River erosion

M. Tech, 1st Semester,

WATER RESOURCE ENGG.

WATER IS THE MOST IMPORTANT NATURAL RESOURCES FOR PLANET EARTH

THE PROSPERITY OF A NATION DEPENDS PRIMARILY UPON THE EXPLOITATION OF THIS

RESOURCES. THUS IT CAN BE STATED THAT THE PRIMARY WEALTH OF A NATION IS WATER, WHICH FLOWS IN THE RIVER OR STREAMS.

AN IMAGE OF A R IVER

AS A RIVER FLOWS, THE FORCE OF ITS MOVING WATER WASHES AWAY LOOSE SOIL & PIECES OF ROCKS. IN THIS WAY THE RIVER CUTS ITS OWN CHANNEL IN THE GROUND. THIS PROCESS IS CALLED EROSION

HYDRAULIC ACTION

ABRASION

ATTRITION

SOLUTION

The force of water wears away the

river bank from underneath. The

pressure of water breaks the rock

particles. Water force hits river banks

and pushes water into cracks. Thus the

pressure expands the cracks and

breaks the rocks into fragments.

Image showing Hydrau l ic Act ion

The sediments carried by the river

scours the bed and banks.

Where depression exist in the

channel floor the river can cause

Pebbles to spin around and turn

hollows into potholes.

An image potholes c reated by abras ion

What i s Attr i t ion ?

Rocks being carried by the rivers smash together and break into smaller particles. Overtime, they become smaller and eventually reduced t fine particles called silt.

CO2 dissolves in the river to form a

weak acid. This dissolves rock by

chemical processes. This process

is common where carbonate rocks

such as limestone & chalk are

evident in the channel.

A typical drawing of four types of River Erosion Process

To prevent the river from changing its coarse & to avoid outflanking of structures like bridges, weirs etc.

To prevent flooding of the surrounding areas by providing a safe passage for the flood waters without overtopping the banks.

To protect the river banks by deflecting the river away from the attacked banks.

To ensure effective disposal of sediment load.

Marginal embankment or Levees

Guide banks

Groynes or Spurs

Levees are generally earthen embankments, running parallel to the river. These embankment-wall retain the river water to carry the

bank soil with the water.

A N IM A GE O F L E V E E S A T T H E R IV E R BA NK

The guide banks are generally provided across a river as to ensure not only a safe and expeditious disposal of flood water but also to ensure a permanent reasonable width of the waterway for the river flow.

Symmetrical and parallel guide banks are usually adopted.

A DRAWING OF A GUIDE BANK

G U I D E B A N K

Groynes are the embankment type structures, constructed transverse to the

river flow to protect the bank by deflecting the current away from the bank. As the water is unable to take a

sharp embayment, the bank gets protected.

A N I M A G E O F A G R O Y N E

Ordinary or normal Groynes

Repelling Groynes

Attracting Groynes

G R O Y N E

River controlling methods mainly depends upon the type of the river, its regime and the flow characteristics of the river. So the methods to control the river erosion varies from place to place.

Hence, no particular method of river controlling can be stated to be the best. A comprehensive planning and model testing is necessary before any measure are undertaken to control the river.