| Summary: | 博士 === 國立中央大學 === 土木工程研究所 === 90 === Generally, a water resources system consists of two major facilities :(1) reservoir; (2) barrage. The reservoir is to regulate the variability of surface water flow and make water available when it is needed, and the barrage is used to divert water through the stream. Study on the firm yield analysis and operating rule curves for such a system will provide a long-term guideline for reservoir system operation. Optimization of water resources planning and management was studied in the last four decades, however, the topic is still a formidable challenges to water resources planner. The major advancement in this thesis, compared with previous studies, is to provide analytic solutions for reservoir releases in firm yield analysis on regional multireservoir and barrage systems. Furthermore, a GA (genetic algorithms) search technique is proposed to find a set of rule curves by using different approaches in coding and decoding. According to several numerical experiments on case studies reveal that automated model for rule-based operation can overcome computationally intractableness due to curse of dimensionality for reservoir operation problems in real world.
The study attaines the following findings and conclusions:
1. A complete simulation model for a reservoir system operation can quickly reveal various factors influencing operation efficiency of the system, and can reduce the difficulties previously encountered. Meanwhile, a pseudo tandem reservoir model was developed to enhance the convenience of model modifications and calibrations. The maximum deviation of the simplification is only 4.08%, therefore, the simlified model is valid for preliminary planning .
2. For a reservoir-river system with its water abstraction point at an intake downstream of the dam, streamflow controlled by the dam can be utilized to significantly increase the water yield of the system. If more than one reservoirs in upstream, joint operation will make more efficient due to the complement by each others. Regarding reservoirs in series, the inflow of a downstream reservoir is the released amount of the upstream reservoir plus the lateral flow between those two reservoirs, and varies with the operation strategies of the upstream reservoir. As those reservoirs have almost the same source of water, the time distribution of inflows of reservoirs is nearly the same. This is the major difference between tandem and parallel reservoir systems. The results of this study indicate that operation of a multireservoir system in series has an efficient way to release for downstream reservoir with first priority for water supply purpose; For reservoirs in parallel, a strategy called balanced level indices (BLI) is verified to be the best for operating the multireservoir system with a water-intake located in the downstream of the confluence of all the related rivers.
3. Joint operation of reservoirs and barrages can enhance operation efficiency for water-supply. To reduce its impacts on environment, ecology and culture, development of water resources should start from building small scale dam incorporated with barrage rather than building a large dam. Traditional yearly reservoir utilization ratio, i.e. the ratio of the yearly firm yield and reservoir effective volume(Y/TV), greater than 1.0 represents a hydrological feasibility for dam construction. But, in the case of joint operation of multireservoir and barrages, the ratio is usually larger than 2.0, and means a high development efficiency.
4. Although each reservoir storage level varies with different operation strategies in a multireservoir system, the total storage function rises due to system joint operation. In order to gain the highest benefits, the system operation needs to obey rule curves. Therefore, deriving a proper rule curves can not only reduce the shortage amount and duration for downstream demand but also enhance hydropower efficiency.
5. Related to the optimization of reservoir operating rules, this study presents a new procedure to find a set of rule curves by different approaches in coding , decoding and choosing objection function . Those objection functions such as (1/SI), (1/SI+hydropower) and ((1/SI+hydropower)+(100-percentage of maximum shortage ratio)), employed to the fitness function of GA, resulted in a set of satisfied rule curves.
6. Nowadays, there is a trend to remain minimum instream flow discharge and the required water riverbed percolation in the downstream of a dam. The minimum instream flow is released for aquatic species and downstream riverbed percolation for recharging groundwater aquifer. The results of present studies reveal that the amount of downstream riverbed percolation is affected by not only the total amount but also the temporal distribution of stream discharge. The paper confirms that appropriate policy for reservoir operation can enhance total amount of riverbed percolation.
7. Because computations of the water yield involves a lot of cumbersome and time-consuming, a visual simulation model developed by Microsoft Visual Basic is presented to reduce the numbers of trial and error and the analysis time for firm yield in multireservoir-river systems.
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