| Gary, it sounds to me like you have misunderstood gravity fed systems entirely. The hole you dig for the filters does not have to be deeper than the pond hole. In fact most filter pits are not deeper than the ponds that feed them.
The term gravity fed has to do with the water level in the pond versus the water level in the setllement chambers and filter chambers. If these are well designed there will generally be only a small (on the scale of 1") water level drop between the ponds and each subsequent filter chamber. IN a 6' deep pond there 6' of water stacked up on top of the bottom drain trying to push water out. if the settlement chamber is sitting next to the pond but only 3' deep then when the pond and chamber are connected the water will still push up and into the settlement chamber until the water levels were equalized.
Just based on my experience, if i could not or was not willing to build in at least a settlement chamber then I would not build the pond. You can easily put the pump right after the sttlement chamber and pump the water up into your above ground bio filters (I think Joe of Joeandgabby has some good pictures of the above ground bio barrels).
The problem with taking the shortcut and not doing a gravity fed settlement chamber is that you will need a much more expensive pump and it will wear out two to three times as fast from constantly sucking in and grinding up all sorts of crud. Plus you downstream filter system will have to be moch larger and more expensive in order to contain enough surface area to filter out all the crud that has been milkshaked up into a fine puree.
The settlement chamber being gravity fed from the bottom drain is the primary key to success in the filter design. Remember that this means the surface water level in the settlement chamber is about 1" lower than the pond surface water level when it is running properly. The water at the surface thinks it is flowing downhill even though the bottom of the sediment chamber is often 2 to 3' higher in elevation than the bottom drain. |