Water Control Structures

The greatest risk to water quality from forestry operations is erosion from forest roads entering a waterbody. Over 90% of the sediment deposited in streams and lakes from forestry activities comes from forest roads. Therefore, the easiest and usually least expensive way to reduce sedimentation on a forestry operation is to limit the size and number of roads needed to complete the job safely and efficiently.

Constructing water control structures when necessary is the next best way to ensure that erosion from the road system and resulting sedimentation into streams and lakes will be minimized. There are several types of water control structures. Each type has advantages and disadvantages. Your experience, as well as your knowledge of the tract will help you determine which structures may work best for a given situation.

Some of the site characteristics that may affect your decision of which types of structures to use may include but are not limited to the following:

• soil type,
• topography,
• drainage patterns, and
• presence of any streams.

Understanding soil type is very important in deciding which structure to install. For example, installing and maintaining waterbars on sandy soils can be very difficult.  Some soil types (such as gumbo) may not even be able to support your equipment without significant damage to the soil.  Carefully considering drainage patterns will help identify where water control structures will be needed to allow water to flow naturally across the tract which can go a long way in saving time and money when it comes to installing and maintaining water control structures.

Water Bars

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.

Broad-based Dips

If the intended traffic will be heavier trucks a rolling dip or broad-based dip may be a better alternative. Both structures act as a stretched out waterbar. The main difference between the two is in the topography in which they are used.

Broad-based dips are better for gradients of up to 12%.

Rolling Dips

Rolling dips should be installed on road grades of up to 15%.

Consult the 2014 Texas Forestry BMP Handbook for further information on constructing either type of structure.

One main disadvantage to these types of structures is that they are more costly and time consuming to build. If the soil type and topography warrant, you may need to use rock to protect the outfall area or to prevent rutting the road surface.

Neither water control structure should be used for cross draining springs, seeps, or intermittent or perennial stream. They are intended only to drain road surface runoff.

Cross-Drain Culverts

Culverts can be a very effective way to get water from one drainage ditch to the other side of the road when needed. Corrugated metal or plastic pipe, wooden open box top culverts or other suitable materials may be used. Culverts can be used in any size operation where cross drainage of water is needed.

Unlike rolling dips and broad-based dips, culverts can be used to safely transmit water from seeps, springs, and intermittent and perennial streams under haul roads and skid trails. They usually last a fairly long time if they are properly maintained and inspected for obstructions.

Although culverts are very good for most operations, they do have some disadvantages. Culverts can be expensive and labor intensive to install. They are also better suited for use on permanent rather than temporary roads.

Other Water Control Devices

In addition to the types of water control structures and methods listed previously, there are several other acceptable and sometimes less costly alternatives.  The use of slash or brush from the site to stabilize a temporary road is often very effective and also inexpensive. Slash should be well incorporated into the ground to prevent washing from beneath. Other methods may include but are not limited to: spreading hay or seeding a road to establish vegetation if natural revegetation may take too long.