Each of the 59 pill-shaped columns weighs about 500 tonnes. In addition to their obvious function of supporting the roof and the 22 metres of ground above, they act as a counter weight against the buoyancy of the cistern in the surrounding groundwater.
It's difficult to appreciate in photos just how huge they are in real life, but to give a sense of scale each column is seven metres long and two metres wide, and an adult standing next to one would be about the same height as the buttressed base.
After an explanation of the system and its construction, we were invited to visit the underground surge tank.
Outside and at the far side of the field, an oblique concrete structure, like a sunken cube, serves as the entrance to the access shaft. A small black and gold plaque at the side listed the dimensions: 177.1 metres long, 78.0 metres wide, 25.4 metres high.
A hundred or so metal stairs down, the temperature steadily falling, then into the middle of the massive, dimly-lit cavern, where an array of giant columns towered, unshakeable.
Inside, greeted by staff, then up to the top floor where the control room is situated adjacent to a large display area, the floor of which features a satellite map detailing the path of the system's main tunnel.
The system is designed to prevent flooding of the basin during typhoons and heavy rain events by draining water from four rivers spread across the region. Each of the rivers has a 32 metre diameter, 60-70 metre deep underground shaft into which water can be diverted. These silos are joined 50 metres below the surface by a 6.4 kilometre long, 10 metre diameter tunnel that feeds the final shaft, which in turn connects to one end of the giant pressure control/surge tank. The tank acts as a buffer to regulate the flow of water so that it can be pumped into the Edo River 江戸川 at up to 200 cubic metres per second.
The taxi arrived, white gloves and auto-door, and we cruised across town, driver and interpreter chatting on the way, lamenting the loss of an ancient ginkgo 銀杏 tree in a recent storm.
There were no people to be seen or cars on the roads, but the tidiness of the farms that cover the countryside suggested a large workforce must exist.
At the facility, the large turbine and control building rises conspicuously at the end of an otherwise unremarkable soccer field. Hiding below it, at the end of kilometres of tunnels, is the mammoth “chika shinden” 地下神殿 (“underground temple”) – the surge tank that regulates the floodwater as it's pumped out of the channel.
At Minami-sakurai Station 南桜井駅 it was decided that a taxi was the easiest way to take the last few kilometres across town and through the farms to the riverside where the facility is located.
While waiting, I looked around a jutting granite monument nearby, rough hewn exterior, smooth inner planes with sakura 桜 pattern. Then, the nearby bicycle parking building, a common sight at stations in Japan, always exquisitely clean.
Taking the JR Saikyō Line 埼京線 about 40 minutes to Ōmiya Station 大宮駅, then changing to Tobu Railway 東武鉄道 and the Tobu Urban Park Line 東武アーバンパークライン (which had been renamed just the previous day from Tobu Noda Line 東武野田線), onward another 45 minutes to Minami-sakurai Station 南桜井駅, above.
During the trip we had plenty of time to get acquainted, chat about the history of the area and watch the concrete landscape skew and slide and eventually become greener and less dense as we reached the outer limits of Kasukabe 春日部市.
Arriving at the statue, the area was unexpectedly empty until a wave of people appeared from the station. The sakura 桜 was a clear focal point, glowing in the rising light.
My morning's plan was to visit the Metropolitan Area Outer Underground Discharge Channel 首都圏外郭放水路, a colossal subterranean flood-prevention system in Saitama Prefecture 埼玉県. Tours can be difficult to organise because the facility is inaccessible whenever it's operational and the tour is delivered in Japanese, so safety dictates that visitors must be accompanied by someone who can understand the language. As such, two weeks prior I took the gamble of hiring an interpreter willing to travel there, while praying there'd be no severe weather events in the meantime. Luckily it all worked out.
Yoshida-san 吉田さん was as punctual as expected, dressed in suit and tie, and before long we were on our way.