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An Eroding System

Washout_5121x219McFaddin National Wildlife Refuge falls within the Chenier Plain, a dynamic ecosystem on the Texas-Louisiana coastline that has for thousands of years ranged from freshwater to intermediate, brackish and saline wetlands.    

Historically, hurricanes and other rain events brought large volumes of freshwater that would slowly flow across the coastal prairies and marshes spilling over into the bayous and blanketing the area with nutrients and sediments.  The natural drainage of the cheniers allowed a pattern of drying and flooding under which wetland plants evolved and adapted. These diverse wetland plants in turn supported a diversity of wildlife.  But man-made changes over the last century have altered the landscape’s hydrology.  

The beaches and dune systems of the upper Texas-Louisiana coastline are not rebuilding like they did historically.  Sediments that moved down various rivers into the Gulf and eventually helped rebuild the coastline are held back by dams and other structures.  Without the replenishing sediments, the beaches and dune systems on this stretch of the Gulf Coast are eroding.  In addition, large-scale channel projects like the Houston Ship Channel, the Gulf Intra-coastal Waterway (GIWW) and oil and gas exploration have significantly altered the freshwater wetlands.  Where once the fresh and salt water were mostly kept separate by a beach and dune system, these and many other channels now provide a direct avenue for the salty waters to consistently encroach deeper into the marsh.    

Over the last 60 years, the eroding forces of weather, currents and tides have washed away the back dune on this stretch of coastline.  The ocean’s salty waters have fewer obstacles preventing it from flowing directly into the marsh.  Even wind-driven tides stack water against the beach eventually overtopping the existing beach ridge.  Not only does this increase the salinity levels in the immediate area, the salty water then flows to the nearest waterways where it spreads across the marsh.  These wetland systems have adapted to occasional saltwater inundation but the vegetation and wildlife found in fresh and brackish marshes are not adapted to consistent saltwater intrusion.  The loss of vegetation makes it less productive for wildlife and leads to greater erosion.  Eventually, the freshwater marsh becomes part of the Gulf. 

The current rate of erosion on McFaddin Refuge averages between 15-45 feet of marsh habitat lost every year.  The trend continues in similar areas to the east and west, where erosion is more than 70 feet per year.  Currently, typical summer winds from the south reaching 20 mph or more can result in sea-strength water washing across the ridge and into the interior marsh along more than 15 miles of coast line.  And this doesn’t even include hurricanes. 

Between 2005 and 2008, three hurricanes struck the refuge, including two of significant size.  As a result, the historical beach dune was destroyed along the Gulf of Mexico.  Hurricane Rita was a category 3 hurricane when it struck on September 24, 2005 just 35 miles east of McFaddin National Wildlife Refuge.  It pushed more than three feet of salt water over the beach ridge.  Hurricane Humberto was a category 1 hurricane that struck on September 13, 2007 with its eye passing directly over the refuge.  It pushed more than two feet of water over the beach ridge.  Hurricane Ike, a category 2 hurricane, struck on September 13, 2008, about 33 miles west of McFaddin and it flooded the marsh with more than 15 feet of marine storm surge.  These tropical events and others pushed storm-created waves against the Gulf shoreline, altering the beach shoreline along this portion the Gulf of Mexico.  

What does this mean for McFaddin National Wildlife Refuge?  Tides now regularly overtop the beach and marsh ridge, flooding the marsh with sea-strength salt water.  Due to the channeling effect, this water flows to the nearest natural waterways and spreads across the marsh.  This regular saltwater inundation has increased salinity levels and removed the largest source of fresh water from the system.  These impacts affect more than 40,000 acres of McFaddin Refuge and can cause long-term salinities to increase permanently.  When loss of the dunes is added to projected sea level rise estimates, 52,800 acres of McFaddin Refuge south of the GIWW may be in jeopardy of being lost because of salt water intrusion. 

Currently, refuge staff is actively working with partners to find ways to strategically reduce salt water intrusion over the beach ridge and into the marsh.  Efforts are underway to mitigate impacts from the loss of the coastal dune system and decrease salt water intrusion, while improving the form and function of our coastal marshes.  

There is no question that this is the most significant threat facing this coastline, including McFaddin National Wildlife Refuge.  It is a large-scale problem that will require a large-scale solution and the refuge and the U.S. Fish and Wildlife Service are exploring all possibilities in an effort to protect this coastal habitat.  

Page Photo Credits — Washout on Hwy. 87 adjacent to the refuge.
Last Updated: Nov 29, 2012
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