There are no bridges across the entire width of the river. For most of its course, the river flows through the Amazon Rainforest , where there are very few roads and cities. Most of the time, the crossing can be done by a ferry , so there is no need to build a bridge. The river is the main route of traffic in the region. Most cities are on the banks of the river.
The biggest city on the river is Manaus , which is also the capital of the Brazilian State of Amazonas. Many native people live in the Amazon, such as the Urarina  who live in Peru. Big ocean boats can get up the river until Manaus , which is almost kilometers miles from its mouth. Smaller ocean ships of 3, tons  and 7. From Wikipedia, the free encyclopedia. Check date values in: Microsoft Encarta Online Encyclopedia. Archived from the original on Retrieved from " https: Views Read Change Change source View history. In other projects Wikimedia Commons.
National Geographic says there at least six possible origin points, based on methods ranging from satellite observation to GPS to "ground truth" examinations.
You can see more details about the ongoing quest in this article. Deforestation in Brazil's storied Amazon basin region skyrocketed more than percent in October from a year earlier, a non-governmental group warned Monday. Deforestation in the Amazon rose 29 percent between August and July of last year to 5, square kilometers 2, square miles , Brazilian officials said Wednesday, posting an amended figure.
Deforestation in Brazil's Amazon accelerated in June, with more than square kilometers destroyed, a 17 percent increase over the previous month, government researchers said Tuesday. A tough question has been where that river actually begins. Naming its source has evidently been difficult as centuries of efforts indicate. Brazil's environment minister says the government has increased the number of its inspectors in the Amazon rainforest to help halt a rise in illegal deforestation. Radioactivity in fracking wastewater comes from the interaction between a chemical slurry and ancient shale during the hydraulic fracturing process, according to Dartmouth College research.
The earliest evidence of navigation is found in the Indus Valley Civilization , which existed in northwestern India around BC. Since river boats are often not regulated, they contribute a large amount to global greenhouse gas emissions , and to local cancer due to inhaling of particulates emitted by the transports. In some heavily forested regions such as Scandinavia and Canada , lumberjacks use the river to float felled trees downstream to lumber camps for further processing, saving much effort and cost by transporting the huge heavy logs by natural means.
Rivers have been a source of food since pre-history. Most of the major cities of the world are situated on the banks of rivers. Rivers help to determine the urban form of cities and neighbourhoods and their corridors often present opportunities for urban renewal through the development of foreshoreways such as river walks. Rivers also provide an easy means of disposing of waste water and, in much of the less developed world, other wastes. Fast flowing rivers and waterfalls are widely used as sources of energy, via watermills and hydroelectric plants.
Evidence of watermills shows them in use for many hundreds of years, for instance in Orkney at Dounby Click Mill. Prior to the invention of steam power, watermills for grinding cereals and for processing wool and other textiles were common across Europe. In the s the first machines to generate power from river water were established at places such as Cragside in Northumberland and in recent decades there has been a significant increase in the development of large scale power generation from water, especially in wet mountainous regions such as Norway.
The coarse sediments, gravel , and sand , generated and moved by rivers are extensively used in construction. In parts of the world this can generate extensive new lake habitats as gravel pits re-fill with water. In other circumstances it can destabilise the river bed and the course of the river and cause severe damage to spawning fish populations which rely on stable gravel formations for egg laying. In upland rivers, rapids with whitewater or even waterfalls occur. Rapids are often used for recreation, such as whitewater kayaking. Rivers have been important in determining political boundaries and defending countries.
For example, the Danube was a long-standing border of the Roman Empire , and today it forms most of the border between Bulgaria and Romania. The Mississippi in North America and the Rhine in Europe are major east-west boundaries in those continents.
The Orange and Limpopo Rivers in southern Africa form the boundaries between provinces and countries along their routes. The organisms in the riparian zone respond to changes in river channel location and patterns of flow. The ecosystem of rivers is generally described by the river continuum concept , which has some additions and refinements to allow for dams and waterfalls and temporary extensive flooding. The concept describes the river as a system in which the physical parameters, the availability of food particles and the composition of the ecosystem are continuously changing along its length.
The food energy that remains from the upstream part is used downstream. The general pattern is that the first order streams contain particulate matter decaying leaves from the surrounding forests which is processed there by shredders like Plecoptera larvae. The products of these shredders are used by collectors, such as Hydropsychidae , and further downstream algae that create the primary production become the main food source of the organisms.
All changes are gradual and the distribution of each species can be described as a normal curve , with the highest density where the conditions are optimal. In rivers succession is virtually absent and the composition of the ecosystem stays fixed in time.
The chemistry of rivers is complex and depends on inputs from the atmosphere, the geology through which it travels and the inputs from man's activities. The chemical composition of the water has a large impact on the ecology of that water for both plants and animals and it also affects the uses that may be made of the river water. Understanding and characterising river water chemistry requires a well designed and managed sampling and analysis. Some rivers generate brackish water by having their river mouth in the ocean.
This, in effect creates a unique environment in which certain species are found. Flooding is a natural part of a river's cycle. The majority of the erosion of river channels and the erosion and deposition on the associated floodplains occur during the flood stage. In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding.
Some examples of this are the building of levees , the straightening of channels, and the draining of natural wetlands. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. Straightening rivers allows water to flow more rapidly downstream, increasing the risk of flooding places further downstream.
Building on flood plains removes flood storage, which again exacerbates downstream flooding.
The building of levees only protects the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks. Studying the flows of rivers is one aspect of hydrology.
Rivers flow downhill with their power derived from gravity. The direction can involve all directions of the compass and can be a complex meandering path. Rivers flowing downhill, from river source to river mouth, do not necessarily take the shortest path. For alluvial streams, straight and braided rivers have very low sinuosity and flow directly down hill, while meandering rivers flow from side to side across a valley.
Bedrock rivers typically flow in either a fractal pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults , fractures , or more erodible layers. Volumetric flow rate , also known as discharge, volume flow rate, and rate of water flow, is the volume of water which passes through a given cross-section of the river channel per unit time. Volumetric flow rate can be thought of as the mean velocity of the flow through a given cross-section, times that cross-sectional area. Mean velocity can be approximated through the use of the Law of the Wall.
In general, velocity increases with the depth or hydraulic radius and slope of the river channel, while the cross-sectional area scales with the depth and the width: River Liffey, Dublin, Ireland.
When the river is subject to vertical erosion , deepening the valley. Hydraulic action loosens and dislodges the rock. The rivers load further erodes its banks and the river bed. Over time, this will deepen the river bed and create steeper sides which are then weathered. The steepened nature of the banks causes the sides of the valley to move downslope causing the valley to become V-Shaped. Waterfalls also form in the youthful river valley.