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Using the Power of a GIS Trail Inventory for Trail Planning

Santa Monica Mountains NRA
Melanie Beck
Santa Monica Mountains National Recreation Area (SMMNRA)is a 153,075-acre unit of the National Park System located adjacent to the greater Los Angeles metropolitan area. Land ownership in SMMNRA is a patchwork of public and private lands, with the public lands owned by federal, state and local agencies. After nearly 25 years of continuous land acquisition, the public trail network has grown significantly to 320 miles of trails and dirt service roads. Several trails now cross parkland jurisdictional boundaries with varying trail management policies. Another recreational development is the growing popularity of mountain biking, generating the need to address user conflicts and safety associated with multiple use on trails. The 60-mile regional Backbone Trail is nearing completion and requires interagency cooperation on trail use, backcountry camps, and signage. An indispensible tool for inventorying the trail network's current conditions has been SMMNRA's GIS. The digital inventory of trail conditions will be integral to preparing a forthcoming interagency regional Trail Management Plan (TMP) and the accompanying Environmental Impact Statement/Report (EIS/EIR). A trail planning team composed of trail management professionals from the National Park Service, California State Parks, and the Santa Monica Mountains Conservancy oversaw the inventory and will be responsible for preparing the TMP. TMP goals are to protect natural and cultural resources as #1 priority, balance resource protection with adequate recreational opportunities, and finally, plan a system that can be maintained within budget constraints. The attached maps illustrate just some of the GIS's virtues in using the Trail Inventory to facilitate the TMP decision-making process.

Map 1: Trail Grade: Steepness Analysis of the Backbone Trail
One of the best features of the GIS is its ability to process data from large geographic areas and generate a map that quickly illustrates patterns. The revealed patterns aid planners in deciding to keep or change a pattern. In the case of trail planning, trail grade is a prime factor in assessing a trail's erosion potential to cause sediment loading in streams. Additionally, trail grade affects user enjoyment and safety on multiple use trails. A major part of the SMMNRA GIS Trail Inventory is trail data collected using the Universal Trail Assessment Process, commonly known as "UTAP'ing" trails. UTAP grade data for the Backbone Trail was processed to show what percent of each section of the Backbone Trail had more than 15% grade, an indicator of both high erosion potential and inconsistency with multiple use standards. The data was then joined with the graphic GIS database and symbolized. The resulting map shows patterns of moderate versus servely steep grade along the Backbone Trail. The TMP Planning Team can now use the information to decide whether the steeper trail segments should be opened to multiple use, or whether they should be re-routed to meet multiple use and erosion control standards. Either decision will require considering of a number of other planning variables, ranging from underlying soil type to current recreational use patterns and future needs.

Map 2: Backbone Trail: Mountain Bike Bypass Around Boney Mountain Wilderness
Another important GIS capacity is to illustrate multiple variables within one symbol, i.e., complex symbols. Symbology for TMP Planning Team maps greatly differs from what would normally be shown on a trail map for the public. Trail planners frequently have to consider at least two or more trail variables at once. The SMMNRA Trail Inventory includes a minimum of ten critical trail attributes; the most commonly used attributes are tread width (road versus trail width); trail status (existing official trail, proposed new trail, existing unofficial trail); and trail use (hiker-only, hiker-equestrian, multiple use, etc.). TMP planning maps frequently must show several Trail Inventory attributes, in addition to future planning options, as illustrated in Map 2. The map illustrates various trail route options, along with tread width and trail status information. The complex symbology of Map 2 would likely not be of use to the public, but is very useful in TMP planning meetings.
April 08, 2004