Assessment of possible hazards in case of Pashdan Dam break - Afghanistan

Dams are important engineering structures constructed for various purposes, such as flood control, water supply, irrigation, and hydroelectric power generation. However, despite the many benefits they provide, they can break due to structural faults, excessive rainfall, or earthquakes. In this case, the sudden and uncontrolled discharge of the large volume of water stored in their reservoirs poses a serious risk to residential areas in the downstream region and flood waves can lead to major disasters. Therefore, it is known that in the event of a possible collapse, there could be significant loss of life and property. In order to minimize the effects of such possible disasters, floods that may occur as a result of dam break must be modeled and analyzed in advance. In this way, potential damages can be determined in advance and risks can be minimized by taking the necessary precautions. In this thesis study, two-dimensional break analyses of the Pashdan Dam, which is currently under construction in Karokh district, 25 km northeast of Herat province of Afghanistan, were carried out. Pashdan Dam is a strategic project that stores the water of the Karokh River and offers multi-purpose uses such as irrigation, hydroelectric power generation, and drinking water supply. With the implementation of the dam, the irrigation of 13,000 hectares of agricultural land is aimed, which will directly contribute to increasing agricultural productivity in the region. At the same time, the dam stands out as an important infrastructure investment that can meet the water and energy needs of the Herat region with its capacity to produce energy and provide drinking water. In this respect, the Pashdan Dam is of great importance for the region in terms of both economic and social development. The aim of the study is to determine whether the flood that will occur in the event of the break of the Pashdan Dam will reach the settlement located downstream and the time it will take to reach it. Digital elevation maps of Pashdan Dam and its downstream region were edited with ArcGIS software and the break analysis was performed with the HEC-RAS program developed by USACE (United States Army Corps of Engineers). As a result of the analyses, it was determined that some residential areas in the downstream region were affected by the flood, and data such as time-dependent flood propagation maps, floodwater level maps, and flood velocity maps were obtained. The analysis was carried out using five different methods (MacDonald et al, Froehlich (1995), Froehlich (2008), Von Thun & Gillete, Xu & Zhang). As a result of the analysis performed, it is seen that the most dangerous scenario is obtained with the Von Thun & Gillete method. According to this method, it was determined that the peak discharge was reached at the 17th hour, and the peak discharge of the break flood at this hour was 16,725.07 m³/s. However, the first 10 hours of this period are the time required for the dam to reach full capacity, and the peak flood discharge reached its highest level within the next 7 hours. According to the Von Thun & Gillette method, it was determined that the maximum floodwater level was 12.23 m, the maximum flood velocity was 8.88 m/s, and the flood area was 353.43 km². According to the Von Thun & Gillete method, at the end of the 1-hour period, it is seen that parts of the villages Chak Mak and Pal Peeri were inundated by floodwaters. At the end of the 2-hour period, it is seen that the villages of Pashdan, Chak Mak, and Pal Peeri were completely inundated by floodwaters. At the end of the 3-hour period, it is seen that parts of the villages Rebat Surkh and Ali Afghan were inundated by floodwaters. Similarly, it is seen that the villages of Jahanda Khan, Nowbadam, Nisan, Imam Shesh Noor, and Sarasiyab Mokhtar were completely inundated by floodwaters. At the end of the 4-hour period, it is seen that the village of Chungar was completely inundated by floodwaters. At the end of the 5-hour period, it is seen that the villages of Kebabyan and Ghaizan Sangar were completely inundated by floodwaters.