The Gulf of Guayaquil and the Guayas River Estuary, Ecuador

Abstract

The Gulf of Guayaquil (3°S, 80°W) of the coastal province of Guayas, Ecuador, is the largest (12,000 km²) estuarine ecosystem on the Pacific coast of South America (Cucalón 1983). The Gulf has historically been defined by an outer and an inner estuary (Stevenson 1981). The outer estuary, referred to as the Gulf of Guayaquil, has a shelf boundary along the 81°W meridian with a distance of about 204 km at the mouth of the gulf. The boundary extends about 130 km inland to Puna Island (80°15’W) at the mouths of Morro and Jambeli channels. The inner estuary, referred to as the Guayas River estuary, can be classified as a tectonic estuary (Stevenson 1981) which extends about 74 km from its mouth at the northern shore of Puna Island to the tidal signature of the Guayas River (Fig. 17.1). To the northwest, a relatively large subestuary, known as the Salado, has freshwater input restricted to wastewater from the city of Guayaquil (population of 2.5 million) and to the southeast, the Churute subestuary is influenced by the Churute and Taura Rivers. More than 20 rivers, with a total watershed of 51,230 km², discharge into the Gulf of Guayaquil (Fig. 17.1). The Guayas River, which forms at the confluence of the Babahoyo and Daule Rivers, has a drainage basin area of about 32,800 km² (64% of total drainage basin) and is the major source of freshwater (20 km³ year⁻¹; Stevenson 1981). The Taura and Churute River drain a watershed of 1,600 and 300 km², respectively. Along the southeast coast, the Jubones and Arenillas Rivers contribute freshwater to the Gulf of Guayaquil and represent 4,830 km² of watershed (9.4% of total). The depth of the Gulf of Guayaquil ranges from 183 m along the shelf to 18 m along the inner shoals. The depth of the Morro and Jamb eli channels at the inner boundary of the Gulf is 56 and 22 m, respectively, and depth in the Guayas River estuary averages about 9 m.