Abe River Research Articles

Visit to valuable water springs (130) Valuable Springs in lower drainage basins of Abe River

Visit to valuable water springs (130) Valuable Springs in lower drainage basins of Abe River

Influence of mega debris flow on geomorphological features of the upper reaches in the Abe River examined from the formation process of the Akamizu waterfall

Influence of mega debris flow on geomorphological features of the upper reaches in the Abe River examined from the formation process of the Akamizu waterfall

Efforts of comprehensive sediment control in the Abe River Sand System

Efforts of comprehensive sediment control in the Abe River Sand System

LONG-TERM TOPOGRAPHIC CHANGES AROUND SAND SPIT AND IMPACT OF EXTRAORDINARY HIGH WAVES DURING TYPHOONS

Around the Mihono-matsubara sand spit in Suruga Bay in Japan, the beach was eroded owing to the decrease in the fluvial sand supply from the Abe River triggered by excess riverbed mining before 1967, together with the discharge of sand into the deep sea via a steep slope near the tip of the sand spit. As a measure against beach erosion, an artificial headland (HL) composed of two detached breakwaters and the breakwaters (BWs) placed along the shoreline have been constructed along with beach nourishment, but the beach is barely maintained by these measures. In 2013, two large typhoons hit the coast, causing rapid beach changes around the structures, and these beach changes were superimposed on the long-term topographic changes that have occurred over a long time as a geomorphological process. In this study, their impact to the beaches was investigated on the basis of the field data.

多目的最適化による複数の水位観測地点の流量を再現するパラメータ推定法

This paper presents the parameter identification of a distributed runoff model applied to the Abe River basin where three water level stations exist. The errors between the observed and calculated discharges at the water level stations are minimized simultaneously by multi-objective optimization algorithms. Comparing the performance of five implementations of the optimization algorithms, two implementations of a genetic algorithm NSGA2 of the statistical software R are better than the others. It turned out to be difficult to represent the whole basin by the parameters optimized to a single water level station. However, it is possible to calculate the discharges which are near the observed ones by selecting the pareto optimal solutions under the limited errors of three water level stations.

Depositional and erosional architectures of gravelly braid bar formed by a flood in the Abe River, central Japan, inferred from a three-dimensional ground-penetrating radar analysis

We conducted a ground-penetrating radar (GPR) survey of gravelly braid bars in the Abe River, central Japan, to clarify the three-dimensional (3D) variations in their depositional facies under various geomorphologic conditions. In September 2011, a ten-year return-period flood in the study area reworked and deposited braid bars. After the flood, we surveyed three bars with different geomorphologies using a GPR system with a 250-MHz antenna and identified seven fundamental radar depositional facies: Inclined reflections (facies Ia and Ib), horizontal to subhorizontal reflections (facies IIa and IIb), discontinuous reflections (facies IIIa and IIIb), and facies assemblage with a large-scale channel-shaped lower boundary (facies IV). Combinations of these facies in\\dicate bar formation processes: channel filling, lateral aggradation, and lateral and downstream accretion. In the Abe River, aerial photographs and airborne laser scanning data were obtained before and after the flood. The observed changes of the surface topography are consistent with the subsurface results seen in the GPR sections. This study demonstrated that the erosional and depositional architecture observed among bars with different channel styles was related to river width and represented depositional processes for high-sediment discharge. The quantitative characterizations of the sedimentary architecture will be useful for interpreting gravelly fluvial deposits in the rock record.

静岡・清水海岸でトレンチ掘削調査により得られた砂と礫の堆積構造

Trenches were excavated to observe the sedimentary strata on three beaches in Shizuoka, Japan. The western trench was near the Abe River, which is the source of sediment transport; the eastern trench was on the Miho Spit that marks the end of the longshore sediment transport, and the third was in between the two. The strata of the walls of the trenches were recorded and the grain-size distribution of each stratum analyzed. It was found that the grain-size accumulation curve could be divided into five groups based on the ratio of gravel to sand. This shows that conditions of sediment transport affect sediment content. Trench wall strata provide evidence of the strata-forming events.

PREDICTION OF BEACH EROSION CAUSED BY REDUCTION OF FLUVIAL SAND SUPPLY DUE TO EXCESS SAND MINING AND BEACH RECOVERY AFTER PROHIBITION OF MINING

Long-term topographic changes since 1968 along the entire Shizuoka and Shimizu coasts including a 17 km stretch extending between the Abe River mouth and the tip of the Mihono-matsubara sand spit were investigated. Beach erosion of these coasts was triggered by the decrease in sediment supply from the Abe River due to excessive riverbed mining until 1967. After 1982/1983, natural sand supply from the river increased and accretion occurred on these coasts. Measured topographic changes were reproduced using the contour-line-change model considering changes in grain size. Not only the movement of the sand body but also the shoreline and bathymetric changes were numerically reproduced. The calculated results were in good agreement with the measured topographic changes.

A numerical study on the transport of eggs and larvae of Sergia lucens in Suruga Bay, Japan

Numerical experiments were performed to investigate the transport processes of eggs and larvae of Sergia lucens in Suruga Bay, Japan, focusing on the physical effects of the river water spreading. In the experiments, labeled particles, which were regarded as the eggs or early larvae of S. lucens with no (or weak) swimming ability, were passively transported in flow fields that were calculated by an ocean general circulation model. In the innermost region of the bay (off the Fuji River mouth) where there is no continental shelf, a retention area where the eggs and larvae could stay in a nutrient-rich environment for a long time was formed, especially in the upper part of their habitation layers, by the large bulge with anticyclonic (clockwise) circulation. No retention area was formed in the western region of the bay (off the Oi and Abe River mouths) or in an additional experiment in which a continental shelf was artificially created in the innermost region. It was estimated that in the retention area, the residence time of the eggs and early larvae is prolonged by about a month. The formation of the retention area is controlled by the dynamics of the river water spreading, affected by the bottom topography and the Earth’s rotation. Moreover, the reason why S. lucens are only caught in abundance in Suruga Bay was discussed.

Invasion Status and Growth Attributes of Naturalized Ryegrasses (Lolium spp.) along the Abe River, Shizuoka Prefecture

Invasion Status and Growth Attributes of Naturalized Ryegrasses (Lolium spp.) along the Abe River, Shizuoka Prefecture

Invasion status of Eragrostis curvula in the Lycaeides argyrognomon praeterinsularis habitat along the Abe River, and the effects of its removal

Invasion status of Eragrostis curvula in the Lycaeides argyrognomon praeterinsularis habitat along the Abe River, and the effects of its removal

Observation of total load in upstream of the Abe river

Observation of total load in upstream of the Abe river

Model for Predicting Formation, Disappearance and Recovery of a River Mouth Terrace Considering Sorting Effect of Sand with Different Grain Sizes

A model for predicting the formation, disappearance and recovery of a river mouth terrace was developed based on the contour-line-change model considering grain size changes. The topographic changes and grain size changes associated with the flushing process of a flood were first investigated, taking the mouth of the Abe River as the example. Predicted change in the river mouth terrace and grain size changes around the river mouth were in good agreement with the measured, showing the effectiveness of the numerical model.

The landslide dam and outburst floods at Warabino area of the Abe River in 1914

The landslide dam and outburst floods at Warabino area of the Abe River in 1914

Evaluation of time‐space distributions of submarine ground water discharge

Submarine ground water discharge (SGD) rates were measured continuously by automated seepage meters to evaluate the process of ground water discharge to the ocean in the coastal zone of Suruga Bay, Japan. The ratio of terrestrial fresh SGD to total SGD was estimated to be at most 9% by continuous measurements of electrical conductivity of SGD. Semidiurnal changes of SGD due to tidal effects and an inverse relation between SGD and barometric pressure were observed. Power spectrum density analyses of SGD, sea level, and ground water level show that SGD near shore correlated to ground water level changes and SGD offshore correlated to sea level changes. SGD rates near the mouth of the Abe River are smaller than those elsewhere, possibly showing the effect of the river on SGD. The ratio of terrestrial ground water discharge to the total discharge to the ocean was estimated to be 14.7% using a water balance method.

Application of GIS to Evaluate Long-Term Variation of Sediment Discharge to Coastal Environment

This paper presents a GIS-based method to calculate the total sediment discharge from river basins to coastal areas. This method uses Revised Universal Soil Loss Equation (RUSLE) to calculate the rate of soil erosion and Gross Erosion-Sediment Delivery method (GESD) to calculate the total sediment discharge in a GIS modeling environment. The model is tested using the data of Abe River then applied to four river basins in Asia. Global data sets are used as the input to the current model. The result shows that there are significant variations of sediment discharges due to the precipitation change in these river basins.

GROWTH OF VEGETATION IN FLUVIAL-FAN SEGMENT DUE TO DECREASE OF DESTRUCTION OF VEGETATION BY FLOODS

Recently in many rivers, vegetation covers wide parts of floodplain of fluvial-fan segment of particularly with a dam on the upstream. Rich vegetation is disadvantageous from the viewpoint of safety against flood but also it is not necessary good for eco-system of fluvial-fan rivers. When the changes of river landscape of the Tedori river (with dam) and the Abe river (without dam) are compared with each other by aerial-photo analysis, the growth of vegetation after dam construction is remarkable in the Tedori river. When the records of floods of the two rivers are compared with each other, it is clarified how the major floods were controlled by a dam in the Tedori river. The previous studies by us show that repetition of medium-size floods and low-stage waters promotes vegetated area to expand. On the other hand, major floods sometimes destroy the vegetation. Usually the growth and destruction are in balance. Thus the obvious growth of vegetation in the Tedori river probably implies the decrease of chances for vegetation to be destroyed by major floods. Then, models to simulate destruction of vegetation by flood and growth of individual trees have been proposed to explain the difference of landscape changes in the Tedori and the Abe river.

STUDY ON DEVELOPMENT OF THE SEDIMENT ROUTING MODEL BASED ON THE DIGITAL ELEVATION MAP

In order to assess the sediment transport in a whole water system, a synthetic sediment routing model based on the river channel networks obtained from the digital elevation map was examined. The sediment routing model was applied to the Haya River basin and the Abe River basin. Through the application using two kinds of scale of channel network element, and the diffelent catchment area, effects of these elements on the simulation of river bed variation were discussed. The results show that the river bed variation in the two kinds of scale, 250m mesh and 500m mesh, shows about the same behavior except upper part of the basin, and themodel has a possibility to be applicable.

STUDY ON THE APPLICATION OF 2-D DEPTH INTEGRATED METHOD TO THE ABE RIVER

STUDY ON THE APPLICATION OF 2-D DEPTH INTEGRATED METHOD TO THE ABE RIVER

Causes of damage of seawall on Hirono coast in Shizuoka Prefecture

Causes of damages of seawall due to storm waves on the Hirono coast in Shizuoka Prefecture were investigated. In 1997 high waves were generated by five typhoons in this area. Direct cause of the failure of the seawall is due to the wave action, but gradual decrease of sea bed due to beach erosion is the indirect cause. Beach erosion of this area is deeply connected with the retreat of river mouth bar of the Abe River.