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I would like to build a really small (~1.5 x 1.5 m2) alpine garden with a water stream in my garden. There is already a plastic pond there, 0.35 m deep and 0.6 m in diameter, from the previous owners, which I am actually going to cover. I have a baby daughter and don't want her to fall into water one day. I need to select the correct pump for the project.

I've read that ideally I should pump the complete volume of water each hour. The pond volume is just below 100 l, and I was unable to find an outdoor pump with the flow rating below roughly 400 l/h. So I am wondering:

  1. Can a pump be actually too powerful for a given task (not in the sense of wasting money, but in terms of creating a ridiculously powerful flow, spitting water all around the place etc?

  2. Can I somehow regulate the actual flow once the pump is in the pond, to make the stream look natural?

  3. The pump I have found is rated for the maximum height of 0.7 m. Can I rely on this value if I want the alpine garden to be 0.6 m high (from the water level), or do I need some safety factor and thus an even more powerful pump?

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Teach your baby daughter to swim as soon as possible - there's plenty of water to fall into that is not in your garden.

A pump rated for 0.7m head should be fine with a 0.6m lift.

If you cannot find a pump with lower minimum flow (though, to be honest, you may find the "waterfall" aspect of 100 l/hr or 1.6 l/minute a bit more like a dull trickle) you can place a pipe from the pump output to the pump input, with a valve that you can adjust so that the actual water pumped out is, say, 100l/hr while the pump is pumping 400l/hr, but 300 of that is recirculating in the pipe.

I suspect the pump rate advisory is intended for a minimum flow rate of ponds with fish, etc. in them - that does not sound like your actual situation, so 400 l/hr (or more) may be a perfectly acceptable flow rate for your application.

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