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UNESCO-IHE Institute for Water Education, Delft (2013)

Dam safety management of selected earth-fill dams in Tanzania

Robert, E.M. 

Titre : Dam safety management of selected earth-fill dams in Tanzania

Auteur : Robert, E.M. 

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2013

Tanzania has been investing a lot of money on dam construction so as to develop water resources for irrigation, HEP generation, domestic, commercial and industrial uses. Due to inadequate and missing dam safety management (DSM), dam failure cases have been frequently reported. In order to reduce the current dam failure status, implementation of DSM plan would minimize the dam failure hazards in the country. In order to assess the existing dam safety management plan, two earth fill dams were selected for detailed dam safety investigations.The study aimed at detecting problems on the two selected dams based on ’’state -of-art’’ standards and recommendations, the safety management plan of the existing dams have been checked and suggestions for their improvement are made. The specific objectives were ; to give the overview of the current existing dam status in the country, safety and risk evaluation of the selected existing earth fill dams and assessment andimprovement of DSM plan.Statistical analyses for main deteriorations classification of 650 existing dams for broad overview of dam safety status in the country have been prepared. For the two selected characteristic dams, a safety evaluation together with physical assessment made on the dam sites, were deployed for computation of the failure risk by a deterministic risk evaluation tool. Safety against overtopping was carried out by analyzing the hydrology of the two catchments and hydraulics of their spillways. Seepage or piping assessment was performed by using Mseep 2D finite element model and slope stability safety was evaluated by using Mstab 2D numerical model. The main findings of the study were ; 11 major deterioration mechanisms of the existing 650 dams were identified. Detailed hydrology analyses for the Mindu and Nyumba ya Mungu (NyM) dam conducted at the return periods of 10,000 and 100,000 years respectively, both embankments are safe from overtopping. The factor of safety against sliding of downstream side slope of NyM dam in all scenarios was less than 1.0 ; according to ICOLD guidelines the dam is unsafe. It was also found that 99.7% of the Mindu dam seepage is through the dam foundation. The risk of the Mindu and Nyumba ya Mungu dam are calculated as 0.13 and 0.14 respectively, and both dams could be classified as high risk dams. The study concluded that the foundation layer of the Mindu dam is under seepage and NyM downstream slope stability is unsafe. Therefore for both dams, Mindu and NyM, further geotechnical investigations and detailed structural calculations (seepage, stability) are recommended. Based on the results of these analyses the reconstruction and improvement measures have to be defined and implemented. For sediment control of Mindu reservoir ; dredging, upstream coffer dam construction and human activities control is highly suggested. DSM plan of the two dams should be reviewed so as to meet the international standards and common practice.

Sujets  : dam safety earthfill dams Tanzania


Page publiée le 14 février 2020