The Yellow River, the second longest river in China, flows through arid and semi-arid areas, providing valuable water resources for northwest and north China, and is an important source of life in the north. The Yellow River basin has serious erosion, unstable riverbed, serious water pollution and fragile ecological environment. The Yellow River Conservancy Committee put forward the slogan of "maintaining the healthy life of the Yellow River", which turned the management of the Yellow River into multi-objective management. According to the experience and lessons of river regulation at home and abroad, the author puts forward the following views on the comprehensive management of the Yellow River.
1. Controlling the undercut of the channel is the basis of controlling erosion.
The Yellow River flows through the loess plateau with the most serious soil erosion in the world. In the past, about 65.438+600 million tons of sediment entered the downstream every year, and about 400 million tons of sediment was deposited on the river bed. It poses a great threat to the lives and property of people on both sides of the lower Yellow River. We usually call the erosion form of slope runoff that strongly erodes soil and parent rock and cuts into the ground to form large gullies as gully erosion. Gully erosion is the inducement of rill erosion and slope erosion. Trench undercutting leads to steep slopes of bank ditches and branch ditches, and rill erosion and slope erosion are intensified, so controlling trench undercutting is the fundamental to control erosion. Erosion leads to the loss of nutrients in the soil and makes the land barren. At the same time, it carries sediment into the Yellow River.
The fundamental way to control erosion is to control the downward cutting of the channel and the upward catching of the channel head, which can be controlled jointly by hydraulic engineering and bioengineering. Water conservancy project mainly refers to the construction of warping dams in the upper reaches of the Yellow River to intercept the sediment generated by scouring, make it accumulate in the river course, raise the river bed and reduce the slope, so as to achieve the purpose of stabilizing the river course. In recent years, the construction of warping dams on the Loess Plateau has played an important role in preventing sand and controlling gully erosion. Bioengineering refers to planting vegetation that can effectively control erosion in the gully or on the slope on both sides of the gully to protect the river and slope and prevent erosion and scouring. The research shows that vegetation cover on slope can reduce gully erosion and sediment yield by more than 75%. The key to controlling erosion by bioengineering is to select suitable species. If species are selected properly, it can not only control erosion, but also increase biodiversity.
From 65438 to 0986, Qian put forward a scientific proposal to speed up the management of the loess plateau by developing seabuckthorn resources as a breakthrough, so that seabuckthorn shrubs could be planted in a large area on the loess plateau. Seabuckthorn, also known as vinegar willow, acid thorn and black thorn, is a plant with good biological and ecological characteristics, strong adaptability, developed root system and strong germination ability, which can spread the population through clonal growth. Through physiological integration and looking for nutrients, the fitness of base plants and the survival probability of ramets can be improved. Hippophae rhamnoides root system has high nitrogen fixation ability, which is of great significance to increase soil organic matter and nitrogen content, improve soil structure and improve forest productivity. It is found that planting Hippophae rhamnoides can effectively stop sand and store water, promote the growth of other local species, improve biodiversity and have good ecological effects.
Second, increasing resistance and slowing down is an important measure to stabilize river regime.
Stable river regime is very important to the health of rivers, and reducing the flow rate is an important measure to stabilize river regime. Reducing the flow velocity mainly depends on the resistance structure of the river bed. Curved river, pebbles in the river and vegetation on the beach are all part of the river bed resistance structure. These resistance structures can reduce the flow velocity, prevent the river from scouring and stabilize the river regime. At present, some river regulation projects have destroyed the resistance structure of river bed. Caused a lot of problems. From the point of view of comprehensive river management, river cutting and straightening, beach cleaning and roughening, and channelization projects are not conducive to the health of rivers. Of course, reducing the flow rate will lead to sediment deposition, so increasing resistance and slowing down should be carried out from top to bottom. As a whole, increasing resistance and slowing down fundamentally reduces the power of sediment erosion and movement, reduces the evolution rate of river bed, and makes the river regime gradually stable.
Bending is the nature of the river, and straightening the winding river is against the nature of the river. Cutting, bending and straightening concentrate the energy of water flow, causing river erosion and bank erosion, leading to river instability, destroying aquatic habitats and affecting the survival of aquatic organisms. Beach vegetation can reduce the flood speed. Extend the flood advance time. Many scholars have studied the mechanism of beach vegetation affecting the hydraulic characteristics and geomorphological characteristics of rivers. Beach vegetation can maintain the stability of river topography by increasing resistance and reducing nearshore velocity, and increase the stability of river banks through their roots, thus accelerating the deposition of beaches and river banks. River channelization project will have adverse effects on river geomorphology and ecology. Hardening the riverbank with concrete has changed the original nature of the river. The roughness of smooth bank is much less than that of natural bank, which leads to the increase of nearshore velocity and threatens the safety of bank. People have realized that smooth banks are not conducive to flood control. In some places, in order to control the nearshore velocity, large stones are embedded in smooth bank protection to increase the roughness of banks.
Reducing the flow velocity is not only beneficial to stabilizing the river regime, but also very beneficial to the river ecology. Through the study of river biological community, it is found that when the velocity in the river is less than 2 meters per second, most aquatic animals and plants live in low-speed waters. Fitness index SI is the fitness of physical and chemical conditions of habitat for biological survival and reproduction. SI= 1 and SI=0 represent the best and worst living conditions respectively. The study of 36 species of fish shows that about 55% of adult fish are most suitable for living in still water. 97% of fish are the least suitable for living in water with a flow rate of more than 3 meters per second. Most fish need a higher spawning speed, while young fish need a lower spawning speed. However, when the flow velocity is greater than 3 meters per second, the adaptive index of all fish, whether adult or juvenile, drops to zero, while the adaptive index of spawning, hatching and fry drops below 1.
Third, the construction of Tonghe Lake wetland is a chain to improve the ecology of the Yellow River.
Rivers are carriers of life and provide habitats for various aquatic organisms. At present, the Yellow River is in a state of serious pollution, more than 60% of the water is undrinkable, and the ecology is also seriously damaged. In addition, the riverbed sediments of the Yellow River are all fine sand, and the aquatic species and biomass of the Yellow River are much less than those of the Yangtze River. The author once led a research team to conduct field ecological investigations in the lower reaches of the Yellow River and the Yellow River Delta, and collected benthic samples from the riverbed and floodplain wetlands of the Yellow River. Through analysis, it is found that there are few benthos.
Tonghe Lake wetland plays an extremely important role in river ecology. In the water system, Tonghe Lake and its branches and tributaries constitute a complete river and lake complex ecosystem. As different ecological units, Tonghe Lake plays its own ecological functions. Many fish are found to lay eggs in rivers and grow up in lakes. The relationship between Tonghe lake and river is beneficial to the survival and development of benthic invertebrates and fish. The running water environment of rivers has high dissolved oxygen, but nutrients. Tonghe Lake has high primary productivity and supports all aspects of water food web. Conversely, lake ecology also depends on rivers. Therefore, maintaining the connection between rivers and lakes is very important for ecology. Studies have shown that the biodiversity of isolated lakes has decreased. Take the Yangtze River as an example. In the past 50 years, many lakes in the Yangtze River have gradually become smaller and isolated from each other. The number of benthos in isolated lakes decreased from 46 to 30. The species of fish has been reduced from 80 to 50. One principle of ecological management is to maintain a high degree of connectivity between rivers and lakes. The construction of rivers and lakes in the Yellow River can significantly improve the ecology. For example, the Xiaobei main stream, the second suspended river floodplain in Henan, Dongping Lake and the north-south flood detention area can all build rivers and lakes.
Another measure to improve the ecology is to increase the water surface area. Increasing the surface area can provide more habitats for aquatic organisms. From this point of view, building reservoirs and dams is beneficial to ecology. Although the construction of reservoirs and dams has isolated habitats and threatened some migratory fish, the increase of habitats has promoted the improvement of ecology.
Aquatic vegetation plays an important role in river ecosystem. Aquatic vegetation can provide benthic animals and fish with food and places to rest and lay eggs, and can absorb the organic matter in the river to achieve the purpose of purifying the river. Juma River in the suburbs of Beijing is a river with well-developed aquatic vegetation. Coastal residents use rivers as domestic water, and the domestic sewage carrying a large amount of organic matter is discharged back into the rivers. These organic substances are constantly absorbed by the vegetation in the river, and after a certain distance of purification, the river becomes very clear. In the Yellow River regulation, aquatic vegetation can be planted in the conditional reach to purify the water quality.
Suitable aquatic plants such as submerged plants (such as Carex, Sargassum, Potamogeton, etc.), emergent plants (such as water wax, reed, etc.) and floating plants (such as lotus, clam, duckweed, etc.) are introduced into Tonghe wetland and lake to establish benthic communities necessary for the life of the Yellow River and create and maintain a complete aquatic ecosystem of the Yellow River. The ecological restoration of water body should consider the restoration of the whole biological chain. For example, when submerged vegetation of water body is restored,
4. Controlling point source pollution is the key to solve the pollution problem.
In recent years, the Yellow River has been seriously short of water and its pollution has intensified. According to the monitoring statistics of 200 1, the over-standard rates of phosphorus and ammonia nitrogen in the middle and lower reaches of the Yellow River are above 90% and 50% respectively. At present, there are point source pollution and non-point source pollution in the Yellow River Basin. However, point source pollution can be controlled by sewage treatment, while non-point source pollution is difficult to collect and treat. Non-point source pollution is mainly nutrition. However, point source pollution contains many toxic substances, which often kill some vertebrates and invertebrates and even vegetation, greatly reducing the purification capacity of rivers. Many examples show that after industrial sewage discharge kills higher organisms, some bacteria and algae can multiply in large numbers, causing the river to stink. Therefore, controlling point source pollution is the key to improve the water quality of the Yellow River. Previous studies show that if point source pollution is fully controlled, the surface water quality of rivers, lakes, reservoirs and other rivers can be significantly improved.