by Dr. Nandkumar Kamat
LANDSLIDES like the one obstructing the road at Porvorim are caused by slope instabilities. A landslide includes all kinds of mass movements on hill slopes that can affect the safety of human settlements, building services or infra-structures. The Porvorim landslide was largely caused by degradation induced by humans and partly caused by high rainfall. The landscape can be considered in equilibrium with the regular meteorological conditions, drastic modifications of the landscape, such as natural hazard phenomena, can thus be linked to extraordinary circumstances.
The critical conditions for triggering superficial slope instabilities have been studied in many regions of the world, to assess the risk of triggering superficial slope instabilities during an ongoing event of heavy rainfall. Geologists Larsen and Simon of US geological survey have studied the relationship between rainfall and landslides under conditions similar to Goa. In India, Professor Suryaprakash at National Institute of disaster management has provided guidelines to avoid slope instabilities. The PWD did a hurried job when the western slope of the Porvorim hillock was cut. No terraces were established similar to those on eastern face which separates the Goa legislative assembly complex from the highway.
On the contrary without any planning , several Acasia trees were planted at dangerous angles posing a serious threat to the traffic. Several of these have now come tumbling down. The first thing which I did after learning about the landslide blocking the highway at Povorim was to locate and study the problem area using Google Earth at a fairly high resolution of five metres. Was this impossible for Government authorities?. They are still hesitant to use this freely available tool for public good. The crisp satellite images and the three dimensional terrain view was an eye opener about the chronic mismanagement of this area. The landslide has occurred on a sharp edge of the hill which forms the ridge above the U shaped Malim valley which still has considerable green cover on its’ slopes.
The unauthorized Kuttcha roads are clearly visible in the satellite image. One foot/cart track distinct in the images measures 500 metres and descends from the hill to Malim jetty indicating a lot of unauthorized pedestrian movement. The denudation of the Malim hill and thinning of the vegetation cover is clear. The illegal encroachments within the green cover can be easily spotted and these are now spreading from the Malim jetty towards the highway. The landslides occurred in a narrow and uniformly lateritic strip, about 400 metres in length, at elevation of 33 to 52 metres from mean sea level, running from road intersection near the assembly complex to the traffic circle near the bridge.
As the satellite images revealed, this strip was continuously subjected to deforestation, illegal road construction, transportation and waste dumping activity without any surveillance or monitoring by any authority. The natural drainages were apparently blocked without the knowledge of the highway authorities. The local panchayat authorities, the forest department and the PWD may have turned a blind eye to the denudation of this strip. The PWD would now find it very difficult to remove thousands of tones of murum soil in shortest possible time. A delay of a few days on the eve of a major Hindu festival of Goa-the Ganesh festival would lead to incalculable losses to trade and business. Thousands of commuters would continue to face hardships.
It is indeed a nightmarish situation, just because the managers of Goa’s roads and highways do not understand their jobs despite best of the expertise available in the world on road design and maintenance. After commissioning of two parallel bridges on Mandovi, the Porvorim intersection has become one of the densest traffic corridor in Goa and for the north south traffic on NH-17 A. A bottleneck at this junction creates a massive “ domino effect “ impacting smooth vehicular movement from Agacaim to Panaji on one side and Banastarim to Panaji on other side.
The Goa Police are under equipped to handle such bottlenecks. PWD despite having 25 divisions and 101 subdivisions, a record for a small state, does not have a map of disaster prone stretches of the roads which pass through areas of slope instabilities. There are several such areas in north and south Goa and in the western ghats. Many human settlements are precariously perched over unstable slopes with nothing but porous laterite to anchor their foundations. Slope instabilities have plagued Panaji’s Alto de Guimares. The other part of this hill known as ‘conception hill’ has been often sliced like a cake and faces possibility of a major landslide. The densely settled slopes from Nirmala institute to Santa Inez and Maruti temple to Fontainhas are prone to landslides and may face a major environmental disaster. Heavy hill cutting between Kundaim to Farmagudi is an example of bad road design and alignments without any inbuilt safeguards against the landslides.
Reckless quarrying between Cortalim to Lotulim has scarred the countryside and similar activity is observed between Sancoale to Vasco. In all these locations the lateritic/basaltic hill slopes have become unstable. The landslide at Porvorim could have been prevented if the the highway division of PWD were to routinely monitor such unstable slopes. But there is poor maintenance of the roads and the shoulders in Goa. The wild growth during monsoon hazardous for the oncoming traffic is seldom cleared regularly and efficiently. For past two years the PWD has not paid any attention to clearance of roadside bushes along the Bambolim-Donapaula major district road frequented by VIPs.
The anti-skidding steel barriers on Bambolim hillslope behind Kenkare estate were damaged in an accident a few months ago but these were not promptly repaired. The failure of the government authorities to tackle the landslide problem at Porvorim has raised a genuine question mark about technical competence, preparedness and professionalism of the government machinery to manage the serious hazard of slope instabilities anywhere in Goa. The PWD needs to create a database of the pluviometric conditions of historically documented events of superficial slope instabilities. It needs to routinely inspect and monitor the conditions of all unstable hillslopes.
Anti-skidding walls, special signals and sensors can be provided in disaster prone areas. Goa is likely to face unpredictable weather pattern in future. This may include periods of heavy rainfalls. Such events can trigger superficial slope instabilities such as soil slips and debris flows, when critical rainfall conditions are surpassed.. The Porvorim landslides may provide an objective lesson for disaster managers to anticipate such events in future. Government needs to order an inquiry in the illegal development on slopes of Malim valley. PWD needs to gear itself with knowledge, men and materials to promptly mitigate any future landslides.
- NT, Goa Daily
