Your Dam Your Responsibility (PDF~1.2MB)

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7
7 Operation and Maintenance of Dams
Uneven spillway cut
(b) Outlet Pipe Blockage
The cleaning of an outlet pipe is a problem
if the gate valve has been closed over the
winter because trash, fish and silt can
clog the inlet on the upstream side of the
embankment. This type of blockage could
place a dam owner in conflict with the
public regulatory authorities, as a condition
PHOTO COURTESY OF SOUTHERN RURAL WATER
of approval of a dam on a waterway
requires the gate valve to be operated so as not to diminish flows during the drier
months, usually November to April. It is recommended that regular flushing be carried
out by opening the valve, to minimise the risk of blockages.
In the event of a blockage, there are different techniques and types of equipment
available to dislodge an obstruction (ie. cleaning rods, flexible sewer pipe cleaner). Most
can only be employed when the storage is empty or close to it. Persons should not be
in the water if flow is passing through the outlet. Seek professional advice.
7.5.9 Outlets and Valves
All valves used for releasing water from
a dam must be properly maintained. It is
important to remember that if you have a
developing problem with your dam you may
need to empty it as quickly as possible. It is
therefore important to service/exercise the
valve regularly to make sure it is operational
at all times. If it starts to get difficult to
operate, you have a developing problem
that requires attention. It is possible to
exercise the valve without losing stored
What are the chances that this valve will work in
an emergency?
PHOTO COURTESY OF SOUTHERN RURAL WATER
water when the spillway is flowing, as the water is being passed downstream anyway. Do
not wait indefinitely for the spillway to flow first before exercising the valve!
Provision should be made at the outlet pipe point of discharge to reduce the velocity of
exiting water. For example, an effective concrete outlet structure or a layer of crushed
rock topped with a layer of large rocks can be used to minimise erosion. The type of
protection will be dependent on the size and the pressure head of the water.
Another problem at an outlet valve is the potential for failure if not in regular use.
Remember that if you have an emergency problem with your dam and need to empty it
quickly to save it from total failure you will need this valve to work.
It is recommended that this valve be operated at least four times a year to make sure it is
operating properly.
Note: The location of water reticulation pipes or other structures within the
embankment should be scrupulously avoided, as leakage from the pipes, or around
the pipes, can cause problems, or even failure of the dam (see also Section 5.5).