We have had great success using Flo-wells. The use or amount of gravel will be determined by the infiltration rate of the soil. If the soil allows water in very quickly, like sandy soil, you may not need any or much clean stone, if it is slow draining like clay, a larger gravel area will be necessary to hold the water from the downspout. NDS also has a simple slide rule type drainage calculator available that will help you determine what products you need and how to set them up. They also have a great support staff that can assist you. Check with your dealer, but they should have the filter fabric made especially for the Flo-well, but you may want to add an additional piece on the bottom. When we use them, we always add a top drain to the Flo-well which can be used as an inspection port along with a surface drain. If the gutters don't have some sort of leaf guard or gutter helmet, it is recommended you use a basin drain box at the entry port of the downspout to eliminate and foreign matter, like leaves or sticks from entering the drain pipe and creating a clog at the first 90 degree elbow. This is a step that is often overlooked due to cost or not knowing any better, but can eliminate the failure of your drain system.
Kirk
