Morphodynamics of a high discharge tropical delta, San Juan River, Pacific coast of Colombia
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2002-12-30
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ELSEVIER SCIENCE BV
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The San Juan River has one of the most extensive and best developed deltas on the Pacific coast of South America, measuring 800 km2. The river drainage basin measures 16465 km2 and is located in one of the areas with the highest precipitation in the western hemisphere. The annual rainfall varies from 7000 to 11 000 mm, and as a result the San Juan River has the highest water discharge (2550 m3 s-1), sediment load (16×106 t yr-1), and basin-wide sediment yield (1150 t km-2 yr-1) on the west coast of South America. The San Juan delta growth began approximately 5000 years BP. The structure of the delta is determined by the interactions between fluvial deposition and the effect of 1.7-m significant swells, mostly from the SW, and strong tidal currents. Analysis of delta progradation indicates that during 1848-1992 the morphology of the delta was characterized by beach ridge accretion, spit growth, narrowing of inlets, and a general advance of the delta shoreline. During the past decade processes such as rapid erosion of the delta shore, narrowing of barrier islands, and breaching of a new inlet, are the result of a long-term relative sea-level rise of 2.6 mm yr-1 due to tectonically induced subsidence coupled with a eustatic rise of sea-level. The delta also experiences strong oceanographic manifestations associated with the El Niño-La Niña cycle, causing regional sea-level elevation of 20-30 cm during El Niño years. Recent coastal subsidence in the delta is evidenced by (1) increased occurrence of non-storm washover events; (2) increased erosion of barrier islands with average loss of 11 m yr-1 during 1993-1997; and (3) a relative sea-level rise of 3.4 mm yr-1 during 1991-1999. The morphology and recent evolution of the San Juan delta are unique when compared to other deltas of South America because of the singular combination of extreme climatic, geologic, and oceanographic conditions under which the delta has formed and the absence of human-induced impact in the drainage basin. © 2002 Elsevier Science B.V. All rights reserved.