New Hampshire's Department of Resources and Economic Development's Bureau of Trails published this article in 2004 on planning, designing and maintaining trails to minimize erosion and negative environmental impact. It begins with some general tips on the importance of thinking ahead when designing your trail and some common guidelines to consider. Whether you're considering joining the Indian Hill Equestrian Club on its next trail-clearing venture or are just interested in the topic, you'll likely find some of these practical project planning tips of interest.
Source: AmericanTrails
Purpose
In addition to providing recreation, trails foster an appreciation and respect of nature. Trail construction and maintenance may involve impacts to wetlands and other natural resources. This publication attempts to create an understanding of these impacts and provide the methods necessary to minimize them. It has been developed as a reference tool to help public land managers, trail clubs, landowners and recreational trail users work together to protect our natural resources. It is necessary to develop erosion control plans for trail projects to minimize erosion, sedimentation and resulting water degradation prior to the initiation of construction.
Trail planning guidelines
The ideal recreational trail is one that requires minimal maintenance. When planning a trail and its construction, you should take advantage of the natural features of the environment rather than transforming the landscape to meet the proposed project's needs. The materials that will be used, the construction and maintenance techniques, and the size of the trail project will help identify the scale of the environmental impact to soils and wetlands.
Should modification to the landscape be required, it is imperative to minimize soil disturbance near wetlands. The first step in trail planning is to visually inspect the area. In general, look for routes that are dry, of moderate grade, and in need of little terrain modifications in order to minimize potential erosion and sedimentation problems. Survey the trail during wet months!
General guidelines
Know the type of trail being constructed. Design for all potential uses.
Good planning and design of recommended trail work should prevent many potential erosion problems.
Whenever possible, use vegetative means of erosion control, such as seeding or planting small trees or other ground cover.
Avoid using heavy equipment whenever possible, thus reducing the amount of disturbances to the natural resources.
Certain forms of recreational trail use can create serious erosion and sedimentation problems. It is essential to integrate erosion control measures when planning, constructing, and maintaining trails, and to assure the measures are appropriate for the type of recreational use the trail receives.
The steeper the slope, the greater the potential for problems.
Multiple-use trails should be designed to the most limiting standard. For example, a snowmobile and cross country ski trail design should not exceed 20% slope, the maximum grade guideline for cross country ski trails.
Trail construction and maintenance
Before beginning any trail construction, install necessary measures to minimize and prevent erosion.
Stabilizing slopes, creating natural vegetation buffers, diverting runoff from exposed areas, controlling the volume and velocity of runoff, and conveying that runoff away from the construction area all serve to reduce erosion.
Careful trail planning and design will create a stable trail that will result in fewer problems with soil erosion and sedimentation.
During trail construction, minimize the amount of soil disturbance at stream crossings.
Trail construction is best done during the dry months when soil saturation and water levels are at their lowest.
The three most important factors to consider during trail construction are the character of the land itself (soil, slope, and vegetative cover), the type of expected use, and the volume of that expected use.
Some trail construction areas may need to be stabilized if heavy traffic is expected on the trail.
Install temporary erosion control measures such as hay bales before construction begins. Keep them in place and maintained during construction and remove them only after the site has been stabilized.
Trails through wet areas may have to be closed during the spring or other wet periods. Plan an alternate route, if possible.
Below are some additional excerpts that go into more detail on designing trails to protect from erosion in and around water, from the longer article attached in the pdf here.
SOIL EROSION AND SEDIMENTATION CONTROL Soil erosion is defined as the loss of soil by the actions of water, ice, gravity, or wind, and includes both the detachment and transportation of soil particles. Soils which contain high proportions of silt and fine sands are more vulnerable to erosion. The potential for soil erosion decreases as the percentages of organic matter increases. The most important factors which affect the potential for soil erosion include: soil particle size, soil structure, soil permeability, and percentage of organic content. Vegetation, slope, and climate are also important considerations which affect the potential erodibility of soil. Vegetation acts as a natural buffer to protect wetlands from erosion and sedimentation. The maintenance of existing vegetation on stream banks is a fundamental principle of erosion and sedimentation control. Vegetation filters runoff and provides a protective cover to the soil from the impact of rain and flowing water. Soil erosion control practices will help to protect water quality, maintain recreational trails, and reduce the costs of maintenance. Such measures include mulching with hay, vegetative restoration, and scheduling trail construction to be done in phases to keep the amount of unstabilized areas at a minimum. In order to maximize effectiveness, erosion control measures must be properly chosen, located, and implemented in a timely manner. Many erosion control practices will not only protect water quality, but also maintain trail integrity and improve usability. Sedimentation is the end-product of erosion. Sedimentation refers to the settling out of soil particles which have been detached and transported, usually by water, in the process of erosion. Sedimentation is minimized by erosion control. The first step in planning for sedimentation control is to control erosion. The second step is to trap sediments which are transported by runoff before they reach streams or wetlands. Sedimentation occurs when moving water in which the soil particles are suspended is slowed to a degree which allows the soil particles to settle out of suspension. Larger, heavier particles, such as sand and gravel, settle out more quickly than smaller, lighter particles, such as clay and silt. This can be seen at the base of slopes on the flatter areas of a trail where small sandy patches or deltas develop.
Below is an example of creating a barrier to prevent erosion or sedimentation due to water flowing through an area.
Guidelines for bale installation
Bales shall be placed in a single row on the contour with the ends tightly adjoining, not to exceed 600 feet in length.
Turn up the ends and begin a new row, if needed
The bales should be embedded into the ground at least 4" deep
After placing bales, they should be anchored in place with two stakes per bale driven through the bale and into the ground
Bales should be used where the area below the barrier has exposed soils and would be impacted by water flowing through a barrier
Inspections should be frequent. Repair or replacement should be done promptly, as needed.
SLOPES AND SOIL Soil which has eroded contributes to both onsite and offsite damages, usually to wetlands and surface waters. The depth, structure, and composition of the soil, as well as the soil’s permeability, texture, and drainage capacity, are all significant in the soil’s ability to withstand erosion. Soil compaction occurring on recreational trails restricts the natural absorption of water. Churning of the soil loosens surface soil particles, which then can be carried away by wind or water. Slopes are especially susceptible to erosion due to the relationship between the grade of the slope and the potential for increased water velocity. Trail construction or maintenance work that is to be performed on hillsides should be carefully planned so as to minimize the trail grade and to incorporate proper cross-drainage. The most effective way to decrease erosion is to avoid modifying slopes. Trails in areas with long, steep slopes should be designed to follow the contours to minimize accelerated soil churning and erosion. Modifying a slope by clearing existing vegetative cover also increases its vulnerability to erosion. Vegetation helps filter runoff water and holds soil particles in place. Vegetation also maintains the soil’s capacity to absorb precipitation. During trail planning and construction, the most desirable slope grade is less than or equal to 5%. This will minimize potential erosion and sedimentation problems. Slope grades in excess of 10% increase the need for maintenance and the potential for erosion.