Imbe Water Purification Plant No. 3 Filtration Pond

The First of the Founding Beds

Imbe Water Purification Plant No. 3 Filtration Pond (忌部浄水場三号濾過池) is a concrete filter bed dating from 1918 at the Imbe water treatment plant in Higashi-Imbe-cho, Matsue City, Shimane Prefecture, and registered as a Registered Tangible Cultural Property of Japan on 18 April 2008. It belongs to the original works that gave Matsue piped water for the first time, and it shares its date with the year supply began.

The bed is a rectangle 22 metres east to west and 31 metres north to south, with a registered area of 692 square metres. Granite coping stones edge the rim, and a round regulating well with a housing stands at the middle of the north side. It lies east of bed No. 2 and north of the discharge well on the conduit.

Despite its number, No. 3 is the westernmost of the four founding beds, Nos. 3 to 6. Nos. 1 and 2 to its west were added in 1929, so in the row it marks where the Taishō-era beds begin.

The Founding Design in Numbers

The Imbe Water Purification Plant No. 3 Filtration Pond is valuable because it shows, in concrete, what Matsue's first modern waterworks was designed to do. The 1913 approval planned for 50,000 people and a peak supply of 6,300 cubic metres a day.

Records from the founding describe the method simply: water filters naturally through the bed, collects in channels in the floor and runs by iron pipe to the clear-water well. Each bed had an effective area of 6,503 square shaku, about 597 square metres. Three were used at a time, filtering at 10 shaku, about 3.03 metres, a day, for a capacity of 5,430 cubic metres daily.

The registered 692 square metres and the effective 597 do not match. The first seems to describe the structure as a whole and the second the sand surface that does the work, so the gap gives a sense of how much the walls and rim take up. The registration criterion is contribution to the historic landscape of the country.

What to Notice

The regulating well is round in plan and sits at the centre of the north side. Housings differ from bed to bed even among the founding four, so it rewards comparison with its neighbours.

The granite coping draws a sharp line between water and ground. Because the same stone band runs round every bed, you can see the whole row was conceived as a single design.

The boundary between the 1918 beds and the 1929 beds falls between this bed and No. 2. The two are so close in size that you would not guess the eleven-year gap from their outlines.

Visiting

The Imbe Water Purification Plant No. 3 Filtration Pond is inside an operating treatment plant and is not open to the public. Visits depend on whether the Matsue City Water and Sewerage Bureau is accepting them, so check in advance.

If you get inside, note how the discharge well lines up with the south side of bed No. 3; it helps you see where raw water is handed over to the beds. Follow staff instructions on photography and on how close you may go.