Determining Average Cross-Sectional Area (A)

Transect #1 (upstream)

Transect #2 (downstream)

...

Interal width (feet)

...

Depth (feet)

...

Interal width (feet)

...

Depth (feet)

A to B

=

2.0

1.0

(at B)

A to B

=

2.5

1.1

(at B)

B to C

=

2.0

0.8

(at C)

B to C

=

2.5

1.0

(at C)

C to D

=

2.0

0.5

(at D)

C to D

=

2.5

0.4

(at D)

D to E

=

2.0 ----

0.0 ----

(shoreline)

D to E

=

2.5 ----

0.0 ----

(shoreline)

Totals

8.0

2.3

10.0

2.5

Average depth = 2.3/4 = 0.575 feet

Average depth = 2.5/4 = 0.625 feet

Cross-sectional area of Transect #1

Cross-sectional area of Transect #2

= Total width X Average depth = 8.0 ft X 0.575 = 4.60 ft2

= Total width X Average depth = 10.0 ft X 0.625 = 6.25 ft2

Average area = (Cross-sectional area of Transect #1 + Cross-sectional area of Transect #2)/2

= (4.60 ft2 + 6.25 ft2)/2 =5.42 ft2

Figure 5.6 A sample calculation of average cross-sectional area