What environment should be paid attention to in water conservancy project construction?

Preliminary study on the theory and method of post-evaluation of environmental impact of water conservancy construction projects

2004- 1 1- 19

Abstract: Post-evaluation of water conservancy projects refers to the retrospective evaluation of completed water conservancy projects, which is the last link of capital construction procedures. Post-evaluation of environmental impact is one of the important contents of post-evaluation of engineering. This paper briefly expounds the meaning of environmental impact post-assessment, analyzes the purpose and function of environmental impact post-assessment, and discusses the methods, steps and contents of environmental impact post-assessment.

[Keywords:] water conservancy project, environmental impact, post-evaluation

1 preface

The post-evaluation of water conservancy projects began in 1993. Over the past few years, post-evaluation work has been carried out for more than ten projects, including Danjiangkou Water Control Project, Gaozhou Reservoir, Shaoshan Irrigation District, Panjiakou Water Control Project and Chen Lai Irrigation District. Some post-evaluation projects include environmental impact post-evaluation. In order to draw up the environmental impact assessment standard of water conservancy and hydropower projects, the special environmental impact assessment of Panjin Irrigation District and Sanmenxia Water Control Project was carried out. The post-assessment of environmental impact of water conservancy projects is not carried out for a long time, there are not many projects to carry out post-assessment, and the theoretical support and rules and regulations of post-assessment of environmental impact are relatively lacking. In order to better carry out post-assessment of environmental impact, it is necessary to study the concept, function, method and content of post-assessment of environmental impact.

2 the meaning of post-assessment of environmental impact

Post-evaluation of environmental impact of water conservancy project refers to investigating the actual environmental impact after the construction project is completed and operated for a period of time, and comparing it with the results of environmental impact prediction and evaluation, checking the differences between the actual environmental impact of the project and the results of prediction and evaluation, so as to test the rationality of the results of environmental impact prediction and environmental protection design and evaluate the environmental quality after the project is completed. In short, the post-evaluation of environmental impact is to evaluate the actual impact of the project on environmental quality, natural resource utilization and ecological balance.

3 The purpose and function of post-assessment of environmental impact

3. 1 Verify the results of environmental impact prediction and environmental protection design.

The results of environmental impact assessment and environmental protection design are put forward on the basis of investigation, research, analysis and prediction before the project construction. Whether the prediction method is reasonable, the parameter selection is appropriate and the conclusion is correct needs to be tested by engineering operation practice. Through the post-evaluation of environmental impact, the rationality of the evaluation method and the correctness of the evaluation conclusion can be verified by comparing the actual environmental impact with the results of environmental impact prediction evaluation.

3.2 To provide scientific basis for further strengthening the management of engineering environment.

After the project was completed and operated for a period of time, the environmental impact caused by the project gradually appeared. Post-evaluation of environmental impact can find out the actual favorable and unfavorable factors of the project by investigating the environmental changes after the project construction, and put forward measures to further exert the favorable impact of the project and reduce the unfavorable impact, thus providing scientific basis for further strengthening the environmental management of the project. The environmental impact of Sanmenxia water control project on the Yellow River was reviewed and evaluated. This paper systematically summarizes the environmental changes in the past 30 years, analyzes and studies the environmental evolution trend, puts forward the main influencing factors, puts forward some countermeasures such as controlling pollution, protecting water sources, eliminating rodents and effectively solving the problems left over by immigrants, and puts forward some suggestions for further strengthening scientific research and environmental management.

3.3 Provide reference for environmental impact assessment and environmental protection design of other projects.

Water conservancy projects are generally large-scale, with a wide range of influences and many influencing factors, and it is difficult to predict and evaluate the environmental impact. The environmental impact assessment of water conservancy projects in China started late, and it was not carried out until the mid-1980s. It has only a history of more than ten years. The theory and method of environmental impact assessment are still not perfect, and some environmental impact prediction and assessment are still difficult to quantify. Through the post-evaluation of environmental impact, we can explore the theory and method of environmental impact assessment, make the prediction method more reasonable and the evaluation result more realistic. The results of post-assessment of environmental impact can also provide reference for environmental impact assessment and environmental protection design of similar projects. For example, the post-assessment results of environmental impact of Sanmenxia water control project provide technical support for the environmental impact assessment of Xiaolangdi water control project on the Yellow River. Sanmenxia water temperature prediction model and parameters have been applied to the water temperature prediction of Xiaolangdi Reservoir and achieved good results.

3.4 Check the implementation of the "three simultaneities" system for environmental protection facilities of the project.

The Environmental Protection Law and the Regulations on Environmental Protection Management of Construction Projects stipulate that the environmental protection facilities that need to be built in a construction project must be designed, constructed and put into use at the same time as the main project. The completion acceptance of environmental protection facilities shall be carried out at the same time as the completion acceptance of the main project. The completion acceptance of environmental protection facilities is a form of post-environmental impact assessment, which can effectively check whether the construction unit has built environmental protection facilities according to the requirements of the environmental impact report (table); Check the completion of environmental protection during the construction period, whether some damaged environment has been restored, and check the development of environmental monitoring during the construction period; Check the establishment and operation of environmental management institutions. Geheyan Water Control Project passed the environmental protection completion acceptance, comprehensively summarized the environmental protection work of the project construction, and comprehensively reviewed and evaluated the implementation of the "three simultaneities" of the project.

3.5 Check the operation of environmental monitoring facilities to provide basis for the adjustment and optimization of environmental monitoring sections and monitoring items.

In the design of the environmental monitoring station network of this project, the environmental monitoring sections and monitoring items are set on the basis of prediction and evaluation according to the original environmental conditions, which may be different from the environmental conditions after the project is put into production. After the project is put into operation, the natural and social environmental conditions are also changing, so it is necessary to test the original environmental monitoring station network design according to the new environmental conditions. In the process of environmental impact post-assessment, systematically investigate the environmental conditions after the project is put into operation, fully understand the quantity and distribution of pollution sources, and systematically analyze the monitoring data. On this basis, the environmental monitoring sections and monitoring items are reasonably adjusted and optimized.

4 methods and steps of post-assessment of environmental impact

4. 1 Post-assessment method of environmental impact

The basic method of environmental impact post-assessment is comparison method, that is, the actual environmental impact and environmental quality after the completion of the project are compared with the environmental background before the project construction and the environmental assessment and prediction results during the project decision-making. Through comprehensive analysis, the environmental quality after the completion of the project is evaluated, the actual favorable and unfavorable factors of the project are determined, and measures to further exert the favorable impact of the project and reduce the unfavorable impact are put forward.

4.2 Steps of post-assessment of environmental impact

4.2. 1 investigation and data collection

Environmental impact post-assessment needs to collect the following five main aspects of information.

(1) environmental impact assessment results. The information of environmental impact assessment results in the feasibility study stage of water conservancy project is the basis of post-evaluation of environmental impact of water conservancy project, and the environmental background before the project construction is the premise of post-evaluation of environmental impact and environmental change trend after the project operation. The prediction results of various environmental factors are also the main content of post-evaluation review. In the post-assessment of environmental impact, the environmental impact report and the approval opinions of the environmental protection department should be collected, including environmental monitoring data and the impact prediction results of various environmental factors (water quality, water temperature, meteorology, soil, terrestrial organisms, aquatic organisms, human health, etc.). ) and environmental protection measures taken to reduce adverse effects.

(2) Environmental protection design achievements. Environmental protection measures and the design results of environmental monitoring station network are important technical documents for implementing environmental protection facilities, the basis for checking the implementation of the "three simultaneities" system of environmental protection facilities, and the important contents to be verified in post-evaluation. After the evaluation, the environmental protection design results and review opinions in the preliminary design stage should be collected.

(3) Relevant information on the implementation of environmental protection measures during the construction period. Construction activities have adverse effects on the surrounding environment, such as waste water, waste gas, noise emission, vegetation destruction, etc. During the post-evaluation period, the environmental protection work and environmental monitoring data during the construction period should be collected, especially the vegetation restoration and reclamation of the temporary land occupied by the construction.

(4) Completion acceptance data of environmental protection facilities. The completion acceptance of environmental protection facilities is an indispensable part of the completion acceptance of water conservancy projects, and it is also a new content of environmental management of water conservancy projects. The contents of the application report for completion and acceptance of environmental protection facilities generally include preliminary environmental protection work and approval, environmental protection facilities to be built and their operation, environmental protection measures to be taken and their completion, environmental protection files, environmental protection personnel and systems, environmental monitoring reports, etc. After the evaluation, the approved completion acceptance report of environmental protection facilities and related materials shall be collected as important basic materials for post-evaluation of environmental impact.

5] Environmental monitoring data. Environmental monitoring data is the most direct reflection of environmental quality, and it is also an important means to analyze and evaluate environmental evolution trend. The integrity and accuracy of environmental monitoring data is also the key to the rationality and correctness of post-evaluation results. After the evaluation, the monitoring data of each monitoring station (point) over the years should be collected, including meteorological elements, water quality, water temperature, terrestrial organisms and aquatic organisms.

4.2.2 Prepare the outline of post-environmental impact assessment.

Through the analysis of collected data, according to the characteristics of the project and the degree of environmental impact, the environmental factors of post-evaluation are determined, the technical route of environmental factor evaluation is formulated, and the outline of post-evaluation of environmental impact is compiled on this basis.

4.2.3 Implementation of post-assessment of environmental impact

According to the work outline, the environmental impact of the project is evaluated by factors, and the environmental impact of the project is comprehensively evaluated on the basis of single factor evaluation, and the conclusion of the environmental impact of the project and the measures to avoid disadvantages are put forward.

4.2.4 Prepare the post-assessment report of environmental impact.

The post-evaluation report of environmental impact includes the general situation of the project, the environmental conditions before the construction of the project, the post-evaluation of the environmental impact of the project, the comprehensive evaluation and the conclusion.

5 The main contents of post-assessment of environmental impact

5. 1 Impact on local climate

The construction of water conservancy projects has changed the area, volume and shape of water bodies, changed the hydrothermal conditions and aerodynamic characteristics between land and water, and affected the air temperature, humidity, wind, precipitation and fog over water bodies and surrounding land. Post-environmental impact assessment is mainly to check the actual changes of temperature, precipitation, wind speed, humidity and fog after the project construction, and compare them with the predicted results of environmental impact assessment, on this basis, predict the climate change trend and put forward countermeasures.

Temperature impact mainly refers to the changes of annual average temperature, lowest monthly average temperature, highest monthly average temperature, annual extreme maximum temperature and annual extreme minimum temperature in the affected area of the project.

Precipitation impact mainly refers to the change of annual precipitation and seasonal (monthly) precipitation in the affected area of the project.

The influence of wind speed is mainly to check the changes of annual, monthly average wind speed and instantaneous maximum wind speed on the upwind and downwind banks of water bodies after the project construction. Humidity and fog mainly check the monthly changes of humidity and fog days in the affected area of the project.

The post-evaluation of local climate impact mainly adopts statistical comparison method. The collected monitoring data of meteorological factors before and after the construction of water conservancy project are compared, and the changing trend of climatic factors in the affected area of the project before and after the construction of the reservoir is compared with the statistical values of meteorological factors in the participating stations in the surrounding areas before and after the construction of the project, so as to determine the influence range of the project on the local climate and the changing trend of meteorological factors.

5.2 Influence on water temperature

The heat transfer mechanism of water body is to transfer heat through the contact surface between water and atmosphere and through the flow of water body. The water flow in natural rivers is turbulent, and the heat absorbed by the surface of water body is quickly transferred to the whole flow section through the turbulence of water body, so the water temperature in natural rivers is mixed, and the change of water temperature lags behind the air temperature, showing periodic changes. After the reservoir is filled with water, the water depth increases and the water exchange speed slows down, thus changing the heat exchange at the water-gas interface and the heat conduction process inside the water. The typical reservoir water temperature effect is thermal stratification in the vertical direction of water body.

The contents of post-evaluation and recheck of water temperature impact include: (1) counting the vertical distribution, horizontal distribution and vertical distribution of monthly water temperature measured in different areas of the reservoir after the completion of the reservoir, and investigating the influence of discharged water temperature on the growth of aquatic organisms and crops; ② Compare the observed and predicted values of water temperature structure stratification and discharge water temperature, and evaluate the applicability of empirical formula and prediction model adopted in EIA.

5.3 Water quality impact

The construction of dams and reservoirs will enlarge the water surface, increase the water depth and slow down the river flow, which will weaken the diffusion ability of pollutants and change the concentration and distribution of pollutants in the reservoir area. The reservoir retains nutrients such as nitrogen, phosphorus and potassium, which promotes the growth of algae and may lead to eutrophication. The development of irrigation area will also bring adverse effects on water quality.

In the post-assessment of water quality impact, the pollution source and distribution, water quality change, eutrophication trend of reservoir, enrichment of pollutants in sediment at the bottom of reservoir, outflow water quality and water quality change in downstream reach should be reviewed. For irrigation development projects, the impact of irrigation on groundwater quality and the impact of irrigation backwater on the water quality of rivers or drainage areas should be reviewed. In addition, the post-evaluation method should collect the water quality monitoring data after the project operation, verify the water quality model and prediction results adopted in the EIA, evaluate the implementation of water quality protection measures during and after the project construction, and put forward countermeasures for further water pollution control on this basis.

5.4 Environmental geological impact

After reservoir impoundment, the additional load of reservoir water and the seepage pressure of water may change the stress state of rock mass, produce local stress concentration and induce reservoir earthquake. After the impoundment of the reservoir, the erosion and immersion of the reservoir water on the bank slope changed the original stable state of the bank slope, which may lead to landslide and bank collapse, and the loess bank is more prone to bank collapse.

Post-evaluation of environmental geological impact is mainly to investigate the time, magnitude and epicenter location of reservoir-induced earthquake after the reservoir is put into operation, investigate the scope, quantity and geological conditions of reservoir bank landslide area, analyze the causes of induced earthquake and landslide bank collapse, analyze and evaluate the development trend of induced earthquake and landslide bank collapse, and put forward the safety precautions of the project; According to the actual situation of reservoir-induced earthquake and landslide collapse, the prediction results are checked.

5.5 Soil environmental impact

The development of irrigation area may lead to the rise of groundwater level, resulting in soil potential and secondary salinization; In arid and semi-arid areas, improper allocation of water resources such as water conservancy projects may lead to the decline of groundwater level and soil desertification in some areas. Engineering construction and resettlement destroy vegetation, which will cause new soil erosion.

Post-evaluation of soil environmental impact is mainly to examine the area and distribution of swamping, potential breeding, secondary salinization and desertification after water conservancy projects are put into operation, as well as the reasons and countermeasures to be taken; The occurrence and development trend of soil erosion during and after the construction of water conservancy projects are reviewed, and the further prevention measures should be taken.

5.6 terrestrial biological impact

The impact of the reservoir on terrestrial plants is mainly flooding, and the adverse effects on wildlife are mainly habitat loss, feeding field transfer, limited range of activities, and many animals are forced to migrate after the reservoir is filled. However, the local climate has improved after the reservoir impoundment, and the vegetation types around the reservoir area are rich. The humid environment provided by the development of irrigation area is suitable for some waterfowl to inhabit.

Post-evaluation of terrestrial biological impact mainly refers to the evaluation of the impact on plants, especially rare plants, and animals, especially rare animals after the project is put into production; Review the implementation effect of protection measures for rare animals and plants, and put forward further protection measures. Post-evaluation can adopt the method of investigation and comparison.

5.7 Impact of aquatic organisms

The construction of water conservancy projects will affect the environmental conditions of fish life. After the completion of the reservoir, the natural hydrological conditions in the lower reaches of the river have changed, among which the change and rising process of the current state have a great influence on the fish. After the reservoir is filled with water, the changes of hydrological conditions and nutrients will also have an impact on zooplankton and benthos.

The post-impact assessment of aquatic organisms is mainly to review the impact of the project on zooplankton, benthos, higher aquatic plants, fish and other aquatic animals, with emphasis on the impact on rare aquatic organisms; Effect of recheck on fish spawning ground; Evaluate the effect of aquatic organism protection measures, and put forward further protection measures, and the post-evaluation can adopt the method of investigation and comparison.

5.8 Population health impact

The construction of water conservancy projects will cause people's health problems to varying degrees. Due to large-scale flooding, large-scale population relocation and concentration of construction workers, it is possible to spread and spread some diseases.

The post-assessment of population health impact should review the occurrence and prevalence of diseases in the surrounding areas after the construction of water conservancy projects, including: ① the epidemic frequency and intensity of natural focus diseases such as schistosomiasis, leptospirosis, paragonimiasis and epidemic hemorrhagic fever; (2) The occurrence and development trend of waterborne infectious diseases such as hepatitis, typhoid fever and dysentery; ③ The epidemic frequency and intensity of insect-borne infectious diseases such as malaria, Japanese encephalitis and filariasis; ④ The epidemic frequency and intensity of endemic diseases such as endemic goiter, endemic cretinism and endemic fluorosis. And should be compared with the prediction and evaluation results, analyze the causes of the disease epidemic, and put forward further prevention and control measures.

Statistical comparison method can be used to compare and analyze the epidemic trends of various diseases before and after the project construction, and compare them with the epidemic trends of diseases in surrounding areas to evaluate the impact of the project construction on people's health.

5.9 Hydrological situation and downstream impact

The construction of water conservancy project has changed the process of incoming water and sediment in the downstream of the project, and the velocity, discharge, water level and sediment transport law in the downstream reach have changed, which may affect the industrial and agricultural water consumption in the downstream, and the river scouring may also affect the downstream water conservancy project and bridges and culverts.

Post-assessment of hydrological situation and downstream impact is mainly to statistically analyze the measured downstream water and sediment inflow process after the project is put into operation, investigate the impact on water conservancy projects and bridges and culverts, and put forward measures to further reduce the adverse impact; According to the actual impact, review the results of environmental assessment and prediction.

5. 10 cultural relics landscape impact

The construction of water conservancy projects may flood, destroy or disturb natural landscapes and cultural relics, and the formation of reservoirs may also add new landscapes. Post-impact evaluation of cultural relics landscape is mainly to investigate the affected degree of natural landscape and cultural relics, analyze and evaluate the effect of protection measures, and put forward measures for further development and utilization of landscape cultural relics.

5. 1 1 Operation of environmental protection facilities and monitoring facilities

Environmental protection facilities refer to the environmental protection facilities that need to be taken to serve the project and reduce the adverse impact of the project on the environment, including water quality (water temperature) protection facilities, soil environmental protection facilities, terrestrial plant protection facilities, terrestrial animal protection facilities, aquatic biological protection facilities, landscape protection and greening facilities, crowd health protection facilities and downstream impact compensation facilities.

Environmental monitoring facilities refer to the monitoring facilities that need to be built to master the dynamic changes of environmental factors after the completion of the project, including surface water quality (water temperature) monitoring facilities, local climate monitoring facilities, ecological monitoring facilities, soil monitoring facilities and groundwater monitoring facilities.

Post-evaluation of environmental impact mainly includes checking: ① whether environmental protection facilities and monitoring facilities are built according to the requirements of "three simultaneities", whether environmental protection facilities and monitoring facilities are put into operation and how they are running; (2) Whether monitoring is carried out according to the monitoring items, monitoring sections and monitoring factors determined in the environmental impact report and environmental protection design, and how accurate and reliable the monitoring data is. ③ Whether the setting of monitoring project can reflect the environmental quality and environmental evolution trend after the water conservancy project is put into operation. (4) Based on the systematic analysis of monitoring data, evaluate the operation of environmental protection facilities and monitoring facilities, and put forward suggestions on adjusting monitoring sections, monitoring projects and increasing environmental protection facilities according to the environmental changes after the project operation.

Yellow River Planning and Design 2004-11-19