Combined with my own understanding, what impact does the current water conservancy project have on the environment?

1 Impact on local climate and atmosphere

The construction of water conservancy projects will change the microclimate environmental conditions in the reservoir area, including temperature, wind speed, humidity and precipitation. Relevant research shows that the air transparency above the water surface is 8% ~ 10% higher than that above the house. Compared with land, the ultraviolet radiation on water surface is 30% higher, the temperature is 4 ~ 5℃ lower, and the relative humidity is high 10% ~ 15%. Generally speaking, the regional climate is controlled by atmospheric circulation, but the construction of large and medium-sized reservoirs and irrigation projects has turned the original land into water bodies or wetlands, which has had a certain impact on the local microclimate, mainly in the impact on meteorological factors such as rainfall, temperature, wind and fog.

1. 1 Impact on rainfall

A. rainfall has increased.

This is because the construction of the reservoir has formed a large area of water storage, and under the irradiation of sunlight, the evaporation increases, resulting in rainfall.

B. the regional distribution of rainfall has changed.

The influence of reservoir low temperature effect can change the distribution of rainfall areas: the rainfall in the reservoir area and its adjacent areas decreases, while the rainfall in the peripheral areas at a certain distance increases; The rainfall on the windward side of the high terrain increases and the rainfall on the leeward side decreases.

C. the temporal distribution of rainfall has changed.

In summer, the water surface temperature is lower than the air temperature, 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.

Effect of 1.2 on temperature

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

1.3 Impact on the atmosphere

When talking about dams and ecological problems, the most important issue is the impact of dam construction on the atmosphere. From a global perspective, this problem is very prominent. Therefore, the international community regards the impact on the atmosphere as the primary issue of the ecological impact of dam construction. However, this problem is not serious in China for two reasons: ① Although domestic power stations are large, most of them are alpine canyon reservoirs, and compared with foreign reservoirs, the water surface area of reservoirs is not large; ② There are not many reservoir areas with large areas of forests in China.

2 Impact on hydrological situation and water temperature

2. Impact of1on hydrological situation

The construction of water conservancy projects, especially water conservancy projects, has changed the hydrological cycle of the basin and affected the whole basin to varying degrees, with advantages and disadvantages. After the reservoir impounded, the original river turned into a lake, and the water level rose and the water surface area increased. On the one hand, it increased the evaporation of the water surface, causing changes in the water cycle; On the other hand, because the rock stratum has certain permeability, the reservoir will leak and the groundwater level will rise. The change of reservoir water level is very different from that under natural conditions. For reservoirs with large storage capacity, the water level changes greatly; However, the water level of runoff reservoir does not change much, and there will be no obvious seasonal change. Compared with natural rivers, the reservoir velocity changes obviously. In different parts of the reservoir, the velocity changes differently. Generally, the closer to the reservoir end, the closer to the natural river channel and the closer to the dam, the smaller the flow velocity. In some special reservoirs, the flow velocity is even close to zero. Damming the river makes the hydrological situation change suddenly, which affects the ecological process and function of the original river. The main changes of hydrological situation include: the stability of flow and the changes of velocity and frequency; With the loss of seasonal peak flow, the velocity slows down and the rapids disappear. The water level difference changes gently, and the arrival time and arrival period change; The upward evaporation and downward leakage of water change the water cycle.

2.2 Influence on water temperature

The change of water temperature refers to the phenomenon of temperature difference between inlet and outlet caused by the special water temperature structure of the reservoir. The change of water temperature caused by reservoir engineering is an inevitable phenomenon in reservoir construction. The velocity of the reservoir gradually decreases from the upstream to the dam site, and the nature of the water body also changes. The heat between the water and the atmosphere in the reservoir for a long time changes, which leads to the change of water temperature and flow pattern.

3. Impact on sediments

The construction of the water control project will change the pattern of sediment transport and settlement in the reservoir area and the upstream and downstream rivers, and have a certain impact on the ecological environment of the upstream and downstream rivers and the project area. After the reservoir is impounded, the upstream flow velocity decreases, and the sediment carried by the reservoir water will be deposited in the reservoir area, and the reservoir sediment deposition will reduce the storage capacity, thus reducing the operation efficiency of the reservoir. Sediment problem is one of the most important environmental problems in water conservancy project construction. Damming the river blocks the natural river, which leads to the change of river flow pattern and sediment movement law, and then leads to the change of hydrological characteristics of the whole river upstream and downstream and estuary. This is one of the biggest ecological problems brought by dam construction, and it is also the most worrying problem, which should be treated with special caution. After the reservoir is filled with water, the flow velocity decreases, the sediment carrying capacity of the river weakens, and the suspended solids in the water body are more or less deposited, which not only affects the use of the waterway, but also reduces the storage capacity of the reservoir and affects its service life. The backwater deposition of the reservoir also has an influence on the river morphology. After the river is intercepted by the dam, the sediment is deposited at the bottom of the reservoir, forming a backwater delta, gradually rising towards the dam, and the sediment particles become finer.

4 Impact on water quality

The construction of water conservancy projects will have a certain impact on water quality. On the one hand, after long-distance transportation or storage for a period of time, the reoxygenation process is fully formed, thus enriching the potential environmental capacity resources of water bodies; On the other hand, the water body in the reservoir area is elevated and the water flow is slow, which is not conducive to the diffusion of pollutants.

Generally, river water has low salinity and total hardness, moderate pH value and rich dissolved oxygen. However, no matter which development method is adopted, the water quality will be affected, especially the reservoir project. After the formation of the reservoir, the flow velocity in the reservoir area is reduced, and the sedimentation of the reservoir is obvious, which is beneficial to reduce dissolved minerals, turbidity and biochemical oxygen demand, and increase the concentration of nutrients. After the completion of the reservoir, the dilution and self-purification ability of the river water flowing into the tributary decreased, which led to the aggravation of the river water pollution. Once the reservoir water temperature is stratified, the reservoir water will form a density barrier, which will turn the bottom cold water layer into an anaerobic microbial layer, and the insoluble solid substances in the reservoir will precipitate at the bottom of the reservoir, resulting in nutrient enrichment. Generally speaking, reservoirs have both positive and negative effects on water quality.

① Positive effects: the large water body in the reservoir has slow flow velocity and long residence time, which is beneficial to the settlement of suspended solids and can reduce the turbidity and chromaticity of the water body; At the same time, due to the slow flow rate of the reservoir and frequent algae activities, CO2 generated by respiration combines with calcium and magnesium ions in the water to generate CaCO3 and MgCO3 and precipitates, which reduces the hardness of the water body and reduces the possibility of increased toxicity due to the increase of alkalinity (pH value).

(2) Negative effects: the low flow velocity in the reservoir reduces the exchange rate of water-gas interface and the migration and diffusion ability of pollutants, so the reoxygenation ability is weakened, making 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. Water stored in front of the dam for months or even years is eutrophic because of the massive 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 matter is deposited at the bottom of the reservoir, which has a long accumulation time and is not easy to migrate. Toxic substances or refractory heavy metals contained in it will form secondary pollution sources. In addition, due to the decrease of ecological water quantity of river basic flow, it may aggravate the shrinkage of river section, increase the total amount of sewage discharge, change the agricultural irrigation and drainage system, increase the proportion of non-point sources entering the river, accelerate the speed of non-point sources entering the river, and worsen the environmental quality of downstream rivers and lakes.

5 Impact on soil and environmental geology

5. Effects of1on soil

After the reservoir is filled with water, the state of groundwater along the coast will change. Usually, the groundwater level near the dam will rise, and the groundwater level around the reservoir will flood the land, turning the land into swamp and salinization.

A. immersion. In flooded areas, due to poor soil ventilation conditions, microbial activities in the soil will be reduced and fertility will be reduced, thus affecting crop growth.

B. submerge. Too much humidity leads to the decline of plant roots and difficulty in breathing. When the phreatic layer reaches the arable layer, the soil moisture is too high, which destroys most of the vadose zone.

C. Salinized groundwater is replenished by reservoir bank leakage and rises to the surface through capillary action. Under the strong evaporation, the salt in the water is concentrated on the surface, forming salinization. Excessive osmotic pressure of soil solution will cause physiological drought of plants. Of course, salinization is not necessarily caused by the construction of water conservancy projects, but may also be caused by improper design and operation.

5.2 Impact on environmental geology

After the completion of the dam, it may cause earthquake, landslide, bank collapse, reservoir leakage and other adverse geological disasters.

A. large reservoirs will induce earthquakes after storing water. The reservoir-induced earthquake is mainly due to the increase of water pressure caused by huge water storage capacity, and the lubrication of rock cracks and fracture surfaces under this water pressure, which changes the original in-situ stress balance between rock strata and crust. It is worth noting that reservoir impoundment can induce strong earthquakes in areas with few natural earthquakes and weak earthquake intensity.

B. the reservoir bank collapsed. After the reservoir is filled with water, the shear strength of the bank slope soil decreases due to the rising water level, and landslides, landslides and unstable dangerous rocks are easy to occur.

C. reservoir leakage. The change of hydrological conditions around caused by reservoir leakage. If the reservoir is a sewage reservoir or tailings pond, it will cause pollution in the area around the reservoir and underground water.

6 Impact on river course

River regulation is an integral part of water conservancy project construction. River is an important carrier of water ecological environment, and revetment engineering is an important measure of river ecological management, which plays an important role in protecting dikes from scouring and preventing soil erosion. At the same time, the impact of water conservancy projects on rivers is also significant, mainly in the following aspects:

(1) The river regulation project has changed the natural water system, made the ecological structure simple, reduced the biological community and weakened the water purification capacity of the river, thus reducing the environmental quality and causing ecological degradation;

(2) The geometric regularization of river sections often changes the complex shape of natural rivers into several geometric regularization sections, and changes the natural pattern of staggered deep pools and shoals in river sections;

③ The construction of dikes will cause lateral discontinuity of rivers. Because the dike hindered the communication between the main stream and the branches in flood season, it prevented the lateral expansion of the water flow and formed another lateral flow discontinuity;

(4) The estuary regulation project may cause changes in the elevation of the shoreline and riverbed, thus affecting the tidal level in this area, and further affecting the total amount of drainage;

⑤ Artificial bending and straightening works will cause river bed evolution, cause river scouring, and cause river water level to drop.

7 Impact on biodiversity

Biodiversity refers to all biological species and their diverse ecosystems in a certain time and space. The decrease of biodiversity is mainly caused by various economic and social development activities of human beings. The great development of water conservancy projects has flooded a large number of forests and grasslands, which is an important reason that can not be ignored. The impact of water conservancy projects on biodiversity can usually be divided into the impact on terrestrial organisms and aquatic organisms.

7. Impact of1on terrestrial organisms

Generally speaking, the impact on terrestrial organisms has two aspects. One is permanent direct impact, which refers to the direct damage to terrestrial plants caused by floods and permanent engineering buildings in the reservoir area; The other is indirect influence, which refers to the influence of local climate change, soil swamping and salinization on the species, structure and living environment of animals and plants.

The construction and storage of reservoirs will flood a large area of land, which will cause danger to the growth habitat and feeding place of terrestrial organisms, so the impact of water conservancy projects on terrestrial organisms is mostly unfavorable. Specifically, the area of riparian vegetation and river plants decreased, the microbial diversity decreased, the habitats of birds, amphibians and insects changed or shelters disappeared, resulting in the decrease of species number and the extinction of some species. The land submerged by water conservancy projects is mainly some farmland, plains, slopes and other low-altitude areas in the river basin or coastal areas, mainly crops, with few animals. Therefore, the inundation of land by reservoir construction has great influence on agriculture and little influence on animals. After the operation of the water conservancy project, the existence of water in the reservoir will improve the relative humidity of the air, reduce the probability of forest fires and reduce the fire protection level around the reservoir, which is conducive to the stability of the terrestrial plant ecosystem structure and the growth of plants around the reservoir. In addition, the construction of water conservancy projects will increase the area of wetlands and swamps along the river basin, which will have a favorable impact on amphibians and waterfowl in this area and increase their species and density accordingly.

7.2 Impact on aquatic organisms

Because the main object of water conservancy project is water, the water ecosystem is directly and obviously affected by the project. The construction of the reservoir raises the water level, changes the aquatic ecosystem of the river, and destroys the hydrological conditions and growth environment necessary for the growth and spawning of aquatic organisms. In addition, the death of the original vegetation and the soluble salt in the soil in the flooded area of the reservoir will increase the content of nitrogen and phosphorus in the water body, and the nutrients in the farmland, forest and grassland around the reservoir area will enter the water body with rainfall runoff, thus forming favorable conditions for eutrophication. The impact of water conservancy projects on aquatic organisms is mainly reflected in the impact on fish resources:

(1) blocked the fish migration channel. Reservoir dams cut off rivers, making it impossible for migratory fish to successfully complete their life cycle, and the cascade development of rivers will aggravate this influence.

② Change the composition of fish fauna. After the formation of the reservoir, the hydrological conditions of the water body have changed greatly, thus changing the habitat environment of fish. Different fish live in different environments, so the composition of fish in the reservoir area often changes obviously.

③ Affect fish reproduction. The existence and operation of reservoirs affect the spawning ground and spawning activities of fish. After the reservoir is filled with water, the water flow slows down, the water depth increases, and sediment is deposited, which is not good for fish who like to lay eggs at the bottom of the rapids. When the reservoir is in operation, the change of reservoir water level is not conducive to the reproduction of fish laying eggs on the grass, because the fluctuation of reservoir water level often exposes their eggs to the bank of the reservoir and leads to their death.

8 Impact on population migration and land use

The construction of water conservancy projects will inevitably bring about immigration problems. Because the reservoir construction has broken the original production system, lifestyle, geography, consanguinity and kinship network of immigrants, the political, economic and cultural systems on which they have been living for a long time have disintegrated; At the same time, resettlement has also caused a series of problems, such as the increase of population in resettlement areas and the improvement of carrying capacity of resources and infrastructure. But for different water conservancy projects, the impact of immigration is also different. For example, Dujiangyan is an ancient water conservancy project, and from the existing data, the immigration problem is not its prominent problem; Wanjiazhai Water Control Project and Yellow River Diversion Project have properly resettled the migrants in the reservoir area, improved their living conditions and living environment, improved the water supply guarantee rate, and had a positive impact on population migration and land use. The ecological water transfer project in the lower reaches of Tahe River is vast and sparsely populated, and there is no population migration problem. Generally speaking, the construction of water conservancy projects will produce a certain phenomenon of population migration, and the contradiction between people and land is more tense because of the flooding and occupation of some land by reservoirs. In addition, the construction of water conservancy projects will inevitably change many environmental factors, such as waste water, waste gas, noise, solid waste, etc., which will affect the environmental sanitation of the construction area and the health of local residents and construction workers.