Chapter 31 Chapter 30 Flood Discharge Documentary of Barrier Lake

"Barrier lake", the 5.12 Wenchuan Earthquake in 2008, made people suddenly notice such a technical term. This is a phenomenon or "landscape" that even some people in the water conservancy industry were not very familiar with in the past. Like the sword of Chris, it hangs high over the heads of the people in the disaster area. This "time bomb" is threatening the national construction and the safety of people's lives and properties in the earthquake-stricken areas and even non-earthquake-stricken areas at any time. What is a barrier lake?Barrier lakes are unstable lakes formed after rivers are blocked by landslides, landslides, and mud-rock flows. Since the dikes of these lakes are not artificially built, they are formed by natural accumulations of rocks, sediment, and tree roots. Therefore, it is extremely unstable, and "dam break" may cause floods at any time. Therefore, it is one of the most important secondary disasters of earthquakes, and the catastrophic consequences often exceed the earthquake itself.

From the 5.12 earthquake to the end of May, according to aerial remote sensing data and field surveys by experts, Sichuan has discovered barrier lakes in 6 hard-hit cities and prefectures, including Aba, Mianyang, Chengdu, Deyang, Guangyuan, and Suining, and 10 rivers. 34 places.Among them, there are 8 large-scale barrier lakes with a water volume of more than 3 million cubic meters, 11 medium-sized barrier lakes with a water volume of 1 million to 3 million cubic meters, and 15 small-scale barrier lakes with a water volume of less than 1 million cubic meters.Later investigations revealed that the actual number greatly exceeded that there were 55 barrier lakes in Mianyang City alone.Among these barrier lakes, the three largest are the Tangjiashan barrier lake in Beichuan, the Xiaojiaqiao barrier lake in Changtun River in An County, and the Donghekou barrier lake in Qingchuan. most.

Tangjiashan was originally about 2,000 meters above sea level, and almost half of it collapsed during the earthquake. A large number of collapsed mountains and two adjacent landslides carried boulders, trees, and soil and rushed to the riverbed of the Jianjiang River, quickly blocking the flow of water, forming a landslide. Huge lake.With the continuous increase of incoming water, the water volume of the lake has increased from 100 million cubic meters to 330 million cubic meters, which is called "the most in the world" by Chinese and foreign experts. On May 14, the water surface area was 76,000 square meters, but it rapidly increased to 150,000 square meters on May 18. The nearby Xuanping Township and Zhangjiaba were all flooded. The barrier lake is flooded with water, and the pressure on the barrier dam is increasing. The barrier dam composed of loose soil and gravel is likely to collapse, especially when the water level reaches the top of the dam, it will pour down with the water flow, causing a huge disaster. It will happen—many downstream towns and Mianyang, the second largest city in Sichuan Province with a population of more than 1.3 million, will be wiped out in an instant.

To add insult to injury and make the situation even more severe, in addition to the aftershocks, according to the weather forecast, "there will be heavy rain in some disaster-stricken areas in Sichuan in recent days." In addition to the large-scale barrier lakes in Sichuan, landslides caused by the earthquake in the No. 109 tunnel section of the Baocheng Railway, one kilometer downstream of Jialing Town, Huixian County, Longnan City, Gansu Province, also caused nearby rocks to roll into the Jialing River, causing water levels in the upper reaches of the Jialing River. Soaring, forming a barrier lake, a dam about 100 meters long, 30 meters wide, and 6 to 8 meters high across the river, threatening the safety of upstream and downstream villages, roads and railways.

In addition to the barrier lakes, 1,803 reservoirs in Sichuan were damaged by the earthquake, of which 379 were in high-risk situations.The outer concrete layer of the Zipingpu Reservoir dam built upstream of Dujiangyan in 2006 has cracked and is leaking.The storage capacity of this reservoir is about 1.1 billion cubic meters, and the water storage capacity during the earthquake was 700 million cubic meters. It poses a fatal threat to Chengdu, which has a drop of 300 meters and is located at the bottom of the Sichuan Basin. Some people vividly call it : "More than 10 million people in Chengdu have a basin of water on their heads!"

As early as May 17, Hu Jintao, General Secretary of the Central Committee of the Communist Party of China and State President, held an earthquake relief work conference in Sichuan and solemnly pointed out that it is necessary to strengthen the monitoring and prevention of geological disasters such as landslides and mudslides, and ensure the safety of key facilities such as reservoirs and dams. operation to prevent secondary disasters. In fact, the pain of dam breaks has happened many times in the history of Sichuan. In the past two hundred years, the tragedy of large barrier lake dam breaks has happened twice.

The Western Sichuan Plateau, located in the Hengduan Mountains and the Longmenshan fault zone, was originally a seismically active area.On the sixth day of May in the fifty-first year of Qianlong in the Qing Dynasty [June 1, 1786] an earthquake of magnitude 7.5 occurred in the south of Kangding, Sichuan.Huge landslides occurred in places such as Luding and Hanyuan along the banks of the Dadu River, blocking the Dadu River and stopping its flow for ten days. On June 11, the Dadu River burst, floods tens of feet high surged down, and the backwater of the river ditch reached tens of miles.As a result, the people along the river in Leshan, Yibin, and Luzhou "have lost more than 100,000 people."On the muddy river, the flood washes away the crops, trees, roof trusses, and livestock... Ragged corpses float down the river and gather in clusters on the water... After the flood recedes, the countryside is wiped out and the houses are in ruins , Hungry and dead, vultures pounce on human corpses... The surviving disaster-affected people helped the old and the young, crying day and night, and the displacement was terrible.As a result, the Dadu River broke down and the lower reaches were sparsely populated and desolate for nearly a century.

On August 25, 1933, a 7.5-magnitude earthquake occurred in Maoxian County on the upper reaches of the Minjiang River in northern Sichuan. With the loud noise of the sky falling and the earth cracking, the second market in Maoxian County at that time, Diexi, known as the important town of Canling—the legendary Huangdi’s wife Lei The place where the ancestors lived sank without a trace in an instant. "The rivers and mountains are easy to change, and the city wall does not remain." All 21 nearby villages were destroyed, and houses in another 13 villages collapsed, killing 6,865 people and injuring 1,925.The strong earthquake caused the surrounding mountains to collapse, blocking the Minjiang River, and the rushing Minjiang River formed a huge barrier lake. After more than 40 days, the lake collapsed. The flood caused huge losses to Maoxian, Wenchuan, Guanxian (now Dujiangyan City) along the river and more than a dozen counties in the Chengdu Plain. Most of the cities and towns along the river were washed away by the flood, and countless people drowned. It caused a rare earthquake in the history of earthquakes in the country. flood.

Today, next to the tourist roads from Chengdu to Jiuzhaigou and Huanglong, among the mountains and valleys, there is still a huge "haizi" left by the barrier lake. In fact, this is still the main channel of the Minjiang River, divided into Shangdiexihai and Xiaxia. Diexihai is connected by a 500-meter-long and 40-meter-wide trench in the middle. The upper and lower seas are nearly 6 kilometers long and store hundreds of millions of cubic meters of water all year round.The water surface is often dark blue or dark green, even in the hot summer, it looks weird and mysterious coldly.The exit of Haizi is very narrow, the water gushes out, the waves splash, and the water mist forms a colorful rainbow under the sun.

And what about the original Diexi City?Only the incomplete east city gate, a few feet of the city wall, the collapsed city god's temple site, a pair of stone lions and a stone roller are left... The Diexi Earthquake Remains is now an important relic for the study of earthquake and flood disasters.On the original site of the Diexi earthquake, later generations erected a stone tablet, engraved with "The 60th Anniversary Ceremony of the Diexi Earthquake". Work. May our generation protect the ecology and develop a source of wealth...Those who suffer from Diexi will last through the ages."

According to incomplete statistics, the Diexi earthquake and floods claimed more than 20,000 lives, and more than 4,000 corpses were salvaged from Baopingkou in Dujiangyan alone. "The essence of the upper reaches of the Minjiang River has been lost here." ". The "Maowen Qiang Autonomous County Chronicle" published in 1997 was named "Diexi Earthquake and Flood Disaster", which recorded some valuable historical materials about the collapse of the barrier lake: In the 22nd year of the Republic of China [1933] at 15:50:30 on August 25, a strong earthquake of magnitude 7.5 occurred in Diexi, which was felt from Xi'an in the north, Wanxian in the east, Aba in the west, and Zhaotong in the south. Songpinggou to the west of Diexi City, Qianggou, Pingdingguan, and Zhenping to the north, and Xiaoguanzi, Manaoding, Dadian, and Shidaguan to the south were all affected by the earthquake.All 21 villages were destroyed, and houses in another 13 villages collapsed.Houses in the county town shook like fans, beams and columns opened and closed suddenly, roof tiles flew down, and the vibration force was 7 degrees.According to the investigation by the Provincial Earthquake Disaster Committee, 6,856 people were killed in the earthquake area, 1,925 were injured, 5,108 houses were lost, and 9,678 livestock were lost.The fields along the Minjiang River in the county were damaged, and more than 4,970 people were left homeless.During the earthquake, rocks at Diexi, Daqiao and Yinpingyan collapsed, blocking the Minjiang River into three weirs, which accumulated water for more than 40 days. At 7:00 p.m. on October 9, the Diexi Weir collapsed, and the downstream villages and towns along the river in Mao County, Wenchuan, and Guan County were washed away, and more than 2,500 people died [incomplete statistics], causing a rare earthquake and flood in Chinese history. According to the survivors of Jiaochang Dam, the days before the earthquake were sunny and the days were especially hot, and most residents had lunch at home.Suddenly there was a thunderbolt, and the surroundings were suddenly dark, the sound of the ground was mixed with the rumble of the ground, people were thrown to the ground, and they felt flying sand and stones, their ears, eyes, mouth and nose were blocked by dust, and there were cracks everywhere on the ground nearby, opening and closing suddenly , the earth's crust collapsed, and the rows of walls seemed to be displaying books on shelves and fell one after another. People couldn't move, and they lost all will, as if in a dream.After about 1 minute, the sound of the underground tunnel stopped, but the rumble continued. Three hours later, the dust and fog subsided, the sun had set, the rivers and mountains had changed, and the city walls were gone.One part of the adjacent river on the west side of Diexi City collapsed into the river, one part subsided, and the other part was covered by rocks on the east side of the mountain. Only the east gate and the southern city wall remained.There are 278 houses in the city, only the broken columns and beams of the Town God's Temple and mud judges with broken arms and legs remain.Except for a statue craftsman in Chenghuang Temple and a woman on the way to the north of the city, 570 people were buried among the rocks.Only foreigners who harvested and traded opium in Hexi two or three miles away from the city survived. Among them, 42 were injured and 82 were outside for some reason.After the earthquake, the refugees returned to their hometowns and gathered at the ruins of the Town God's Temple. At the same time that Diexi City fell, Longchi Village on the West Bank fell.Longchi and Diexi collapsed and blocked the Minjiang River with sand and rocks, forming a 100-meter-high ridge in the valley.In the north of the city, Jiaochangba and Diexi were originally located on a platform. After the earthquake, a mile of land collapsed, and they have not been connected so far.During the earthquake, the ground cracked, and yellow mist rose from the cracks, and five people were swallowed by the cracks in the field.All the cracks are arranged along the mountains on the east side to the south, 0.4-5 feet wide, and the soil in the cracks is stepped, ranging from inches to feet deep.The largest fault crack is at the point where the platform is 70° west by south, and extends southwest to the riverside. It is about 200 meters long, 20 meters wide, and the existing depth is 16 meters. It drops to 5-6 meters in the south.The earthquake caused the mountains to collapse wildly. From Maoer Mountain in the south to Pingqianggou in the north, the mountains along the river were crumbling and jagged.In the middle of January and February after the earthquake, whenever the strong wind picked up sharply, or the slight earthquake continued, a rock rolled down and the whole rock collapsed.In the earthquake, Yinpingyan, Daqiao, and Diexi collapsed the most. Three major barrages were formed because the rock mass blocked the Minjiang River, causing the river water to flow back above the confluence of the Heishui River and the Minjiang River, and the river water in the Yinpingyan Barrage carried sand. The stone poured down. One hour later, it flooded to Shawan, cleaning up all the remnants of the village after the earthquake.Shawan Post Fort was built in the Hongwu period of the Ming Dynasty. It is 10 miles north of Diexi. There are more than 80 residents. On this day, 200 pack horses transport goods to the top, and when the local mosque gathers, most of the residents and merchants are not here. Escaping the catastrophe, including the Shawan flood and earthquake, more than 300 people died, including 103 Hui people.Houerzhai was also underwater that night. On August 27, the Minjiang River flooded to the ruins of Pu'an. On September 6, the lake water poured back to the spring rock, submerging the Guanyin Temple.There is a flat lake in the alpine gorge, and the lake is winding with the mountains, with a meander of 12.5 kilometers and a width of 2 kilometers at the widest point. It is called Dahaizi today. On September 14, Dahaizi overflowed the bridge weir and washed down with sediment and gravel, forming Xiaohaizi. The earthquake-damaged Xinjie beside the bridge and the Guanyin Temple, Water Mill, and Oil House on the opposite bank were all submerged. On September 30, water from Xiaohaizi poured into Diexi Weir [about 1,500 meters away from Banshang North Road, Shaziheba].The weir is more than 260 meters high, and the weir crest exceeds Yinpingyan and the bridge weir crest, so the two weir crests are flooded backwards, connecting the three seas into one. On October 7, the Diexi Weir began to overflow, and the Minjiang River resumed its trickle flow. After the Diexi Earthquake Lake was formed, after 45 days of water storage, it was triggered by an aftershock at 7:00 pm on October 9, 2022. Songping The Gongpeng, Baila and other Haizi waters in the ditch collapsed, and the Songpan area in the upper reaches of the Minjiang River continued to be cloudy and rainy. The water head above Changdadian was as high as 20 feet, and the flow broke out rapidly. It reached the county seat at 9:00 p.m., Wenchuan at 11:00 p.m., and Guan County at 3:00 a.m. the next morning.Houses and fields in villages and towns along the way were devoured.According to statistics, 24 people died in Dadian County, 23 people died in Shidaguan, 21 people died in Changning, 32 people died in Jiaoyuan, and 71 people died in Daheba. , 340 people died [not including merchants and travelers]; 2,579 shi of grain were washed away, 2,170 livestock died; 353 shi of fields and 346 houses were washed away in Wenchuan County, 2,315 livestock were drowned, and 483 people died; Shudi was destroyed in Guan County More than 4,000 mu, more than 1,600 people died; Xinyuzui and Feishayan under Yulei Pass in Dujiangyan were destroyed.The Diexi earthquake and floods have aroused the attention of the whole society, and social organizations such as the Lurong Association of Mao County have appealed to the government. Half a month after the earthquake [September 8 at 10:50 p.m.], the Sichuan Provincial Government sent a report to the Executive Yuan, Military Commission, Ministry of the Interior, Ministry of Finance, and Relief Committee of the Nanjing Nationalist Government to report the earthquake situation, requesting a huge amount of money for emergency funds. Relief. Nearly one month after the earthquake, Sichuan Rehabilitation Supervisor Liu Xiangshi sent more than 10 people including Quan Qingchuan, technical director of the Chengdu Water Conservancy Governor's Office, to Diexi for investigation. On October 9, Quan waited to return to Mao County to report the investigation results to the government and asked migrant workers to dredge the stagnant water.It was the night of staying in the ancient temple of Dadian. In the evening, Quan Qingchuan was chatting with the old monk. He heard the roar of the river. When the two went out, the water had already ascended the stairs.In an instant, the ancient temple was washed away, and none of the investigators was spared except Quan Qingchuan. In October, Chang Zhaoning [Chang Longqing] and Luo Xiyi, directors of the Geology Department of the Western Academy of Sciences, were ordered by the Geological Survey Institute of the Ministry of Industry to go to Diexi to investigate, collect, and photograph a large amount of seismic data, and made a preliminary analysis of the cause of the earthquake.Written into "Sichuan Diexi Earthquake Investigation Records" a book. On December 7th, Liu Xiang, the governor of Chengdu Water Conservancy, sent Zhou Yuru, governor of Chengdu Water Conservancy, and Guo Yuzhong, a staff officer of the supervisory office, to lead more than 30 people to Diexi for a 5-day on-site investigation. Only Haizi, Gongpeng, and Yuerzhai Haizi are condescending, and if they collapse into the downstream, it will cause disaster.With the support of people from all walks of life, the Diexi Drainage Project Office was established in January 23, and the project cost was 12,000 yuan.Staff officer Guo Yuzhong was in charge of mobilizing 500 migrant workers from the county. It took 4 months to dredge the pond water at the beginning.At this point, the first phase of the project was completed, and the "Monument for Diexi Water Diversion" was engraved next to Dianjiangtai. Although this record is incomplete and does not reflect the full picture of the Diexi earthquake and floods, it still gives people a glimpse of the severity of the disaster at that time, as well as the slow and weak response of the government of the Republic of China.It should also be pointed out that the Kangding earthquake during the Qianlong period and the Diexi earthquake in 1933 both occurred in sparsely populated places. Higher and more intense, the dam break of the Dadu River dammed lake during Qianlong caused "more than 100,000 people to drift away", and the dam break of Diexi also caused disasters in more than a dozen counties and more than 20,000 people were killed. The Tangjiashan dammed lake burst, and the downstream area bears the brunt of the densely populated Mianyang area.According to experts' prediction, after the dam breaks, a 20-meter-high mudslide will pour down the valley, and the flood will destroy everything along the way. It will reach Mianyang, the second largest city in Sichuan Province, which is less than 100 kilometers away, within 4 hours, completely destroying it. In all the towns and villages along the way, more than 1.3 million people may suffer disasters, and the number of victims will far exceed that of a major earthquake. The serious consequences make people shudder! As a result, Tangjiashan Barrier Lake has become the focus of the whole country and the world.President Hu Jintao gave instructions in person, and Premier Wen Jiabao visited the barrier lake twice to inspect the scene. More than 60 foreign media successively contacted the Mianyang City Earthquake Relief Headquarters, hoping to know the situation of the barrier lake relief, and many media from the United States, Britain, France and other countries reported on it many times.The British "Financial Times" stated that "the scale of this crisis is unprecedented in the modern world." Andy Hughes, director of dams and water resources at a multinational engineering company, said that natural dams formed due to landslides are just random piles of "blocks." rocks” rather than carefully constructed man-made structures equipped with spillways, potentially far more dangerous and unpredictable than man-made dams.According to the BBC website, Stephen Edwards, a geologist and professor at the University of London, said: "Topographically it's terrible. These dams are basically weak, loose rubble piles, and the rising water level is very difficult for them. It's a huge pressure. ... It's a fragile situation. Another aftershock could turn loose earth and rock into a destructive cascade of mud and water. It then pours down, threatening and burying everything in its path." The decisive battle against Tangjiashan is imminent. However, 5.12, the most serious natural disaster that occurred in China in the past 30 years, not only claimed many precious lives, but also completely destroyed the transportation and many infrastructures in Sichuan. Among them, the decisive battle in Tangjiashan not only has a huge workload, but also faces huge tests in decision-making, technology and organizational work... Can the decisive battle be won? On the afternoon of May 13, 2008, Jing Dazhong, the magistrate of Beichuan County, who was directing the earthquake relief work on the ruins, suddenly received a panicked report from a village official who had escaped from Xuanping Township: "County magistrate, it's terrible! Tangjiashan was destroyed by the earthquake, and the water was closed on it and couldn't flow down. In the morning, the water entered the streets of our Xuanping Township, and the township government office building was flooded..." Jing Dazhong quickly came to the bank of the Jianjiang River next to the ruins of the county seat. Sure enough, there was only a trickle of the formerly wide Jianjiang River, and the flow was getting smaller and smaller.Jing Dazhong’s heart tightened—Tangjiashan is only 3.2 kilometers away from Beichuan County, and there is a barrier lake here. Not only will several towns upstream be submerged, but once the dam breaks, huge floods will pour down like thunder. Downstream townships and Mianyang urban areas bear the brunt, and the consequences are disastrous! So while reporting to his superiors, he sent people to upstream towns to lead the people to move to a safe zone. At the same time, the General Staff of the People's Liberation Army also discovered this huge barrier lake through satellites, and immediately notified the situation to relevant parties. On May 14, the aviation unit also discovered this major danger during the rescue work, and quickly reported the danger to the National Earthquake Relief Headquarters.On the same day, researchers from the Earth Observation Center of the Chinese Academy of Sciences, while processing the aerial photography data of the unmanned aircraft, also found vigilantly that in the canyon near Beichuan County, an earthquake suddenly shook a dam, and the dam was blocked. Jianjiang formed a barrier lake. On May 15, the situation had been brought together to the Ministry of Water Resources.The earthquake relief headquarters of the State Council, Sichuan Province and Mianyang City at all levels have all set their sights on this "time bomb".Rumors arose among the common people. Some people thought of the Diexi earthquake and floods in the past, so rumors such as "the flood is about to come down, Beichuan is about to sink", "Mianyang is in danger" and so on made some people panic. In order to thoroughly understand the specific situation of the Tangjiashan barrier lake and to take countermeasures, the Mianyang City Earthquake Relief Headquarters established a water conservancy group, dispatched staff and water conservancy experts to the site to conduct hydrogeological data surveys and barrier lake danger monitoring, and organized The upper reaches of the crowd quickly evacuated. On May 15th, the staff and water conservancy experts headed towards Tangjiashan in six batches. They braved the threat of aftershocks and went through hardships and dangers. However, due to the mountain fracture and continuous landslides, they could not reach the top of the dam until May 16th. Accurate hydrological and geological data cannot be grasped. Amid people's anxiety, aftershocks are still continuing, and the water level of the barrier lake is still rising. On May 16, the Air Force sent two helicopters to transport water conservancy experts to inspect the Tangjiashan barrier lake by flying at low altitude. At that time, because there was no apron, the plane could not land on the barrier dam, and the weather was very bad. It was foggy everywhere, and the visibility was extremely low. situation.They believe that the Tangjiashan barrier lake is the largest of more than 30 barrier lakes formed by the Sichuan earthquake. Due to the landslides and collapses of the Tangjiashan mountain, a large amount of sediment and rocks have accumulated in the Tangjiashan of the Tongkou River, forming an 800-meter-long lake. The dam with a width of more than 600 meters, a height of 82 to 120 meters, and a volume of more than 20 million cubic meters cuts off the rushing Jianjiang River... How big is a dam with more than 20 million cubic meters of earth?Some people have calculated that if these earthworks are built into a wall 1 meter wide and 1 meter high, it can be built to 20,000 kilometers, which is equivalent to the length of half the earth's equator. In the middle of the night on May 17, Guo Yongxiang, deputy director of the Standing Committee of the Sichuan Provincial People's Congress, rushed to Mianyang, and Liu Ning, chief engineer of the Ministry of Water Resources, also arrived at the same time to discuss urgent countermeasures with the leaders of Mianyang City.The conference room of the Mianyang Earthquake Relief Headquarters was brightly lit all night. After careful study of satellite images and other data by experts from various fields, it was decided to continue to use aerial observation to monitor the water regime of the barrier lake. In addition to aerial observation, on May 18, the hydrology professional group of the Ministry of Water Resources urgently dispatched more than 30 technical backbones to form 10 on-site survey commandos of barrier lakes.On this day, water conservancy experts from Chengdu and experts from the Ministry of Water Resources once again took a helicopter to inspect the Tangjiashan barrier lake.However, the plane was still unable to land on the spot. After aerial observation, experts estimated that if the barrier lake was filled with water, the storage capacity would be more than 300 million cubic meters. The storage capacity of 300 million cubic meters is second only to Zipingpu Reservoir in the Minjiang River Basin, and a flood of 100 million cubic meters is enough to swallow a city with a population of 500,000 to 1 million! Experts estimate that if a third of the Tangjiashan barrier lake breaks, nearly 160,000 people in Mianyang City alone will be submerged; if half of the dam breaks, more than 1.2 million people in Mianyang City will be flooded. Catastrophe; if the dam breaks in an all-round way, more than 1.3 million people in Mianyang City will be wiped out in the raging flood! Therefore, the Tangjiashan barrier lake was listed as "No. 1 risk" by the frontline experts of the Earthquake Relief Headquarters of the Ministry of Water Resources, and ensuring its flood control safety immediately became the overriding task. Aftershocks and rainfall continued, and the water level of the barrier lake was still rising at a rate of about two meters per day.Water conservancy experts and Mianyang City have taken measures to strengthen the monitoring and forecasting of rainfall and incoming water in the upper reaches of the barrier lake; promptly clean up various accumulations in the river below Beichuan County; establish monitoring points to monitor flow changes 24 hours a day; Remove persons upstream who may be within range of flooding.The survey commando also quickly contacted the Hydrological Bureau of the Ministry of Water Resources, and urgently allocated ADCP flow measuring instruments for hydrological observation... and monitoring data show that as the main flood season approaches, the threat of barrier lakes will become greater and greater, even without considering In the case of rainfall in the upper reaches, it is expected that the water level will reach the overflow elevation in 18 to 24 days, and if no measures are taken, a flooding collapse is likely to occur. The situation is extremely critical.An urgent report handwritten by Liu Ning, chief engineer of the Ministry of Water Resources, was sent to Beijing.After review by the Party Central Committee and the State Council, the eight-character policy of "actively rescue and actively avoid danger" was determined.General Secretary Hu Jintao called Hui Liangyu, the Vice Premier of the State Council who was instructing the earthquake relief work in Sichuan late at night, and demanded that we must adhere to the people-oriented principle, put the safety of the people first, carefully organize, carefully arrange, strengthen inspections, and make emergency plans , make scientific decisions to deal with the dangerous situation of the Tangjiashan barrier lake, so as to ensure that there will be no major problems in emergency situations. On the evening of the 19th, the Ministry of Water Resources held an emergency meeting, conveying the disaster relief instructions of Hu Jintao and other central leaders, and decided to monitor and guard Tangjiashan 24 hours a day, and propose a disposal plan and an emergency plan for personnel transfer as soon as possible. On the 20th, Yang Jie, a famous hydrogeological expert in Sichuan and a 66-year-old retired senior engineer from the Provincial Bureau of Geology and Mineral Resources, took the initiative to come to Mianyang, took three college students and hydrological monitoring instruments, and airdropped them to Yuli Township, where the barrier lake is located, and established a hydrological project. key points.This monitoring point effectively monitors the water level and storage capacity of the Tangjiashan barrier lake. Every day, the satellite phones of other units or troops are used to report the monitoring data to the headquarters, so that the headquarters can know whether there will be disasters in the downstream and the consequences of disasters. What is the speed, whether it can win the time for emergency rescue, etc., to provide detailed evidence in order to make correct decisions. After monitoring, Yang Jie and others also wrote the "Report on Landslides and Debris Flow Geological Hazards Survey in the "Beichuan-Zhicheng-Yangjiaping" Section of the Upper reaches of the Jianjiang River", suggesting to find out the location and scale of geological disasters in this area, and Assess the possible disasters to avoid the terrible consequences of a new round of geological disasters after the earthquake. In the afternoon, Jiao Yong, the leader of the Ministry of Water Resources' earthquake relief front leading group, Vice Minister of the Ministry of Water Resources, and Cai Qihua, director of the Yangtze River Committee of the Ministry of Water Resources, led experts to take a helicopter to the sky above the barrier lake in Tangjiashan.Through more than four hours of careful aerial observation, we once again understood the situation of the dam. However, aerial observation alone is still not enough, and on-the-spot investigation is still an indispensable basis for formulating rescue measures.After research, on the morning of the 21st, two helicopters carrying more than 20 hydrology and observation experts and officers and soldiers of the Armed Police Hydropower Force went straight to Tangjiashan again, taking a risky on-the-spot investigation.Since the Tangjiashan dam was unable to land on the dam, the people on the plane jumped off one by one when it was more than one meter above the ground.The airflow from the propeller of the plane knocked down many people, but after struggling to stand up, they patted the dirt on their bodies and started working. Standing on the top of the barrier lake and looking around, it is like standing on a small mountain. The boulders and gravels on the surrounding rocks are still falling into the lake water, making a loud "cracking" noise, splashing bursts of water and water. The fog, the loud sound of rocks falling into the water and the "earth sound" of aftershocks echoed each other. With the aftershocks, more rocks fell, and the sound of "rumbling" shook the sky. Tangjiashan was originally a place with dense vegetation and green hills, but after the earthquake, the mountains on both sides were cut off like knives and axes, and turned into bare dangerous rocks.The dam formed during the earthquake was also completely different from the dams of ordinary reservoirs. It was high and low, full of mud and large and small stones with sharp edges, and broken trees and thorns were mixed in, making people have no place to stay.From the top of the dam to the bottom of the dam, from one end to the other, there is no way at all.The experts walked on the steep boulders, among the fallen trees, on the deep mud and loose gravel and sand, using their hands and feet on the ground. If they are not careful, they may be buried at the bottom of the lake.After a while, everyone was dripping with sweat. After difficult on-site monitoring by experts, the Tangjiashan dam body is about 803 meters long along the river, about 611 meters at its widest point across the river, and the top area is about 300,000 square meters, all of which are composed of stones and hillside weathered fossils.As of 5 pm on May 21, the water level in the lake was 716.01 meters, the corresponding volume was 97.7 million cubic meters, and the head difference between the upstream and downstream was 52 meters. In addition, the experts also summed up the four major risks facing the Tangjiashan barrier lake.The first is meteorological risk: The upper reaches of the Tangjiashan barrier lake have entered the main flood season. According to the forecast of the meteorological department, the rainfall in the upper reaches will reach 400 mm to 500 mm in June and July, which is significantly larger than in previous years.The increase in upstream water has challenged the flood discharge capacity of the barrier lake.The second is geological risk: the dam body is formed by landslides, and the geological structure is composed of rocks and granular soil. Some seepage points have been formed under the dam body, and the seepage volume is slowly increasing. possibility of collapse.The third is the risk of aftershocks: After May 12, dozens or even hundreds of aftershocks occurred every day. Frequent aftershocks and continuous landslides and mudslides constantly tested the safety of the barrier.Fourth, landslide risk: there are still some large landslides in the upper reaches of the barrier lake, which pose a threat to the barrier body in the case of strong aftershocks and rainfall. After returning to Mianyang, according to the first-hand information from the scene, experts from the Ministry of Water Resources' earthquake relief front leading group immediately studied countermeasures with Sichuan Province, Mianyang City, and the Armed Police Hydropower Force, and quickly reported to the National Defense Headquarters and the Ministry of Water Resources. On the afternoon of May 22, Premier Wen Jiabao came to Mianyang again after the earthquake. Immediately after getting off the plane, he took a helicopter and went to Tangjiashan Barrier Lake for field inspection. The helicopter traveled through the mountains and valleys in northwest Sichuan, and arrived over the barrier lake after more than half an hour.After observing the situation of the barrier lake, the plane landed in Yuli Township.This township is located in the upper reaches of the barrier lake in Tangjiashan. According to local legend, it is the hometown of Dayu, a hero of water control.In order to prevent the backwater from continuing to rise and submerge the village, the army is organizing the transfer of the local affected people. Wen Jiabao walked among the villagers, shook hands with everyone cordially, asked carefully about the situation of the disaster, and told everyone that "the biggest threat now is the barrier lake", and comforted: "Don't worry, we will solve this problem well. There will be a meeting at night to study and take the initiative to deal with it, the sooner the better, it will definitely ensure the safety of the masses.” In the evening of the same day, Wen Jiabao convened a meeting of the State Council’s Earthquake Relief Headquarters on the train to study and deal with the problem of the barrier lake, and decided to set up a frontline headquarters for the Tangjiashan barrier lake emergency dredging project, with Jiang Jufeng, governor of Sichuan Province, as the general manager. The commander, responsible comrades from the Ministry of Water Resources, the Armed Police Hydropower Unit, and the Air Force of the Chengdu Military Region participated.At the meeting, Wen Jiabao proposed three principles for dealing with barrier lakes: 1. Take the initiative to deal with it and avoid being passive; 2. Based on early treatment to prevent the difficulty of treatment after the increase in water volume; , To ensure the safety of the masses, to ensure the safety of troops and rescue personnel, and must not cause casualties again. Since then, "zero casualties" and "no one died" have become the soul and core of Tangjiashan Barrier Lake rescue plan. From the military to the Ministry of Water Resources to the local government, all work and details are based on these three words as the highest standard.Party and government officials in Mianyang City told the public that the earthquake is a natural disaster and cannot be predicted, but the barrier lake is different and can be predicted. On the day of its establishment, Jiang Jufeng organized various personnel to hold a meeting of the frontline headquarters to make specific arrangements for emergency rescue and avoidance.In order to ensure the progress and quality of the project, from this day on, Jiang Jufeng has been running between Mianyang and Tangjiashan almost every day, and has worked on the dam top site many times to study and solve various problems in the rescue in a timely manner. On the evening of May 23, after intense research, analysis and calculation, the barrier lake treatment plan was completed.According to the consequences of the dam failure of the barrier lake, the experts proposed three sets of plans: The first set of plans is based on one-third of the dam failure. The evacuation population is about 160,000, the urban area is about 4.6 million square meters, and the housing area is more than 4.1 million square meters, involving Beichuan County, Jiangyou City, Santai County, Mianyang Fucheng There are 33 townships and 11 communities in the two major urban areas of Youxian and Youxian, involving 44 important units. The main urban area of ​​Mianyang is basically not greatly affected. The second set of plans is based on the consideration of half of the dam failure. The evacuation population is about 1.2 million, and the urban area of ​​5 counties, cities, and districts including Beichuan is submerged. The area is more than 53.68 million square meters, and the housing area is more than 19.03 million square meters, involving 33 towns and 1.69 million people. community, 182 important units. The third plan is based on the consideration of a complete dam failure. More than 1.3 million people will be evacuated, more than 62.34 million square meters of urban area will be submerged in Mianyang City, and more than 21.25 million square meters of houses will be submerged, involving 175 communities in 35 towns and 192 important units. Later, it was considered that the population and submerged area involved in the second and third plans were not much different. To ensure safety, after the alarm was issued, the evacuation plan for the complete dam collapse was implemented. Experts have also calculated that if a third of the dam breaks, it will take about 6 hours for the flood to reach Mianyang City; if a complete dam breaks, the time for the flood to reach Mianyang will be shortened to 4.4 hours.During this period, as long as the organization is in order, personnel can be transferred safely. However, in view of some factors that cannot be simulated in advance, such as shock waves, air currents, and large flows that may cause mudslides and landslides, there are still uncertainties in the number of people who must be evacuated after a dam break. Therefore, from the perspective of safety, the leaders of the Ministry of Water Resources suggested that Prepare plans for transferring people in advance to avoid temporary accidents. On the afternoon of May 26, the Mianyang Municipal Party Committee and the Municipal Government held an evacuation and evacuation mobilization meeting, informing millions of people in the city of the danger of the Tangjiashan barrier lake in detail, and clearly pointed out: "To avoid danger, emergency evacuation is imperative! In the afternoon of the same day, the Mianyang Meteorological Observatory issued important weather news-from the 26th to the morning of the 27th, there will be obvious heavy rainfall in the east and west of Mianyang, with moderate to heavy rain in some areas, and thunderstorms and heavy rain in some areas.The Earthquake Relief Headquarters believes that this kind of weather forecast is better to be trusted than not; it is better to be believed in the big than the small; The tragedy of crying after the disaster repeats itself! That night, nearly 40,000 people were evacuated from Beichuan County and Jiangyou City, and more than 30,000 people were evacuated one after another. Due to the complexity of the situation, the risk removal plan for the Tangjiashan barrier lake has been changed repeatedly. Initially, the dredging plan of the experts was: dig a trapezoidal discharge channel on the dam body of the barrier lake, with an upper width of 60 meters and a lower width of 20 meters. The water level can reduce the pressure of water on the dam body and prevent large dam failures; the second is the scour during the discharge process, which can gradually increase the discharge channel, which is equivalent to letting the dam body collapse slowly, thereby reducing the impact on the downstream. threaten. 方案通过后，挖渠的任务交给了武警水电部队。为了集中优势兵力打歼灭战，武警水电一总队、二总队、三总队和三峡指挥部的精干队伍齐聚唐家山，共同参加对堰塞湖的决战。这些官兵都至少有三年以上的实战操作经验，是一支能打硬仗的队伍，而在一个工程上集中了这么多“精锐之师”，在武警水电部队成立的40多年中，实属罕见。 这个泄流渠共设计了高、中、低三种不同的方案。高泄流渠口方案需挖土5万立方米，中泄流渠口方案需挖土7万立方米，低泄流渠口方案需挖土10万立方米。从泄流效果来看，低方案泄流量最大，最有利于保障坝体安全，但工程量大，施工时间较长，而且需要天气良好。武警水电部队领导经反复权衡后，决定先采取挖掘量最大、保险系数最高的低方案，如果发生强降雨，则可能被迫采用中或高方案。如天气情况正常，应急泄流渠将于10天之内突击完成。 武警水电部队政委贾方亮少将在进行战前动员时强调，这次工程的施工难度前所未有，坝顶因山体滑坡形成，地形异常复杂而不稳定，要在上面修筑出一条导流槽泄洪，并建造铅丝笼护坡，初步测算，开挖的土石方约在7.5万立方米左右，建造铅丝笼护坡的施工量约在2万立方米左右，更为严重的是，余震随时可能发生，而由于龙门山脉地区气象条件和地理环境都非常恶劣，对直升机的运输也会构成严重威胁。面对种种不利条件，贾方亮少将强调：“只要人民有需要，武警官兵就必须排除万难，奋勇前进！” 决战唐家山的战斗已经打响。武警水电部队、空军、陆军航空兵、成都军区某集团军、海军陆战队分别做出应急部署，24小时不间断地为排险施工进行准备。一支支具有专业技术素质的施工队伍齐聚绵阳，一台台专用重型机械设备也在绵阳集中，80多台重型机械包括35辆推土机和15辆挖掘机都集结待命。但是一个巨大的难题却摆在了大家面前：大部队，特别是重型工程机械设备怎样才能进入唐家山？ 走陆路？通往唐家山的山路上游已经被淹没，下游桥梁断裂，道路变形，许多路段还被垮塌的山石泥沙堵死。 走水路？有人建议从堰塞湖上游用船只往唐家山运送抢险人员，但经过侦察，发现上游的水面上有大量漂浮物——破损的屋架、折断的树木、死去的家畜乃至杂草等等，积成厚厚的一层，让船只寸步难行，而且上游5公里处还有一个巨大的山岩在不断地滑坡…… 看来，唯一的办法是开辟出一条“空中通道”了。5月22日在温家宝出席的总指挥部会议上，已决定了由空军负责打通“空中通道”。 从绵阳到唐家山空中距离只有短短的60多公里，但沿途多是高山峡谷，高压线密布，飞机贴着山谷超低空飞行，万一螺旋桨打上了电线，后果就不堪设想；再加上山区气候多变，气象条件复杂，当时又正值雨季，雷电、雨雾频繁发生，严重威胁着飞行安全；而飞行员进入这种陌生的空域后又没有地面导航设施……因此，短时间内要在这里开通航线，把人员、设备安全运到抢险现场，谈何容易？ 陆军航空兵接受了这个艰巨的任务。指挥员和飞行员在图上、沙盘上反复模拟飞行，设想出各种不同的情况以及应该采取的措施，决心克服一切困难完成任务。 5月20日上午，成都军区陆航团特级飞行员姜广伟带领机组人员，受命运送水利地质专家前往堰塞湖。但直升机到达堰塞湖的坝体后，却找不到可以降落的地方，反复盘旋，反复观察，最后不得不冒险单轮强降在堰塞湖坝顶上的一个小土堆上——这是惊险的“空中杂技”，是对飞行员技术、勇气和意志力的巨大考验，稍一不慎或稍有犹豫，便可能造成机毁人亡的可怕后果！ 第二天，直升机又采取类似的方法把25名武警水电的抢险官兵运送到了唐家山堰塞湖坝顶。 但是，这种“空中杂技”并不能运送大量人员，更不能运送重型工程机械设备，必须开辟出一个临时“机场”，让飞机可以起降。 在堰塞体上修建机场和别的地方不同。机场的地面必须有一定的承重力，但是这里的堰塞体是由烂泥、杂树和垮塌的石头组成的，平整出合格的地面十分困难。从21日到25日，25名武警水电官兵没日没夜地突击，用最简单的工具，清除淤泥、填平石块、夯实地面、加固四周，终于修出了一个8平方米的袖珍“机场”，这个小小的机场可能创吉尼斯纪录之最，但在唐家山堰塞湖排险中却发挥了极其重要的作用。 “机场”修好了，但天气状况仍然没有好转，接连两天的阴雨和大雾，让远山近谷都隐藏在雾影之中，直升机仍然无法飞行。24日上午，济南军区某陆航团的一架直升机奉命运送五名抢险施工的指挥员到堰塞湖堤坝上去，当时天空仍然笼罩在一片雾霭之中，地面的情况根本看不清楚，特级飞行员张茂生驾机反复盘旋后，终于刹那间在厚厚的云层中捕捉到一丝空隙，立即采取单轮悬停的办法，把人员和一些生活补给品送到了大坝上。 这天下午，张茂生率领机组人员再次起飞，运载了八名武警水电部队官兵和简易施工工具前往唐家山。但是，途中云层越来越厚，直升机只能拉高后在云层上面飞行，到达堰塞湖上空时，根本看不见下面哪里是山峦，哪里是悬湖，哪里有大坝，来回盘旋半个小时后，只能无奈地返回。 24日下午，和张茂生机组一起，执行救灾任务的还有两架直升机，但也都被迫返航，有两架运送物资的民用直升机和他们一样，也不得不返回。 25日上午，参与抢险的空军某部直升机再次起飞，试图打开一条吊运工程机械的“空中通道”，但厚重的云层再一次阻挡了他们，飞机到安县上空时探测到前方有雷阵雨，于是不得不返航。 这已经是三天以来空中飞行无数次地受阻了。 但是就在这几天，堰塞湖的水位竟每天以两米左右的速度不断上涨，距离坝顶最低处仅29米，而根据气象台预报，近几日灾区还会有强降雨…… 溃坝的危险迫在眉睫，能等待天气好转吗？cannot! 于是指挥部召开了紧急协商会议，决定对抢救方案进行重大调整，一是开挖导流渠的方案由过去以大型机械开挖为主，改为施工与爆破同时进行，并以爆破为主；二是人力和设备的进入从过去的空运为主变为空运与徒步运输同时进行，并以徒步进入为主。一方面继续伺机空投武警水电部队官兵到唐家山堰塞湖坝顶，继续监测湖水水位；另一方面派出地面部队，克服一切困难，强行向唐家山挺进。 从25日下午开始，武警水电和成都军区组成的1800人突击队，便背着炸药、雷管、铁镐、干粮，从北川擂鼓镇出发，徒步向唐家山堰塞湖艰难前进。从下午一直走到了深夜。实际上并不是“走”，许多地段不得不手脚并用地“爬行”和攀登。在被大地震摧毁的山区，根本没有道路，头上是余震和滚石的威胁，脚下是地震形成的多条断裂带，较大的山体滑坡和泥石流就遭遇了三次，而且他们的身上还背着20多公斤重的炸药和一些别的抢险物资！官兵们早已把生死置之度外，天黑了，没有星星，没有月亮，漆黑的山谷间伸手不见五指，突击队只能靠着指北针指引方向，靠着手里的电筒发出微弱的亮光……步步坎坷，处处陷阱，六个多小时后，26日凌晨零时35分，终于来到了堰塞湖的坝顶。 这时，有人激动地唱起了《团结就是力量》，立即引起千人应和。《团结就是力量》的歌声响彻山谷，震动天地，在堰塞湖的水面上也激起了阵阵涟漪…… 突击队上去了，但重型机械没有上去，排洪抢险仍然无法进行。5月26日早晨，堰塞湖的水位已经上升到725.3米，距警戒线不足26米！从空中往下看，上涨的湖水似乎很快就要到达坝顶，广阔无边的堰塞湖似乎就要冲破大坝决堤而去。 堰塞湖陷入危急之中。 万幸的是，这天早晨持续数日的阴霾终于慢慢散去，气象预报的大雨并没有降临。于是，一架架雄鹰立即展翅高飞，其中包括两架米—26重型运输直升机，一架从俄罗斯直接飞到了我国，一架来自中国飞龙专业航空公司。这种飞机被人们爱称为“大力士”和“空中巨无霸”，是世界上最大的直升机，普通直升机可载重2吨，而橘红色的米—26可载重20吨，一些大型机械只有通过这种飞机才能运输。它降落的那一刻，整个坝体甚至整个峡谷都在震动，螺旋桨刮起的气流远达100米开外。这种飞机又有“油老虎”之称，耗油量极大，每执行三至四次任务就要补充一次油料，每次需加油2.5吨到3吨，每吊运一台重型机械往返一次唐家山，各种费用加在一起约需3万元。 据米—26的中方领航员介绍，“无论中方还是俄方，都是第一次在高原山区执行这种任务，可以说这是世界上最困难的飞行吊装任务。”“这次任务并不符合飞行标准。堰塞湖附近的山体最窄处相互之间间距不足100米，而米—26要求障碍物的间距在120米以上。而且湖面上空水汽氤氲，能见度常常不到500米，因此其实我们是在冒险飞行。” 为了抢险，空军紧急开辟了飞行“绿色通道”——组成军地联合飞行管制指挥机构，把绵阳—安县—北川划为专用航线，并以堰塞湖为中心，半径30公里、高度600米以下为临时空中限制区。限制区规定，首先要保证北川到堰塞湖方向的抢险飞行。一天之内，各种直升机除了加油和吊装的时间外，每隔15分钟左右就出动一次，当天便给施工现场送去了挖掘机、装载机、推土机等各种大型设备15台，还送去了汽油、柴油、帐篷、被褥、食物、饮用水等各种物资。先期到达堰顶的官兵们欢呼着团团围住了直升机，他们已经两天两夜没吃东西没喝水了。 唐家山堰塞湖应急处置工程终于按原计划方案全面展开，人们期待已久的堰塞湖攻坚战终于打响！ 到26日下午3点钟，经过紧张施工，堰塞湖坝顶终于被削下了两米，从752米下降到750米。而抢险方案也相应再次调整，原先准备的炸坝计划考虑到堵塞体的体积非常大，地震后山体又极不稳定，到处都有裂口，到处都在滑坡，怎么炸？放多少炸药才能保证既能炸开一个缺口放水，又能够保证上面的山体不再滑坡，而且不会把大坝炸掉一半或完全垮塌？这些都是难题，风险太大、不易掌握，炸坝计划属于不得已而为之，于是暂时停止执行，仍改以机械挖掘为主。应急抢险设备和炸药的使用原则定为：挖爆结合，先挖后爆，平挖深爆，以爆助挖。 经过15台重型机械26日的通宵施工，到27日早晨，唐家山堰塞体的坝顶已经被削低了3至4米，形成了一个20至30米宽、40至50米长的工作面。但湖水水位仍然在继续升高，较前一天又升高了近两米，水面距堰顶的垭口只有23米多了。27日下午，配合施工，实施了一次小规模的爆破，主要是炸断坝侧的大树桩，为开挖泄流渠扫除障碍。 与此同时，绵阳市抗震救灾指挥部也在紧张地动员群众撤离。为便于群众转移，市区规划了50多条撤离路线，最长的也不超过两公里。26日前，把三种不同的疏散方案传达到了每一个乡镇、村，每一个居民、村民。堰塞湖下游的几百万民众，通过广播、电视、报纸和口头传达，了解了三套不同的撤离预案，明白了自己要往哪里撤，跟谁一块撤，走哪条路，上哪个坡，过哪座桥，上去后找谁安置……下游所有的城区和乡镇，都在醒目的建筑物、电线杆或大树上用红漆画出了明显的标记：三分之一溃坝的淹没线，二分之一溃坝的淹没线，全溃坝的淹没线…… 为了避免在大规模疏散时发生各种难以预料的问题，5月27日下午，绵阳市抗震救灾指挥部按三分之一溃坝的要求，在下游可能被淹没的通口河，涪江沿线的游仙区、涪城区组织群众进行了紧急撤离疏散的演习；江油市青莲镇、西屏乡等地也进行了唐家山堰塞湖二分之一溃坝的撤离疏散演习。包括拉警报、吹哨子、设路标、清人数、设调整哨，以及干部带领群众扶老携幼转移到预定地点等等。随着警报声，西屏乡50分钟内，1300多人便紧张有序地撤离到离场镇300米至1公里的几座小山上。在这次撤离预演中也暴露出了许多琐碎而又重要的问题，当天晚上市抗震救灾指挥部便召集各级各部门进行研究，对群众提出的实际问题逐一拿出了解决方案，完善和细化了撤离预案，为以后的20万人大撤离争取了主动。 从26日开始，抢险部队便是24小时开足马力，不间断地争分夺秒，昼夜施工，轰轰隆隆的机器声响彻山谷，夜间，整个河谷灯火通明。由于气象台预测的暴雨并没有如期而至，空运的各种重型机械便迅速增加到80余台。趁着晴好的天气，抢险工作更热火朝天。战士们的工作大致分为三个部分：一部分负责砍伐树木、清除巨石，为重型机械的操作扫清障碍；一部分是重型机械的操作手，人停机械不停，驾驶着挖掘机分三段同时开工，开挖泄洪渠；还有一部分则是负责石料储备，直升机运来了一批铅丝笼，要用石料填装这些铅丝笼，然后堆积在泄洪口，以避免泄洪时水流过急发生问题。 由于帐篷不够，许多战士不得不在满是碎石的大坝上露天和衣而眠。 28日晚上到29日上午，一场大雨突降唐家山堰塞湖抢险工地，给抢险工作再次带来很大困难。由于道路泥泞，空运进入工地的四台自卸车无法工作；直升机不能起飞，施工急需的物资和油料无法运进；特别严重的是，持续降雨使堰塞湖来水量增大，险情再一次加剧。于是抢险队伍便以更大的紧迫感和责任感投入工作，连夜冒雨作业，不少战士连雨衣都没有穿。从28日下午4时到第二天上午8时，便突击开挖土石方1.9万立方米，是自施工以来进度最快的一个夜晚。 29日下午，天气终于逐渐好转，直升机又抓紧时间，来回穿梭在堰塞湖的上空，抢运了大量油料和其他物资。据天气预报，未来几天还可能有大雨，于是部队又做好了第二手准备，调集1000名士兵随时待命，在直升机无法起飞时，采用徒步背运的方式，向施工现场运送油料等抢险急需物资。 经过武警水电部队昼夜抢工，和上涨的湖水抢速度，从26日正式开挖到完工，水电部队和水利专家们仅仅用了六天——较原计划提前五天，一条长475米、宽50米、深12米的泄流渠便出现在唐家山堰塞湖坝体上。专家们说，这种速度在世界上都是一个奇迹。 原计划泄洪渠土石方的挖掘量是10万立方米，实际上却挖掘了14万立方米，由于挖掘得更深，湖水流到泄流渠中便延缓了溢出的速度，从而给下游留下了更多的安全撤离时间，突然溃坝的可能性也变得微乎其微，大大减轻了泄洪可能带来的险情。工程取得了决定性胜利。 武警水电官兵提前超额完成了任务，由于进展顺利，经过周密计算和分析，工程放弃了预定的用炸药爆破溃坝的方案，采用让湖水随着水位上涨自动地流入泄流渠，避免了爆破可能带来的各种意想不到的危险和问题。 6月1日凌晨0时，正式停止了挖掘机的工作，抢险官兵除留下少数人继续进行监测外，其余的人采取坐直升机和徒步的方式，分批撤离。 完成泄洪渠开挖工程后，仍然有两个方面的工作不能放松：一是由于上游的集雨面达3350平方公里，如果发生持续性、大范围的降雨，对堰体的破坏力就会非常大，因而必须加强对雨情、水情的监测，这对下一步预警和应对都非常重要；二是对堰塞体的过流情况和堰塞体的稳定性进行监测，一旦发现堰塞体有异常变化，就要采取相应的预警措施，对下游群众进行转移。而堰塞体完全排除险情也需要一个很长的过程，堰塞体最后用什么方式解决，还需要在监测过程中进一步观察判断。 为了保证唐家山堰塞湖在大部队撤离后继续处于良好的监控状态，并记录相关的水文资料，抢险指挥部在中科院专家组的帮助下，在堰塞湖上下游设立了四个观测点。四川省水文局的四套宽带无线监控系统，可以实时监测无人状态下的唐家山堰塞湖水位变化情况。这种利用先进的高科技手段装上的“天网”和“千里眼”，可以从不同方向、不同角度对堰塞湖泄流后的流量、堰体状况进行记录，并迅速传输到抢险指挥部，包括北京、成都和绵阳。在指挥部只要轻点鼠标，便可以接收到清晰的监控图像，甚至可以看清堰塞湖中的水波。 由于堰塞湖坝体下端近日来陆续出现了十多处管涌，为了观察管涌是否会造成溃坝的危险，指挥部决定，留下12名水电部队的官兵在坝上继续进行24小时监控。 为了确保群众和抢险人员的安全，除在唐家山堰塞湖周围外，在沿岸的安全地带也设立了险情观察站，一旦发生溃坝险情，上游观察站将每间隔20秒钟连续发射30发信号弹作为警报，警报发出后，绵阳市指挥部将同时使用热线电话、短信、广播电台、电视台、高音喇叭等各种辅助方式向社会公告相关信息，并组织群众按预定方案转移。 在泄洪渠施工结束后，并不会立刻出现溃坝或者