National Institute Of Oceanography( NIO ) - Canacona Flash Floods Study Committee Report

Canacona Flash Floods Study Committee Report

Executive Summary of Report (for complete report click here)

The Government of Goa constituted the Canacona Flash Floods Study Committee with the following two objectives. (1) Assemble and analyse available information to describe and identify causes behind the flash floods in Canacona Taluka on 2 October 2009. (2) Suggest measures to be adopted in Goa to minimize damage arising from similar episodes in future. This report of the Committee is based on the study carried out with the help of a team set up at the National Institute of Oceanography (NIO Team). The team conducted field surveys, analysed available data, particularly data on precipitation, and assisted the committee in arriving at a description of the event and its causes. This work has permitted the Committee to infer that the flash floods in Canacona were directly related to about 271 mm of rain that fell between approximately 9.30 AM and 4.30 PM on 2 October 2009. While this approximately 7-hour long precipitation event was the direct cause, there were indirect causes that set the stage for the flash floods. These were:

a) Talpona and Galjibag Rivers which got flooded on 2 October 2009 are located in an area with average rainfall of 2953 mm during June-September. This area had a normal rainy season in 2009 with 2875 mm of rain. As a result, by end-September, the soil is expected to have had high amounts of moisture.

b) Between 8.30 AM on 29 September and 8.30 AM on 2 October 2009 Canacona Town rain-gauge recorded 252 mm of rain. This spell is expected to have saturated the soil in the entire Canacona Taluka with moisture, and river channels would have been full with water.

c) About three-fourths of the catchment area of the upper Talpona River is located on mountain slopes. Galjibag River too flows through a valley surrounded by mountains. The mountain slopes of such areas are vulnerable to mudslides and the plains or valleys amidst mountain ranges are vulnerable to flooding.

The water reaching the surface due to the 7-hour precipitation event on 2 October cascaded down the slopes whose soil was already saturated with water. The resulting damage at a location depended on altitude of the location. On steep slopes with altitude in excess of 300 m, the cascading water led to mudslides. At altitudes of about 50 m or more, agricultural and horticultural areas were submerged and cattle were washed away. At lower altitudes (about 50 m or less), where topography is flatter, accumulation of water submerged buildings, and as the water made its way towards the sea, the flow destroyed houses and commercial establishments, particularly those that were weak (mud houses, for example).

There are no records to suggest that flooding of this magnitude occurred in Canacona taluka in recorded history. Nevertheless, the elements that contributed to the event are not uncommon in Goa. Hence, this incident of intense precipitation is best looked upon as a warning on what can happen. The Committee feels that, because such events cannot be prevented, the State of Goa should focus on awareness and preparedness for minimizing the impact of an intense precipitation event, such as the one that occurred on 2 October 2009.

The Committee has one general recommendation and four specific recommendations. The general recommendation is that the well known practices in forest management for preventing mudslides (aforestation of mountain slopes, for example) and in river management (such as de-silting of river bed) should receive emphasis and increased investment. These measures should be able to minimize damage from precipitation events of lesser intensity, but higher frequency, that occur in Goa.

The specific recommendations are:

(a) The areas vulnerable to mudslides should be mapped and site-specific disaster management plan to face them should be in place at each location with high vulnerability.

(b) Areas with high vulnerability to flooding due to an intense precipitation event should be identified and a disaster management plan should be evolved at locations that are particularly vulnerable.

(c) A mechanism for keeping a careful watch should be in place whenever a situation arises with high potential for an intense precipitation event in a vulnerable area. The Meteorological Centre of the India Meteorological Department (IMD), Panaji, should form the nerve centre of such a watch.

(d) The State of Goa should make IMD's "Cyclone Warning Dissemination System" operational in the state.

In order to enlarge the state's awareness for damage from precipitation events, (a) and (b) above should be carried out using the services of faculty and students from Goan undergraduate and postgraduate institutions, and then circulated widely amongst local policy and decision makers. To assist this process, the NIO Team should prepare one report on one site on each of the two aspects described in (a) and (b). These reports could then be used as a model for carrying out case studies by undergraduate and post-graduate institutions in Goa to examine other vulnerable locations. The Department of Science, Technology and Environment, Government of Goa, should provide funding for such research by Goan institutions. The NIO Team should also prepare a report on (c) to assist the government to set up watch-keeping for intense precipitation event.

Please do provide your feedback in the form of comments and views on the report by e-mail to Dr S.R. Shetye (shetye@nio.org), the Chairman of the committee and Director, NIO.

Copyright NIO, Dona Paula-Goa, 403 004, India. EPABX:+91(0)832-2450450; Fax:+91(0)832-2450602, -2450603; e-mail:ocean@nio.org

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