Guidelines for Establishment and Operation of Cattle Feedlots in ...

9 metres per second or less.
In areas where sufficient clay is not available or the clay is not suitable, it will be necessary
to use a synthetic liner. The synthetic liner must be equipped with a leak detection system.
The volume required to achieve the required velocity and settling is determined by using the
relationship
Equation 3:- V = Qp x (l/w) x (λ/0.005)
Where V = the volume of the sedimentation system
Qp = peak inflow rate for the design storm in the Controlled Drainage Area
l/w = length to width ratio, where l is in the direction of flow. Typical values are shown in
table 11.
λ = scaling factor which takes account of sediment accumulation and frequency of
removal. Values are shown in table 11.
0.005 is the maximum flow velocity in metres / second.
It is recommended that the Rational Method as described in "Australian Rainfall and Runoff 1987"
should be used in determining Qp for the above relationship.
The sedimentation area should then be cleaned out and the solids directly spread onto agricultural
land or temporarily stored in the manure stockpile area. The sedimentation area cleaning schedule
for different classes of feedlots is outlined in Appendix 3.
10.4 Sedimentation Control Weir
The function of the sedimentation control weir is to slow the flow of the effluent in the
sedimentation system to the critical velocity to allow entrained solids to settle, and also enable the
liquid to drain from the sediments deposited on the upstream side. During the process the weir
regulates the depth of the ponding within the sedimentation system and the rate of discharge into
the storage lagoon.
Sedimentation weirs should be designed to safely discharge design storm events up to the 50
year ARI design storm without overtopping the earthen bank. A minimum freeboard of 900 mm
should be provided between the top of the weir and the top of the embankment.
Suitable types of weirs are
the horizontal drop board type - consisting of one, and occasionally two rows of removable
drop boards installed within a concrete channel through the bank of the sedimentation
system. The boards are wedged apart to facilitate drainage, and the gaps can be
progressively widened to hasten drainage from the sediments. The boards can be
completely removed to assist cleaning.
the vertical timber type - consisting of timber boards mounted vertically within a concrete
channel through the bank of the sedimentation system. The gaps between the boards can
not be adjusted, and generally the structure can not be removed to allow access for
cleaning.
the adjustable vertical slot throttle weir - consisting of two steel plates installed across the
sedimentation terrace on the upstream side of a short concrete masonry wall. The gap can
be adjusted to facilitate drainage, and the plates can be completely removed to allow
access for cleaning.
Guidelines for Establishment and Operation of Cattle Feedlots in South Australia, 2 nd Edition 41