For any longtime resident or frequent visitor of lower Cameron Parish, it is obvious that we have coastal marsh being converted to open water. Aside from the catastrophic changes caused by hurricanes and their associated storm surges, land loss has been gradual over the last few decades. Many factors have contributed to the rate of loss, such as channel and canal dredging which connect interior marshes with higher salinity waters of the Gulf of Mexico.
A natural factor that does not garner much attention is drought. The area has been hit with a series of droughts over the last 15 years. Short, seasonal dry periods are a healthy part of the marsh ecology. Typical dry periods in the summer lower water levels allowing many species of vegetation to sprout when the surface of the marsh dries. Normal rainfall keeps these plants growing into the fall and winter when water levels rise again. However, prolonged dry periods associated with droughts dry the marsh soils, which are high in organic matter, to the point of decomposing the organics and causing the soil to compact. When normal rainfall returns the area holds more water due to the compaction that occurred during the drought. This has happened in Cameron Parish in 1999-2000, 2005, 2010 and 2011.
Adding to the problem is sea level rise. Whether you believe that man has had any effect on Earth’s climate or in global warming, the science is out there to show that the sea level along the Gulf Coast is rising. The world’s oceans have been on the rise since the peak of the last ice age more than 18,000 years ago. The combination of sea level rise and land subsidence is referred to as “relative sea level rise”. In most journal articles and government reports on sea level rise, Louisiana is listed as the area to be most impacted by relative sea level rise. While Cameron Parish’s coastal area is experiencing the least impact of any coastal parish from relative sea level rise, it is quite significant.
The two National Weather Service tide stations to Cameron’s east and west, which have more than 100 years of data, show an average relative sea level rise of 5.66 millimeters per year (mm/yr) for Sabine Pass, Tx., and 9.65 mm/yr for Eugene Island, La. This converts to one third of an inch per year or three inches per decade. Three inches over a decade does not seem like much until you consider that much of Cameron Parish is at three feet or less above sea level.
What does this mean for Cameron Parish and its residents?
- Let’s assume that a high tide of three feet puts water in the street in downtown Cameron. A three-foot tide is not the norm, but does happen several times per year. Using the three-inch per decade average in relative sea level rise, in 30 years (nine inch increase in relative sea level) a two-foot, three-inch tide will put water in the street. A two-foot, three-inch tide is quite common.
- Assume the life of a tidal marsh management project with water control structures is 30 years. The management goal of the project is constructed to maintain water at a set level.Over the 30-year life of the project, tide water levels will be nine inches higher than planned for, making management goals of the project nearly impossible.
Relative sea level rise will affect every aspect of coastal activities. This is not meant to alarm anyone, only to raise awareness and to plan for sustainable future activities. Anyone who has lived on the coast for 30 years or so realizes, in normal years there is more water to land ratio than ever before.
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