What is the highest mountain in Japan?
Yes, it's Mount Fuji.
What's that height?
You all know this, 3776m. You remember, "Let's be everyone (3776)".
By the way, he remembers the height of Skytree as Musashi (634m).
So, where is the height of Mount Fuji standard?
Yes, that's right. This is "Japan Standard Base" located in 1-1 Nagatacho, Chiyoda-ku.
Finally one more thing. When and where was the standard of Japan established?
You may not know that this is a bit of a pass.
The answer was "Meiji 24 (1891), based on the Reiganjima Water Level Observatory."
That's why today's theme is Reiganjima Water Level Observatory.
In 1873, water level station was established on Reiganjima as one of the water markers to measure the estuary level of major rivers. For six years until Meiji 12 (1879), except for four months of absence, we observe the water levels at high tide and low tide here every day, and based on the data, the average sea surface of Tokyo Bay, that is, the national height standard was established.
Later, in 1891, when setting up the Japan standard base point in Nagata-cho, Chiyoda-ku, the standard survey was conducted from the Reiganjima Water Level Observatory to the starting point, and the height was 24.5000m as the reference point (Note 1).
The Reiganjima Water Level Observatory can be said to be the cornerstone of modern Japanese surveying.
The Reiganjima Water Level Observatory is still used to observe basic data such as construction plans (Note 2). In addition, due to the revetment work on the Sumida River Terrace, it was relocated 36m downstream from its original location in 1994.
The current Reiganjima Water Level Observatory photographed from Chuo-ohashi Bridge
The observation room is made so that the shape of a square, a square hexagon, an octagonal shape can change as you move the viewpoint along the river.
(Note 1) Due to the plate tectonic caused by the Great Kanto Earthquake, it was revised to 24.4140m in 1928.
(Note 2) Due to reclaiming of Tokyo Bay, Reiganjima Observatory is no longer an ideal location for verifying the base points, so we are currently verifying the base points at the oil pot observatory in Misaki, Kanagawa Prefecture.
For a detailed history of the Japan Standard and Reiganjima Water Level Observatory, please refer to the local information board ↓ and the Geographical Survey Institute website of the Ministry of Land, Infrastructure, Transport and Tourism (click on the photo to enlarge it).
What is the water level today...?
In addition, there is a "first-class level point / cross-section" located just upstream from the Reiganjima Water Level Observatory and up the stairs connecting Chuo-ohashi Bridge and Sumida River Terrace.
It is famous that there is a road ticket in Nihonbashi, which is the "starting point" of the Japanese road network.
The "starting point" of the height of mountains and land nationwide was also here in Chuo Ward.
