Ministry of Environment Terrain

Introduction

General

Terrain stability mapping involves mapping the terrain to delineate areas that are stable and areas of existing and potential landslides, assessing the probability of those landslides occurring, and may include assessing the associated landslide risks. Landslide hazard and risk mapping, or simply landslide hazard mapping, are other terms commonly used to describe terrain stability mapping.

In British Columbia terrain stability mapping is used for resource development planning (for example in the forest industry); for land use and development planning; and for planning of linear projects such as for roads, railways, pipelines, and transmission lines.

The Earth Science Task Force of the British Columbia Resources Inventory Committee retained Thurber Engineering (Robert Gerath and Oldrich Hungr), in association with VanDine Geological Engineering (Doug VanDine), to review terrain stability mapping methods currently used in British Columbia, the Northwest United States and elsewhere in the world, and to suggest methods appropriate for a wide range of uses. This report is a summary of the review and the suggested methods.

The purposes of establishing standard methods are:

• to define reasonably uniform procedures, levels of effort and expertise for professionals involved in mapping projects;
• to develop common terminology, classifications, and symbols to improve communications among professionals involved in mapping, and between mappers and non-professionals who use such maps; and
• to prepare for technological changes, such as the introduction of computerized data bases and Geographical Information Systems (GIS).

Method and Scope

The review included a literature review and discussions with individuals experienced in terrain stability mapping and with map users. The suggested methods are based on the findings of the literature review, the discussions, and the collective experience of the authors.

Chapter 2 introduces landslides and the concepts of landslide hazards, consequences and risks. Chapters 3 and 4 provide a summary of the findings of the review. Chapter 5 presents general aspects of the suggested terrain stability mapping methods. Chapter 6 discusses specific aspects of terrain stability mapping in the context the forest industry, land use planning and linear project planning. The documents reviewed and referenced are listed in the bibliography in Chapter 7. Throughout the text a number of examples are referenced. The referenced examples are by no means exhaustive, and have purposely been limited.

Terrain stability mapping is based partly on scientific principles and partly on the intuition and experience of the mapper. It is therefore difficult to codify and standardize. The most valuable insights in terrain stability mapping are often obtained by experienced mappers with a flexible imagination. The suggested methods outlined in this report are intended to aid the work of the mapper, not stifle it by the imposition of rigid procedures. The authors hope that this report will serve as a summary of useful procedures and as a guide for improved communication between mappers and map users.

Although this report specifically addresses landslide hazards, many of the findings and suggestions can be applied to other forms of mass movement, such as snow avalanches and surface soil erosion, as well as other natural hazards.

The authors wish to acknowledge the numerous individuals who have contributed to this study and report in many different ways.