Hydraulic Construction Hypothesis

Some observers have argued that the recent fall and rise in sea level were the result of human activities. They suggest that the widespread development of hydraulic structures (e.g., dams, reservoirs, irrigation systems) in the Volga River basin, beginning in the 1950s, led to a sharp decline in Volga flow. The filling of many reservoirs built along the rivers flowing into the Caspian, the increase in industrial and muni cipal water use by several times, and changes in the water regime of the floodplains led to a decrease of streamflow into the sea. Such a hypothesis could be tested by constructing a water budget model for the Caspian. Such a model would need to identify all the inflows into the Caspian Sea (such as from rivers and groundwater) and all outflow from the sea (such as evaporation and water diversions). While it is a seemingly straightforward task, identifying all the sources and sinks of Caspian water is not easy.

There is also a hypothesis about an Aral Sea connection. Yet another suggestion that seems to be made at just about every Aral or Caspian Sea conference is that the decline in the level of the Aral Sea is linked to the rise in level of the Caspian. The reasoning is that water diverted from the Aral basin to the Caspian basin to irrigate the desert sands for cotton production in Turkmenistan ends up either being evaporated into the air or seeping into the groundwater, which eventually makes its way into the Caspian. However, it is important to point out that both the recent fall and rise in the Caspian Sea level occurred during three and a half decades of a constant decline in the Aral's level.

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