| The construction of water diversion project creates favorable condition for human survival, development and brings tremendous economic and social benefits for society. At the same time, the construction will change hydrological characters and structures of natural rivers, weaken dilution efficiency and self purification capacity of water body, resulting in the change of hydrological regime and water quality and exerting certain impacts on river water environment. Impact study of diversion project on water environment is very important for analyzing river water resources sustainable utilization and a major research problem for water diversion project. It has great significance for water diversion project feasibility.The main contents of river water environment impact study are to analyze impact on river hydrological regime and water quality, and yet river hydrological regime analysis is foundation and key for river water environment impact analysis. River water environment impact study refers to water resources, hydrology, hydraulics, hydraulic engineering, ecological environment, computer science and many other fields. It is characterized by deep theory, difficulty technology and high academic value and is a comprehensive research task which has great practical value. Therefore the paper mainly studies the impacts of Nenjiang River Water Diversion Extension First Phase Project (hereinafter referred as "First Phase Project") on water environment of Nenjiang River mainstream so as to provide scientific base for water resources sustainable utilization plan of Nenjiang River mainstream.The impact study is based on the construction and the operation of Ni'erji hydraulic complex and focuses on the impact study on hydrological regime. The main study contents include: hydrological characteristic of Nenjiang River mainsteam,especially runoff characteristic after Ni'erji hydraulic complex is built;status of Nenjiang River Water Diversion Project and First Phase Project planning;impact analysis and prediction of First Phase Project on hydrological regime, water quality in Nengjiang River mainstream;feasibility study of First Phase Project;In the course of the study, by means of data collection, analysis and calculation , one-dimension model of hydrological regime change law is established for the firsttime and the model is solved using the software MIKE11 developed by Demark Hydraulic Research Institute. At the same time quantitative analysis is used in the study in the impact study on water quality The study findings are as follows:1. The runoff of Nenjiang River mainly comes from precipitation and natural runoff varies greatly in a year and in different years. The construction and operation of Ni'erji Reservoir will change the runoff in a year and in different years.2. Exsiting Nenjiang River Water Diversion Project in Heilongjiang Province includes NorthNenjiang River Water Diversion Project, Middle Nenjiang River Water Diversion Project, South Nenjiang River Water Diversion Project and Dayi Canal. Only North Nenjiang River Water Diversion Project and Middle Nenjiang River Water Diversion Project are under normal operation with average annul diversion volume of 11.25xl08m3. Water supply capacity of existing projects can not meet the need of regional development due to the problems of incomplete for Ni'erji hydraulic complex and decentralized management.3. First Phase Project is an extension project and the overall layout is consistent with existing project. The project includes major project and irrigation project. After the complete of First Phase Project, annul diversion volume will be 23.53><108m3 increasing diversion volume of 12.28x 108m3 comparing with existing average annul diversion volume.4. The error of flow model established in the paper is in the allowable range and selected parameters can basically present the flow characteristic of the simulated reaches. The model is able to describe the spatial and temporal variation law of water level and discharge in the simulated reaches and can be used to predict hydrological regime for different engineering conditions.5. The simulating and calculating results indicate that:1) The water level and discharge below the Ni'erji Dam will change greatly after First Phase Project is completed both for normal annual and in the special dry years. Comparatively speaking, the water level and discharge at the normal annual diversion condition (Condition 2) after First Phase Project is completed are basically same with the change characteristic of the normal annual for the existing engineering;At P=90% special dry years (Condition 3), the project will have distinct impacts on the Nenjiang River, mainly resulting in water level lowering and discharge decrease. The impact on hydrological regime from First Phase Project mainly concentrates the period from middle April to middle October. Out of water diversion period, First Phase Project has no impact on hydrological regime. At the special dry years, the water diversion of First Phase Project has significant impacts on hydrological regime of the river in August, September and October. Viewing the impact from spatial angle, it is within 220 km of intake of North Nenjiang River Water Diversion Project and it shows a week impact at Dalai cross section.2) The discharge hydrograph of Nenjiang River mainstream is chiefly controlled by Ni'erji Reservoir discharge. Since the regulation* of the reservoir the discharge at the downstream increases greatly, therefore water diversion has a little impact on hydrological regime. The discharge period from Ni'erji Reservoir is the same with the period of water diversion of North Nenjiang River Water Diversion Project and Middle Nenjiang River Water Diversion Project;the reservoir can regulate and compensate water consumption downstream. Compared with existingnormal annual discharge, water diversion would have significant impact on downstream hydrological regime if there is no the regulation of the reservoir. Predicting shows that the minimum dry-monthly discharge in Fula'erji cross section meets river course ecological water requirement of 35m3/s. ?6.Water quality monitor carried out in high flow period ( middle July) and normal flow period (middle October) in 2004 are as follows: Water quality at Laha cross section is Grade III for high flow period and normal flow period, pollutant exceeding standard for high flow period is permanganate index and pollutant exceeding standard for normal flow period is total nitrogen;water quality at Dadengke cross section is Grade III for high flow period and Grade IV for normal flow period, pollutant exceeding standard for high flow period is permanganate index ,total phosphorus and total nitrogen, and permanganate index ,total nitrogen for normal flow period is total nitrogen. Analysis shows that high permanganate index is related to environmental background in Heilongjiang Province and total phosphorus and total nitrogen exceeding standard indicate serious pollution in two cross sections, mainly from village rubbish, excreta and residual pesticide of irrigation areas along the river which enter water body with rain off and runoff.7. After First Phase Project puts into operation, water diversion volume will be increased, discharge in Nenjiang River will decrease, and hydraulic dynamic condition change will influence pollutant movement, giving rise to dilution efficiency and self purification capacity weakness and exerting impact on the water quality at Nl'erji Reservoir downstream. Out of diverting period it has no impact on water quality, and it has significant impact on Nenjiang River water quality in August, September and October in special dry years. In addition, water requirement will increase due to irrigation area increase and increased return water will carry more pollutants into the river. Predicted return water volume is 871 xl04m3, and it is 15 times of existing return water volume. CODCr, ammonia nitrogen .. total phosphorus, total nitrogen entering the river with return water are 65.33t/a, 6.02t/a, 1.13t/a> 10.53t/a respectively, increasing 61.05t^ 5.61 t/a, 1.06t/a> 9.851/a compared with existing volume. Through paddy field irrigation the salts in soils will be moved into receiving water and predicated salt entering Nenjiang River is 1141 t/a, increasing 1078t/a compared with existing volume and they will have impact on water quality.8. The construction of First Phase Project will enhance the water resources bearing capacity for regional and social development in Songnen Plain and lay a sound foundation for Qaqing old industry base reform, national foodstuff safety, ecological province construction and poverty relief of poverty counties. At the same time the Project will promote greatly regional economy.The Hydrological regime change in Nenjiang River resulting from the project has a little impact on downstream water users and the minimum dry-monthly discharge meets river course ecological water requirement. Therefore from the hydrological regime point of view, First Phase Project is feasible.9. Since the data are limited, the study only carries out qualitative analysis for mainstream water quality. We suggest that predicting study for water quality should be carried out on the basis of the study by using mathematical model in order to demonstrate the feasibility of First Phase Project.
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