Mayor's Update - September 15, 2021

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Mayor's Update - September 15, 2021

Dear Cranbury Residents,

I hope you are enjoying this warm weather and the hint of fall in the air. Below is a long but comprehensive summary of Monday’s Township Committee meeting, as well as some upcoming events.

Cranbury Day. THANK YOU to all who made Cranbury Day such a special re-start to our annual tradition. The energy was palpable as people re-connected with neighbors in person. THANK YOU to the Helene Cody Foundation for a successful 5K and Fun Run in Heritage Park. THANK YOU to the Cranbury Business Association for a successful Cranbury Day street fair. Finally, a big THANK YOU to Tess Staples and Gavin and Donovan Mavoides for organizing the moving display of 2977 flags in Heritage Park to support the Day of Remembrance for 9/11.

Township Meeting: After-Action Report on Hurricane Henri. Chief Owens gave a thorough Hurricane Henri after-action OEM report, and Township Engineer Tom Decker spoke about the lake project, the dam performance, and our stormwater management efforts.

OEM Summary – Chief Owens. In the OEM report, Chief Owens shared the pre-storm planning for Hurricane Henri, which was widely expected to be a wind event with 1-3 inches of rain. As we know, the storm sat over Cranbury and dumped 9 inches of rain in a few hours. Chief Owens showed dash camera and body camera footage of his department responding to a few of the 70+ emergency calls received on August 22, including several car rescues. He also showed footage of Main Street and the river flowing from Plainsboro Road toward the lake, as well as drone footage of the lake area. He thanked all the agencies who helped out that day, including the fire rescue boats and additional efforts from surrounding towns who assisted. Finally, he reviewed the communications history and the disaster aid efforts in progress.

Engineering Update – Tom Decker. In his engineer’s report, Tom Decker shared that the design benchmark for a “100-year storm” is 8.63 inches over a 24-hour period (increased over the past 30 years from 7.3 inches based on historic weather patterns), so this storm (8.91 inches in two hours) was far above those benchmarks and would have overwhelmed any stormwater management system.

Background on Brainerd Lake and Dam. As additional background, Tom explained that Brainerd Lake is a man-made lake created around 1840 by constructing a 382-foot earthen fill roadway embankment dam running the width of the lake. This dam is classified as a Significant Hazard Potential, Class II Dam by NJDEP; the significant hazard potential refers to the impact downstream population and properties should the dam be breached. A horseshoe shaped spillway controls the hydraulics of the dam and is set approximately 3 feet lower than the top of the dam. There is a sluice located approximately 7 feet below the spillway that remains closed during normal operations and can be opened periodically for maintenance purposes. The control structures were fully rehabilitated in 2014 as part of the dam project. The dam and its spillway are solely for the purpose of impounding the Cranbury Brook to Brainerd Lake while maintaining the natural stream flow depths both upstream and downstream. The dam and spillway are not for the purpose of flood control.

Dam Functionality. Tom summarized that the dam and its controls functioned as designed during the intense rainfall of August 22. The concrete spillway successfully regulates typical storm events so as not to overtop the dam/Main Street. However, for an unpredictable storm event, the dam functions much the same way as an emergency spillway in a stormwater management basin. Tropical Storm Henri was an unprecedented storm that impacted Cranbury Township and its surrounding municipalities more so than any other region of the State. It could not be predicted nor modeled. Essentially it was an emergency condition. Water overtopped Main Street without breaching or compromising the dam’s integrity. This is how an emergency spillway is meant to function and how the dam was originally designed.

Brainerd Lake Storage Capacity. Tom also indicated that the available stormwater runoff storage of Brainerd Lake is limited to the volume above the standing water surface elevation to the top of the dam. The lake dredging project that will be starting in the upcoming weeks will have no impact on available flood storage; the dredging project is solely for the purpose of removing 50 years of accumulated sediment, restoring the natural bottom and aquatic health of the lake.
Lake Lowering Permit. Tom indicated that there have been questions whether lowering the lake prior to a storm event would provide additional flood storage. This is not permitted. A Water Lowering Permit is required from the NJDEP Division of Fish and Wildlife whenever the lake is to be lowered. For example, a permit was obtained for the upcoming lake dredging project. Other than the timeframe associated in the application and review process to obtain a Water Lowering Permit, the permit has limitations. These limitations are for all lowering permits, not just the one issued for dredging. For example, lowering of the lake may commence no sooner than September 15 and no later than November 1; Division’s Bureau of Freshwater Fisheries is to be notified 24 hours prior to initial water lowering; and during the lowering the rate of release must be controlled such that there is no over-bank flow of the primary downstream channel. In no case shall the lake be lowered by more than 1 foot within a 24-hour period. These regulations are put in place for a reason. While lowering Brainerd Lake in anticipation of a storm event may mitigate some flooding, consideration must be given to the downstream receiving water bodies. An uncontrolled release of water from Brainerd Lake could impact the available storage in downstream ponds in other municipalities who will be experiencing the same predicted rainfall event. The required notification process of the lowering permit helps to ensure that the water release is controlled, coordinated with downstream waterways, and does not coincide with a predicted storm event.
Limitations of Lowering the Lake. Even if lowering the lake were permitted and could be done in advance of Tropical Storm Henri, flooding would have likely still occurred given the intensity and short duration of the storm. Brainerd Lake has a drainage area of approximately 11.9 square miles (sq-mi). Nine (9) inches of rain over that area has a volume of approximately 332 million cubic feet, or approximately 80 times the volume of Brainerd Lake if empty and after dredging. Of the 11.9 sq-mi Brainerd Lake watershed, only 1.56 sq-mi (13%) originates in Cranbury Township (Monroe Township contributes approximately 9.63 sq-mi (81%) and Millstone Township the remaining 0.71 sq-mi (6%).
North Main Street Flooding. North Main Street and Areas to the West also experienced flooding. This flooding first occurred before Brainerd Lake crested. This is due to the carrying capacity of the storm drainage system being overwhelmed. These systems are typically designed for the 25-year storm event with the understanding that higher event storms may surcharge the inlets and continue along the road gutter line.
At the end of the work session, we identified some potential actions around clearing the Cedar Brook (in coordination with the DEP), exploring an interrupted drain line west of Main Street, and building a resiliency plan.

Disaster Relief Update. We’ve been working behind the scenes to secure all possible aid for residents and businesses affected by Hurricane Henri. The application for the Henri/Ida Business Assistance Grant Program will open at 9:00 a.m. on Friday, September 17. More information and materials to help small businesses and nonprofits prepare to apply are available at https://www.njeda.com/henri-ida-relief.

Brainerd Lake Dredging. The lake has begun to be lowered TODAY as part of the lake dredging project. NJ DEP rules do not allow us to lower the lake without a permit, and the lake can only be lowered one foot per day. Stay tuned for updates on the project as the fall progresses. Updated FAQs can be found here.

Rabies Clinic (September 1. Please bring proof if animal previously vaccinated to receive a three-year vaccination. 1:00 to 2:00 pm at the Cranbury Fire House.

October 2 and 3 is Clean Up Weekend. Bring your unwanted items to the DPW Yard at 100 Dey Road; the hours of operation will be 7:00 am to 3:00 pm, rain or shine. The DPW crew will be on site to help unload your unwanted discards. Acceptable materials include household items that are too large to fit inside your trash tote. NO household trash, paint or hazardous waste items will be accepted. This service is open to Cranbury residents only.

Regards,

Michael Ferrante, Mayor
Cranbury Township Committee

https://www.cranburytownship.org/home/news/mayors-update-september-15-2021