This document discusses various characteristics of catchments that affect surface runoff, including: 1. The area, shape, slope, and drainage patterns of a catchment determine the volume and timing of surface runoff from storms. 2. Important geometric parameters that represent catchment characteristics are the stream order, stream density, drainage density, relief, slope, length, shape, and hypsometric curve. 3. Drainage density indicates the level of drainage development and influences how quickly runoff moves from the catchment, with higher densities associated with steeper slopes and less permeable soils.

1. 5.4 Catchment Characteristics
A catchdnt. also known as drainage basin, drainage area and watershed, Is thee
basichydrologic unit in the analysisofrunoffphenomenon. Physical characteristics
of the catchment such as area, shape, slope, and drainage channel patterm in the
catchmentare some of the major static characteristics that affect the volume of the
surtace runoff and shape of the runoffhydrograph from a catchment due to a storm.
Study of the catchment characteristics forms an important component ofthe subject
ofgeomorphology and is studied under the topic head ofquantitativegeomorphology.
Some of the important geometrical parameters ofthecatchment as related to runoff
process are briefly described below.

2. 170 Engineering Hydrology
1. Area
chmer
Ca1s probably the most used parameter to represent
the
characteristics
ofacatch
hOT2ontal projection ofthecatchment boundary. The usual units are hectare he
Small catchments and square
kilometer (km*) for larger drainage areas.
he area of the catchment is defined as the area of the closed curve
hectare
formin
(ha fo
Catchment Boundary
2. Stream Order
lt is a classification reflecting the pattern of
branches that unite to form the trunk stream
leaving the catchment. The smallest stream
at the start of the network is designated as
of 'onderl'. Two channels oforder I when
JOined produce a stream of 'order 2.Two
channels of order 2 when joined produce
a stream of order 3, and so on. Note that
when a lower order stream (say order 2)
meets a higher order stream (say order 3)
the order of the resulting stream is still the
higher order stream entering the confluence
viz.. order 3 in this case. The trunk stream
2
2
3
3
3
discharging out ofthe drainage basin has the
highest order. Fig. 5.5 shows schematically
a drainage basin with a stream system of FIg. .5 Stream Channel Ordering ina
Catchment Outlet
Fourth-Order Stream
order 4.
Streams of order 1 to 3 are called headwater streams and constitute waterwavs
in the upper reaches of the catchment. Nearly 80% of the world's waterways are of
order 1 through 3. The size of a stream becomes larger as its stream order increases
Also, the slope of the stream decreases with its increase in the stream order number
Streams of size 4 to 6 are usually medium-size streams. Streams of order 1larger tha
6 are called as rivers. The largest stream order known is 12; for example. the nver
Amazon has a stream order of 12.
Stream order is helpful in designating the nature of drainage patterm of acatchmen
and is ofuse in locating watershed treatment structures like check dams and Nala buns
3. Stream Density, Sa
The ratio of the number of streams (N) of all orders to the area of the basin ta
known as stream density (S) of the basin. Thus, S, = - Stream density represens
N
A
the number of streams per unit area and is indicative of the pattern of drainage c
in the catchment.
hannels
4. Drainage Density, D
Drainage density is the ratioofthe total length of streams of all orders wi
to its area. Thus, if L =length of a stream in a basin, then D,
. The draina
A
density is a measure of how well the drainage basin is drained by thestc
c stream netwo

3. Runoft 171
The
drainage
density is calledo
coarse, medium or fine
depending
or fine depending on the value of
D
D,>5 km/km
Drainagedensity o
age density aepends upon the climate and physical characteristicsd and
as
follows: CoarseifD5
km/km*;
mediur
Medium if D, =
5--10 km/km"an Fine if
Drahment. Generally, impermeable soil material in the
catchmen
ofthecatchment
and steep slopeae more channels to move the runoffrapidly. Hence, a
nug
tnin
cover
and steep slope cause mo
drainage density may 1ndicate one or more of the following:
.Existence of amature, well
developed channel system
Surface runoft ives rapidly from the edge of thecatchment
.Thin/deforested land cover
. Low infiltralioin so Or
impervious geology.
Drainage density a very useful numerical measure of the runoff potenta
texture of the catchmneni and is measured fairly casily
through use of GIS. This
arameter finds considerable use in
manage
lairly
of
easily
watershed
through
erosion.
use of GIS. This
5. Relief
Maximum basin relier Is the elevation difference Cin meters) between the catcnnC
outlet and the highest point on the basin perimeter.
6. Slope
Usually, a slope profile prepared along the main stream is used to characterize tn
slope of the catchment. For a given stretch of the stream, the ratio ofhorizonta
distance between the two end parts of the stretch to the difference in elevation between
these two points gives the slope of the stretch. As a rule, the catchment slope is the
highest at the beginning of the stream and gradually decreases as one moves along
the stream to the basin outlet. Slope is an important parameter in many watershed
Simulation models.
7. Length, L
The length of the catchment is defined as the length of the main stream measured
from the basin outlet to the remotest point on the basin boundary. The main stream
identified by starting from the basin outlet and moving up the catchment. At any
branching point the largest order branch is taken. If there is a branch of two streams
of the same order, the one with the largest catchment area is taken as the main steam.
8. Shape
here are a number of ways ofdesignating and quantifying the shape ofa catchment.
omeofthecommonly used shape parameters are shown in Table 5.I along with their
CTintions. In this table A =
catchment area, L = catchment length and P= perimeter
of the catchment.
9.Hypsometric Curve
His a
plot of ho
horizental cross-sectional drainage asin area to elevation. It is usual
piot the curve in a nen-dimensional form as relative height h/H plotted against
Telativ area d
S relief). a =basin area at contour h andA = total basin area.
height
aA as shown in Fig. 5.6. In this h =heig of a given contour, H = basin

4. 172 Eng1neeringHydrology
Table 5.1 Different
C a t c h m e n t
Shape
P a r a m e t e r s
Formula
Definition
Parameters A
Formfactor
Catchment area
(Catchment length)*
Shape factor
(Catchment length)
Catchment area
0.2821P
Perimeterofthecatchment
A
Compactness
coefficient
Perimeter of the circle whose area is that of the basin
12.57A
Catchment
area
Circulatory
ratio Area ifcircle ofcatchment perimeter
Diameter ofcirclewhoseareaisbasin area
Catchment length
1.128A
Elongation L
ratio
1.0 Bankri Nala
(A 5h OrderStream in MP)
0.8
0.6
h/H
0.4
0.2
0.2 0.4 0.6 0.8 1.0
alA
Fig.5.6 Hypsometric curveofa 5h order Stream
(Ref. INSA, Vol.40A, No.1)
Hypsometric curve describes the proportion of basin area that is above
certain basin elevation. It represents an overall basin slope and embodiesmu
of geomorphic information of the basin. These days, hypsometric curve>
are
generated through use of GIS and its applications are many. Major applicatio
include watershed treatment, planning and design of rainwater harvesting
and
erosion control programs. Further, the hypsometric curve finds use in some
w
a t e r s h e d
models