The town of Oakland NJ had a somewhat similar slope failure caused by the Ramapo River. Their firm (Boswell Engineering) that did the repair in Oakland was recommended. Boswell was engaged at a cost of $80,000 to propose a design for repair and to obtain DEP approvals for the design.
The Boswell proposal involves the stabilization of the erosion along a 650 linear foot section of the western bank of the Rockaway River. The area in question is located approximately 1,500 feet west of the intersection of Route 202 and Interstate 287 within Grace Lord Park. The slope erosion is the result of severe storms, the presence of erodible soils and changing stream dynamics as the Rockaway River attempts to reach equilibrium.
The geometry of the river through this section of the channel has created a cutting situation along the western bank in the "washout area" with slopes in excess of 1:1 (1 foot vertical to 1 foot horizontal) with an 85' +/- change in grade. In addition to constant erosion and sedimentation, the washout area is devoid of woody vegetation and large trees have fallen into the channel.
Boswell Engineering considered several bank stabilization designs (including stone weirs, rip rap stone, bio-engineering, etc.), the preferred design proposes the installation of multi-tiered rubble walls within the most severely eroded portion of the embankment (washout area), as well as, selective grading to blend the new system into the surrounding topography.
The rubble walls would range in height from 3' - 10' and all stone would be supplied to the contractor from a local quarry. The area between each tier would be planted with a variety of native shrubs to promote food and shelter for local wildlife and create a healthy root system below the soil. The upper portion of the slope above the flood hazard area elevation would be regraded to achieve a slope of 2:1 then hydro-seeded to establish a dense ground cover specifically designed to provide erosion control. After applying the hydro-seed, a National Resources Conservation Services (NRCS) approved erosion control blanket would be installed to provide temporary stabilization while the seed mix fully germinates over a one and half to two year period.
The design includes the relocation of a storm water outfall which is located within the washout area and exacerbated the current condition during periods of intense rainfall. It will also include critical components of a trail system that connects Grace Lord d Park to a parking lot on Morris Avenue that had been lost in the collapse.
The project requires several permits from the New Jersey Department of Environmental Protection (NJDEP) due to the proposed disturbances to riparian zones, flood hazard areas and State open waters. The proposed stabilization design is intended to protect the natural environment to the greatest extent possible while providing adequate stability to the western embankment.
The NJDEP has approved the technical aspects of the design and overall approval by the NJDEP is expected in October, 2016. At that point, the Mayor and Board of Aldermen are expected to begin open discussions with the public regarding the project.