[Mapping and Assessing Terrain Stability Guidebook Table of Contents]
Map legends and reports for RTSM and DTSM projects
A legend must be attached to each terrain and terrain stability map sheet. The legend must show the date of publication, the extent and date of field-checking, and the TSIL. The legend must also summarize or define any terrain or interpretive classifications and any on-site symbols used on the map. The location of ground checks should be shown on the map. Each map sheet must show latitude and longitude, UTM grid references, and map sheet numbers and boundaries for the corresponding forest cover maps. See Guidelines and Standards for Terrain Mapping in British Columbia (Resource Inventory Committee, 1996a) and the Standard for Digital Terrain Data Capture in British Columbia (Resource Inventory Committee, 1998) for examples of map layout and other terrain mapping conventions. The professional accepting responsibility for the mapping must sign and seal each map sheet.
A brief report should accompany all RTSM and DTSM projects. For small projects, an expanded legend or marginal notes on the map may be sufficient. The following information should be presented in the report or marginal notes:
- An introductory section outlining pertinent background information and any previous mapping or terrain stability assessment work, and a statement of the objectives of the mapping project.
- A description of the project area, including project boundaries, physiography, topography, general climatic regime, biogeoclimatic zone, general Quaternary history and bedrock geology.
- Descriptions of the landforms, surficial materials and general Quaternary stratigraphy of the area, as well as of the soil types and soil drainage conditions associated with different landforms or surficial materials.
- A description of the active geomorphic processes, particularly the type, magnitude and frequency of landslides present in the map area, and the landforms or portions of landforms or terrain units typically associated with landslide activity (in terms of the initiation, transport and deposition or runout zones of landslides).
- An inset map showing the location of all helicopter traverses and foot traverses, as well as:
- brief descriptions of the mapping methods, the percentage of polygons ground-checked, and the reliability of the map data, and
- a description (with delineation on a map, if necessary) of the areas of high-intensity versus low-intensity field-checking.
- The criteria and rationale used to develop terrain stability classes and other interpretations.
- If background data have been collected on areas of previous timber harvesting, summary tables or summary statistics should also be provided. The report should describe the limitations of the interpretations.
- A concise summary that discusses any specific recommendations or concerns with regard to terrain stability and forest management practices in the project area.
The professional accepting responsibility for the report must sign and seal it.
Additional Tips for RTSM and DTSM:
- Ensure mapping contractors have appropriate qualifications, competence and experience.
- Ensure that an experienced reviewer with extensive terrain and terrain stability mapping experience in forested and mountainous terrain in British Columbia is included in the project, to guide, supervise and correct the work of less experienced mappers.
- Allocate adequate time for field-checking and data collection. Inexperienced mappers will require more time than experienced mappers.
- Ensure air-photo typing is as precise as possible. Carefully position boundaries that follow obvious slope breaks and other discontinuities in the landscape that are clearly visible on the air-photos.
- Avoid messy symbols, sloppy linework, thick lines, etc. These create an impression of haphazard, inaccurate and unreliable mapping.
- Box the air-photos and ensure that terrain polygon boundaries are never on more than one air photo. Duplicate linework, especially lines that vary in location, waste time, create the impression of inaccurate mapping, and may cause errors during line transfer.
- Ensure that the final air-photos have complete polygon labels and finalize mapping on the air-photos, as well as on the maps.
- Make neat, systematic and comprehensive field notes. Where less experienced mappers are employed, field notes should be sufficiently detailed to allow an experienced mapper/reviewer to evaluate mapping quality and the accuracy of terrain/surficial material designations.
- Develop local criteria for interpretations and provide a supporting rationale.
- Ensure that interpretations are consistent and are linked to terrain attributes described for the terrain polygons mapped.
- Ensure that the terrain polygons mapped are consistent with known geomorphic history and that landforms are identified correctly.
- Ensure that the conventions for terrain polygon descriptors, on-site symbols, map polygon boundaries, etc., presented in the "Terrain Classification System for British Columbia" (Howes and Kenk, 1997) and other supporting documents are applied correctly.
- Update or modify terrain stability map class criteria and/or interpretations if new studies show that the current criteria and/or the interpretations are no longer valid. For example, TSFAs for cutblocks and road locations can serve as part of the field-checking requirement for terrain mapping and terrain stability mapping if the two activities are carried out concurrently. The results of a single TSFA, however, should not be used to modify a pre-existing reconnaissance or detailed terrain stability map. If TSFAs repeatedly indicate that the existing RSTM or DTSM for a forest development plan area is overly conservative or unreliable, then consideration should be given to revising the mapping.
- Map large generalized polygons that have substantive internal slope breaks or terrain boundaries.
- Use photocopies for stereoscopic air-photo interpretation or line transfer to digital files. Photocopies are not dimensionally accurate, and they lack the resolution of the original air photos.
- Assume that terrain polygons mapped for purposes of terrain stability equate to terrain polygons outlined for terrestrial ecosystem mapping and vice versa. There can be differences.