Source: Cuiying ZHENG, IWHR, CHINCOLD

Henan Province, China was hit by heavy rains in late July. Some media reported that a 20-meter crack appeared in the Yihetan dam in Yichuan County, Luoyang and the retaining dam was blasted to release flood on 21 July.

According to experts from the local water department, with a height of about 2m, Yihetan is a concrete overflow barrier across the river to raise water level for irrigation. This project does not conform to the definition of the “large dam” given by the International Commission on Large Dams: A dam with a height of 15 metres or greater, or a dam between 5 metres and 15 metres impounding more than 3 million cubic metres.

Since July 19, Yichuan County of Luoyang City, Henan Province has suffered heavy rainfall. The junction connecting the Yihetan overflow barrier and the embankment dyke (left bank) had a breach due to scouring which spread quickly and developed to 20m wide on 20 July night, endangering the safety of the left dyke.

In order to avoid flooding caused by dyke break, the overflow barrier was blasted at about 6 a.m. on July 21, which formed a flood diversion outlet with a width of about 5m and a depth of about 1m to release flood. The water level of Yihe River dropped rapidly thereafter and the river dyke is now under repair.

The breach at the junction connecting the Yihetan overflow barrier and the embankment dyke (20 July night)

The water level of Yihe River dropped with the diversion outlet (21 July morning)