The increasing number of dams in existence, the lapse of time, and the effects of ageing, are all acting to increase the probability of dam failure. In the last century there have been dam failures in most countries, and some have resulted in grievous disasters and huge economical losses — for example South Fork in the US, Vajoint in Italy and Malpasset in France. Although no high dam or large reservoir has yet failed in China, it is a profound lesson that a catastrophic storm in August 1975 broke both the Banqiao and Shimantan dams in Henan.

The potential economic and social losses of dam failure have prompted governments to develop safety-related legislation and establish safety management organisations, and there are only a few small countries which have not passed specific laws on dam safety. Dam safety legislation, management and specific measures vary between different countries, as do the sizes and numbers of dams and the likely effects of failure. A World Bank report of 36 questions on dam safety covering 26 countries, published in July 1994, bears out this variation. In most countries an appropriate government department is responsible for dam safety management, while a few countries have assigned the responsibility to the dam owners. It is encouraging that countries where hydro development has been rapid and which have many dams have paid great attention to dam safety and taken forceful measures.

In Canada, for example, 80% of the water resources are utilised and there are now 580 large dams. The Canadian Dam Safety Committee has developed the Canada Dam Safety Regulations, while the federal government authorised the state and parliament to develop corresponding legislation. Administrative agencies were set up in the Canadian government for water resources and hydro power, while hydro power bureaus in the states were made responsible for routine management. Canada pays great attention to dam safety monitoring, and automatic monitoring systems are installed in every dam.

In the US there are more than 80,000 dams, 90% of which are earthfill dams, and almost 100 of which are higher than 100m. The US basic national law on dam safety is the National Dam Safety Act (Public Law 92-367), passed by Congress in 1972 and revised in 1984. This was followed, in 1979, by the Federal Dam Safety Guidelines.

In Italy there are 591 large dams and 800 small dams, with an average age of 45 years. The largest dam owner is the Italian National Electric Power Bureau. Dam safety is managed under Presidential decree No 1369, issued in 1959 and revised in 1982. It has three aspects: installing monitoring systems, establishing effective supervision by the owners and enforcing supervision by the government.

Chinese experience

China is a country with abundant water resources — exploitable hydro power resources in China are estimated at 378GW. At the end of 1998, installed hydro capacity totalled more than 60GW. There are around 84,000 reservoir dams now in existence (excluding the island of Taiwan), among them 19,000 dams higher than 15m.

Chinese dams are divided into those for water resources and for power generation. The first category comes under the jurisdiction of the Ministry of Water Resources (MWR), while the second is the responsibility of the State Power Corporation. Both these Ministries were previously part of the Ministry of Water Resources and Electric Power (MWREP). Within the provinces or autonomous regions the electric power authority bureaus are responsible for the management of the dams associated with their hydro power stations, while the power plants are responsible for dam operation. Thus, dam safety management has three levels: ministry, network or province, and power plant.

In 1998 the Ministry of Electric Power was disbanded and replaced by the State Power Corporation of China. Similarly, the electric power bureaus became provincial electric power companies. This did not change the principle of three-level management.

The Large Dam Safety Supervision Center (LDSSC) of the State Power Corporation was set up in 1985, and was soon followed by the Dam Safety Monitoring Center (later known as the Dam Safety Management Center, under MWR). The establishment of these two centres was a milestone in managing dam safety.

In response to the Interim Statute issued by MWREP in 1987, LDSSC performed a ‘first round dam safety periodic inspection’, in which it undertook a general survey of the dams under its jurisdiction. It lasted 12 years, and saw completion of periodic inspections of 96 dams, focusing on those dams that were constructed before 1980. The LDSSC found some dams with safety deficits, such as inadequate discharge capacity, serious dam body cracks, or excessive foundation seepage. Measures had to be taken to remedy the faults. The first round inspection also eliminated some concerns over safety and provided a scientific basis for general remedial measures to improve dam safety conditions, promoted the implementation of rehabilitation projects and the use of monitoring devices, and permitted large scale data analysis. As a result safety awareness of officials at all levels increased, dam safety professionals were trained, and dam safety archives were augmented. Periodic inspection has become an important institution.

A second round of periodic inspections is now being carried out, in which 132 dams will be examined. By October 1999 14 dams had completed the second periodic inspection.

In step with the first round periodic inspection, programmes of rehabilitation and treatment were extensively implemented. Measures included increasing dam height, treating cracks in the dam body, taking measures to treat seepage in dams and their foundations, modifying discharge devices, modifying monitoring devices and so on.

Thanks to a great effort for over 10 years, with extensive commitments in financial and material resources, the rehabilitation programme significantly improved dam safety, with remarkable benefits in generation and flood control. For instance, after the Hongmen, Nanshui and Dahonghe dams were strengthened the pre-flood reservoir levels were increased and generating capacity was increased by 57GWh/year.

An extreme flood event that occurred in 1998 was a severe test for the hydro power dams in China. Many dams stood the test of flood events with return periods of 20, 50, 100 or even 400 years.

After the Guidelines for Dam Safety Register of Hydropower Stations were issued in 1997 LDSSC accepted the implementation of a register for dams. LDSSC implemented and managed an annual recheck and assessment for power. By 1998, LDSSC was able to classify 110 hydro power dams: among them, 100 dams were assessed as class A.

Dam safety and flood control

China’s vast territory and varied climates mean it must be prepared for extreme flood and drought events every year. Chinese flood control is governed by a single State Flood Control and Drought Relief Headquarters. Dam safety is the basis of flood control as regards hydro stations. In the relationship between flood control and generation, dams play an important role, managing discharge, cutting peaks in flood control, relieving downstream flood pressure and reducing the resultant losses.

For example, a basin-wide extreme flood event occurred in the Yangtze river in 1998, and the hydro power dams performed valiantly in the battle against flood. The reservoirs of Fengtan, Wuqiangxi and Zhexi hydro power stations cut the inflow peak by 47.1%, 31% and 6.1%, respectively, impounding in total an inflow peak of 2.7 x 109m3. This equals a 1m gain on the past highest level of Dongting lake, and it greatly relieved the pressure on the lake. In order to guarantee the normal operation of the Beijing-Jiulong railway and Nanchang-Jiujiang highway, the reservoir of the Zhelin hydro power station controlled the discharge throughout the flood and the reservoir level exceeded the historical maximum level by 1.32m. The safety of Zhelin dam withstood this severe test.

Among the general surveys conducted by LDSSC in 1985, most dams showed problems with monitoring processes or equipment. Most dams had the following problems:

• Incomplete monitoring equipment.

• Obsolete monitoring devices.

• Out of date monitoring methods.

• Poor precision of instruments.

• Poor condition of the monitoring work.

The Dam Safety Monitoring Modification Programme of Hydropower Stations was published by the former Ministry of Energy in 1992 in direct response to this finding. The programme initiated modification work on monitoring devices at dams covered in the first round dam safety inspection. After eight years of effort, modification is now complete at most dams, and extra monitoring devices have been installed to improve the monitoring precision, stability and reliability of current devices.

On several of the dams automatic monitoring systems have been installed. It is more and more obvious that dam safety monitoring devices must play the role of ears and eyes in ascertaining the operational efficiency of the dam, as well as detecting latent deficiencies in good time, verifying design and guiding construction. Some brief instances illustrate their value:

• Information on foundation leakage, abnormal values of the plumb lines and cracks imply that the bedrock on the right bank of Meishan dam may have moved: emergency measures were taken in good time to avoid a severe failure.

• Monitoring devices were installed during modifications at Ship Lock 2 at Gezhouba. A system was installed to provide continuous automatic monitoring. The power plant could analyse the variation in lock foundation uplifts and lock levels and ascertain the operation regularity.

• Seepage monitoring at Hongmen main dam was modified. The new data acquisition system soon captured abnormal results from the piezometric level of B10 at the fault F23 of the main dam foundation. By analysing information from the new monitoring equipment experts determined that the contact face between the clay core and foundation formed a centralised seepage passage. The reservoir level was drawn down and a significant failure was avoided.

• In several dams the stable temperatures of the dam body were found to be higher than the original design value. The assumptions made in adopting reservoir temperature were changed so as to increase the grouting temperature of the dam body, speed up the construction and produce economical benefits.

• A vacuum laser alignment automation monitoring system at Fengman dam rapidly and effectively measured the extent of dam deformation at critical times during a flood event that occurred in 1995, and provided a reliable basis for decision making.

A history of instrumentation

In the 1950s China had no technical criteria on dam safety monitoring. Along with the improvement of dam safety legislation, standards and documents were developed. These documents standardised and guided dam safety monitoring work.

They included:

•Criteria of dam safety monitoring technology for concrete dams.

•Criteria of dam safety monitoring technology for embankment dams.

•National standards for Carlson-type observation instruments.

•Series on types of monitoring instruments for embankment dams.

•Series on types of monitoring instruments for concrete dams.

China had begun to develop and manufacture monitoring instruments in the mid 1950s. Since then, and especially in the last decade, China has made great progress in the principle, variety and performance of instrumentation. More than ten kinds of instruments (including the Carlson-type, vibrating-wire, capacitive and the step motor) have been developed for concrete dams, and rather fewer for embankment. To meet the needs of automated systems, a series of new instruments, especially deformation monitoring devices, have been developed. They include plumb line co-ordinators and wire alignment transducers. For example:

•New step motor-type plumb line co-ordinators and wire alignment transducers were equipped with two collimating devices and two data bars, to overcame early shortcomings of low malfunction and self-calibration.

•The problems of temperature, humidity and data that affected the performance of capacitive instruments were analysed and studied to further improve instrument performance.

•The three-dimensional plumb line co-ordinator was developed to reduce costs, simplify monitoring systems and implement automatic monitoring for dam body settlement. It is now being improved further. The plumb line co-ordinator uses an electromagnetic differential principle: by using the magnetic field as medium, the transducer can be totally sealed, reducing malfunctioning.

•With the construction of high dams and division projects of high water head, a new hydraulic-balance Carlson-type strainmeter and jointmeter have been developed, and traditional Carlson-type instruments have been adapted to indicate standing external water pressure. The measuring scale of the Carlson-type jointmeter has been greatly enlarged.

•The large scale displacement meter supports construction of high embankment dams and high concrete dams. The different type two-dimension and three-dimension jointmeters are used to measure the peripheral joints of high concrete face rockfill dams.

•In the early 1990s, China applied GPS technology to monitor geodetic deformation. In 1998, GPS was installed at Geheyan dam to monitor external deformation.

•In the early 1970s, China began work on laser collimating systems, and at the end of the decade began studying vacuum laser collimating systems. In 1981, such a system was used in the crest of Taipingshao dam. In the late 1990s, progress has been made on new measures and new technology, such as the application of sealed laser luminaire.

•Work has also been done on using optical fibres and CCD technology to study the new transducers. Some products have been developed that make use of fibre optics’ advantages of heat and cold-resistance, humidity-resistance and lightning resistance. Development is still under way.

•In the mid 1970s, China began to study remote measurement using plumb line co-ordinators and Carlson-type instruments. By the1980s, automation installations had been developed but they were not suitable for practical application. It was not until the 1990s that single-purpose or multiple-purpose automatic monitoring systems were installed, at more than 20 dams.

New electronics, computer technologies and communication technologies have significantly improved the reliability and applications of automatic systems. They have been used at projects including Chencun, Xinanjiang and Feilaixia dams. Distributed dam safety monitoring systems with high reliability will be the focus of automation in future: when considering cost-benefit ratios, indigenous automation systems have a bright future.

Data acquisition and analysis

Dam safety data analysis and information processing began late in China. However, the number of large projects starting construction in the 1980s and 1990s, the implementation of periodic inspections and the rapid development and extensive application of computer technology are all contributing to the rapid development of data analysis and processing technology.

Three conventional mathematical models (statistical, deterministic and hybrid) have been used extensively for quantitative analysis of dam safety monitoring. Based on these models, Chinese scholars have developed multiple-point and multiple-dimension models. The multiple-point model is a unified model established for multiple effect quantities from a group of points for the same item. The factor number of this model is much greater than that of a single point model, and model formation is more sophisticated. Compared to the single point model, it can reflect simultaneously the time and space states of the quantities and can analyse dam behaviour effectively.

Chinese scholars have also studied the form of factor, estimation methods for parameters, the confidence region and the formula to establish a unified multiple-dimension model, forming a complete mathematical model technology to monitor dam displacement in time and space. They have also applied neural network technology in analysing dam monitoring data. The neural network model is a latent model with self-organising and self-adapting functions. It is rich in flexibility and manifestation. The stress, strain and displacement models established, based on the neural network model, provided better results than those from the traditional statistic model.

Research on synthetic technologies of dam behaviour has been combined with a work on real subjects, such as the Three Gorges project. Researchers designed a tree-type structural system for synthetic evaluation of monitoring behaviour. This system can cover monitoring results from all monitoring points of each hydraulic structure of a hydro power project and can perform synthetic evaluation.

Regarding evaluation indicators, Chinese scholars have proposed the concept of normalisation with aspects of measured values and behaviour evaluation, designed the evaluation vector of five levels and demonstrated the normal degree of a series of measured values of a point from two angles of number expression, and the variation tendency of measured values. In this way the normal degree of a structure can be reflected by syn-thesising level for level. The eval-uation methods were studied from various angles, in-cluding the hybrid synthetic judgement method, hybrid model identification method and sudden change theory. Regarding synthetic analysis, Chinese scholars have studied the weight assign-ment methods of all concatenation factors, including level analysis weight assignment, main component analysis weight assignment and combination weight assignment. The above-mentioned systems, indicators and methods are combined to form a complete multiple-level evaluation system of measured dam behaviour, convenient for practical application.

Design values of dam stress and uplift are generally regarded as monitoring indicators but identifying dam deformation monitoring indicators is complex. In recent years, Chinese scholars have spent much time on this, using the confidence region method, computer simulation calculations and mechanical calculations. It is now usual to adopt the confidence region method, regarding the boundary of the mathematical model confidence region as the monitoring line. In recent years, Chinese scholars have achieved many research results, such as the requirements of mathematical models to be as monitoring basis; the approach required to verify, calibrate and improve the model; determination of the branching point of the multiple-point model confidence belt; and determination of the multiple-dimension model confidence region. It is important to develop monitoring indicators by using mathematical models to estimate the normal threshold which may be produced in future.

The artificial analysis method is used to perform computer simulation calculations by means of mathematical models based upon the long term real historical conditions and combination conditions The most unfavourable effect is used as a monitoring indicator. The mechanical calculation method is used to search for the corresponding deformation value of the structure as a monitoring indicator — physical mechanical calculations are used to determine safety thresholds. For instance, at Three Gorges dam, the deformation monitoring indicators are classified as A, B and C. After the three-level indicators are expressed using mechanical definitions and classification standards, deformation monitoring indicators are developed for two typical dam blocks using the theory of viscoelasticity and viscoplasticity.

In parallel with monitoring systems, automation and data acquisition, China began to research and develop information processing systems. In the 1980s, data management software for PCs was developed to monitor hydro power plants, and by the 1990s some dams had information processing systems to process the monitoring results. In some cases these are being extended to decision making and network functions. For example:

• A PC-based data processing system was developed in 1989 for Longyangxia dam for storing and managing data, and calculating statistics, establishing models and curve outputs and reporting.

• Dahua hydro plant installed a data management system in 1995, using a Windows NT platform and operating in real time. It can perform off-line analysis and on-line monitoring for all monitoring instrumentation The same software is applied in ten or more dams, including Yantan, Daguangba and Fengtan.

• At Three Gorges a safety monitoring database management system was installed for the construction stage, and a safety monitoring decision making system is being developed.

•General design of the safety monitoring information processing system for Xiaolangdi, which is under construction, was completed in 1996 and implemen-tation began in 1997. It includes central control, input system, output system, synthetic analysis and inference system, multiple-base routines, databases and management systems for methods, models, intellectual property, diagrams, images etc.

•Northeast Electric Power Network established a dam safety monitoring information system for eight dams in its jurisdiction, including Fengman, Yunfeng and Taipingshao. It is a wide-region network adopting the client/server system structure. Its core is a distributed database. Its data processing analysis system has functions including synthetic examination and analysis, mathematical model establishment, data management, diagram and chart output, calculation and analysis for internal monitoring instruments.

Facing the future

The tasks confronting us are arduous. Legislation on dam safety must be strengthened. The deficiencies of dams, dams at risk and normal dams still have not been addressed completely. The general level of indigenous monitoring instruments and automatic systems must be improved and it is still difficult to modify monitoring devices. Safety awareness, personnel quality and management level should still be improved.

At the same time, existing dams are deteriorating as they age. As a result safety conditions are constantly changing.

As dam engineering develops, a number of new dams are entering operation, including large projects such as Ertan and Xiaolangdi. The construction of the huge Three Gorges project, which attracts worldwide attention, is a new challenge to dam safety supervision work.

China’s territory is vast, and floods and other natural disasters occur frequently. The El Nino and La Nina phenomena remind us not to overlook flood events and effects. In summary, for dam safety work, the burden is heavy and the road is long.

Since dam failure is a low probability event and China’s hydro power dams are well designed, constructed and managed, no hydro power dam break has occurred in China. But this makes it easy to lower the guard of officials and public, weakening safety awareness. Some unsafe practices are seen frequently, for example recklessly felling trees, reclaiming land and building structures within the reservoir area; causing wanton damage to electric power equipment; erecting obstructions in downstream channels. Legislative awareness and safety awareness are still weak, and for their part dam owners and personnel have not given safety the prominence it deserves. The warning systems are not in place. Work has not yet begun on dam-break analysis and an emergency action plan. The safety awareness of the whole society must be strengthened: only then can dam safety can be fully guaranteed.

The Chinese government recently conducted a significant reform of the electric power industry, incorporating it into enterprises. It has reiterated that the responsibility of dam safety belongs to the owner, and has stipulated that ‘who governs the hydro power station, undertakes the responsibility of dam safety’. This stipulation prompted efforts to strengthen dam safety management in real earnest. Dam owners must have the responsibility of guaranteeing dam safety operation while their power plants are producing benefits. But since dam safety is involved with the public safety, and closely related with national economy, people’s livelihood and social safety and stability, it should not just be a function of the company. The government must fulfil a supervisory function, so the governmental supervision and enterprise responsibility supplement each other.

The governmental functions of the former Ministry of Electric Power have now been transferred to the State Eco-nomic and Trade Commission. At the beginning of 1999, the State Economic and Trade Commission and State Power Corporation of China issued documents to define the practice of the LDSSC in governing dam safety works. They emphasised that LDSSC must fulfil the functions of ‘programme, supervision, guidance and service’ for the safety of hydro power stations. In this new setup, LDSSC’s duties fulfil two kinds of service, meeting the needs of the State Economic and Trade Commission and the State Power Corporation of China. The former is a service for government, giving counsel and advice on dam safety management of hydro power stations. The latter is a service for owners, by which LDSSC should not only implement national policies and guidelines, supervise and guide dam safety management works, but also completely bring into play the enthusiasm and initiative of the owners.

When we are stepping forward into the 21st century, we must be sure to fasten tightly the string of dam safety which is linked to lives and properties.

A history of safety legislation

1980: Water Code of People’s Republic of China.
1983: Guidelines for Hydropower Projects, issued by MWREP.
1985: Establishment of Large Dam Safety Supervision Center.
1987: Interim Statute for Dam Safety Management of Hydropower Stations, issued by MWREP, the first comprehensive legislative document on dam safety management of hydro power stations.
Start of the First Round Dam Safety Periodic Inspection, carried out by LDSSC.
1988: Practical Code for Safety Inspection of Existing Dams.
Statute for Flood Control Management of Hydropower Plants, issued by the Ministry of Energy.
1991: Dam Safety Management Regulation for Reservoirs, issued by the Council of State.
Flood Control Regulations of Peoples Republic of China, issued by the Council of State.
1992: Start of the Dam Safety Monitoring Modification Programme of Hydropower Stations, under the Ministry of Energy.
1995: Electric Power Code of Peoples Republic of China.
1996: Guidelines for Dam Safety Register of Hydropower Stations.
1997: Interim Statute (1987) revised and issued as Statute for Dam Safety Management of Hydropower Stations.