|Forest Roads Editing in MapInfo Pro
||Phosphorus pollution is an ongoing problem in Lake Champlain, the inland waterbody that separates north-western Vermont from New York State and the Canadian province of Quebec. There are many possible sources of phosphorus in the watersheds that surround the lake, including runoff from impervious surfaces such as paved roads and parking lots and also from agricultural fields with exposed soils.
Whatever the origin, phosphorus is an important nutrient for plants and animals that in excessive quantities can cause explosive growth of blue-green algae, creating blooms that reduce levels of dissolved oxygen and produce toxins dangerous to other forms of life. The result can be destruction of aquatic habitats supporting fish, impaired drinking water supplies, and loss of recreational opportunities such as swimming. What can GIS do to help this problem?
A Forgotten Source of Phosphorus
Scientists, regulators, and concerned citizens are working diligently to understand the severity of the phosphorus problem and to identify solutions for reducing pollution loading into the lake. Runoff mitigation is one important approach – prevent or slow water from rain or snowmelt entering unfiltered into streams and rivers that drain the lake’s watersheds. Tree planting in suburban and urban environments, vegetated buffers around farm fields, and well-designed and maintained catchment systems are all measures that can help reduce runoff, and there is much effort to encourage municipalities, businesses, farmers, and homeowners to adopt these strategies.
Despite this general recognition of phosphorus pollution, there is a contributor to the problem that is little understood and often overlooked: runoff from logging roads and trails in the forests that surround the lake. To reach mature forest stands and later transport cut timber offsite, it is often necessary to construct a network of tote roads, skidder paths, and log landings. Most of these roads are unpaved and often temporary - they are not intended for regular automobile travel and usually receive less design engineering and maintenance. It is thus possible that some of the roads will be subject to erosion and ultimately a source of phosphorus pollution.
How can the pollution risk from these roads be examined and reduced by appropriate mitigation measures? Logging roads are often located in rural areas and can form extensive networks that cover large geographic areas, and usually they are not represented in the road centerline databases available in many states. Even in areas with recent, high-quality aerial imagery, logging roads and paths are difficult to identify because they are often obscured by overhanging tree canopy, and in any case imagery provides no information on the specific nature of ground features. Traditional imagery and GIS road datasets simply do not have enough information to adequately map roads and characterize their erosion risk.
The Role of LiDAR
Fortunately, there is another data type that overcomes these limitations: LiDAR. LiDAR point clouds provide 3-dimensional representations of landscapes, providing a unique capability to characterize both terrain and aboveground elements (e.g., buildings and trees). For topographic analysis, the point clouds can be converted into high-resolution digital elevation models (DEMs) that capture fine-scale topographic features such as ditches, gullies, and excavated road beds. Features that were once too small or easily obscured in aerial imagery can now be identified and described.
In a recent study, the University of Vermont Spatial Analysis Laboratory (SAL) used LiDAR in conjunction with object-based image analysis to automate mapping of forest roads in the Vermont portion of the Lake Champlain Basin. The overall goal was to identify individual road segments that may be at risk to erosion and pollution loading. A LiDAR-derived DEM was used to develop additional surface models for visualizing fine-scale topographies, including a landform layer that highlighted concavities and other landscape depressions where roads could occur. The surface models were segmented into objects and classified into road features depending on their terrain characteristics and geometry (i.e., are the objects linear, like roads?). The initial raster output was then exported to vector format for use in a GIS.
MapInfo Puts It All Together
This is where MapInfo came in. The SAL used MapInfo Pro Version 15.2.0 (64-bit) to review the draft output against the source LiDAR surface models and to edit the roads directly. The program easily accommodated high-resolution LiDAR surfaces along with additional reference data such as aerial imagery (Figure 1), easily panning across broad geographic extents and displaying large, multi-band datasets quickly.
Figure 1. A LiDAR-derived landform surface model (left) displayed alongside 4-band National Agricultural Imagery Program (right) in MapInfo Pro. Both layers were used as reference data in manual review and editing of draft forest roads.
The line-editing capabilities were also very useful, permitting rapid drawing of missing road segments and snapping them to already-drawn features (Figure 2). The editing tools similarly permitted efficient selection, cutting, and deletion of false-positive segments or other linear features that were occasionally misclassified as roads (e.g., streams).
Figure 2. Road review and editing in MapInfo using the Spatial\Insert\Lines tool. The original, automated output (left) is manually edited to produce a comprehensive road network (right).
The final product was a detailed, comprehensive set of logging roads and paths that had not been previously mapped by any other analysis (Figure 3).
Figure 3. Final edited forest road network for a section of the Lake Champlain Basin in Vermont.
All of the work in MapInfo was performed by undergraduate students and recent graduates. They found the program easy to learn and use, and its tools were well designed and intuitive. The ribbon-based arrangement of tools and processing functions was especially helpful to beginners, providing a design logic similar to many other software programs. This project was a two-fold gain for undergraduate GIS education – students broadened their expertise in mapping software, learning new tools and conceptual approaches to data creation and management, and they also contributed to a real-world study that will directly benefit an important issue in environmental modelling and management. When students leave the academy, their future success in GIS will depend in part on their ability to apply the right tools to specific tasks and research questions, and MapInfo offers them the functionality and power to thrive in their post-graduate fields of study and practice.
The Road Ahead
Logging roads are not the primary source of phosphorus entering Lake Champlain, but they are contributing factors whose role and magnitude must be better documented. Subsequent research will focus on identifying the specific road segments that are mostly likely erosive and quantifying their annual contribution to phosphorus loading. It will then be possible to design and implement remediation efforts that reduce pollution by re-routing or stabilizing problem roads. GIS will lead the way.
Funding was provided by an innovation grant from the Natural Resources Conservation Service, with in-kind matches from Pitney Bowes, the Vermont Department of Forests, Parks and Recreation, and the Cold Hollow to Canada Forest Link. The project was coordinated by Bear Creek Environmental, LLC.
Article by Sean MacFaden, Kyle Onofreo, Jarlath O’Neil-Dunne, and Anna Royar
Sean and the entire SAL team spend their workdays using high-resolution data to map trees, wetlands, vernal pools, structures, roads, and any other features that are important to our natural and human landscapes. Away from the office, they like to explore these landscapes in person.