Why the Pequannock River floods: Butler, Bloomingdale, Riverdale and Pompton Lakes
The Pequannock starts in protected forest and Newark's reservoirs, then drops through Butler, Bloomingdale and Riverdale, where Main Street and the river sit side by side. Two gauges record how quickly that stretch turns from trout stream to flood.
The Pequannock River drains a largely forested Highlands watershed that holds the City of Newark's five main water-supply reservoirs, then runs past Butler, Bloomingdale and Riverdale before joining the Ramapo to form the Pompton River. National Weather Service gauges at Macopin and Riverdale set flood stage at 5.5 and 8 feet, and the record crests, in April 1984 and during Hurricane Irene in August 2011, went far above both. This guide explains what the gauges show, which streets flood at each level, what the reservoirs do and do not do, and what the record means for people who live and work by the river.
The short version
- The upper Pequannock is a protected watershed holding Newark's five main reservoirs; NJDEP describes them as water-supply reservoirs.
- At the Macopin gauge, flood stage is 5.5 feet; at 6.5 feet the NWS expects both Main Streets in Butler and Bloomingdale to flood.
- At Riverdale, flood stage is 8 feet; the record is 13.6 feet in April 1984, with Irene second at 12.57 feet.
- The Pequannock joins the Ramapo about 1,600 feet below the 1928 feeder dams to form the Pompton River.
- FEMA records 87 flood claims in Bloomingdale and 127 in West Milford, against 2,535 in Pompton Lakes downstream.
A water-supply river
Most of the upper Pequannock exists to supply drinking water. NJDEP's statewide water supply plan places the City of Newark's water sources in the Pequannock watershed, in Kinnelon, West Milford, Jefferson, Hardyston and Vernon, and lists five main reservoirs, Echo Lake, Canistear, Oak Ridge, Clinton and Charlottesburg, all on the Pequannock or its tributaries. Oak Ridge Reservoir sits at the dam on the Pequannock itself. The New Jersey Office of Emergency Management describes most of the watershed as forested and protected for water supply and parkland. Riverdale's natural resources inventory adds that the large undisturbed area north of Butler gives the river its high water quality, that land use becomes more intensive south of Butler, and that summer flows through Riverdale are regulated mainly by releases from Charlottesburg Reservoir in West Milford. None of these sources describes the reservoirs as flood-control works. They are built and run to store water. Below them the river leaves protected land and meets the towns.
The Macopin gauge: Butler and Bloomingdale
The US Geological Survey gauge on the Pequannock at Macopin Intake Dam drains 63.7 square miles. The National Weather Service sets action stage there at 5 feet, minor flood stage at 5.5, moderate at 6.5 and major at 7.5, and its impact statements are about Butler and Bloomingdale. At 5.5 feet road closures begin in both boroughs. At 6.5 feet both Main Streets, in Butler and in Bloomingdale, flood, several commercial properties take on water, the Hamburg Turnpike floods significantly, flooding spreads to the east side of Bloomingdale and Sloan Park goes under. At 7.5 feet the NWS expects major flooding at the Main Street and Hamburg Turnpike intersection in Butler, more commercial properties affected, and significant flooding on Main Street, Van Dam Street and Brandt Lane in Bloomingdale. Irene reached 7.42 feet on August 28, 2011. March 2011 brought 7.17 feet, January 2024 6.76 feet, March 2010 6.56 feet and April 2007 6.38 feet. The two highest crests on the NWS list, 9.4 feet in October 1903 and 8.9 feet in April 1984, were read on an older datum.
The Riverdale gauge
Downstream, the USGS gauge at Riverdale drains 83.9 square miles. Here the NWS uses 7 feet for action stage, 8 for minor flooding, 10 for moderate and 11 for major. At 8 feet businesses on Main Street in Bloomingdale closest to the river begin to flood and Brandt Lane starts to flood. At 9 feet more Main Street businesses take on water. At 10 feet Brandt Lane floods in several places and becomes impassable. At 11 feet Main Street, Van Dam Avenue and Hamilton Street in Bloomingdale flood and houses on Garden Avenue in Riverdale begin to flood, and at 12 feet Riverview Terrace in Riverdale floods with water in houses. The record crest is 13.6 feet on April 5, 1984, with a flow of 8,000 cubic feet per second. Irene is second at 12.57 feet on August 28, 2011. Since then the gauge has reached 9.74 feet in December 2023, 8.99 feet during the remnants of Ida on September 2, 2021, and 8.55 feet in January 2024. The gauge has not always been running: in 2011 the state flood commission recommended reactivating it.
Why the Pequannock rises fast
The state Passaic River Flood Advisory Commission describes the upper Passaic basin, the Highlands country the Pequannock drains, as parallel ridges deeply cut by steep-sided valleys that produce runoff of high velocity and high volume. Butler, Bloomingdale and Riverdale sit where that water leaves the hills, and the NWS impact lists show what is in its path: town centres, commercial frontages on Main Street and the Hamburg Turnpike, and parks along the bank. The pattern of crests also shows that this river floods in every season. Its high marks include a hurricane in August, nor'easters in March and April, a December storm in 2023 and January storms in 1996 and 2024. Conditions beforehand matter as much as the storm. The commission records that the October 1903 flood followed three months of excessive rain that left the ground saturated, and that snowmelt had been raising streams in northern New Jersey for ten days to two weeks before the March 2010 storm. A river that floods in winter as readily as in hurricane season gives no safe months.
Where it meets the Ramapo
Below Riverdale the Pequannock heads for its meeting with the Ramapo. The state commission reports that the Pequannock feeder dam, built in 1928 to replace the old Morris Canal dam, crosses the river in Pequannock Township with a 300-foot spillway, joined by an earthen dike to the Pompton feeder dam on the Ramapo. About 1,600 feet below the dams the two rivers meet and form the Pompton. The commission found that the dams raise water levels just upstream in normal flows and storms, and in 2011 recommended removing both to relieve Pompton Lakes, Wayne and Pequannock. It also recorded that both dams are already submerged in a 10-year flood, which limits what removal could do in a large event. The Pequannock's water then becomes part of the Pompton, whose gauge at Pompton Plains reached its record 25.24 feet during Irene.
What the FEMA claims show
Butler, Kinnelon and Riverdale are in Morris County, and their claim counts are not in the Passaic County data used here. For the Passaic County towns on the river, FEMA NFIP claims data records 87 flood claims in Bloomingdale, a borough of about 7,700 people by the US Census Bureau count. Its worst year was 2011, with 28 claims, followed by 2010 with 15, and Irene accounts for 17 and the March 2010 nor'easter for 15. FEMA lists 14 repetitive-loss properties in Bloomingdale. West Milford, which holds much of the reservoir country, has 127 NFIP claims, 33 of them from Irene, and 13 repetitive-loss properties, 3 of them severe. These are small totals next to Pompton Lakes downstream, which has 2,535. That reflects the geography: the upper river is protected land, and the flood damage is concentrated where the Pequannock and its neighbours reach the flat ground around Pompton Lakes.
What this means if you own or rent here
If you live or run a business near Main Street in Butler or Bloomingdale, or on Garden Avenue or Riverview Terrace in Riverdale, the NWS gauges at Macopin and Riverdale are the ones to bookmark. Their impact lists tell you which road closes first, and a forecast of 6.5 feet at Macopin or 10 feet at Riverdale is a signal to move vehicles and stock rather than wait. Do not count on the reservoirs to hold a storm back. Keep valuables and records off floors that have flooded before, and never drive through water on the Hamburg Turnpike or any road the NWS lists as closing. Flood is excluded from standard homeowners, renters and most business property policies; it needs separate flood cover, and whether a given loss is paid is decided by the insurer under that policy. FEMA notes a new flood policy usually takes 30 days to begin. For a particular address, the FEMA Flood Map Service Center shows the mapped flood zone.
Common questions
What is flood stage on the Pequannock River?
The National Weather Service sets minor flood stage at 5.5 feet at Macopin and 8 feet at Riverdale. Major flood stage is 7.5 feet at Macopin and 11 feet at Riverdale.
Do the Newark reservoirs prevent flooding on the Pequannock?
The sources describe Echo Lake, Canistear, Oak Ridge, Clinton and Charlottesburg as water-supply reservoirs, and none describes them as flood-control works. Summer flows below them are regulated by releases from Charlottesburg, but a large storm still reaches Butler, Bloomingdale and Riverdale.
What was the worst Pequannock River flood?
At Riverdale the record is 13.6 feet on April 5, 1984, with Hurricane Irene second at 12.57 feet in August 2011. At Macopin the highest readings were in October 1903 and April 1984, on an older datum; Irene reached 7.42 feet there.
Which streets flood first?
At 5.5 feet on the Macopin gauge road closures begin in Butler and Bloomingdale. At 8 feet on the Riverdale gauge the Bloomingdale Main Street businesses closest to the river begin to flood and Brandt Lane starts to flood.
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