Geheyan Dam

Geheyan Hydropower Station is built on the main stream of the Qingjiang River, a tributary of the Yangtze River in Changyang County. It lies 62 kilometres upstream from the river’s confluence with the Yangtze and 9 kilometres away from Changyang County seat. The project adopts a concrete gravity arch dam with a maximum height of 151 metres.

The total storage capacity of the reservoir stands at 3.4 billion cubic metres. The installed capacity of the power station reaches 1.2 million kW, with a firm power output of 187,000 kW and an annual power generation of 3.04 billion kWh. The project mainly generates electricity, while also providing flood control and navigation benefits. A flood control storage capacity of 500 million cubic metres is reserved. It can cut down flood peaks in the lower reaches of the Qingjiang River and stagger the arrival time of Qingjiang floods and Yangtze River floods. As a result, the need for the Jingjiang Flood Diversion Project can be reduced, and flood diversion can be postponed.

Construction broke ground in January 1987. The first generating unit came online in June 1993, and the whole project was completed in 1995.

At the dam site, the mountain tops on both banks are roughly 500 metres above sea level. During the dry season, the river width ranges from 110 to 120 metres. The lower 50–60 metres of the river valley feature steep banks. The upper valley is asymmetrical, with a steep right bank and a gentle left bank.

The dam foundation consists of Cambrian Shilongdong limestone. The strike of the rock formation is nearly perpendicular to the river flow, dipping upstream at an angle of 25° to 30°, with a total thickness between 142 and 175 metres. The upper abutments on both banks are composed of interbedded limestone and shale of the Pingshanba Formation. The basic seismic intensity is Grade VI, and the design seismic intensity is Grade VII.

The catchment area above the dam site covers 14,430 square kilometres. The multi-year average discharge is 403 cubic metres per second, and the average annual runoff totals 12.7 billion cubic metres. The measured maximum flood peak discharge is 18,900 cubic metres per second, and the minimum dry-season discharge is 29 cubic metres per second. The multi-year average sediment concentration is 0.744 kg per cubic metre, with an annual sediment load of 10.2 million tonnes.

The dam is designed for a once-in-a-millennium flood with a discharge of 22,800 cubic metres per second, corresponding to a reservoir water level of 202.77 metres. It is checked against a once-in-ten-thousand-year flood of 27,800 cubic metres per second, with a corresponding water level of 204.59 metres and a storage capacity of 3.77 billion cubic metres. The normal pool level is 200 metres with a storage capacity of 3.4 billion cubic metres. The dead water level is 160 metres, and the usable storage capacity reaches 2.2 billion cubic metres. The reservoir inundates 1,138 hectares of cultivated land and requires the resettlement of 26,086 residents.

The Qingjiang River is the first major tributary flowing into the Yangtze after the Three Gorges. It stretches 423 kilometres with a drainage area of 17,000 square kilometres, mostly mountainous terrain. The basin enjoys a mild climate with abundant rainfall. The annual precipitation averages about 1,400 millimetres, and the average river discharge is 440 cubic metres per second. The development of the Qingjiang River can produce abundant electric power, alleviate flood control pressure on the Yangtze River, and improve inland water transportation in mountainous southwestern Hubei. It bears great significance for the economic development of Hubei Province and ethnic minority areas in southwestern Hubei