The undecided edge between land and
water teems with life. Wetlands and
marshes, reefs and mangrove forests, estuaries and tidal flats demonstrate the
physical result of ebb and flow. They
embody the indeterminacy of the physical status between liquid and solid,
dissolving into vapor on foggy mornings.
Productive ribbons along coastlines create shadow nurseries for finfish
and crustaceans, filter suspended material, stabilize and trap sediment, and
assimilate dissolved nutrients. The
living plants here are unusual species, halophytes, which thrive in salty
conditions; botanical amphibians that can survive choking mud and desiccating
heat to naturally break storm surge and absorb wave action.
Coastal
wetlands are bioshields for the continental edge. Marshes and maritime forests protect coastal development and infrastructure from
hurricanes and other storm surges. Where they do not exist, such as in south Florida , property damage caused by storms is much more
devastating than in Louisiana , where a buffer
of coastal wetlands separates cities from the Gulf of
Mexico . “By serving as a buffer to destructive marine forces and
the episodic impact of storms, Louisiana ’s
coastal wetlands help to protect the vast infrastructure of nationally
significant oil and gas facilities.” The marshes protect other infrastructure,
too, such as roads - and more than 400 million tons of water-borne cargo,
including ten federal navigation channels that provide access to port
facilities handling 25% of U.S.
exports.
Most
threats to the wetlands seem like a personal challenge to continued occupation. A New York
Times article explored the barrier islands of North Carolina , and the changes due to
rising sea levels – 7” in the last 100 years, with an additional 2’-3’ rise by
2100 – and the communities affected by coastal erosion. “Dr. Riggs predicted, major storms will turn
many parts of the Banks into underwater shoals or flats that are above water
only at low tide. If Highway
12 were abandoned and the islands allowed to find their natural equilibrium, he
writes, the resulting villages would be ‘situated like a string of pearls on a
vast network of inlet and shoal environments.’”[i] Loss of the connecting roadways would lead to
isolation, accelerating decay, and the abandonment of the community, first by
the hundreds of thousands of tourists each year, and then by the inhabitants.
It
is a constant battle against the sea to postpone but never halt completely the shifts
along the edge. The constant toil of
dredging and beach renourishment, of building levees, breakwaters, seawalls,
groins, piers, jetties, and dunes signify the impermanent quality of the line
between water and land. With the
added pressure of climate change, chances of erosion and flooding increases.
One way to respond to the threat of
rising waters is to plan now for their eventual extent by creating space along
the coastlines for water to occupy. “Immediately
after the tsunami (in 2004), the Sri Lanka government through its Coast
Conservation Advisory Council declared a conservation buffer zone along 1,000
kilometers of coastline prohibiting rebuilding and new construction. The buffer varied in width: in the south it
was 100 meters and along the east coast it was 200 meters. Many viewed the ban, an attempt to safeguard
the country from future flooding disasters, as a government land grab to
promote the lucrative tourism trade. The
resulting public outcry ultimately caused officials to relax the blanket
post-tsunami ban; it is now 15 to 40 meters.”[ii]
Managed
retreat from the coastal edge was a topic during the post-Katrina political
discussions, but was abandoned faster than a flooding building. The result illustrated a linear park at the
western edge of Mississippi , a green buffer
with boardwalks and bayous at the lowest lands on the coast, and an extension
of the already-protected cheniers and marshes stretching to the Pearl River
which forms the dividing line with Louisiana . But residents were not ready to hear that
their beachfront lots were the target of a buy-out program to avoid future government
flood program payments… and communities didn’t look forward to the loss of the
highest property tax dollars, plus the prospect of inheriting maintenance on
the empty lots. (The program proceeds
quietly and voluntarily, the impetus fueled by older people who just cannot
afford the emotional and financial toll of life on the beachfront, accompanied
by a sharp rise in insurance and construction costs.)
Wetlands across the globe show
evidence of a system well into collapse.
In the 1600’s, the continental United States had 220 million acres
of wetlands, but by 1997 there were less than half of that, a total of 105.5
million acres remaining. Only about 5%
of these wetlands are along coastlines; the remaining 95% are inland marshes,
meadows, forests, and swamps.
At inland locations, most floods
come from the clouds above. Planning
space for stormwater runoff is the reasoning behind requirements for retention
ponds as an alternative to structured drainage, but most examples fail to
contribute to the aesthetics of the community, or to ecological functioning. Ringed with chain link, home to invasive
species and windblown litter, retention ponds at the edge of big-box parking
lots may provide space for water to infiltrate, but they certainly don’t come
close to replicating authentic wetlands, which (along with tropical rain
forests) are among the most biologically productive habitats on earth, supporting nearly 200 species of
amphibians, 5,000 plant species, one-third of all native bird species, and a
similar diversity of plant life.
After devastating spring floods in
2011, people along the Mississippi River better
understand the value of wetlands as flood control. Because of the loss of wetland areas for
catchment and percolation, damage to buildings, infrastructure, and industries
along the river banks was estimated at $6 to 9 billion. The bottomland hardwoods and wetlands along
the river could store at least 60 days of floodwater in the early 19th
century, but can now store only 12 days of floodwater. This loss of capacity led to dramatic rises
along the hard-edged river, with more episodes expected in the future.
Drainage woes plague many towns,
especially in flat areas, coastal plains, or valleys threatened by
flooding. Storm drainage, whether
surface or subsurface, must handle the overflow and keep water moving to safe
discharge areas. Constructed culverts
and drains are durable, but also susceptible to obstruction. Surface drainage, such as swales, filter
non-point source pollutants and handle higher capacities during significant
rainfall.
Water plazas in cities are the
newest idea for creating a multi-functional open space to be used as a park, a
grassy field, a stepped amphitheatre, playground, skate park or labyrinth in
fine weather; giant catchment areas, mega-sponges, when the rains arrive. Rotterdam ,
a city where the elevation is below sea level, is flirting with the idea. No single catchment area is big enough – even
Central Park cannot drain New York City alone. A system of smaller
units, spread across neighborhoods and linked, will help to offset the
accelerated and intensified stormwater in cities.
The solution may be as simple as
replacing structures with soils. Not to
form dead-end canals which lead water into sites, but to create more places for
percolation. Water in the city
reintroduces habitat for wildlife, and provides space for children to dream, and
adults to meditate. Water, that least
mysterious element of two hydrogen molecules and one of oxygen, has secret
powers within the urban environment that can lead to more vibrant and congenial
social spaces where neighbors talk, and adults play, and children imagine
entirely different worlds. Meanwhile, the focus of all this dreaming and
thinking and planning, the water silently percolates through sand and clay to
the infinite cracks and fissures below, swelling the earth with fecundity once
more.
Green filters are “non-structural”
methods for restoring capacity along coastal edges and within cities to handle
the increasing demands of storm waters: storm surge, flood, excessive rain,
tidal flow, and sea level rise. Creating
green buffer zones allows water to safely pool before affecting the lives and
works of man. Until recently, wetlands
were seen as wastelands. Their
productivity remained unmeasured – they occupied the undervalued edges, the
barriers to contiguous development patterns, and the places of last resort for
the poor and the latecomers to the urban environment. The pressures of low densities and high
population growth have nudged growth ever outward, knocking down the mangrove
forests and bottomland hardwoods, filling estuaries with concrete and asphalt.
Wetlands are critical to humans’
continued occupation of the fragile edges between land and water. They endure the most extreme conditions of
flux, and provide greater value (by diverting, filtering, recharging, and
evaporating stormwater) than much of the grey infrastructure which underpins
cities. Wetlands may be the most
valuable lands on earth, without a single “improvement” made by man. Man should not
build with permanence on their indeterminate ground.