river diversion

RIVER DIVERSION

Presented by-Mousumi Bania (CIB09004) and Azaz Ahmed (CIB09015)Department of Civil Engineering, Tezpur University.

RIVER DIVERSIONThe need for DiversionCofferdamsDiversion TunnelsDiversion DamOther alternative

methods

WHAT IS RIVER DIVERSIONIt is the act of diverting a portion of river

water from the main course to another natural or man-made channel.

NEED FOR RIVER DIVERSION?

For securing a site in the main river course for construction or repair works of dams, bridges, artificial islands etc

Dam-site, Lower SubansiriGerukamukh, Assam

For procuring water from a stream having a high flow into one having low flow.

For extracting water out of the main course into natural or artificial channels serving the purpose of distributing water to agricultural fields and industries.

For proper flood control measures and river basin management.

Flood-control efforts in the Wairau River valley culminated with the opening of the Wairau diversion on 30 April 1963.

RIVER DIVERSION FOR CONSTRUCTION OF DAMWe need-Cofferdams- To secure a water tight

construction site

Diversion tunnels- To channel the water from the main river course around the construction site

COFFERDAMSA cofferdam (also called a coffer) is a

temporary enclosure built within, or in pairs across, a body of water

It is constructed to allow the enclosed area to be pumped out, creating a dry work environment for the major work to proceed.

The word "cofferdam" comes from "coffer" meaning box

A cofferdam on the Ohio River near Olmsted, Pulaski County, Illinois, USA. The cofferdam was constructed by the U.S. Army Corps of Engineers for the purpose of constructing the Olmstead Lock and Dam on the Ohio River.

KEY NOTESCofferdams are temporary enclosures to

keep out water and soil so as to permit dewatering and construction of the permanent facility (structure) in the dry.

A cofferdam involves the interaction of the structure, soil, and water. The loads imposed include the hydrostatic forces of the water, as well as the dynamic forces due to currents and waves.

Cofferdams usually deviate from their initial design.

This is because of-

Offshore construction

Adversities in the weather

Deformation due to varying loads

Cofferdam under construction

VARYING LOADS ON COFFERDAMS DUE TO-Construction equipments

Various installations and related process

Construction of the dam itself

Changes in the river

TYPES OF COFFERDAMBRACED

EARTH-TYPE

TIMBER CRIB

DOUBLE WALLED SHEET PILE

CELLULAR

BRACED TYPEIt is formed from a single wall of sheet

piling which is driven into the ground to form a “box” around the excavation site.

The box is then braced on the inside and the interior is dewatered. It is primarily used for bridge piers in shallow water (30 - 35 ft

A Braced type cofferdam

EARTH TYPEIt is the simplest type of cofferdam. It

consists of an earth bank with a clay core or vertical sheet piling enclosing the excavation.

It is used for low-level waters with low velocity and easily scoured by water rising over the top.

Earth type cofferdam

TIMBER-CRIB TYPEConstructed on land and floated into

place.

Lower portion of each cell is matched with contour of river bed.

Timber crib type cofferdam

DOUBLE- WALLED SHEET PILE TYPEThey are double wall cofferdams.

Comprises of two parallel rows of sheet piles driven into the ground and connected together by a system of tie rods at one or more levels.

The space between the walls is generally filled with granular material such as sand, gravel or broken rock.

Double-Walled sheet pile type cofferdam

CELLULAR TYPECellular cofferdams are used only in those

circumstances where the excavation size precludes the use of cross-excavation bracing.

In this case, the cofferdam must be stable by virtue of its own resistance to lateral forces.

Cellular type cofferdam

DIVERSION TUNNELSCarries water from the mainstream to

other channels or across the construction site.

Can be permanent, or temporary structures

Diversion tunnels of Lower Subansiri hydel project

Jinsha river diversion tunnel, China

Cofferdam is breached to allow the river to flow through the Diversion Tunnel

DIVERSION DAMA dam that diverts all or a portion of the

flow of a river from its natural course.

Diversion dams do not generally impound water in a reservoir.

Instead, the water is diverted into an artificial water course or canal, which may be used for other purposes

The Faraday Diversion Dam, Clackamas River. This dam slows a normally fast and shallow river for partial diversion to a hydroelectric dam.

The Imperial Dam diverting the Colorado River in the southwestern United States.

The earliest diversion dam - and the second oldest dam of any kind known - is the Ancient Egyptian Sadd-el-Kafara Dam at Wadi Al-Garawi, located about 25 km south of Cairo.

Built around 2600 BC for flood control, the structure was 102 m long at its base and 87 m wide. It was destroyed by a flood while still under construction.

RIVER FRIENDLY ALTERNATIVES

Infiltration galleries and wells

Screened pipe intakes

Seasonal dams

Consolidated diversions

INFILTRATION GALLERIES AND WELLS

Are of two types-

Vertical wells

Horizontal infiltration galleries

Horizontal infiltration galleries are also known as "Ranney wells.”

Both types typically require pumps to draw water from the stream’s gravel substrate through perforated pipes.

In certain sites, infiltration galleries can function by gravity alone.

VERTICAL WELLSVertical wells draw water through

perforated pipes placed vertically into the stream or floodplain substrate and water table maintained by the surface flow.

Vertical wells can be located very near the stream or at some distance from the channel, depending on stream conditions.

Images of Vertical well

INFILTRATION GALLERIESTypical construction of an infiltration

gallery involves placing perforated pipes in the streambed and connecting them to a collection area, or “sump”.

Water seeps into the perforated pipes and flows to the sump where it is pumped out (or flows by gravity) for immediate use or storage. 

Sucker Creek Infiltration Gallery

ADVANTAGESEliminating the impacts of dams on natural stream dynamics.

Avoiding the risk of fish entrainment.

Reducing the visual impact of the diversion.

DISADVANTAGESThe perforated pipes gets blocked with fine sediment;

When relying on vertical wells, there is a risk that wells could dewater the stream where the subsurface water is connected to the surface water. Eg in california where groundwater pumping is unregulated.

SCREENED PIPE INTAKESWater is pumped out of rivers by placing

screened pipes

Screened pipe intakes can safely divert water to a distribution system for immediate use or into a surface or subsurface storage site away from the stream for later use

Water intake pipe of the Kinston Water Works

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DISADVANTAGESScreens can be expensive to install and maintain.

SEASONAL DAMSTemporary structures that can be erected

to store water for immediate or later diversion, or removed to allow flows and (in most cases) fish to pass. 

Inflatable dams and flashboard dams (also known as stop log dams) are the most common types of seasonal dams.

SEASONAL DAM IMAGE:

INFLATABLE DAMSInflatable dams are made of thick,

laminated rubber and nylon tubes that are anchored to a concrete foundation across the streambed.

The tube can be filled automatically or manually with air or water to create a barrier, and subsequently deflated to lie flat on the foundation.

Inflated Dam on Alameda Creek 

The same dam when deflated

FLASHBOARD DAMSFlashboard dams usually involve a concrete

foundation and frame into which boards are inserted to block the stream flow and raise the water level to allow for diversion.

ADVANTAGESProvide the flexibility to store and divert water or allow water, sediment and fish to pass when the dam is not in use.

In certain cases, pools created by temporary dams can provide cool water habitat for species to over-summer in warm streams

DISADVANTAGESRequires lot of continuous monitoring

It can increase water temperatures, harbor predator species, eliminate water flows and associated aquatic habitat downstream

Induce erosion of the bed and banks of streams and introduce major fluctuations in water levels upstream of the dam impacting biota, aquatic vegetation and residents

CONSOLIDATED DIVERSIONS

When several diversion dams are located close together on a single stream, it is possible to consolidate the number of diversions to a single diversion point, allowing the elimination of some of the dams.

The concept is known as consolidated diversions

ADVANTAGESEliminate some or all of the diversion

dams involved, and typically reduces the number of diversions that require screens to prevent fish entrainment.

DISADVANTAGESIt requires the need to relocate diversion

pipes or canals to the new diversion point, and hence adds to the cost.

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