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HOME > No.12, Feb 2018 > Understanding the Sea Close to Us

Understanding the Sea Close to Us

Grasping the sand movements of coasts, estuaries, and bay areas By Shigeru Kato
Robotic Support for Regional Agriculture
Professor Shigeru Kato (left) with his laboratory members

In Japan, with its very long coastline, coastal erosion has become a serious problem due to factors such as the decrease in the supply of sediment from land area as well as the interruption of sediment flow caused by structures. At the Department of Architecture and Civil Engineering at Toyohashi University of Technology Professor Kato and his team are conducting surveys and studies to ascertain changes in coastal topography and the movement of sand, with the goal of achieving appropriate sediment management in coastal areas.

Japan is a small island country surrounded by sea, but it has one of the longest coastlines in the world. The coastline is about 35,000 km, which is about 85% of the distance around the Earth (about 40,000 km). Every day, this extremely long coastline is exposed to high waves generated by low atmospheric pressure and storm surges due to typhoons, and the topography of the coastal area is constantly changing. The coastal environments we are so familiar with, such as sandy beaches and tidal flats, have up to now been maintained by sediment supply from the land carried by rivers and other sources.

However, not only is this supply drying up, but the development of coastal areas due to land expansion and the construction of coastal structures on landfills have also damaged the balance of sediment dynamics (movement of sand). This delicate balance depends upon the preservation of the thin layer of sediment in coastal areas. Serious coastal erosion is occurring across the country as a result.

Fig.1: Result of long-term shoreline monitoring on the Omotehama coast

Toyohashi University of Technology is located in a place surrounded by rich marine environments such as the open sea and bays as well as freshwater rivers and lakes. Our Coastal Engineering Laboratory has been actively engaged in monitoring the changes of such areas. For example, we have been monitoring in cross-section profiles and shoreline positions of sandy beaches, analyzing the chemical element characteristics of beach sand and investigating sediment transport in tidal flats in order to get an understanding of sediment dynamics. This work is carried out primarily in the coastal areas of the open sea, bays, and estuaries. We are continuing the work of monitoring the sand beach sectional topography and shoreline positions of the Omotehama coast, which was started by Prof. Aoki in 1999.

Fig.2: Survey of sediment transport and morphometry of tidal flat Setting up color sand (left), morphometry of tideland (right)

To date we have accumulated the data over about 18 years (Fig.1). The data is also used as basic data for the decisions regarding shoreline management under the Aichi Prefecture’s coastal conservation plan. By analyzing the chemical element properties of beach sand using fluorescent X-ray analysis, we have determined that the content of elements such as Fe (iron), Mn (manganese), and Ti (titanium), all of which are always detected, can be used as an index to judge erosion / deposition tendencies of beaches, elevation above sea level (height) of sandy beaches, and size of sand grain. We are also conducting surveys that locally track the movements of the sand by injecting color sand (artificially-colored sand) into the tidal flat and measuring the topography of the tidal flats (Fig.2). Recently, we have also been attempting morphometry of tidal flats using UAVs (drones) (Fig. 3), and we are also conducting surveys and research on monitoring and conservation of the nearshore environment.

Fig.3 Topographical monitoring of the Tombolo tidal flat
(Survey area: Higashihazu-cho, Nishio-shi, Aichi prefecture),
Composite photograph of the full view of the tidal flat (left),
Three-dimensional shape of the constructed tidal flat (right).

It is important to properly ascertain the abundance of sediment (Stock) and its movement (Flow) in the coastal areas in order to develop countermeasures and solutions to the problem of coastal erosion. The purpose of our coast survey and topography monitoring by UAVs is to grasp the actual situation by actually investigating the site. In addition, our goal with the chemical element analysis is to establish it as a new tool for understanding sediment dynamics in the coastal regions. We are conducting these surveys and research while experiencing the richness, bounty, and constantly changing face of these natural sites first hand.

Part of this activity was supported by the following funds.

  • Grants-in-Aid for Scientific Research (Challenging sprout research, assignment number 24656294)
  • Mitsui & Co. Environment Fund (Research grant for 2013, Representative: Aichi Fisheries Research Institute)


By 加藤 茂







  • 科学研究費補助金(挑戦的萌芽研究、課題番号24656294)
  • 三井物産環境基金(2013年度研究助成、代表:愛知県水産試験場)

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Researcher Profile

Shigeru Kato
Name Shigeru Kato
Affiliation Department of Architecture and Civil Engineering
Title Professor
Fields of Research Coastal Engineering / Coastal Disaster Mitigation