A COMPUTERIZED METHOD FOR DETERMINING CABLE LOGGING FEASIBILITY USING A DEM.

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1 A COMPUTERIZED METHOD FOR DETERMINING CABLE LOGGING FEASIBILITY USING A DEM Woodam Chung 1 and John Sessions 2 1 Assistant Professor, School of Forestry, University of Montana, Missoula, MT wchung@forestry.umt.edu 2 Professor, Department of Forest Engineering, Oregon State University, Corvallis, OR john.sessions@orst.edu ABSTRACT This paper introduces a computerized method designed to determine cable logging feasibility by analyzing ground profiles using a digital elevation model (DEM). This method involves a series of computer algorithms to extract topographic information from a DEM, analyze payload and ground profiles, find proper intermediate support locations, and consider the full suspension requirement over the riparian management areas. A computer program has been developed to implement this method. Providing the users with interactive functions, the program can be used to identify feasible cable logging areas, find efficient tower locations, estimate load carrying capacity, and find proper intermediate support locations. INTRODUCTION Cable logging systems are often used to harvest timber in mountainous areas where road access is limited or additional protection to the ground is required. Cable logging involves expensive equipment and high-risk operations. Well-designed operational plans are crucial for successful applications of cable logging. Planning cable logging operations is a challenging task. It requires consideration of the physical feasibility of the system, economic efficiency, and environmental concerns. The identification of cable logging feasibility necessitates the consideration of topographic conditions, yarding system capacity, tower and tailspar locations, intermediate support locations, and other environmental requirements such as full suspension requirement over the riparian management areas. Several computerized methods for ground profile analysis have been introduced to assist forest engineers in planning cable logging operations. LoggerPC (Jarmer and Sessions 1992) is a widely used computer program that analyzes the load carrying capacity of yarding systems over specified terrain profiles that are derived from survey data. Interacting with GIS (Geographic Information System) database, PLANS (Preliminary Logging Analysis System) developed by the USDA Forest Service (Twito et al. 1987), extracts topographic information from a DEM and analyze harvest units based on specified landing locations and cable logging systems. However, neither PLANS nor LoggerPC automatically consider full suspension requirements over the riparian management areas or search for intermediate support locations along cable corridors for multiple span skylines. CPLAN (Chung 2002) does have this functionality as a subcomponent of an overall road and landing location optimization problem, but the planner cannot use the corridor analysis as a stand alone module. Recently, a cable logging feasibility stand alone module has been developed as an extension to the work done in CPLAN.

2 This paper describes the computerized method designed to determine cable logging feasibility by analyzing ground conditions while considering yarding systems, intermediate support locations, load carrying capacity, and full suspension requirements where necessary. GIS produced data such as a DEM and a stream coverage are used in this method to provide the topographic information and the riparian management areas (stream buffers). A computer program developed to implement this method extracts topographic information from a DEM and searches for the feasible cable corridor configuration which satisfies minimum load carrying capacity and the full suspension requirement above the riparian management areas. The method and the computer program are briefly introduced in this paper. LOGGING FEASIBILITY ANALYSIS In this method, users specify landing locations and a computer algorithm developed for this analysis projects 36 cable corridors at 10-degree intervals from each landing. The algorithm then evaluates each of the projected cable corridors for its logging feasibility and searches for a feasible cable corridor configuration (Figure 1). Two evaluation criteria are used: 1) the userdefined minimum payload per yarding cycle and 2) the full suspension requirement over the riparian management areas. Each of the cable corridors has to meet both requirements in order to become a physically feasible cable corridor. Identify an initial tailspar location on a DEM Identify grid cells located along a cable corridor on a DEM Set the tailspar at the lowest allowable height Place intermediate supports where necessary This cable corridor is feasible Elevate tailspar height Shorten the skyline length by moving tailspar location toward headspar by one grid cell Yes Yes No Physically feasible and load capability is greater than the design payload No Tailspar height < Upper range? No Is the skyline length shorter than the minimum limit? Yes This cable corridor is not feasible Figure 1. The algorithm to determine the logging feasibility of an individual cable corridor. The computer algorithm determines the initial tailspar location of each cable corridor on a DEM using the maximum external yarding distance of the specified cable logging system with the

3 assumption that an adequate tailspar is available. The algorithm then identifies the grid cells that are located along each cable corridor on the DEM. Each of these cable corridors is evaluated for its logging feasibility for a specified cable yarding system. Currently the analysis is limited to standing skyline systems. The algorithm applies the Phase I procedure suggested by Brown and Sessions (1996) to identify the maximum log load that can be carried along a given ground profile by a standing skyline system. The algorithm automatically places intermediate supports on convex terrain in order to ensure the minimum clearance of the skyline from the ground. The algorithm also allows the planners to input the available range of tailspar heights and searches for the minimum height satisfying the minimum payload per yarding cycle, which is referred to as the design payload in this paper. Locating intermediate supports Intermediate supports are required to ensure the minimum clearance of the skyline on terrain with a convex slope or a long constant slope. An automated algorithm to place intermediate supports developed by Sessions (1992) is implemented in this method with some modifications. The algorithm begins by placing intermediate supports on all terrain with a convex slope, then eliminating unnecessary supports using several design criteria. Since identifying intermediate support locations is mainly associated with consecutive terrain points, which are represented by grid cells on a DEM, the algorithm may place more intermediate supports than necessary. If the users limit the allowable number of intermediate supports along a cable corridor, the algorithm tries to keep the total number under the limit by eliminating the intermediate supports that have the least effect on payload as long as the user-defined design payload is achieved. The steps in the algorithm are presented below: Step 1. Examine ground slopes between three consecutive terrain points along the profile and place intermediate supports on all terrain points where convex slopes are found (Figure 2a). Step 2. Examine the slope change of the skyline at each intermediate support and eliminate the support if the slope is not convex (Figure 2b). Step 3. Evaluate the deflection at each intermediate support assuming the support does not exist. If enough clearance is ensured, then eliminate the support. Otherwise, keep the support at the current terrain point. The allowable percentage deflection of the skyline and minimum skyline clearance above the ground are provided by the users (Figure 2c). Step 4. Examine the slope change of the skyline at the intermediate support. If the slope exceeds the user-defined maximum slope change of skyline required for carriage passage, then this cable corridor becomes physically infeasible (Figure 2d). Step 5. If the total number of intermediate supports is greater than the user-defined maximum number, then temporarily eliminate an intermediate support one at a time and calculate the payload. Record the payload, restore the intermediate support, and move to the next intermediate support and repeat this process. Step 6. By comparing the payloads calculated from Step 5, eliminate the least effective intermediate support. Step 7. Repeat Steps 5 and 6 until the total number of intermediate supports meets the userdefined allowable number. If the maximum load carrying capacity is not greater than the user-defined design payload, then stop the routine and this cable corridor configuration becomes infeasible.

4 TP1 TP2 Slope change shows that TP2 is on a convex slope (a) TP3 Ground profile TP4 Intermediate supports (b) The slope change of the skyline on both sides of an intermediate support Deflection Skyline Intermediate support Clearance from the ground (c) Intermediate support (d) The slope change is too large for the carriage to pass Figure 2. Design criteria on placing intermediate supports. Full suspension requirement over the riparian management areas Full suspension is often required over riparian management areas to protect vegetation and minimize disturbance to beds and banks of streams (Figure 3a). The algorithm overlays a stream coverage on a DEM to identify the riparian management areas (Figure 3b) and checks the log clearance when cable corridors cross any of those areas. If a cable corridor cannot produce enough payload per yarding cycle while satisfying the full suspension requirement, the current cable corridor configuration becomes infeasible and the algorithm searches for a new tailspar location along the corridor that satisfies both the design payload and full suspension requirements. Terrain points where full suspension is required Riparian management area Stream Riparian management area (Full suspension required) (a) (b) Figure 3. Riparian management areas requiring full suspension. Terrain points along a cable corridor

5 APPLICATIONS OF THE LOGGING FEASIBILITY ANALYSIS This method has been implemented in a Windows based computer program, written in Microsoft Visual C++. Providing users with interactive functions, the program can be applied to identify feasible cable logging areas from specified landings (Figure 4a) while considering minimum design payload and full suspension requirement over the riparian management areas (Figure 4b), select efficient tower locations (Figure 4c), and find proper intermediate support locations while providing estimated load carrying capacity (Figure 4d). Stream buffers Forest roads Cable logging feasible areas from the specified landing locations (a) DEM Landing location A selected tower location (a black dot) that provides the largest logging feasible area among other alternative locations (shown in a white rectangle) (c) Full suspension over the riparian areas Selected intermediate support locations (b) (d) Figure 4. A computer program developed to conduct ground profile analysis and determine cable logging feasibility using GIS produced data. CONCLUSIONS An automated method to efficiently analyze ground profiles and determine cable logging feasibility is introduced. Incorporating modern computer programming languages and GIS technologies, a computer program has been developed to implement the method. Hopefully, the program can help forest planners efficiently analyze timber harvest areas and develop better cable logging plans that reduce the costs and environmental impacts of timber harvesting.

6 ACKNOWLEDGMENT This study was supported in part by funds provided by The University of Montana. REFERENCES Brown, C. and J. Sessions The standing skyline: a maximum log load solution procedure. Forest Science. 42(2): Chung, W Optimization of cable logging layout using a heuristic algorithm for network programming. PhD dissertation, Oregon State University, Corvallis, OR. 209 p. Jarmer, C. and J. Sessions Logger-PC for improved logging planning. In Proceedings of Planning and Implementing Future Forest Operations, International Mountain Logging and 8th Pacific Northwest Skyline Symposium, December 14-16, Bellevue, WA. Sessions, J Unpublished software developed for educational use. Oregon State University, Corvallis, OR. Twito, R.H., S.E. Reutebuch, E. Stephen, R.J. McGaughey, and C.N. Mann Preliminary logging analysis system (PLANS): overview. Gen.Tech. Rep. PNW-GTR-199. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 24p.