Hydraulic Capacity of Control Devices for Water Table Management Systems

Abstract

In the design of water table management systems, the hydraulic capacity of the drain tubes and the outlet are usually assumed to be adequate to carry drainage and runoff from the fields and, thus, outlet limitations are not addressed. Unfortunately, some of the devices developed for closed control systems may sacrifice a portion of the outflow pipe area in the control mechanism and restrict the outflow rate. Three commercial outflow control devices were evaluated for outflow rate and were compared to a hypothetical flashboard riser system. Each of the devices restricts the flow by about 70% as compared to the flashboard riser when the head is about 0.15 m (0.5 ft). However, at an area of about 0.45 ha (1.11 ac), the flow capacity of the 15 cm (6 in.) tubing will begin to limit the mainline outflow rates for the site and system conditions in the analysis. With proper design, currently-available, commercial flow-control devices will be of sufficient capacity and will not be a limiting factor in determining drainage system performance.