Guidelines for the preparation of landslide - Hazard zonation maps in mountainous terrains, Part 2: Macro-zonation

IS 14496 Part 2: Scope & Key Specifications

This part of IS 14496 focuses on landslide hazard zonation (LHZ) mapping using geological and geomorphological data.

Scope Highlights:

• Utilizes topographic maps (1:50000 scale), aerial photos, satellite imagery, and geological maps.
• Covers preparation of various thematic maps:
  • Slope Morphometric Map (Slope classes with angles)
  • Lithological & Structural Map
  • Relative Relief Map
  • Rock Outcrop & Soil Cover Map
  • Land Use & Land Cover Map
  • Hydrogeological Map
• Assigns Land Hazard Evaluation Factor (LHEF) ratings to different categories.
• Calculates Total Estimated Hazard (TEHD).
• Produces a Macro Zonation Landslide Hazard Zonation (LHZ) Map.

Slope Morphometry Classes (Clause 6.3):

Procedure Overview (Fig. 1 Concept):

flowchart TD
    A[Acquire Topographic Maps 1:50000] --> B[Acquire Aerial Photos & Satellite Images]
    B --> C[Acquire Regional Geological Maps]
    C --> D[Prepare Thematic Maps]
    D --> E[Assign LHEF Ratings]
    E --> F[Calculate TEHD]
    F --> G[Prepare Landslide Hazard Zonation Map]

References:

• IS 7422 Parts 1-5 for geological symbols and abbreviations.
• Mountain Risk Engineering Handbook for methodology guidance.

This standard integrates multi-source data for systematic landslide hazard evaluation and zonation.

IS 14496 Part 2 — References Summary

This part of IS 14496 references key Indian Standards related to geological symbols and abbreviations used in geological mapping and subsurface logs:

Key Notes:

• These standards define uniform symbols and abbreviations for geological features.
• They ensure consistency in geological documentation.
• Users should consult the latest editions for updated symbols.
• The standard also draws from the Mountain Risk Engineering Handbook for guidance.

No specific formulas or tables are given here; this section mainly lists referenced standards to maintain consistency in geological symbol usage.

IS 14496 Part 2: Factors for Macro-Zonation Landslide Hazard Zonation (LHZ) Maps

Key Factors (Clause 3.1)

• Lithology: Rock types influencing slope stability.
• Structure: Geological discontinuities (faults, joints).
• Slope Morphometry: Slope angle, shape, and length.
• Relative Relief: Elevation difference influencing gravitational forces.
• Land Use & Land Cover: Vegetation, urbanization affecting infiltration and stability.
• Hydrogeological Conditions: Groundwater presence, seepage affecting pore pressure.

Hazard Classification (Clause 6.7)

Interpretation Guidelines (Clause 7.1)

• VLH & LH: Suitable for development.
• MH: Requires detailed geotechnical investigations.
• HH & VHH: Detailed slope mapping (1:1000 or 1:2000 scale) and mitigation needed.
• Risk assessment based on hazard rating, failure modes (e.g., debris flow, toe erosion), and damage potential.

Preparation Method (Annex A)

1. Slope Facet Maps: Divide study area into slope facets.
2. Pre-field Maps: Transfer geological, morphometric, relief, land use data onto facet maps.
3. Factorial Maps: Validate and prepare individual maps for lithology, structure, slope, relief, land use, hydrogeology.
4. LHZ Map: Combine factorial maps to generate hazard zonation.

flowchart TD
    A[Topographical Map] --> B[Slope Facet Division]
    B --> C[Pre-field Maps]
    C --> D[Field Validation]
    D --> E[Factorial Maps]
    E --> F[LHZ Map Preparation]
    F --> G[Hazard Classification & Interpretation]

Note: Revise LHZ maps after major earthquakes (>5 Richter), floods, cycl

IS 14496 Part 2: Landslide Hazard Evaluation Factors (LHEF) & Rating Scheme

1. LHEF Maximum Ratings for Macro-Zonation (Table 1, Clause 4.1)

2. Detailed Rating Scheme (Table 2, Clause 4.2)

• Lithology (Rock & Soil Types):
  Ratings depend on rock type and weathering correction factors (C1=4, C2=3, C3=2).
  Example:

  • Quartzite & Limestone (fresh): 0.2
  • Granite & Gabbro Gneiss: 0.3 - 0.4
  • Schist: 1.3
  • Shale with clay beds: 1.8
  • Soil types range from 0.8 (older compacted alluvial) to 2.0 (younger loose debris).

• Structure:
  Ratings based on discontinuity-slope relationships:

  • Parallelism between slope and discontinuity dip direction (0.20 to 0.50)
  • Dip of discontinuity vs slope inclination (0.3 to 1.0)
  • Dip of discontinuity itself (0.20 to 0.50)
  • Depth of soil cover modifies rating (e.g., <5m = 0.65, 16-20m = 2.0).

• Slope Morphometry:

  Slope Category	Slope Angle	Rating
  Escarpment/Cliff	>45°	2.0
  Steep slope	36° - 45°	1.7
  Moderately steep slope	26° - 35°	1.2
  Gentle slope	16° - 25°	0.

IS 14496 Part 2: Procedure for Macro-Zonation Landslide Hazard Zonation (LHZ) Mapping

Key Steps (Clause 5.1, Annex A)

1. Desk Study

   • Use aerial photos, satellite imagery, and toposheets.
   • Prepare pre-field maps at 1:50,000 scale:
     • Lithological map
     • Structural map
     • Slope morphometry map
     • Relative relief map
     • Rock outcrop & soil cover map
     • Land use & land cover map
     • Hydrogeological map

2. Field Investigations

   • Validate and modify pre-field maps.
   • Prepare detailed lithological and structural maps.
   • Collect facet-wise data for hazard estimation.

3. Slope Facet Mapping (Annex A-1)

   • Divide watershed into slope facets using topographic maps (Fig. 2 & 3).

4. Factorial Maps Preparation (Annex A-3)

   • Assign ratings to each factor (see Table 2 in the code).
   • Structural discontinuities analyzed via stereonets.
   • Visual stability noted.

5. LHZ Map Preparation (Annex A-4)

   • Assign extra rating (1.0) to 100-200 m strips along major faults/thrusts (Clause 1.0).
   • Combine factorial ratings to classify zones:
     • VLH (Very Low Hazard)
     • LH (Low Hazard)
     • MH (Moderate Hazard)
     • HH (High Hazard)
     • VHH (Very High Hazard)

Hazard Zone Usage (Clause 7.1)

• VLH & LH: Generally safe for development.
• MH: Local unstable pockets; detailed geotechnical investigations needed.
• HH & VHH: Mostly unstable; require detailed slope mapping (1:1000 or 1:2000 scale) and mitigation.

Revision (Clause 9)

• Update LHZ maps after major earthquakes (>5 Richter), floods, cyclones, or significant anthropogenic changes.

Example: Factorial Rating Combination (simplified)

IS 14496 Part 2: Presentation of Results (Clause 6)

Key Points for Presentation of Results:

• Maps are the primary mode of presenting results, showing spatial distribution of parameters facet-wise.
• Prepare Terrain Evaluation Maps first, depicting individual parameters.
• Superimpose these maps to calculate Total Estimated Hazard Degree (TEHD) for each facet.
• Use TEHD values to create a Landslide Hazard Zonation (LHZ) Map with zones:
  • High Hazard (HH)
  • Very High Hazard (VHH)

Suggested Symbols for Slope Morphometry (Clause 6.3):

Procedure for Macro Zonation (Fig. 1 Summary):

flowchart TD
    A[Acquire Topographic Maps 1:50000] --> B[Acquire Aerial Photos & Satellite Imageries]
    B --> C[Acquire Regional Geological Map]
    C --> D[Identify Hazard Evaluation Factors]
    D --> E[Prepare Pre-field Geological Map 1:50000]
    E --> F[Lithological & Structural Map 1:50000]
    F --> G[Slope Morphometric Map]
    G --> H[Relative Relief Map]
    H --> I[Assign Land Hazard Evaluation Factor (LHEF)]
    I --> J[Rock Outcrop & Soil Cover Map]
    J --> K[Land Use & Land Cover Map]
    K --> L[Hydrogeological Map]
    L --> M[Calculate TEHD]
    M --> N[Prepare Landslide Hazard Zonation (LHZ) Map]

References for Symbols and Abbreviations (IS 7422):

• Part 1: Abbreviations
• Part 2: Igneous Rocks
• Part 3: Sedimentary Rocks
• Part 4: Metamorphic Rocks
• Part 5: Line Symbols for Contacts & Structures

Summary: Present terrain and hazard data as layered maps, calculate TEHD facet

Interpretation of Macro-Zonation Landslide Hazard Zonation (LHZ) Map (IS 14496 Part 2)

Key Hazard Zones & Their Meaning (Clause 6.7 & 7.1)

Factors Considered (Clause 7.1)

• Hazard rating based on slope stability
• Modes of failure: boulder jumping, debris flow, toe erosion, choked drainage, gully meandering
• Damage risk to life and property

Preparation Steps (Annex A)

1. Slope Facet Map: Divide topographic map into slope facets.
2. Pre-Field Maps: Transfer geological, morphometric, relief, land use, and hydrogeological data.
3. Factorial Maps: Prepare lithological, structural, slope morphometric, relative relief, land use, and hydrogeological maps; analyze structural discontinuities.
4. LHZ Map: Combine desk study and field data (scale 1:25,000 or 1:50,000).

Revision of LHZ Map (Clause 9)

• Update after major earthquakes (>5 Richter), floods, cyclones, mining, or cloud bursts.

Summary Flowchart of LHZ Mapping Process

flowchart TD
    A[Topographical Map] --> B[Slope Facet Division]
    B --> C[Pre-Field Maps Preparation]
    C --> D[Field Verification & Modification]
    D --> E[Factorial Maps Preparation]
    E --> F[Structural Analysis & Stability Assessment]
    F --> G[Landslide Hazard Zonation Map]
    G --> H[Periodic Revision after Major Events]

Note: Use scale 1:25,000 or 1:50,000 for macro-zonation; detailed slope mapping at 1:100

Revision of Macro-Zonation LHZ Map (IS 14496 Part 2)

Key Specifications:

• Revision triggers: After major events like earthquakes (>5 Richter), floods, cyclones, mining, developmental activities, or cloud bursts affecting the watershed.
• Scale for detailed slope mapping: 1:1000 or 1:2000 for unstable slopes (HH, VHH zones).
• Hazard assessment basis: Hazard rating, failure modes (boulder jumping, debris flow, toe erosion, etc.), and damage type.

Landslide Hazard Zonation (LHZ) Categories (Table 3, Clause 5.3):

Preparation Steps (Annex A):

1. Slope Facet Maps: Divide topographical maps into slope facets.
2. Pre-field Maps: Overlay geological, slope morphometric, relief, land use/cover, and wet patches data.
3. Factorial Maps: Validate pre-field maps; prepare lithological, structural, morphometric, hydrogeological maps; plot structural discontinuities on stereonets.
4. LHZ Map: Combine all factors using LHEF rating to compute Total Estimated Hazard Degree (TEHD).

flowchart TD
    A[Topographical Map] --> B[Slope Facet Division]
    B --> C[Pre-field Maps: Geological, Morphometric, Land Use]
    C --> D[Field Validation & Factorial Maps]
    D --> E[LHEF Rating & TEHD Calculation]
    E --> F[Landslide Hazard Zonation Map]
    F --> G[Revision after Major Events]

This process ensures updated and accurate hazard zoning for safer development and mitigation planning.

IS 14496 Part 2: Detailed Method for Preparation of Landslide Hazard Zonation (LHZ) Map

Key Steps & Specifications:

1. Slope Facet Maps Preparation (Annex A-1)

   • Divide topographical map (1:50,000 scale) into smaller slope facets (1:1,000 or 1:2,000 for detailed study).

2. Pre-field Maps Preparation (Annex A-2)

   • Transfer geological data, slope morphometric, relative relief, land use/cover from topo maps.
   • Use aerial photos/satellite images to identify wet patches and land cover.

3. Factorial Maps Preparation (Annex A-3)

   • Validate pre-field maps in the field.
   • Prepare:
     • Lithological map
     • Structural map
     • Slope morphometric map
     • Relative relief map
     • Land use/cover map
     • Hydrogeological map
   • Use stereonet plots for structural discontinuities and failure modes.

4. Slope Morphometry Classification (Clause 6.3)

   Slope Category	Slope Angle (°)
   Very gentle slope	≤ 15
   Gentle slope	16 – 25
   Moderately steep slope	26 – 35
   Steep slope	36 – 45
   Escarpment/Cliff	> 45

5. Hazard Rating and Zonation (Clause 7.1)

   • Zones: VLH (Very Low Hazard), LH, MH, HH, VHH (Very High Hazard).
   • Detailed geotechnical investigations in MH, HH, VHH zones.
   • Assess hazard rating, failure modes (e.g., debris flow, toe erosion), damage potential.

6. Revision of LHZ Map (Clause 9)

   • Update after major earthquakes (>5 Richter), floods, cyclones, mining, cloud bursts.

Procedure Flowchart (Simplified):

flowchart TD
    A[Acquire Topographic Maps 1:50000] --> B[Acquire Aerial Photos/Satellite Imageries]
    B --> C[Acquire Regional Geological Map]
    C --> D[Prepare Pre-field Geological Map]
    D

Composition of Technical Committee (IS 14496 Part 2)

The Technical Committee responsible for this standard is the Hill Area Development Engineering Sectional Committee, CED 56. The detailed composition is given in Annex B and includes:

Alternates are nominated for many members ensuring continuity.

Key Notes:

• The committee includes experts from government departments, research institutes, universities, and industry.
• This multi-disciplinary composition ensures comprehensive coverage of hill area development and landslide hazard zonation.
• Refer to Annex B of IS 14496 Part 2 for the full detailed list.

Related Reference Table (for geological symbols & maps):

This composition ensures expert inputs for landslide hazard zonation and hill area engineering standards.