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Environmental Hydrodynamics

Professor TANAKA, Hitoshi •Associate Professor UMEDA, Makoto •Research Associate YAMAJI, Hiroto •Secretary KANNO, Chiaki

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Our research activities

Study on river mouths:

Nanakita river mouthNanakita river mouthRiver Mouths are located at the place where a river and the sea come across. There are complicated external forces such as ocean waves, tides and the river flow. Study on river mouths is an interesting reseach field related to the flood control, irrigation, and other engineering problems. Recently, the environmental importance of lagoons often seen at river mouths has been recognized. Our research group have kept working on topography changes and hydraulic characteristics of the Nanakita river mouth, SENDAI, JAPAN since 1988. The following picture is an aerial photograph of the Nanakita river mouth. Around the River mouth at the Nanakita, we can see Gamo Lagoon famous as wild birds, the Teisan Canal and many precious historic waterfront area. Sendai Port, located 2km north from the River mouth, is expected as the international port. Therefore, the project of expanding the Sendai Port to the region of the Nanakita River mouth has been under consideration. Like this, enviroment of the Nanakita River mouth is fairly complicated. Now we should lay stress on the harmony between these various desires and the primary problems such as flood control. The following picture is the view of the field measurement at the Nanakita River mouth.

Shoreline changes on Sendai Coast :

Nanakita river mouthFeild observations and analyses of wave climate statistics are carried out to investigate short-term shoreline changes on Sendai Coast. The photograph on the left shows detached breakwaters on Fukanuma Beach in Sendai City. Significant deposition behind the coastal structures and the recession of the shoreline on both sides of the breakwaters.

The study of the river overflow :

Nanakita river mouthOn 22-Sep-1994, the heavy rain had occured at the regin of the Masuda River which runs through Natori-shi, Miyagi. The maximum amount of precipitation per hour was 89mm and total amount of precipitation was 478mm. The direct discharge from the upper reaches of the River at the Tarusui Dam caused the serious damage to the lower part of the River (see the picture below).

Nanakita river mouthNanakita river mouthNanakita river mouthNanakita river mouthNanakita river mouth

Research for the inflow pollution load in the fish culturing ground:

Nanakita river mouthIn the region of Sanriku Coast, the fish culturing has been very common industry. But recently, with the expansion of fish culturing area, the water pollution is proceeding in the Bay. And in some area, it badly affects the amount of landed quantity. But the fish culturing is not only cause of water pollution actually. We also need to evaluate another factors quantitatively, for example, inflow from living wasted water, wood, agricultural area through the river. Then forcused on the area of Sizugawa Bay at South Sanriku Coast, we have been investigating continuously about the amount of water, water quality of Hachiman River which flows into Sizugawa Bay. Just below photograph shows a glance of the invesigation for water quality.

The study of the velocity distribution and the water quality in the Sendai Bay:

Nanakita river mouthOn 22-Sep-1994, the heavy rain had occured at the regin of the Masuda River which runs through Natori-shi, Miyagi. The maximum amount of precipitation per hour was 89mm and total amount of precipitation was 478mm. The direct discharge from the upper reaches of the River at the Tarusui Dam caused the serious damage to the lower part of the River (see the picture below).

Study of sediment movement and Boundary layer properties under oscillatory flow:

Nanakita river mouthThe experiments are performed by using oscillating tunnel (U-Shaped one as shown below picture) and the detailed measurement of velocity is carried out by Laser Doppler Velocimeter (LDV) under various flow conditions. The understanding of boundary layer characteristics in coastal environments is important to estimate the sediment movement with reasonable accuracy.

Study of turblence phenomenon and numerical computating:

Nanakita river mouthA great development of numerical computating is getting brought lately. Numerical computating is available especially to the water engineering and wind engineering where experiments and field measurements are hardly done. To understand the current flow properties and the wave motion, we study the turblence models and numerical computating. The photo shown below shows the profile of fluctuating velocity properties under wave flow. You can see the fluctuating generated near the wall extends from the wall to the upper side.

The formation of chanel networks and the drainage basin development:

Nanakita river mouthThe topography of the Earth's surface is self-formed through the interaction between the Earth's surface and the flow on the surface. Periodic patterns of gullies or inceptive channels are formed on the initially flat surfaces, and they develop into complicated channel networks. It is important to study the formation of channel networks because gullies and inceptive channels tend to amplify soil erosion.

Nonlinear dynamics of bars, dunes and ripples:

Nanakita river mouth
A variety of bed waves such as bars, dunes and ripples are formed on river beds. The formation of bed waves is a kind of the self-formed patterns due to the interfacial instability between flow and beds. Dunes and ripples cause flow resistance, so that understanding of the mechanism of bed waves is one of the important problems in river engineering. We are studying the nonlinear dynamics of bed waves.

The formation of submarine canyons:

Nanakita river mouthA large number of canyons are observed at continental margins under the ocean. As the cause of the formation of submarine canyons, turbidity currents have received researchers' attention. The turbidity current is a density flow containing a large amount of fine suspended sediment, which is further accelerated by entraining sediment on the ocean floor. The formation of submarine canyons is one of our subjects of study.

The formation of beach cusps and the nearshore current system:

Nanakita river mouthBeach cusps are uniformly spaced, arcuate scallops formed at beaches. They are inseparably connected with nearshore currents. It is thought that beach cusps and the near shore current system are formed by the dynamic instability between the radiation stress of waves and the near shore bathymetry. We are studying the formation of beach cusps and the nearshore current system.


Graduation Theses (last 3 years)

2004
Field observations of flow charactyeristics in Nagatsura lagoon (KANESATO, Manabu)
Field observation of hydraulic characteristics of tidal area at the Natori river mouth (SUGAI, Risa)
Study on short-term topographical change at the Nanakita river mouth (NAKAYAMA, Daisuke)
Field observations on the transport process ofsuspended solid during low and high flow period in the Nanakita river (HARA,Yuko)
2005
Relationship between water level variation and water depth at the mouth of Natori River(ASAYAMA, Jun-ichi)
Fundamental study on seepage flow in a river channel (OHTOMO, Hirotaka)
Study on long-term morphology change at the NatoriRivermouth (KOHRAI, Mikihiro)
Study on gully formation (MIZISHIMA, Daiki)
2006
Study on long-term shoreline change using historical maps (TAKAHASHI, Genki)
Analysis of shoreline change using aerial photographs (KHANG, Truong Thien)
Equiliburium cross section in an alluvial channel (MORII, Yu)
Chracteristics of turbidity current on continental shelf (YAMAGUCHI, Kenji)
Hydraulic characteristics in Nagatsura-Ura Lagoon (MORINAGA, Akio)

Master Theses (last 3 years)

2004
The development process of roll waves (IGARASHI, Akira)
Field observation of salinity variation at the Nanakita river mouth (ENDO, Ken)
Hydrodynamics and water quality in Nagatura lagoon (OKAJIMA, Naoya)
The study in regard to the method of measuring suspended sediment concentration profiles in the river mouth (SUGAWARA, Ryoji)
The generation of beach cusps (TANIKAWA, Asako)

2005
Shoreline change on sendai coast and its prediction (SAKAUE, Takeshi)
Sand waves on erodible river bed (SHIMADA, Norikazu)
Morphology change on Ishinomaki Coast after headland construction (TAKAHASHI, Toru)
2006
Hydrodynamics and water quality change in Nagatsu Lagoon on Sanriku Coast (KANESATO, Manabu)
Field observation of morphlogy change using a automated camera system at the Nanakita River mouth (NAKAYAMA, Daisuke)

Dissertations

2003
Nonlinear analysis of dunes (YAMAGUCHI, Satomi)
Fundamental study on water level rise in river entrances (LEE, Hyun-Seok)
2004
Study on the physical and chemical characteristics and the transport behavior of fine particulate matter in the river (PILAILAR, Sitang)
2005
Study on river mouth morphodynamics responding to wave, tide and river flow (Patchanok Srivihiok)
2006
Shoreline change and sediment budget analysis on Sendai Coast (KANG, Hyun-woo)
Study on water level change in a tidal estuary (WATANABE, Kazuya)

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