Table Of Content

•infT> A 1 1 i •*-' ’ . ^ i’T _'m ' Vsi i. mJkfi Managing Erosion Chapter 1: Introduction ^^lorf/i Carolina's estuarine areas As the demand for estuarine shoreline property owners understand various include nearly 4,500 miles of estuarine and property rises, the value also increases. options. A more comprehensive discussion ocean shorelines, and more than 2.1 million Thus, landowners become concerned about of erosion is found in the companion North acres of estuaries and coastal rivers. The property loss due to erosion and must make Carolina Sea Grant guide. Shoreline abundance of bayfront vistas and recreational decisions regarding whether or not to Erosion in North Carolina Estuaries by opportunities is paralleled by the dynamic and stabilize waterfront property (Figure 1, Stanley R. Riggs. changing nature of these regions, often creating facing page). These are complex decisions • Basic elements of site evaluation are conflicts between the increasing demand for because there are numerous options for presented, including parameters for shoreline properties and the ongoing erosion shoreline stabilization. evaluating specific sites. processes. Estuarine property owners and local • A range of stabilization options is Shoreline erosion is a natural process governments face difficult choices as they presented: wetlands planting options, stone involving prevailing wind, wave and current strive to select appropriate strategies to structures and vertical walls. In some cases, conditions. The actual erosion rate within an control erosion that are cost-effective and property owners may handle the task alone. area may vary within estuarine systems and environmentally sound. In others, professional services or guidance over time, depending upon individual site Managing Erosion on Estuarine are required. Some property owners may conditions and the frequency of storms or Shorelines is part of The Soundfront Series. choose to live with the conditions. other causes of erosion. This guidebook provides a basic understand¬ • An overview of the permit process North Carolina's estuarine landscapes ing of the nature and causes of shoreline provides readers contact information for have changed considerably over centuries. erosion, and introduces a number of the North Carolina Division of Coastal Agricultural areas, residential subdivisions and management strategies. This publication is Management (DCM). Updated regulations commercial and industrial facilities have intended to provide general guidance, and are available online or at DCM offices in replaced once-forested shorelines. As a result, not to be considered a construction Raleigh and the coastal region. increased runoff containing sediment and other specifications manual. A landowner may • Additional resources will assist pollutants has entered the surface waters and undertake some approaches, while other landowners in making and implementing groundwater supplies. Natural marsh fringes options should be pursued with the erosion-control decisions. that once buffered and protected uplands have assistance of an experienced professional. Individual property owners, develop¬ eroded due to natural and man-made causes, fit order to provide practical shoreline ers and local officials may have interest in resulting in higher rates of upland erosion and management options, this guide focuses on specific segments of estuarine shoreline. associated water quality concerns. several topics: This guide will put decisions regarding • Causes and effects of erosion are these specific segments into a larger discussed briefly in this guidebook to help perspective. Page 3 Managing Erosion Chapter 2: Planning for Estuarine Shoreline Stabilization Options F L-stuarine property owners often have Table 1. Shoreline Management Goals compared to vertical walls. However, difficult decisions regarding specific sites with planting a marsh with no structural enhance¬ active shoreline erosion. Their options may be • Stabilize storefront lands and structures ment is generally recommended only for influenced by permit and policy decisions against erosion. lower energy areas. In addition, two or more made by resource managers who must • Protect and/or enhance property values. approaches may be considered for a balance land-use options with the long-term • Provide for human safety. particular site, but evaluation of costs, access health of the estuarine environment. • Achieve cost-effective solutions. for equipment or availability of materials The first step in developing a shoreline • Protect water quality by reducing runoff may narrow the options. management strategy is to define goals that and preserving buffers. Shoreline management decisions are benefit the property owner and reduce • Preserve, enhance or restore natural based on a variety of factors, including negative impacts on the natural environment wedands, sandy beaches and other priorities, goals, cost site conditions and land (Figure 2, facing page). Once appropriate goals intertidal habitats. use. Information sources include consultants are selected, the property owner should » Protect existing or create new uses such and contractors with experience in the determine the specific nature of the erosion as boating access or swimming. following areas: problem, evaluate the existing site condition, • Ensure compatibility with adjacent land • Coastal erosion and choose one or more options to success¬ uses. • Shoreline management options fully address the erosion problem and achieve • Natural resource protection the management goals. Table 1 identifies eight In some cases, one goal may be • Marine construction possible goals. Other site-specific goals may achieved at the expense of another. Priorities • Permit requirements depend upon the use, geography or access. may vary within different stretches of • Relative costs for various strategies shorelines or among neighboring properties. In choosing a consultant or contractor, Also, it is difficult to achieve all goals at the take time to visit completed projects and talk lowest cost. For example, the option of with the property owners to assess their level wetland plantings is environmentally of satisfaction. beneficial and may be relatively inexpensive Table 2 provides a spectrum of shoreline Table 2. Shoreline Management Options Land Management Vegetation Beach Fill or Nourishment Shoreline Hardening Sand Traps • Development setbacks • Planted native marsh • Add sand to an existing • Bulkheads • Groins • Live with erosion grasses, such as cordgrass natural beach • Revetments ® Breakwaters • Managed buffer of mixed and black needlerush • Marsh sills shoreline vegetation in intertidal area Page 5 The Soundfront Series shorelines. Give consideration to the need for, and possibility of. a cooperative project between neighboring properties or within a community. Joint projects may cost signifi¬ cantly less than a piecemeal approach, while avoiding the "domino" effect of unwanted erosion. Measures should be considered to minimize damage to adjacent or nearby properties, and to protect natural estuarine habitats. Compare costs and availability of materials: Assuming all other factors are equal, costs and material availability may be the deciding factors between two effective options. In addition, property owners should consider the accessibility of the site for materials and equipment, costs of labor and Figure 3. Increased erosion of forested shoreline between the two bulkheaded lots. equipment for each approach, site adaptations needed for each measure, and long-term management options, generally in order of Identify management goals and set durability’ and expected lifetime for an increasing site modification and intervention priorities for the site: Use Tables 1 and 2 to erosion-control measure. While costs are in the land/estuary interface. Within each begin the assessment. Setting goals for a always important, a less expensive alternative management option, a range of costs and shoreline project is a critical step in moving may not realize the level of benefits that may impacts should be considered during the forward with any approach. Goals to stabilize be achieved from another approach, such as planning process. The options are explained land and protect structures may conflict with long-term stability, protection and/or in detail in Chapter 5. goals to protect habitat. On the other hand, enhancement of marshes or beaches, and some projects may be designed to achieve aesthetic appeal. PLANNING several goals. Once goals are established, Compare complete costs of ap¬ CONSIDERATIONS property owners may identify’ more specific proaches: For example, compare the cost priorities and make decisions about what per linear foot of the structure versus the cost Determine the specific nature of the w'orks best for each unique situation. per foot for the overall protection. In some erosion problem: Does the property have Consider potential effects and interac¬ cases, it may be more cost-effective to choose an eroding beach, marsh or upland? What tions of the project on adjacent properties and the "no action" alternative over any structural are the forces causing the erosion? Is the the natural environment: Many strategies to measure. For certain site conditions, property shoreline considered a low-, moderate-, or protect the property from shoreline erosion owners may prefer to move structures and high-energy site? Is the erosion due to long¬ can result in increased erosion of adjacent infrastructure or retreat from the property term conditions or a single event, such as a properties (Figure 3). Some options reduce rather than to spend money on costly major hurricane? Evaluating the nature of the sediment supply normally feeding a approaches that may be unsuccessful against the erosion may be limited to one property sandy beach or marsh area (Figure 4). A the existing high-eneigy forces. or may require review of a much more project may cause wave and current energy Develop a realistic approach: In complex length of shoreline. to be redirected to adjacent unprotected evaluating site conditions and design for a Page 6 Managing Erosion shore-protection strategy, keep your may be too costly or result in greater adverse also will need to follow development rules expectations realistic. The forces of nature impacts for the adjacent properties and specific to the Area of Environmental Concern are often unpredictable and dynamic. Both natural environment. (AEC) in which the property is located. the advantages and relative risks of living Consider permit requirements: Any In addition to a CAMA permit, a project along the shoreline should be factored into evaluation should include an assessment of may also need other federal, state, and/or developing an approach for shoreline federal, state and local permits needed to local approvals. For current information on management. Structural approaches are implement a given approach. Information permit needs for shoreline erosion-control generally designed to be effective for regarding application procedures and rules measures, contact the N.C. Division of Coastal moderate storm conditions, and to remain governing approvals should be obtained Management. On the Web, go to www.nc relatively stable for longer periods of normal from the appropriate agencies. coastolmanogement.net and follow the links conditions (although materials may fail in In North Carolina, property owners for rules and permits for the CAMA Guide to shorter time periods). It may be unrealistic to likely will need a Coastal Area Management Development in Coastal North Carolina. design for catastrophic weather conditions Act (CAMA) permit for any development Also, see Chapter 6: Regulations and such as extreme hurricanes, as the structures on or near the shoreline. An estuarine project Permits, later in this guide. Figure 4. Increased erosion of beach and marsh shoreline adjacent to a bulkheaded lot. Page 7 Managing Erosion Chapter 3: Estuarine Shoreline Erosion Causes and Effects F L-.stuarine shoreline erosion can be EROSION CAUSES shoreline — sometimes all at the same time. simply defined as the wearing away of Once the shoreline sediments are set into shoreline sediments — the loss of land into the Shoreline erosion in the estuaries is motion by the waves, gravity always has the estuary. Erosion is a normal geological process, caused by moving water, usually waves or edge, gradually moving sediment of all sizes and the rate of shoreline erosion will vary from currents. Breaking waves only several away from the higher positions along the place to place. However, when a specific inches tall have the power to move sand and shoreline to deeper parts of the estuary. shoreline is disappearing, it becomes far more other sediments both offshore into deeper Shoreline erosion also can be caused or than a geological process for the owners (Figure water and along the shoreline to someone increased by boat wakes. Recreational and 5, facing page). Erosion may be natural, but it else’s property. Once coastal sediments are commercial boats can generate closely also can become a threatening personal issue. in motion, they are often redistributed based spaced, steep waves that are particularly This chapter helps assess the causes and on grain size and weight. The finest and prone to cause erosion. The larger and faster explain the range of erosion on a shoreline lightest sediments, silts and clays, are the boat, generally the larger the wave segment. Chapter 5 describes a variety of suspended in the water column and created. On wind-sheltered shorelines, wave erosion management alternatives. Combined, transported to deeper, less turbulent water heights can still exceed three feet due to boat the guidebook will discuss the generally where they settle to the bottom of bays and wakes. This is particularly the case along inevitable tradeoffs that occur when using sounds. Larger and heavier sediment, such the Intracoastal Waterway (ICW). The ICW erosion-management techniques. as gravel and boulders, are rare in North was constructed to provide an inland route, Carolina’s estuaries. They are too heavy to sheltered from ocean waves, for commercial be moved very far by the small waves of the vessels to transit the East and Gulf coasts. estuaries. Where present, most of the gravel In many areas, the waterway was con¬ and boulders remain in place near the structed as a straight canal through marshes shoreline, but may settle as finer sediments and even upland property (Figure 6). Prior are removed from around and under the to construction, the builders obtained a larger material. Sandy sediment is bounced wider easement on both sides of the original along the bottom under the waves. canal, anticipating future erosion. Many of The circular motion of waves causes these excavations have doubled in width reversing currents as the wave form passes. since construction was completed in the First the current moves in the same mid-1930s. direction as the wave. But then it reverses to opposite the wave motion under the wave TIDES AND WEATHER trough. Thus, waves give sand-size sediment more complex motion patterns. Depending Changes in water level, due to lunar or on the shoreline conditions, sand may be wind tides, can affect the shoreline. Higher moved away from, back to, and along the waters allow larger waves to reach the Page 9 The Soundfront Series Figure 6. Overhanging peat sediment with marsh grass, probably due to waves and tidal currents. shoreline rather than break in shallow water continue in the range of four inches to nearly erosion should be expected from year to offshore. In tidal areas, most erosion of the two feet per century. This seemingly small year. upland property takes place at high tide rather v ertical change would be greatly amplified When deciding how to address any than low tide (Figures 7.8). by the flat slope of the coastal plain. erosion on a shoreline segment, consider Storms and hurricanes also can On any particular shoreline at any both the long-term erosion that might occur drastically alter water levels. Stomi surge and particular time, the w ave conditions and over the next few decades as well as the sustained w inds can cause the water level to water levels in the estuaries are determined potential erosion during an infrequent but rise along some shorelines, while dropping by the weather, primarily the direction, severe storm such as a hurricane. The best the water level on others. When onshore speed and duration of the wind. Shoreline solution for long-term erosion is often winds and waves accompany the storm erosion is most often a weather-driven different titan the best choice for relatively surge, erosion of the shoreline is more likely. phenomenon. Like many familiar weather rare, storm-induced erosion. The apparent Although often thought to be constant, conditions, shoreline erosion can be threat of erosion is usually perceived by sea levels are gradually rising on most world expected to be highly variable over a period recent losses over a day, a month or a year. shorelines. The rise is measured not just in of years or decades. Consider rainfall. North Understanding both the long-term, chronic geologic time but also by tide gauges in place Carolina never seems to have an “average" erosion on your shoreline and the effect of for tens to hundreds of years. In North rainfall year — usually there is a drought or any recent severe storms will aid in Carolina sea-level rise has been estimated to flooding. Likewise, wide variations in choosing the best solutions. Page 10