Description: This article points out that the concept, content and core of inland waterway dredging problems combined with a section dredging renovation project and discusses the way of inland waterway dredging.

The ecological maintenance problems of channel dredging projects are becoming more and more obvious, and the challenges they face keep increasing. On the international scale, the real purpose of clearing the polluted silt from the lakes is to restore the ecology of the lakes, but the environmental dredging problem in the channel dredging level is not extensive. On the basis of discussing the nature of the action mechanism of waterway dredging on the natural environment, this study gives the definition of the corresponding environmental dredging of the waterway and provides the reference and theoretical basis for the corresponding environmental dredging of the waterway.

1.Definition, connotation and key problems of channel environmental dredging

 1.1 Definition of channel environmental dredging

The significance of environmental dredging lies in the removal of contaminated silt from the water. The foundation after dredging can continuously create more basic conditions for ecological restoration work. Its source is the integration of the project, environment and nature, and the sustainable deepening of the lake or the restoration of the lake “ecological niche”. The waterway dredging project joins the concept of environmental dredging. In the process of the deepened channel, pay attention to clean, properly solve sediment pollution in course; reduce the operation on the ecological environment pollution and damage. The secondary pollution in the whole process of dredging should be strictly managed to create corresponding conditions for the maintenance and restoration of the aquatic ecosystem in the waters where the shipping line is located.

 1.2 The connotation of environmental dredging of the waterway

The content of environmental dredging of air route mainly includes the following four levels: (1) Accurate dredging: high precision positioning and high accuracy mining to achieve the dredging requirements and minimize the corresponding over-excavation value, that is, to minimize the excavation of native soil under the precondition of the benefit of the bag-cutting dredging project. Normal hull operation accuracy is between 20cm and 50cm, and environmental dredging usually requires accuracy of less than 10cm. (2) diffusion benefits in dredging management: with the help of sophisticated dredging equipment and its corresponding technology, it can ensure its own high concentration of inhalation and manage the thick consistency of suspended solids. (3) Manage the leakage process of dredging soil transportation: carry out the corresponding detection on the dredging soil transportation process, control the total amount of leakage within the minimum range, and prevent the secondary pollution of water caused by the leakage in the transportation process. (4) Disposal and reuse of dredging soil: the materials contained in dredging soil are relatively complex and have different properties. Therefore, reasonable treatment is required to reduce the effect of dredging soil on the environment, so as to avoid secondary pollution and maximize the use of waste soil resources.

 1.3 The key problem of channel environmental dredging

Channel dredging mainly consists of three stages: dredging, transportation, and dredging disposal. How to reduce the secondary pollution caused by dredging and how to solve the dredging with high quality and high efficiency is the main content in the course of environmental dredging. The form of environmental dredging proposed in recent years is the main means to implement the ecological channel dredging. In this process, the detection of operation links and the disposal of dredging soil are the core of the environmental dredging process.

2.Construction process control of environmental dredging of the waterway

 2.1 Determine the appropriate construction period

It is relatively important to determine the dredging time of sediment, and the proper dredging time can minimize the dredging effect on the benthos. It is required to avoid the deterioration of water bodies in accordance with the pollution conditions in the areas waiting for dredging routes, and to avoid the regenerating period and breeding period of underwater species. Proper dredging time can effectively reduce the consistency of dredging suspended matter and reduce its effect on the water quality of the shipping line. The development of the project links the dredging to the corresponding sections of the operation, increases the construction period, minimizes the intensity of its operation and contributes to the restoration of the damaged natural environment. When dredging operations avoid the period of abundant water, the density of suspended matter decreases, and the effect on water quality is relatively weak.

 2.2 Strict control of secondary pollution

Secondary pollution is effectively controlled in the operation: (1) In order to reduce the pollution and diffusion of suspended substances, the relatively advanced harrow suction dredger is selected to carry out high-pressure flushing according to the consistency of fine sand and silty clay in each river section. DGPS (differential global positioning system) is used to carry out the corresponding plane management, and its positioning accuracy is within the error range of 3m. Strict management of the link and regular inspection of its equipment can ensure dredging accuracy. According to the soil condition, high-pressure flushing is opened to reduce the diffusion and pollution of pollutants. All discharge pipe flanges belong to cast steel members and have strong water-tight property. The rubber hose in the operating time is also stable and both ends of the flange turn into a general to prevent the former clamp connection leakage situation.

 2.3 Transport and disposal of dredged soil

The project reduces pollution in the dredged soil environment by limiting overflow time and avoiding overflows in transportation and limiting pumping areas. In the process of dumping sediment, the total amount of sediment should be controlled, and the independent inspection system of dredging vessel assembly should be carried out in time. After sediment casting, it is strictly forbidden to carry out relevant pumping work in the sediment casting section, so as to minimize the remaining water in the cabin and strengthen the tightness of the cabin.

 2.4 Effect testing after dredging

After the dredging process has been carried out, relevant assessments are carried out in the corresponding sections of the project to facilitate timely ecological restoration. After the project is carried out, the vegetation will be restored and the existing land environment will be restored in terms of the operation area. In the course of operation, consistent with the aquatic units, the operation of fishermen in the surrounding environment of the salvage work is limited.

3.Disposal of channel environmental dredging soil

 3.1 Analyze the properties of dredging soil

In the process of environmental dredging, it is not only necessary to study the sediment mechanism of the river bed, but also to establish the pollution status of dredging waste soil. A simple, efficient test to determine whether dredged soil is contaminated is: The bed wet sediment of the dredged site and the water in the sludging area were proportionally mixed at 1:4 and violently shaken. After 30min, the supernatant was allowed to precipitate for 1h, and then the corresponding filtration was carried out on the supernatant. Or it can be disposed of by centrifugation to remove granular ions and test for soluble contaminants and determine the total amount of oxygen required by the organism.

 3.2 How to deal with dredging soil

Dredging operations depend largely on their physical and chemical properties. According to the different functions of dredging sediment, with the help of the corresponding treatment properties, pollution can be prevented and its reuse can be realized.

3.2.1 Ordinary sediment

For conventional soils that are not contaminated nor have very low levels of contamination, they can be directly dumped or reused. In the process of dredging, the dredged soil is relatively clean and basically unloaded in the nearest dam field.

3.2.2 Polluted sediments

If the sediment is polluted, special treatment technology is required to prevent ecological pollution to the environment. Nowadays, the conventional treatment forms of contaminated dredging soil mainly include: (1) Store the contaminated sediment to the bottom of the sediment storage site or carry out the corresponding sediment puddle sealing measures. In the project of river section disposal, the corresponding landfill work is carried out on the soil quality of serious pollution. The actual means of operation is secondary segregation of the bottom sediment: The dirt is first separated from the garbage, and then the sediment from the sludge is separated from the sewage. The separated solid waste is transported to the “solid waste treatment plant of old ports” for relevant landfills, and the other mud is transported to the mud warehouse through a 5km pipeline with the help of a mud pump, and the corresponding organic treatment is carried out. Sewage can be recycled after treatment, but the sludge requires the corresponding landfills to be developed after sedimentation, including dredging waste soil with local pollution level in the standard category which is regarded as the soil used for greening. Such a form of disposal has relatively strong disposal benefits, and it has been widely used nowadays. It is suitable for all contaminated soil, and its corresponding cost is not large. (2) The contaminated sediment is excavated and transported to the factory for corresponding treatment and recycling. The dredging vessel only dredged mud to the corresponding processing plant. In the factory, the pollutants are removed in the form of physical, chemical, or biological forms, and then related recycling work is carried out on the treated soil. This treatment project has carried out relevant research and application on the reuse technology of contaminated sediment, including the use of cement materials in local dredging soil, which are used in the cement production process. This treatment form is relatively expensive and its corresponding treatment performance is poor.

4.Conclusion

In conclusion, the ecological effects of channel dredging are mainly reflected in the continuous deterioration of the living environment of aquatic organisms caused by the increase of suspended matter density and the re-suspension of polluted sediment during dredging. In the treatment project of this construction, with the help of control operation link and scientific selection of corresponding operation form, the density of suspended matter and its effect on the ecological environment are effectively controlled, the natural ecology of the project section is maintained, and the experience reference is provided for the disposal of polluted sediment by inner navigation environmental dredging.