Water bars are very effective structures when installed properly. They should be built 1-2 feet high, and at a 30 to 45 degree angle to the road, firebreak, or trail. The uphill end of the water bar should be tied into the bank to fully intercept any road surface runoff. They are usually most effective when used in conjunction with cross drains and/or wing ditches to allow for the water to be safely dispersed onto the undisturbed forest floor.
Water bars are much easier to construct in clay soils than sandy soils. They are also usually intended for roads which will have limited traffic (i.e. temporary or secondary roads), as they are inefficient for travel and can be very easily knocked down or breached with heavier traffic loads.