1998 Flood Disaster

In the 1998 Yangtze River flood fight, under the strong leadership of the Party Central Committee and the State Council, millions of soldiers and civilians fought bravely and achieved an all-round victory. Currently, people across the country are concerned about how to further regulate the Yangtze River. This is not only related to the long-term peace and stability of the people in the Yangtze River Basin, but also a huge project in the national economic construction. To this end, the two academies organized some relevant academicians and experts outside the academies to analyze and study the relevant information and opinions from all aspects, and then submitted the following report.

1. Understanding of the 1998 Yangtze River Flood and the Fight Against Floods

The 1998 flood was another river-wide disaster that occurred in this century after the two floods in 1931 and 1954. type of catastrophic flood. According to preliminary data, comparing 1998 with 1954, the peak flow and flood volume in the upper reaches were close to those in 1954. Since the peak flow in the middle reaches is not comparable, compared with the most concentrated 30-day flood volume, the total flood volume above Hankou in 1998 was The water volume is more than 30 billion cubic meters less than that of 1954; the peak flow rate downstream is more than 10,000 cubic meters less than that of 1954, and the flood volume is more than 50 billion cubic meters less than that of 1954. Due to insufficient data in 1931, we can only make a rough comparison. The upper and middle reaches may be slightly larger than those in 1931, and the lower reaches may be smaller than those in 1931.

It should be noted that in the last century and earlier, the Yangtze River had experienced greater floods than this century. According to research, since 1153, the peak flow of Yichang Station has exceeded 80,000 cubic meters per second eight times (63,600 cubic meters per second in 1998 and 66,800 cubic meters per second in 1954). Among them, the peak flow in 1860 and 1870 Reaching 92,500 and 105,000 cubic meters per second respectively.

Currently, what everyone is more concerned about is, although the flood was not as big as that in 1954, why the flood level of the main stream of the Yangtze River in 1998 was higher than that in 1954, except for the Wuhan and Huangshi sections. Of course, there are many factors that can cause the flood level to rise, but the most critical one is that the amount of flood storage is significantly reduced compared to 1954. In 1954, due to the low flood resistance of the embankments in the middle and lower reaches, many embankments naturally breached. In order to reduce the flood level and protect key areas, in addition to using the Jingjiang Flood Diversion Project, flood diversions were also opened in many places, totaling flood diversion and breaches. The water volume reaches 102.3 billion cubic meters, of which the capacity to effectively reduce flood peaks is about 70 billion cubic meters. According to the flood volume in 1998, if the water level in 1954 is to be maintained, the effective flood storage volume required is about 40 billion cubic meters. However, the total volume of flood diversion breaches in 1998 was only about 10 billion cubic meters, of which the capacity to effectively reduce flood peaks is estimated to be about 5 billion cubic meters. In this way, the flood diversion volume will be reduced by about 35 billion cubic meters, which is equivalent to reducing the flooded area by 7 million acres. In other words, the fight against floods in 1998 was to strengthen flood control and rescue operations and strive to resist higher flood levels, so as to increase flood discharge and reduce flood losses. For example: in 1954, when the Jingjiang flood diversion project was used, the highest flood level in the Jingjiang embankment was 44.67 meters. According to the Yangtze River flood control plan, in order to reduce the utilization opportunities of the Jingjiang flood diversion project, the design flood level of the Jingjiang levee was raised to 45.0 meters. In 1998, in order to avoid using the Jingjiang flood diversion project, the Jingjiang levee was used beyond the design standards, and the flood level in Shashi reached 45.22 meters. Another example: at Lianhuatang Station, the outlet of Dongting Lake, the flood level was 1.85 meters higher than in 1954. This is because in 1954, most of the enclosures in the Dongting Lake area above Lianhuatang and most of the areas on both sides of the Yangtze River below Lianhuatang were Most of the embankments, including the Honghu Levee, have breached or opened to divert floods. In 1998, there were far fewer breaches and flood dikes in the upper and lower parts of Lianhuatang than in 1954.

It should be said that this was a major decision in the fight against floods in 1998, and it was also a very difficult decision made under the specific conditions of 1998. The engineering basis for the flood fight in 1998 was: According to the flood control plan for the middle and lower reaches of the Yangtze River, some water conservancy projects were completed. In addition to the construction of controlled reservoirs for Hanjiang, Qingjiang, Yuanshui, Zishui, Xiushui and other tributaries, the Jingjiang levee and Wuhan City embankment were also completed according to the increased design flood level (about 0.5 meters higher than in 1954). Heightening and reinforcement projects for key embankments on the main stream of the Yangtze River such as the Wuwei Dike and Wuwei Dike, as well as key enclosures in the Dongting Lake District and Poyang Lake District. All these provided a certain basis for the fight against floods in 1998. However, there are still a considerable number of embankments that have not been completed as planned. In particular, the safety facilities of the plain flood diversion and storage area projects were not considered enough in the original plan and were not implemented during implementation. This has brought great difficulties to the fight against floods and made the decision-making process of the fight against floods difficult. We are in a dilemma: if the flood is diverted according to the original plan (according to the increased design flood level, an effective flood diversion volume of 20 billion cubic meters is still required), great losses will be suffered; if the flood is not diverted according to the original plan, the embankment will withstand more than the designed Standard flood level, bearing great risks. Taking into account that the flood in 1998 was smaller than that in 1954, and the huge potential of the army and civilians to unite to fight the flood, the central government was determined to further raise the flood level, strictly guard against it, and strive to reduce breaches and flood diversion losses. This was an extremely difficult decision, and practice has proven it to be correct. Of course, it should also be noted that this was only possible under the condition that the excess flood in 1998 was more than 30 billion cubic meters less than in 1954. If the flood in 1998 was comparable to or even greater than the flood in 1954, it would still be impossible not to divert the flood.

About the disaster in the Yangtze River Basin in 1998. Based on multi-phase and systematic monitoring and analysis of the middle reaches of the Yangtze River by satellite and aerial remote sensing: the maximum flooded area in Hunan, Hubei and Jiangxi provinces is approximately 15.86 million acres, which is much smaller than the statistics of the three provinces due to different statistical calibers and other reasons. . According to statistics from the Yangtze River Water Conservancy Commission, 1,705 floodplains in the five middle and lower reaches of the Yangtze River were flooded, submerging 2.95 million acres of cultivated land and affecting 2.3 million people. The above figures show that most of the breaches used to divert floods are smaller enclosures, with an average area of ??less than 2,000 acres per enclosure. According to disaster statistics, most of the affected farmland is due to waterlogging. The death toll in 1998 was 1,432. This is very different from the disaster situation in 1954, when most of the other areas were flooded except for the Jingjiang Embankment and the Hankou Embankment, and 33,169 people died. It is completely different from the tragic situation in 1931 when the middle and lower reaches were covered with vast oceans, boats were sailing in the streets of Hankou, urban Nanjing was flooded, and 145,000 people died. Therefore, the fight against floods in 1998 indeed achieved great results.

A question of common concern to all sectors of society is whether the rise in flood levels in the Yangtze River is due to the siltation of the Yangtze River bed. According to long-term observation data, the main stream of the Yangtze River is basically stable, which is fundamentally different from the Yellow River. Due to certain factors, some river sections have experienced changes in erosion and siltation. The most obvious one is the Jianli-Honghu River section below the Jingjiang River. This section is affected by the Jingjiang Bend Cutting Project. There is erosion above the cut-off section and siltation below. According to data from the Yangtze River Water Conservancy Commission, its representative station, Luoshan Station, the water level rises due to sedimentation at low water levels. However, at high water levels, because the siltation area accounts for a small proportion of the flood area, the rising trend is not obvious. . The flood level at Luoshan Station in 1998 was 1.78 meters higher than that in 1954. According to investigation, it was mainly due to the flood diversion at Pakou of Jiangjia Wharf and the breach at Laowan and other places below Luoshan in 1954, which caused the flood level to drop significantly.

About lake sedimentation. Since 1949, the capacity of Dongting Lake has been reduced by more than 4 billion cubic meters due to siltation. Due to the reclamation of 1,600 square kilometers since 1949, the capacity has been reduced by nearly 10 billion cubic meters. The amount of siltation in Poyang Lake is very small, but 1,400 square kilometers have been reclaimed since 1949, resulting in a loss of approximately 8 billion cubic meters of lake capacity. Since all lakes on both sides of Hubei Province were closed, their area was reduced by 5,700 square kilometers. Since 1949, the five provinces of Hunan, Hubei, and Jiangxi, together with Jiangsu and Anhui, have increased their cultivated land by an estimated 14 million acres due to reclamation.

Soil erosion and sediment conditions in the Yangtze River Basin. Within the 1 million square kilometers of the upper reaches of the Yangtze River, according to survey statistics, the average annual erosion of solid matter on the ground is 1.568 billion tons. The average annual sand transport at the Yichang Station on the main stream of the Yangtze River is 530 million tons, with a transport ratio of 0.33. This is different from the Yellow River. Because the upper reaches of the Yangtze River are mainly rocky mountainous areas, the ground erosion materials are mainly rock weathering materials with coarser particles. They generally take the form of piedmont slope accumulation, depression deposition, ditch mouth alluvial fans, pond reservoirs and small and medium-sized tributaries. In the short term, It is deposited at a distance and cannot be transported by rivers over long distances; while the ground erosion material of the Yellow River is loess, with extremely fine particles, and almost all of it can be transported to the main stream of the Yellow River. Below Yichang, the average annual sediment transport volume at Hankou Station is 430 million tons, and the downstream Datong Station is 468 million tons. The difference between Yichang and Hankou is mainly deposited in the Dongting Lake area in normal water years, while in flood years it is deposited in the Dongting Lake area, the river beach and the enclosure of the breach. Most of the sediment transported from Datong Station is sent to the East China Sea. The amount of sediment transported to Yichang in each year varies greatly due to different distribution of heavy rains. For example, the average annual sediment transport volume from 1990 to 1997 was only 380 million tons, which was a year of low sediment load; while the sediment transport volume from June to August 1998 reached 605 million tons, exceeding the sediment transport volume in the same period in 1954 ( 527 million tons), which is a sandy year. According to preliminary analysis, the main sources of sediment in 1998 were the Jinsha River and the Jialing River. This is a phenomenon worthy of further study.

The above situation shows that the serious flood and drought disasters in the Yangtze River Basin, in addition to the objective reasons of meteorology, are mainly due to the imbalance of the ecological system in the basin, which is mainly reflected in the following: in the context of rapid population growth , overuse of land resources and unreasonable development. In mountainous areas, forests are destroyed and steep slopes are reclaimed; in plains, lakes are blindly reclaimed for farmland and flood banks are occupied. These invite revenge from nature. In the Yangtze River Basin, soil erosion in mountainous areas is more harmful to the local area than that of the Yellow River. This is because the Yangtze River Basin is a rocky mountainous area with very thin topsoil. After a certain period of erosion, the topsoil is washed away and the rocks are exposed, forming "petrification", which completely deprives the local people of their living conditions. Guizhou Province already has many "petrified" mountainous areas, which is shocking.

The blind reclamation of lakes in plains and the occupation of flood banks are the main reasons for the rise in flood levels in the Yangtze River in recent years. From the perspective of long-term natural laws, alluvial plains of rivers are formed by the sediment carried by rivers. The economy of the Chinese nation also developed on the basis of the development of the alluvial plains of the seven major rivers. However, if development is inappropriate or overdeveloped, it will be punished by flooding. Now, we are facing this problem when developing and utilizing the land on both sides of the middle and lower reaches of the Yangtze River. Not only are the flood levels getting higher and higher, the burden of flood control is getting bigger and bigger, but the risks of flood control are also getting bigger and bigger.

The fundamental reason for the imbalance of our country’s ecological system is that there are too many people and too little land.

To rebuild the ecosystem, it must be combined with the adjustment of the economic structure, with the goal of comprehensively improving productivity, and attention should be paid to the coordination of development, reform and stability. We believe that the central government’s principles of comprehensive planning, overall consideration, addressing both symptoms and root causes, and comprehensive management are completely correct.