Flow Section Channels - Geometric Relationships
Geometric relationships like area, wetted perimeter and hydraulic diameter.
Area, wetted perimeter and hydraulic diameter for geometric sections like
- rectangular channels
- trapezoidal channels
- triangular channels
- circular channels
Rectangular Channel
Flow Area
Flow area of a rectangular channel:
A = b h (1)
where
A = flow area (m2, in2)
b = width of channel (m, in)
h = height of flow (m, in)
Wetted Perimeter
Wetted perimeter of a rectangular channel:
P = b + 2 h (1b)
where
P = wetted perimeter (m, in)
Hydraulic Radius
Hydraulic radius of a rectangular channel:
Rh = b h / (b + 2 h) (1c)
where
Rh = hydraulic radius (m, in)
Trapezoidal Channel
Flow Area
Flow area of a trapezoidal channel:
A = h (b + T) / 2 (2)
Wetted Perimeter
Wetted perimeter of a trapezoidal channel:
P = b + 2 (((T - b) / 2)2+ h2)1/2 (2b)
Hydraulic Radius
Hydraulic radius of a trapezoidal channel:
Rh = (h (b + T) / 2) / (b + 2 (((T - b) / 2)2+ h2)1/2) (2c)
Triangular Channel
Flow Area
Flow area of a triangular channel:
A = z h2 (3)
where
z = see figure above (m, in)
Wetted Perimeter
Wetted perimeter of a triangular channel:
P = 2 h (1 + z2)1/2 (3b)
Hydraulic Radius
Hydraulic radius of a triangular channel:
Rh = z h / 2 (1 + z2)1/2 (3c)
Circular Channel
Flow Area
Flow area of a circular channel:
A = D2 / 4 (α - sin(2 α) / 2) (4)
where
D = diameter of channel
α = cos-1 (1 - h / r)
Wetted Perimeter
Wetted perimeter of a circular channel:
P = α D (4b)
Hydraulic Radius
Hydraulic radius of a circular channel:
Rh = (D / 4) (1 - sin(2 α) / (2 α)) (4c)
