News & Events
Current News & Upcoming Events
NIO in Press
Canacona Flash Floods: NIO submits the reports to Govt. of Goa
Canacona Flash Floods: Summary to enhance awareness and preparedness
(Please download individual reports at the end of this summary)
The damage caused by the Canacona flash floods of 2 October 2009 led the Government of Goa to constitute the Canacona Flash Floods Study Committee to (1) assemble and analyse available information to describe and identify causes behind the flash floods, and (2) suggest measures to be adopted in Goa to minimise damage arising from similar episodes in future.
The committee submitted a report based on a study carried out with the help of a team set up at the National Institute of Oceanography (NIO). The NIO 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 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.
The committee noted that though there were no records to suggest that flooding of this magnitude had occurred in Canacona taluka in recorded history, the elements that contributed to the event were not uncommon in Goa. This intense-rainfall event could be looked upon as a warning of the potential of such events to cause damage. Though such events cannot be prevented, the committee suggested that the state should focus on awareness and preparedness for minimising the impact of similar intense-rainfall events. The committee made one general and four specific recommendations. The general recommendation was the well-known practices in forest management for preventing mudslides (afforestation of mountain slopes, for example) and in river management (such as de-silting of river beds) should receive emphasis and increased investment. These measures would be able to minimise damage from rainfall events of lesser intensity, but higher frequency, that occur in Goa.
The specific recommendations were the following.
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.
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.
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.
The State of Goa should make IMD's "Cyclone Warning Dissemination System" operational in the state.
The idea was to involve faculty and students from Goan undergraduate and postgraduate institutions in carrying out activities (1) and (2) above. Hence, the committee suggested that NIO should assist the state in this process of creating awareness and preparedness by preparing three reports on each of items 1–3 above. Accordingly, three reports have been prepared by NIO. This document provides a brief introduction to these reports.
The first report, by Kessarkar, Srinivas, Suprit, and Chaubey, proposes a method for mapping landslides. It describes the geological reasons behind the landslides that occurred in the Canacona taluka. As noted by the Canacona Flash Floods Study Committee, these landslides occurred on steep slopes; the cascading water triggered the landslides. The method described in this report makes considerable use of satellite data, but relies critically on the field observations at Kuskem. The report list the factors identified as important for landslides in this area and prescribes a method to estimate a Landslide Potential Index and to prepare a landslide-susceptibility map. Though this method has been developed for a specific area, the methodology, with suitable modification, is applicable to other regions as well.
The second report, by Suprit, Kalla, and Vijith, presents a methodology for assessing flood risk and issuing a warning during an intense-rainfall event. The method analyses topography for river flow and for converting rainfall to river flow. It uses an open-source Geographical Information System (GIS) called GRASS and a simple hydrological model called the rational method. Based on this method and using rainfall data from online AutomaticWeather Stations (AWSs), an algorithm is developed for a flood-watch. The potential discharge computed from the data using the rational method is used to develop a simple, graphical method for issuing a warning. Its viability is tested for the event of 2 October 2009 for the Talpona River, but it can be applied to other rivers too.
The third report, by Sundar, presents the outline of a watch-keeping mechanism with the Panaji observatory of the IMD as its nerve centre. Sundar uses elevation data from the Shuttle Radar Topography Mission (SRTM) and publicly available geographical information such as Google Earth and Google Maps to ascertain which regions of Goa are likely to be prone to floods. An evaluation of the existing network of AWSs and Automatic Rain Gauges (ARGs) then leads to identification of sites where AWSs need to be located in order to augment the existing network in the state.
The methods outlined in the first two reports can be implemented by undergraduate and postgraduate students in Goa. The report on landslides prescribes a method that should be accessible to students of geology and the report on flood-risk assessment prescribes a method that should be accessible to GIS students. Both reports present practical examples that can be adapted for case studies or dissertations in other places and should be a part of the awareness campaign of the state government. As noted by the Canacona Flash Floods Study Committee, its analysis was made possible by the existence of an AWS in Canacona. This AWS had been set up under a programme sponsored by the Indian Space Research Organization (ISRO). The third report suggests what needs to be done to ensure availability of real-time data for preparedness.
We hope that these three reports will assist in increasing awareness about the potential for similar floods in Goa and help improve our preparedness to face them.
NIO, Dona Paula-Goa, 403 004, India. EPABX:+91(0)832-2450450; Fax:+91(0)832-2450602, -2450603; e-mail:email@example.com