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DRAINAGES- Western Ecuador has many small rivers running independently into the Pacific Ocean. These can generally be divided into five major drainage systems that vary from being composed of a series of tributaries converging into one major river through which the entire system drains (as is the case for the Guayas drainage) to a series of isolated rivers draining independently to the Pacific, located in the same geographic region (as is the case for the Northern and Southern Coastal Drainage Systems). Besides the Andes Mountains, the Coastal Mountain Range (Cordillera Costanera- Gomez, 1989) plays an important role in separating river systems and determining flow patters in western Ecuador. It runs generally parallel to the coast from the Esmeraldas River to Guayaquil and is composed of low elevation mountains (< 800 m; Gomez, 1989). From north to south the major drainage systems in western Ecuador are: 1. The Santiago-Cayapas Drainage System: This is the northernmost major drainage in western Ecuador and includes the Santiago and Cayapas Rivers and their tributaries in Esmeraldas Province, close to the border with Colombia (Table A). This is the region in western Ecuador with the greatest precipitation and includes regions of rain forest. The fishes in the Santiago-Cayapas system include many new species that do not occur farther south like the gasteropelecid Gasteropelecus maculatus, a freshwater hatchet fish, combined with some species from the Esmeraldas and southern drainages. Jimenez-Prado et al. (2015) report 62 species of freshwater fishes from this drainage of which 15 (24.2%) are endemic to the drainage. Table A. Annual Water Volume and Surface Area drained for the Santiago-Cayapas drainage. The ratio of annual water volume drained to surface area gives a measure of relative flow, with larger numbers indicating a greater volume of water per unit of surface area. River data based on Gomez (1989, 2001). Species Data based on Jimenez-Prado et al. (2015).
2. The Esmeraldas Drainage System: This drainage is south of the Santiago-Cayapas drainage and is the second largest drainage in western Ecuador both in terms of area and water volume drained (Table B). It receives a good deal of precipitation and includes some rainforest as well. The fish fauna is composed of some species that occur in the Guayas drainage and other rivers combined with some species that are unique to this drainage or shared between the Esmeraldas and Santiago-Cayapas drainage. It appears in some respects to represent a transitional drainage between the Guayas and Santiago-Cayapas drainages. Jimenez-Prado et al. (2015) report 65 species of freshwater fishes from this drainage of which 17 (26.2%) are endemic to the drainage. Table B. Annual Water Volume and Surface Area drained for major rivers in the Esmeraldas Drainage. The ratio of annual water volume drained to surface area gives a measure of relative flow, with larger numbers indicating a greater volume of water per unit of surface area. River data based on Gomez (1989, 2001). Species Data based on Jimenez-Prado et al. (2015).
3. The Northern Coastal System: This drainage system is composed of a relatively large number of small isolated rivers running between the Coastal Mountain Range and the Pacific Ocean. The major rivers in the system include the Chone, Portoviejo, and Zapotal Rivers in the coastal regions of Manabi and Guayas Provinces. This drainage system includes rivers running through some of the driest parts of the country (notice the drainage volume to surface area ratio for the Zapotal River for example, which is located in the Peninsula of Santa Elena; Table C) and some of the smaller rivers are seasonal. Reliable species lists for this region are currently not available although species diversity is likely much lower than in the other major drainage systems. Table C. Annual Water Volume and Surface Area drained for major rivers in the Northern Coastal System. The ratio of annual water volume drained to surface area is the same as above. Based on Gomez (1989, 2001)
4. The Guayas Drainage System: This is the largest drainage system in western Ecuador. The Guayas River drainage spans an area of approximately 32,674 km2 between the Coastal Mountain Range and the Andes Mountains in the provinces of Guayas and Los Rios (Gomez, 1989, 2001). The Coastal Mountain Range plays a key role in separating the Guayas drainage system from the Northern Coastal Drainage System and (together with the Andes) in funneling water south over a larger area towards the Gulf of Guayaquil. The major tributaries include the Babahoyo, Daule, Vinces, Quevedo, Yaguachi, and Congo Rivers. Guayaquil, the largest city in Ecuador, sits on the shores of the Guayas River in the interior Gulf of Guayaquil. The Guayas drainage has both the highest number of freshwater fishes of any of the major drainage systems in western Ecuador and the greatest percentage of endemic species. Jimenez-Prado et al. (2015) reported 70 species of freshwater fishes from this drainage of which 24 (34.3%) are endemic to the drainage. Table D. Annual Water Volume and Surface Area drained for major rivers in the Guayas System. The ratio of annual water volume drained to surface area is the same as above. River data based on Gomez (1989, 2001). Species Data based on Jimenez-Prado et al. (2015).
5. The Southern Coastal System: This is the southernmost drainage system in western Ecuador. It is composed of a series of small isolated rivers flowing from the western slopes of the Andes to the Pacific Ocean. The major rivers in this system include the Taura, Canar, Balao, and Jubones Rivers. Water flow in these rivers can change tremendously between the wet and dry seasons, with several rivers being notorious for overflowing in the rainy season (Gomez, 1989). The freshwater fishes in this region seem to be mostly a subcomponent of those present in the Guayas drainage system. Table E. Annual Water Volume and Surface Area drained for major rivers in the Southern Coastal System. The ratio of annual water volume drained to surface area is the same as above. Based on Gomez (1989, 2001)
Created and Maintained by Windsor Aguirre Last Updated August 19, 2017 |
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