Friday, August 13, 2010

DAM GOOD: Indus changing its course By Shamim-ur-Rahman

The River Indus is the lifeline of Pakistan. However, due to inadequate maintenance of its embankments and massive silting, fears have been expressed that the Indus might change its course again, which will have a grave impact on the economy of Sindh. Every time the Indus changed its course in the past, the irrigation system was destroyed resulting in political upheavals. Sukkur Barrage is vital to the country’s agro-economy, especially Sindh and Balochistan. A warning was sounded when two of the gates on its right side had to be repaired during General Musharraf’s tenure. There were even suggestions to build another barrage at a convenient place upstream to tame the Indus. If urgent steps are not taken, historians may accuse us of destroying our civilisation. Recently at a Sindh Assembly briefing Elahi Bux Soomro, the former Speaker of the National Assembly (himself an engineer), pointed out the dangers faced by Sukkur Barrage in northern Sindh.

The danger became noticeable because of non-maintenance. If immediate corrective measures are not taken, the barrage may not last for more than eight to 10 years. There is also a danger of large-scale destruction and the river changing its course permanently in the case of high floods, which are not unusual. Due to silting the barrage cannot withstand the pressure of high floods, as witnessed in the past.

Silt has been allowed to accumulate in upstream of the barrage. As a result, new islands have appeared. One large island is blocking seven gates of the barrage. The areas of the old natural islands of Sadhu Bela and the one which connects the Lansdown train bridge to the main banks at Rohri and Sukkur have increased manifold due to the accumulated silt along the river banks. The size of the channel has been reduced to one-third of its original size.

What is worst is the fact that parks, restaurants, houses, mosques and other structures have been allowed to be built on these new islands and silt banks. Large scale cultivation with embankments erected to keep out the high flows of the river can be seen all over within the river course. In the original design of the barrage two-mile long guide walls were built on both banks of the river. These walls went right up to Lansdown Railway Bridge.

No structures or encroachment was allowed within these walls in order to ensure that the width of the river was protected at all times. Regular cleaning of the silt from the river banks was carried out to ensure that the depth of the pond was maintained. Sukkur Barrage is known to have taken high-floods of one million plus cusecs easily. In 1973 and 1976 it withstood flows of 1.4 million cusecs. With the width of the channel reduced to one-third, obstacles and encroachments have appeared within the guide walls and experts feel that a flow of 500, 000 cusecs may be difficult to pass.

They also fear that in the case of high-floods the river may break its banks upstream of Sukkur and the cities of Jacobabad, Larkana, Shikarpur and hundreds of villages in the area may come under water. The river may also adopt a new permanent course after breaking its banks making Sukkur Barrage redundant. The protective walls at the mouth of the canals on both banks are a part of the design and were built in order to stop silt from the mainstream from going into the canals and heavily silting them up.

Canals draw their water from the narrow channels between the protective walls and the canal heads. The width of these channels on the two banks covers five gates of the barrage on the right side and six on the left bank. Removing silt accumulating in these channels is part of the maintenance routine of the barrage. Under this procedure depth-soundings are taken within these narrow channels on a daily basis in order to ascertain the amount of silt collecting at the bottom. Whenever the amount of silt goes above the maximum permissible level, the gates of canals are closed and those of the barrage are opened for a few hours to let the silt pass downstream with the flow.

Usually this scarring operation, as it is called, is undertaken every 30 or 40 days. For the last four years depth soundings have not been recorded and the scarring operation is being conducted only presently after a gap of almost four years. Naturally the gates of the barrage on side channels are being opened for as long as 48 hours in the present operation instead of the usual six to eight hours. The operation may not succeed as the silt accumulated over the years may have transformed into a firm riverbed. In that case, a large scale and costly dredging would be the only available option. With the bed of the river having gone up and demands in the re-modelled canals rising, a grave situation is emerging. Now water is flowing above the gates of the barrage in the canal but the gates have been designed to let the water flow under them and not over them.

New pressure on the gates is developing and if one or two gates of the barrage give way, there will be no barrage left. Irrigation officials are in a fix as to how this problem could be tackled while ensuring increased flow into the canals. However, there cannot be a compromise on removing the encroachments within the guide walls and restoring the width of the pond to its designed size. There may be a problem because of the construction of three mosques which may be difficult to remove.

An expert, however, believes that in the case of a flood of 500,000 cusec plus, not only these three, but many other mosques situated on the right bank will go under water apart from damaging the barrage. Some analysts believe that changes in the course of the River Indus and decline in the irrigation system had made the conquest of Sindh easy for Mohammad bin Qasim. Experts are also of the view that choking up of the canal’s mouth or falling into the level of the river will create precarious conditions for farmers. Sukkur Barrage is meant to maintain the desired level of water on the upstream side of river. When the water in the river is in excess, surplus must be allowed to flow downstream by raising the gates. When there is shortfall, the flow of water downstream is either reduced or cut off to maintain the desired level on the upstream. REFERENCE: DAM GOOD: Indus changing its course By Shamim-ur-Rahman Saturday, 11 Oct, 2008 | 12:56 PM PST |

Mr. Shamim-ur-Rahman is a Senior Correspondent with Daily Dawn - Pakistan.

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