62
Exercise 5
Table 5.2. Basin and channel characteristics."
Definitions of topographic characteristics
Basin length (Ln)
Basin width (W B)
Basin perimeter (P B)
Basin land slope (Sn)
Basin diameter (B D )
Basin shape (SHB)
Compactness ratio (eR B )
Main channel length (Lcl
Main channel slope (Sc)
Sinuosity ratio (P)
"Modified from Winter (1985).
Straight-line distance from outlet to the point on the basin divide used to
determine the main channel length, Le.
Average width of the basin determined by dividing the area, A, by the
basin lcngt h, L B:
Wn=A/Ln
The length of the line that defines the surface divide of the basin.
Average land slope calculated at points uniformly distributed throughout the basin. Slopes normal to topographic contours at each of 50-and
preferably 100-grid intersections are averaged to obtain SR' The
difference in altitude for the two topographic contours nearest a grid
intersection is determined, and the normal distance between these
contours is measured.
The diameter of the smallest circle that will encompass the entire basin.
A measure of the shape of the basin computed as the ratio of the length of
the basin to its average width:
The ratio of the perimeter of the basin to the circumference of a circle of
equal area. Computed from A and PB as follows:
Pn
CR = - - -
B
2(nA) I /2
The length of the main channel from the mouth to the basin divide.
An index of the slope of the main channel computed from the difference
in stream-bed altitude at point 10% (E , ,,) and 85% (Ess) of the distance
along the main channel from the outlet to the basin divide. It can be
computed by the equation
(Ess - E 10)
Sc=-'~~-0.75Le
The ratio of the main channel length to the basin length:
Lc
P=LB
Table 5.3. Drainage network characteristics for a hypothetical drainage basin.
Order
1
2
3
4
5
6
7
8
Number
of streams
200,000
65,000
20,000
5500
1500
400
150
40
Average
length
(km)
0.02
0.03
0.06
0.16
0.40
1.0
2.4
5.6
-~--~---~~
Average
drainage
area
(km")
0.00018
0.00091
0.00414
0.0129
0.0906
0.388
2.20
9.06
--~~--~-Average
discharge
(l/see)
0.005
0.025
0.12
0.36
2.5
11
62
250
- - - - - - -
Exercise 5
Table 5.2. Basin and channel characteristics."
Definitions of topographic characteristics
Basin length (Ln)
Basin width (W B)
Basin perimeter (P B)
Basin land slope (Sn)
Basin diameter (B D )
Basin shape (SHB)
Compactness ratio (eR B )
Main channel length (Lcl
Main channel slope (Sc)
Sinuosity ratio (P)
"Modified from Winter (1985).
Straight-line distance from outlet to the point on the basin divide used to
determine the main channel length, Le.
Average width of the basin determined by dividing the area, A, by the
basin lcngt h, L B:
Wn=A/Ln
The length of the line that defines the surface divide of the basin.
Average land slope calculated at points uniformly distributed throughout the basin. Slopes normal to topographic contours at each of 50-and
preferably 100-grid intersections are averaged to obtain SR' The
difference in altitude for the two topographic contours nearest a grid
intersection is determined, and the normal distance between these
contours is measured.
The diameter of the smallest circle that will encompass the entire basin.
A measure of the shape of the basin computed as the ratio of the length of
the basin to its average width:
The ratio of the perimeter of the basin to the circumference of a circle of
equal area. Computed from A and PB as follows:
Pn
CR = - - -
B
2(nA) I /2
The length of the main channel from the mouth to the basin divide.
An index of the slope of the main channel computed from the difference
in stream-bed altitude at point 10% (E , ,,) and 85% (Ess) of the distance
along the main channel from the outlet to the basin divide. It can be
computed by the equation
(Ess - E 10)
Sc=-'~~-0.75Le
The ratio of the main channel length to the basin length:
Lc
P=LB
Table 5.3. Drainage network characteristics for a hypothetical drainage basin.
Order
1
2
3
4
5
6
7
8
Number
of streams
200,000
65,000
20,000
5500
1500
400
150
40
Average
length
(km)
0.02
0.03
0.06
0.16
0.40
1.0
2.4
5.6
-~--~---~~
Average
drainage
area
(km")
0.00018
0.00091
0.00414
0.0129
0.0906
0.388
2.20
9.06
--~~--~-Average
discharge
(l/see)
0.005
0.025
0.12
0.36
2.5
11
62
250
- - - - - - -