Field Mapping Introduction. Field Mapping. Steven Williamson Maunsell Aecom

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Bridget May
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1 A Practical Guide to Natural Terrain Hazard Studies Field Mapping Steven Williamson Maunsell Aecom Field Mapping Introduction Purpose Scope Site Reconnaissance Detailed Mapping Approaches Difficulties and problems Summary

2 Purpose of Field Mapping Validate API and/or Desk Study Findings Collect Field Data/measurements Facilitate an assessment of natural terrain hazards within catchment with reasoning/justification based on direct evidence and observations of features including: Landslide Drainage lines Depressions Breaks in slope Regolith vegetation Scope of Field Mapping Work Depends on nature of project. For typical Site/Catchment Specific NTHS (e.g. LPMit) Site/Catchment Specific Natural Terrain Hazard Review (NTHR) (Regional/Area Scale NTHS) Field Reconnaissance Site/Catchment Specific Natural Terrain Hazard Assessment (NTHA) Detailed Field Mapping

Purpose of Field Mapping Area or Regional NTHS Field Reconnaissance Detailed Field mapping Design verification mapping Desk study and Field Reconnaissance Determine whether further

Determine the mitigation options INPRINCIPLE OBJECTION Hazard Severe DEVELOPMENT PROPOSAL INITIAL SCREENING Study Required? REVIEW (NTHR) Further Study Required?

138 No No No SITE PLANNING STAGE FEASIBILITY STAGE ASSESSMENT STAGE Detailed design for the preferred mitigation strategy based on quantified hazards MITIGATION STRATEGY (NTHM)

3 Purpose of Field Mapping Area or Regional NTHS Field Reconnaissance Detailed Field mapping Design verification mapping Desk study and Field Reconnaissance Determine whether further study is necessary Determine the nature (type) of hazard Detailed Field Mapping Specify GI as necessary for design event Quantify the design event Natural Terrain Hazard Study (NTHS) Determine the mitigation options INPRINCIPLE OBJECTION Hazard Severe DEVELOPMENT PROPOSAL INITIAL SCREENING Study Required? REVIEW (NTHR) Further Study Required? ASSESSMENT (NTHA) Mitigation Measures Required? Yes Yes Yes To be carried out in accordance with Section 1.5 of GEO Report No. 138 No No No SITE PLANNING STAGE FEASIBILITY STAGE ASSESSMENT STAGE Detailed design for the preferred mitigation strategy based on quantified hazards MITIGATION STRATEGY (NTHM) DESIGN STAGE Specify GI as necessary for construction Site Reconnaissance (1) Overview of (whole) site and adjacent study area Use best available vantage point, e.g.: Building Access to roof Ridge line Spurline view across catchment in profile Roads and footpaths

Site Reconnaissance (2) Traverse upslope boundary of catchment/study area.

stream courses or in small cuts along the site boundary, or boulder clusters May give

orthorectified base plans to map onto use at suitable scale to map/measure features

4 Site Reconnaissance (2) Traverse upslope boundary of catchment/study area. :look for processes that may affect the site such as thick colluvial lobes exposed in stream courses or in small cuts along the site boundary, or boulder clusters May give some indication to potential magnitude and frequency of landslide events Use of orthorectified base plans to map onto use at suitable scale to map/measure features directly on plan If air photos not available then photos taken from tall building or helicopter can sometime be orthorectified

. may be overlain with recent ortho photos to enhance reading of terrain Use of 3D plans

5 Use of 3D plans to visualize terrain and processes, to give feel for setting whilst mapping.. may be overlain with recent ortho photos to enhance reading of terrain Use of 3D plans to visual terrain and processes, may be overlain with photos in this case 63 If available use LiDAR plans which at appropriate contour resolution can give enhanced terrain perception

Field Mapping Approaches Traversing hillsides and access to drainage lines

Limited vegetation clearance to access key features Use of safety ropes

colluvium and saprolite 60 45 sheeting joint controlled granite slabs

6 Field Mapping Approaches Traversing hillsides and access to drainage lines Location from API, survey points or distinctive landforms Use of machete Limited vegetation clearance to access key features Use of safety ropes Cliff area Source Colluvial lobe with large, undercut boulders Erosion of colluvium and saprolite sheeting joint controlled granite slabs Ephemeral drainage line Steep rock slope Debris transported over colluvium and saprolite

7 Access and location Often terrain will be densely vegetated. Use API and desk study (or review report) to focus traverses within terrain. Some access paths may be necessary Location may be difficult for mapping. Survey markers or GPS may help where no suitable surface features exist Drainage lines

8 Field Mapping Approaches Measurement of drainage line characteristics Use of survey rod Clinometer Laser distance measurer Reel tape Hip Chain 1993 About 40 squatter structures within the September Lei Pui St debris flow path! Debris trail Former quarry site

9 Distress/disturbance Source floor 100 mm Sandy infilling Fractured moderately decomposed granite rock mass adjacent to sheeting joint surfaces Field Mapping Detailed MappingApproaches Base of cliff Debris transported over colluvial lobe Eroded edge of colluvial lobe Granite bedrock Abraded Saprolite Colluvial Accumulations

Field Mapping Equipment Slope angle measurement Hand held

Measurer Difficult access/dense vegetation Machette Walking

Rock outcrop steps Irregular drainage lines Practical

10 Field Mapping Equipment Slope angle measurement Hand held Clinometer Distance measurement Hip Chain Laser Distance Measurer Difficult access/dense vegetation Machette Walking Rope Field Mapping Problems & Difficulties Steep Terrain Rock outcrop steps Irregular drainage lines Practical Issues Summer heat clothes, water, time of day Access Flora and fauna

11 Thank You

Geomorphology and Landslide Hazard Models

Geomorphology and Landslide Hazard Models Steve Parry GeoRisk Solutions Key component of interpreting geomorphology and therefore hazard at a site is the use of API The purpose of this talk is not to try