Put unneeded roads to bed

Roads have been implicated repeatedly in causing erosion and sediment delivery to watercourses. In order to protect water quality, all roads should be continually inspected and maintained. This takes time and money. When a road is no longer needed, you can save this time and expense by closing it.

Goals of road retirement

Closing a road is more than simply blocking it off from traffic. It must be left in a condition that requires little or no maintenance. Most problem areas arise from:

• stream diversions (the leading cause of serious gullying in many areas)
• stream crossing washouts and fill failures
• gullies and landslides fed by road runoff
• surface erosion from road surfaces and fillslopes

These problems can be avoided with the use of techniques that can minimize long-term damage to natural resources. Since the purpose is to avoid erosion and sediment delivery to streams, only those parts of the road with potential problems need to be treated.

An added benefit of proper closure is that fewer costly repairs will be needed if the road is later reopened.

Stream crossing excavations

Stream crossings need to be completely removed for closure. This involves excavating and removing all materials that were used to make the crossing as well as reshaping the stream channel to its original contour.

Fill material should be excavated to recreate the original channel grade (slope and orientation) with a channel bed as wide or wider than the original watercourse (see illustration). The sideslopes should be graded back to a stable angle and bare soils mulched, seeded and/or armored to minimize erosion until vegetation can take over.

Culverts and log crossings also need to be completely removed. It is not enough to simply excavate and remove a culvert; the entire fill must also be removed with no soil left in or next to the channel. The excavation should extend down to the level of the original channel bed, with a channel as wide or wider than the original.

Unstable areas

Any potentially unstable road material should be excavated and treated during road closure. These sites most often occur around landings, on roads built on steep slopes, where roads have been built over springs or seeps, or where they have been cut into steep headwater swales or dips in the hillside. All excavated material should be put in a stable location and revegetated.

No active ditches should be left at the base of an unstable cutbank since they are likely to eventually become plugged and cause water to be diverted onto the road surface.

Road surface runoff and other drainage structures

Retired roads should have adequate, self-maintaining surface drainage so that the road surface will not erode to a stream. Any ditched segments should be outsloped or drained with cross road ditches. Inside road ditches should be eliminated so that water is not diverted to form gullies. Outside road berms should be removed to encourage continuous drainage.

Cross-road drains should occur frequently enough to prevent erosion. Cross drains that carry spring flow may require armoring at their outlet and should be discharged into vegetation to filter water and sediment before runoff reaches a stream.

Planting roadbeds

Unused roads can be ripped and planted to reduce runoff and erosion. A benefit of this is the increase in forested land. The road surface should be ripped to a depth of 15–24 inches, outsloped at least 4% more than the road grade, waterbarred, seeded and planted. Tree growth on compacted or rocked road surfaces is generally much slower than adjacent areas unless the roadbed is mechanically ripped.

Erosion Control

Most erosion control is accomplished by:

• physically excavating stream crossings, unstable fills and landing sidecast
• installing cross-road drains
• road ripping
• local road outsloping

These techniques are usually performed by heavy equipment while mulching, installation of energy dissipators (e.g., rocks and woody debris), seeding and planting is done by hand.

The banks of all excavated stream crossings, as well as all bare soil areas adjacent to a watercourse, should be mulched with straw at 3,000 to 5,000 lbs/acre. On slopes over 45%, or where high winds are common, mulches need to be tacked, punched or secured to the ground. Mulches can also be purchased in rolls that can be secured to the ground.

Rock and/or woody debris can be placed at the outlets to cross-road drains expected to carry substantial spring-flow. Rock armor is generally preferable because it is more permanent and adjusts its position when there is minor channel downcutting.

Revegetation

Vegetation is the ultimate, long-term erosion control agent so it is important to encourage the growth of appropriate species.

Erosion control measures such as mulch or silt fences are often needed for the first year or two following road closure. Early successional plants, eg. grass and legumes, can come in quickly and reduce surface erosion while improving soil condition. Legumes add nitrogen to poor soil. Trees and shrubs are established more slowly but provide longer-lasting cover and stronger root systems to enhance slope stability.

Seeding should be done immediately after the surface is disturbed; the rough surface provides a more favorable environment for germination and growth. Mulches increase seedling establishment by improving germination and controlling erosion until the plants become established. Seeding can be done by hand or vehicle or by hydraulic seeding from a pump truck or trailer. The seed must be evenly distributed to provide continuous cover.

Fertilizers may be necessary in severely disturbed sub-soils and cutbanks. Soils can be tested for nutrient content or a commercial mix used.

Seed mixes are a good way to get a variety of plant types. Consider:

• Timing. Seeds should be planted immediately after soil disturbance and a minimum of 6 weeks before periods of drought or frost. Fall seeding is best.
• Mixtures should include annual grasses (for quick growth), perennial grasses (better root systems), and legumes (for nitrogen).
• Use native plants adapted to the area. Be sure to avoid exotic pest species that may get out of control!

After seeding, plant bare soils with trees and shrubs to provide the long-term ground cover and soil binding capabilities needed for effective erosion prevention, soil development and slope stability on heavily disturbed sites.

—from the Handbook for Forest and Ranch Roads: A Guide for planning, designing, constructing, reconstructing, maintaining and closing wildland roads by William Weaver and Danny Hagans. Available from the Mendocino County RCD (707) 468-9223 for $20. It’s a bargain and a superb resource!

Another good road book is A Landowner’s Guide to Building Forest Access Roads by Richard L. Wiest. It is available online at http://willow.ncfes.umn.edu/accessroads/accessroads.htm where you can also order a hard copy.