SECTION 6 :
PREVENTION AND MANAGEMENT OF LANDSLIDES

Experiences in Japan, Hongkong, and USA, has shown that proper management of slopes on sound scientific principles can lead to mitigation of landslide hazard to a large extent

Drainage correction: The most important triggering mechanism for landslides is the water infiltration during heavy rains and consequent increase in pore pressure within the overburden. Poor drainage density in heavy rainfall areas has been correlated to higher landslide incidence. This is due to less surface runoff, which results in high infiltration and increased pore-water pressure (Kumar, 2005). The author has identified more than 250 cm of annual average precipitation in the Western Ghats of central Kerala as a triggering factor for landslides in the region. Hence the natural way of preventing this situation is by reducing infiltration and allowing excess water to move down without hindrance. As such, the first and foremost mitigation measure is drainage correction. This involves maintenance of natural drainage channels both micro and macro in vulnerable slopes. Drainage channels should be identified in all vulnerable areas, properly widened if necessary and pavements built wherever strengthening is required.

Regulations on building constructions: In all identified, potential hazard zones no fresh permission should be granted for construction of new buildings, at least until such time when foolproof safety measures are implemented.

Engineering solutions: Remedial techniques such as buttresses, shear keys, well designed surface and sub-surface drains, soil reinforcement, retaining structures along the toe of the hills, etc. to be adopted in existing and potential landslide areas.

Landslide hazard zonation maps: LHZ  mapping, at 1:50,000 scale, has been carried out for parts of Western Ghats. A micro-level geological and landslide zonation mapping at 1:1000 scale is necessary for all potential hazard zones. The methodology has been already evolved through participation of various scientific-technical institutions by the Department of Science and Technology, Government of India, under the Natural Resources Data management System. Karwar taluk hills with habitations and roads needs to be delineated into high hazard, moderate hazard and landslide  free zones.

Study needs: More attention needs to be paid to some critical aspects of landslide studies. These studies with micro-level focus on geotechnical aspects and soil mechanics need to be specially be carried out for all apparently vulnerable areas of Karwar taluk. Slope stability analysis needs to be carried out for all hillside human habitations of the taluk. In co-ordination with landuse zonation maps and carrying capacity studies it would be possible to better planning for the taluk to prevent and mitigate landslide hazards. Various terrain parameters to be studied for landslide risk evaluation, estimation, assessment and management using geoinformatics.

Restoration of vegetation cover: Post disaster studies on bio-restoration have been proposed by the Geological Survey of India for overburden slopes (http:www.gsi.gov.in/landslide/postdis.htm). All the landslide areas, although they appear to be covered with a mantle of vegetation, have extremely poor tree cover. The hills of Kadwad are almost bereft of any notable trees except for poorly grown cashew. A replanting programme should be undertaken, preferably using also the soil spread area after the landslide. Soil removal from the landslides of Kadwad has to be minimal, so as to provide a healthy and raised surface for afforestation. Only very site specific and erosion and water logging resistant trees should be used for afforestation of the lower parts of Zariwada landslides. These could be mangrove species for the soil spread close to the brackish water swamps. Mangroves are very tolerant of water logging and salinity. Their efficient root systems will protect any further rush of loose soils into the Kali River estuary.

At next higher level may be planted in alternative rows mangrove associates. Some of these associates like Pongamia pinnata (Hongay), and Ficus racemosa (Atthi) are tolerant of water logging as well as desiccation. Their efficient root systems enable them to grow close to water courses and can tolerate periodical rise in water levels and strong currents. These trees would provide excellent binding for loose soils and can be planted at any height in the denuded hills. Calophyllum inophyllum, is also an excellent tree for planting at the lower slope of the hill. As it is a large and heavy tree when full grown, it should not be used for upper slopes and hill tops. It cannot also stand the dryness of the hill top during summer months. Planting of all large sized tree species in the upper slopes and summit should be avoided so as to minimize the weight on the hill to avoid any gravity triggered  landslide in future. Under proper management and absolute protection in about ten years time the hill could covered with reasonably good vegetation, specially designed for landslide prevention. The Baithkol hill also should be brought under proper vegetational cover almost on the same lines as Kadwad hills.

The hills bordering the NH-17 are presently under poor cover of trees. Most plants there are shallow rooted shrubs, climbers and bamboos. These surface rooted plants cannot stabilize the hill slopes efficiently. There should be minimum of 400 hundred trees/hectare on these hills, whereas at present hardly 50 trees/ha are found here. The basal area/ha is much less than 10 sq.m, whereas what is ideal would be over 25 sq.m/ha. It is notable that landslides have taken place only in those hills bordering the NH-17. It should be therefore borne in mind that the landslides are the result of general deforestation and unscientific slope cutting for the sake of road. The interior hills, though under biomass extraction pressure from coastal people, still have adequate tree numbers and biomass to stabilize their slopes. A choice of native leguminous trees and pioneer evergreens could be considered for revegetation. Revegetation has to be carried out with site specific plans and not by any centralized designs.

Regulation of human activities in sensitive and buffer zones: Many studies point out human activity in unfavourable slopes is the real causative factor triggering landslides. Buffer zone areas are to be identified between steep hill slopes and human settlements at the toe of the slopes. Awareness programmes on landslides may be conducted for the inhabitants here especially highlighting the aspects of care that they need to take of the buffer zone, such as: participation in vegetational development; desist from toe cutting for expansion of holdings; hazards of soil removal from sensitive slopes. The District Administration should not permit soil or stone quarrying from sensitive slopes and buffer zones. Any new developmental projects involving physical structures have to be avoided in such areas.

Recommendations:  Based on the field visit on 14th Oct 2009 and subsequent land use analysis, We suggest the following to mitigate landslides in the region.

1. Planting of native vegetation on hilltops and slopes. The roots of the native vegetation aid as a good soil binding and provide slope stability. The removal of trees (with deep tap roots) and subsequent taking over of secondary vegetation with fibrous or shallow roots has reduced the soil binding properties.
2. Restoration of natural drainage network. Alteration in hydrological regime due to changes in drainage network consequent to deforestation - Inappropriate locations of human habitations on the first and second order streams in Kadwad has also hindered the water movement and water has removed all the blockages –evident from collapse of houses (in Zariwada)
3. Discouraging monoculture plantations– the land given to cashew plantation should be taken back and the afforestation has to be carried out  with the native species of flora
4. Banning Illegal soil mining on the hills (especially in places like Zariwada).
5. Improving drainage connectivity. The collective rainfall of many days has enhanced the pore water pressure. This with lateral pressure due to swelling of oversaturated clay rich horizon has enhanced the driving force resulting in displacement and collapse of human habitations resulting in trapping of humans and loss of properties (at Zariwada, Kadwad).
6. Need to investigate the suitability of human habitations in regions prone to landslides.

1. The Konkan Railway track connecting Karwar town with Goa and other places passes through this Zariwada paleo-river valley and also crosses the lineaments. The vibration generated by movement of trains has devepeloped the cracks on hill tops and also has resulted in the loosening of the soil (subsequent to soil mining). Long spell of high intensity antecedent rainfall has triggered the mud slide.
2. Geomorphologically, the valley area was a paleo-river channel that formerly drained into the Kali River that flows in the north of Zariwada/Kadwad. The shift of the river course might have led to the formation of hills/mounds.  Composition of this mound which is mainly of laterite clay further confirms the existence of paleo stream in this region. The paleo-river channel is still connected to the Kali River and the groundwater seepage into the channel increases or decreases rhythmically according to high and low tides in the River.
3. Soil formation for centuries on the hillocks and heavy rain might have led to the swelling of clay inside the hillocks resulting in the landslips.

7. Immediate banning of large scale illegal quarrying of granite stones, soil mineral mining considering the hazards proneness of the region (Karwar) and presence of sensitive pockets (Naval base, Kaiga nuclear plant, eco sensitive Anshi-Dandeli tiger reserve). Weathered granites on the hills and weakening of soil due to excessive rains have triggered the landslides near Binaga, National Highway.
8. No large scale developmental projects in Uttara Kannada district that are likely to harm the ecology and biodiversity of the Western Ghats. Considering the implementation of large number of mega projects in Karwar, it appears that the region has exceeded the carrying capacity and further implementation of any mega projects would prove detrimental to the local population. The region has already prone to hazards and could be categorized as hazard hotspot. This also emphasizes the need for carrying capacity study for Uttara Kannada district.
9. Considering the hazard proneness of the region it is necessary to set up 'Disaster management centre (DMC)’ to assist in regional planning, management of disasters and also to assist the administration in rehabilitation measures in case of eventualities. Also, the region around 25 km radius of Karwar is seismically sensitive and also constitution of lineaments further emphasizes the need for setting up a seismic monitoring cell (within DMC) in the district to assist the district administration in the predication and also mitigate measures. Disaster management  centre shall house seismic monitoring cell, and shall have the state of the art gadgets to predict calamities due to natural as well as human induced.
10. Naval authorities should be asked to remodel the protection wall considering the natural drainages on priority. Construction of the protective wall by the naval authorities without any due consideration to natural drainage systems has resulted in large scale flooding of the region, which also has triggered series of landslides all along the Highway (NH 17). Removal of the protection walls at many locations during the floods, highlights the need for holistic approaches in planning and implementation of large scale projects. Many such projects have seriously impaired the ecology of the region, affected the livelihood of nature people and also have posed serious threats to the existence of local population.
11. Shifting of all affected families (located on the hill side) to appropriate locations without affecting their current livelihood dependence.
12. Afforestation with native vegetation in the region considering the large scale deforestation in recent times. At present many hill tops are barren. The hanging crown part of the current landslides need to be graded on priority, as cracks were observed at the crown apart from subsidence.
13. Setting up special Uttara Kannada package to restore ecosystems – The  funding shall be from all developmental projects in the district. Karwar taluk, in all probability, has transgressed its limits of growth, beyond the carrying capacity - Series of landslides consequent human tragedies and property loss is the indication of the lack of integrated approaches in planning and the region has crossed the thresholds of carrying capacity. Large scale land cover changes has resulted in alterations in hydrological regimes evident from the conversion of perennial streams to seasonal streams, enhanced siltation in the catchment evident from increased sedimentation in reservoirs in recent years.  The region being one among the global biodiversity hotspots call for immediate measures to restore the ecosystems. Large scale projects such as hydro power plants, project sea bird, Kaiga nuclear plants have played significant role in degradation the ecosystems which have also affected the livelihood of local people.  These projects shall also make provision to provide  a recurring grant to sustain the proposed Disaster Management Centre at Karwar and also for Ecological Research in Karnataka part of Western Ghats.
14. Considering the level of devastations in Karwar, landslide susceptibility mapping should be carried out to delineate potential zones of instability, particularly in areas where human lives and properties are involved. If any indication of slope instability is noticed in an area which has major risk elements, the fact should be shared with society in a proper way. This suggestion has two major implications.

1. First, with the increasing large scale environmentally unsound development activities in the region, the risk posed by natural hazard must also be evaluated. This is well-exemplified by a series of natural hazards (landslides) in the region. Considering rainfall-intensity and changes in climate / hydrologic regimes (due to global warming) stochastic relationships have to be developed to assess high-risk areas.
2. Secondly, with the successful establishment of relationship between rainfall and landslide activity, analysis of palaeo landslides would provide insights based on the past variation in rainfall patterns. Equally, such relationships aid in predicting changes in mass movement activities based on modelled regional impacts of global climate change.

15. Apart from forestation of barren hill slopes and hill tops,  sealing of cracks, slope-grading, proper drainage measures, soil reinforcement using geo-grid and biotechnical measures have to be done. However, appropriate selection of these measures along with their design is only possible after an in-depth geological and geotechnical study of the slide area.

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