Shohoji River Erosion Control Facilities

About the Shohoji River Erosion Control Facilities

The Shohoji River Erosion Control Facilities (正法寺川砂防施設, Shōhōjigawa Sabō Shisetsu) are a group of stone check dams and river groynes built by Yamagata Prefecture between 1922 and 1927 on the Shohoji River in Shimo-Oginoto, Tendo City, Yamagata Prefecture; in 2005, 29 of them were each listed as a Registered Tangible Cultural Property.

The Shohoji River rises on Mount Amayobari (雨呼山) and runs through the southeast of Tendo before joining the Kuratsu River and, eventually, the Mogami. Yamagata Prefecture gives its length, including the Kuratsu, as 16.2 kilometres, with a catchment of 34.3 square kilometres. For generations it fed irrigation channels downstream, and in heavy rain it flooded them.

The great flood of 1913 set the works in motion. The first phase ran on the Kitasawa (north ravine) between 1922 and 1925, the second on the Minamisawa (south ravine) in 1926 and 1927. According to the prefecture, the Kitasawa received 21 stone dams, 2 stone groundsills, 10 stretches of stone revetment and 32 wire-gabion groynes, and the Minamisawa 15 stone dams and 6 revetments. The 29 best-preserved structures make up the Shohoji River Erosion Control Facilities on the national register.

Three Ravines, One System

The Shohoji River Erosion Control Facilities are spread across three ravines in the upper Shohoji. On the Kitasawa the dams are numbered from No. 1 at the top downward, with an extra dam, No. 1-Ko, set about 55 metres below No. 1. There is no No. 11 among the registered Kitasawa dams; the count jumps from 10 to 12.

Dams No. 1 to No. 10 are dry-laid (Karazumi), built in 1922 and 1923. From No. 12, about 190 metres below No. 10, the method changes to diagonal Tanizumi coursing bonded with mortar, continuing to No. 15 between 1923 and 1925. Below No. 15 lies the Kitasawa Iron Wire Gabion Groyne of 1924, and below the No. 16 dam (1925) the Kitasawa Downstream Iron Wire Gabion Groyne.

Just above the Kitasawa No. 2 dam, the Tanukisawa ravine joins from the right. Three small mortared dams of 1923 are packed into its narrow bed, 30 to 35 metres apart.

Eight of the second-phase dams on the Minamisawa are registered, built in 1926 and 1927 and numbered from No. 5 to No. 14 (No. 9 appears as No. 9-1; Nos. 10 and 11 are not on the register). All but No. 8, which is dry-laid, are mortared tanizumi. The Agency for Cultural Affairs notes that the Minamisawa dams were built to an almost uniform height of 10 shaku, about 3.0 metres.

Technique and Significance

What makes the Shohoji River Erosion Control Facilities rewarding is the way the masonry changes as you move down a single small river. On the upper Kitasawa the dams are dry-laid dressed stone in level courses (Nunozumi); lower down they turn to mortared tanizumi. The Agency for Cultural Affairs calls the Kitasawa No. 12 dam one of the early mortared erosion-control dams in Japan, and singles out the dry, level-coursed dressed stone of the Kitasawa No. 1 dam as a rare construction.

The groynes use Kawasaki-type iron wire gabions, baskets machine-woven in a hexagonal mesh and filled with stone. They are stacked two high with more gabions draped over the top like saddles, a form called kurakake. The Agency describes the downstream groyne as one of the sturdiest forms of the flexible gabion groyne. Yamagata Prefecture presents the combination of dry and mortared stone dams with saddle-hung groynes as an early example nationwide.

The surveys were led by prefectural engineer Kohata Chōmei (木幡長命), and the site supervisor is said to have been Satō Sōichirō (佐藤總一郎), an assistant civil engineer. The 29 structures were registered in 2005 in two batches, 19 on 12 July and 10 on 10 November. The criteria differ: the dry-stone Kitasawa dams as structures difficult to reproduce, the mortared dams as contributing to the historic landscape, and the two groyne sets as models of design.

Visiting the Shohoji River Erosion Control Facilities

The Shohoji River Erosion Control Facilities are not a developed sightseeing spot, and neither Yamagata Prefecture nor Tendo City publishes a walking route or parking area. The nearest station is JR Tendo-Minami on the Ou Line (Yamagata Line); the valley lies in the foothills about 4 to 5 kilometres east of it in a straight line on the map. No bus runs close, so plan on a car or taxi to get near the stream, then walk in.

As open-air river structures they have no admission fee or opening hours, and official sources mention no restriction on photography. On the upper Kitasawa the dams follow one another every few dozen metres, so once you find one the next is easy to trace. The ravines are steep and the footing poor: stay away after rain or when the water is high, and expect snow to block the streams in winter. Go equipped as you would for a forest walk.

For current conditions, contact the Commerce and Tourism Division of Tendo City (+81 23-654-1111).

Names and Readings

The Japanese name of the Shohoji River Erosion Control Facilities is read Shōhōjigawa Sabō Shisetsu. The three ravines are read Kitasawa, Tanukisawa and Minamisawa in both the Agency for Cultural Affairs database and the prefecture's materials.

For the No. 1-Ko dam, the Agency and the prefecture read 甲 as kō, while Tendo City's tourism site reads 甲石 as kabutoishi. Tendo City's list also includes a Kitasawa No. 11 stone dam, which does not appear on the Agency's database or in the prefecture's list of registered structures. This site follows the Agency and the prefecture.