Land-use planning in coastal zones

In order to designate appropriate coastal land use, policymakers must take into consideration geological processes, recognizing that coasts are zones of rapidly evolving landforms, sedimentary deposits, and environments. Much of the American coastal zone has undergone rapid development without the benefit of landscape evaluation. Future development, as well as corrective measures, must be grounded in knowledge of geology and the interactions of climate and oceanography.

Evaluation of Coastal Zones

The dependency of the United States on its coastal zone cannot be exaggerated; national leaders learned this lesson in 1969 when the Stratton Report, “Our Nation and the Sea,” revealed that coastal areas contained more than 50 percent of the nation’s population (a percentage that has likely grown), seven of the nation’s largest cities, 60 percent of the petroleum refineries, 40 percent of industry, and two out of three nuclear or coal-fired electrical generating plants. Not surprisingly, the Stratton Report became the primary impetus for the passage of the National Coastal Zone Management Act (NCZMA) of 1972 and 1980. NCZMA provides federal aid to coastal states and territories for the development and implementation of voluntary, comprehensive programs for the management and protection of coastlines. In 1982, Congress passed the Coastal Barrier Resource Act, which declared millions of acres of beachfront on various barrier islands ineligible for federal infrastructure funding. By denying funding for roads and other construction projects, the act discourages development on sensitive coastlines.

Geologic information and analysis, the first step of all land-use planning, is complicated in the coastal zone by the fact that the major value of the area is water; indeed, water is the determining factor of the suitability of the microenvironments under consideration. Landscape evaluation must also recognize that the zone is not static but the locus of rapid geologic change. Such change involves a complex sediment dispersal system that responds rapidly to human modifications. The coastal zone also includes fundamental legal boundaries between private and public ownership, and the boundaries themselves are high-energy geological boundaries. The presence of barrier islands demands a highly specialized set of land-use practices. Natural hazards in the coastal zone include hurricane attacks on the Atlantic and Gulf coasts, landslides on the cliffed coasts of the Pacific, and tsunamis in the Pacific Northwest region and the coastal zones of Alaska, Hawaii, and Puerto Rico. Superimposed upon the dynamic processes of the coastal zone is a global sea-level rise, initiated some 18,000 years ago with the termination of the Late Wisconsin glaciation. Sea-level rise is currently accelerating, possibly in response to such human-induced atmospheric changes as the greenhouse effect.

A major resource of the area is the estuarine zone, encompassing less than 10 percent of the total ocean area but containing 90 percent of all sea life. Estuaries trap the nutrients that rivers wash down from the land and use them to produce an extraordinary quantity of biomass that sustains a variety of marine life. It is estimated that 60 to 80 percent of all edible seafood is dependent on estuaries for survival. Estuarine zones and coastal wetlands also serve as natural flood control devices by absorbing the energy of damaging storm waves and storing floodwaters. If not overloaded, these wetlands have the ability to remove large quantities of pollutants from coastal waters.

and Shoreline Retreat

The great financial potential of beachfront properties makes the consequences of beach erosion—as well as efforts to halt shoreline retreat—of vital concern in coastal zone land-use issues. Although some beach erosion is rightly attributed to sea-level rise, much is the direct result of human activities. The damming of major rivers has essentially cut off the sediment supply to the nation’s beaches. Loss of dredged sediment through maintenance of shipping channels results in rapid erosion on the downdrift beaches to which wave action would normally deliver sands. Both jetties and groin fields act as dams to sediment transport and create erosion on adjacent beaches. Dune destruction removes the reservoirs for sand storage and the natural barriers to storm surges. The emplacement of sand on the beach from offshore or inland sources (beach renourishment) and pumping sediment across navigation channels (inlet bypassing) represent more acceptable “soft engineering” alternatives to the armoring of the shoreline.

On the Atlantic and Gulf coasts, hurricanes account for many of the sediment distribution patterns. These tropical cyclones modify barrier islands, removing beach sand offshore and over the dunes. Overwash, in which large quantities of sediment are moved inland, is the primary means by which barrier islands retreat before the rising sea. The inevitability of hurricanes mandates land use that is compatible with predicted flooding patterns, as well as building codes based on hurricane-force winds and tidal storm surges, and the maintenance of up-to-date evacuation plans.

Retreat of the shoreline along the West Coast is more frequently related to seacliff erosion. Erosion along cliffed coasts is caused by a combination of wave scouring at the base and landsliding higher on the bluffs. In winter, the large tides and waves force the rain-weakened cliffs to retreat. The degree of failure depends on wave energy, the hardness of the cliff rock, and internal fractures and faults. Weathering processes further weaken rocks and aid erosion. The human activities that accelerate cliff retreat include septic tank leaching, landscape irrigation, alteration of drainage patterns, and introduction of nonnative vegetation.

Gulf and Atlantic Coastal Development

The low, sandy Gulf and Atlantic coasts, characterized by estuaries, marshes, and inlets, are separated from the open ocean by barrier islands. Major features of the lower coastal plain include abundant forests, a diversity of wildlife habitats, and a unique potential for water-based recreation. The area is largely unsuited for urbanization because of the high water table, but remnant ancient barrier island chains, or “terraces,” represent elevated sites suitable for building. The largely sandy soils are poorly suited for widespread agriculture, though some fertile alluvial, or river valley, soils are present. The high water table makes aquifer pollution an ever-present threat; the abundant forests, which support a major pulp and paper production region, are fire-prone.

Because the broad coastal plains of the depositional coasts were formed by barrier island migration during the sea-level fluctuations of the Pleistocene “ice ages,” the resulting sediments are largely barrier island sands or marsh muds and peats. Rapid, unplanned growth in the coastal zone has resulted in widespread use of septic tanks in these unsuitable, sandy soils, allowing waste water to percolate too rapidly and releasing improperly treated effluent. The degradation of coastal waters by septic tanks can be avoided through the tertiary treatment of waste water, which may in turn be used for wetlands recharge or irrigation. A sanitary landfill properly sited in mud or peat has low permeability, which limits the flow of leachate and contaminated landfill runoff. The most heavily developed resort areas with the greatest need for landfill space also have the highest land prices, making suitable land acquisition difficult.

Marshland Development

The vast marshes of the coastal zone grade from fresh to brackish to salt water. The river-swamp system, interrelated with the marsh-estuary system through flows of water, sediments, and nutrients, plays a major role in determining the impact of inland development on the estuary. In their natural state, swamps buffer the coast from the many impacts of land-use activities; if drained, filled, or altered, this contribution is lost. An increase in stormwater runoff related to urbanization reduces their ability to hold and absorb floodwaters. This problem could be avoided by placing limits on development and requiring that nonhighway “paving” be of permeable material such as crushed limestone instead of asphalt. The river swamp’s ability to filter and absorb pollutants also improves the quality and productivity of downstream coastal waters; if overloaded with pollutants from industrial effluents, agricultural practices, or improperly sited septic tanks and landfills, the closing of shellfish beds is inevitable.

The “low marsh,” inundated daily by the tides, is well recognized as an area so valuable and productive that conservation is mandatory. Although protected by state laws, estuarine marshland continues to experience some destruction as a result of marina construction and the disposal of dredged sediments from navigation channels. Marshland is also lost to the boat-wake erosion that undercuts the banks, causing slumping of the rooted clays.

At a slightly higher elevation is the “high marsh,” sandy marshland occasionally wetted by storms or extreme tides. This marsh, unprotected by law, is known to be an important wildlife habitat but has not been widely studied. The role of the high marsh and its relationship to the low marsh is unknown. The widespread exploitation of this area for residential and commercial development will make it impossible for the low marsh to reestablish itself landward in response to sea-level rise. The resultant loss in a real extent of the salt marsh will cause a great decline in estuarine-dependent marine life and a corresponding rise in pollution.

Barrier Island Development

The barrier islands that front low-lying coastal plains consist of such dynamic geologic features that they are clearly unsuited for widespread development. These islands are composed of unconsolidated sediments that continuously seek to establish equilibrium with the waves, winds, currents, and tides that shape them. Early settlements were wisely constructed on the landward-facing, or back-barrier, portion of the islands. The beachfront was considered too dangerous because of hurricanes.

Ideally, high-density barrier island development should be confined to the back-barrier part of the island, protected from storms and hurricanes. Low-density development should thin out in both directions, and open island should be preserved along the high-energy beachfront. This would ensure the scenic and recreational value of the island and protect the sand supply and natural maintenance of the system. If stabilization of inlets for shipping is necessary, the sand built up on the updrift side should be bypassed downdrift to reenter the system. Many islands should be preserved free of development for sand storage, as well as for educational, recreational, and aesthetic benefits.

The barrier island uplands, or high ground, consist of maritime forest on ancient oceanfront dune ridges; these dunes were left behind as the island built seaward, a process that was caused by a fortuitous combination of sediment supply and fluctuating sea level. This forested region is appropriate for environmentally sensitive development as long as care is taken to conserve ample wildlife preserves. Freshwater sloughs and ponds are located in the low swale areas between dune ridges, where rainfall floats on salt water within the porous material of the island subsurface. These wetlands represent important wildlife habitat and, on developed islands, serve as natural treatment plants for storm runoff and natural storage areas for floodwaters. They may also be recharged with tertiary treated waste water, if not overloaded. Unfortunately, there has been a great loss of freshwater wetlands on the mainland and on the islands to developers who have drained and filled them to produce construction sites.

Beachfront Development

Beachfront construction should first be considered in the context of available data on historical change to the shoreline. If the area under consideration has a suitable history of stability or accretion, development should be limited to a setback line that is landward of the heavily vegetated and stable dunes. Construction should be compatible with historical hurricane storm-surge data, and, at elevations below recorded storm surges, dwellings should be elevated on a foundation of pilings.

Access to the beach should be via dune walkovers to avoid damage to the plants that stabilize the fragile dune environment. The dunes that are closest to the ocean and tied to the beach for their windblown sand supply are constantly changing landforms. Storm waves scour away the front of the dunes, and fair-weather waves return the lost sand to the beach to rebuild them. These ephemeral features, vital as buffers to storm attack, should be protected not only from construction but also from any sort of human activity.

The updrift and downdrift inlet beachfronts are best utilized as nature preserves or public beaches, free of construction, because of the natural instability of both zones. The updrift inlet is constantly reestablishing its channel in response to tide-deposited sand mounds, causing alternating and far-flung advances and retreats of the north-end shoreline. The downdrift end represents the geologically younger and most recently constructed part of the island. Because the area is barely above sea level, hurricane storm surges can readily cut through an elongated downdrift spit, creating a new inlet and freeing the sand to migrate downdrift.

Pacific Coastal Development

The geologic instability of the rocky Pacific coast demands land-use planning strategies that will protect its rugged beauty and minimize the threats of natural hazards. Development in the available coastal zone regions of cliff tops, dune fields, and beachfront is potentially hazardous.

On the beachfront, a wide beach between cliff and shoreline should not be mistaken for a permanent feature. Developed beachfront areas at the bases of cliffs are subject to periodic floodings by large waves combined with high tides; after much of the beach sand is removed by the storm, the wave energy is expended against the buildings. Houses in this zone collapse when their foundations are undermined or their pilings smashed through after being uplifted by waves. If beachfront development is allowed, it should be based on a comparison of the site elevation and expected tidal ranges, storm surges, and storm-wave heights. A secure piling foundation below any potential wave scour should elevate the structure above any maximum inundation.

Although the presence of dune fields is restricted on young mountain range coasts, existing dunes have not escaped urbanization, and the resultant problems are identical to those of the East Coast. Where homes and condominiums have been built on conventional foundations, periodic dune erosion has undermined and threatened the structures, forcing emplacement of sea walls constructed of boulders. The dynamic nature of sand dunes makes the total prohibition of construction there the only appropriate course of action for wise land-use planning.

The zone consisting of bluff or cliff tops is the West Coast environment that faces the greatest potential for development. Construction should not proceed here without a large enough setback behind the cliff edge, so that the structure can endure for at least one hundred years based on long-term erosion rates. The increased runoff associated with urbanization, if not collected and diverted away from the seacliff, results in serious slope failure. Homes, patios, swimming pools, and other construction also decrease the stability of the seacliff by increasing the driving forces, forces that tend to make Earth materials slide. Although seacliff erosion is a natural process that cannot be controlled completely, regardless of financial investment, it can be minimized by sound land-use practices.

Principal Terms

coastal wetlands: shallow, wet, or flooded lowlands that extend seaward from the freshwater-saltwater interface and may consist of marshes, bays, lagoons, tidal flats, or mangrove swamps

coastal zone: coastal waters and lands that exert a measurable influence on the uses of the sea and its ecology

estuarine zone: an area near the coastline that consists of estuaries and coastal saltwater wetlands

estuary: a zone along a coastline, generally a submerged valley, where freshwater system(s) and river(s) meet and mix with an ocean

groundwater: water that sinks into the soil, where it may be stored in slowly flowing underground reservoirs

land-use planning: a process for determining the best use of each parcel of land in an area

mass wasting: the downslope movement of Earth materials under the direct influence of gravity

saltwater intrusion: aquifer contamination by salty waters that have migrated from deeper aquifers or from the sea

water table: the level below the earth’s surface at which the ground becomes saturated with water

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