New dam construction is a rapid growth area in China, but at the same time the country is striving to develop a comprehensive rehabilitation and dam safety programme for its existing structures. Zhuang Wenzhong reports
Dams play an important role in economic and social development in China. China’s Ministry of Water Resources and the State Power Corporation has to manage more than 86,000 dams in both the water resources and hydro power generation industries. China is also one of the few areas in the world where dams are still being constructed.
Large populations living downstream from dams and rapid economic growth have led to a greater emphasis on rehabilitation and dam safety programmes. Consequently, dam safety has been improved but more work is still needed. According to an international dam safety conference held in September 1999 at the Three Gorges dam site in China, 20% of existing large to medium sized dams and 40% of small dams are unsafe or in a dangerous condition. Most of these dams were built between the late 1950s and 1960s when there were limited technological criteria, which were often ignored in favour of quick results.
There are two groups responsible for national dam safety management and supervision in China: the Dam Safety Management Centre (DSMC) which is managed by the Ministry of Water Resources; and the Large Dam Safety Supervision Centre (LDSSC) which is controlled by the State Power Corporation. The DSMC is responsible for the management and review of water resources dams which belong to the Ministry of Water Resources and its local authorities. The LDSSC is responsible for supervising the safety of hydro power dams, which belong to the State Power Corporation and its local authorities. Both DSMC and LDSSC are responsible for dam review and periodic inspection; rehabilitation; dam safety registration; training and education; and updating and renewal of dam safety monitoring systems.
Rehabilitation of unsafe or dangerous dams is urgently needed in China. In the Hunan and Hubei Provinces of the Yangtze Valley there are 209 dams in total, including large, medium and small projects. Of these, 93 dams (44.5%) have been identified as dangerous.
Most of the earth rockfill dams which are dangerous (due to past management techniques, limited design criteria and construction control) have an inadequate and low capacity for flood discharge, seepage and landslides.
Dam safety is reduced most significantly by seepage through the dam body and its foundation.
China has made a great effort in dam rehabilitation over the past ten years, and over the past two years the central government has invested 1B RMB (US$125M) into the national dam rehabilitation plan. Increasing dam height, enlarging and strengthening spillway facilities, and updating and renewing old monitoring systems are areas where work has been concentrated. A typical example of such effort is the flood control capacity of Zhanghe dam in Hubei Province, which has been increased from a 200-year return to 1000 years. According to statistics from Hubei Province, 210 medium to large sized
dams have been rehabilitated, 200 spillways have been enlarged and rebuilt, and 70 delivery culverts and shafts have been updated.
As part of the commitment to improved dam safety, a Sino-Canadian dam safety monitoring and management project has also been developed between the Ministry of Water Resources of China and the Canadian International Development Agency (CIDA). The project involved an improvement in the dam safety review process, coupled with the installation of state-of-the-art monitoring systems at ten different dams and reservoirs, two provincial subcentres and one national monitoring and control centre, plus an additional command post affiliated to the Ministry. The monitoring systems will allow automatic data acquisition and comprehensive data processing, and the preparation of surveillance reports and data to aid structural dam safety assessments. The monitoring systems were installed at the ten dam sites by the end of 1999.
Water resources dams
The Chinese central government is planning to provide 50% of the required money to help local authorities with their own safety rehabilitations at water resource dams. So it is a critical challenge for China to get financial, advanced management and technical resources for dam safety improvements.
Meanwhile, national real-time dam safety information systems, in the form of a sub-project under the National Flood Control Command System, are being implemented. The system will cover eight existing dams and three still under construction, plus the ten dams within the Sino-Canadian dam safety project.
The Ministry of Water Resources is also developing a long term plan to build a national real-time dam safety information system covering more than 198 large dams and reservoirs. Provincial sub-centres will be established for each province and dam safety surveillance will be conducted using cutting edge technologies. By then, any dam incident will be directly reported under the China State Office, making any safety issue a national concern instead of just a single dam event.
Hydro power dams
Safety issues which have been identified at ageing hydro power dams include inadequate discharge capacity, serious cracks in the dam body and excessive seepage through the foundation and bank slope side. LDSSC will establish a dam behaviour database by using advanced instrumentation, monitoring devices and technology to improve national monitoring systems. The current technology, developed both in China and abroad, will be advanced and applied continuously to meet future challenges.
A warning system is also planned and will include: dam safety monitoring to detect changes in dam behaviour; rainfall gauges and water level gauges in reservoirs to enhance early flood warning; and cutting edge technology to improve the accuracy of analysis and predictions related to dam safety. A great effort will be made to monitor dam behaviour accurately and provide information on dam performance.
Due to rehabilitation and an efficient national dam safety programme, the number of dangerous dams has been greatly reduced. As a result, the rate of dam failures has declined and remarkable benefits have been achieved in flood control and power generation. For example, after the Hongmen, Nanshui and Dahonghe dams were strengthened, pre-flood levels were raised and generating capacity was increased by an additional 57GWh/year. Progress is also being made toward a new, solid and viable dam safety programme and rehabilitation plan.
Despite these efforts, there is still demand for further improvements to the dam safety review process both for water resources and hydro power dams all over China. The authorities acknowledge the following reasons:
•Faults identified in dangerous and normal dams have not been completely treated.
•20% of large to medium sized dams
and 40% of small existing dams have been identified as unsafe or dangerous without receiving proper rehabilitation.
•Dams are getting older, so their safety conditions are constantly changing.
Many large dams have recently been completed in China and more will be constructed in the next few years. It is anticipated that numerous dam projects of significant size will be planned in the future, since approximately 86% of the vast hydro power potential in China has not yet been developed. With vast territory in China, flooding and water-logging events occur frequently. Therefore new emergencies and deficiencies may also occur for ageing dams. Monitoring instruments, automatic data acquisition and data processing systems still need to be updated and improved, or even re-established. Public awareness of dam safety needs to be improved and the legislation and regulation issues in dam safety management strengthened. The following issues will also need to be addressed in the future:
•Proper safety management of dams and reservoirs and adequate flood control.
•Dam break analysis and emergency preparation plans.
•Structural safety and risk assessment of all retaining structures.
•Summary data necessary to register and classify dam structures.
With the above in mind, China’s authorities are planning an integrated approach to dam safety programmes
and dam rehabilitation for the 21st century.