Washington State Forest Preserves Trail Use And Fish Habitat

IMBA Trail News
Volume 11, Number 5
November 1998

By Gary Sprung

The fine, very small, sediments released into salmon spawning streams by trail erosion can cause direct, negative impacts on a critical wildlife habitat. At IMBA's Pacific Northwest Summit in September, managers of the Tahuya State Forest in Washington state explained how they are greatly reducing this problem through trail improvements and improved relationships with trail users.

The 23,000-acre Tahuya State Forest is located 15 miles northwest of Tacoma, on the Kitsap Peninsula. The many streams flowing through the Tahuya all provide the gravel spawning beds, fresh water and shelter needed for reproduction by coho, winter steelhead and summer chum – varieties of salmon which may soon be protected by the Endangered Species Act. On the same landscape are 180 miles of trails, largely created over the past 40 years by motorcyclists, and now enjoyed also by mountain bikers, hikers, and equestrians. The trails cross the streams in about 100 places.

Early in 1994, managers of the Washington Department of Natural Resources (DNR) recognized that these recreational trails could be harming water quality and fish habitat, so they began conducting soil and hydrology assessments of the trail system. The managers also began discussions with trail users and experiments in erosion control measures. The results provide some of the best scientific data on trail erosion and excellent information on trail design and tread hardening.

At the IMBA conference, held at a beautiful Girl Scouts facility adjacent to the Tahuya, Forest Soil Scientist Ken Schlichte recalled how "a fall rain event changed all our scientific views. We had not anticipated that much water flowing down the trail, with consequent gullying and sediment transport."

To gather more detailed measurements, the scientists enlisted the aid of students from the nearby North Mason High School. Schlitke and other managers taught the students how to measure a variety of parameters. They measured silt caught in sediment traps, soil loss on trail surfaces, rainfall, and numbers of trail users.

The "Students in the Watershed" project resulted in four main conclusions:

• Roughly 150 metric tons of sediment would have eroded into streams each year from the 180 miles of trails, if not for the erosion control measures.

• Increases in steepness of trail segments significantly increase the potential for surface drainage flow, trail rutting, and sediment delivery to streams. Trails with grades over 20% cause much more erosion than trails with more gentle grades.

• Heavy trail use during wet soil periods significantly increases erosion. But trail surfacing, such as cement garden blocks, can significanly reduce erosion caused by trail users.

• Longer stretches of trail without water diversions will cause more erosion. Well-designed, well-located, and well-constructed water diversions can effectively minimize rutting and sediment at low cost.

These conclusions are not unique to the Tahuya. What is new is the quality of the data. During three years of study, the students and scientists were able to create scientifically credible charts which clearly demonstrate these effects of rainfall, trail steepness, and trail design.

Trail Hardening No Substitute For Good Design

Tahuya managers have spent hundreds of thousands of dollars on trail improvements ranging from new bridges brought in by helicopter to the laying of geotextile fabric and heavy concrete blocks. "We had to bring our trails up to a specification where we could say we're doing no damage to the streams," said Forester Philip Wolff.

Wolff noted they have had great success with Grass Grid and Turf Stone, two products used primarily for fire lanes around apartment buildings. Each block is 16"X24" and weighs around 60 pounds, so they are impractical for deep backcountry. The Tahuya has a long history of logging and a consequent network of roads, so the blocks there are feasible. The foresters have also successfully employed Geo-Webb, Geo-Textile and recycled, crushed asphalt.

But Wolff concluded, "The first rule of trail hardening is to avoid it at all costs. All the trail hardening in the world won't help a poorly designed trail…. We have found it critically important that trail reroute possibilities are given a serious and creative look before trail hardening is used. Trail construction is much easier and less costly than trail hardening. For example, if hardening is needed in a wet area, perhaps it would be better if the trail were not there. In steep areas, a climbing turn might be preferable to a hardened switchback."

Ken Schlichte offered a most encouraging point for trail users. The problem of erosion "does not require limitations on trail use. We can have trail use year-round if we have adequate water diversion." He noted that the trail building knowledge gained in the Tahuya may allow the DNR to eliminate some seasonal restrictions on other state forests.

Users Get "Ownership"

In 1994, the Department of Natural Resources realized they needed a more thorough management program for the Tahuya trails, and also recognized the potential for conflict with and between trail users. "We could have huddled as an agency," said Vicki Christiansen, Hood Canal District Manager, "and made a bunch of regulations and then asked people what they think." Instead, the agency chose to initiate a "focus group" collaborative process where all trail users, the agency, and other people interested in the landscape – "stakeholders" – discuss values, goals, and problems, and jointly create solutions.

For Dave Simms, a white-haired, stocky man who has worked as a forester for 24 years, this was a big change from old priorities. He said his job responsibilities had been relatively simple: "put up timber sales, keep mud out of creeks, and put out fires." Those tasks remain, but now he must also manage the complex social dynamics of recreation. One of the most difficult challenges was the need to communicate the concept, "Multiple use is not a right. Its' a privilege… Allowable uses can become disallowed." For example, the agency once allowed, but no longer tolerates, indiscriminate shooting with AK-47s.

Tommy Thomson of the Bremerton Cruisers Motorcycle Club applauded the process. His group initially felt threatened, but eventually decided to join as enthusiastic partners. They helped the agency to map all the user-built trails in the forest.

The agency avoided much potential conflict by not discriminating among user groups. All trails in the Tahuya are open to all users. "It's not worth the energy to prove current damage by recreationists," Said Christiansen. "Instead, we work for our future."

Christiansen felt the agency "took a big risk" with the focus group. She was concerned that the plan could lead to closure of 20 miles of trail to protect salmon streams. Yet the group finally came to consensus on closing 40 miles. Because of the focus group process, "the users now had ownership in the trail action plan."