Pond construction - bottom drains

A Guide to Modern Koi Pond Construction Bottom drains
It is generally accepted that bottom drains are a must and should be fitted to all ponds under construction, those being modified, or alterations such as fitting a new liner. There are a few cases where it is not possible to connect into the main drains but even in those cases the problem can probably be overcome by use of a soakaway if you do not have nearby neighbours.. If the main drain is above the height of the pond then it is possible to have a discharge chamber, and then you can pump it to the drain, using a pump with a float level fitted. This will be discussed later. If your dealer says don't fit bottom drains because they will be blocked up by blanket weed , etc, then do ask around amongst other koi keepers because this is one of the few topics where everyone seems to agree. There are a large number of bottom drains on the market at various prices, and it is up to the individual to look at as many as possible at the dealers and then make a decision.
	This photo shows a typical PVC bottom drain. This one is for use with a liner. The holes for the screws can be clearly seen, and the seperate flange can be seen on the floor. In general they have a deep large sump usually 10 to 12 inches diameter and about 6 inches deep. These usually have a 4 inch socket to take pressure pipe and this is then taken directly to the drain box where a 4 inch stand pipe with `O' ring is fitted. There are also some available that can be used with ordinary 110mm soil waste pipes. It is also possible to purchase bottom drains made of fibreglass, and they are about the same price but these are not very popular now.
	When the pond is completed then you can fit the mushroom cover as shown fig. 2. This is the type now supplied by many dealers. The gap between this cover and the top flange is set at about ½ inch and so gives a good purging effect when the stand pipe is pulled. It is advisable to fit the dome when there is say one foot of water in the pond to ensure that no air is trapped underneath, otherwise the dome may be forced up when the pond is full and very difficilt to replace. Many koi-keepers drill two 7mm holes in the top of the cover so that air cannot be trapped underneath.
TIP. The spindle on the dome or air diffuser is a push fit into the spigot in the bottom drain and should not be glued.
Installing bottom drains. The number of bottom drains required will depend on the size and shape of the pond, and also the preferences of the owner. With a rectangular pond say 12ft x 10ft then two bottom drains would normally be used, and with a pond say 18ft x 12ft then three bottom drains are usually used. The diagram below, fig 1, gives a view of a typical layout.

Each drain should have its own pipe direct to the Vortex or filter system. This pipework should be as straight as possible with only one bend at right angles up to the stand pipe so that a maximum flow rate is obtained without too much friction in the pipe..

It is suggested that instead of a 4" elbow a 4" long radius bend should be used, but this is a lot more expensive and more difficult to buy but many koi keepers consider it essential. If you are using terrain pipe then the elbows are not as tight as those supplied for pressure pipe, and in this case it is acceptable to use elbows. In the case of connection to a Vortex then it will be necessary to use more than one elbow to connect up with the inlet, but it is still necessary to make the flow as smooth as possible.
	This photograph shows most of the ideas we have mentioned above. The pipes are all pressure pipe, and bends have been used instead of elbows. The pipes are direct, and only have one bend between the bottom drain and the drains box. The open bend at the bottom drain box will be taken to the main drains.
This pipework will be buried in concrete in the base of the pond so make sure you get the design right the first time. TIP. The vertical pipework outside the base of the pond should be covered with stone dust or sand and not concrete so that it can be removed later if you need to alter the pipework. Many builders tend to use concrete so do not let them do this.
	The latest idea is to fit air diffusers to the top of the bottom drain, and this is now the most popular way and recommended by most koi-keepers.
It is a good idea to get all the pipework for the bottom drains laid out in position and then cut to shape, so let us next look at Pipework for bottom drains.
Check Questions & Answers for more information on bottom drains and pipework.

N.Design Studio