Flooding in Demarest, New Jersey: the flood zone, the record, and what to do
The Tenakill Brook runs through the middle of Demarest and widens into the Duck Pond at the centre of town. It is the borough's main flood source, though a modest one: the record is real but small, and concentrated in a handful of storms.
The Bergen County 2026 Hazard Mitigation Plan maps 6.67 per cent of Demarest in the 1 per cent annual chance flood zone. FEMA's National Flood Insurance Program has recorded 30 flood claims in the borough, spread across Floyd, Irene, the March 2010 nor'easter and Ida, and lists four repetitive-loss properties, one of them severe. The Tenakill Brook and its tributaries, Demarest Brook and Cresskill Brook, are the streams FEMA studies here.
The short version
- FEMA records 30 NFIP flood claims in Demarest, spread across Floyd, Irene, the March 2010 nor'easter and Ida.
- FEMA lists four Demarest repetitive-loss properties, one of them severe repetitive loss, as of August 2026.
- The Bergen County 2026 Hazard Mitigation Plan maps 6.67 per cent of the borough in the 1 per cent annual chance flood zone.
- The Tenakill Brook, which forms the Duck Pond, is joined in this stretch by Demarest Brook and Cresskill Brook.
- An October 2021 nor'easter damaged a small private dam on Cresskill Brook in Demarest, worsening flooding downstream in Cresskill.
Thirty claims across four storms
FEMA's OpenFEMA data show 30 NFIP claims in the Borough of Demarest. No single storm dominates. Hurricane Floyd and Hurricane Ida are each linked to five claims, Irene to four and the March 2010 nor'easter to two. By year, 2021 is highest with seven, followed by 1999 with five, 2011 with four and 2010 with three. FEMA's multiple-loss records, as of 2 August 2026, list four Demarest repetitive-loss properties, one of them in the severe repetitive loss category. Four properties with repeat losses in a borough of 1,748 housing units, as counted by the US Census Bureau, suggests that flooding here is narrow rather than widespread: the same few low-lying lots near the brooks, again and again. The county plan reports 21 active NFIP policies in the borough as of October 2024.
The flood zone
The county plan's Table 4.6-1 counts just under 89 acres of Demarest, 6.67 per cent of the borough's 1,331 acres, in FEMA's Special Flood Hazard Area. The 0.2 per cent annual chance zone adds a little, bringing the share to 8.05 per cent. Unlike its reservoir neighbours to the west, Demarest has almost no open water inside its boundary, so nearly all of that mapped area is land along the streams. FEMA's first flood study for the borough, by Leonard Jackson Associates under subcontract to NJDEP, dates from March 1981; it is now part of the countywide study revised in 2019.
The Tenakill Brook and its tributaries
The Tenakill Brook flows north from Cresskill through Demarest, where a section of it forms the Duck Pond, and on through Closter to the Oradell Reservoir. FEMA's Flood Insurance Study maps two tributaries that join it on its way north: Cresskill Brook and Demarest Brook, each with a drainage area of 2.2 square miles at its confluence. The study estimates the brook's 1 per cent annual chance flow at about 1,120 cubic feet per second above the Demarest Brook junction and about 1,700 where it enters the reservoir, so the brook grows substantially as it crosses the borough. Downstream in Closter, USGS has recorded the brook's largest peaks in April 2007, Ida in 2021 and Floyd in 1999.
Small dams and the October 2021 nor'easter
The county plan lists two state-regulated dams in Demarest, both rated low hazard by NJDEP. It also records that in October 2021, weeks after Ida, a nor'easter damaged a small privately owned dam on Cresskill Brook in Demarest, and that officials in neighbouring Cresskill reported the failure contributed to flooding there. News 12 New Jersey reported the same event as a partial collapse. An earlier structure on the same brook, the Wrubel Swimming Pool Dam, was removed in 2013. Small private impoundments like these were never built to hold back floods, but when one fails, the homes downstream feel it.
Drainage on the streets
Demarest's summary in the county plan is about drainage rather than rivers. The borough says it has adopted all of NJDEP's stormwater management ordinances, has prioritised paving its unimproved roads so that drainage can be added, and carries infrastructure upgrades in a five-year capital plan. It has also published maps of its storm-water outfalls, which show where street drainage enters the brooks. The Census Bureau puts the median year built of Demarest homes at 1967, newer than most of the Northern Valley, but a fifty-year-old basement can still take water through its walls or floor drain in heavy rain without any brook rising.
What this means if you own or rent here
If your house is near the Tenakill, the Duck Pond, Demarest Brook or Cresskill Brook, check it on the FEMA Flood Map Service Center and treat Floyd, Irene and Ida as the storms to plan around. Elsewhere in Demarest, river flooding is unlikely to reach you, and the more common problems are a failed sump pump, a blocked downspout or a backed-up floor drain. Flood insurance is a separate policy, and FEMA states that a new policy normally takes 30 days to take effect. Fewer than 6 per cent of Demarest homes are rented, according to the Census Bureau; if you are one of those tenants, your landlord's policy does not cover your belongings. Whether a particular loss is covered is decided by your insurer and your policy wording.
Common questions
Does Demarest, NJ flood?
Occasionally, and in a limited area. FEMA counts 30 flood insurance claims in Demarest over several decades, mostly from Floyd, Irene and Ida, and about 6.7 per cent of the borough is in the mapped 1 per cent flood zone along the Tenakill Brook and its tributaries.
Does the Duck Pond flood?
The Duck Pond is part of the Tenakill Brook, so it rises with the brook in heavy rain, and the land around it is within the mapped flood zone. Check individual addresses on the FEMA Flood Map Service Center.
What happened to the dam in Demarest in 2021?
According to the Bergen County hazard mitigation plan, an October 2021 nor'easter damaged a small privately owned dam on Cresskill Brook in Demarest, and Cresskill officials said this added to flooding in their borough.
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