Monday, October 4, 2010

Ecology of a man-made disaster I: Dams and Barrages

First, an aside: I would like to apologize to all my readers for my unplanned hiatus from blogging. To put it succinctly, I was busy with thesis related work as well as figuring out what direction I want to take this blog in. As most of you know, I comment mostly on political and religious events in Pakistan, South Asia, Middle East and the world. But given my background in science, I have decided to incorporate on occasion the overlap between science and society from a Pakistani/Canadian/Middle Eastern/South Asian/global perspective. The post below belongs to a series of articles in which I will be exploring these interactions. Let me know how you feel. Do you like it? Hate it? Don't care? Any questions, comments or thoughts on this development is welcome. 


By now, all of us (Pakistanis, expats, regional/political junkies and news buffs) know the stats all too well. Approximately 2,000-3,000 deaths have been reported (official death tolls haven't begun to update information). Twenty two million people are affected directly. One fifth of the country is under water. The arterial network of roads and bridges connecting the country together have collapsed. Then, there is the political side. The incompetency of the elected elites has been revealed (again). Their disinterest in the welfare of the Pakistani people has been duly noted . The political ambition of the armed forces had become evident (no surprise). On a social scale, the deep rooted xenophobia against Ahmadis with the withholding of government aid has risen its ugly head, only months after the mass murder of more than 80 Ahmadi muslims in their mosques in Lahore. And let's not forget about the marginalization of Christian, Hindus and other religious minorities affected by the flood. I'm going to stop here. Bloggers more informed and educated  than myself have explored these issues previously in their posts. There is nothing enlightening that I can add to these debates. However, what is missing from the discourse around these floods is an understanding of the basic ecology of this disaster.

Before I proceed, I would like to clarify my stance on these floods. These floods are a man-made disaster. They are the direct consequence of the incompetence of our ruling elite (civilian or military) to recognize flood vulnerability, develop necessary infrastructure and agencies capable of dealing with disasters and reveal the lack of basic geophysical understanding of the region which they rule.

 Let's start with some basic facts about the Indus. The hydrology (rate of water flow) is influenced by three factors: seasonal snow melt, glacial and permanent snow melt from the Himalayan, Hindu Kush and Karakorum mountain ranges and monsoon rains from July to September. These three flow components vary seasonally in fairly consistent patterns which are termed 'hydrological regimes'. As we all know, greater than normal monsoon rains caused an increase in seasonal flow leading to flooding. But why did these monsoons deviate from the norm in the first place? Consider the diagram below:


(Image taken from New Scientist , Aug 2010)
According to Dr. Mike Blackburn from University of Reading UK,  there has been a shift in the normal pattern of the jet stream; a fast flowing narrow air current which separates areas of high and low pressure, moving  north and south as it rushes around the globe from west to east. Its wave-like shape is caused by Rossby waves – powerful spinning wind currents that push the jet stream north and south. Under normal conditions, the jet stream moves eastwards during the summer months carrying with it moisture and rain. However, meteorologists noticed a change in this regular pattern. Instead of moving eastwards, the jet stream is currently fixed in place, dumping all of the rain in the northern Pakistan resulting in greater than normal flows.

The floods may start here, but their impacts have been exacerbated by human mismanagement. Firstly, there is excessive sedimentation. According to the Climate Himalaya Initiative, the Indus is one of the most sediment producing rivers on the planet.  The Indus transports 250 megatons (Mt) of sediments, the equivalent of 15 million dump trucks to the Arabian sea annually. This amount has fallen to100 Mt, with construction of dams and barrages which trap the majority of the sediment. The massive sediment deposition at Tarbela Dam specifically, is the most problematic. Completed in 1976, Tarbela Dam was assumed to have a lifespan until 2030. However, given that over 6 billion tons of sediment (sand, silt and mud) have already accumulated in the first twenty-five years, forming an underwater delta slowly growing towards the dam and greatly affecting its structural stability and electricity production, it is very possible that Tarbela Dam may become ineffective over a shorter than predicted period of time.

 Close up of Tarbela Dam (Image Credit: Through the Sand Glass)

Following in this vein, I would also like to point out the engineering failure at Taunsa Barrage, which was highlighted in this article (August 20th 2010) by Mushtaaq Gaadi:
The main problem with Taunsa barrage is the rising riverbed owing to huge sediment deposition in the upstream areas(...)Taunsa barrage traps huge sediments left over from the upstream storage and diversion structures. Moreover, the pond area is additionally fed annually with large amounts of silt eroded from the highly degraded catchment areas of the Suleiman Range. These heavy silt loads are transported through western tributaries (hill-torrents) of the Indus River.
Sediment deposition due to dams and barrages becomes a problem in the light of the river's base level. Base level refers to the lowest point at which it can flow. In the context of the Indus, the base level is equal to the sea level which has been shown to profoundly impact its structure and behaviour. When a dam/barrage is erected, it behaves like a base level on a local scale causing the upstream part of the river to respond. Because the base level of the river upstream from the dam has been raised, the flows react with sediment deposition. This should not be a problem, if a constant reservoir level is maintained (a new stable state is achieved). However, if this level remains unstable, the flow will alternate between deposition and erosion. For both Tarbela Dam and Taunsa Barrage, the reservoir levels have been raised, inducing more deposition. This has lead to major modifications in the riverbed upstream, resulting in large changes in local flow. Consider this: the floods upstream of Tarbela were more deadly and destructive as compared with downstream.

(Image Credit: Critical Threats)

With every dam and barrage, the system of the Indus is modified. Every time the base level changes, the Indus changes. The system of barrages and dams across the region have resulted in a unnatural riverine system, with no checks and balances. If these structures are built, proper maintenance is crucial.  However, at this time Pakistan does not possess the technology or the expertise to maintain reservoir levels and control this massive sedimentation problem. As one Pakistani civil engineer told me, "it's not as if we are not aware of the problems surrounding sedimentation, it's just that we can't deal with it." 

All of this is not to say that the flood would not have occurred if proper measures were taken. But it would be dishonest to not point out the ways in which human modifications across the Indus river considerably heightened these impacts.

Coming Soon: Ecology of a man-made disaster II: The implementation gap

Appendix: For those of you who would like to know more about the river management system currently in place in the Indus, click here to view a map of all of Pakistan's dams and barrages (source: UN World Food Programme)