Indus River Delta - Geography

Geography

The estimated coastline of the Indus delta with the Arabian Sea (the maximum length in the direction of the coast) is approximated at 210 km, 220 km, and 240 km. Because the Indus river has switched its location at various points in history, it has an "active" delta region, and total delta region (all area that was once a part of the delta). The total area is estimated at 29,524 km², 30,000 km² and 41,440 km². The active area is estimated at 4,762 km², and 6,000 km². The length of the total delta along the axis of Indus is estimated at 240 km (150 mi), whereas the current delta stretches from the Arabian Sea to just south of Thatta (~100 km). There are currently 17 major creeks and numerous minor creeks.

The delta receives almost all of its water from the Indus river, which has an annual flow of approximately 180 billion m3, and is accompanied by 400 million tonnes of silt. Since the 1940s, dams, barrages and irrigation works have been constructed on the river Indus. (In fact the World Bank has characterized the works as the "world's largest" and the Indus Basin Irrigation System as the "largest contiguous irrigation system developed over the past 140 years" anywhere in the world.) This has served to reduce the flow of water and by 1994, the annual flow of water into the delta was 43 billion m3, and annual amount of silt discharged was estimated to be 100 million tonnes. Since 1994, the water flow has decreased as Punjab has been allocated a higher share of the water.

The climate of the delta is described as arid. It receives only 250–500 mm (10–20 in) of rain in a normal year. Average temperatures for the delta region range from 21-30°C (70-85°F) in July, and 10-21°C (50-70°F) in January. During the summer, the delta experiences intense monsoonal winds from the southwest, causing parts of the delta to be covered by sea-water. When this water retreats, it leaves behind salts in the delta's soil. During the winter the winds in the delta come from the northeast.

The summer monsoonal winds also contribute to high wave energy levels. In fact, the delta is subjected to the highest wave action of any river delta in the world. (The amount of wave energy the Indus delta receives in a single day is greater than that received by the Mississippi River Delta in a year.) Throughout history the delta has survived this wave action because of the large discharge of fresh water to counter the erosional impact of waves. This large amount of wave energy, coupled with lack of silt flowing in from the Indus river (as mentioned above), has resulted in the formation of sand beaches.

The Indus river started to form some 50 million years ago. 25 million years ago, the Indus Plain was lifted.