Water Hydraulics - Wastewater Operators - page 60

figure 2.6 Laminar (streamline) flow.

Streamline Turbulent

figure 2.7 Turbulent flow.

(a) Now we can determine the discharge in cfs:

q = v × a = 10 ft/s × 0.785 ft 2 = 7.85 ft 3 /s (cfs)

(b) We know that 1 cfs is 449 gpm, so 7.85 cfs × 449 gpm/cfs = 3525 gpm
(rounded).

(c) 1 million gallons per day is 1.55 cfs, so:

7.85 cfs
1.55 cfs/MGD

= 5.06 MGD

Note: Flow may be laminar (i.e., streamline; see Figure 2.6) or turbu-
lent (see Figure 2.7). Laminar low occurs at extremely low velocities.
The water moves in straight parallel lines, called streamlines or lam-
inae , which slide upon each other as they travel, rather than mixing
up. Normal pipe flow is turbulent flow, which occurs because of friction
encountered on the inside of the pipe. The outside layers of flow are
thrown into the inner layers. The result is that all of the layers mix and
are moving in different directions and at different velocities; however,
the direction of flow is forward.

Note: Flow may be steady or unsteady. For our purposes, we consider
steady-state flow only; that is, most of the hydraulic calculations in this
manual assume steady-state flow.

2.6.1 area and velocity

The law of continuity states that the discharge at each point in
a pipe or channel is the same as the discharge at any other point (if
water does not leave or enter the pipe or channel). That is, under the