held public hearings, with more than 100 participants, to ensure that property owners understood the project and to give them the opportunity to “buy-in” to the project and its funding mechanism. Not only did the residents “buy-in” to the project, they were enthused, and said that they wished the work had been done much earlier. The New Jersey Environmental Infrastructure Trust granted a $4.2 million, 20-year low interest loan to the Township. The loan provided for land acquisition of two critical properties, engineering, design, construction, construction administration, as well as stream maintenance equipment for the township to ensure that the improvements made to the situation would be maintained in the coming years. During the hearings, it became clear that a collaborative effort would be required to secure and administer the funding, permitting, and construction for a project of this magnitude.

As a result, the project, which is the first of its type in New Jersey, was an orchestration between residential and commercial property owners, township officials, the New Jersey Department of Environmental Protection, the contractor and the Schoor DePalma project team.

An Increased Quality of Life in Ewing

The Shabakunk Creek snakes its way through a residential area now protected through a variety of erosion control methods. In June 1996, a 100-year storm event brought over seven inches of rain in less than four hours to the town of 34,000. The downpour resulted in over $10 million in damages.

While, arguably, thousands, if not millions, of dollars will have been saved when the next major storm comes to Ewing Township thanks to the measures taken to tame the Shabakunk, it is the peace-of-mind this project has provided township residents that is its most valuable result.

“Flooding always had an impact on the business district. In 1996, I was out of business for 13 days”, said Randy Martin of Martin’s Auto Service. “These improvements have allowed us peace of mind. We can operate without the fear of major financial loss”.

“The Shabakunk Creek project is a testimony to how economic and development opportunities can be synonymous with an increased quality of life”, said Kathleen Wollert, former Ewing Council president. “The end result of this initiative is the overall benefit to local businesses and residents.”

As surrounding communities monitor the success of this project, the Shabakunk Creek will serve as a catalyst for a regional solution that ultimately could lead to millions of dollars in savings for multiple towns throughout the area during the next major storm event.

The success of the Shabakunk Creek project has underscored the value of proactive thinking and will be the future model to reduce economic loss to residents and businesses and encourage development opportunities for generations to come.

Recognition

The 1/2 acre of disturbed wetlands were mitigated by the planting of new trees and a variety of wetland plant species. The New Jersey Environmental Infrastructure trust granted a $4.2 million, 20-year low interest loan to the Township. The loan provided for land acquisition of two critical properties, engineering, design, construction, construction administration and equipment. The project was an orchestration between residential and commercial property owners, township officials, the New Jersey Department of Environmental Protection, the contractor and the Schoor DePalma project team.

• New Jersey Society of Professional Engineers –

2000 Project of the Year Award in the Management Category.

• New Jersey Society of Professional Engineers, Mercer

County Chapter – 2000 Project of the Year Award.

• New Jersey Concrete and Aggregate Association. –

2001 Merit Award in the Public Project Category.

• New Jersey Department of Environmental Protection –

Certificate of Appreciation and Recognition for the Division

of Watershed Management Awards Program.


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October 30, 2014, 10:24 am EST

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