Mozitan Reservoir

Mozitan Reservoir

Mozitan reservoir is located 25 kilometers away from the dam site of Foziling reservoir, with a controlled drainage area of 570 square kilometers. The reservoir dam is a concrete head dam, also known as double buttress concrete rib pier dam. It is composed of 12 double buttresses, 3 single buttresses on both sides of the East and the west, and the gravity dam at the turning section of the West Bank.

brief introduction

The crest elevation of the dam is 202.9 meters, the crest elevation of the wave wall is 204 meters, and the total storage capacity is 337 million cubic meters. The spillway is located on the west side of the dam, with a bottom elevation of 196 meters, 6 holes, and a net width of 10 meters for each hole. It is controlled by radial gate. There is a reinforced concrete lined spillway tunnel at the west end of the dam, with an inner diameter of 5.7m and an inlet bottom elevation of 132.7m. The east bank Bahou power plant has an installed capacity of 16000 kW and an annual power generation capacity of 58 million kwh.

In order to improve the flood control standard of Foziling reservoir and fully develop water resources, Mozitan reservoir is determined to be built. In September 1956, open channel of tunnel was excavated. Dam foundation cleaning, workshop layout and sand and gravel mining also started one after another. In December of the same year, the Ministry of Water Resources approved the concrete pouring of the dam. On June 9, 1958, all the dam concrete was poured to the top. The hydropower station was connected to the grid in December 1959, and completed in January 1960. The whole project of the reservoir was completed in 1968.

The completion of Mozitan reservoir has improved the flood control standard of Foziling reservoir, regulated runoff, irrigated Pihe irrigation area with Foziling and Xianghongdian reservoirs, and brought into full play the comprehensive utilization benefit. In July 1969, a torrential rain occurred and the flood overtopped the dam. Before the flood season in 1970, the scoured part of bedrock behind the dam was reinforced. After the rainstorm in August 1975 in Henan Province, it is determined that Mozitan reservoir needs to appropriately heighten the dam and expand the flood discharge facilities in the future while strengthening and heightening the Fuziling reservoir and expanding the flood discharge capacity.

Danger elimination and reinforcement

Mozitan reservoir is located in Huoshan County, Anhui Province. The reservoir project is a second-class project, and its main permanent buildings are grade 2. The dam is a concrete dam with a total storage capacity of 347 million cubic meters, the highest dam height of 82m and the installed capacity of 16mw. Mozitan reservoir, Foziling reservoir and Xianghongdian reservoir are jointly used to provide irrigation water for 6.6 million mu of farmland in Pihe irrigation area and supplementary water supply for Industry and life in Lu'an and Hefei. Since the completion of the dam in 1958, almost all the longitudinal construction joints of the buttress wall have cracked in the initial stage of operation. At present, there are 305 cracks in the dam, including 114 cracks in the upstream dam surface and 191 cracks in the downstream dam body.

The total investment of the reservoir reinforcement project is 99.7 million yuan, with a construction period of 30 months. The main projects include the barrage, dam body reinforcement, dam foundation treatment, reconstruction of the old flood discharge tunnel, construction of a new flood discharge tunnel, renovation of metal structure and reconstruction of management facilities, etc. The normal operation flood standard of the reservoir is once in 100 years. After the completion of the project, the short-term flood control capacity of Mozitan reservoir is required to reach 1000 year return period. In the long term (after the construction of Bailianya Reservoir), the flood discharge facilities of the reservoir will not be controlled, and the check flood control standard of the reservoir will reach 5000 year return period.

History of reservoir

1、 Survey Planning

The geological survey of Mozitan reservoir dam site began in 1951. In November 1955, geologists from the Institute of geology, Chinese Academy of Sciences and the Design Institute of Huaihe River Regulation Commission completed the geological map of the dam site. In February 1956, the 931 team of the Ministry of geology of the people's Republic of China, together with the geologists of the Huaihe River Commission, surveyed the geology of the dam site. There are three dam sites to choose from: Mozitan, Shicao and jilongjian. After preliminary comparison, the upper dam site of Mozitan is selected as the main site and the lower dam site as the auxiliary site for geological drilling. The geological exploration report was put forward in May, and then the drilling work was supplemented. Finally, the second dam line of the upper dam site was selected. The geology of the dam site belongs to the pre Sinian metamorphic rock series, with hornblende gneiss, hornblende quartz gneiss, paragranite schist and hornblende schist exposed. Although the joints are well developed, they close quickly in the deep part, and only some fault zones extend deeply with weak water permeability.

In February 1955, the survey team of Huaihe River Commission measured the topographic map of the reservoir area, and measured the reservoir capacity curve.

According to the planning report of Pihe River basin reservoir group in 1955, the main purpose of building Mozitan reservoir is to solve the problem that the flood control standard of Foziling reservoir is too low, and to solve the problem of Xingli power generation to ease the power load demand in central Anhui. Therefore, the planning of Mozitan reservoir is closely related to the measures to improve the flood control standard of Foziling. During the preliminary design in 1956, Mozitan reservoir was planned according to the standard of once-in-a-thousand-year design and once-in-ten-thousand-year check, according to the measures for the expansion of the spillway of Foziling reservoir. The principle of reservoir flood regulation is to forecast that when the water level of Foziling reservoir exceeds a certain water level, Mozitan reservoir will store flood for Foziling reservoir without releasing flood; when the flood volume of Foziling reservoir is small and the water level drops, the flood discharging equipment can be turned on to discharge flood; when the water level of Mozitan reservoir exceeds a certain water level, in order to ensure the safety of Mozitan reservoir, all flood discharging equipment can be turned on.

After the preliminary design of the reservoir was submitted for approval, the Ministry of water resources and electric power put forward the approval opinions on the design standard of Mozitan reservoir in cooperation with Foziling reservoir, the design of secondary hydraulic structures and the comparison of flood discharge equipment. According to the approval opinions, the characteristic water level of the reservoir and flood discharge and overflow facilities are determined in the technical design documents. During the construction of the tunnel, it is found that the geological rocks at the outlet are broken and the joints are developed, so the tunnel diameter is changed, the bottom height and clear width of the spillway are adjusted, and the spillway is installed with gate control. Based on this, the document of "technical design of Mozitan reservoir project, modification design of spillway tunnel" is compiled and reported. According to the document, the dead water level of the reservoir is 163 meters,

The limited water level in flood season is 177 meters, the water level after flood season is 187 meters, the water level once every 100 years is 197.2 meters, the water level once every 1000 years is 202.2 meters, the dam crest elevation is 202.9 meters, and the crest height of wave wall is 204.0 meters. The total storage capacity is 278 million cubic meters. The diameter of the spillway tunnel is 5.7m, the crest elevation of the spillway weir is 194.0m, the net width of each hole is 8m, and the gate is controlled by reinforced concrete. The hydropower station has an installed capacity of 16000 kW and an annual power generation of 61 million kwh.

At the end of 1958, the main works of the reservoir were basically completed and began to store water. However, due to limited funds, the tunnel could not be used and the spillway gate was not installed by the end of 1962. The area of the basin controlled by Mozitan reservoir has been corrected from 670 square kilometers to 570 square kilometers according to the new aerial survey map. The corresponding hydrological data has been changed and various water levels have been adjusted. Since then, due to the expansion of Foziling hydropower station, the development of Pihe irrigation area and the change of hydrological data, various water levels of the reservoir have changed. After the flood in August 1975, the flood control standard of Foziling and Mozitan reservoirs was calculated according to the reanalysis design flood in 1976. The flood control standard of Foziling and Mozitan reservoirs was only 200 year return period, and the 300 year return period did not overflow the dam. Therefore, the engineering plan for safety reinforcement and construction of Bailianya Reservoir of Foziling and Mozitan reservoirs was compiled in June 1978, and the construction of Bailianya Reservoir was approved by the Ministry of water resources and electric power in 1979. In 1980, the preliminary design for safety reinforcement of Foziling reservoir was compiled and reported. In April 1981, the Ministry of water resources and electric power approved that the Foziling reservoir should be designed according to the secondary buildings, and the reinforcement design standard should be designed according to 100 years in the near future, and checked according to 1000 years; it is preliminarily agreed that the Foziling dam should be increased by 1.5 meters, and the schemes of the east bank spillway tunnel can be compared according to the insufficient parts checked in 1000 years. According to this, Foziling reservoir has selected the original spillway expansion scheme of one hole through comparison of various flood discharge schemes, and determined the characteristic values of various water levels of Mozitan reservoir in the near future, as shown in table 4-1-5.

The final scale of Mozitan is related to the scale of Bailianya Reservoir and the reinforcement measures of Mozitan reservoir. Various water levels, flood discharge facilities and dam crest elevation of Mozitan reservoir need to be determined later.

2、 Design

According to the valley topography, dam site geology, building materials, construction equipment and experience, the concrete gravity dam, Datou dam, slab dam and multi arch dam are compared. Finally, through the comprehensive comparison of economy, safety and durability, construction difficulty and so on, the concrete head dam is selected. At that time, this type of dam was the first in China. It is the first time in China that the finite difference equation of stress function method (network method) and photoelastic test method are used to calculate the stress of dam body in the design.

In the design, the ratio of the width of the retaining surface of the rib pier to the basic section of the rib pier, the relationship between the slope of the upstream and downstream sides and the volume of the rib pier and the project cost are studied. Under the conditions of both stability and stress, the most economical section size of the dam is determined. The dam has double buttresses in the riverbed. In order to save the excavated stonework, reduce the lateral height difference of pier foundation and improve the lateral stability of the slope section on both banks, the bedrock along the slope on both banks is excavated into steps, and the single pier is used for the dam body. The axis of the dam is influenced by the geology of the West Bank and turns to the upstream. There are faults in the bedrock of some rib piers on both sides of the East and the west, so the excavation and backfill concrete are carried out, and the curtain and consolidation grouting are strengthened. The joint between the big end of the dam and the buttress is arranged with dowel bars, and the joint grouting system is set in the contraction joint of the buttress. Expansion joints are set between the adjacent stack heads, two U-shaped copper sheets are set up at the upstream and downstream of the joints, and an oil well is set in the middle. Embedded in well

Chinese PinYin : Mo Zi Tan Shui Ku