Flooding in Allendale, New Jersey: the flood zone, the record, and what to do
Allendale is laced with small brooks, more than its size would suggest, and a larger share of its land is mapped as flood zone than in any of its immediate neighbours. The flood insurance record is still modest. Here is how the two fit together.
The Bergen County 2026 Hazard Mitigation Plan puts 11.49 per cent of Allendale in the FEMA one per cent annual chance flood zone. FEMA's National Flood Insurance Program has recorded 48 claims in the borough, 16 of them from Hurricane Floyd in 1999, and five properties are on the repetitive-loss list. Three brooks carry the mapped risk: the Ho-Ho-Kus Brook, Ramsey Brook, which joins it, and Allendale Brook, which flows on into Waldwick.
The short version
- The Bergen County 2026 Hazard Mitigation Plan puts 11.49 per cent of Allendale in the one per cent flood zone, 13.55 per cent including the 0.2 per cent zone.
- FEMA records 48 NFIP claims in the borough, 16 from Hurricane Floyd, and five repetitive-loss properties.
- The Ho-Ho-Kus Brook, Ramsey Brook and Allendale Brook carry most of the mapped risk; USGS gauges two of them.
- FEMA revised the Allendale Brook flood zone and floodway in 2007.
- Recent borough work has focused on stormwater drainage, including a flood-prone park.
More flood zone than its neighbours
Table 4.6-1 of the county plan gives Allendale 229.12 acres of FEMA Special Flood Hazard Area in 1,994.55 acres of land, or 11.49 per cent. With the 0.2 per cent annual chance zone, the share is 13.55 per cent. That is higher than Waldwick, Ho-Ho-Kus, Ridgewood, Wyckoff or Franklin Lakes. It does not mean the borough floods often. It means that several small streams, each with its own mapped corridor, cross a fairly small town, so the strips add up. FEMA's countywide flood study lists Allendale Brook, Ramsey Brook, the Ho-Ho-Kus Brook and Valentine Brook among the streams it studied here. The borough's first flood study is dated January 1979 and was revised in August 1992.
Three brooks and two gauges
The US Geological Survey has gauged two of Allendale's streams. One is on the Ho-Ho-Kus Brook at Brookside Avenue, where the brook drains about 9.11 square miles; the other is on Ramsey Brook, which drains about 2.55 square miles at its gauge and, according to FEMA's study, flows past Route 17, Crystal Spring Lake Dam and Brookside Avenue before joining the Ho-Ho-Kus Brook. The third, Allendale Brook, is still tiny where it enters the borough, crosses Franklin Turnpike and leaves for Waldwick, where it too joins the Ho-Ho-Kus Brook. FEMA revised the flood zone and floodway along Allendale Brook in February 2007 through a Letter of Map Revision, so maps older than that may be out of date. Neither Allendale gauge is a National Weather Service forecast point; the nearest is downstream at Ho-Ho-Kus.
The claim record
FEMA's OpenFEMA data list 48 National Flood Insurance Program claims for Allendale. The year 1999 stands well clear of the rest, with 17, followed by 2011 with 11, 2007 with 5 and 2021 with 3. FEMA attributes 16 claims to Hurricane Floyd, 10 to Hurricane Irene, 5 to the April 2007 nor'easter and 3 to Hurricane Ida. Floyd's dominance matches the gauge record downstream, where it produced the largest flood ever measured on the Ho-Ho-Kus Brook. As of 2 August 2026, FEMA lists five repetitive-loss properties in the borough, one of them severe repetitive loss. The county plan counts 38 active flood policies in October 2024, against 2,690 housing units in the US Census Bureau's estimates.
Dams and drains
The county plan counts four state-regulated dams in Allendale, all classed as low hazard. Low hazard refers to the expected consequences downstream if a dam failed, not to its condition. Most of the borough's recent flood work has been about drainage rather than brooks. Since 2021, according to the 2026 plan, Allendale has cleaned and repaired its stormwater drainage, installed drainage in a borough park described as a flood-prone area, and added three emergency generators. For the next five years it lists updated flood mapping and further flood mitigation among its priorities. The US Census Bureau puts the median year built at 1965 and the renter share at about 19 per cent.
What this means if you own or rent here
Look up your address on the FEMA Flood Map Service Center, and if you are near Allendale Brook make sure you are reading a current map, since the 2007 revision changed its zone. Homes beside the Ho-Ho-Kus Brook or Ramsey Brook should follow the Ho-Ho-Kus gauge on the Weather Service's water site during heavy rain or a tropical storm. A new flood policy normally takes 30 days to start. For houses away from the brooks, which is most of the borough, the realistic risks are groundwater in the basement, drain backups and pump failures. Check your homeowners policy for its sewer backup and seepage wording; whether a loss is covered is decided by your insurer and the policy. Tenants need contents cover of their own.
Common questions
Does Allendale, NJ flood?
In narrow strips along its brooks, and mainly in the largest storms. FEMA has 48 flood insurance claims on record, with the most from Floyd in 1999 and Irene in 2011, although the county plan maps 11.49 per cent of the borough in the one per cent flood zone.
Which brooks flood in Allendale?
FEMA's flood study maps the Ho-Ho-Kus Brook, Ramsey Brook, Allendale Brook and Valentine Brook in the borough. Ramsey Brook joins the Ho-Ho-Kus Brook, and Allendale Brook joins it in Waldwick.
Is there a flood forecast for Allendale?
Not for a point inside the borough. The USGS gauges at Brookside Avenue and on Ramsey Brook record levels, but the National Weather Service forecast point is the Hohokus Brook at Ho-Ho-Kus, downstream.
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