Geophysical and Geological Environment of Kalabagh Dam
To fully comprehend the KBD impacts in the long run, its geophysical and geological environment alongwith the mechanics of water flow through soils needs to be understood in more detail.

In this respect, two important pointers appear in the topographic view of the proposed site of KBD i.e., the salt range and the location of the five oil fields near the proposed dam site.

To be able to visualize the role of the salt range in the KBD’s feasibility, it is necessary to magnify and elaborate the section of the ground between the Murree thrust and Salt Range thrust. 

Reference: Saeed A.Rashed, KBD, A Scientific Analysis, 1995, Print Associates, Islamabad.

The harmless geological formations of Pothwar Plateau become more complicated due to the folding of salt strata into the shape of a bowl.

It is believed that, about 210 million years ago, the movement of tectonic plates forced the salt formation to fold over into the shape of a bowl, due to which the northern edge of the bowl appeared close to the Kalachita Range, north of KBD reservoir, while the southern rim appeared in the form of the famous Salt Range, south of Kalabagh Dam site.

River Indus bifurcates the southern rim so that Kohat Range falls on its west side and the Khewra Range on its east side.

The layer of salt rock, sitting 2000 meters under the KBD site, is perhaps of no consequence as the vertical permeability of water is not likely to reach that level. However, there are salt deposits and alkali brines at low to medium depth near the rim of the bowl. And these brines tend to be at high pressure and free flowing in nature.

Under the tremendous load of the dam structure and tons of stored water (70 tonnes per square meter), the salt solutions are likely to rise in vast sheets to mix with the water of the reservoir.

This becomes more important, if the relation of Indus Basin soils’ permeability is studied with respect to the geological history of the formations. Which suggests that the lateral permeability of any formation tends to be greater than its vertical permeability, for the possible reason that the soil particles are more consolidated under the vertical pull of the gravity than the laterally acting forces, which are less systematic than the gravitational force.

A relation of vertical and lateral permeability of local soils, in the different canal commands of Pakistan, is presented in the following table, so as to emphasize the importance of this very vital factor in the ultimate operation of the KBD.

Reference: Dr. Nazir Ahmad; Ground Water Resources of Pakistan

From the above table, it is evident that the lateral permeability of soils gradually decreases, as we move downstream towards the south, and the lateral permeability of DIKhan command is five times that of South Rohri command.

This shows that, in the Indus Basin Model, the lateral permeability is greater in the Kalabagh area and within the area of the pond, and the water is feared to flow in the lateral direction, more swiftly, as compared to the vertical direction.

 The relatively high permeability values of the soils, in the vicinity of KBD, are important with respect to the possible long term impacts of the reservoir in terms of increased salinity and enhanced water seepage, to further exacerbate the already experienced system management problems. These are discussed in the next section; long-term impacts of KBD, in more detail.

However, for the moment, the geophysical and geological environment of the KBD site cannot be anything but worse for the erection of a storage reservoir of such a huge mass of water, meant for irrigating the downstream lands.

Reference:

KBD; A Scientific Analysis, by Saeed A. Rashed

Groundwater Resources by Dr.Nazir Ahmad