This seems to be an afterthought or not even considered on many systems I have seen. However, overlooking this is a big mistake. The water feature or components may need to be partially of fully drained (water changes or maintenance). You need to have a plan for removing waste water and runoff.
Drain Lines: These are water-filled plumbed connections from components or the pond that usually drain under pressure. Drain lines end where they pour into larger, air-filled “waste” lines powered by gravity.
Waste Lines: Most waste lines are gravity powered. This means as long as you have a slope in the line, the water will run on its own away from the pond to somewhere safe for disposal. You want a minimum slope of 1” per 4’ (or ¼” per foot). There are lots of choices for waste lines such as corrugated black plastic coils. Most come in 3” or 4” sizes and some are solid while others are perforated. Obviously, if you have soils that readily take in water, the perforated type will allow some water to be absorbed into the soil. However, if you are near your house foundation, crossing a septic field, or in soil that has high water content and doesn’t easily absorb additional water, use the solid type. They sell many accessories that fit these coils such as storm drain grills, connectors, reducers, tees and wyes, and outfall cage ends.
Existing Waste Systems: If you are lucky, there may be existing downspout lines, sewers or other waste or drain lines that you can hook into nearby (provided you are running down towards them). This would allow water that enters into your waste line to get shuttled onward to another system already in place. Just ensure you are not overloading these lines. If you are in doubt, create a standalone waste line.
French Drains and Outfalls: If you have an area away from your pond that water can be reabsorbed into the soil safely (not near a home’s foundation, a septic field, or into wet ground), creating a French drain or outfall may be a possible solution. A French drain is a pipe filled with holes. Some have filter material or large rocks around them so that the holes will not get plugged with soil. Water from your waste lines enters the French drain and slowly is absorbed into the soil. Depending on how much the soil can readily take will dictate how much French drain length you will need. If you are even luckier and have a downhill slope with nothing below, an outfall may be right. This will simply be the end of your waste line where it pours onto the surface. Create a depression and fill with large rocks to prevent erosion (catch basin). The water will flow out onto the surface and absorb into the soil moving away from your pond.
Plumbing Sewer Lines: If the water feature is below any existing waste or drain systems, you can always run your waste lines into its own sump pump cistern. When water from your pond is drained, the sump will turn on and raise the water to a higher elevation to where you need it to go. You will need a pump, electricity and housing for this. At this point you can dump it into a waste line higher up and follow the directions as described above, OR create sewer lines following the same rules as house plumbing for drain, waste and vent lines. However, especially in closed plumbing, always use the 1” per 4’ slope.
Runoff: If you are constructing a new water feature in the midst of where downspouts or roof water pours onto the ground, pool water is splashed nearby, or natural rain water passes through the yard during storms, you need to divert these away from the water feature. This water will wreak havoc on your pond’s water upsetting the balance, or even harming plants and animals in the pond. Design waste lines for all of these sources and integrate them into your pond’s waste lines sending the runoff elsewhere.
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