The lecture discusses the concept of catchment areas, defined as the land draining into a specific stream, and their classification into fan-shaped and fern-shaped types, influencing flood intensity and discharge timing. It also covers various stream patterns formed based on geological features, including dendritic, trellis, radial, and rectangular patterns, each determined by the underlying topography and rock structure. Finally, it highlights how these patterns and classifications impact water flow and drainage in different environments.

1. Lecture 12:
Catchment and
Stream Pattern

2. Md. Arifur Rahman Bhuiyan
Assistant professor
Department of Environmental Science
Bangladesh University of Professionals

3. Key Discussion Points

4. • Catchment: The area of land
draining into a stream or a water
course at a given location is
known as catchment area. It may
be defined as the area from which
the surface runoff is derived. It is
also known as watershed area,
drainage area, drainage basin or
simply basin or catchment.
Catchment

5. Catchment
The unit for the catchment area is
km2. If the catchment area is less
than 25 km2, it is mentioned in
terms of hectares. The catchment
areas formed by the divide lines at
A and B are shown in Fig.

6. • The line which divides the
surface runoff between two
adjacent river basins is called
topographic water divide or
watershed divide or simply
divide.
• The divide follows the ridge
line around the basin crossing
the stream only at the outlet
point.
• It marks the highest points
between the basins.

7. https://www.youtube.com/watch?v=B6Nt-_NSFG4
https://www.youtube.com/watch?v=VqQJ0n-_sAE

8. Classification of Catchment:
Catchment can be classified into
two shapes.
1) Fan Shaped- The shape of a
catchment may be similar to
a fan i.e. circular.
2) 2) Fern Shaped- The shape of
a catchment may be similar
to a fern leaf i.e. elongated.
Classification of Catchment

9. A fan-shaped catchment
produces greater flood intensity
since all the tributaries are nearly
of the same length and hence the
time of concentration is nearly the
same and is less,
whereas in the fern-
shaped catchments, the time of
concentration is more and
discharge is distributed over a
long period.
Classification of Catchment

10. Stream Pattern
When a region is homogenous to
the flow of water, the resulting
stream runs in all directions with
no preference to any particular
direction, then the stream pattern
developed is called dendritic or
tree like.

12. • The trellis drainage pattern
develops when the underlying rock
is strongly folded or sharply dipping.
The longer streams will have
preference to one particular
orientation and the other tributaries
will have an orientation at right
angles to this.
Stream Pattern

14. Stream Pattern
The drainage pattern from dome
mountains and volcanoes is of
radial type where the streams
emanate from a central focus and
flow radially outward.

16. Stream Pattern
Owing to the internal
geologic structure of the
land, sometimes, the
parallel or subparallel
drainage patterns are
formed.

18. The streams which form in the
weaker strata of a dome mountain is
of circular or annular pattern. The
annular pattern may be treated as a
special form of the trellis pattern.

20. • The drainage pattern marked by right-angled
bends and right-angled junctions between
tributaries and the mainstream is known as
rectangular drainage. A region consisting of
many rectangular joints and faults may
produce a rectangular pattern with streams
meeting at right angles. It differs from the
trellis pattern in so far as it is more irregular
and its tributary streams are neither as long,
nor parallel as in trellis drainage.

21. • In a pinnate stream pattern, all the
main streams run in one direction with
the tributaries joining them at an
oblique angle.

22. THANK YOU!