Standards and Procedures:
Rock Water Bars
A rock water bar built on the Appalachian Trail in North Carolina. Note the low-profile of the rocks, which barely protrude above the tread surface, and the approximately 45 degree angle of the bar relative to the trail. The excavated drain is an essential part of the design - water should flow out the drain without actually contacting the rocks. The drainage outlet on this bar could benefit from being widened significantly.
Water bars have become a bit controversial within the trail building community. The USFS 2007 Trail Notebook notes: “Most waterbars are not installed at the correct angle, are too short, and don’t include a grade reversal. Poorly constructed and maintained waterbars become obstacles and disrupt the flow of the trail. The structure becomes a low hurdle for travelers, who walk around it, widening the trail.” The Notebook goes on to consider the fact that water bars clog easily, often cause problems for cyclists, and that horses can kick log water bars out of place. Finally, the Notebook suggests: “You can build a good rolling grade dip quicker than you can install a waterbar, and a rolling grade dip works better.”
So are water bars ever worth building? Yes, in some cases the topography of the trail will make the added reinforcement of a water bar useful. A modern water bar is ultimately just a reinforced drain, and in steeper or unstable spots, that reinforcement can help to stabilize a drain. Keep in mind though, that it is essential to build water bars properly. Otherwise, as the USFS notebook warns, they can cause more harm than good. In most cases a good drain will suffice without the added work of building a structure so don't do more work than you need to.
In the Pisgah Ranger District, the ability to build with rock is limited. We are constrained by NEPA rules, which limit the harvesting of rock to that which is already within the trail corridor. Harvesting rock outside the corridor requires additional NEPA surveys and approvals, a process which can take years and so must be reserved for major projects.
Due to the limitations in rock, it may be necessary to use black locust instead to construct a log water bar, which serves the same function as a rock water bar but is slightly different in form.
Key Points:
- Tools and Equipment
- General Specifications
- Construction Guidelines
Tools and Equipment
Below is a recommended list of essential tools for building a rock water bar.
Basics:
- Rock bars (at least 2)
- Pick mattock
- Shovel
- Double-jack sledge hammer
- Single-jack sledge hammer (several)
- McLeod - useful for finish work and tamping soil
- Prospectors pick/mini-pick/rapid-digger - for digging in tight spaces
- Cargo/rock net
- Drag slings
- Buckets or canvas rock bags for transporting gravel/crush
Optional:
- Carbide-tipped stone-shaping hammers and chisels
- Griphoist rigging setup for major rock projects
- Tennis ball for testing drainage
General Specifications
- Large, long, tablet shaped stones are preferable, although a variety of sizes can be used in combination.
- Rocks should be buried so the tops are flush with the original tread surface. Minimize the amount of rock protruding from the surface. The rocks merely reinforce a drain, and should not create an obstacle that trail users may avoid.
- Line rocks as tightly as possible, with good contact, to eliminate gaps between rocks. Rocks can also be shingled, but be sure to shingle them properly (see diagram below).
- Line the rocks at a 45 degree angle to the trail to facilitate water moving off the trail without losing speed. If water hits a sharp turn and slows down, it will deposit sediments and clog the drain more quickly.
- Extend the bar 12” into the backslope/bank. This prevents water and users from cutting around the side.
- Fill around with crushed rock as you install each stone. Pack tightly in place with hammers.
- Water bar rocks should not wobble at all when stepped on. They should be large and virtually all buried beneath the surface. They should not be in danger of being kicked out by a horse.
- Dig a wide (4ft or more), substantial drain (adhering to the principles in the Drainage section) just above the bar.
- The drain should ramp up to the bar. The low point of the drain should be several feet before the bar. Flowing water should never actually touch the structural bar.
Construction Guidelines
These procedures are intended to provide a helpful reference guide. If you have never built one of these structures before, please learn from an experienced trail builder.
A. Survey the Site
1. Determine whether a water bar is needed or if a regular drain would suffice.
2. Is there sufficient rock available?
3. Determine the layout before you start building. Line out your angle.
B. Quarry Rock
1. Use rock within the trail corridor. Do not dig off trail unless approved by NEPA survey.
2. Search for long, flat, rectangular rocks if possible.
3. Dig/transport to site with rock bars, nets, slings, and/or rigging
C. Set Rocks
1. Dig a trench for each rock to minimize empty space.
2. Set rock vertically, top flush with the tread surface.
3. Pack empty space with crush to stabilize.
4. Line/shingle rocks appropriately.
5. Extend bar into backslope.
D. Dig Drain
1. Start 2-3 feet uphill from the bar and dig a wide outlet.
2. Sculpt a ramp between the bar and the low point of the drain so that rocks are barely exposed.
3. Sculpt a gradual ramp extending uphill, creating a wide, subtle drain.
E. Finish Work
1. Tamp all soil thoroughly.
2. Revegetate work area, including visible craters from quarrying