Filters and Sponges

The undecided edge between land and water teems with life.  Wetlands, marshes, mangrove forests, estuaries, and tidal flats embody the consequences of ebb and flow.  Productive ribbons along the coastline create shadowed nurseries for finfish and crustaceans, filter suspended material, trap sediment, and stabilize the edge.  Plants living in this zone are unusual species, halophytes, which thrive in salty conditions, botanical amphibians that survive choking mud and desiccating heat to naturally break up storm surge and absorb wave action.

Coastal wetlands are the 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 higher than in Louisiana, where a buffer of coastal wetlands separates communities from the Gulf of Mexico. The marshes protect not just homes but other infrastructure: major highways and interstates, water wells and pipelines, and sewage treatment facilities. In Louisiana, saltwater marshes defend more than 400 million tons of water-borne cargo, including ten navigation channels to port facilities handling 25 percent of U.S. exports.  The same wetlands protect the vast infrastructure of oil and gas pipelines, extraction, and refineries.

Threats to wetlands seem like a challenge to the continuing presence of mankind at certain locations.  The barrier islands of North Carolina have experienced changes due to rising sea levels of 7” in the last 100 years, with an additional 2’-3’ rise predicted by 2100.  Communities along coastal Highway 12 are likely to become a string of independent shoals, islands connected by a causeway over a dynamic network of inlets and islands.  Loss of the connecting roadway would lead to isolation, accelerating decay, and the abandonment of the community, first by the hundreds of thousands of tourists each year and later by inhabitants.

It is a constant battle against the sea to postpone, but never halt completely, the migration of sand and sediment along the edge.  The constant toil of dredging and beach renourishment, and the building of levees, breakwaters, seawalls, groins, piers, jetties, and dunes signify the impermanent boundary between water and land.  With the added pressure of climate change, erosion and flooding will increase and tidal surge extend its reach inland.

The threat of rising waters demands a plan for their eventual extent, creating space along the coastlines for water to occupy. Following the 2004 tsunami in the south Pacific which devastated parts of Indonesia, India, and Sri Lanka, the government of Sri Lanka declared a conservation buffer zone 1,000 kilometers long and 100-200 meters wide.  The coastal zone prohibited rebuilding and new construction.  Residents viewed the conservation zone as an attempt to convert modest fishing villages into tourist guesthouses and amenities, and fought back.  The result was a modified conservation zone 15-40 meters wide

Managed retreat from the coastal edge was raised during the post-Katrina political discussions, but the topic was abandoned faster than people in a flooding building.  The Mississippi Renewal Forum illustrated a green buffer with boardwalks on the coast, protecting the second tier  of houses behind a 500’ riparian zone, an extension of the cheniers and marshes present before European settlers arrived in 1699.  But residents of the first tier of houses were not ready to give up their beachfront status, and communities didn’t look forward to the loss of their highest property tax dollars, plus face the prospect of inheriting the maintenance burden on the empty lots.  Although the land use planning did not proceed officially, the sharp rise in insurance and construction costs resulted in a default green space along many sections of the coastline as resources for rebuilding proved inadequate.

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 only half remained in 2009.  Only about 5 percent of these wetlands are coastal salt marshes; the remaining 95 percent are inland marshes, meadows, forests, and swamps.  Between 2004-2009, the U.S. lost 84,100 acres of coastal wetlands, equivalent to one football field every 38 minutes.   Louisiana hosts 25 percent of the coastal wetlands in the continental U.S., once over 4,000,000 acres.  Since 1932, Louisiana has borne the brunt of wetland erosion, for a total of 1900 square miles lost to nature and human activity.  Hurricanes Katrina and Rita eliminated 217 square miles of coastal wetlands, the equivalent of the amount expected to erode over fifty years lost in a single day.

Most of the wetland loss in Louisiana is due to the hubris of man and our predilection for intervening. The Mississippi River flood of 1927 sparked a period of levee-building that protected homes and croplands but prevented sediment from the river to naturally rebuild the lands at the base of the river.  Instead, 160 million tons of sediment each year are carried to the Outer Continental Shelf and jettisoned.

The Army Corps of Engineers was charged with containing the Mississippi River, a still-controversial decision nine decades later.  In the 21st Century they are defending coastal edges with an expanded toolbox which includes the built systems they are known for such as seawalls, bulkheads, revetments, breakwaters, and groins, but also living systems: living shorelines, oyster reefs and sills to act as biological wave dampers, and restoring wetlands and barrier islands with vegetation to trap sediment, extend the shore and absorb wave energy, and create a second line of defence.

Wetland filters are non-structural methods for restoring capacity along coastal edges to handle the increasing impacts of storm waters: storm surge, flood, excessive rain, tidal flow, and sea level rise.  Until recently, wetlands were seen as wastelands.  Their productivity remained unmeasured because they occupied the undervalued edges, formed interruptions to continuous development patterns, and were the places of last resort for the poor and the latecomers to the urban environment.  The pressure of low density coupled with high population nudge growth ever outward, resulting in clearcut forests and filling in estuaries with concrete and asphalt.

“There’s this thing called progress. . . . It’s progress if you can stop the world slipping away. My humble model for progress is the reclamation of land. Which is repeatedly, never-ending retrieving what it lost. A dogged and vigilant business. A dull yet valuable business. A hard, inglorious business. But you shouldn’t go mistaking the reclamation of land for the building of empires.” ― Graham SwiftWaterland

Wetlands are critical to humans.  They are among the most valuable lands on earth, for their ceaseless work to divert, filter, recharge, and evaporate stormwater; to treat pollutants and sewage in runoff to provide clean water; and as nurseries for the rich seafood resources along the ocean’s edge.  Wetlands defend the built works of mankind.  Man should not build with permanence on their indeterminate ground.