New Jersey’s flood risk isn’t just for coastal areas

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Flooding and storm surge are becoming increasingly problematic for New Jersey’s coastal communities. According to the New Jersey Department of Environmental Protection, more than half a million acres of state land are highly vulnerable to coastal hazards, with nearly two-thirds of New Jersey’s coastline at high risk of coastal erosion and nearly all of the coast facing the inescapable sea. level up.

However, residents of inland areas—even those located well outside federal floodplains—should not feel that they are insulated from flood risk. River flooding is another dangerous form of flooding that can spread quickly and leave devastation in its wake.

River flooding is the result of a water channel entering the floodplain. This may be caused by blockages downstream or by excess rain or snow flowing from the watershed into the riverbed. The severity of river flooding usually depends on the surrounding area and the speed of the moving water. Flash floods are an even more serious type of river flooding, in which massive storm deposits on the tops of hills and mountains quickly flow into the valleys below, turning uprooted trees and other debris into dangerous projectiles along the way. Flash floods are more common on the Pacific Coast due to the presence of mountains, but communities on the Atlantic Coast are not immune to the devastation these floods bring.

Fortunately, many flood mitigation measures that improve coastal resilience are readily applicable to floodplain structures.

In 2021, Hurricane Ida struck the Atlantic Coast, inundating Rahway with floodwaters. Stormy conditions caused the Robinson Branch of the Rahway River to overflow; combined with the topography of the area, this created ideal conditions for devastating river floods. Public venues such as the Hamilton Stage at the Union County Performing Arts Center filled with floodwater, damaging the facility’s interior and causing toxic mold to grow.

New flood mitigation measures for the Hamilton Phase include dry flood mitigation technology. Dry flood protection involves insulating the structure to allow no more than 4 inches of water to penetrate in a 24-hour period. For example, watertight doors are pressed against the door frame as rising floodwaters apply increasing pressure, creating a watertight seal. These doors also feature manual release latches to ensure a tight seal without the required flood water pressure.

On larger sites, horizontal passive flood control systems use the increasing hydrostatic pressure of flood waters to automatically move barriers into place and create a watertight seal. As the water continues to rise, so does the flood barrier; as the water recedes, the flood barrier follows suit, lowering back into place. Regardless of which dry flood defense systems are used, it is important that they are capable of self-activating without electricity, mechanical assistance or human intervention.

Fortunately, many flood mitigation measures that improve coastal resilience are readily applicable to floodplain structures.

Conversely, wet flood control allows a limited amount of water to enter the structure through vents and tear-off wall systems that direct flood waters to areas more resistant to water damage. Premises constructed from concrete, masonry, porcelain or any other material that is resistant to fungal and bacterial growth are ideal end points for wet flood control systems. The benefit of allowing water into the structure is that it equalizes the pressure on both sides, whereas dry flood defense systems are technically always at risk of sagging under one-way hydrostatic pressure. However, wet flood protection is not feasible everywhere and may not work if some rooms or areas cannot be raised.

The specifics of any flood defense strategy depend on a wide range of factors, from building material to elevation and topography of the area. Other valuable strategies include elevating critical facilities and equipment, and strengthening the foundations of buildings that may be susceptible to erosion even outside the floodplain. In areas with an increased risk of flash flooding, property owners should create safe zones around their properties by keeping trees and other potential hazards a safe distance from structures at risk.

Experienced architects and civil engineers, especially certified floodplain managers, are ideal consultants for determining which flood mitigation strategies are best suited for a given property. By tailoring mitigation plans to the specifics of the property and its owner’s needs, these experts can address multiple risk variables and provide peace of mind to communities adjacent to the river.

Kevin Paul is a Certified Floodplain Manager with over 40 years of design and construction experience in both the residential and commercial industries. He leads the Private Sector Real Estate discipline at H2M Architects + Engineers, where he manages and facilitates all phases of architectural and design projects, from initial studies to construction management.