dredging system presentation

PRESENTED BY

S.V.VAIDYAB.E (Civil), F.I.E., STRUCT E.(I), F.I.C.A., F.I.C.C

CHARTERED ENGINEER

PRESIDENTGayatri projects Limited6-3-1090, b-1, T.S.R. Towers,Rajbhavan Road, Somajiguda,

Hyderabad – 500 082, A.P., India Tel : +91 40 2331 0330 / 4296 / 4284Direct : +91 40 2339 8435Fax : +91 40 2339 8435Cell : 098494 56821 / 098901 98945E-mail : [email protected]

[email protected]

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HYDRAULIC DREDGING SYSTEM1. WATER MANAGEMENT2. PRESENTATION3. METHOD STATEMENT / METHODOLOGY4. TECHNICAL INFORMATION

WATER MANAGEMENT

• Water is a precious and scarce commodity. There is no alternative but to store rain water at whatever place possible. Most suitable places are impounded reservoirs of dams and natural lakes.

WATER MANAGEMENT

• So far not enough efforts are applied to desiltation of dams and lakes. Over the years siltation has reduced impounding capacity to the extent as low as 20 %. Reasons are many, prominent among these is lack of working methodology.

WATER MANAGEMENT

• Due to many restrains and constrains conventional desilting methods have limitations. The ideal solution would be to have compact dredge units having easy assembly, low operation cost and minimal loss of water.

WATER MANAGEMENT

• All these features are available when you adopt dredging by Hydraulic System, commonly known as HDS (Hydraulic dredging System). It consists of submersible heavy duty pumps and cutters operated on Hydraulic power supplied by HPP (Hydraulic Power Pack).

WATER MANAGEMENT

• Motors run on Electrical OR Pneumatic power are having many working problems while working at greater depths.

WATER MANAGEMENT

• Motors powered by hydraulic system are ideal for working at greater depths of water. Hence this method is extensively used in Developed countries in Europe and America.

WATER MANAGEMENT

• Today pumps capable of discharge flow of 200 M3 solids per hour from depth upto 50 M are available in European markets

WATER MANAGEMENT

• Even these pumps and cutters and their prime movers could be manufactured in India except may be for few parts such as seals, which makes meager part of whole assembly, could be imported.

WATER MANAGEMENT

• The secret of working at greater depths in water is to prevent water entering in bearings and some components of pumps and motors. It is here special seals made out of alloy of various metals plays crucial role.

WATER MANAGEMENT

• One Hydraulic unit consists of following components.

1. Suitable Catamaran Pantoon

2. Heavy duty electrically operated winch to handle dredge unit.

3. Generator to supply power to winch, few workshop tools and

lighting. 4. Heavy Duty submersible pump and cutters units.

5. Polyethylene discharge pipes.

6. Hydraulic power Pack.

WATER MANAGEMENT

7.Suitable capacity tug to move Pantoon.

8. Usual Marine operations items such as Floats, Anchors, boats, ropes etc.

9. Booster pump as per requirement.

10. Boat equipped with latest electronic equipment and instrument to position pantoon, record depths, Computer for calculating volume dredged and many Survey related items.

11. Boat equipped with Diving gear and Diving team consisting 2 divers and 1 Forman having expertise in deep diving.

12. Service boat for transporting Crew and materials.

WATER MANAGEMENT

Out of above we may have to import items 4 & 6 initially. Later only seals could be imported, as explained above, thereby reducing cost considerably. Item 10,11 and 12 can serve up to 4 units.

WATER MANAGEMENT

Considering average capacity of one dredger comprising two dredge units as 300 cum solids [2 x 200 x 0.75] per Hr and 16 Hrs of actual working per day and 22 days of working in a month the silt removal rate could be around one Lakh cum per month.

WATER MANAGEMENT

Disposal of silt faces many problems particularly when loss of water can not be afforded. Since plenty of water is also pumped out along with the silt/dredge material it is necessary to have arrangement by which only water flows back into reservoir/lake. This aspect is well explained in methodology annexure-I.

WATER MANAGEMENT

Applications of this system are many yet each location may have different approach depending upon topography of adjacent land/area, type of silt formation and availability of constructing work harbour in the proximity of dredging area.

WATER MANAGEMENT

Generally following categories are identified.

1. Impounded Reservoir of Dam.a. Without loss of water. b. With loss of water.

2. Natural lakes.

3. Canals.

4. Reclamation of Land with sea sand.

5. Perennial dredging for Fisheries Harbour to maintain adequate draft for

fishing boats

WATER MANAGEMENT

Silt in impounded Reservoirs of dams have rich manure value. This could be called by-product of such dredging.

PRESENTATION PRESENTATION ONON

CAPACITY RESTORATION OF CAPACITY RESTORATION OF RESERVOIRS & LAKESRESERVOIRS & LAKES

BYBYHYDRAULIC DREDGING SYSTEMHYDRAULIC DREDGING SYSTEM

JUNE 2006

CAPACITY RESTORATION OF RESERVOIRS & CAPACITY RESTORATION OF RESERVOIRS & LAKESLAKES

• Water, Air and Food is the basic need for human being as well as for all living creatures.

• Man has used his intelligence to create artificial lakes, storages by constructing dams to retain water for the use of drinking and irrigation purposes.

• The history of construction of dam goes back about 1000 years

• In the last century, a large number of dams have been constructed all over the world. In India also, dam construction has taken a quantum leap after Independence.


• Dams are categorized by their storage capacities as large, medium or small. Dams are also categorized by the construction material namely earthen dams, masonry dams and concrete dams.

• Normally, the life of a dam is taken as 60 to 100 years.

• The water storage behind a dam has been used for the purpose of irrigation and drinking by the population downstream of the dam.

• The capacity of a dam is ascertained from the need of the population and the irrigation requirement and this is achieved by providing adequate height of dam at a suitable location.


LIVE STORAGE CAPACITY OF RESERVOIRS IN INDIA (CUBIC KM)

• The Reservoir of the dam extends to about a few kilometers on the upstream side.

• During monsoon, water flows through the river and gets accumulated in the Reservoir behind the dam.

• The flow of water brings all types of material such as earthen silt, stones, trees, etc and this gets deposited behind the body of the dam as the velocity of the water reduces when it enters into the reservoir.


• Thus, over the years, the live storage capacity of the dam starts dwindling or gets reduced due to the siltation and collection of other materials.

• Siltation of dams results in the reduction of in storage capacity and is a perennial problem.

• Though dams are designed for a life of 60-100 years, there are examples of heavy siltation behind the dam within 30 – 40 years, thus reducing their storage capacities.


CAPACITY RESTORATION OF RESERVOIRS CAPACITY RESTORATION OF RESERVOIRS & LAKES& LAKES

Annual Rate of Silting (Hecatre/Metres of Silt) per 100 km2 of Catchment Area

Project Assumed siltation rate while dam was built Observed in surveys

Malthon 1.62 13.10

Mayurakshi 3.61 16.43

Ramganga 4.29 18.19

Ghod 3.61 15.24

Beas Unit 2 4.29 14.29

Ukai 1.47 10.95

Narmada 1.55 5.62

Tawa 3.61 11.15

Source: Alvares and Billorey 1987, 69.

The biggest dams in the India are located in eastern Gujarat and many more are still being planned today. One of the largest and most controversial is the Ukai dam, (see Figures). It began construction in 1971 and included as net catchment area of 62,225 km2. Unfortunately performance was slowed by siltation. The engineers assumed a siltation rate of 1.47 hectometers/100 km2 of catchment, however the actual rate was ten times that, 14.29 hectometers/100 km2 (Tapas, 1993).

This image shows the continuing submergence of areas under water due to large-scale dam projects from 1976-1980. Dark areas show extreme vegetation loss.

Reservoir at the Ukai Dam 1980 Vegetation Change 1976-1980


• There are various ways to arrest the deposition of silt by providing small check dams in the river body. However, still the problem of silt deposition is a great menace.

• To increase the storage capacity or restore its earlier capacity, one way is to increase the height of the dam, which may not be feasible from construction point of view or due to submergence of areas larger behind the dam.


• Another option is to remove the silt. We are going to discuss the second aspect in the further slides.

• For shallow depths (3m to 5m), initial dredging could be carried out either by clamshell bucket or hydraulic excavator with long arm installed over ordinary pontoon. The dredged / excavated material is dumped into barges which are towed to jetty head where these are emptied mechanically only to be disposed off to the designed areas by tippers. Where permitted bottom openings barges are employed to dispose off muck on to location of large depths of water.

• For depths below 5m regular Hydraulic dredging system on catamarine pontoon is suitable & ideal.

• For deeper depths, a cutter section dredging equipment can be deployed.



• Pump and Excavator / Cutter mounted on Hydraulic Excavator for desilting of shallow depths.

SILT REMOVAL BY CLAMSHELL METHOD

• As explained earlier for shallow depths of water a crane attached with clamshell shall be deployed on floating pontoon.

• The pontoon is to be towed to the desired location by boat.

• The Silt from the bed is removed by the clamshell and dumped on another pontoon or flat barrages and this silt is taken away to the shore.



HYDRAULIC DREDGING SYSTEMS

• Heavy duty submersible pump with attachment of Right


HYDRAULIC DRIDGING UNIT

• For deeper depths, a cutter suction pump-dredging unit shall be deployed on a catamaran pontoon.

Hydraulic dredging unit operating on impounded reservoir of dam for high depths.

Hydraulic dredging unit on Loader arm operated by winch on catamarine pantoon.



DREDGING APPLICATIONS

DISCHARGE OF THE SILTDischarge of the silt along with muddy water is transported to the desired area by providing floating pipes over the Reservoir Lake and further pipe on the land.

High concentrated mixture of mud and water being High concentrated mixture of mud and water being pumped to reclaim area.pumped to reclaim area.

Booster pumps using the same parts as the Booster pumps using the same parts as the submersible pumps allowing long pumping distances.submersible pumps allowing long pumping distances.


• The silt is then deposited on the selected area by providing a suitable small check dam and the water is allowed to flow back to the dam reservoir. Thus the silt gets deposited in the silt pond and can be removed once it is dried, further, it can be used in barren lands due to its higher fertility value.

• Such silt removal or restoration of reservoir shall be done in one of the small dams on a pilot project to establish its economic viability.


SUGGESTED STEPS FOR THE PILOT PROJECT

• Identification of a small dam with a reservoir where siltation has already taken place.

• Topographic Survey of the area.• Identification of the location for Silt deposit pond.• Geotechnical Investigation of the areas.• Construction of a small check dam• Identification of the equipment for silt removal• Formation of a team to plan and execute the operations.• Monitor the performance of the system.



If this experiment is found successful, it can be used for many dams to improve its live storage capacity and increase its life.

METHOD STATEMENT / METHODOLOGY

DESILTING METHOD STATEMENTDESILTING OF RESERVOIRS AND LAKES

• Methodology for complete scheme of Desilting of Reservoirs impounded by Medium and small dams and Natural Lakes.

1. Survey2. Civil Works3. Import of Machineries4. Fabrication of Pantoon5. Installation of Machineries on Pantoon6. Mobilisation of Marine Units7. Operation of Hydraulic Dredging. 8. Marine Survey and computation of volume

dredged


•We shall now describe all above in details.1. Survey

Once location is decided complete information such as original depth of Reservoir, Present status and Surrounding areas will have to be collected from concerned Department.


Two types of Surveys are envisaged. Topographical and Investigative. Topographical survey is basically to prepare contour plan of area where disposal of dredged materials is proposed. It also establishes special features those need to be taken into account while planning civil works. Investigative Survey includes taking bore holes upto original bed levels and ascertain “N” values of silted layers. Hydraulic dredging units have limitations of removing silt depending upon Mix proportion of Silt, Sand and Gravel as also ‘N” values which determines to what extent silt is consolidated and compacted.


2.Civil Works

Once Survey is complete the scope and Methodology is decided. If disposal of dredged material is possible on surrounding land a cofferdam cum weir may have to be constructed at suitable location. This cofferdam cum weir will allow water to flow over it back to Reservoir after settlement of dredged material. Later this dredged silt could be used as manure

In case there is constraint on adjacent land dredged material will have to be sent down the stream. In this process water loss is inevitable.


Work harbour construction is necessary to carry out Marine operation. This platform of required area is constructed at suitable place where adequate draft of water will always be there for uninterrupted activities of Marine operation. This platform should be approachable by motorable land and/or short length jetty may have to be constructed. A small 5 ton derrick will be installed over this platform for loading and unloading Machinery parts and sundry materials


3.Import of Machineries

Hydraulic dredging units comprising heavy duty pumps, cutters,power pack etc.will have to be imported either from Belgium, Italy, Taiwan or USA. Already Agencies are identified and correspondence is in progress with them. We have to furnish them information regarding composition of Silt, Sand and Gravel of material to be removed. Depending upon composition, capacities of various units will be decided and only after that we shall know cost of various equipments. It is expected Foreign Exchange will be made available for these imports.

Agency will have to depute their Service Engineer for installation of units and commission the dredger. Cost of such services will have to be paid in US Dollars.


4.Fabrication of Pantoon

Once the weight and size of Machineries to be installed over Pantoon is known we can design the pantoon and accordingly fabricate. Agency for such works are also identified. Loader Arm, “A” frame, winches, Generators, 10 inch dia MS pipes, floats and various marine equipments will be procured in Domestic market. The responsibility of getting Marine Worthy certificate for such Pantoon will be on Fabricator.


5. Installation of Machineries on Pantoon

Entire operation of installation of all Machineries, including imported and Domestically procured, on Fabricated Pantoon will be done under expert supervision of Service Engineer of Agency from whom Hydraulic Dredge units are imported.


6. Mobilisation of Marine units

Small Tugs minimum 2 nos. two service boats, Required number of Floats and Misc. equipments will be required to be mobilized to carry out dredging operation. All these are common items and are available in Market.


7. Operation of Hydraulic DredgingThis involves 3 operations as under :

a. Pantoon ManagementUnder senior Marine Superintendent Skilled Khalasis will manage Pantoon movements.

b. Hydraulic Dredging We shall get one Marine Forman trained under Service Engineer from Agency from whom we have imported Dredge units over a period of minimum one month. He shall then control Dredging operations.

c. Delivery Pipes on Floats A. well trained Khalasis team will organize Floated Pipes, control their movements and attend Disposal end.


8. Marine Survey and Computation of volume dredged

Expert team of Marine Survey well versed with modern techniques of positioning Marine vessels and Echo Sounding methods will be deployed. Apart from field activity they shall also compute dredged volume with latest Computer Software. Agencies for such works are also identified. They are well equipped with all latest instruments and experienced technicians. We shall provide them only suitable boat.


Pricing of all above activities on approximate basis is possible once Volume of Dredging and Period and cost of Foreign element is known. Our suggestion for Pilot Project is as under.

A. The Govt. should appoint M/s RSVP Infrastructure Pvt.Ltd. to prepare feasibility report. Cost estimate for such report could be given once location and volume of works is known.

B. All activities shall be paid on actual cost plus 30% basis.


While part A is inevitable our suggestion for actual cost plus basis is justified on the ground there are many hidden costs and many variables. Once pilot project is completed successfully it will be possible to give offer on Turn-key basis for future projects on Dredged volume basis.

Trust we have made complete Methodology clear. We shall be glad to give clarifications whenever asked.

dredging system presentation

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