Rolling grade dips can be more resilient than waterbars. Unskilled riders can skid and create ruts on the back side of the waterbars because they use too much rear brake on steep downhills. Other riders swerve around the structure, widening the trail. Although education is a good idea, the almost imperceptible rolling grade dip prevents these problems from happening in the first place. Here's how IMBA's Trail Care Crew "rolls their own" rolling grade dip.
• Start with a properly cut sidehill trail (one that hugs the side of the hill), with the outslope (outside) edge of the trail lower than the backslope edge by about 3 degrees. "The goal is to always keep water sheeting off the trail rather than running down it," explains the Crew. If you have a trail going straight up the fall-line, this technique won't work.
• Locate your dips, starting with one at the top of the trail. If possible, visit when it's been raining so you can put the dips immediately below water entry points. Avoid rocky and rooty sections where possible.
• Mark the center of each structure with two stakes at either edge of the trail. The line between the stakes should be not quite perpendicular to the trail, at about 60 degrees. When you're laying out the structure, imagine the dip having a cross-section of a soup spoon. The dip is like the bowl of the spoon, with a small berm rising up below it like a curved spoon handle.
• Use a Hazelhoe or Macleod and begin digging the dip into the trail surface about 5-6 feet above the stakes, and work your way down. The deepest point at the outslope edge need only be about 3-4 inches deep. Near the backslope edge, the dip should become short and shallow so that it blends in with the hill.
• Use the excavated dirt to build a 6-9 inch high berm across the trail below the stakes. Build a ramp from the top of berm to the trail surface 8 feet down the trail. (Note: These specifications are appropriate for a 12% grade trail, meaning 12 feet of elevation gain for every 100 feet traveled. For steeper trails, make the structures slightly deeper and much longer.)
• Smooth out the dip with a Macleod or rake so that it's barely noticeable. Compact the surface with the end of the Macleod or the back of a shovel. Remove your stakes, and you're ready to rock n roll.