Tuesday, 16 October 2007

River ramblings......

One of the most striking features of the geography of the north of India is the influence which the rivers have on both the physical and human environments of the region. The Ganges and its huge tributaries dominate not only the map but also the distribution of population and the ability of that population to support itself.

Today, Mark has headed east of Lucknow and for much of the day he will have cycled parallel to the south bank of the River Ghaghara, which is one of the largest tributaries of the Ganges. The river and its immediate floodplain provide some interesting examples of river processes at work...There is much evidence of silt being carried and deposited by the river. One of the reasons for the Ganges and its northern tributaries carrying so much silt is the deforestation of steep slopes surrounding the Himalayan headwaters. As trees are removed, so the soil has nothing to bind it and it is easily washed away by monsoon rains. This creates huge problems downstream as the silt builds up in the river channels, impeding navigation and also making them more likely to flood. The advantage to these areas is that every flood spreads more fertile silt on the land hence these areas close to the river may be cultivated but not inhabited! There is a very good example of this if you zoom in on the view above..
The fertile floodplain is seasonally cultivated but the settlement clearly keeps 'back from the edge'! Just to the north of the river is an area of 'textbook' river features.. These crescent shaped lakes are ox bows - the cut off remnants of former meanders.
Sometimes, when a river is in flood it discovers that it is quicker to flow across the neck of a meander. This increases the speed of the flow, quickly eroding a new and more efficient channel. The old meander is cut off as the river deposits material on the sides of its new channel. Gradually, the abandoned meander silts up and slowly disappears from view.....

Click on the image to the left and you will link to a short animation which explains how ox bows form.

No comments: