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Landslides at Karwar, October 2009 : Causes and Remedial Measures
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Annexure I: Report of the Department of Mines and Geology

BRIEF REPORT ON STUDIES OF LANDSLIDE AROUND KARWAR, UTTARA KANNADA DISTRICT.

ABSTRACT : Landslides usually occurs during the monsoon seasons along the hill slopes of  Western Ghats.  These are one of the natural disasters endangerous to life and property.  The present study is aimed to know the cause of landslides.  Field visit was conducted  around the landslide areas. It revealed that the factors which caused the landslides are: slopes, landuse, lithology, structures, climate, geomorphology and soil.  Field investigation was carried out during 13.10.2009 to 14.10.2009.  During the course of investigation number of landslide occurred areas were examined.

INTRODUCTION : Landslides are simply defined as the mass movement of rock, debris or earth down a slope and have come to include a broad range of motions whereby falling sliding and flowing under the influence of gravity dislodges earth material.  They often take place in conjunction with earthquakes, floods and volcanoes.  The objective of the present study is identification of landslides areas around Karwar taluk of Uttara Kannada district.

STUDY AREAS :

  1. The Kadwad (Zariwada) area lies between 75o05’35” to 75o10’45” East longitudes to 14o46’10” to 14o50’55” North latitudes falls in the survey of India toposheet No. 48 J/1 of 1:50,000 scale.
  2. The Kadwad (Near Forest Naka)  area lies between 74o10’47.6”  East longitudes to 14o49’59.2” North latitudes falls in the Forest Sy.No.71 A1A1.
  3. The Shirwad  area lies between 74o09’22.7”  East longitudes to 14o48’38.7” North latitudes falls in the Forest Sy.No.230.
  4. The Mandralli  area lies between 74o10’57.3”  East longitudes to 14o50’50.2” North latitudes falls in the Forest Sy.No.269.
  5. The Makeri  area lies between 74o10’17.6”  East longitudes to 14o49’21.8” North latitudes falls in the Forest Sy.No.47.
  6. The Makeri area lies between 74o10’17.5”  East longitudes to 14o49’15.5” North latitudes falls in the Forest Sy.No.47.
  7. The Makeri area lies between 74o10’17.5”  East longitudes to 14o49’15.3” North latitudes falls in the Forest Sy.No.47.
  8. The Baad (Murlidhramath) area lies between 74o08’13.2”  East longitudes to 14o48’25.1” North latitudes falls in the Forest Sy.No.47.
  9. The Baad (NH 17) area lies between 74o07’22.4”  East longitudes to 14o48’14.5” North latitudes.
  10. The Binaga (NH 27) area lies between 74o06’53.5”  East longitudes to 14o47’26.2” North latitudes falls in the Forest Sy.No.16A.
  11. The Binaga (NH 17) area lies between 74o06’59.0”  East longitudes to 14o47’27.9” North latitudes falls in the Forest Sy.No.16A.
  12. The Binaga (NH 17) area lies between 74o08’10.0”  East longitudes to 14o46’53.9” North latitudes falls in the Forest Sy.No.9A.
  13. The Arga (NH 17) area lies between 74o08’29.2”  East longitudes to 14o46’58.9” North latitudes falls in the Forest Sy.No.52A.
  14. The Arga (NH 17) area lies between 74o08’29.2”  East longitudes to 14o46’58.4” North latitudes falls in the Forest Sy.No.52A.
  15. The Arga (NH 17) area lies between 74o08’43.1”  East longitudes to 14o46’53.4” North latitudes falls in the Forest Sy.No.52A.
  16. The Arga (NH 17) area lies between 74o08’47.3”  East longitudes to 14o46’51.2” North latitudes falls in the Forest Sy.No.52A.
  17. The Baithkhol (Near Port) area lies between 74o06’49.7”  East longitudes to 14o48’13.3” North latitudes falls in the Forest Sy.No.16.
  18. The Baithkhol (Near Port) area lies between 74o06’49.3”  East longitudes to 14o48’16.1” North latitudes falls in the Forest Sy.No.16.
  19. The Baithkhol (Near Port) area lies between 74o06’47.9”  East longitudes to 14o48’16.5” North latitudes falls in the Forest Sy.No.16.
  20. The Baithkhol (Near Port) area lies between 74o06’50.8”  East longitudes to 14o48’09.8” North latitudes falls in the Forest Sy.No.16.
  21. The Baithkhol (Near Port) area lies between 74o06’49.8”  East longitudes to 14o48’07.5” North latitudes falls in the Forest Sy.No.16.

PHYSIOGRAPHY : Study area forms a part of Western Ghats comprises of hilly terrain .  The hilly ranges having elevation from 65 mtr. to 552 mtr. above mean sea level.

DRAINAGE : Study area No.1 comprises of camping denetritic pattern.  Northern part of the drainage joins Kali River.  The other areas comprising denetritic drainage. These drainages joins valleys and Sea.

ROAD NETWORK : A study area contains a well laid road network connecting different parts of Karnataka State.

LANDSLIDE AREAS :   Landslide is noticed in several parts of the Karwar taluk.  The region where rock and debris fall are noticed around Arga village limits.  In the Baitkalgudda, earth flow in larger quantity is seen, causing sea food loss (Fishes). Major landslide was noticed at Kadvad village to the northeast of Karwar, where 8 to 9 houses were washed with earth flow causing 21 deaths of humans.

FACTORS FOR LANDSLIDES : Important factors that caused landslides are: Slope, landuse, litholoty, structure (joints, faults, etc.), climate (Rainfall), geomorphology (Weathering), and soil and man made causes like: excavation (Particularly at the toe of slope), loading of slopes crest, draw down (of reservoir), deforestation, irrigation, mining / quarrying, artificial vibrations, water impoundment and leakage from utilizes. An overall evaluation of the pattern  and nature of  landslide occurrences around karwar taluk of Uttara Kannada District reveals the following.

  1. Almost all mass movements occur during monsoon.
  2. There seems to be a relation between intensity of rainfall and slope facilities.
  3. Majority of the catastrophic mass movement is confined to the overburden.
  4. Improper landuse practices such as agricultural practices and settlement patterns have contributed to creep and withdrawal of toe support in many cases.
  5. A common factor noticed in most of these vulnerable slopes deforestration in the recent past, cultivation and increase in settlements.
  6. In some areas developmental activities like construction of buildings, road cutting, embankments, cut and fill structures caused modification of natural slopes, blocking of surfaces drainage, loading of critical slopes and withdrawal to toe support promoting vulnerability of critical slopes.

SOME MITIGATIONS FOR LANDSLIDES :   In general, the important mitigatory measures to be adopted for such areas are:

  1. Drainage correction;
  2. Proper land use measures;
  3. Reforestation  for the areas occupied by degraded vegetation;
  4. Creating of awareness among local population.

CONCLUSION :    The most important triggering mechanism for mass movement is the water infiltrating into the overburden during heavy rains and consequent increase in pork pressure within the over burden.  When this happens in steep slopes the safety factor of the slope material gets considerably reduced causing it to move down.  Hence natural way of preventing this situation is by reducing infiltration and allowing excess water to move down without hindrance.  That is the drainage correction. As many as 25 land slides have taken place in Uttara Kannada District, on the particular date, i.e., 2nd October 2009, such a large scale land slide points to an after effect of possible mild tremor in the area.  Hence the seismic data particularly from 1st October to 3rd October 2009 is to be collected from Bhabha Atomic Research Centre to understand, whether there is any tremor on these days.  Based on that data, further studies can be taken up. The afforestation programme should be properly planned.  The selection of suitable plant species should be such that can withstand the existing stress condition in their study area.

Move to Annexure II