Marsh Grass for Shoreline Stabilization
(Published July 2005)
The current Northumberland County Comprehensive Plan states (p. 5:10) “Vegetation as an alternative to structures is to be promoted as erosion prevention mechanisms.” Grammar aside, NAPS agrees, and for the last several years we have promoted the use of marsh grass for shoreline stabilization and re-colonization of marshes from which invasive Phragmites is being removed. This spring (2004) we purchased 60 flats of three kinds of marsh grass (3000 plants) and we, or the property owners, planted them at 25 locations. This is in addition to the grass purchased by Reedville Fishermen's museum and planted with NAPS' help as part of the shoreline restoration project with Bethany United Methodist Church. We now have enough information to make much better projections about what works and what does not work. One of the lessons we have learned is that the success of using marsh grass to stabilize shorelines is highly dependent on the motivation of the property owner. "Plant it and forget it" is rarely successful. Here are two examples.
A moderate energy south-facing beach on the Little Wicomico River was sprayed for Phragmites in the fall of 2003. The beach was planted in the spring of 2004 and by the fall of that year it was occupied by a lush stand of common cordgrass.
Photo looking east – beach to left, grass to right here.
The beach to the west was not planted with grass and has undergone erosion whereas the beach stabilized with grass has actually accreted.
Photo looking west with rip-rap
The beach on the adjacent property to the east, which had already been stabilized with rip-rap, was planted at the same time and has almost no grass remaining. The property owner did not maintain the grass. Note that, just as is true to the west, that erosion has taken place in front of the rip-rap whereas the beach stabilized with grass has accreted. Why has the beach stabilized with grass accreted where the adjacent beaches have undergone erosion? Because the property owner nurtured his grass. He religiously replaced grass plugs as the waves (mostly from boat wakes) washed them out, and once the grass began to grow, he fertilized it lightly. FERTILIZER IN THE BAY you shout. Yes, but how does pollution caused by a small amount of fertilizer applied for a few years to a small patch of grass compare to the long-term advantage of erosion control, groundwater nutrient uptake and habitat provided by the grass? Consider the pollution caused by land-application of poultry litter or municipal sewage sludge to one acre of farmland. To provide 120 pounds of nitrogen needed by most crops, 200 pounds of nitrogen is applied in poultry litter (IF application is done according to a "nutrient management plan" which is currently only required for poultry litter derived from either Maryland or Delaware, where cost-sharing is provided for dumping it in Virginia), and 400 pounds of nitrogen is applied in sewage sludge. Animal waste is a highly inefficient form of fertilizer and about half the applied nitrogen is pollution. This inefficiency is “on top” of the roughly 50% efficiency of chemical fertilizer. So that single acre of farmland to which poultry litter was applied contributes more than 80 pounds of nitrogen pollution to one of our local waterways or the Bay. That compares to the few pounds of nitrogen that were applied to the beach in question for a couple years, or less than 5 pounds of nitrogen each year that enters the groundwater from my septic system (I measure it).
Another site, on Cockrell's Creek, has a beach in front of a cliff. NAPS installed coconut logs at the base of the cliff in the spring of 2003 and planted grass in front. Again, the property owner nurtured the grass by replanting plugs that washed out (boat wakes were, again, the main culprit) and fertilizing lightly. In addition, he planted several kinds of ground cover on the cliff to stabilize it. The coconut logs are beginning to decay, but the cliff is stabilized and the grass out in front is doing its job of breaking the waves and trapping sediment. We do not know if a similar result would have been obtained without installing the coconut logs, but we suspect they were not necessary.
We added small amounts of grass to both these sites in spring of 2004 and again this year, for the last time. A word of caution is in order, however. Any form of natural stabilization is less permanent than rip-rap or bulkhead. In the face of sea level rising about 4 mm each year (actually sea level is rising 2 mm each year because of global warming and we are sinking 2 mm each year - see the NAPS Stewardship Tip on erosion), erosion is inevitable. The best one can do is to retard the erosion, and shoreline stabilization with grass is worth the effort, considering the cost of "hard" stabilization. All you need is moderate to low energy, suitable substrate exposed at mid tide, plenty of sunlight, and the willingness to persevere. Contact NAPS if you think we can help.