Do any irrigation experts here know about filters?

[slowmotion]

I have a friend who has a large pond somewhere in the middle of nowhere near Inverness. It might also be described as a very small lake. His problem is that it is fed by a very small trickle of water coming off the hillside, and that in the height of summer, the supply is inadequate. We batted some ideas around and came up with a possible solution. There is a burn 125 metres away which is 7 metres above the pond. You just lay a 28mm internal diameter black MDPE pipe on the ground and siphon off some water from the burn to feed the pond when it gets low. You can prime the siphon pipe with a few strokes of a marine bilge pump to get the siphon started. Total budget, about £200 tops.
According to this engineering calculator, the flow rate should be a quite useful 0.7 litres a second with a velocity of about 1 metre per second through the pipe.

http://www.calctool.org/CALC/eng/civil/hazen-williams_g

The problem is that the feed water is full of all kinds of debris that could clog the pipe so a filter on the inlet is essential. I have absolutely no idea how big the mesh should be. It isn't the end of the world if the filter needs cleaning fairly often because the siphon pipe is not supposed to run all the time. What would be a PITA is the pipe getting blocked a long way from the inlet.
Can anybody suggest the mesh size for a filter? My wild guess is about 1-2 mm but I wouldn't want to go for a really fine mesh as that might reduce the flow rate too much. I would imagine that a metre per second of velocity would be partly self-cleaning.
Thank-you

 

[classic33]

http://www.irrigationtutorials.com/filters.htm

I've used a mesh filter designed for a tractor mounted spraying unit for a similar purpose. Something along these lines,

What about a plain nylon curtain? You could use a two stage filter.

 

[Milkfloat]

Does he actually have rights to the water in the burn?

 

[srw]

Does he actually have rights to the water in the burn?

Do people with small lakes care about such niceties?

I look forward to the gift of smoked trout that will no doubt result...

 

[welsh dragon]

You're still going to have the same problem with filters as without. Instead of the pipe clogging up, the filter will. Whatever you use, you will have to unblock it on a regular basis. But saying that, it isn't that much trouble to do so.obviously the smaller the filter, the quicker debris will build up. Its sods law im afraid.

 

[PeteXXX]

What about the water running through a settling tank just before it enters the pond/lake?
If necessary, a UV light could be incorporated to kill off and nasties.

 

[Levo-Lon]

If you can mount the filter so its mid stream and not so likely to suck up silt then a filter like classic sugested should be ok.
the tank idea will be handy..
Are you keeping the pipe above ground?

 

[slowmotion]

Does he actually have rights to the water in the burn?

I have no idea. North Scotland isn't exactly short of water, I have heard.

Do people with small lakes care about such niceties?

I look forward to the gift of smoked trout that will no doubt result...

Spookily enough, there are a certain number of trout in his lake and he does have a smoker.

If you can mount the filter so its mid stream and not so likely to suck up silt then a filter like classic sugested should be ok.
the tank idea will be handy..
Are you keeping the pipe above ground?

Above ground. Burying 125 metres of pipe is a bit of a pain. I'm not sure how well black MDPE stands up to frost just yet.

 

[classic33]

How about filtering in stages, with a fine gauze coming after something a bit less fine etc. culminating in the whole thing being in a mesh basket?

Similar to two stage filtering?

As for the pipe, large bore on a short run. It'd take something major to block it, left with no filter. Frost shouldn't be a problem, but icing up inside may be.

 

[Levo-Lon]

Winter wont be a problem as the water level will be more stable..no frost in summer.
id hire a small mini digger with a pipe ,cable trenching bucket..you would dig a foot deep trence in a few hrs.
the pipe is like an angry python when your fighting with it above ground.

a trench alows you to roll it in and back fill as yo go..so much easier.
you can sink a filter tank and simply put a lid on it ,metal inspection cover.
only my 2p from lots of water pipe laying..

 

[Tim Hall]

(re rights to the burn)

I have no idea. North Scotland isn't exactly short of water, I have heard.

So that makes it alright does it? SEPA are the people to ask if it's OK to do this.

 

[User482]

(re rights to the burn)


So that makes it alright does it? SEPA are the people to ask if it's OK to do this.

SEPA operate (as far as I know) on a similar basis to the English EA - low risk abstractions would not generally require a licence provided they can demonstrate compliance with general binding rules. However, @slowmotion your calculation suggests c. 60m^3/day: the flow rate would be over the threshold (assuming it's the same as the EA) and a licence would be required.

 

[slowmotion]

SEPA operate (as far as I know) on a similar basis to the English EA - low risk abstractions would not generally require a licence provided they can demonstrate compliance with general binding rules. However, @slowmotion your calculation suggests c. 60m^3/day: the flow rate would be over the threshold (assuming it's the same as the EA) and a licence would be required.

The siphon is only going to be operated infrequently to top up the pond. Nowhere near 60 cubic metres per day could go into it without it overflowing catastrophically.

 

[User482]

The siphon is only going to be operated infrequently to top up the pond. Nowhere near 60 cubic metres per day could go into it without it overflowing catastrophically.

You're welcome.

 

[slowmotion]

Winter wont be a problem as the water level will be more stable..no frost in summer.
id hire a small mini digger with a pipe ,cable trenching bucket..you would dig a foot deep trence in a few hrs.
the pipe is like an angry python when your fighting with it above ground.

a trench alows you to roll it in and back fill as yo go..so much easier.
you can sink a filter tank and simply put a lid on it ,metal inspection cover.
only my 2p from lots of water pipe laying..

Very good point about the pipe having "memory". Thank you.