Sand Dredging Equipment Used for Reservoir and Lake Desilting

Sand dredging equipment, including portable dredge, cutter suction dredger, jet suction dredger, submersible dredger, etc,  is the most commonly used machining process for the removal of sediments and debris from the bottom of lakes, rivers, harbors and different water bodies. Followed is the typical sand dredging application in Uzbekistan.

1. The necessity of reservoir and lake desilting. Uzbekistan is rich in water resources, with various reservoirs, lakes and rivers, such as Aydar Lake and Charvak Lake. These lakes have artificial dams, which have the functions of water storage, irrigation, production and living water, and natural scenic spots. As an important project for optimizing water resources allocation and flood control and disaster reduction, reservoirs and lakes play huge economic, social and ecological benefits in flood control and security, drought relief and water supply, water conservation, climate regulation, and eco-tourism. Because these reservoirs and lakes were built and formed early, after years of operation, and the rivers carry a lot of sand, the sedimentation is serious, which reduces the flood control and storage capacity of the reservoirs, and affects the comprehensive benefits of the reservoirs. In addition, with the development of urban industry, a large number of chemicals from sewage sludge and garbage are deposited on the bottom of reservoirs and lakes, causing ecological damage to the water system, poor water quality, eutrophication, and a serious impact on the growth of aquatic organisms. In order to ensure the full play of the comprehensive benefit of the reservoir, it is necessary to use the sand dredging equipment to carry out appropriate dredging works for the reservoir.

1.1 Flood control and security protection

The most important function of reservoirs and lakes is flood control. The capacity of flood control reservoirs is an important indicator to measure the flood control capacity of reservoirs, protect the safety of people and infrastructure. A large amount of sand in the river channel is deposited in the reservoir, which will inevitably lead to the reduction of flood control reservoir the capacity, and reduce the flood control capacity of the reservoir. In addition, siltation in the inflow river section will lead to the narrowing of the flood-carrying section of the river, reducing the flood-carrying capacity and affecting the safety of the people and arable land on both sides of the river.

1.2 Promoting profit and increasing efficiency. Utilizable capacity is the basis for the reservoir project to play the benefits of water supply, irrigation, breeding, power generation, etc. A large amount of silt in the utilizable capacity will reduce the storage capacity of the reservoir, and then affect the capacity of the reservoir, reduce to promote profit and increase efficiency.

1.3 Ecological and social benefits. The reservoir dredging project can restore the water quality of the reservoir, improve the ecological water system environment, remove harmful substance, heavy metals and other harmful chemicals that affect aquatic organisms on the bottom of the reservoir.

1.4 Economic benefits. Convert harmless sludge into usable organic fertilizer or construction sand. Recover useful fine metal particles in sludge, reducing the cost of dredging.

2. Desilting Implementation and Precautions.

• Determination of the scope of bottom sediment
• Flood control safety and economic benefits
• Dredging project safety and reservoir bank stability
• Perimeter infrastructure security and impact to third-party
• Water quality safety, preventing secondary pollution caused by disturbance

3. Implementation of Reservoir and Lake Desilting

Because the siltation conditions of the reservoirs are different, to carry out the dredging work, it is necessary to conduct a specific investigation and research on the conditions of the silted reservoirs one by one. The sand dredging equipment and construction methods to be adopted are different, these depend on the deposition conditions. Generally, jet sand dredging equipment, cutter sand dredging equipment, chain bucket sand dredging equipment, pneumatic pump and hydraulic sand dredging equipment are used for reservoir and lake dredging.

3.1 Main sand dredging equipment for desilting

A. The jet sand dredging equipment, also called jet suction dredger, is mainly composed of floating body, silo, sand suction pump, water pump, suction salon head with water gun, upper suction pipe, lower suction pipe, power, walking device, etc. The biggest highlight of the jet sand dredging equipment is the suction salon head which is equipped with a high pressure water gun. The water pump directly sprays the bottom sediment through the water gun. The sediment splashes around the suction salon head under the jet of high-pressure water, and is extracted by the sand pump through the suction salon head and discharged into the silo by the upper suction pipe. The jet sand dredging equipment has the features of low cost, simple structure and easy operation. Jet sand dredging equipment is suitable for the reservoir areas with few entanglements such as underwater plants, and working in river bottoms and artificial lakes, etc.

B. Cutter sand dredging equipment, also called cutter suction dredger, is the main type of dredging vessel.The cutter sand dredging equipment consists of floating body, reamer, upper suction pipe, lower suction pipe, sand pump, power, etc. The sediment at the bottom of water is cut, stirred and loosedned by the reamer and the rake head device at the front of the lower suction pipe, and is extracted by the sand pump through the lower suction pipe, then is discharged through the upper suction pipe to the designated position. The cutter sand dredging equipment is efficient and low cost. Depending on the dredger type, the cutter sand dredging equipment can process sand-water mixture 50 to 500 cubic meters per hour. The super-large cutter sand dredging equipment has a processing capacity of over 1,000 cubic meters per hour.

C. Bucket sand dredging equipment, also called bucket dredger, including chain bucket type, grab bucket type, bucket type and others.Bucket sand dredging equipment is a kind of sand dredger that uses single or continuous buckets for underwater dredging operations through the action of bucket wheels, cranes and bucket arms. This type of sand dredging equipment generally performs fan-shaped swing dredging by throwing anchor claws which are on the front, rear, left, and right sides of the sand dredger. Bucket sand dredging equipment can excavate relatively hard and dense soil, and directly excavate the original soil without destroying the properties of the bottom mud. The excavation efficiency is high. This type of sand dredging equipment is not suitable for soft silt excavation. In addition, the bucket sand dredging equipment is also equipped with auxiliary equipment such as barges, loaders, transport vehicles, mud pumps, dehydrators, conveying pipelines, conveying belts, and generators.

3.2 Construction plan

According to the different hydrological data and the bottom sediment composition, the construction methods are also different. The environmental protection cutter suction construction scheme is currently the most advanced environmental protection dredging method and is widely used. The plan uses an environmentally friendly cutter sand dredging equipment to excavate the silt at the bottom of the lake. The excavated silt is transported to the designated reclamation area through a fully enclosed pipeline. When the discharge distance is long, a relay pump boat with the same characteristics is used for relay delivery in the middle.

A. Construction process

1. Construction preparation
2. Sand dredging equipment positioning arrangement
3. Perform dredging work by division and strip for excavation.
4. Fully enclosed pipeline transportation
5. Slurry screening, dewatering, treatment
6. Relay pump pressurization
7. Slurry transportation and disposal

B. Features of cutter sand dredging equipment

Environmental protection cutter sand dredging equipment is the most widely used sand dredging machine in river, lake and reservior dredging projects. Cutter sand dredging equipment integrates a variety of advanced construction technologies, it has the characteristics of high excavation accuracy, small disturbance and low pollution. The features of cutter sand dredging equipment are as follows.

1. Adopt environmentally friendly reamer excavation technology to avoid secondary pollution. The special environmentally friendly reamer head is a new type of reamer that can excavate the underwater polluted sediment with high precision and minimal disturbance to the surroundings. The special environmentally friendly reamer is equipped with mud guide baffle, reamer sealing cover, reamer level adjuster and other devices, no matter how the dredging depth changes, the reamer is always kept level by the reamer level adjuster. When dredging, the bottom edge of the reamer cover is flat against the river bed, the sludge within the disturbance area of the reamer is effectively covered by the reamer seal covers and fully extracted by the sand pump. Compared with the conventional open reamer, the special environmentally friendly reamer effectively prevents the bottom mud particles from spreading to the water body outside the reamer seal cover due to the disturbance of the reamer, avoids secondary pollution caused by excavation during the construction process, and eliminates the phenomenon of silt escape. The mud removal rate can reach more than 96%.
2. Realize automatic dredging construction, the excavation accuracy is high and dredging effect can be guaranteed. Environmentally friendly cutter sand dredging equipment is equipped with the instruments that reflect basic operating data such as excavation depth indicator, compass azimuth gauge, reamer pressure gauge, concentration indicator, in addition, the cutter sand dredging equipment is equipped with measurement equipment such as marine GPS global locator, echo sounder, it has an advanced and all-round quality monitoring system. These guarantee high excavation accuracy.
3. Cutter sand dredging equipment adopts reliable and fully enclosed pipeline mud conveying technology, which can prevent the mud scattering and leakage during transportation, and can flexibly choose the location of mud stacking.At the same time, the underwater diving pipes can be laid in the lake area to the greatest extent according to the water conditions, so as to reduce the disturbance to the environment.
4. The environmentally friendly cutter sand dredging equipment has a variety of advanced construction performance, can be disassembled and assembled separately, and is suitable for a variety of working conditions, breaks through the limitation that the project can only be dispatched on land.
5. Efficient, safe and environmentally friendly construction. The project has a good image, and the entire production line is bright and clean, which is conducive to improving the project’s image.

C. Brief introduction of dredging construction plan

1. Uzbekistan is a landlocked country, and the reservoirs and lakes are not connected with the outside river.Therefore, all construction equipment was transported to the construction site by road truck, and the sand dredging equipment was dismantled and transported to the construction area for assembly and welding.
2. Sludge pipeline laying. In this project, a mud discharge pipeline matched with the cutter sand dredging equipment is laid. The design of the sludge discharge pipeline is based on the principle of shortening the discharge distance as much as possible, and the impact on the environment should be minimized. It is planned to be equipped with a small number of floating pipes and shore pipes necessary for production. The floating pipe on the water is connected with the stern of the cutter sand dredging equipment according to the actual requirement. Then the floating pipe is connected with the land pipeline and extends to the soil enclosure area and enters the sludge dumping yard. Before the official dredging production, the pipeline is subjected to a clean water pressure test to ensure that the entire line is sealed without leakage, and then the dredging production can be officially started.

c. Main construction methods—by division and strip for excavation.

• The lake dredging area is large and wide. During construction, the reservoir lake is divided into several blocks.Input the coordinate system and the coordinates of the division boundary point used in the project  into the computer terminal of the marine GPS global locator to accurately locate the excavation.
• By strip. The width of the lake bed construction banner is basically determined to be 35m, and the construction overlap between the banners is 1~2m. In principle, the excavation direction is from upstream to downstream.

d. Sludge conveying

Environmentally friendly cutter suction dredger is a kind of sand dredging equipment integrating excavation and transportation. The sludge cut by the reamer is directly extracted into the sand pump, and after being pressurized by the sand pump, the sludge is transported to the storage yard through the discharge pipeline connected to the rear of the sand dredging equipment. The whole process is completely closed. Compared with the secondary transportation by automobiles, fully enclosed pipeline transportation has the advantages of environmental protection, safety, high efficiency and economy.

• The construction method integrating excavation, transportation and stacking makes the whole construction process fully enclosed.The long-distance pipeline transportation solves the distance limitation of the silt yard, and there is no secondary vehicle transfer, which effectively avoids the secondary pollution caused by the leakage of the silt transportation.
• Compared with automobile transportation, it not only improves the transportation efficiency, but also avoids damage to the roads along the route and reduces road maintenance costs.
• Eliminate the hidden safety hazards caused by the frequent vehicles transportation and ease the traffic pressure.
• Avoid environmental pollution such as noise and dust along the way.
• Lower cost than silt vehicle transportation.

e. Quality control. The plane positioning of the sand dredging equipment is controlled by GPS. Through the simulation animation, the excavation trajectory of the sand dredging equipment can be observed intuitively to avoid missed excavation. Before excavation, set up several sets of precise water level gauges. During excavation, the excavation depth is controlled by the excavation depth indicator on the sand dredging equipment, combined with the feedback data of the echo sounder, to accurately locate the depth of the reamer, strictly control over-excavation, and strictly prohibit under-excavation.

f. Sludge storage area control. A number of grid ridges are set in the sludge storage area, and the sludge outlet of the discharge pipeline is arranged away from the water return port during blowing and filling, so that the sludge flows in an “S” shape to the water return port under the action of the grid ridge. In order to prevent the local earthwork from being piled high at the mud outlet, it is necessary to move the pipeline frequently to extend to the interior of the filling area along the grid, and adopt the construction method of filling by division and staging to ensure the flatness of the sludge storage area.

g. Residual water treatment. The residual water in the reclamation area of this project needs to be treated and then returned to the lake area to ensure the balance of water supply in the lake area. Using the most advanced environmental protection and rapid residual water treatment technology, the suspended particles contained in the residual water in the sludge yard are rapidly precipitated, and the treated residual water will not cause secondary pollution.

4. Comprehensive Treatment and Utilization of Sludge

A large amount of sludge is produced in reservoir and lake dredging. First, analyze the type and composition of the sludge, and carry out different processing and utilization according to the ratio of sand, gravel and mud, heavy metal content, nutrient content, and harmful substances. In the actual sludge treatment project, the appropriate treatment scheme can be selected according to the basic properties of the sludge to be treated and the treatment conditions.

A. Sand for building. If there is a lot of sand and gravel in the excavated silt, the stones and sand that can be used for construction and paving can be separated by screening. Large-grained sand and gravel can be used for slope protection and road construction in the downstream river channel, filling the huge pit formed by the massive mining of sand and gravel in the downstream channel, and improving the safety of the river channel.

B. Metal Particle Recovery. There are free fine monometallic mineral particles in the rock of the mountain, which flow into the river channel after being washed by rainwater, and finally flow into the reservoir and lake, where they are deposited. The silt at the bottom of the reservoir and lake is cleaned and recycled through different advanced processes, such as using strong magnets to collect iron sand in the silt, and using chute to collect gold particles in the silt.

C. Organic fertilizer. After the sand and large particles are separated, the fine fluids are left. If the organic matter content in the sediment is high, it can be directly used as fertilizer for agriculture and forest to improve farmland soil. Sludge is rich in various trace elements, which can improve soil structure, increase soil fertility and promote crop growth when applied to farmland.

D. Solidification treatment. If there are harmful substances or heavy metals in the sediment, it can be treated by sludge solidification. The solidification treatment is to add solidified materials to the sludge, and use a series of physical and chemical effects between the solidified materials and the sludge to reduce the moisture content of the sludge, and to seal the organic matter, harmful substances and heavy metals in the soil particles. The water permeability coefficient of the solidified sludge is very small, which makes it difficult for harmful substances to be leached and dissolved again to form secondary pollution. Therefore, the dredging sludge solidification treatment technology is an environmentally friendly new technology, which is suitable for a large number of sludge treatment projects.

About OCEAN Pump

Tai’an OCEAN Pump Co. Ltd. (referred to as OCEAN Pump)specializes in the development, production and sales of sand pump machine, sand dredging machine, submersible dredger, sand dredger, portable dredger, sand pump, submersible slurry pump, heavy duty sand pump, etc. As the leading sand dredging equipment designer, manufacturer and exporter, OCEAN Pump has been dedicated in supplying sand dredging machines to worldwide customers for over 20 years. OCEAN Pump has won the praise and trust of customers with rich industry experience, professional technology and excellent service.