118-22 Correspondence - Jenne Associates.pdf

To: Township of West Orange Re: Engineering Services for Investigation into Stream Flooding along the Tributary to Wigwam Brook FULL ENGINEERING ANALYSIS Date: April 11, 2022 Page 3 of 4 JENNE ASSOCIATES, LLC Consulting Engineers 8. Develop a hydraulic model of the stream, in accordance with NJDEP requirements, to predict the water surface (flood level) elevations that can be expected for each rainfall event assuming the pipe inlet flows frequently, to serve as a basis in evaluating the reduction in flooding that can be expected from alternative improvement options investigated. Part of this effort will include obtaining actual rainfall information for recent storms in an attempt to correlate with the flooding experienced based on observed blockages of the pipe inlet. 9. Develop alternate improvement measures, to a conceptual design level, that could be implemented, to predict the affect each would have on reducing the flooding being experienced. Initial measures identified during the preparation of this proposal include: • Modify the existing pipe system inlet and debris catching grate to improve its function and clog less frequently. This could include changing the shape of the inlet itself to improve its capacity (the ability of water to get into it). This should qualify for construction under an NJDEP Permit-By-Rule 2 – Repair of Lawfully Existing Structure. • Construct one or more debris catching structures upstream of the pipe inlet providing for additional storage for the debris before it reaches the inlet debris rack and blocks it. This will most likely require an NJDEP Individual Permit for construction. • Raising the ground elevations between the pipe inlet and the adjacent land on Park Drive West to hold the ponding water to a higher elevation before overtopping and flowing downstream across the properties. This could include evaluating an alternate path for the ponded water to flow (instead of across the private properties) such as over to and down Bloomfield Way, as long as it could be accomplished in a safe and controlled manner. • Alter the ground elevations on the properties where the flooding is being experienced to reduce the damage (including possibly protecting areas/features that are damaged) and safely direct it back into the underground pipe system or down Park Drive North. • Evaluate potential modifications to the underground pipe

ing possibly protecting areas/features that are damaged) and safely direct it back into the underground pipe system or down Park Drive North. • Evaluate potential modifications to the underground pipe system other than at the inlet location to improve the ability of the pipe to safely carry the floodwaters and reduce the impact that blockage at the inlet will have on flooding of the private properties. • Evaluate the establishment of an ongoing program for debris/tree limb removal along the stream to reduce the amount of debris that can potentially flow down the stream and cause a blockage at the pipe inlet. This effort will include identification of the properties/owners whose land abuts (or includes) the stream. When investigating this in the past for the Llewellyn Park Committee of Managers it was determined that the stream is located on individual properties and no easements existed allowing for, or requiring, maintenance of the stream and/or the adjacent lands including removal of debris that could readily make it to the stream, 10. Prepare a report summarizing the findings of the investigation including the methodology utilized. A detailed description and conceptual design will be presented for each alternative improvement investigated including feasibility of addressing the issue (expected reduction in flooding magnitude or frequency), order-of-magnitude cost estimate, and initial evaluation of required permitting. Recommendations will be made as to how to proceed including the next steps to be implemented for each feasible alternative evaluated.