The potential impact of Mekong hydropower on the flood peak at Kratie

The Mekong basin, located in South East Asia is experiencing extensive hydropower dam constructions in both tributaries and mainstream. Mainstream damming was initiated in the upper Mekong basin, which is currently regulated by five large scale dams. Concerns have been raised about the consequences of the dams on the Mekong sediment budget, ecosystem, livelihoods and food security, with the proposals of eleven hydropower cascade in the lower Mekong mainstream. This research assessed the potential impact of the existing and future mainstream dams on the flood peak at Kratie using a combination of MIKE HYDRO Basin and MIKE 11 numerical models, coupled with the basin inflows extracted from pre-established SWAT hydrological model (by MRC). The potential impacts were evaluated concerning two main components, the best usage of mainstream reservoir flood control storages and hypothetical dam breaks (during 2000 flood event). The study found that the proposed Lower Mekong mainstream reservoirs have no capacity for the flood control (run-off river reservoirs). Consequently the study concluded the impact of Lower Mekong mainstream reservoirs as insignificant on the flood peak at Kratie. The upper Mekong reservoirs (the largest storage capacities of the Mekong basin) impact indicated max 6% potential flood peak reduction at Kratie during the high floods in 2000 and 2002. However this was changed from flood event to event depending on the main contribution of the flood peak comes from. The impact of upper Mekong mainstream flood control was highest at the upper and lower basins boarder (29% average flood peak reduction). Chiang Saen and Vientiane average flood peak reduction was 25% and 11% respectively. Further, the study identified 3S, Nam Mun, Se Bang Hieng, Se Bang Fai, Nam Ngum, Nam Ka Dinh and Nam Ou as Mekong's major tributaries which are shaping the Kratie flood peak. Since mainstream reservoirs showed a small potential impact on the Kratie flood peak, this research encouraged future studies to find out, the flood control capacities of tributary (above mentioned) reservoirs. Because that would be the only solution to maximise the flood peak reduction at Kratie while merging with upper Mekong flood control. The study disclosed, the maximum possible flood peak rise percentage at Kratie from single proposed lower Mekong dam breaks (Pakbeng, Luangprabang, Xayaburi, Paklay, Sanakham, Pakchom, Bankum, Latsua and StungTreng) as 14% and impact was expanded to max. 14 days. The resulted impact was small at Kratie due to high flood peak attenuation in between dams. Therefore study concluded that the impact of above dam breaks would be rather high at the flood plain along the Mekong than downstream Kratie. The potential of cascade dam breaking was evaluated couple with pre-releasing associated with Paklay and Sanakham dams. The reasons behind the cascade dam break were short distance in-between dams and small spillway capacity of Sanakham dam. The Sambor (the most downstream) dam break model presented the highest impact at Kratie, 106% and 243% flood peak increase and 90% and 213% flood volume increase (duration 2 days) for piping and overtopping failures respectively. This is because of Sambor having the largest storage in the lower Mekong mainstream and it is planned to locate just upstream Kratie