CWC National Flood Forecasting Network

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Flood Forecasting Services

Flood causes considerable damage to human lives and property almost every year. Since adoption of National Flood Policy by Government of India in 1954, it was realized that a total protection against flood by structural means alone is not possible and that optimum solution would consist of a mixture of structural and non-structural measures. Therefore, stress has been laid on non-structural measures like flood forecasting and warning, which is most important among such means to minimize the damage potential from floods. Accurate and timely flood forecasts and advance warning have, therefore, to be aimed for providing valuable time to the people and to civil authorities in taking preventive measures like evacuation, relief and rehabilitation measures, preparedness for flood fighting by engineering authorities etc. and thus mitigating such loses from floods.

Flood Forecasting Network in the Country

Flood Forecasting has been recognized as the most important, reliable and cost effective non-structural measures for flood mitigation. Recognizing the great importance of this measure, flood forecasting of river Yamuna at Delhi was suggested by Reddy Committee set up by Prime Minister, Govt. of India to manage flooding of Delhi. Accordingly in the year 1958, CWCCentral Water Commission commenced the flood forecasting service in a small way by establishing flood forecasting unit for issuing water level forecasts of the Yamuna for the National Capital, Delhi. On the recommendation of various committees/panels, a "Flood Forecast & Warning Organisation" was set up in CWC in 1969 to establish forecasting sites on inter-state rivers at various flood prone places in the country. 41 forecasting sites were added in 1969, making total number of forecasting sites to 43. The Salient Features of Flood Forecasting System is given in the following Table:

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The “National Flood Forecasting and Warning Network” of Central Water Commission, which comprised of 175 flood forecasting sites including 28 inflow forecasting sites in flood season 2012 is shown in Map-1. The number of flood forecasting sites on each of the nine major inter-state river systems, which constitutes 71 river sub-basins in the country, are given in the Table 1.1.

Table 1.1: Number of flood forecasting sites in major inter-state river systems

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The above flood forecasting network covers the following 15 states, one Union Territory and NCT of Delhi as shown in the Table 1.2

Table 1.2 State-wise Flood Forecasting Network in CWC

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A list of 175 FF Stations is at Annex-I.

Central Water Commission through its twenty flood forecasting divisions issued forecasts to the various user agencies, which includes various civil / engineering agencies of the States/ Central Governments such as Irrigation/ Revenue/ Railways/ public undertakings and Dam/ Barrage Authorities/ District Magistrates/ Sub Divisional Officers besides the Defence Authorities involved in the flood loss mitigation work. During the flood season, the Hon’ble Minister of Water Resources, Government of India, the Chairman and the Member (River Management) of Central Water commission were also being apprised of the latest flood situations in the above river basins in the country.

Classifications of Various Flood Situations

The Central Water Commission has categorized various flood situations, for monitoring the floods in the country though its flood forecasting network, into the following four different categories, depending upon the severity of floods i.e. based on floods magnitudes.

Level Forecast

Low Flood

The river is said to be in “LOW FLOOD” situation at any flood forecasting sites when the water level of the river touches or crosses the warning level, but remains below the danger level of the forecasting site.

Moderate Flood

If the water level of the river touches or crosses its danger level, but remains 0.50 m below the Highest Flood Level of the site (commonly known as “HFL”) then the flood situation is called the “MODERATE FLOOD” situation.

High Flood

If the water level of the river at the forecasting site is below the Highest Flood Level of the forecasting site but still within 0.50m of the HFL then the flood situation is called “HIGH FLOOD” situation. In “High Flood Situations” a special “Orange Bulletin” is being issued by the Central Water Commission to the users agencies which contains the “special flood message” related to the high flood.

Unprecedented Flood

The flood situation is said to be “UNPRECEDENTED” when the water level of the river crosses the “HIGHEST FLOOD LEVEL” recorded at any forecasting site so far. In “Unprecedented Flood Situations” a special “Red Bulletin” is being issued by the Central Water Commission to the users agencies which contains the “special flood message” related to the unprecedented flood.

Inflow Forecasts

Inflow Forecasts are issued for 28 dams/reservoirs/barrages in various river basins in the country. The project authorities have identified the threshold inflow limits for issue of forecast considering various factors such as safety of the dam, status of reservoir, downstream channel/ canal requirements.

Standard Operating Procedure (SOP) for Flood Forecasting & Warning

The basic activity of data collection, its transmission and dissemination of flood forecasts to the local administration is carried out by the field divisions of CWC. The modelling centres and Divisional Flood Control Rooms (DFCR) are located in the premises of the field divisions. The field divisions perform these activities as per existing Manual on Flood Forecasting which contains the following critical activities as the general SOPs

1. Nomination of Nodal Officers of CWC for interaction with the Nodal Officers of concerned State Governments before monsoon every year. 2. Gearing up of flood forecasting network before monsoon every year. 3. Operation of Divisional Flood Control Room during monsoon every year 4. Operation of Central Flood Control Room (CFCR) during monsoon every year. 5. Issue of flood forecasts to designated officers of concerned State and transmission thereof through FAX/Telephone/E-mail/ through Special Messengers during monsoon every year. 6. Sending flood alerts through SMS on Mobile Phones to the concerned officers of State/ Central Government during high and unprecedented flood situations as per Standard Operating procedure (SOP) for issuing alerts and electronic messaging in the event of disaster situations issued by National Disaster Management Division, Ministry of Home Affairs, vide letter No: 31-32/2003-NDM-III / II dated 10th April 2006, made effective from 24th April 2006.

For the purpose of dissemination of alerts to PMO/ Cabinet Secretariat, a uniform system has been devised by categorizing each type of alert in stages- Yellow, Orange and Red.

Categories of alerts for flood in respect of level forecasts is as indicated below.

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In order to meet the requirement of real-time data collection, automatic data transmission and flood forecast formulation, expeditious data / information dissemination, the Central Water Commission has undertaken modernization of its data collection and flood forecast network. During IX Plan, 55 telemetry stations in Mahanadi and Chambal Basins and two Earth Receiving Stations ( ERS) at Jaipur and Burla were established. During X Plan, modernization of 168 stations and 11 Modeling Centers was undertaken which has been completed in XI Plan. During XI Plan, additional 222 telemetry stations, 10 Modeling Centers and one more ERS at New Delhi have been installed. During 12th Plan, remaining stations are proposed to be modernized. New stations proposed during 12th Plan, are proposed to be equipped with modern equipments.

Expansion of FF Network

Extension of the service followed from time to time and now the river forecasting has been expanded over the years to cover nine major inter-state flood prone river basins, which comprises of 71 sub-river basins traversing the country. The year-wise positions of the number of flood forecasting sites till the flood season 2012 in the network of Central Water Commission are shown in the Table 1.3:

Table-1.3: Yearwise positions of number of forecasting sites in CWC

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Performance of Flood Forecasting Network

A number of techniques are being utilised for formulation of river stage and inflow forecasts by Central Water Commission. While inflow forecast is being provided for assisting project authorities in reservoir regulation, the stage forecast is done for warning the civil and engineering authorities about the predicted water level well ahead of its occurrence. An accurate forecast is one where the forecast level and corresponding actual observed level exactly synchronize or have such a small difference that it can be taken as reasonably accurate. In an ideal situation, not only the forecast and the corresponding observed value of river stage/ inflow should be the same but also the time of such occurrence should be the same as that predicted.

As per present practice, all the level and inflow forecasts are being judged by the single criteria of accuracy i.e. the actual level attained is within ± 15 cm of forecasted value for stage forecasts and the actual inflow/ volume received in the dam/ barrage is within ± 20% of the forecasted value for inflow forecast.

The flood forecasting performance of the level forecasting as well as inflow forecasting sites from 2000 to 2012 is given as Fig1.

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