Design of a subsurface drainage research facility with LANDRAIN and SEDCAD 4

The design of a subsurface drainage research facility at the University of Minnesota Southern Research and Outreach Center, in Waseca, Minnesota, is described herein. Two computer-aided-design (CAD) software applications used in this design are highlighted: LANDRAIN 5.0 for topographic modeling, and subsurface drainage system layout and design; and SEDCAD 4, for designing an outlet structure for a natural wetland that will receive new surface and subsurface inflow. The facility comprised nine individual drainage systems of 0.8 to 2.4 ha (2 to 6 ac) in size, plus six individual controlled drainage systems, each 0.2 ha (0.5 ac) in size. Drainage depth and spacing are research variables for this facility. The software enabled a drainage depth design tolerance of ± 7.5 cm (3 in.) to be used for all drainage systems and helped define field locations where this design tolerance was exceeded. An outlet structure was designed for the receiving wetland by modeling it as a pond with constraints on maximum elevation (because of topography) and minimum elevation (because of wetland regulations), between which outflow will occur. A custom spillway riser was designed using SEDCAD 4, for slow early flow and passive dewatering of the wetland to the minimum drainable pool level. Design dimensions and elevations for the outlet structure, and the predicted performance of the wetland for the 25-, 50-, and 100-year, 24-h storms, are presented.