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Posts tagged Erosion

Environmental Issues Affecting Orange River, South Africa

28.6S 16.4E

February 16th, 2013 Category: Climate Change, Rivers

South Africa – January 27th, 2013

Draining an area of just under 1million km2 or 77% of the land area of South Africa, the Orange River has its source in the Drakensberg mountains, but starts as the Senqu River in Lesotho. From here it flows westwards to the Atlantic Ocean. Here, it can be seen flowing more or less horizontally across the upper left quadrant of the image.

The headwaters are located at an altitude of 3300 m and consequently parts freeze in the winter months. After the town of Kimberly the river is joined by the Vaal river, its main tributary and from here it enters the arid region of the southern Kalahari and Namib desert. Dams along the river provide water for irrigation and hydropower, however because of the unpredictable flow and sand bar at the river mouth navigation is limited.

Given the length of the Orange River, combined with its range of altitude and climacteric zones, the basin covers a wide range of ecological systems, and can be regarded as being a linear oasis. Its bio-geographical isolation means that potential for re-colonisation from adjacent rivers and wetlands is very low. The river biota is therefore unusually susceptible to the permanent loss of species.

Its biomes contain a vast array of faunal and floral species variety with several endemic species. However, they also comprise areas facing environmental threats, such as the extinction of species and changes brought about by desertification. The economic utilisation of the Orange River’s water as well as the land use patterns in the basin strongly influences the environmental state of the river basin.

In this context four issues are of particular significance, namely the problem of soil erosion and wetland losses in Lesotho (the most severe problem), the impact of industrial and municipal effluent in the Vaal River system, agricultural pollution in the Vaal and Orange River and the environmental threats to the Orange River Estuary Ramsar site at the mouth (click here for more information).

Sediments Along Western Coast of Madagascar

18.8S 46.2E

October 4th, 2011 Category: Sediments

Madagascar - October 2nd, 2011

The island of Madagascar can be divided into three broad geographic zones. These include the highlands, a plateau region in the center of the island ranging in altitude from 2,500 to 4,500 ft (762 to 1,372 m) above sea level; a narrow and steep escarpment that runs the length of the eastern coast and contains much of the island’s remaining tropical rain forest; and a wide, dry plain that gently slopes from the western boundaries of the highlands toward the Mozambique Channel.

The central highlands is the most densely populated part of the island and is characterized by terraced, rice-growing valleys lying between grassy, deforested hills. Here, erosion has exposed the island’s red laterite soil, source of the country’s sobriquet “The Red Island”. Some of this red soil can be seen, carried by rivers, as orange-colored spilling off the coast.

The western coast features many protected harbors, but silting is a major problem caused by sediment from the high levels of inland erosion carried by rivers crossing the vast western plains. Once again, these orange-red sediments can be observed along the western coastline in this image.

Erosion from Deforestation Turns Madagascar’s Rivers Red

15.4S 48.0E

June 28th, 2009 Category: Rivers

Madagascar - June 8th, 2009

Madagascar - June 8th, 2009

The Sofia River (above) and the Betsiboka River (below) are red in color due to sediments originating in the central highlands, where red lateritic soils predominate. The Betsiboka River discharges its sediments into the Bombetoka Bay, which then connects to the Mozambique Channel.

The red waters of the river demonstrate soil erosion, one of Madagascar’s greatest environmental problems, caused by deforestation in the central highlands. Such soil erosion is widespread exceding 400 tons/ha per year in some areas.

Soil erosion has also made the Betsiboka Estuary into one of the world’s fast-changing coastlines. The land has been cleared and incredible rates of erosion have occurred due to about 100 years of extensive logging in rainforests and coastal mangroves.

After every heavy rain, exacerbated by tropical cyclones, the bright red soils are washed from the hillsides into the streams and rivers, clogging the coastal waterways with sediment.

Erosion from Krishna River, India

15.7N 80.8E

June 16th, 2009 Category: Rivers

India - June 8th, 2009

India - June 8th, 2009

The Krishna River, whose name translates to “the Dark-Colored River”, is one of the longest rivers in central-southern India at about 1300 km in length.

The Krishna rises at Mahabaleswar in Maharashtra, in the west, and meets the Bay of Bengal at Hamasaladeevi in Andhra Pradesh, on the east coast. The delta of the river is one the most fertile regions in Bharat.

Ecologically, this is one of the disastrous rivers in the world, in that it causes heavy soil erosion during the monsoon season, when it flows fast and furious, often reaching depths of over 75 feet (23 m).

The highest degree of erosion occurs between June and August. During this time, Krishna takes fertile soil from Maharashtra, Karnataka and western Andhra Pradesh towards the delta region. Here, such sediments can be seen spilling into the Bay of Bengal and framing the coastline.

Sofia and Betsiboka Rivers, Madagascar

April 30th, 2009 Category: Snapshots

Madagascar - April 8th, 2009

Madagascar - April 8th, 2009

Reddish sediments spill into the Mozambique Channel from the Sofia River (top right) and Betsiboka River (center) along Madagascar’s west coast.

The Betsiboka River discharges its sediments into the Bombetoka Bay, which then connects to the Mozambique Channel.

This discharge of reddish sediments is due to erosion caused by heavy deforestation in Madagascar. Here, the presence of Tropical Cyclone 26S (Jade) near the country’s east coast, also contributed to the high flow of sediments by provoking heavy rainfall.

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