The Amazon River: Case Study

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The Amazon River: Case Study

Introduction

The Amazon River in northern South America, largely in Brazil, ranked as the largest in the world in terms of watershed area, number of tributaries, and volume of water discharged. Measuring about 6275 km (about 3900 miles) from source to mouth, it is second in length only to the Nile among the rivers of the world. With its hundreds of tributaries, the Amazon drains a territory of more than 6 million sq km, roughly half of which is in Brazil; the rest is in Peru, Ecuador, Bolivia, and Venezuela. It is estimated that the Amazon discharges between 34 million and 121 million litres of water per second and deposits a daily average of 3 million tons of sediment near its mouth. The annual outflow from the river accounts for one-fifth of all the fresh water that drains into the oceans of the world. The outpouring of water and sediment is so vast that the salt content and colour of the Atlantic Ocean are altered for a distance of about 320km from the mouth of the river.

Course and Physical Environment

The major headstreams of the Amazon are the Ucayali and Marañón rivers, both of which rise in the permanent snows and glaciers of the high Andes Mountains and follow parallel courses north before joining near Nauta, Peru. From this confluence the main trunk of the Amazon flows in a generally eastern direction to the Atlantic Ocean. The Amazon enters the Atlantic through a broad estuary, roughly estimated at 240 km (about 150 miles) in width. Here delta deposits have formed a maze of islands that separate the river into branches. The mouth of the main stream is 80 km (50 mi) wide. This branch, known as the Pará, is separated from a smaller branch by Marajó Island, which has an area of more than 36,000sq.km. During new and full moon a tidal bore, or wave front from the ocean, sweeps some 650km upstream at speeds in excess of 40mph. This phenomenon often causes waves up to 5m in height.

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The Amazon watershed includes the largest and wettest tropical plain in the world. Heavy rains drench much of the densely forested lowland region throughout the year but especially between January and June. The width, rate of flow, and discharge volume of the river reflect seasonal variation in rainfall. During the months of maximum precipitation, broad areas traversed by the Amazon are subject to severe floods. In Brazil the width of the river ranges between 1.6 and 10 km (1 and 6 miles) at low stage but expands to 48 km (30 miles) or more during the annual floods; the rate ...

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