Flood threat at ancient city

Published: May 19, 2017
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The writer is a professor at Mehran University of Engineering and Technology, Jamshoro

The writer is a professor at Mehran University of Engineering and Technology, Jamshoro

Already battered by soil salinity, waterlogging, humidity, temperature and rainfall, Mohenjo Daro is facing a new threat of flooding due to the migration of the Indus River towards the right bank and the possible break of the levee near Hakra village. The shift in the course of the river began in 2016 towards Hakra Pattan, which is about four kilometres upstream of Mohenjo Daro.

After eroding the floodplain consisting of slums and a cemetery, the course of the Indus River is now hitting the Larkana-Sehwan flood protection levee and the water flows about half a kilometre along it. This rapid rightward migration of the river poses a threat not only to Mohenjo Daro but also a flood risk to the Cadet College and Benazir Bhutto Medical University in Larkana as well as Mohenjo Daro airport and several villages in the vicinity.

In 1980, Unesco declared Mohenjo Daro a world heritage site by launching a campaign to preserve and protect it from floods. Up to five T-shaped spurs measuring between 220 and 980 metres in length and an average height of six metres were constructed along the right bank of the river to divert the flow towards the left bank.

Out of fear of a possible break of the levee, many villagers staged a protest. They appealed to the Sindh government to assess the gravity of the flood risk. Recently, a petition was filed by locals in the Sindh High Court’s Larkana registry asking the irrigation department for stone pitching and strengthening of the levee near Hakra Pattan. A two-member bench has been set up to hear the case. In fact, according to reports, Unesco sent a hydrologist in 2016 to visit the site and assess the degree of intensity of the situation. But no actual report could be prepared because the required data about river discharge, sinuosity, river migration and other related parameters was unavailable.

However, a study has been conducted at the US-Pakistan Centre for Advanced Studies in Water at the Mehran University of Engineering and Technology, Jamshoro, with remote sensing and GIS tools using satellite data. The initial results of the study revealed that the river remained highly meandering within the considered reach. The sinuosity of the river increased the flow from 1.4 in 1972 to 1.61 in 1990, to 1.42 and 1.47 in 2010 and 2016, respectively. The river migration rate was calculated as 45.12 m/year with net migration of 17.5 m/year rightwards. The Digital Elevation Model (DEM) of the Mohenjo Daro and the neighbouring areas was analysed for flood flow direction in the case of any breach of the Larkana-Sehwan levee.

The analysis of the DEM showed that Mohenjo Daro lies at a low-lying area and if the levee at Hakra is broken the resultant flood flow after submerging the cadet college, the airport and villages, will directly hit the ancient city and Balhreji village. Analysis of the satellite data from 1972 to-date revealed that the river flow has never been so close to the right bank of the river.

Though the protection at Hakra provides a second line of defence, the fears expressed by locals and the analysis of the satellite data shouldn’t be ignored. The possibility of a flood poses serious risks to the 5,000-year-old heritage of the Indus Valley civilisation.

Based on the analysis of the satellite data and nature of the river flow, it would be wise to not only strengthen the Larkana-Sehwan levee through stone pitching but also construct a sixth T-shaped spur measuring 300 metres in length nearly one kilometre upstream of the already constructed spur at Nai Gudd village. The proposed spur will help in diverting the river flow leftwards and thus minimise the risk of a flood.

Published in The Express Tribune, May 19th, 2017.

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