Flooding in Old Tappan, New Jersey: the flood zone, the lake, and what the record shows
On paper Old Tappan has one of the largest flood-zone shares in Bergen County. Look closer and a good part of that zone is a reservoir. Here is how to read the numbers, what FEMA says about Lake Tappan, and what the insurance record actually shows.
The Bergen County Hazard Mitigation Plan puts 26.51 per cent of Old Tappan in FEMA's 1 per cent annual chance flood zone, the highest share of any town in the Northern Valley. Yet FEMA records only 37 flood insurance claims there and three repetitive-loss properties. The gap is largely explained by Lake Tappan, a water-supply reservoir on the Hackensack River that covers about a fifth of the borough's area. This page explains the lake, the river below it, the claim record and what owners should check.
The short version
- The Bergen County Hazard Mitigation Plan puts 26.51 per cent of Old Tappan in the FEMA 1 per cent flood zone, but the figure includes Lake Tappan's open water.
- The US Census Bureau counts 0.848 square miles of water in Old Tappan, about a fifth of its area.
- FEMA records 37 NFIP claims and three repetitive-loss properties; many claims date from 1979 to 1984.
- FEMA says Lake Tappan is run for water supply, not flood control; its record level was 55.67 feet on 17 September 1999.
- Only 11 active flood policies were in force in October 2024, according to the county plan.
Why the flood-zone share looks so high
Table 4.6-1 of the county plan gives Old Tappan 2,664.39 acres, of which 706.21 acres are in the FEMA Special Flood Hazard Area: 26.51 per cent, or 28.07 per cent with the 0.2 per cent zone. That acreage matches the borough's total area including water. The US Census Bureau counts 3.315 square miles of land and 0.848 square miles of water in Old Tappan, which together come to the same 2,664 acres. The water, roughly 540 acres by our arithmetic, is almost all Lake Tappan, and a reservoir is normally mapped inside the flood zone. The table does not split open water from dry land, so we cannot say exactly how much of the 706 acres is lake. But it is likely to be a large part, and the share of homes and streets in the zone is very probably much lower than 26 per cent.
Lake Tappan: what it is and is not
Lake Tappan is a dammed stretch of the Hackensack River that straddles Old Tappan and River Vale and reaches a short way into Rockland County. FEMA's Bergen County flood study says its level is controlled by a series of bascule gates and a sluice gate, that it has operated since 1967, and that its normal level is 55.0 feet. Its highest recorded level, 55.67 feet, came on 17 September 1999, the day after Hurricane Floyd. FEMA is clear that Lake Tappan and Woodcliff Lake are run for public water supply and are not designed or used for flood control, though their storage has a natural dampening effect on most flood peaks. The state lists Lake Tappan Dam as a high hazard potential dam, a classification based on what would happen downstream if it failed, not on its condition.
The river on the western edge
The Hackensack River and the lake form Old Tappan's western side, along the border with River Vale. FEMA puts the river's drainage area at 50 square miles at the Lake Tappan spillway and 57.1 square miles where it leaves Old Tappan. Just downstream, the National Weather Service gauge at Rivervale sets minor flood stage at 5.5 feet and major at 8 feet. Its two highest crests are 12.26 feet in Hurricane Irene on 28 August 2011 and 12.19 feet in the nor'easter of 16 April 2007. Because most of Old Tappan's river frontage is reservoir rather than open channel, the borough sees less of that river flooding than towns further down, but properties close to the lake and its feeder brooks are where the mapped zone matters.
The claim record: older floods weigh heavily
FEMA's National Flood Insurance Program data list 37 claims in Old Tappan over the life of the programme. The pattern is unlike most of its neighbours. The busiest year was 2011, with eight claims, but the next three were all decades ago: 1984 with six, 1979 with five and 1980 with four. By named event, Hurricane Irene and FEMA's "late winter storms" category account for three each, and Hurricane Ida and the March 2010 nor'easter for two each. FEMA's multiple-loss records, as of 2 August 2026, list three repetitive-loss properties and none in the severe category. The county plan records only 11 active flood policies in the borough in October 2024, few for a town of 2,044 homes, and a small policy base means recent flooding is less likely to appear in the claim count at all.
Newer homes, almost all owner-occupied
The US Census Bureau puts the median year built of Old Tappan's housing at 1986, among the newest in Bergen County, and only about 6 per cent of households rent. Homes built after the borough's first FEMA flood study in October 1976 were generally built with the flood maps in view, which may help explain the low claim count. In the county plan, Old Tappan says its priority is sanitary sewer infrastructure that is susceptible to flooding, with some projects in planning. That points to a practical concern for residents: in heavy rain the risk to a house is often from the sewer and drains rather than from the lake.
What this means if you own or rent here
Do not assume the 26 per cent figure applies to your street, and do not assume it does not. Look up the address on the FEMA Flood Map Service Center and check where the building sits relative to the zone line, especially if you are near the lake or a brook. With so few policies in force, many owners outside the zone carry no flood cover at all; if you want it, a new policy normally takes 30 days to start. For the more common water problems, test your sump pump before the wet season, keep gutters and downspouts discharging away from the foundation, and ask a plumber whether a backwater valve makes sense if your drains have ever backed up. Sewer backup is usually a separate endorsement on a homeowners policy, and whether a loss is covered is decided by your insurer.
Common questions
Does Old Tappan, NJ flood?
Less than its flood-zone share suggests. FEMA records 37 flood insurance claims over the life of the programme. Much of the mapped zone is Lake Tappan itself. Properties near the lake and local brooks are where the risk is concentrated; check your address on the FEMA Flood Map Service Center.
Does Lake Tappan protect Old Tappan from flooding?
It is not built for that. FEMA's flood study says Lake Tappan is operated for public water supply and is not designed or used for flood control, although its storage tends to dampen most flood peaks on the Hackensack below it.
Which gauge should I watch?
The National Weather Service gauge on the Hackensack River at Rivervale, just below Lake Tappan. Minor flood stage there is 5.5 feet and major flood stage 8 feet.
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