Drainage Diversion

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

The Huang He

north China The Huang He has been called "China's Sorrow" because of its frequent and catastrophic floods. The diagram above shows its drainage diversions during recorded history. In U.S. terms, the diversions above, spanning almost 400 miles, would be roughly equivalent to the Mississippi changing its outlet from Houston, Texas to Pensacola, Florida.

The river has filled in a former strait between the mainland and the Shandong Peninsula, which was once an island. The river exits the highlands laden with silt derived from China's loess deposits and has constructed a vast flood plain which is actually a gigantic alluvial fan. The surface of the fan is a gentle cone with a nearly uniform slope, which is maintained by frequent changes in the course of the river as old channels are abandoned.

The map is based on p. 114 in Chao, Sung-ch’iao (Zhao Songqiao), 1986, Physical geography of China: Beijing, China: Science Press; New York, N.Y.: Wiley, 209 p.

With almost no topographic relief in the region, there is no place to seek refuge when the river floods. The diversions of the Huang He have produced some of history's greatest disasters:

River Diversions in the Caspian Region

Caspian Region

The Volga and the Don

The Volga and the Don almost meet (red circle). Between the two rivers is Volgograd, formerly Stalingrad, site of one of the fiercest and most pivotal battles of World War II. Both rivers have a sharply barbed drainage, but which captured which? The Don flows to the Black Sea and can only erode to sea level, but the Volga flows to the Caspian, which is 92 feet below sea level. The dark shading shows the region below sea level. (Trivia question: name a major river whose delta is below sea level) Clearly streams flowing to the Caspian have a competitive advantage in capturing drainage, and it seems likely that a former small river cut back into the former Don river, diverting most of its drainage and creating the present Volga.

The Ural River

The Ural River also has a sharp bend and possibly might also have diverted a former tributary of the Volga. The possible former connection is shown with question marks.

The Aral Sea

In what has been called one of history's greatest environmental catastrophes, water from the Amu Darya, main water source for the Aral Sea, has been diverted for irrigation. The area of the lake is half of what it was in 1960 and the lake is now too salty to support fish.(The former outlines are shown)

The plain of the Amu Darya, like that of the Huang He, is a giant alluvial fan. Excess runoff from irrigation runs not to the Aral Sea but to Lake Sarikamysh. Not far away is the head of an intermittent stream, the Uzboy, that flows to the Caspian. It seems certain that the lower Amu Darya, like the Huang He, has seen frequent diversions and that at least some of the time it has flowed via Lake Sairkamysh and the Uzboy to the Caspian.

Very little is known of the history of the Aral Sea. A number of test borings in the lake were described by William Last and others at the 1998 meeting of the Geological Society of America in Toronto. These showed heavy concentrations of evaporites at several levels in the bottom sediments, including magnesium and potassium salts, evidence of extreme dessication. Thus, the lake has experienced several purely natural episodes of river diversion and drying during the last few thousand years.

Why is the Danube Blue?

You'd be blue, too, if you'd been robbed. One reason a cruise on the Rhine is so scenic is that Western Europe underwent gentle uplift in the last few million years. The Rhine rejuvenated and carved a deep gorge, complete with entrenched meanders. The nearby headwaters of the Danube were also uplifted, but the Danube flows across half the length of Europe to the Black Sea. Clearly, tributaries of the Rhine have a competitive advantage over the Danube in carving valleys.

Danube diversion One small tributary of the Rhine, the Wutach, flows along a belt of soft Triassic rocks. It rapidly eroded its valley headward and captured a former tributary of the upper Danube. In the map, Switzerland is shown in purple. This is one of the world's more peculiar international borders; there really are two little isolated pockets of Germany completely surrounded by Switzerland.

The Danube drainage basin is shown above in green, the drainage captured by the Wutach in yellow. The Wutach itself was pirated by yet another small tributary of the Rhine, and that captured drainage is shown in light blue. Drainage divides are red.

Danube diversion

A detailed map of the diversion by the Wutach. The upper Wutach originally flowed via the Schtellebachte and Altrach to the Danube. Note the peculiar drainage at the mouth of the Muhlegraben ("mill valley" in German). The Muhlegraben has been mostly diverted but still sends some water down its old channel to the Altrach. This sort of divided drainage is purely temporary and will not last much longer. (The "bach" ending on a number of stream names is simply a German word for stream or creek,)

Danube diversion An oblique view of the same area looking northeast.

Danube diversion The Wutach itself was pirated. Here a small tributary of the Rhine, the Rotenbach (on the west), has diverted the upper headwaters of the Wutach. It's difficult to say which diversion happened first.
Danube diversion An oblique view looking east.

Return to Course Notes Index
Return to Professor Dutch's Home Page

Created 21 November 1998, Last Update 15 September 1999