FOUR SPATIAL PATTERIS OF LAMDSLIDE DISTEIBUTIOI CHAPTER FOUR Spatial Patterns of Landslide Distribution 4.1 Introduction Slope failures are common in Western Ghats and undulated Konkan plains of Maharashtra. Western slopes of Western Ghat escarpment and slopes of isolated hills in the central uplands are prone to slope failures of varying magnitudes. The undulating topographical features in this area combined with heavy monsoon rainfall in this area cause landslides along major communication routes during monsoon season that is from Jime to September. Landslides along major communication routes cause losses to the man-made structures, vegetation cover, vehicles, agricultural land and sometimes even to lives of commuters. One of the catastrophic landslide episode recorded in the month of July 2005, in village Jui near Mahad claimed 95 deaths followed by over hundred fatalities around Mahad town of Raigad District (The Times of India; July 27, 2005). Another major landslide event in Malshej Ghat on 25* July 2013 blocked the Ghat road for over eight days (Times of India; 27* July 2013). Pune - Mumbai expressway, one of the busiest roadways in India is affected by landslides almost every year near Adoshi tunnel (Kumar, et.al 2010). The data obtained from Times of India news archives reveals that 89 landslide events reported during 2004 to 2014 in the study area claimed over 331 lives and many more injured (Table 4.1). Table 4. 1 Details of damage caused by landslides in North Konkan (2004 -2014) No. of reported No. of No. of people Year landslides fatalities injured 2004 10 0 0 2005 10 279 21 2006 3 1 2 2007 4 2 7 2008 4 0 0 2009 4 15 29 2010 5 14 10 2011 6 1 3 2012 11 2 40 2013 19 14 14 2014 13 3 9 Total 89 331 135 (Source: Time of India News paper Archives) 79 In India, landslide disaster management activities are associated with post disaster rescue and rehabilitation. However, little attention is paid to assess landslide hazards for finding out effective mitigation measures to minimize impact of slope failures. In fact, significant amount of losses due to slope failures can be reduced if they are predicted well in advance (Brabb, 1993). Therefore, Landslide hazard assessment at various spatial scales is necessary for sustainable landslide hazard management. Preparation of complete landslide inventory with considerable details is the primary requirement for effective landslide hazard assessment. Detailed landslide inventory requires mainly the data inputs such as, location of landslide, date of the event, frequency of landslides, causes and type of mass movement (van Westen, 2006). Past landslide records, multi-temporal satellite images, aerial photographs and newspaper archives are proven database for preparation of landslide inventories. Landslide inventory provides necessary database for Landslide Hazard Zonation mapping. Complete and reliable landslide inventories provide necessary database for identification of landslide prone areas and also for evaluation of validity of LHZ models. This chapter describes landslide inventory, that is spatial and temporal patterns of landslide distribution in North Konkan using past landslide records and field investigations. The relationship between distribution of landslides with slope, elevation, drainage, geology and rainfall data is established to determine the role of geo-environmental parameters in slope instability in the study area. 4.2 Methodology This section of the study focuses on the assessment of spatial and temporal patterns of landslide distribution in North Konkan using past landslide records and field investigations. Past Landslide data were obtained from Public Works Department Government of Maharashtra, Disaster Management Cell, National Highway Authority of India (NHAI) subdivisions. Times of India news archives for the period of eleven years from 2004 to 2014 (Table 4.2). The sites of slope failures along major roads were visited and data pertaining to landslide location, slope angle, and landslide type have been recorded in the field using Global Positioning System (GPS), Laser 80 distance meter and measuring tape. Besides slope failures along the roads, few landslides located in the interior areas have been identified using data from news paper archives. The identified landslide sites were visited and discussion with local people was carried out for confirmation. Subsequently, the landslide data are plotted using Google Earthpro and Road Development Plan (2001-2020). The annual and monthly landslide frequency is obtained usuig temporal data of landslides. The annual and monthly landslide frequency is compared with rainfall data to establish relationship between rainfall and landslide occurrences. Based on the data obtained from government offices and observations recorded during field investigations, major zones of landslide concentrations are identified and mapped. The spatial distribution of landslides in the study area is compared with lithology, slope, aspect, elevation and zones of structural discontinuities (faults and lineaments). Besides, an attempt has been made to identify the role of human interventions in slope instability process along major communication routes. Land use and land cover is also compared with spatial distribution of slope failures to know the effect of land use. Land cover is also compared to understand any effect of it on occurrence of slope failures or vice versa. The details of the methodology adopted are given in Fig. 4.1. 81 METHODOLOGY Landslide Distribution Map (preliminary landslide prone zones) Google Earth Images and Road Development Plan (2001-2020) Digital Elevation Model (SRTM and ASTER) Relationship between Rainfall Data Monthly rainfall and landslide frequency (IMD) no. of rainy days and rainfall Results Fig.4. 1 Methodology Flow chart 4.3 Spatial patterns of Landslide distribution Assessment of spatial patterns of actual and potential landslides is an important step in Landslide Hazard Assessment (LHA). Past landslide records and field survey are proven data sources for landslide studies (Jaiswal et al. 2010). For the present study landslide affected areas have been identified using past landslide records of Technical Survey register (TS register) of Public Works Department, Natural Disaster report of National Highway Authority of India (NHAI), News paper archives and Disaster Management Cell (DMC of Thane Municipal Corporation). The data obtained from these government offices have been supplemented with the field survey. The details of landslide locations provided by PWD have been identified and confirmed by using GPS locations and road chainage. A total of 199 actual landslide affected locations were visited during field work and data related to landslide scar geometry were recorded in the field. 82 Table 4. 2 Landslides in North Konkan (2004-2014) areas / roads > • >> 5 > Year 1 Z u o .£3 H H X! 2004 08 11 DNA DNA 10 DNA 10 DNA 33 62 2005 48 DNA 14 DNA DNA 32 15 91 47 251 2006 0 07 14 DNA DNA 13 06 45 11 96 2007 0 02 46 DNA 01 100 07 46 19 221 2008 0 03 36 DNA 02 18 0 14 04 77 2009 01 01 11 01 01 35 04 15 02 71 2010 01 0 35 01 0 26 64 10 0 137 2011 0 0 09 05 01 19 22 25 01 82 2012 04 0 04 04 01 17 03 0 0 32 2013 01 01 08 01 0 18 01 0 02 32 2014 0 01 01 0 03 01 0 02 01 09 Total 63 26 178 12 19 279 127 248 120 1072 (Source: Public Works Departments, National Highway Authority of India, India Meteorological Department, Times of India news paper archives) North Konkan is a part of Konkan and is one of the three major landslide prone areas in south Asia (SDMA, 2007) and is susceptible to landslides of different magnitudes. 83 73°30'0"E z b b. a> V^'ITCS V^^ LS_prone areas (PWD DataM .\l|d^/•'Wp/7 T A LSJocations (field data) fX \' '•^TJSL^aiV *S»- ^—^ Expressway 1 T^NI J^^-^^Jl^^ ' l/'i State Highway ^ ''^^km\^ ^*^k'^'^rt\ National Highway JWVw''^*Vnr OaK^^^V Elevation (m) r ANL^A^^ '^^V^ll^rjii^^ < 250 MHattiKaCLiSA^jr^v 1 Z N b b- H 250-500 ^xJr ^^^^f <9-'?»IW co )• 500-750 '5-5^ 'w^T^^^r ^1 750-1000 \ <Mi^mry'' A N. ^iF^^ 0 10 20 40 Km >1000 ^v.^ ^^^ 1 1 1 1 1 1 Boundary 73°30'0"E (Source: SRTM DEM, Field Survey) Fig.4. 2 Distribution of slope failures in North Konkan region 84 North-Konkan is susceptible to slope failures of different magnitude Most of the reported landslides in the study area are confined to the western slopes of Western Ghats escarpment, slopes of isolated hillocks in the central uplands and along the edges of low level plateaus (Fig. 4.2). The records of past landslide events show significant variation in their distribution pattern (Table No. 4.2). Major concentrations of landslide affected locations in North Konkan are: 1) Daberi- Behedpada circle 2) Khodala area (Devbandhar) 3) KasaraGhat 4) Parali-Ujjaini Road 5) MalshejGhat 6) Kalwa_Mumbra 7) Pune-Mumbai-express way (Khandala section) 8) Neral Matheran Road 9) SukeliPass 10) Shrivardhan-Shekhadi Road 11) VarandhGhat 12) Mahad circle 13) Poladpur circle 4.3.1. Dhaberi-Behedpada circle This area is located in the N.E comer of the study area. Administratively the area is in Mokhada Tehsil. This area is marked by highly dissected topography several landslides locations have been identified along SH-28 Debris slump and Debris slide are common types of slopes failure where as wedge failures are also observed at places. This area is covered with the oldest basaltic formation (Salher) and classified as Magacryst flow. A major landslide with run out distance of 500 meters is observed near Behedpada village which destroyed agricultural field, a well and few hamlets in July 2005. Steep slopes (25°), heavy rainfall barren upper slopes and slope cutting for road construction are major landslide factors in this area.