Download Geological work by river

Compiled by:
SUKHWANT MOHAN
ABHISHEK ARYAN
CONTENT
SL.N
NAME OF
O
CHAPTERS
1. Geological work by
river
2. Introduction of
streams
3. TYPES OF STREAMS
4. Drainage system
5. Types of drainage
ABOUT THE GEOLOGICAL WORK
When a piece of the Earth’s crust
first emerges from the sea and rain
begins to fall on it, the water running
off begins to erode it. As the first
gullies develop into channels, the
drainage of this new land gets
organized by an interplay of two
principle factors: differential erosion
& stream capture.
DIFFERENTIAL EROSION
As the water runs down hill, it
erodes channels that become organized into
a drainage pattern. As running water
deepens its channel, it encounters rocks of
different hardness and adjusts its channel in
response. Soft layers erode faster than hard
layers. This simple statement is an
important principle of erosion which that
applies to almost every natural scene.
Eventually, hard layers or other hard parts
of rocks stand out in bold relief, and softer
layers or parts retreat into swales, gullies,
and valleys. Geologists call the process
differential erosion.
STREAM CAPTURE
Stream capture or piracy,
is the process whereby a stream
easily deepening its valley in soft
rock can cut headword across a
drainage divide to capture a
portion of a neighbouring stream
that is working away slowly in
harder rock. Examples of pure
stream capture are hard to find in
the North Cascades because of the
overriding disruption of drainages
by the growth and retreat of the
Canadian Ice Sheet, but the overall
parallel conformity of most North
Cascade streams and rivers to the
northwest-southeast-trending
structural grain, indicates stream
piracy has ruled for millions of
years. The figure above,
representing an idealized
situation, illustrates the process.
ABOUT STREAM
Streams
alter
the
Earth's
landscape through the movement of water
and sediment . Streams are powerful erosive
agents moving material from their bed and
banks. In mountainous regions, stream
erosion often produces deep channels and
canyons. Streams also deposit vast amounts
of sediment on the terrestrial landscape and
within lakes and ocean basins.
TYPES OF STREAMS
 CONSEQUENT STREAM:- In any area these are the first stream to
have developed in accordance with the topography of the area.
 SUBSEQUENT STREAM:-These are the generally tributaries to the
consequent streams. The characters of the rocks over which they
flow controls their direction of flow
 OBSEQUENT STREAM:-These are tributaries to the subsequent
streams. In most cases their direction of flow may be opposite to
the main or consequent stream.
 INSEQUENT STREAM:-They may also be called irregular stream.
These are found to flow in canals that show no well defined
relationship with either the slope of the area or the character of
the rocks.
DRAINAGE SYSTEM
A drainage system is the pattern formed by the
streams, rivers, and lakes in a particular drainage
basin. They are governed by the topography of the
land whether a particular region is dominated by
hard or soft rocks, and the gradient of the land.
Geomorphologists and hydrologists often view
streams as being part of drainage basins. A drainage
basin is the topographic region from which a stream
receives runoff, through flow, and groundwater flow.
Drainage basins are divided from each other by
topographic barriers called a watershed.
TYPES OF DRAINAGE SYSTEM
 TRELLIS DRAINAGE:-When a consequent stream receives a number
of subsequent stream from right and left at approximately right
angles to its direction of flow, a trellis drainage system is said to
develop.
 DENDRITIC DRAINAGE:-This type of
drainage system develops
when the strems of different types are all fairly common in a
region and none a pairs to dominate other group.
 RADIAL DRAINAGE:-This type of
drainage system develops in a
region which are either elevated or depressed with reference to the
surroundings topography.
 SUPREMEPOSED DRAINAGE:-It is developed in geologically old
and complex folded region.
 ANTECEDENT DRAINAGE:-Gradual uplift of the crystal blocks
forming the mts system is believed to be a well-established
geological phenomenon.