Polders as flood mitigation measure? Ask the Dutch

Polders as flood mitigation measure? Ask the Dutch 2017-08-17T03:36:10+00:00

By Steve Spinello | FBW | March 19, 2013

In the aftermath of superstorm Sandy, coastal communities like Hoboken have debated potential ways of mitigating the impact of future storms. Perhaps less obvious than erecting a wall to keep out rising water, another idea considers leveraging the natural landscape as a flood-defense mechanism. A polder is a low-lying tract of land, typically marsh or wetland, that is enclosed by man-made dikes. The polder serves as a sort of holding tank for excess water so that, in the event of heavy rainfall or a large tropical system like Sandy, the overflow is to an extent contained within a specially designated area. This idea was recently suggested by Dr. Philip Orton, a marine scientist at Stevens Institute of Technology, who points out that polders serve as one component of floodplain management in the Netherlands. Such a system has an immense capacity for capturing and storing floodwaters during a storm.

Controlled flooding

Traditional polders in the Netherlands have been formed since the 12th century onwards. Polders were conceived by Dutch farmers primarily for agricultural purposes. Present-day polder landscapes are notable for their rich diversity of flora and fauna made possible by extensive drainage channels and accompanying water-related infrastructure. Smaller drainage channels lead into canals which eventually flow into nearby rivers. The prevailing system has allowed Dutch farmers to continue farming the land despite the presence of water.

The Dutch, having dealt with the effects of flooding for more than six-hundred years, are now in the process of rethinking their entire flood-defense strategy. Although Holland is internationally recognized for its massive flood protection system known as Delta Works, the Dutch have shifted gears as they grapple with the combined effects of climate change, rising sea level, and a shrinking coastline. Rather than rely completely on engineered structural solutions for flood control, the Netherlands has embraced the idea of “controlled flooding”. In future flood events, the Dutch will choose which areas flood and those which are spared.

A good idea on the surface

While polders are a long-standing agricultural practice in the Netherlands, in densely populated northern New Jersey there are few farms and a notable absence of a similar water management system. This is not to say that a polder or something akin to one is unworkable or would provide little to no relief for at-risk populations like Hoboken or Jersey City. In fact, there exists a vast area of suitable land less than five miles away from Hoboken’s western border — the New Jersey Meadowlands. An area once cultivated by 17th century Dutch settlers, on its surface the Meadowlands would appear an ideal location for situating a polder.

Dr. Orton recently considered just such an idea. Orton identified an area southeast of Secaucus –Penhorn Creek– where there exists a considerable tract of wetlands and tidal flats (see accompanying image). This area could potentially be reconfigured as a Dutch-like polder. In the event of a storm like Sandy, flood gates on the western tip of the city could open up allowing water to flow down-slope to the polder located a mile away. However, as Orton notes, the area is surrounded by industrial parking lots. Its capacity to function as a flood mitigation measure is constrained by encroaching development. Moreover the Meadowlands is not immune to flooding.

For the City of Hoboken, a more realistic scenario might involve identifying solutions closer to home.

The Meadowlands Penhorn Creek, one mile west of Hoboken.

At one point in time, the Meadowlands encompassed more than 25,000 acres of wetlands. Today, however the area has been reduced to a third of its former size. Any plan to reconfigure the area with polders would require a significant transfer of land ownership to a governing body capable of water management like the Meadowlands Commission or a state environmental agency. In the Meadowlands, the combination of overdevelopment and pre-existing flood risk could prevent a polder from actually being built.

Reality-based solutions

For the City of Hoboken, a more realistic scenario might involve identifying solutions closer to home. During and immediately following Sandy, areas particularly affected by flooding included the southwest and northeast portions of the city. While these areas are already heavily developed, there still exists opportunities for building more resilient structures or repurposing with flood mitigation in mind.

An alternative flood mitigation strategy might include the use of green infrastructure in combination with polder-like structures such as underground water-catchment basins. Parking garages can be retrofitted as multi-dimensional infrastructure that serve as holding tanks for excess water during storms. Streets and parallel sidewalks can be designed in ways that limit stormwater runoff by incorporating permeable surfaces and dense pockets of vegetation. Retail spaces at the ground level can be rebuilt using floodproof materials and by ensuring that water is allowed to run both in and out of the building, what is known as “wet floodproofing” by FEMA standards.

Related links

A serious conversation about Sandy
Dutch Dialogues: A model for Hoboken
Flood insurance rates will skyrocket
Monarch Towers now in FEMA’s High Hazard Zone
79% of Hoboken falls into FEMA’s flood zone
Post Sandy: After repairing the damage, then what?
12-Point Plan in preparation for the next Sandy

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