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Trail Construction and Maintenance Notebook
The waterbar is the second most common drainage structure, after outsloping. Water moving down the trail is turned by contact with the waterbar and, in theory, is directed off the lower edge of the trail. Waterbars are usually the most dysfunctional tread structures in all of the trail world. Yet trail crews annually install or reinstall them by the thousands.
We encourage the use of reinforced grade dips instead of waterbars at most locations where waterbars have been traditionally used. Here’s why— By design, water hits the waterbar and is turned. The water slows down and sediment drops in the drain. The number one cause of waterbar failure is sediment filling the drain until the water tops the bar and continues down the tread. The bar becomes useless. You can build a good grade dip quicker than a waterbar, and it works better. |
On grades less than 5 percent, waterbars are less susceptible to clogging (unless they serve a long reach of tread or are in very erodible tread material). On steeper grades (15 to 20 percent), waterbars are very prone to clogging if the bar is at less than a 45° angle to the trail. Waterbars are mostly useless at grades steeper than 20 percent. At these grades a very fine line exists between clogging the drain and eroding it (and the bar) away.
Most waterbars are dysfunctional because they are not installed at the right angle and are too short. The waterbar needs to be anchored 300 mm (12 in) into the cutslope and still extend 300 mm (12 in) into the fillslope. If your tread is 600 mm (24 in) wide, the bar must be 1.7 m (5 ft 6 in) long to be correctly installed at a 45° angle. A bar fitted at an angle of 60° must be 2.4 m (7 ft, 7 in) long. Wider tread requires a longer bar. When the bar is cut too short, the usual response is to install it at a lesser angle. Then it clogs.
Poorly constructed and maintained waterbars also become obstacles. Most waterbars are installed with one-third to one-half of the bar material above the existing tread surface. Some crews even install bars with exposed faces taller than 150 to 200 mm (6 to 8 in). On grades steeper than 7 percent (particularly in erodible soils), the soil placed on the tread below the waterbar is rapidly lost to traffic and water erosion. The structure becomes a “low hurdle” for travelers.
Wimpy little wooden bars less than 150 mm (6 in) in diameter wear or clog quickly into uselessness. Often they rot away in just a few years. Another problem with wooden waterbars is that horses kick them out.
Cyclists of all sorts hate wooden waterbars because of the hazard they present to wheeled traffic. The exposed angled surface can be very slippery, leading to crashes when the wheel slides sideways down the face of the bar. The rider continues down the trail without the cycle. As the grade increases, the angle of the bar (and often the face height) is increased to prevent sedimentation. This raises the crash-and-burn factor.
Are waterbars ever useful? Sure. Wood or rock waterbars are useful on foot and stock trails where a tripping hazard is acceptable, especially at grades less than 5 percent. Also consider reinforced waterbars where you don’t have much soil to work with and in areas that experience occasional torrential downpours (Figure 20).
![[diagram] Blocked waterbar with riprap tray](images/fig020.jpg)
Figure 20—Reinforced or armored waterbars.
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