We are all familiar with the idea of a dam. But have you heard of an underground dam? If you think the idea is unreal, you must stop by Miyakojima Underground Dam Museum (宮古島市 地下ダム資料館) when you visit Miyako-jima Island! The idea of an underground dam is simple. Instead of damming up rainwater, it is the underground water that the dam holds. In the museum, dioramas, short films, and other exhibits will give you a good idea of the dam’s construction and underground water.
While you might think your home country should have a few underground dams so the land above the ground can be used for something else, this unconventional dam isn’t suitable anywhere else in the world. Miyako Island is entirely covered with limestone, so water can easily penetrate the ground surface into the limestone layer. The island’s underground thus accumulates ample water in the limestone layer so a dam can be built!
The limestone layer is also why Miyako Island is blessed with some of the most beautiful beaches in the world. Because the water’s penetration rate is too fast, no rivers can form on the island. This means nothing can bring the soil from the mountain to the ocean. The seawater at the beaches is thus highly transparent.
But without a river, the islanders had a hard time sourcing underground water in the past without modern technology.
Underneath the limestone layer is another layer of mudstone and sandstone before water can penetrate further. Thanks to this layer, water that leaks through the limestone layer accumulates. It is this characteristic that enabled an underground dam to be completed successfully.
You Can’t See the Underground Dam
Before you get too excited, we have to break it to you. You can’t see this unique dam, unfortunately. It is underground, after all. But, there is a water level observation facility close to the museum. It is an essential part of the dam for the staff to know when a discharge is necessary.
The facility also enabled water sampling and the ability to measure water temperature.
Since the dam was completed, Miyako Island’s farmers have largely benefited from it. Not only do they not need to worry about drought, but their crops have also got a boost of nutrition from the mineral-rich water accumulated by the limestone layer!
Tip: As usual, you can get a “Dam Card (ダムカード)” from the staff. Although all in Japanese, this card has the dam’s key facts written and an image of the dam printed.
Miyakojima Underground Dam Museum’s Opening Hours, Admission Fee, and Access Information
- Miyakojima Underground Dam Museum is open daily from 9 am to 5 pm except on Mondays.
- The museum is closed from the 29th of December to the 3rd of January.
- The admission fee is
- 330 yen for adults
- 220 yen for university and senior high school students
- 110 yen for elementary and junior high school students
- Miyakojima Underground Dam is a less than a 10-minute walk from Miyako Kyōei Bus’s (宮古協栄バス) Aragasuku Boraga Line (新城保良線) bus stop, Ōhara (大原).
Discover Other Stunning Beaches on Miyakojima Island
Speaking of Miyakojima Island, it is a destination filled with amazing beaches! In fact, whenever TripAdvisor announces Japan’s top 10 beaches, Miyako-jima often fills up most of their list! The beaches are also one of the main reasons the Japanese relocate to the enchanting island. So if you plan on visiting Okinawa soon or are keen on doing some watersports on your next Japan trip, Miyako Island should be your must-visit destination!
For more information, refer to our article on The Beaches on Miyako-jima Island!
