Dodogawa Sunadome (Stone Check Dams)

A Staircase of Stone in a Granite Valley

The Dodogawa Sunadome (堂々川砂留群, Dōdōgawa Sunadome-gun) are a chain of dry-stone check dams on the Dōdōgawa stream in Kannabe-chō, Fukuyama City, Hiroshima Prefecture, begun in the late Edo period and repaired and raised ever since; eight of them were registered as Registered Tangible Cultural Properties on 3 August 2006.

A sunadome, literally a "sand stop," is not a reservoir. It is a barrier built across a mountain stream to catch the sand and gravel that heavy rain strips off the slopes. Water spills over the top and the sediment stays behind, flattening the streambed so that the next flood arrives with less force. Nearly two centuries on, the Dōdōgawa dams are still doing that work.

Six of the registered dams stand on the main stream and carry numbers, counted upstream from No. 1. The other two, Tobigasako and Uchihiro, guard side valleys on the right bank. Registration numbers run in sequence from 34-0075 for Dodogawa No. 1 Sunadome to 34-0082 for Uchihiro, and all eight belong to the national government through the Ministry of Land, Infrastructure, Transport and Tourism.

Why a Small Stream Needed So Much Stone

The Dōdōgawa is only about 4 kilometres long. It rises on Higashiyama in Higashinakajō and runs south into the Takaya River, itself a tributary of the Ashida. Hiroshima Prefecture's erosion-control office describes a catchment of Cretaceous biotite granite and rhyolite, with the granite weathered to a great depth. Rotten granite crumbles into loose grit, and grit is exactly what a cloudburst carries downhill. On most days the stream is barely visible in its raised bed. After a downpour it turns into a torrent of sand.

The prefecture cites a letter in which the lord of the Fukuyama domain, troubled by typhoon damage in 1641, wrote to his senior retainers; landslides were becoming a regular problem from about then. Local memory supplies a grimmer date. According to the history compiled by the Dōdōgawa Hotaru Dōkōkai, a residents' firefly conservation group, the embankment of Ōhara Pond at the head of the valley gave way in 1673. The debris flow that followed is said to have buried the Bingo Kokubunji temple downstream and killed 63 people.

Serious dam building on the Dōdōgawa is thought to have followed that disaster. The same group notes that a land survey of 1700 lists sand-choked fields along the "Tōtō" valley and takes this as a sign that some kind of sand barrier already existed. The domain went on to build stone check dams across much of its territory, and the eight on the Dōdōgawa survive as its best-known examples.

Six on the Main Stream, Two in the Side Valleys

The dams follow the stream in numerical order. The Agency for Cultural Affairs places No. 2 about 180 metres above No. 1, No. 3 about 60 metres above that, No. 4 about 130 metres further, No. 5 about 180 metres further and No. 6 about 220 metres beyond No. 5. The whole sequence fits into roughly 770 metres of valley.

Their size varies enormously. Dodogawa No. 1 Sunadome, at the bottom, is a fragment 9.6 metres long and 3.2 metres high. No. 5 rises to 8.8 metres, and No. 6 at the top is 56 metres long and 13 metres high. Even the addresses shift along the way: No. 1 lies in Yuno, Tōtō-dani; Nos. 2 to 4 in Yuno, Sakoyama; Nos. 5 and 6 in Nishinakajō, Tōtō-dani.

The Agency dates each dam separately. Most are assigned to the late Edo period, between 1751 and 1829, while No. 3 is placed around 1832 and No. 5 around 1835. Every one of them was extended or rebuilt later, in the Meiji era (between 1868 and 1911) or the early Taishō era (between 1912 and 1925), so each wall carries a visible change of masonry style somewhere in its face.

The two side-valley dams sit outside the numbering. Tobigasako stands on the right-bank tributary that joins above No. 5; at 39 metres long and 11 metres high it is second in height only to No. 6. Uchihiro lies in the upper part of the right-bank tributary that joins above No. 6 and is 21 metres long and 3.8 metres high. The Agency dates both to the late Edo period and records two rounds of extension at Tobigasako, in the Meiji and Taishō eras.

What the Registration Recognises

All eight were registered under the criterion of contributing to the historic landscape of the country. Individually, what catches the eye is the anatomy: large granite blocks stacked in steps, upper courses raised in Nunozumi or tanizumi masonry, wings of Ranzumi random walling and corners locked with Sangi-zumi quoins. Taken together, they let you compare late Edo stonework with Taishō stonework within a single valley walk. That is the point the Agency makes when it describes No. 2 as showing the period character of stone masonry techniques.

None of this is ruin. The dams remain working flood-control structures, and the prefecture records that No. 6 did its job during the heavy rain of June 2016, when the seasonal rain front caused damage across the Bingo region.

Walking the Valley and Getting There

The natural base is Dōdō Park, laid out on the sediment flat trapped behind No. 6. The firefly group records that the prefecture built it as a waterside park in 1976 and that Fukuyama City now manages it. It has a 344-metre watercourse lined with rough fieldstone and neatly clipped planting. The prefectural tourism association lists it as open every day, free of charge, with parking for about 50 cars.

From the park you come out onto the crest of No. 6 and look straight down its 13-metre face. Follow the stream downhill from there, past No. 5 and No. 4, and the changes in scale and masonry unfold one dam at a time. Nos. 1 to 4 sit close to the houses of Yuno. Paths along the streambed can be muddy after rain, so wear sensible shoes.

Tobigasako and Uchihiro lie up right-bank side valleys, away from the main stream. According to the Dōdōgawa Hotaru Dōkōkai, Uchihiro is northwest of the park toilets. The side-valley paths are unimproved and slippery after rain.

By car, allow about 20 minutes from the Fukuyama-Higashi interchange on the Sanyō Expressway. By public transport, take a taxi of about 15 minutes from Kannabe Station on the JR Fukuen Line; or ride the Ikasa Bus service between Fukuyama and Ibara for about 35 minutes from JR Fukuyama Station to the Yuno Iriguchi stop and walk about 20 minutes; or walk about 30 minutes from Yuno Station on the Ibara Railway. These times come from the prefectural tourism association and were checked in September 2026.

All eight dams are outdoor river structures with no admission charge and no booking. No official photography restrictions are published, but stay off the crests and spillways.

Fireflies and Spider Lilies

The Dōdōgawa Hotaru Dōkōkai has spent years clearing the streambed, cutting grass and releasing the freshwater snails that firefly larvae feed on. On June evenings fireflies drift in front of the dams. Autumn belongs to cluster amaryllis, and the group has planted white and yellow forms alongside the usual red.

For the stonework itself, winter and early spring are best, when the vegetation dies back and the joints between the blocks are easy to read.