Water Level Drops when Waterfall Pump is Running. Where is Leak?
Q. I am sure our waterfall is leaking water somewhere, but I cant be sure where. The water level in the bottom pool only drops when the waterfall is running. How can I find where the leak is?
A. You dont say whether you have constructed the waterfall or it is a preformed unit. Either way it is matter of turning on the pump and looking carefully at the flow of water for some time as it builds up. This is a good time of year to troubleshoot a problem like this since running up to Christmas there are often prolonged dry spells and a lot of the vegetation has died back.
With both preformed units and waterfalls constructed with flexible liners, check the top edge at the back. Over time the weight of the unit plus the associated rocks causes the whole scene to sink at the back. I recently went to examine a waterfall and stream I had helped construct nearly 15years before, and that had sunk by just two inches at the back, just enough for water to begin find its way out, but only when the system was in full flood. This sinkage had only begun to occur when a tree from behind the waterfall had been removed two or three years earlier.
With preformed units in particular, if the pump is a little bit too powerful for the unit, water can overflow particularly at the base of falls. On the other hand, if the flow is somewhat lazy at the final drop, it can finds it way back along the lip of the unit back to the rock edge.
Concrete waterfalls and streams and flexible liner creations, if they are constructed properly the level areas should hold water at the point of overflowing to the next level. If they dont, suspect the fault to be at that level. But first things first, l check the flow.
Check the inlet hose is not leaking backwards. Also check that when it is switched off, it is not siphoning the water in the header pool back down to the pool at the bottom through the pump.
With the waterfall running, watch for stray rivulets, seepages sideways and
upwards in particular at the point where the stream liner meets the pool liner.
If there is underlay protecting the liner down through the stream or waterfall,
it will act as a siphon for all the water in the feature back down into the
pool. Also if the underlay comes over the liner and out over the sides of the
feature, it will siphon water out into the rockery. Remove edging stones and
sill stones so that you can cut or trim the underlay to prevent this.
The pressure downwards from waterfalls can cause water to flow sideways or even upwards between stone and liner. Placing little drainage tubes or holes underneath the bottom stones of a fall as it is being constructed can relieve this pressure; too late now perhaps but something to bear in mind if you decide on a complete reconstruction.
One problem that has plagued me in waterfalls constructed with flexible liner in rural areas is mice or moles, which decide that rubber or PVC might make a useful addition to the current years nesting material. Mix a heaped shovel full of cement powder or lime ashes to every six or eight of sand that goes in to cushion the liner. That will cause it harden up and go-off putting a stop to those little ambitions.