A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out or drained. This pumping creates a dry working environment so that the work can be carried out safely. Cofferdams are commonly used for construction or repair of permanent dams, oil platforms, bridge piers, etc., built within water. They also form an integral part of naval architecture .
30-501: Subansiri may refer to: Subansiri Lower Dam , India Subansiri River , in India and Tibet Lower Subansiri district , Arunachal Pradesh, India Upper Subansiri district , Arunachal Pradesh, India Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Subansiri . If an internal link led you here, you may wish to change
60-474: A stream of water to obstruct its flow and raise its level'). For dam construction, two cofferdams are usually built, one upstream and one downstream of the proposed dam, after an alternative diversion tunnel or channel has been provided for the river flow to bypass the foundation area of the dam. These cofferdams are typically a conventional embankment dam of both earth- and rock-fill, but concrete or some sheet piling also may be used. Usually, upon completion of
90-403: A unit, or prefabricated panels can be joined during erection. When partial cofferdams are used, it may be necessary to compensate for hydrostatic pressure on the deck by shoring the decks. With both complete and partial cofferdams, there is usually a large free surface in the spaces being pumped. Sometimes this can be limited by dewatering one compartment at a time, or in groups, taking into account
120-703: Is an under construction gravity dam on the Subansiri River in North Eastern India. It is located 2.3 km (1.4 mi) upstream of Subansiri River in Arunachal Pradesh . Described as a run-of-the-river project by NHPC Limited , the Project is expected to supply 2,000 MW of power when completed. The project has experienced several problems during construction to include landslides, re-design and opposition. By early 2019, work had stalled on both of
150-488: Is no opening to the interior of the vessel, or the interior is pressurised in this area. The air space is at the pressure of the water surface at the bottom of the chamber. Open top cofferdams allow surface access to the work area below the waterline, and are at atmospheric pressure. Openings through the hull to the interior of the ship are possible. Portable cofferdams can be inflatable or frame and fabric cofferdams that can be reused. Inflatable cofferdams are stretched across
180-408: Is not practical to put a ship in drydock for repair work or modernization. An example of such an application is the lengthening of ships. In some cases a ship is actually cut in two while still in the water, and a new section of ship is floated in to lengthen the ship. The cutting of the hull is done inside a cofferdam attached directly to the hull of the ship; the cofferdam is then detached before
210-517: The IJsselmeer in 2023 using a cofferdam, allowing for close examination of the wreckage, as well as to locate and repatriate the remains of its crew. A 100-ton open caisson that was lowered more than a mile to the sea floor in attempts to stop the flow of oil in the Deepwater Horizon oil spill has been called a cofferdam. A cofferdam over 1 mile long was built to permit the construction of
240-819: The Livingstone Channel in the Detroit River. See main article at Stony Island . The museum battleships USS Alabama (BB-60) and USS North Carolina (BB-55) have had cofferdams since 2003 and 2018, respectively. This saves much money compared to towing and dry docking them after the tow and this also provides additional security so there is a low chance of the ships sinking and becoming impossible to repair. Several types of structure performing this function can be distinguished, depending on how they are constructed and how they are used. In civil and costal engineering applications cofferdams are usually made from interlocking steel sheet piles which are driven deep into
270-584: The Subansiri Project will submerge a 47 km (29 mi) length of the Subansiri river and occupy 37.5–40 km (14.5–15.4 sq mi) which includes Himalayan subtropical pine forests , Himalayan subtropical broadleaf forests , part of the Tale Valley Wildlife Sanctuary, an elephant corridor and some subsistence agriculture fields. Thirty eight families will be displaced if
300-440: The adjacent structure. There are two common types of dry chambers used in underwater ship husbandry. Open bottom cofferdams allow divers direct access to the enclosed hull area, system, or opening. The flange sides of the chamber secure and seal against the hull, acting as an airtight boundary. Open bottom cofferdams are typically used as diver work space for rigging or welding and ventilation for welding or epoxy cure, where there
330-441: The beam strength loads on the ship induced by the load distribution. Small cofferdams are used for pumping or to allow salvors access to spaces that are covered by water at some stage of the tide. They are usually prefabricated and fitted around minor openings. Diving work on cofferdams often involves clearing obstructions, fitting, and fastening, including underwater welding, and where necessary, caulking , bracing and shoring
SECTION 10
#1732844753824360-460: The bed of the water source in order to create a temporary dam behind which the engineering contractors can carry out their works. After the construction project is complete the sheet piles can then be removed and the area behind them rewetted. A cofferdam is a space between two watertight bulkheads or decks within a ship. It is usually a void (empty) space intended to ensure that the contents of nearly adjacent tanks cannot leak directly from one to
390-399: The construction of the dam's other half. Cofferdams are used in ship husbandry to allow dry access to underwater equipment and to close underwater openings while work is done on the fittings inside the ship. This is more common in naval vessels where a cofferdam may fit several vessels of a class. The cofferdam is also used on occasion in the shipbuilding and ship repair industry, when it
420-405: The dam and associated structures, the downstream coffer is removed and the upstream coffer is flooded as the diversion is closed and the reservoir begins to fill. Depending on the geography of a dam site, in some applications, a U-shaped cofferdam is used in the construction of one half of a dam. When complete, the cofferdam is removed and a similar one is created on the opposite side of the river for
450-495: The dam is completed, according to official data. Water flow downstream will be regulated by the dam which is expected to result in low releases (6 m /s) during winter and very high releases (2,560 m /s) when energy is being generated. The project has met stiff resistance from several groups including All Assam Students’ Union and the Krishak Mukti Sangram Samiti , who are apprehensive about safety and
480-420: The dam reached an elevation of 138 m (453 ft), just below the spillway elevation of 145 m (476 ft). On 16 December 2011, construction equipment was halted by protests. The construction cost has gone up by about ₹ 1,200 crore owing to forced suspension of work since December 2011. NHPC has already spent about ₹ 6,600 crore, according to a status report prepared by the company. By mid-2023,
510-580: The dam's design for stability. While the dam was being re-designed, concrete was placed over the foundation to protect it from the upcoming monsoon floods as the cofferdams stood a good chance of not protecting the foundation from the strong floods. The re-design was completed in October 2008 and soon after the foundation was once again cleared. In May 2009, work was suspended because of the monsoon season and re-commenced in November of that year. As of November 2011,
540-479: The elevation of the dam had reached 210m above sea level. In October 2023, another landslide impacted construction, as part of a hill collapsed into the reservoir, blocking a tunnel and stopping water flowing into the Subansiri river. Some environmental impacts unique to very large dams will result from completion of the Subansiri Project, both upstream and downstream of the dam site. These impacts will include ecosystem damage and loss of land . The reservoir of
570-415: The hull sections are floated apart. The cofferdam is later replaced while the hull sections are welded together again. As expensive as this may be to accomplish, the use of a drydock might be even more expensive. Cofferdams are also used in some marine salvage operations. Cofferdams have been used to recover aircraft from water as well, as in the case of Avro Lancaster ED603 , which was recovered from
600-442: The hydrostatic and other loads that they will have to withstand. Large cofferdams are normally restricted to harbor operations. Complete cofferdams cover most or all of the sunken vessel and are equivalent to extensions of the ship's sides to above the water surface. Partial cofferdams are constructed around moderate-sized openings or areas such as a cargo hatch or small deckhouse. They can often be prefabricated and installed as
630-501: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Subansiri&oldid=811267711 " Categories : Disambiguation pages Place name disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Subansiri Lower Dam The Subansiri Lower Dam , officially named Subansiri Lower Hydroelectric Project (SLHEP),
SECTION 20
#1732844753824660-511: The main deck of a sunken ship is submerged, flooded spaces cannot be dewatered until all openings are sealed or the effective freeboard is extended above the high water level. One method of doing this is to build a temporary watertight extension of the entire hull of the ship, or the space to be dewatered, to the surface. This watertight extension is a cofferdam. Although they are temporary structures, cofferdams for this purpose have to be strongly built, adequately stiffened, and reinforced to withstand
690-415: The need to handle high flood flows and poor rock conditions. The design of the dam has undergone drastic and repeated revisions that have affected the schedule and planning of the construction work. In December 2003 the contract to build the dam and its associated structures was awarded to a consortium of Boguchandgesstroy, Soyuzgidrosptsstry and Soma Enterprise Ltd. Due to difficulties acquiring land around
720-419: The other which would result in contamination of the contents of one or both of the compartments. The cofferdam would be kept empty at all times and the ship may have sensors within it to warn if it has begun to fill with liquid. If two different cargoes that react dangerously with each other are carried on the same vessel, one or more cofferdams are usually required between the cargo spaces. When all or part of
750-441: The project’s downstream impact. Cofferdam These cofferdams are usually welded steel structures, with components consisting of sheet piles , wales , and cross braces . Such structures are usually dismantled after the construction work is completed. The origin of the word comes from coffer (originally from Latin cophinus meaning 'basket') and dam from Proto-Germanic * dammaz meaning 'barrier across
780-803: The reservoir's surface will cover 33.5 km (13 sq mi). The surface powerhouse , located on the right bank, will contain eight 250 MW Francis turbine generators using 86 m design head out of 91 m gross head available. There will be eight horse shoe shaped head race tunnels, each being 9.5 m (31 ft) in diameter and having a length from 608–1,168 m (1,995–3,832 ft). There will be eight horse Shoe shaped surge tunnels, each being 9.5 m (31 ft) in diameter and having length from 400–485 m (1,312–1,591 ft). There will be eight horse shoe/circular shaped penstocks with varying diameters of 7–9.5 m (23–31 ft) and lengths of168–190 m (551–623 ft). The tail race channel, which will transfer water discharged by
810-432: The river bed and 210 m (690 ft) from the deepest foundation. Its length will be 284 m (932 ft) and the dam will have a structural volume of 2,250,000 m (2,942,889 cu yd). The reservoir created by the dam will have a gross storage capacity of 1.37 km (1,110,677 acre⋅ft ), of which .44 km (356,714 acre⋅ft ) can be used for power generation or irrigation. At normal level,
840-528: The site, construction could not begin in earnest until 13 months after the contract was awarded. Unexpected geological conditions at the dam site led to landslides and slower tunnel excavation. By November 2007, the river was successfully diverted and in April of the next year, the foundation was clear for construction. Before the foundation was fully prepared it was discovered that bedrock was reached 10 m (33 ft) sooner than expected. This led to an alteration in
870-465: The turbines back to the river, is 206 m (676 ft) wide and 35 m (115 ft) long. When complete, the hydroelectric generators will begin generating 500 MW of electricity, gradually increasing to 2000 MW. Construction of Subansiri Lower Project involves many challenges. These include land not being available when construction was scheduled to commence, a limited annual construction time because of monsoons (from mid-April to mid-October),
900-614: The two major dam projects in the Assam region, the Dibang and the Lower Subansiri. The project construction resumed from October 15, 2019, after the clearance by National Green Tribunal. The remaining work of radial gates was expected to be completed after the monsoon season and electricity generation was expected to begin by the end of Financial Year 2023-24. The concrete gravity dam is designed to be 116 m (381 ft) tall, measured from
#823176