Introduction

The geometry, position, and type of the shoreline of the Orinoco Delta are a result of geologic setting, sediment supply, and fluvial and oceanic processes. Figure 1 reveals two principal sectors: the southeastern quarter of the coast along Boca Grande and Boca Araguao, where the shoreline geometry is complex, and the northwestern three-fourths, where the shoreline geometry is much less complex and mudcapes, such as Punta Pescador, are prominent features.

Previous studies (Van Andel and Postma, 1954; Van Andel and Sachs, 1964; Van Andel, 1967; Herrera and others, 1981; Coleman, 1981) demonstrate that the broad shallow shelf and lack of high-intensity storms (such as hurricanes) result in a low- to moderate-energy wave regime along the Orinoco coast. The position of the Delta in the Intratropical Convergence Zone makes it subject to wind and waves from the east and northeast. Mean diurnal tides range from ~1.6 to 2.0 m. Tidal ranges are higher in the southeastern and northwestern estuaries and relatively lower along the central Delta coast. The coast is also strongly affected by the Guayana Current (fig. 24), a primarily northwest-directed littoral current with velocities of 50 to 75 cm/s in the spring and 25 to 40 cm in the autumn (Van Andel, 1967). The Guayana Current transports Amazon sediment northwestward, providing ~50 percent of the sediment deposited along the Orinoco Delta shelf and coast (Meade and others, 1983).

More than 75 percent of Orinoco River discharge is through Boca Grande. The high-volume river discharge and diurnal tides are principal processes in forming the complex coastline in the southeastern quarter of the Delta. The Guayana Current is the principal process acting on the regional configuration of the northwestern three-fourths of the Delta. This last observation is substantiated by examining the shoreline geometry of the Suriname coastal plain, which is characterized by small rivers and mudcape development (Roeleveld and van Loon, 1979), and appears remarkably similar to the northwestern three-fourths of the Orinoco Delta. Both the northern Orinoco Delta coast and Suriname coast are controlled by relatively weak wave regime, relatively minor river discharge, and a strong littoral current that supplies large volumes of sediment from the southeast.

Within this regional context, Bureau efforts focused on developing a preliminary classification system that describes Orinoco Delta coastal features and processes. The study area included the central and northwestern Orinoco Delta between Boca de Guanipa and Boca de Araguao. The classification scheme is specifically for the Orinoco Delta shoreline. Identifying and mapping distinct shoreline types increases understanding of the patterns of shoreline change and can help reconstruct the recent history of the lower delta so that future trends can be inferred. Once refined, the resulting shoreline classification map will also be useful for oil spill contingency planning and design of coastal infrastructure.

Devising a comprehensive shoreline classification involves determining those features of a coast that are indicative of the important ongoing processes and geologic settings. For the Orinoco Delta coast, the following characteristics are considered: (1) sediment grain size, (2) vegetation type, (3) stability (accretional/erosional/stable), (4) shoreline form (that is, many indentations or relatively smooth shoreline), (5) geomorphic process (for example, prograding spit), (6) landward, beach and nearshore elevation profile, (7) energy level of tidal and oceanic currents, and (8) exposure to wave energy.