are given below:

day's dredging supernatant in a reasonable

amount of time, six to eight hours, without veloci-

ties that would resuspend the poorly consolidated

water above weir in meters)

settled solids or damage the filtering fabric located

2 m behind the weir.

in meters)

g = 9.81 (gravitational constant, m/s2)

The following analysis of the drainage of the

Spoils Retention Basin, sited on the EOD at Eagle

m3/hour [Hicks 1972]).

River Flats, Alaska, uses the Francis Formula for

(3)

fluid flow over a rectangular, sharp-edged weir.

In a normal eight-hour dredge cycle, approxi-

Figure 5 is a graph of the instantaneous flow rate

mately 2400 m3 of water will be pumped into the

over a 3.2-m (10 ft) weir. The volume retained in

retention basin, assuming a 380-m3/hour produc-

the 0.8-ha retention basin above the weir can be

tion rate and a 4:1 ratio of water to spoils (by vol-

expressed as

ume).

The initial analysis is of flow rates over a 3.2-m

(4)

weir for a given head. The height of the weir is

given as about 15 cm. Although the weir height

One of the primary concerns in the retention

affects the flow rate, it will not be considered here,

pond design is the flow over the weir, which will

as the effect is minimal for low heads (< 0.3 m).

be impacting the silt fence located between the

We will be operating with heads of 0.1 m or less.

weir and the basin outflow culvert. To get a

The reason for this is to minimize the turbulence

handle on this, we can analyze the effect of differ-

in the sheet flow towards the weir. Boundary con-

ing weir length for a given head on the flow rate,

ditions and the instantaneous flow rate equation

in cubic yards per hour. This is an extension of

50

40

30

Q(H)

(m 3/hr)

20

10

0

0.02

0.04

0.06

0.08

0.10

H, Head (m)

9