Study On The Limited Water Levels During Flood Season Considering Storm Types

In the actual "operating schemes during flood season of the large and medium size reservoirs" of Shandong province, the determination of the limited water levels during flood season (Z_L)usually needs to consider three factors, i.e. to ensure the necessary impoundment, to assure the safety of the lower reaches of the river and to guarantee the safety of the dam, then the water level is determined through analyses and comparisons. Therefore, the design flood has great effect on the determination of Z_L. Shandong province is short of water resources, however, during the flood season, in order to make sure of the safety of flood control, water level must be kept below a lower limited water level during flood season for many large and medium size reservoirs. It results in a discomfiture situation that great amount of water is discarded and no enough water will be recharged after the flood.In order to coordinate the conflict of the flood control and the benefit to utilize water resources, and to alleviate the water shortage in this area, this dissertation focuses on exploiting the means to control Z_L from the point of view of checking design flood by resampling annual maximum data. It has been recognized that storms occurring in Shandong province are mainly brought by easterly wave, typhoon or typhoon-related meteorological systems, moreover, typhoon more likely induces heavy rains. Therefore, procedure to modify the design flood and Z_L of a reservoir is prescribed as: in the annual maximum flood data serious which usually are taken as samples to estimate the design flood, eliminating those data caused by typhoon, instead adding the largest flood which is not brought by typhoon, thus obtaining a new annualsample serious for design flood analysis. As such a design flood is usually smaller than that of estimated by using samples containing typhoon data, the result is that it increases the designed value of Z_L of the reservoir. Whenever the typhoon is forecasted to be approaching, pre-releasing the water to lower down the reservoir water level to the original designed Z_L to satisfy the needs for flood protection. By taking advantage of this strategy, storing extra water resources in case of no typhoon rains or big floods occur, while retaining the reservoir' s function of flood control if there comes the typhoon rain or heavy flood.As an example, variations of Z_L of two large size reservoirs in Weihai city namely Mishan reservoir and Longjiaoshan reservoir, were studied. Results indicate that, for Mishan reservoir, the original designed Z_L is 29. 0 m, while the newly estimated Z_L is 29.45m, it enhances 0.45m, thus bringing an increase of water storage by 11 million m~3. For Longjiaoshan reservoir, the two water levels are 41m and 41.32 m respectively, bringing 0.32 m increase in water level and 3. 8 million m~3 in storage. It concludes by these figures that, if implements the means proposed by this study for actual reservoir operation, each year more or extra water resources is likely stored and less water is discarded in the flood reason, thus improving the efficiency of utilization of the water resources in the flood season.