Analysis of the impact of water conservancy and hydropower project construction on ecological environment?

The following is an analysis of the impact of water conservancy and hydropower project construction on the ecological environment brought by Zhongda Consulting for your reference.

At present, the hydropower development rate in most developed countries is very high, and some countries even reach more than 9%, while the level of hydropower resources development in developing countries is extremely low, generally around 1%. At present, the development of hydropower resources in China has only reached more than 1%. China is in a period of rapid economic growth. The research shows that in the next 2 years, in order to solve the problem of water shortage, realize rational allocation and meet the requirements of flood control and power supply, large-scale water conservancy and hydropower projects still need to be built. However, the impact of the construction of large-scale water conservancy and hydropower projects on the ecological environment has received unprecedented attention. Most countries in the world are more seriously researching, studying, delaying, and even suspending or giving up new hydropower development plans in some extreme cases than ever before. Therefore, in the future, ecological problems will become an important constraint factor for the further development of hydropower construction and even the whole water conservancy cause in China.

to correctly handle the relationship between the construction of large-scale water conservancy and hydropower projects and the protection of the ecological environment, we must scientifically and realistically analyze what kind of ecological environment problems may be caused by the construction of large-scale water conservancy and hydropower projects, and what are the specific manifestations of ecological constraints, and make concrete analysis of specific problems in combination with reality, distinguish primary and secondary, grasp the key, correctly understand and properly handle the problems encountered at this stage with the scientific development concept and the concept of harmonious coexistence between man and nature, so as to ensure the rapid and healthy development of China's hydropower industry. Generally speaking, the environmental impacts of water conservancy and hydropower projects mainly include immigration, sediment and river courses, climate, hydrology, geology, soil, water, fish and biological species, cultural relics and landscapes, and people's health.

1. Analysis of the impact of water conservancy project on natural environment

1.1. Impact on climate

Generally, the regional climate is controlled by atmospheric circulation, but after the construction of large and medium-sized reservoirs and irrigation projects, the original land has become a water body or wetland, which makes the local surface air moist and will have a certain impact on the local microclimate. Mainly manifested in the impact on meteorological factors such as rainfall, temperature, wind and fog [1].

1.1.1 Impact on rainfall

(1) Rainfall has increased: this is due to the large area of water storage formed by the construction of the reservoir, which is caused by the increase of evaporation under the sunshine radiation.

(2) The regional distribution of rainfall has changed: the influence of low temperature in the reservoir can change the distribution of rainfall. Generally, the evaporation in the reservoir area increases and the air becomes moist. The measured data show that the rainfall in the reservoir area and adjacent areas has decreased, while the rainfall in the peripheral areas at a certain distance has increased. Generally speaking, the rainfall on the windward side of the high terrain has increased, while the rainfall on the leeward side has decreased.

(3) the distribution of rainfall time has changed: for large reservoirs in the south, the water surface temperature is lower than the air temperature in summer, the gas layer is stable, the atmospheric convection is weakened, and the rainfall is reduced; However, in winter, the water surface is warmer, the atmospheric convection is enhanced and the rainfall is increased.

1.1.2 Impact on temperature

After the completion of the reservoir, the underlying surface of the reservoir area changed from land surface to water surface, and the mode and intensity of energy exchange with air changed, which led to the change of temperature, and the annual average temperature increased slightly.

1.2 Impact on hydrology

After the construction of the reservoir, the flow process of the downstream river course has been changed, thus affecting the surrounding environment. Reservoirs not only store flood in flood season, but also intercept the basic flow in non-flood season, which often causes the water level in the downstream river to drop sharply or even cut off, and causes the surrounding groundwater level to drop, thus bringing a series of environmental and ecological problems: downstream natural lakes or ponds dry up when the water source is cut off; The groundwater level in the downstream area drops; Sedimentation at the estuary caused by the decrease of river flow at the estuary leads to seawater backflow; Due to the decrease of river flow, the self-purification ability of the river is reduced; Reservoirs, which mainly generate electricity, mostly serve as peak loads in the power system, and the daily variation range of discharge is large, which causes the water level in the downstream river to change greatly, which has a great impact on shipping, irrigation diversion level and fish farming. When the water level in the lower reaches of the reservoir drops sharply and even stops, it will inevitably lead to the deterioration of water quality.

1.3 the problem of sediment deposition

take Sanmenxia reservoir as an example to illustrate the problem of reservoir deposition. The reservoir was impounded in 196. One and a half years later, 1.5 billion tons of sediment was deposited in the Tongguan-Sanmenxia reach, and the Tongguan river bed was raised by 4.5m m. The siltation zone extended to the Weihe River mouth in the upstream, forming bar sand, and the groundwater level on both sides of the river also rose, thus causing the impact of secondary salinization of farmland on the water body on both sides of the river.

1.4 < P > After the water originally flowing in the river stagnated in the reservoir, some changes will occur. The first is the impact on shipping, for example, it takes time to cross the lock, which will have an impact on the upstream and downstream speed; The water temperature of the reservoir may rise, and the water quality may deteriorate, especially in the ditches and branches of the reservoir, which are prone to water pollution, such as water bloom; After the reservoir is filled with water, with the expansion of water surface and the increase of evaporation, water vapor and water mist will increase, and so on. These are the effects of water changes after dam repair. After the reservoir is filled with water, it can have both positive and negative effects on the water quality.

(1) beneficial effects: the large-volume water in the reservoir has slow flow velocity and long retention time, which is beneficial to the settlement of suspended solids and can reduce the turbidity and chromaticity of the water; The flow velocity in the reservoir is slow, and the algae activities are frequent. CO2 generated by respiration combines with calcium and magnesium ions in the water to generate CaCO3 and MgCO3, which are precipitated, reducing the hardness of the water.

(2) Adverse effects: the low flow velocity in the reservoir reduces the exchange rate of water and gas interface and the migration and diffusion ability of pollutants, so the reoxygenation ability is weakened, which makes the self-purification ability of reservoir water weaker than that of rivers; The flow velocity in the reservoir is small, and the transparency is increased, which is beneficial to algae photosynthesis. The water stored in front of the dam for months or even years is eutrophic because of the large growth of algae. Submerged vegetation and rotten organic matter will consume a lot of oxygen in water and release biogas and a lot of carbon dioxide, which will also lead to the greenhouse effect; Suspended sediment is deposited at the bottom of the reservoir, which is not easy to migrate for a long time. If it contains toxic substances or refractory heavy metals, it can form secondary pollution sources.

1.5 Impact on Geology

After the dam is built, adverse geological disasters such as earthquake, bank collapse and landslide may be triggered.

(1) Large reservoirs can induce earthquakes. The main reason is the increase of crustal stress caused by the weight of water body; Water infiltration into faults can lead to an increase in lubrication between faults; Increase the pore water pressure in the rock stratum.

(2) the bank of the reservoir collapsed. After the reservoir impoundment, the water level rises, and the shear strength of the bank slope soil decreases, which is prone to landslides, landslides and instability of dangerous rock masses.

(3) reservoir leakage. Leakage causes changes in the surrounding hydrological conditions. If the reservoir is a sewage reservoir or a tailings reservoir, leakage will easily cause pollution in the surrounding areas and underground water bodies.

1.6 Impact on soil

Reservoir impoundment causes land immersion, swamp and salinization in the reservoir area.

(1) Immersion: In the immersion area, due to poor ventilation conditions in the soil, microbial activities in the soil are reduced, fertility is reduced, and crop growth is affected.

(2) Marsh and incubation: the rise of water level causes the groundwater level to rise, and the soil becomes swampy and incubation, which leads to the decline of plant roots and difficulty in breathing.

(3) salinization: groundwater recharge by reservoir bank leakage rises to that surface through capillary action, and salt in the wat is concentrated on the surface under strong evaporation, thus forming salinization. Excessive osmotic pressure of soil solution can cause physiological drought of plants.

1.7 impact on fish and biological species

here, fish is specific, while biological species generally refer to animals, plants and microorganisms. At present, the society is extremely concerned about the impact of dam construction on migratory fish. In fact, due to different species, migratory fish live in different environments, such as sturgeon, and a considerable part of them migrate between Hokkaido, Japan, about 45℃ north latitude, Wusuli River, Heilongjiang River, Songhua River and other rivers and seas in China. Moreover, not every river has migratory fish. Countries around the world usually adopt two methods to solve the problem of fish migration when building dams: one is to take engineering measures to build fish ladders and fishways; The other is artificial breeding of migratory fish. In the construction of Gezhouba dam on the Yangtze River in China, artificial breeding was chosen to solve the migration problem of Chinese sturgeon, which proved to be quite successful. It should be emphasized that building dams on different rivers in different areas will have different impacts on fish and biological species, so it is necessary to make a concrete analysis of specific rivers, and we cannot generalize them.

(1) Impact on terrestrial plants and animals:

(1) Permanent and direct impact. Flooding in the reservoir area and permanent engineering buildings will cause direct damage to terrestrial plants and animals;

② Indirect impact refers to the impact on the species, structure and living environment of animals and plants caused by local climate, soil swamping and salinization.

(2) Impact on aquatic organisms: mainly refers to the impact on aquatic algae plants. The death of the original vegetation in the submerged area and the submerged area of the reservoir, as well as the soluble salt in the soil, will increase the content of nitrogen and phosphorus in the water body, and the nutrients of farmland, forest and grassland around the reservoir area will enter the water body with rainfall runoff, thus forming favorable conditions for eutrophication.

(3) Impact on fish: cut off the migration channel of migratory fish; The water temperature discharged from the deep hole of the reservoir is low, which affects the growth and reproduction of fish downstream; The discharge of clear water affects the bait of downstream fish and the yield of fish; When the high dam overflows and floods, the high-speed water flow causes the nitrogen and oxygen content in the water to be too saturated, resulting in bubble disease of fish. For example, Gezhouba on the Yangtze River has a discharge of 41,3 ~ 77,5m3/s, an oxygen saturation of 112% ~ 127% and a nitrogen saturation of 125% ~ 135%, resulting in a juvenile mortality rate of 32.24%.

2. Impact on social environment

2.1 Impact on human health < P >. For example, after Danjiangkou Reservoir and Xin 'anjiang Reservoir were completed, the original land became a wetland, which was conducive to mosquito breeding, and malaria was once prevalent. Because the Three Gorges Reservoir is located between two schistosomiasis endemic areas (Chengdu Plain in Sichuan and the middle and lower reaches of the Yangtze River), the water surface increases and the flow rate slows down after the reservoir is built. Therefore, whether snails can migrate from the upstream or downstream to the reservoir area and breed there is an environmental issue that needs attention [2].

2.2 Impact on immigrants

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