Siting In Hilly Terrains-w

SUSTAINABLE ENVIRONMENT

Siting of Human Settlements in Hilly Terrains Amitava Sarkar

India Earthquake Zone Map

Solutions for risk management in hilly regions through Good Siting Practices...

40 ARCHITECTURE - Time Space & People December 2008

or thousands of years, the majestic Himalayan mountain range is looking after India. The Himalayan range has protected and nourished India and is still doing it. India is crowned with hills stretching from Kashmir and Himachal Pradesh in North-West to Arunachal Pradesh and Nagaland in extreme North-East covering the whole of the Himalayan range. These mountains are contributing immensely in the overall development and progress of the coun-

F

try. These Hills have accommodated human settlements of various sizes, which have flourished over the years. The crunch of the situation at present is that these settlements are both growing in number and size. The entire stretch of hilly region has wide variations in geology, geomorphology, climate, altitude and materials resources. The varying geological situations and ongoing development activities, climatic variation, hydro-geological

Damages caused by landslides

conditions result in different types of hazards like landslides, avalanches, mud flows, flash floods which occur frequently

Adverse Human actions affecting hills

in these areas. Among the various catastrophic calamities, these hilly regions also have high risk due to earthquakes.

These areas are prone to seismic activity as most regions fall under seismic zones IV and V. Unprecedented exploitation of the Himalayas is another reason for occurrence of landslides. North, North-West Himalayan areas consisting of Jammu and Kashmir, Himachal Pradesh and Western Uttar Pradesh are more prone to avalanches, earthquakes, floods and high speed winds. Sikkim is highly prone to landslides and seismic activity. North-East Himalayan area consisting of Arunachal Pradesh, Mizoram, Nagaland, Meghalaya, Tripura, Manipur and Assam are mostly affected by floods and fall under seismic zone V. These hilly areas are prone to two or more types of natural calamities, such as floods and landslides, earthquakes, avalanches and landslides. There may be also overlapping of occurances of disasters. December 2008 ARCHITECTURE - Time Space & People 41

CLIMATE IN INDIAN HILLS Hilly regions of the Himalayan range from North-West to extreme North-East fall under cold humid and temperate humid climate. The climatic conditions shall be categorised on the basis of average of daily mean temperature and relative humidity for the month. Temperate 20°C 30°C, cool 15°C -20°C and cold < 15°C temperature, and dry 25-30, humid 50-75 and very humid 75- 100 percent humidity. These hilly regions are having following climatic conditions during the stated months. Month

North

North-East

January May

Cold humid Cold dry

August

Temperate very humid Cold humid

Cold humid Temperate humid Temperate very humid Temperate humid

November

Residential buildings shall essentially be a form of protection against the external climate. The prevailing climatic condition shall, therefore, be a major factor for consideration in design of a house to ensure a reasonable degree of thermal comfort to the occupants. Traditionally, house facing the east direction are preferred by the inhabitants in North and North-East regions of the Himalayas due to exposure to sunlight.

BASIC GUIDELINES OF SUSTAINABLE GROWTH All the developmental activities in hilly areas must be done in an integrated manner with the existing settlement structure of the surroundings resulting into a coherent and sustainable growth. Through proper guidelines, the concerned agencies must ensure: • Selection, Planning, Designing and Use of Appropriate Sites for Specific Purposes / Activities to stimulate Sustainable Development and Safer Human Habitat. 42 ARCHITECTURE - Time Space & People December 2008

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•

•

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Enacting Roles & Responsibilities of Professionals, Builders, Homeowners and Authorities Creation of scientific databases through investigations and mapping at local level for zonation practice & landuse regulation for sensitive areas. Timely Technological Intervention and Counter-disaster measures in hazardous situations for effective risk management solutions. Siting as a compulsory part of an integrated building design process.

The Development authorities should, • Regulate Land-use through Microlevel Hazard Zonation Studies to minimise risks due to natural hazards and physical vulnerability. • Discourage casual approach and encourage systematic siting, construction and maintenance approach. • Restore and Rejuvenate degraded, abandoned and waste lands. Guidelines are recommended actions for best practices to achieve better goals but not mandatory to follow. Standards and codes are mandatory to follow to avoid any techno-legal implications.

GUIDELINES FOR SITING Siting guidelines refers to searching, selecting, evaluating, planning, designing, development, maintenance and monitoring of sites for safe and sustainable landuse through micro-level site investigations & zonation practices. Integrate physical, ecological and environmental elements with development process and also consider the potential slope instabilities and failures. • No house shall preferably be located closer than 1 m to another house. • No house shall preferably be located closer than 10 m to a steep slope. • No house shall be built on a land fill or on the edge of a slope known to have been levelled.

Following points shall be kept in view with reference to particular risks. Earthquake • Available data on disposition of faulting and spread of poor bearing soils and unrestrained sands should be used. • Narrow ridges, steep slopes, narrow valleys and sites near cliffs or large gullies that are within 150 m should be avoided. • Sites with hard bedrock at or near the surface should be preferred. • Sites where landslides are unknown in surrounding area should be preferred. • Sites where there is no sign of active faulting should be chosen and offset rock lays, row of ponds or swamps and deep or long cracks in ground should be avoided. Landslides • All available data on disposition of risk area should be used. • Local geographical conditions shall indicate severity of risk. Snow avalanches • Use all available data on disposition of risk area. Heavy snow fall may be associated with heavy rains. • Prefer sites away from avalanches sites. • Avoid formation of snow pockets on roof and on site. • Design roofs with slopes greater than 50º to disregard snow load.

GOOD SITING PRACTICE •

•

Advantage of natural site features such as topography, geology, hydrology, sunlight / shade, breeze, existing landuse, landcover & infrastructure should be utilised. Integrate the building architecturally into natural context of site,

• •

• • • • • •

which minimize the appearance and aesthetic views. Minimize site clearing, excavation and earthworks to reduce costs. Preserve existing vegetation, which can reduce landscape maintenance costs. Mitigate erosion to reduce topsoil loss. Manage for stormwater runoff and erosion. Minimize groundwater and surface water pollution. Minimize disturbance to natural drainage & hydrological system. Reduce the risk of natural hazards through prevention & mitigation. Investigate ground conditions before planning design & construction.

Many a times design opportunities emerge from the existing site constraints. In order to exploit the full potential of the site the inventory and analysis of following features should be made: • Proximity to hazardous areas / sensitive / critical areas. • Topography & Slope Conditions (gradient, aspect etc.). • Geology & Geomorphology. • Neotectonics, Active Tectonics & Paleo-Seismicity. • Seismological records and historical data. • Meteorology, Micro-climatology & Hydrogeology. • Vegetation / Landcover. • Existing & Proposed Infrastructure.

• •

Existing structures and Adjacent Landuse. Easements, views.

INVESTIGATION OF SITES Investigation of sites must be carried out by conducting thorough field observations & Mapping and by collecting samples of soils from the site for laboratory and in-situ testing. All data thus collected will be integrated for computations, analysis and inferences. Following information will be generated from the site-investigation: ■ Preparing Engineering Geologic Mapping: Topographic Maps, Aerial Photos, S a t e l l i t e I m a g e r i e s a n d Fi e l d Observation / Data.

The site constraints in Hill areas December 2008 ARCHITECTURE - Time Space & People 43

Conducting Field Survey ■

Conducting Laboratory Tests: M a t e r i a l C l a s s i f i c a t i o n ( D e n s i t y,

Examples of Good Hillside practice 44 ARCHITECTURE - Time Space & People December 2008

Compressibilty, wave velocity etc.) and Characterization for engineering

design & evaluation of landslide / liquefaction / settlement potential in adverse conditions; Repor ting Sampling & Testing Procedure; Data, Results & Interpretation ■ In-situ / Field Testing: Geophysical (cross hole, down hole, GPR, Resistivity) Geotechnical: Surface & Subsurface (SPT, CPT, Shear Wave Velocity etc.) ■ Computations: Integration of all data / information (creating the GIS), Analysis and Inferences ■ Producing Professional Reports with comments and Peer review of Reports. An integrated ground – structure (foundation and superstructure) – hazard interaction analysis should be carried out by

conducting Site-response analysis based on - conditions for Ground Failures and Slope Stability Analysis in adverse conditions (considering high seismic accelerations and pore water pressures). Also the Structural Response Analysis (Vulnerability) will be carried out based on Performance based fail safe / safe failure analysis. The Frequency, Magnitude & Duration of all Hazardous events must be listed down for consideration. Along with the above mentioned analytical data, the information regarding the Risk Assessment, Mitigation Measures, Maintenance & Monitoring, Warning & Alert, and Preparedness & Emergency Response with respect to the location of the settlement should be obtained for safety.

Good Practices to avoid Landslides

Examples of Poor Hillside practice December 2008 ARCHITECTURE - Time Space & People 45

MICROLEVEL LANDSLIDE HAZARD ZONATION FOR LANDUSE REGULATION AND DEVELOPMENT OF SAFER SETTLEMENTS The topographical map of the study area is obtained and divided into smaller segments of slope facets. On the slope facet map, a number of the pre-field maps are prepared so that these can be carried to the field, verified and modified wherever required. The geological data from the already available regional scale maps are collected and transferred on the facet map. The slope morpho-metric map and the relative relief map shall be prepared from the topographical maps. The available information regarding land use and land cover from the topographical maps shall also be transferred to a slope facet map. If aerial photographs or satellite imageries of the area are available, more accurate data on land use and land cover can be obtained. The wet patches on the slopes shall be identified using satellite imageries or aerial photographs and the same shall be transferred on a slope facet map for field validation. The pre-field maps are carried to the field and they are validated facetwise. While working on one bank of the river, the facets on the other side are also carefully observed. Using data from the Standards, individual factorial maps namely lithological map, structural map, slope morphometric map, relative relief map, land use and land cover map and hydrogeological map are prepared. For awarding ratings on structures, the observed structural discontinuities are plotted on stereonet and the preferred orientation as well as possible types of failures is also obtained. Moreover the visual stability conditions may be noted for comparison after analysis. The LANDSLIDE HAZARD ZONATION (LHZ) map is prepared by calculating 46 ARCHITECTURE - Time Space & People December 2008

A Typical map of the study area the total estimated hazard (TEHD) by adding the ratings of all the causative

factors within a facet using the following Table.

Landslide Hazard Zonation on the Basis of Total Estimated Hazard (TEHD) Zone I II III IV V

TEHD Value <3.5 3.5 to 5.0 5.1 to 6.0 6.0 to 7.5 >7.5

Description of Zone Very low hazard (VLH) zone Low hazard (LH) zone Moderate hazard (MH) zone High hazard (HH) zon Very high hazard (VHH) zone

A typical Slope Morphometry map Major roads, important towns and villages shall also be shown on the final LHZ map for the purpose of regional planning.

CONCLUSION Impact of Road Construction, Deforestation, Mining, Shifting Cultivation, Forest Fires / Wild Fires, Overgrazing, Dams / Reservoirs / Irrigation / Water Supply /Sewerage Systems, Power & Telecommunication Lines, Blasting Activities (mining, road, hydel etc.), heavy machinery – all these activities endanger building-safety in

Landslide Hazard Zonation Map for the study area hill-regions. For the integrated and sustainable socio-spatio-economic development of the hill regions in India the requisites, roles, responsibilities & liabilities of the professionals, authorities, builders and homeowners involved must be ensured. Professionals, Builders and Contractors must have the necessary qualifications & experience to carry out the construction activities in the hilly areas. The Scientists, Engineers and Decision makers must be trained and made aware of all the guidelines applicable in the hill regions. Building

Permit Regulations must be enforced for Development Control, Public Awareness and Education on Landslide Management Strategies. The individual homeowner’s must be also made aware of their obligations and responsibilities to avoid any disaster and casualty by training them through demonstration about the good practices of construction in hill terrains. Techno-legal & Techno-financial aspects like, Building Loans, Tax Reliefs, Insurance Premiums, Incentives, should be used to attract the local people to adopt the good and safe construction practices. It should December 2008 ARCHITECTURE - Time Space & People 47

to retain the beauty, glory and sanctity of the Hills, which are treasures of India and also the universe at the larger context.

REFERENCES

Construction on Slope be clear from the above discussions that all the stakeholders involved in the developmental activities in the hilly

region must carry out their duty by taking a holistic approach towards their action and must always be sensitive

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National Building Code 2005

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IS 14496 (Part 2):1998 Guidelines for preparation of landslide – Hazard zonation maps in mountainous terrain: Part 2 Macro Zonation

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IS 14680:1999 Guidelines for Landslide Control IS 14804:2000 Guidelines for Siting, Design and Selection of Materials for residential buildings in Hilly Areas

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BMTPC, New Delhi

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Amitava Sarkar is a Lecturer, Architecture Department, NITHamirpur (H.P.) Photographs: Cour tesy the Author.

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