I. Floods and droughts
According to historical data, the causes of flood and drought disasters are basically influenced by climate factors, high water level of rainstorm in the Yangtze River, engineering measures and human factors.
The city is greatly influenced by the monsoon, so it has the characteristics of uneven distribution of rainfall during the year and great interannual variation. Summer (June-August) has the highest rainfall, accounting for 50% of the annual rainfall. Spring (March-May) takes the second place, accounting for 30% of the annual rainfall. There is less rain in autumn and winter. Summer is the season when crops need a lot of water. In rainy years, Tangba Reservoir has insufficient water storage and is prone to drought. For example, in 1978, the rainfall was 473.3 mm, and most of the Tangba Reservoir dried up and the drought was serious. In rainy or sudden rainstorm years, floods are prone to occur.
The city is vulnerable to floods mainly in polder areas. The ground elevation of the polder area is between 7 and 8 meters, which is closely related to the water level of rivers such as Chaohu Lake, and the water level of Chaohu Lake is affected by the water level of the Yangtze River. In flood season, the water level of the Yangtze River is often higher than that of Chaohu Lake, so the lake water cannot be discharged into the Yangtze River, and the polder area is often oppressed by the external water level above the ground. In particular, some dikes are thin and low, with low gully and pond rate, low flood storage capacity and low drainage capacity. In the event of heavy rain, it is easy to flood when it is attacked from inside and outside. For example, 1969, 1980 and 1983 after the founding of the People's Republic of China were all caused by high water levels and heavy rainstorms in the Yangtze River and Chaohu Lake.
The water storage capacity of Tangba Reservoir in this city is small, the overall supporting and management of irrigation and drainage water storage projects are not suitable, and the ability to resist floods and droughts is weak. There are few hills, hills and dikes supporting ditches, canals, roads and forests, and supporting projects such as canal system buildings and cross buildings are far from meeting the planning requirements. Some rivers are silted up, and the drainage is not smooth. Reclamation of rivers, lakes and beaches correspondingly reduces the flood detention capacity.
According to the article "Analysis of Historical Data of Flood and Drought Disasters in Anhui Province" published by the Provincial Water Conservancy Design Institute, this city belongs to Luzhou area and Jianghuai area. According to the comprehensive statistics of the number of historical floods and droughts in recent 500 years, there are 185 floods with a recurrence period of 2 ~ 3 years; There are 190 droughts with a recurrence period of 2-3 years. Most disasters occur in summer and autumn. There are many opportunities for continuous flood and drought, and there are many opportunities for continuous water supply, once every 20 years; The chances of continuous drought, first waterlogging and then drought, and first drought and then water are all once in 30 years. According to the statistics of recent 500 years, the recurrence period of catastrophic flood year and catastrophic drought year (including catastrophic drought year) is about 70 ~ 100 years. General flood return period is about 4 years, and general dry year return period is about 6 years. According to the analysis of disaster data after the founding of the People's Republic of China, the period of major floods in this city is generally about 10 years, such as 1954, 1969, 1980 and 1983. Drought occurs once every 2 to 3 years on average, and severe drought occurs once every 4 to 5 years on average. The drought cycle is about 10 years, such as 1958, 1966, 1978. Great floods and droughts alternate. Continuous droughts occurred in 1958 and 1959, 1978 and 1979.
(a) Historical records of floods and droughts
In the 11th year of Qing Daoguang (183 1), there was a flood.
In the 13th year of Qing Daoguang (1833), floods brought roads to hungry people.
Fourteen years of Daoguang reign (1834), drought and locust plague.
In the eighteenth year of Qing Daoguang (1838), there was a flood. The heavy snow in winter collapsed houses, bamboos and trees.
In the 28th year of Qing Daoguang (1848), rain and hail occurred in August, and crops were harmed.
In the twenty-ninth year of Qing Daoguang (1849), floods flooded, leaving no fields, houses, people and animals, but some people went deep into the market.
In the thirty years of Daoguang Qing Dynasty (1850), there were more than 100 beautiful tails in the East Huangshan Mountain, and the fishy water was harmful to crops.
In the sixth year of Xianfeng in Qing Dynasty (1856), there was a locust plague in Luxian County, and the price of rice soared, making it desolate.
In the fifth year of Tongzhi in Qing Dynasty (1866), the flood caused the lake to burst, and ... Sixteen counties were exempted from the old and owed three years of silver rice.
In the eighth year of Tongzhi in Qing Dynasty (1869), there was a flood.
Ten years of Tongzhi in Qing Dynasty (187 1), wind disaster and insect disaster.
In the twenty-seventh year of Guangxu in Qing Dynasty (190 1), the heavy rain in May suddenly made the river grow a few feet, and Wuwei, Hezhou, Chaoxian and Hanshan, which belonged to Luzhou, were flooded.
In the 28th year of Guangxu in Qing Dynasty (1902), there was a great drought.
In the second year of Xuantong in Qing Dynasty (19 10), a severe drought occurred.
In the Republic of China 14 (1925), there was a severe drought.
In the Republic of China 15 (1926), drought and locust plague occurred.
In the twentieth year of the Republic of China (193 1), there was a great flood, the passenger water was extremely heavy, dikes, dams and dams completely collapsed, and people, animals, houses and crops suffered great disasters. The Yangtze River is the biggest flood in 40 years, which is the worst in a century. The flooded farmland in Chaoxian County is 233,500 mu.
In 2 1 (1932) of the Republic of China, there was a serious drought and locust plague, which greatly reduced the production of farmland.
In the 23rd year of the Republic of China (1934), a severe drought occurred, with an affected area of 380,400 mu and a population of more than 260,000, resulting in a loss of rice 152438+0536 million tons.
In 37 years (1948), there was a flood.
Among them, in the 20th year of the Republic of China (193 1), the flood was the most serious, with a wide range, long duration and huge losses. The flood level was as high as11.30m. In the 23rd year of the Republic of China (1934), there was a severe drought, ditches and ponds dried up, fields cracked and seedlings died.
(B) after the founding of the flood and drought disasters
1949 The annual rainfall was heavy, rivers flowed backwards, and mountain torrents gathered. In summer and autumn, there are 240 dikes and 40 earthquake dikes, and the flooded fields are about 19 18000 mu, of which the polder fields are about 13 1000 mu, with 489,700 people suffering severe disasters and 489,700 people suffering minor disasters.
1954 Annual rainfall 1604 mm, April rainfall 104.5mm, May rainfall reached 263.5mm, June rainfall reached 257. 1mm, July rainfall reached 483.6mm and August rainfall reached 50.6mm, all of which were on the high side. The rainfall from May to August alone reaches 1054.8mm, which is close to or exceeds the annual rainfall in normal years. On April 20, the water level began to rise and the river flowed backwards. Coupled with flash floods, the surrounding rivers are flowing downwards. At the end of June, the water level reached11.32m, and most of the dikes were flooded. In July, the water level reached11.30m. On 23rd, all dikes burst, and on 25th, Tongcheng Sluice burst. The highest water level reached12.93m in August. After the dike burst, the water level rose sharply above 1m, which was 0.9 1m higher than the highest water level 193 1 and 0.66m higher than the highest flood level 1949. The county's flooded fertile land is about185,200 mu, and the inland river tributaries are about 90,000 mu of flat land and low-lying land (including 25,000 mu of mountain torrents, about127,700 mu after the dike burst), with a total of about 275,200 mu flooded. About 4 1.000 households and 1.652 million people (including 4,535 households in cities and towns and population 1.9 million people) were affected. There are about 48,700 flooded houses and about 1.34 million collapsed houses. 1 1 One person drowned, and eight people were injured in emergency rescue and fell into the wall. Poultry and livestock drowned in large numbers. In that year, the grain output was reduced by 8 1.487 million Jin.
It has been sunny for a long time since 1 958 May1. Silverscreen and Phoenix lasted 90 days, while Huangshan, Gao Zhe, Jiong, Huailin and Bantang lasted 65,438+003 days without rain. During this period, the county's average rainfall was 99. 1mm, 6 13mm less than the same period last year, and the annual rainfall was only 864mm. The weather is very hot, the outdoor temperature is above 40℃, the maximum evaporation is 10 mm, usually 7 ~ 8 mm, and drought occurs in some areas in late May. By mid-June, the county was generally affected by drought, with an area of 6.5438+0.232 million mu, accounting for 654.38+02.3% of the sown area, including 9.65438+0.3 million mu of rice and 3.65438+0.9 million mu of dry crops. Since then, the drought has gradually worsened, the seedlings have withered, the pond has cracked, and the spring at the bottom of the well has been cut off. The maximum drought-affected area is 873,300 mu (572,800 mu of rice accounts for 94.5% of the sown area and 300,500 mu of dry crops). The affected area is 750,000 mu, and the output is reduced by 5 1.25 thousand Jin. In 2058 villages in the city, about186,500 people have difficulty drinking water, and there are more than 100 households in Sun Jia Village, Ji Fang Township. The water for washing rice and vegetables should be picked from the mountain stream 4 miles away. More than 400 households in 30 villages, including Jiedun Village in Tuanshan Township, also went to fetch water 3 miles away.
1959 From June 3rd to the end of August, it didn't rain for 88 days, covering 670,000 mu and 580,000 mu.
196 1 year from spring drought to autumn drought, covering an area of 520,000 mu. The more serious areas are Cyclobalanopsis, Evonne, Liuji, Ji Fang, Lu Fen, Miaogang, Fenghuang and Qiyang in the north of the Bird's Nest. The grain harvest in this county was not good that year.
In the rainy season of 1969, the rainfall was heavy and concentrated. From July 14 to July 18, the rainfall was 350.9mm, of which the rainfall in July 120.7mm was 15, and the continuous rainstorm caused the water level of rivers and lakes to skyrocket. The affected area of the whole city is 22 1 10,000 mu, and the non-harvested area is 2 1 10,000 mu, with a yield reduction of about 65.438+0.3 billion Jin and a population of 65.438+0.5 million.
1978 is the worst drought in summer and autumn in a century. The annual rainfall is only 473.3 mm, and the annual evaporation is 1540 mm, with less rainfall and more evaporation, and most of the Tangba Reservoir has dried up. The affected area is 3 1 10,000 mu, and the affected area is 290,000 mu. 244,300 people were affected, accounting for 42% of the total agricultural population; Among them, about 1.22 million people were seriously affected, accounting for 50% of the total affected population.
During the period of 1980, from mid-June to early September, Yuxi River did not encounter floods for 25 years, and Chaohu Lake did not encounter floods for 10 years. In 80 days, it rained for 42 days, and there were more rainstorms, with the rainfall reaching 642 mm. Among the eight rainstorms, there were four flood peaks, each higher than the other. On September 2nd, the water level of Yuxi River 1 1.35m exceeded the highest flood level 1969 12cm. The fourth flood peak, the water level of Chaohu sluice 1 1.54 m, is close to the highest flood peak 1969, and the water level is above1/m for 32 days. The whole flood has the continuity of 1954 and the tension of 1969.
During the flood season, there were 25 levees, covering an area of 965,438+10,000 mu, with 20 levees broken, flooded fields 1.3 1.000 mu and flooded mountains 1.99 million mu. 6 flooded market towns, 2 villages1village, and 5698 houses; 3086 affected households, about 13600 people; Collapsed straw house 1 1, tile house 1379, 58 flooded irrigation and drainage stations, machine room 127, 33 motors and 3 diesel engines.
From 65438 to mid-May, 1983, it began to rain for several days, and some low-lying areas of No.43 William, the avant-garde of Gushan and Bazhen Town were flooded. After the end of June, heavy rains caused disasters and flash floods. From June 25th to July17th, the accumulated rainfall is 428mm, accounting for 40% of the annual average rainfall, and the maximum daily rainfall is 129mm. On July 5th, the 6-hour maximum rainfall 106 mm in some areas to the south, and the water level of lakes and rivers rose rapidly. On July 26th, the highest water level of Chaohu sluice was 12.29 meters. On July 14, the highest water level outside Fenghuang Neck Gate14.52m exceeded the highest flood level 1969 and 1980, and the warning water level lasted for two and a half months. Dangers of dikes, large and small, keep appearing. There are 605 culverts and steep gates, 576 dangerous dikes, 376 dikes leaking and 554 breakdowns. On July 19 and July 27th, it was hit by a southwest wind of magnitude 6 or above twice, and was hit by a northwest wind of magnitude 6 or above at 2-6 a.m. on August 23rd, and the danger at the big wai mouth such as Zhongyan and Nandawei Yu Lian was aggravated. There are 83 dikes in the county, which inundate about 52,000 mu of farmland, accounting for 34.7% of the total area of dikes. The drilling mountain flooded about 4 1.4 million mu, the flood damage area was1.51.0 million mu, and other flooded areas were about 43,700 mu. There are 6,568 households in 436 flooded towns, with about12,700 houses and 20,700 victims. There are 2 flooded electric irrigation stations18, 236 machine rooms and 0/00 motors.
Autumn drought occurred again after August, and the affected area was about 4 1.5 million mu, including about 1.93 million mu of grain crops and about 22,300 mu of cash crops.
Second, the earthquake
This city and the neighboring Wuwei county are the intersection of several groups of faults. These groups of faults are: the Tancheng-Lujiang deep fault zone and the lower Yangtze fault zone in the northeast; Chuhe fault and Chaohu-Xiangquan fault in northeast China; The bridgehead group in the northwest-Dongguan fault; The Gaolinqiao fault in the northeast direction and the Lighting Mountain fault in the east-west direction.
From the analysis of satellite photos, Qiaotouji-Dongguan fault, Gaolinqiao fault and Dengguangshan fault are relatively new active faults. 1585, an earthquake of magnitude 6 occurred near the intersection of Gao Lin Bridge and Lightning Mountain Fault. Hot springs on Xiangquan fault in Chaohu City are well developed.
The famous Tanlu Deep Fault Zone is the oldest and longest active fault zone in eastern China. The city has not studied its seismic geological characteristics. 1On September 25th, 984, two felt earthquakes occurred in Sanhumei, southwest of Huatang Town in the south-central part of the fault.