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A natural barrier to the destructive forces of wind and waves, sand dunes are our first line of defense against coastal storms and beach erosion. They absorb the impact of storm surge and high waves, preventing or delaying flooding of inland areas and damage to inland structures. They are also sand storage areas that supply sand to eroded beaches during storms and buffer windblown sand and salt spray.
Due to the high energy "washing" effect of ocean and bay waves, soil, as we are accustomed to thinking of it, is converted to clean, relatively coarse mineral fragments (sand). The deposit of sand along the shore is subjected to the high winds common to the area where the sea meets the land, and is blown in every direction throughout the year. Where vegetation can get a foothold in the dry, unfertile sand, the windblown sand grains get batted down to the base of the plant and the sand surface incrementally rises, one grain at a time.
Over days, weeks and years, depending upon how hard the wind blows, dunes rise up out of the flat beach. Beach grass has adapted to being buried by the sand and it makes its way to the new surface as it gets buried. In time of large ocean storms waves crash into the dunes and the sand is re-supplied to the beach on front, which has been eroded in the early stages of the storm. The relationship of the beach and dune is an important symbiosis. One which we respect and shape our beach management program around.
Increased development and recreational use of the Barrier Island threatens the stability of our dunes. Structures built too close to the shoreline are inhibiting the landward movement of the dune in response to sea level rise resulting in a decrease in the dune width. Driving and walking on the dunes in areas not designated for such use, causes deterioration of beach grass and other vegetation that helps to trap and hold the sand in place.
Although beach grass is a hardy plant, amazingly tolerant to high salinity conditions, direct sun, extreme heat, lack of fertile soil and a fluctuating water supply, it can not survive being trampled by vehicle or man. As part of its resistance to salinity and drying conditions the plant has developed a thick brittle stalk which unfortunately snaps easily when trampled or driven upon. The passage of only one vehicle or a few people over the dune at the same point will kill a strip of grass. Without vegetation, the dune is exposed to wind erosion resulting in blowouts or breaches in the dunes.
These breaches or low spots not only create a weak spot in the dune but, become channels for floodwaters to move inland during storm events. As a result, inland areas become more vulnerable during coastal storms. Protecting dunes helps prevent loss of life and property during storms and protects the sand supply that slows shoreline erosion.
The Shoreline and Waterway Management Section has been working for many years through our Construction Regulations Program and Dune Maintenance Program to enhance, protect and preserve the beaches and dunes of Delaware.
To succeed, dune improvement and protection efforts should not only be the responsibility of the governmental entities involved. Even more valuable are the efforts of those individuals who live on and use the shoreline.
How to plant beachgrass:
- Beach grass is sold in bundles of 50 or 100 culms (stems)
- Plant two stems per hole. Placing more than two stems per hole will increase competition for nutrients causing loss of plants
- Plants (holes) should be spaced 18" apart.
- There should be 18" between rows.
- The rows should be staggered to provide maximum wind erosion control. (See illustration.)
Step 1: Open a hole 10 to 12 inches deep with a pointed stick or spade. Place 2 stems, with roots facing down, in the hole to a depth of 8 inches. If plants are not planted 8 inches deep, they may dry out or be blown out by the wind.
Step 2: Press next to the plant to firm the sand and eliminate air space in the root zone.
Newly planted and old beachgrass responds well to fertilizer. Fertilizer should be applied 30 days after planting but not before April 1. For up to date fertilizer rates contact your local nursery or the Shoreline & Waterway Management Section.
What can I do to help?
There are several ways property owners can preserve and protect the dunes. In addition visitors and property owners can take certain precautions to prevent damage to the dunes and vegetation. Property owners can increase the height and width of the dunes, repair damaged dunes or establish dunes where none exist by conducting a few inexpensive activities:
Plant Beach Grass: Planting ‘Cape’ American beachgrass (Ammophila breviligulata) is the most effective way to stabilize existing dunes and build new dunes along our coastline. This vegetation is easy to plant and it spreads rapidly. It reduces wind velocity near the ground and traps windblown sand around the grass. As the sand deposits accumulate, the grass grows up through it maintaining a protective cover.
Individuals or groups can help the Shoreline and Waterway Management Section vegetate the dunes along Delaware’s coastline by volunteering to plant as part of the section's annual beach grass planting.
Property owners can plant beach grass individually or as part of a community effort. Working in groups of two or three people, large areas can be planted by adults and children in a relatively short period of time. The best time to plant is from October 15 to April 15.
Help conserve Delaware's beaches by telling friends and family about the importance of beachgrass and reminding them to stay off of the dunes.
Erect Sand Fencing: Beachgrass must be protected from foot traffic otherwise stems are broken and the plant dies. Sand fencing erected at the base of the dune and along walkways helps to keep people from walking on the beachgrass. Sand fence is also effective in trapping wind blown sand.
Sand fencing should be erected at the base of the dune on both the seaward and landward sides to block access. Fencing should be supported with wooden posts (4" x 4") at 10’ intervals. Fencing can be secured to the posts using wire or staples. Fencing should be placed on the landward side of the posts to prevent loss of the posts when fencing is destroyed during a coastal storm.
Use Community and Public Crossovers: In order to protect the dunes and maintain the effectiveness of these barriers as storm buffers, pedestrian and vehicle dune crossovers have been constructed and identified with signs by the DNREC. Damage to dunes from pedestrian traffic can be avoided by using these designated crossovers.
Although beachgrass is a hardy plant its stems can be easily broken and killed if it is walked upon. Without the anchoring protection provided by the grass, the wind quickly erodes a cut into the dune that enlarges with time. If not repaired, this cut becomes susceptible to breaching by waves during a coastal storm. Once the dune is breached, water flows through flooding low-lying areas directly behind the dune while at the same time widening and deepening the breach.
Construct an elevated crossover: To minimize construction on the dune and the potential for weak spots, property owners should make every effort to use community crossovers. If this is not possible then sharing of a crossover with a neighbor is less intrusive. Sharing of crossovers is required in newer subdivisions.
The crossover should begin landward of the primary dune and extend approximately 5 feet seaward of the base of the dune, The width of the crossover should be based on the expected use. If it is infrequently used a width of 2-3 feet should be sufficient. Crossovers 4’ wide are sufficient for those intended for two way passage. The height above the dune should be at least one to one and a half times its width to allow sunlight to reach the vegetation underneath. The deck of the crossover should be of sufficient elevation to allow an increase in the dune height. Roll-out crossovers laid directly on the dune are another alternative. Spacing of slats for the decking should be sufficient to allow sunlight and rainfall to penetrate to plants below. This will also prevent sand from accumulating on the deck. Property owners are required to apply for a Letter of Approval from the Shoreline and Waterway Management Section prior to construction of a crossover. For an application and example of drawings, click here.
To enable handicapped people to use a crossover inclined ramps with 20 percent slope can be built at each end of the structure.
Don’t throw trees, yard waste, tires or other debris on the dunes: In the past beach managers promoted the placement of Christmas trees and other vegetation on the beaches to help build dunes. Over the years we have learned that this practice does not really help as well with established dunes as the use of native vegetation and sand fencing and it can smother existing beachgrass. We have also learned that dead trees and brush are fire hazards that can lead to the destruction of established dunes.
Mowing and burning beach grass destroys its ability to trap sand and may kill the plant.
Other debris such as car parts, concrete, cinderblocks, wire, tires, patio pavers, brick are not effective materials for dune building. They do not degrade and are hazardous to people walking on the dune. In addition, during storm events advancing waters can pick up this debris and carry it inland and drive them it into landward structures.
Keep boats off of the dunes: In some areas it is common practice for property owners to drag their boats over the dune or to store their boats on top of the dune. It is important to remember, the dune provides protection for you and your neighbors. The vegetation will eventually be killed in the area where you drag or store your boat. Once the vegetation is gone this area becomes vulnerable to wind erosion. As the elevation of the dune is lowered from removal of sand this area becomes vulnerable to breaching and flooding during coastal storms subjecting your property and your neighbors property to flooding and damage.
Tell others about sand dunes: If you aren’t a good steward of the environment, who will be? Tell others about the importance of protecting sand dunes and the coastal environment.