The resource characteristics of flood refer to the property of providing water and soil resources and ecological environment resources.
Before the formation of human civilization, river floods were not disturbed by human beings. In the process of natural floods, a large number of sediments, nutrients and species carried by floods are widely deposited and propagated in the middle and lower reaches of the basin, forming a vast, fertile and diverse plain and a large area of wetlands along the river. Thanks to this resource, human civilization can develop, expand and progress.
With the formation and development of human civilization, floods not only provide resources, but also pose threats and losses to life and production. In order to develop, it is inevitable for human beings to build dikes and compete for land with water, which not only reduces disasters, but also inhibits the development of flood resources. Before entering the industrial society, human beings' ability to control floods was limited, and only residential houses and cultivated land occupying a small part of the river basin could be protected. Because of the low flood control ability, the protected cultivated land is often flooded, and the flood control project has little effect on the characteristics of flood resources.
With the development of flood control engineering technology, the flood control capacity has been improved unprecedentedly, which restricts the development of flood resources characteristics. For example, due to the construction of tall dikes in the plain rivers in the middle and lower reaches of the basin, the wetlands rich in ecological environment resources formed over thousands of years have shrunk in a large area, and some basins even no longer exist; In some basins in the north, an important source of groundwater recharge in the plain tends to be interrupted due to the sharp reduction of flood opportunities; A large number of nutrients carried by the flood were either intercepted by the upstream reservoir or directly transported into the sea, losing the function of nourishing the land and wetlands in the flooded area.
Flood control and the exertion of flood resources characteristics are a pair of contradictions. Without flood utilization measures, flood control standards are inversely proportional to the probability of exerting the characteristics of flood resources.
In areas where there are no flood control projects or flood control standards are low, under normal circumstances, the disasters caused by floods are far greater than the resource benefits provided by floods, and flood control projects with higher standards provide conditions for the safe use of floods.
Second, flood utilization and flood resources utilization
History of flood resources
Flood resources have existed since ancient times. It is not uncommon to replace soldiers with water in the army. The earliest record is that in 359 BC, the State of Chu decided to attack the city on the south bank of the Yellow River, and flooded the army with the help of floods, until Chiang Kai-shek decided to release the Yellow River flood to stop the Japanese army. This method is still in use.
During the Warring States period, Li Bing and his son built Dujiangyan, which was a model of ancient flood utilization. At the same time of using flood, due to the decrease of river flood flow, flood utilization project has the dual functions of promoting benefit and flood control.
Since the Ming Dynasty, the general plan of harnessing the Yellow River has been formed, that is, guiding the use of floods, controlling water and attacking sand, and diverting floods and silting beaches. It is believed that "the river should be governed by people, not by the river." Fuhe River is impatient, if it is convinced by its nature, it will be shallow and deep, and it will be ruled by me (quoted from China Water Conservancy History Draft). The way is: "If you want to be deeper than the north, you will be deeper than the south; To be deep in the south, we must be deep in the north and deep in the south; If you want to be deep in the middle, the north and south dikes are tied together and the middle is deep (the source is the same as above). If you want to silt the beach and strengthen the dike, use this method instead. During the reign of Kangxi in the Qing Dynasty, on the basis of Pan Jixun's river management in the Ming Dynasty, the Yellow River formed a flood control system by harnessing water with dikes to attack sand, controlling flood with dikes and reducing dams (gates) by rolling dams. This flood control strategy has been used to this day.
Haihe river basin has also carried out the practice of flood utilization in modern times. 1927 After the flood of Yongding River, a large amount of sediment flowed into the main stream of Haihe River, resulting in siltation in many places on the riverbed, which greatly affected flood discharge and navigation. 1929, the Yongding River flood was introduced into the low-lying area east of the North Canal, so that the clear water after siltation and sedimentation was discharged into the Admiralty River, which reduced the siltation in the main stream, and at the same time, the depression silted up, forming a siltation area in the north of Diandian, turning100000 mu of alkali wasteland into fertile soil.
During the eight years from 1932 to 1939, Yongding River discharged silt 1 1 times to the north of Dianbei and 4 times to the south of Diannan. The amount of siltation in southern and northern Yunnan is 865,438+420,000 m3 and 65,438+65,438+650,000 m3 respectively, totaling 92.58 million m3. Generally speaking, the siltation height of the ground (759km2) in the lake is 1 ~ 2m, which reduces the siltation of the Haihe River and maintains the flood discharge and shipping functions of the main stream.
During the period of the Republic of China, according to the statistics in the past 35 years, 35 projects were built in Datong, Yanggao, Shuoxian, Yingxian, Tianzhen and Yin Shan on the Sanggan River, covering an area of more than 2 million mu. This not only reduces the amount of sediment from the upper reaches of Yongding River, but also reduces the flood.
During the Republic of China, Mr. Li Yizhi wrote articles such as Gully and Using Flood to Store Groundwater, focusing on the utilization of flood and flood resources. He thought that the northern region has always been dry, and when it rains heavily, the river surges, several times, ten times and dozens times larger than usual. It's a pity to let it flow downstream to the sea. The flood breaks through the dike, and if it is not controlled, it will do more harm. There are five advantages in running ditches and streams in plain areas: ① reducing waterlogging disasters; (2) reducing soil erosion; (3) store water underground for use in case of drought; (4) transferring river floods and nutrients to fields or re-injecting them into the ground; (5) When there is a big flood, divide the water potential in a guiding way to reduce the threat or disaster of flood. The regulation, construction, management, maintenance and benefit of the catchment ditch are also discussed in detail. At that time, the flood control standard was low, the ability to control and guide floods was not strong, and the conditions for large-scale operation of the ditch system were not available. However, in modern times, the development of science and technology enabled human beings to build high dam reservoirs to prevent floods and promote profits, and to extract a large amount of groundwater for production and life. The gully system advocated by Li Yizhi has not been widely implemented.
(B) foreign understanding and adjustment of the relationship between flood control and flood utilization
While providing resources, floods have also caused disasters to the achievements of human civilization and become one of the natural factors that restrict economic development. In the period of industrialization and modern civilization, limited by the level of understanding of resources and ecological environment and the full confidence of human beings in transforming and utilizing nature, the impact of flood disasters has intensified. In view of the flood and its negative effects, countries all over the world have successively launched large-scale flood control projects aimed at controlling the flood.
The United States is one of the first countries to enter modern civilization, and it is also one of the countries most affected by flood disasters. In order to eliminate the influence of flood disaster, the American government has been involved in flood control on a large scale since the middle of19th century. 65438+In the 1960s, the US Army Corps of Engineers proposed to build large-scale dams along the banks of the Mississippi River to improve navigation and control floods. This kind of levee theory, that is, the flood is confined between two levees, became the main flood control strategy of major rivers in the United States at that time. By the early 20th century, the banks of the Mississippi River were covered by a dam system designed and invested by the federal government.
1927, the lower reaches of the Mississippi River flooded about 20,000 square miles (about 5180,000 hectares), 700,000 people left their homes, more than 200 people died, and135,000 buildings collapsed or were damaged, making it one of the worst floods in the United States. This prompted the rapid promulgation of 1928 flood control law for the lower reaches of Mississippi River. The Flood Control Law authorizes the construction of reservoir dams, the regulation of river courses, the setting of flood detention areas, and the opening of spillway to control floods, ending the policy of "dike-only theory". On the other hand, before 1927, the US government believed that flood control was mainly the responsibility of local governments. After 1928, great changes have taken place in flood control policy: "controlling" floods has become a national policy issue and the responsibility of the federal government.
The floods in 1930s prompted some people (represented by Gilbert White) to study flood disasters from a brand-new perspective, and advocated that flood risks should be considered in flood control engineering construction, supplemented by land use management, forecasting and early warning system and flood insurance, so as to adapt to the local geographical and economic environment. This diversified management idea is embodied in the National Flood Insurance Law and the National Flood Insurance Plan (NFIP) of 1968, which constitute the core parts of the national flood control policy and flood control security system: "non-engineering" floodplain management and flood insurance based on risk theory. Although this flood control strategy does not explicitly consider the utilization of flood resources, it gives up the concept of simply relying on engineering to control floods, which objectively provides conditions for the development of flood resources characteristics.
With the deepening of people's understanding of flood and its environmental and ecological functions, after the flood in the United States 1993, in high-risk areas with sparse population and low asset density, the flood was not reinforced or rebuilt, leaving the flood stranded on the land once protected by dikes, which not only utilized the ecological and environmental functions of the flood, but also eased the flood control pressure in other important areas. In the National Comprehensive Flood Control Plan issued by 1995, restoring the ecological and environmental functions of flood-prone areas is one of the four major goals of flood control in the next 30 years.
Since 1960s, Japan has tried to realize the flood control strategy of "safety guarantee". After more than 30 years of operation, a higher standard flood control engineering system has been established. Recently, people have realized that it is neither possible nor economical to ensure safety through flood control projects, and the concept of flood control has been transformed into a "risk selection" strategy under certain flood control standards. In terms of flood utilization, measures such as local digestion of rain and flood, flood resource utilization, artificial beach building, wetland construction and aquatic species cultivation have been taken to form a "multi-natural river" similar to the natural state on the original channelized river.
(III) Assumption of flood utilization in Haihe River Basin
Since 1950s, China has started large-scale river basin management, and flood control has become the main goal of river basin management. At present, there are 86,000 reservoirs in China, and almost all plain rivers are bounded by dikes, and frequent floods are controlled. At the same time, the negative impact of flood control projects has gradually emerged, especially in the Haihe River Basin.
After decades of flood control engineering system construction and 1963 flood in 1950s, the reservoir has been able to control more than 80% of the mountain runoff, and the Haihe River Basin as a whole can defend against the flood once every 50 years. In 1970s, the original large-scale Wadian wetland in the lower reaches of the river basin rapidly shrank and disappeared. The interception of upstream runoff leads to the general disconnection of downstream rivers, and the water consumption mainly depends on groundwater. At first, the underground water level was high, the water storage was abundant, clean and sanitary, and it was convenient and economical to take it on the spot, which not only met the needs of production and life, but also increased the irrigation area. At the same time, with the gradual decrease of groundwater level, a large area of saline-alkali land has been improved and become a good field with high and stable yield. In the 1970s and 1980s, the Haihe River Basin was in the dry season, and there was no flood threat outside the middle and lower reaches of the plain, but there was groundwater recharge inside, which was a peaceful scene. However, with the development of economy and the increase of population, the water consumption increases sharply, and the shallow groundwater is not enough, so the motor wells generally go deep into the deep groundwater that is difficult to regenerate. The original lack of precipitation in Haihe River Basin, coupled with the depletion of groundwater, led to a year-long shortage of water resources, which directly threatened the sustainable development of the basin. At the same time, the ecological environment and social problems caused by river cut-off and water shortage are becoming more and more serious. Industrial and domestic wastewater has been stranded in the river for a long time, and pollutants have accumulated over time and infiltrated into the ground. Agricultural irrigation uses a lot of wastewater from rivers, which makes pollution spread to land and food; Rivers cut off, wetlands disappeared, making dependent organisms extinct and the long-term biological chain of the basin interrupted. At present, although there is no special study on it, it can be predicted that its ecological environment impact will be far-reaching and long-term, even irreversible.
The annual precipitation in Haihe River basin changes greatly. In wet years, the precipitation can reach more than 700 mm, and in dry years, it is less than 400 mm. In wet years, heavy rains and floods caused large-scale floods in the basin, which caused huge losses. In dry years, the drought is severe and there is no water available.
Before the 1960s, the shortage of water resources and ecological environment problems in Haihe River Basin were not outstanding. At that time, due to the low flood control ability, flood was the most harmful to the development of the basin and life and property, and it was the main goal of basin management. The flood control project is planned according to the principle of "drainage first", with the aim of discharging all the floods into the sea to avoid flood disasters. In less than 20 years, great changes have taken place in the basin, and the flood control capacity has been greatly improved. The shortage of water resources and the deterioration of ecological environment have seriously threatened the sustainable development of the basin. Even if the flood problem cannot be ignored, it is only a short-term impact. For the arid and water-deficient areas in the north, the occurrence of floods can improve the ecological environment and alleviate the shortage of water resources.
1996, the biggest flood in Haihe river basin since 1963. Although the scale of the flood was far less than 63 years, it still caused huge losses. During the evolution and flooding of this flood, an unprecedented scene appeared: a large amount of surface runoff was lost along the way, and the flood evolved downstream, far less than the estimated magnitude, and the arrival time was obviously delayed. Due to the over-exploitation of groundwater, the ability of surface to absorb runoff and the ability of underground water storage have increased dramatically. According to the estimation after the flood, the runoff coefficient is only half of that in flood period 1963, which is 0.24, and the amount of water seeping into the ground is as much as 8 billion m3. The average buried depth of groundwater level in plain area is 2.02 meters higher than that before flood season and 0.84 meters higher than that in the same period of last year, which exceeds the exploitation amount. In addition, the flood washed away pollutants such as waste residue and wastewater accumulated in the basin for many years, greatly improving the environmental landscape. After 1996, agriculture in Hebei province has been bumper harvest for three consecutive years, which is not unrelated to the massive recharge of groundwater and the alleviation of water shortage contradiction after 1996 flood.
Haihe river basin was in the high water period in 1950s and 1960s, in the transitional period of high water and low water in 1970s, and in the low water period in 1980s and 1990s. It is predicted that it will enter the rainy season again at the beginning of 2 1 century. How to seize the opportunity, take effective measures while flood control, make full use of the resource characteristics of flood, and alleviate the problems of water shortage and ecological environment deterioration in the basin is of great significance to the sustainable development of the basin.
Historically, because the river basin flood control engineering system has not been built, it is difficult to defend against frequent floods, so there is no way to talk about flood utilization and flood resources utilization. Although the existing high-standard flood control system has an impact on the development of flood ecology and resource characteristics, it can basically ensure the safety of important areas and has a high ability to dispatch and control floods, thus providing conditions for the safe and rational use of floods.
In view of the present situation of Haihe River Basin, the author suggests the following aspects for flood utilization and flood resource utilization.
(1) On the basis of full demonstration, raise the limited water level or flood storage level of the reservoir in flood season and store more floods. Reservoirs in Haihe River Basin were mainly built in the large-scale mass water conservancy construction movement in 1950s and 1960s, and there are some problems such as low quality and low dam protection standard. After continuous reinforcement since 1980s, most reservoirs have reached the ministerial standards. After the test of "96.8" flood, it is feasible to raise the flood limit water level of some reservoirs or even exceed the flood storage. As for the extent to which the flood limit water level and flood control storage capacity are improved, it needs to be determined on the basis of full demonstration.
(2) In case of flood, use flood peak to clean up river pollutants. In recent 20 years, Haihe River Basin is in the dry season, and it is also in the stage of rapid social and economic development. With the sharp increase of water consumption, many rivers have been cut off, and a large amount of untreated production and domestic garbage has been stranded in the rivers for a long time, causing serious pollution. After the "96.8" flood, the water quality of the water system affected by the flood was generally significantly improved due to the erosion and dilution of the self-purification by the flood, and the environmental benefits of the flood were remarkable. Flood utilization should not only play its role in improving the environment, but also make up for the shortage of water resources and restore the ecology of the basin. Therefore, it is not appropriate to discharge all the floods into the sea. In principle, the water before the flood is used to clean the river and improve the environment, and the rest is used to supplement water resources and restore the ecology of the basin as much as possible. It is suggested that the amount of flood needed to clean up the river and improve the environment should be determined by the water resources department in cooperation with the environmental protection department.
(3) Build a flood utilization project to lead the flood to the field and recharge the groundwater. The "96.8" flood replenished 8.2 billion m3 of groundwater in Haihe River Basin, about twice as much as many years ago. In addition to infiltrating into rivers, flood detention depressions and local rainfall, floods have caused huge losses, but they have also replenished a considerable amount of groundwater. 1996 the average precipitation in the basin is 600 mm. According to statistics, the average annual precipitation in the 43 years from1956 to1998 shows that 10 is the year with precipitation greater than 700mm, and1970 is the rainy season. Under the current situation of the river basin, it is roughly estimated that when the annual average rainfall is more than 600mm, the groundwater recharge is more than 8 billion m3, and when it is more than 700mm, the groundwater recharge is more than 65.438+0.5 billion m3 (according to the "63.8" rainstorm recurrence study made by Hebei Provincial Defense Office 1994, the groundwater recharge in Hebei Province reaches146. In order to make full use of flood resources and replenish groundwater, we can learn from the flood utilization gully system designed by Mr. Li Yizhi, and combine flood diversion gates, rolling dams, flood detention depressions and other projects to guide floods in criss-crossing gullies in the vast plain area, which is expected to further increase groundwater recharge. Its five main functions are described above.
(4) restore partial depression. Before 1970s, the Haihe River basin was full of depressions and lakes, which was not only a place for flood storage, but also an important part of the long-term natural ecological environment. After 1970s, due to the sharp increase of water consumption in dry season and river basins, except for a few depressions, they dried up one after another and became agricultural production land. The ecological and environmental functions of depressions were basically lost, and the flood storage function was greatly reduced. Because perennial water storage in depressions and lakes not only has the functions of improving the ecological environment and regulating floods, but also has the benefits of water supply, aquaculture and tourism, which may be more beneficial than being used as agricultural land. Considering that the basin will enter the flood season again and the South-to-North Water Diversion Project will be implemented soon, it is suggested to carry out preparatory work for water storage in Wadian where conditions permit (if there is a regulating reservoir or near the main canal of the South-to-North Water Diversion Project, the ecological environment has a strong improvement function, the flood storage effect is good, and the resettlement is easy), including the resettlement planning, the construction and improvement of water storage projects, and the formulation of the cultivation plan for wading industry. Once in the flood season, water storage will be carried out in a planned way.
⑤ Make use of the regulation and storage function of the river network in the basin to make the flood stay in the plain area for a longer time. After large-scale flood control project construction, several relatively independent water systems have been formed in Haihe River Basin, each with its own access to the sea and connected by inland rivers. In case of large flood, it can be discharged into the sea alone, and in case of medium and small flood, it can be discharged into the sea relatively centrally through river network dispatching, which will increase the flood detention time in plain areas and replenish more groundwater. Combined with the above measures, the purpose of making full use of flood can be achieved.
Three. conclusion
Flood resources have existed since ancient times, and in the period of low flood control ability, flood utilization is only sporadic. With the improvement of human ability to control floods, the increasing demand for water resources and the concern for ecological and environmental problems, it is not only possible but also urgent to use floods safely and reasonably on a large scale. In the northern region where water resources are relatively scarce, the use and utilization of floods are particularly important. Because the research on flood utilization and flood resource utilization has only recently begun, the suggestions on flood utilization in Haihe River Basin, such as making full use of existing reservoir channels to store stagnant water, using flood peaks to clean up pollution, diverting flood to fields and repairing depressions, are still too shallow for reference.
(