Devices installed in swales, storm flow zones of channels, and ditches that are designed to slow the velocity of concentrated flows, and filter sediment. Size of channel, steepness of grade and volume of storm water runoff are all factors that go into choosing the correct device and how many are needed. It is important that the lowest point of the check is in the middle of channel so that during heavy rain events water flows over the top of device and not around, which will result in erosion and undermining the device.