Manville basements where two rivers meet

A gauge with more than a century of floods

The National Weather Service gauge on the Raritan at Manville has records going back to 1903. Flood stage there is 14 feet, and the river had passed it 127 times by January 2020 (NWS). Floyd crested at 27.10 feet in September 1999, Irene at 26.24 feet in August 2011, and Ida set a new mark of 27.66 feet on September 2, 2021 (NRCC).

Ida left an estimated 125 to 150 homes uninhabitable, and gas explosions destroyed houses and the Saffron Banquet Hall (CBS New York). Borough Hall itself took on water (NJ DCA).

The flood line was drawn too low

Ida ran roughly 3 feet above the FEMA flood map in Manville, and the borough answered with a draft ordinance that regulates the "true" floodplain instead of the mapped 100-year line (MyCentralJersey). That matters for anyone whose house sits just outside the shaded zone: the map said you were dry, and the river disagreed.

The state has also marked a repetitive-flooding area where homes "have been flooded in most major and minor flooding events." Repair applicants there are offered buyouts instead. Of 75 Manville applications to the state repair programs, 45 came from that area (NJ DCA). About 120 homes have been sold to the state over the past decade, with 53 more in progress (WAMC). The Lost Valley section in eastern Manville sits on the flood plain, and Royce Brook affects the southern end of Main Street (Wikipedia).

What interior work can and cannot do here

No sump pump keeps out a river that is standing 3 feet deep in the street. If your house is in the buyout area or takes surface water through doors and windows, a waterproofing system is the wrong purchase, and we will say so.

Most Manville calls are something else: seepage at the floor joint after days of high water, a pit that cannot keep up, block walls that stay damp long after the river drops. Six in ten homes in the borough were built before 1960, about 2,828 of 4,639, and 64.5% are single-family detached (ACS 2024). That is a lot of older block and poured walls sitting in wet ground. A drain channel along the inside of the footing, piped to a properly sized pump with a battery backup, is the usual answer for that kind of water.

We look at the pit, the discharge line, the wall type and the high-water marks before suggesting anything, and the estimate spells out which water the work addresses and which it does not.