Increase in Surface Water Salinity 

Water of the Indus River system carry a variety of salts that are left on the surface of irrigated land, while the irrigation water filters down or evaporates. To comprehend this, we need to understand the relation of irrigation water suitability to that of its salt contents.

 Soil scientists believe that, when the contents of salt deposits increase to about 2.5%, the productivity of the land is visibly impaired and when it reaches a level of 7.0 %, no biological life is then possible in the soils. 

The following table describes the categorization of the quality of water with the varying degree of salt content in the soils. 

Reference: Dr. Iqbal Ali; Irrigation Engineering, 1975

Some authors propose slightly lower permissible limits for chlorides than for sulphates, due to their more injurious characteristics.

 To study the potential of Indus water to induce salinity, the following table from Dr. Nazir Ahmad’s research describes the salinity ratings at various points in Indus River:

Reference: Dr.Nazir Ahmad, Groundwater Resources of Pakistan

From the above table, it can be observed that the quantum of salinity between Attock and Kalabagh (52 gms/tonne) is 100% more than between any other of the two (2) points observed in the analysis.

 To visualize the effect of the use of saline water in irrigation systems, Saeed A. Rashid, in his excellent Treatise "KBD; A Scientific Analysis" has stated the problem in the following words

"If 10 inches of water carrying 200 PPM of dissolved salts leave behind 4.72 gms of solids per cubic foot and if 10 inches of such water is given to a piece of land and is allowed to soak and evaporate in the same pattern as is practiced in our canal irrigated agriculture, then 4.72 gms of salt will be deposited in each cubic foot of soil.

Given the salinity of water of River Indus at DIKhan of 226 PPM for every 3 soaking per year, or 30 inches of water, about 16 gms of salt will be added to each cubic foot. And in 30 years time, about 2.54% salts will be added to the top 8 inches of soil making the damage to crop field perceptible".

Saeed A. Rashid advances the interesting theory that, "perhaps that is the reason why the crop yield has started declining in the command areas of the canal system below DI Khan, 30 years after the commissioning of the barrage system when maximum coverage is achieved".

 To study the effect of saline water’s use in the backdrop of KBD, it is revealed that, the billions of tons of the stored water in KBD is likely to exert tremendous pressure on alkali brine strata, which will then rise in vast sheets to mix with water of the reservoir and further increasing its saline content to unacceptable limits.

This water when used for irrigation purposes will play havoc with any soil that comes in contact with it through irrigation, or otherwise.

 These observations indicate a very grave threat of destructive salinity to all agricultural lands below KBD site, if a dam were to be built at the proposed site, and its waters used for irrigation purposes. This needs to be further viewed into the purview of the already saline 24 million acres of irrigated land, out of our total of 34.5 million acres of irrigated land of Pakistan.