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An amphidromous goby, Sicyopterus japonicus , migrates from the ocean to upstream regions of many streams and rivers in the Pacific coasts of Japan and Taiwan. Using its mouth and fused pelvic fins (pelvic sucker), this gobiid species exhibits a rock-climbing behavior and surmounts sizable waterfalls, which block the upstream movement of many of its competitors and predators. When gobies emerge from the water to commence their climbing behavior, the change in effective density (i.e. lack of buoyancy) that occurs in this transition substantially increases the force required for adhesion. Consequently, these fish must exert adhesive suction strong enough to support their body weight against gravity during climbing on the rock surface. Suction performance for adhesion and modulatory capacity of S. japonicus were evaluated with two different sets of experimental conditions: climbing on the vertical surface with no water flow versus climbing on a 60°-inclined surface with 2 L/min flow. Individuals of S. japonicus showed 50.7% greater mean safety factor (suction force for adhesion/gravitational force) and 56.6% shorter time to reach maximum pressure differential during climbing on the 60°-inclined surface with water rushing over their bodies than during climbing on the vertical surface with no water flow. These results indicate that when climbing with drag force from flowing water, greater functional demands are imposed and therefore, S. japonicus is required to increase neuromuscular stimulation of the pelvic muscles to elevate suction performance. In addition, S. japonicus individuals at different ontogenetic stages modulate their climbing behaviors and strategies to accommodate changing functional demands as they make transitions between different inclines, as well as media, while ascending waterfalls. [ABSTRACT FROM AUTHOR]

River-blocking events induced by tributary debris flows occur frequently in mountainous areas. If a dam formed by a river-blocking debris flow were damaged, a massive outburst flood could induce downstream hazards. Therefore, early identification of areas potentially at risk of river blocking is essential for hazard mitigation, particularly in extensive mountainous areas. This study proposed a dimensionless volume index (DVI) to evaluate river-blocking formation by considering the relationship between the deposition volume of a tributary debris flow in a river and the minimum river-blocking volume. The values of both parameters can be established based on the theory of debris flow run-out distance, deposition width, and deposition thickness with consideration of the effects of drag force, hydrostatic force, and buoyancy. The efficacy of the proposed method was demonstrated through two case studies of mainstream blocking/nonblocking by tributary debris flow events in Taiwan during Typhoon Morakot. The results indicated that early identification of river blocking could be achieved using the DVI based on a pre-established database of potential debris flow hazard areas, including local site information, rainfall intensities at potential debris flow hazard areas under varying recurrence periods, and mainstream discharge at varying recurrence periods. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical solution for the dynamic stability of the ocean current turbine system developed in Taiwan. This system is tethered to the sea floor and uses the Kuroshio Current to produce electricity. To maintain the performance of the turbine system in the presence of the Kuroshio Current, the stability of the surfaced turbine needs to be considered. The proposed system is composed of a turbine, a buoyance platform, a traction rope, and a mooring foundation. The two-dimensional theoretical solutions treat the turbine as a rigid body with a movable structure that is moored with two cables. In this model, the gravity, buoyancy, and drag force generated by the wave on the turbine structure are considered. In addition, an analytical solution is proposed for the general system. Finally, the effects of the wave on the pitch motion and dynamical stability of the ocean current turbine system are investigated. [ABSTRACT FROM AUTHOR]