Morphological evolution of Indus shelf region under the influence of hydrodynamic conditions in 20th century

Abstract

Indus shelf region, located offshore of the Indus delta, is characterized by several unique and diversified features with dynamic potential of expansion and regression.The growth of this subaqueous part of Indus Delta is the result of the enormous amount of sediments discharge from the Indus River since the Oligocene period. Intervention in the natural flow of the Indus River System (IRS) in the 20th century, due to water diversion and water storage activities on the IRS has created many changes on the continental shelf and shelf-slope in the offshore Indus Delta. The available data of sediment discharge from the Kotri barrage and other previous studies provide information that sediment discharge in natural waterflow conditions before the half of the 20th century was more than 250 million (106) tones per year, but after the construction of canals, barrages and dams in upstream area of the IRS, a gradual declining trend was occurred in the flow of water and sediment discharge.Morphological changes those occurred over the shelf of delta in the 20th century have been evaluated using geoinformatic approach. Two bathymetry maps of the 19th and 20th centuries were used in view to determine the temporal difference on the continental shelf. Ten cross-sections were drawn on both the bathymetry maps in northeast-southwest direction. Profiles from the cross-section of both periods have been developed to analyze the temporal variation on the continental shelf of the offshore Indus Delta. Sediment accumulation was found from 1895 to 1995 on the western edge of the shelf and erosional activities on some places were also noted from the eastern profiles of the continental shelf. Low depth near the coast observed from the map of later period indicates the process of accretion activities near the shore. General trend shows morphologically changes in the shelf region.