Investigation and modeling of two sequential dam failures under different scenarios (Case study Golpayegan and Kucherei dams)

Dams have many essential benefits to serve the ever increasing demand of human population in making world a better place for living. Dams are purposely built for irrigation, power generation, flood mitigation, water supply and even for recreation and fishing activity. However, substantially huge amount of water body stored behind the standing dam structure could seriously pose severe risks to many. Great level of energy stored in the impounded reservoir will cause unbearable impacts should it be released suddenly to the downstream area. It is therefore important to conduct a dam break study to determine the outflow resulted from such unwanted dam break event. The art of dam break modeling lies primarily in the prediction of the outflow hydrograph as a result of dam failure. This can be done via physical model and laboratory experiment and numerical modeling technique. Physical model is not always financially viable hence the numerical modeling is often taken as a better alternative. Numerical modeling techniques estimate the outflow hydrograph via four methods; 1) physically based methods 2) parametric models 3) predictor equations 4) comparative analysis With the rapid development of computer hardware and computing techniques, numerical study on dam break flows has been a popular research subject. This study had therefore used the MIKE modeling package to simulate the dam break event and to determine the outflow hydrograph to be routed to the downstream area and eventually to obtain the flood maps. Furthermore, animation tool available in MIKE software offers better appreciation of the dam break event, added with enhanced graphics of inundation maps to visualize the movement of flood wave in variation of time and space.

In the present study, simulation of dam failure in Golpayegan and Kucherei earth dams in Isfahan province was investigated using MikeFlood software. The MikeFlood is software that integrates relationship between the one-dimensional model Mike11 and two-dimensional model Mike21. The way it operates is when the Mike11 is activated at times before the flow section fills in the main river and conducts flood routing in the main waterway. As the discharge increases and the cross-section fills in the main river and the stream enters the floodplain, the Mike21 model is activated and begins to simulate two-dimensional flow in the floodplain. Due to different boundary conditions, different scenarios occur which need to be introduced into the model. In this research, three possible scenarios are: 1) failure of both Golpayegan dam and Kucherei dam due to overpass; 2) Golpayegan dam due to piping and Kucherei dam overpass, 3) non-failure Golpayegan dam, and failure of Kucherei dam by piping has been tested and compared.

In the first scenario, after 53 minutes of Kucherei dam failure, the maximum flow rate is reach 118727 m3/s. In the second scenario, the maximum flow rate is achieved 110717 m3/s after 51 minutes of the Kocherei dam breakdown, and in the third scenario, the maximum discharge occurs about 50208 m3/s, 43 minutes after the Kocherei dam breaks. Flood alert time and zoning division have also been compared in different scenarios. When the first scenario is in place, the floodplain has more area and the rate of advance is faster. In third scenario, the flow rate is lower than in the first and second scenarios. Also, Alvand town will not be flooded due to its location in a higher area than Golpayegan city, and Saeed Abad industrial town will not be flooded. The alert time, the peak arrival time, and the flood recession time in the sections are directly related to the increase in the distance from the sections to the dam and increases. The results showed that due to dam failure in all three different scenarios, Alvand town and Saeed Abad industrial town which are among the important areas below the dam will not be flooded.