This guideline offers detailed procedures for creating large-scale landslide hazard zonation (LHZ) maps in mountainous regions at map scales of 1:25,000 or 1:50,000. It provides a comprehensive methodology for evaluating slope instability by analyzing primary causative elements such as rock type, geological structures, slope geometry, relative elevation, land utilization, and groundwater conditions. The code serves as a crucial resource for planners, geotechnical experts, and environmental specialists engaged in regional hazard evaluation and risk reduction in hilly areas.
Overview
This guideline offers detailed procedures for creating large-scale landslide hazard zonation (LHZ) maps in mountainous regions at map scales of 1:25,000 or 1:50,000. It provides a comprehensive methodology for evaluating slope instability by analyzing primary causative elements such as rock type, geological structures, slope geometry, relative elevation, land utilization, and groundwater conditions. The code serves as a crucial resource for planners, geotechnical experts, and environmental specialists engaged in regional hazard evaluation and risk reduction in hilly areas.
Audience
Contents
Structure
This section defines the extent and key aspects of landslide hazard zonation mapping in mountainous terrains, emphasizing the use of geological and geomorphological data sources. It details the utilization of 1:50,000 scale topographic sheets, aerial photographs, satellite imagery, and geological maps to prepare thematic maps like slope morphometric classification, lithological and structural distributions, relative relief, rock outcrop and soil cover, land use and hydrogeology. The section also describes the assignment of hazard evaluation factors and the calculation of total hazard indices culminating in the creation of a macro-zonation LHZ map. Additionally, slope morphometry classes are specified, and an illustrative workflow diagram is presented to guide the mapping process.
This portion lists pertinent Indian Standards related to geological symbols and abbreviations essential for consistent geological documentation. It covers IS 7422 Parts 1 to 5 which standardize symbols for igneous, sedimentary, metamorphic rocks, and structural features. The section underscores the importance of consulting the latest editions for updated symbols and mentions supplementary methodology references such as the Mountain Risk Engineering Handbook.
This chapter outlines the primary causative parameters for macro-scale landslide hazard mapping, including lithology, geological structures, slope geometry, relative relief, land use and vegetation cover, and hydrogeological conditions. It provides hazard classification categories with descriptions ranging from very low to very high hazard levels. Guidelines for interpretation emphasize suitability for development and the need for detailed investigations in moderately to highly hazardous zones. The section also details the preparation methodology involving slope facet division, pre-field and factorial map development, field validation, and final hazard zonation mapping, supported by a flowchart illustrating the sequential process.
This part describes the Landslide Hazard Evaluation Factors (LHEF) and their maximum ratings applicable to macro-zonation. It includes a detailed rating scheme for key causative factors such as lithology, structural discontinuities, slope morphology, relative relief, land use, and hydrogeological conditions. Ratings are assigned based on rock/soil type, weathering status, discontinuity orientations relative to slope, slope angle categories, and vegetation cover intensity, providing a quantitative basis for hazard assessment.
This section lays out a systematic approach for preparing macro-zonation LHZ maps. It begins with desk studies utilizing aerial and satellite data, followed by creation of pre-field thematic maps at 1:50,000 scale. Field investigations validate and refine these maps, with data collection organized by slope facets. Factorial maps are prepared by assigning hazard ratings, including detailed analyses of structural discontinuities. The methodology incorporates special consideration of fault zones with elevated hazard ratings. The final LHZ map classifies hazard levels into five categories, and recommendations for periodic revision after significant natural events are provided.
This segment emphasizes presenting results primarily through layered maps illustrating spatial variability of each causative factor on a facet-wise basis. Terrain evaluation maps for individual parameters precede the computation of the Total Estimated Hazard Degree (TEHD) for each facet. TEHD values are then synthesized into a comprehensive landslide hazard zonation map delineating hazard categories. Symbol conventions for slope morphometry classes are detailed, and a process flowchart summarizes the steps from data acquisition to hazard map production.
This chapter explains the interpretation of macro-zonation LHZ maps by defining hazard categories from very low to very high hazard and their implications for development and risk management. It discusses factors influencing hazard ratings such as slope stability, failure mechanisms, and potential damage. The preparation steps involve slope facet mapping, integration of geological and morphometric data, field verification, and combined hazard zoning. The importance of map revision after major natural disturbances is highlighted, supported by a flowchart illustrating the entire mapping process.
This section outlines the criteria and methodology for revising landslide hazard zonation maps following impactful events like earthquakes exceeding magnitude 5, significant floods, cyclones, mining activities, or cloudbursts. It specifies the use of detailed slope mapping at finer scales (1:1000 or 1:2000) for unstable zones and describes the reassessment of hazard ratings considering new failure patterns. The revision process involves field surveys, updating factorial maps, recalculating hazard indices, and producing updated zonation maps to ensure accurate reflection of current hazard conditions.
Annex A provides detailed instructions for preparing slope facet maps by segmenting topographic maps into smaller units suitable for detailed evaluation. It guides the development of pre-field maps by integrating geological, morphometric, relief, land use, and hydrogeological data. The annex elaborates on factorial map creation after field validation, including lithological, structural, morphometric, and hydrogeological aspects supported by stereonet analysis. Slope morphometry classification tables and hazard zonation criteria are included, along with protocols for periodic map updates following natural or anthropogenic changes.
Annex B lists the members of the Technical Committee responsible for this standard, namely the Hill Area Development Engineering Sectional Committee (CED 56). The committee comprises representatives from government bodies, research institutions, universities, and industry stakeholders involved in hill area engineering and landslide hazard studies. The annex includes a tabulated list of member organizations, chairperson details, and alternate members, highlighting the multidisciplinary expertise contributing to the standard's development. It also references related Indian Standards on geological symbols and mapping.
Frequently Asked
The primary factors considered in macro-scale landslide hazard zonation include lithology (rock and soil types), geological structures such as faults and joints, slope morphometry encompassing slope angle and shape, relative relief representing elevation differences, land use and vegetation cover, and hydrogeological conditions like groundwater presence. These factors collectively influence slope stability and are mapped on a facet-wise basis to produce factorial maps that integrate into the overall hazard zonation.
TEHD is calculated for each slope facet by summing the Landslide Hazard Evaluation Factor (LHEF) ratings assigned to every causative parameter such as lithology, structure, slope morphometry, relative relief, land use, and hydrogeology. Each factor receives a rating based on its contribution to slope instability, and their aggregate forms the TEHD value. This facet-specific TEHD is then used to categorize hazard level into zones ranging from very low to very high hazard.
For macro-zonation landslide hazard mapping, a scale of 1:50,000 is recommended for topographic, geological, and aerial/satellite image-based data preparation. For detailed slope instability analysis in high and very high hazard zones, finer scales ranging from 1:1,000 to 1:2,000 are suggested. This stratified scaling approach allows effective identification of hazards at regional and local levels, facilitating appropriate planning and mitigation.
Land use and vegetation cover significantly influence slope stability by affecting erosion and soil reinforcement. Dense forest cover enhances slope stability through root reinforcement and reduces weathering, thereby receiving lower hazard ratings. Conversely, barren or sparsely vegetated areas are prone to rapid erosion and higher instability, leading to elevated hazard ratings. Agricultural lands generally exhibit moderate stability due to controlled watering and gentle slopes. These variations are quantitatively reflected in the hazard rating scheme, contributing up to a maximum rating of 2.0.
Post-major natural events such as earthquakes exceeding magnitude 5, significant floods, cyclones, cloudbursts, or impactful developmental activities, landslide hazard zonation maps must be revised. The update process involves conducting field surveys to identify new landslides and altered slopes, revising factorial thematic maps accordingly, reassessing hazard ratings based on observed changes, and employing detailed mapping at finer scales for unstable zones. The revised LHZ maps ensure current hazard conditions are accurately depicted, guiding safer land use and mitigation planning.
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