Tuesday, April 2, 2013

Huh? Thousands Of Rivers Wiped Off Map Of China

The first national water census pointed out that thousands of rivers (28 thousand was the figure given) shown on previous maps are now missing from China' s state water maps. See this article.


Official- Climate change is to blame for the drying of some waterways. Plus some earlier mistakes by cartographers

Environmentalists: Ill conceived development and over use of underground water resources.

That last one is an important point. Much of the base flow of rivers, especially those which are not sourced from glaciers comes from groundwater discharging as springs. That means the water you see flowing in the river channel months after the rains are over is actually groundwater seeping out along river banks. Even rivers connected to glaciers may have a significant component of their flow provided for by groundwater discharge. A survey in the Nepal Himalayas revealed that groundwater contributes more than melting glaciers to the annual discharge of the rivers. 

Rivers may gain water from groundwater over long stretches. Such streams are called effluent (fig on left: source: USGS) . Rivers that lose water to groundwater are called influent.  Here is an excellent USGS  primer on the impacts of groundwater exploitation on surface water.

All the important monsoonal rivers in Peninsular India as well,  Narmada, Mahanadi, Cauvery, Krishna and Godavari depend on groundwater discharge to remain perennial. If the local water table plummets well  below the river bed due to over extraction of groundwater then discharge into the river will cease.

River management must include management of groundwater resources as well. The USGS article I linked to points out: " From a sustainability perspective, the key point is that pumping decisions today will affect surface-water availability; however, these effects may not be fully realized for many years".

A lesson not taken seriously in China and in India as well.

No comments:

Post a Comment