Page - 891 - in Book of Full Papers - Symposium Hydro Engineering

Areas that may be affected or risk areas due to emergency cases of dams or much drainage from dams include dam downstream areas along both banks of the Mae Suai River in Mae Suai District to the confluence of the Mae Lao River, where floods will also take place. The boundary of risk areas in each event of emergency cases of Mae Suai Dam varies according to flood conditions as a result of the analysis. This depends on the reservoir water volume at that moment, inflow, dam failure types and the existing flood conditions in dam downstream areas prior to the incident. It is summarized as follows: Zone 1 (downstream of Mae Suai Dam-Ban Rim Thang) The severity of floods will be very high, especially in Ban Rim Thang, in which Zone 1 ends .There are a mountain pass and a narrow waterway .As a result, flood water levels are very high .Therefore, warning should be issued to people immediately and houses and buildings should not be constructed along the banks because this may cause harm to lives and properties. Zone 2 (Ban Rim Thang-Mae Lao Weir) In Zone 2, the severity of floods will be very high because of a narrow mountain pass throughout the area. As a result, the overflow from the Mae Lao River will occur. However, the population in the area is not dense. Warning should be issued to people to evacuate to higher grounds as specified. The wave will take about 2-3 hrs to travel to this area. Zone 3 (Mae Lao Weir-the confluence of the Mae Kok River) According to the analysis of all cases, Zone 3 will not face much risk because flood levels will be low or about 0.5-1.0 m. It will take about 4-9 hrs in total for waves to travel. This may not affect people’s way of life. It is not necessary to move people to higher grounds. People in such area should monitor the situation closely and cooperate with agencies concerned or seek how to prevent impacts caused by floods. 4.3. ACTION PLAN FOR UNUSUAL CONDITION DAM SAFETY Generally, when uncommon situations occur, for example, downpour, earthquakes, landslides in reservoirs, the officers in charge of dam maintenance have to examine and evaluate the dam conditions immediately. If unusual conditions or damage of the dams, appurtenant structures or control devices are found, the officers have to report the conditions to the dam safety section to analyze the causes and provide solutions as well as the prevention and monitoring measures intensively. The action plan for the Mae Suai dam safety in unusual conditions can be summarized as follows: 1] In case of downpour or unusual flood; excessive downpour over 200 mm within 24 hours, continuous downpour over 48 hours or flood that causes water levels in reservoirs change rapidly (over 30 cm per hour), the operation approach will be as below: [1] Analyze and evaluate the volume in the reservoir that will increase from the rainy storm . 891