Effects of the Karkheh Dam construction on haze generation due to geomorphological changes in the Khuzestan Province, Southwest Iran

The construction of the Karkheh Dam is an important factor contributing to the occurrence of dust storms in the Khuzestan Province of Iran. It has reduced the annual mean flow discharge in the Karkheh River from 120 to 50 m3/s and dried land around the river. The area of dried land is 90.17 km2 around the river and 333.45 km2 in the Hawr-al-Azim wetland. The Rosgen method, Fluvial-12 software, and Shulits equation demonstrate the instability of the plan, cross sections and longitudinal slope of the river, respectively, around Pay-e-pol hydrometric station (upstream of the river). After dam construction, extreme erosion occurred in this part of the river. The type of sediment is clay and silt with D50 = 8 μm. The eroded sediment settles downstream (around Hamidiyeh hydrometric station) and the Hawr-al-Azim wetland. The wind can easily lift these particles especially from May to July. Because of the size of these particles, the haze concentration increased from 25% to 45% in dust storms. After construction of the dam, the dust storm days increased to 90 days in 2008. By increasing the stability of the river, the dust storms reduced from 2011. The annual volume of generated haze by geomorphological characteristic changes is almost 3107 m3.