Dam rehab to improve irrigation in Kyrgyzstan5 October 2011
Turkish company Temelsu has been involved with a World Bank supported project to rehabilitate irrigation projects in the Kyrgyz Republic.
Following the collapse of the former Soviet Union and the ensuing changes in organisations and management systems, many large dams and agricultural infrastructures of the new Central Asian Republics started to suffer significant problems. Likewise, economic shortcomings and lack of maintenance have meant that the majority of irrigation systems, dams and appurtenant components of Kyrgyzstan have also aged and deteriorated, resulting in significant reduction in agricultural products and incomes. This has had crucial social and economic impacts on local people, and created environmental and ecological problems too. As a result, the Government of Kyrgyz Republic has initiated a long term, World Bank supported Irrigation Rehabilitation Project for its irrigation systems and storage reservoirs.
Within the broad scope of the overall rehabilitation project, the urgent and essential component was planning prioritised actions for the safety of irrigation dams and their operational improvements. Seven of these dams were selected by the World Bank Mission in 1997 for rehabilitation or completion. These dams were generally in poor condition, gates and valves were exhausted after many years of service, steel works and electric equipment needed replacement, while piezometers were out of order and needed to be cleaned or replaced. Some of them had considerable seepage, therefore surface protection and drain systems also needed rehabilitating.
During the first phase of the World Bank-financed Kyrgyz Republic Irrigation Rehabilitation Project (IRP), Orto Tokoi and Karabura dams were selected for rehabilitation. The project started in October 1997 and was awarded to a joint venture between Temelsu International Engineering Services (Turkey) and Gibb (UK). This phase of the project was successfully completed in May 1998. During phase-II, which was started in September 1998 and completed in December 2001, five dams (Papan, Bazaar Kurgan, Kirov, Ala Archa and Spartak dams) and their relevant irrigation infrastructure of 95,000ha were rehabilitated. The main tasks included:
• Carrying out a comprehensive site examination for each dam.
• Reviewing all available data including hydrology, geology and seismicity of the dam sites, construction, operation, and maintenance records.
• Evaluating the risks and recommending remedial works to improve safety to acceptable levels.
• Preparing detailed designs for the proposed measures and tender documents and construction supervision.
In phase-III, (February 2002 to December 2003) engineering consultancy services were provided by the same JV for Papan, Kyrgyz Ata and Naiman dams and canal systems including their irrigation sub-projects.
The ongoing World Bank financed Water Management Improvement Project (WMIP), which is the logical continuation of IRP, was awarded to the consultants Temelsu in association with Mott MacDonald (UK) in 2007. This project includes investigations, surveys, environmental impact assessments, preparation of designs and tender documents for 19 irrigation systems covering an area of about 85,000ha and safety plans for Naiman dam. Construction supervision and quality control of all above project components and on-the-job training are also within the scope of the consulting services.
The assignment included developing the rehabilitation projects for each selected off-farm irrigation system for re-construction or repairing/cleaning the headworks, concrete canal lining and associated control structures. The major remedial work for Naiman dam was the evaluation of seismic safety, rehabilitation of the draw-off structures, strengthening the water intake and outlet structures, plus renovating the gate shaft and replacement of hydro-mechanical equipment with necessary mechanical and electrical auxiliaries.
Completion of these works will result in the provision of:
• A more reliable water supply for irrigation.
• Reduced seepage of water from canals and leakage from structures.
• Better water management with a reduction in management, operation and maintenance requirements.
• Possible prevention of catastrophic failure of structures.
The major components of this phase are almost at completion with only some minor works remaining due to budget limitations and social events which occurred in the summer of 2010 in Kyrgyzstan. However, investigations and design works as the first tasks of the prioritised remedial measures for Naiman dam and the urgent rehabilitation works have been finished. Expected completion of WMIP is December 2012.
Rehabilitation of Naiman dam
Naiman water reservoir, situated in Osh Oblast, is an off-stream type reservoir impounded by the excess water diverted from Kyrgyz-Ata and Chili-Sai rivers through a canal of 35m3/sec capacity and from the Abshir-Sai river through a canal of 8.5m3/sec capacity. It was designed to provide a secure source of water supply to the downstream 6000ha Too-Moyun (TMR) irrigation scheme. Construction started in 1961 and was completed in 1966.
The 40.5m high dam has a crest length of 265m. Freeboard is 2.4m plus the wave wall. It is an earthern fill embankment structure consisting of sand/gravel and pebble sized outer shoulders and a wide core of low permeability loamy soil. The upstream and downstream face slopes vary from 1:2.5 to 1:4.0 from top to bottom.
Review of dam safety
Very limited design and construction data could be made available to consultants for reviewing. The present condition of the dam therefore has been assessed on the basis of information obtained from field inspections and discussions with operating staff on the site. Since the available information was not sufficient to prepare tender design documents for remedial works, a comprehensive geotechnical investigation programme was planned, tendered and supervised.
The objective of this programme was to investigate in-situ strength characteristics of the construction materials used in different parts of the dam body and foundation soil, the pore pressure distribution within the dam body and seepage that emerges at the downstream face at high reservoir levels. Since all of the existing piezometers were out of order, 12 new standpipe piezometers were installed along the dam body and monitored. The main difficulty at this stage of the investigation was the unavailability of qualified local contractors having the capability to perform geotechnical field and laboratory tests in conformity with accepted international codes and standards; such as standard or static cone penetration tests or in-situ density measurements, three-dimensional tomography through geophysics etc. These are of upmost importance in establishing a reliable database for further seismic analyses.
The embankment appeared to be in good condition, with no indications of distress or other signs of excessive deformation. There is some amount of settlement and cracks at the concrete road pavement locally. Total crest movement is reported as 40mm vertically but this is not a systematically measured value, just an order of magnitude given by local dam staff. Some of the concrete slabs at the upstream slope seem to be slightly damaged and need repair or replacement. The downstream slope seems in a good condition with no obvious signs of deformation or surface erosion.
There are puddle areas in the downstream toe of the embankment covered with bush and grass with seepage emerging from the ground surface. The measured seepage during the period of 1966 to 2000 is reported as 200L/sec and even more in 2010 when the reservoir level is at maximum, although it was estimated in the original design as 20L/sec. Particularly, the left abutment of the dam site possesses unfavourable water seepage conditions, mainly due to the effects of tectonic movements; and so requires the conduction of significant special seepage control measures.
Since the dam is an off-stream type and the catchment area is very small, there is no spillway. Incoming water is bypassed to the TMR irrigation system when the reservoir is full. The 8.5m3/sec capacity water outlet structure, constructed on the right abutment conglomerates, consists of a reinforced concrete submerged culvert (d=1600mm, L=47m) laid from inlet to the tunnel. The tunnel is 181m long and 2.2m in diameter, equipped with a 1.4m diameter gate valve at the bottom of a tower shaft and a 1.6m diameter butterfly valve at the downstream end. An entrance house is located at the top of the shaft tower, furnished with a 5ton capacity crane for erection and dismantling of equipment installed at the bottom of the shaft.
The most important deficiencies that will impair the smooth operation of the dam are as follows:
Although the inside of reinforced culvert should have steel lining in the original design, it has been reported by dam staff that this steel lining has never been erected.
After 45 years of operation, the reliability and safety of pipe might have considerably reduced due to the abrasion of the concrete cover and the corrosion of the reinforcement.
The shaft and its auxiliary structures like the entrance shed, access bridge, steel stairs, gate valve and peripheral concrete slabs are all worn out. External water isolations are totally obsolete. Although these are not directly impairing dam safety, refurbishment is of vital importance for safe and smooth operation.
Electrical and mechanical equipment
In general, all the mechanical equipment and their electric supplying units are aged and outworn due to 45 years of operation. The 5ton capacity crane has already completed its service life. The drainage pump has not been functioning since 1990. The fan was dismantled so the air duct and pump pipes have corroded heavily in a highly humid environment.
Although original designs had been for regulation of the water flow by three gates, only two gates, one sluice gate at the shaft and one butterfly at the downstream, had been constructed. The sluice valve is always open during agricultural seasons and fully closed in dry periods. From time to time, the screw-nut couple has failed and the thread is wearing out. Similarly, the downstream butterfly gate cannot be operated properly because of vibrating problems. Its electrical drive was removed and operated manually.
Tunnel outlet exit portal
Due to rock boulders hanging over the exit portal of tunnel outlet in the steep hillside, there is a potential of rock fall over the control room. Therefore, it is important to rehabilitate the exit portal in order to protect outlet structures.
Remedial works for safe and smooth operation
The safety of the dam has been estimated based on site specific seismic risk assessments and results from performed geotechnical investigations. Results of the nonlinear seismic analyses have indicated that the freeboard is satisfactory for the operating basis earthquake level with a peak ground acceleration (PGA) value of 0.46g. However, the dam is unsafe under a maximum credible earthquake level of 0.70g for a return period of 5000 years and catastrophic failure is likely. Therefore, strengthening the downstream slope by constructing a rockfill toe of about 30,000m3 has been recommended. However, the seismic strengthening of the dam was not originally within the scope of the project. No budget has been allocated for these retrofitting tasks. Therefore the proposed strengthening measures are postponed to a later stage. For reducing the risk of any catastrophic failure in the short term, the consultant has proposed to keep the reservoir impounding level about 3.5m lower than the normal service level as a temporary precaution.
Other remedial works are summarised below. They have been tendered and will be finalised by the end of 2011.
• Rehabilitating electro-mechanical equipment including the heavily damaged valve, cranes and their appurtenant structures.
• Refurbishing the access bridge, shaft building, steel stairs, isolations etc.
• Replacing the broken concrete slabs around the tower.
• Providing a proper drainage pipe system.
• Replacing all electrical systems.
Electrical and mechanical works have been completed while the structural repair works are partially completed. The valve has not been replaced yet, waiting for plugging of the conduit inlet and dewatering tunnel at the low water level season.
• Inspection through diving.
• Comprehensive repair and strengthening works.
Not completed yet, waiting for low reservoir water level season.
• Strengthening of the tunnel outlet portal slope, walls and valve room.
• Replacing existing heavily damaged gate.
Strengthening of the tunnel outlet portal is partially completed, the valve room has been refurbished and the gate valve replaced. At the time of writing 7.5 m3/sec water has started to be released to the downstream irrigation channel.
Because of budget limitations, the following rehabilitation work is also required but has not been programmed yet:
• Approximately 30% of slabs at the upstream dam face need repair or replacement.
• Construction of a toe drain collector and a weir to measure and monitor seepage through the embankment and abutments,
• Provision of a standby generator.
Dr. Fikret Gurdil, Head of Structural Design Department at Temelsu, Temelsu House Yildizevler, 721. Sokak No: 6 Cankaya Ankara Turkey. Email: [email protected]
TablesMain irrigation dams