Official

The Sumida River is one of the largest tourist spots in Chuo-ku, such as the wide surface of the water, the boats coming and going, the Sumida River Terrace on the waterside of the promenade, and the cherry blossoms on the embankment. On the other hand, rivers and seas can cause disasters in the city with the great power of nature.
dike is one of the facilities that protect the city from water disasters. Seawalls are installed on the Sumida River and Nihonbashi River in response to storm surge disasters. The Toyomi Bridge is built at the point where the Nihonbashi River joins the Sumida River, and you can feel that the height of dike is different between the upstream and downstream sides of this bridge.
The photo on the left is the downstream side of the bridge (the embankment of the Sumida River), and the photo on the right is the upstream side of the bridge (the embankment of the Nihonbashi River). The difference in height is 80cm. Both the assumed "planned storm surge level" are the same at A.P. + 5.1m, but depending on the size of the river, the height added to it (excessive height) differs.
It seems natural that dike is there, but "Why is it like this?" If you ask, "Why is this size?", You can see that many engineers are involved in research, planning, design, construction, maintenance, etc.