THE WORLD DELTA DATABASE

THE AMU-DARYA DELTA

DELTA ID     #01

Contributed by Huh et al, 2004.

CLIMATE DESERT (BWk)

DISCHARGE WATER, 1500 M3/S, SEDIMENT 100X106 TONS/YR, KM2

DRAINAGE BASIN AREA 64,000

Contributed  by Professor James Coleman, LSU. From: Coleman and Huh, 2004.

The Amu Darya River, known in ancient times as the Oxus, is the largest river in central Asia and is formed by the junction of the Pandj and Vakhsh rivers. It extends some 2,550 km from its headwaters in the high mountains of Afghanistan and Tadzhikistan to the end of the delta (Samajlov, 1956) where it enters the Aral Sea. The drainage basin is some 466,200 sq km in area and is dominated by a relatively dry climate. The average annual rainfall is 464 mm with a maximum of 2,009 mm (and a minimum of 69 mm. Rainy months occur from November through May. Vegetation in the central basin is mostly xeric shrublands and desert vegetation. The headwaters of the river originate in the Paleozoic Tian Shan Foldbelt and approximately 70% of the basin drains Tertiary sedimentary sediments. Over the centuries the river has shifted its course several times. In the 3^rd and 4^th millennia BC, the river flowed westward into Lake Sarykamysh, and from there to the Caspian Sea. Since the 17^th century, the river has emptied into the Aral Sea. The receiving basin, the Aral Sea, is some 64,000 sq km in area and experiences less than 1,100 mm of annual precipitation. Evaporation is dominant, with approximately 1 m of water stripped from the surface annually. This water is replaced by inflow from the two major rivers that drain into the Aral, the Amu Darya and Syr Darya.

In its alluvial valley, the river flows through the extremely arid Turan lowlands, where evaporation removes a high percentage of the total flow, resulting in extremely high sediment concentrations. The delta, illustrated in the Landsat image (01-i02), is bordered by the Kara Kum desert on the west and the Kyzyl Kum desert on the east. The Kara Kum consists of a denuded desert plain with abundant salt flats, soft sediment bluffs, and karst topography. The initial flow of the river was into a low depression of this desert referred to as the Sarykamysh Depression. Some of the former river courses that fed into this depression can still be discerned on aerial photographs. To the east lie the eolian sand fields of the Kyzyl Kum desert. Quaternary linear dune fields, some of them presently active, are shown in the image. Note that many of these linear dune fields have been inundated by the Aral Sea, giving a striking example of the linearity of the dune fields.

The lower reaches of the river once contained a large delta that supported extensive vegetation, but most of the delta has dried up due to reduced water flow. The eastern part of the delta was active until the 10th century, when the major courses shifted to the west. The modern course began to form in the late 17th and early 18th centuries. The modern channel displays active meandering within the upper delta plain; in the lower delta plain, the channel bifurcates, and many distributaries feed water and sediment to the Aral Sea. The presently active part of the delta is characterized by relatively small bifurcated channels that deliver a high volume of sediment to the Aral Sea annually. The turbid river plumes are dramatically shown in the image. The river has an average discharge of 1,397 m³/sec, with a peak flow of 3,145 m³/sec during flood (May through September) and a minimum flow of 464 m³/sec during low river stages (October – April). The image was obtained near the end of May, a period of spring flooding just before the major floods that occur in June and July as a result of glacial melt. Sediment load is extremely high in the active channel; in excess of 100 million metric tons of suspended sediment and 5 million metric tons of bedload is delivered to the delta annually. The various abandoned channel courses are well defined and consist of abandoned meander scars. In many instances, land reclamation in this arid delta follows these courses, and irrigation schemes are abundant along their courses.

The relatively inactive abandoned delta plain dominates much of the scene in the image. The various abandoned channel courses are well defined and consist of abandoned meander scars. In many instances, land reclamation in this arid delta follows these courses, and irrigation schemes are abundant along their courses. Modifications by man are not as prominent in the image shown as 01-i03 as they are on low-level photographs. However, the general trend of the former courses can be easily discerned and mapped from the satellite imagery. The eastern part of the delta was active until the 10th century, when the major courses shifted to the west. The modern course began to form in the late 17th and early 18th centuries.

A large percentage of the delta plain is composed of evaporation flats and salt playas. Some of the lower lying depressions, formed during the prior delta progradation, have not been totally infilled and now exist as high- salinity algal flats and saline lakes. Other partially filled depressions are barren of higher vegetation and consist of algal flats and salt marshes. Along the coast, waves and currents have reworked parts of the older delta plains into a series of beach-barrier complexes, often covered with small coastal dunes and backed by salt and algal flats. Along the fringes of the older abandoned delta are coastal sand and mud flats.

The influence of humankind.

Since the 1950’s the Amu Darya has been heavily tapped for irrigation, which has greatly reduced its water level and the amount of water reaching the Aral Sea. During the 1980’s, several years passed in which little or no water reached the Aral Sea from the river. Inflows from the Syr Darya, which empties into the Small Aral sea from the east, have also drastically diminished in recent decades. As a result, the volume of the Aral Sea has dropped by about 80 percent between 1960 and 1996. In the 1960’s, the Aral Sea was fourth among the world’s largest lakes with an area of 66,458 sq km (25,660 sq mi). The lake is generally shallow, with an average depth of 16 m (53 ft) and a maximum depth of 69 m (226 ft). Its salinity averaged about 10 ppt or slightly less than a third of normal sea water. By the end of 1996, the Aral’s total area had decreased by 57 percent to 31,220 sq km (12,050 sq mi) and its water volume had decreased by 80 percent (P. P. Micklin, "Aral Sea", Microsoft Encarta Encyclopedia, 2001). As a result of water loss by evaporation and lack of fresh water input by the Amu Darya, the salinity rose to 35 ppt or normal sea water. With continued evaporation, the salinity will continue to increase.