Studies on optimum design and conservation of artifical reefs

目的是通过水工模型试验，明确防止浅海人工建筑物(如人工鱼礁)倾覆和掩埋的优化设计和养护方法。特别是与本研究相关的水力学问题是波浪控制和引起泥沙运动的牵引力。(1)Ohashi和Kainou在近岸波浪试验池(20m*15m)中建立了内海诸岛常见的袖珍海滩的定床模型。这个模型被缩小到原型机的四分之一。主要通过设置具有鱼礁功能的透水性近海防波堤来控制波浪，进行了规则波试验。从试验结果可以看出，改进的效果很明显，只在防波堤中心附近才被认识到。因为t…的存在此外，渔港和袖珍海滩两侧的小海角对袖珍海滩的波浪条件影响很大。因此，对进一步的改进进行了检验。考虑到复杂的波浪特性(如三维绕射波、越浪率分布等)，最终确定了防波堤的最佳长度和开口宽度。(2)Ohashi和Fujihara在不规则波试验水池中设置了四种类型的礁石(台阶式和杆式，顶宽分别为30 cm、50 cm、70 cm)，进行了波高衰减试验。在两个不同能量水平下进行了7-9个水位(间隔2 cm)的试验，测量了8个点的波高。根据试验结果(波浪反射率、有效波高、最大能量、总能量和设定值)，探讨了每种礁石作为消浪建筑物的最佳水力条件，这些结果不仅对暴风雨时的防御措施有参考价值，而且对休闲时平静时的利用措施也有参考价值。较少

The aim is to make clear the optimum design and conservation method to keep the man-made structures (e.g.artificial reefs) set in the shallow sea area from overturning and burying thorough the hydraulic model experiments. In particular the hydraulic problems concerning to this study are the wave control and tractive force which induces the sediment transport. Their hydraulic characteristics are revealed experimentally in this research(1) Ohashi and Kainou constructed the fixed bed model of the pocket beaches, which are commonly seen at the islands in the Seto Inland Sea, in the coastal wave test basin (20m*15m). The model is scaled down to one-fortieth of the prototype. Mainly to control the waves by setting the permeable offshore breakwater, which can function as fish reef, the experiments with the regular waves were conducted. From the experimental results, it was clear the effect of the improvement, was recognized only around the center of the breakwater. Because the existences of t … More he fishing port and the small promontory at both sides of the pocket beach affect largely the wave condition in it. Therefore, further improvement were examined. Considering the complex wave characteristics (e.g.three dimensional diffracted wave and the distribution of overtopping rate, and etc.), the optimal length and opening width of breakwater were finally decided.(2) Ohashi and Fujihara experimented the decay of wave height by setting the four types of reefs (step type and bar type with 30cm, 50cm, 70cm of crown width) in the irregular wave test tank. The experiments under two different energy levels with 7-9 cases of water level (2cm interval) were conducted and wave heights were measured at 8 points. The Optimal hydraulic conditions of each type of reefs as wave control structures were investigated from the experimental results (wave reflection ratio, significant wave height, maximum energy, total energy and set-up value).These results are useful not only for a defending measure when stormy, but also for a utilizing measure when calm from the point of leisure. Less