FLOOD FORECASTING AND WARNING

 

Flood Forecasting

• Data Collection: By Using Automatic Sensors

• Data Transmission: Using Modern Automatic Data Transmission Technique e.g. Satellite, VSAT, Internet/Email, Mobile Phones etc.

• Forecast Formulation: Using Computer Based Comprehensive Catchment Models.

• Forecast Dissemination: By Using Computer Network and Satellite e.g. Internet, E-mail etc.

 

Water Forecasting can be done in two ways

• Level Forecasting

• Inflow Forecasting

 

Level Forecast

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.

• LOW FLOOD - water level of the river touches or crosses the warning level, but remains below the danger level.

• MODERATE FLOOD - water level of the river touches or crosses its danger level, but remains 0.50 m below the Highest Flood Level of the site.

• HIGH FLOOD - water level of the river is below the Highest Flood Level of the forecasting site but still within 0.50m of the Highest Flood Level.  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”

• UNPRECEDENTED FLOOD - 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”

 

Inflow Forecast

The threshold inflow limits were identified base on various factors such as safety of the dam, status of reservoir, downstream channel/ canal requirements. Inflow Forecasts are issued for 28 dams/reservoirs/barrages in various river basins for India.

A network of flood forecasting stations established in major and interstate river basins

Total Flood Forecasting Stations

• Inflow - 28

• Stage - 147

 

 

 

 

 

 

 

 

 

 

 

 

 

Evaluation of Flood Forecast Performance

• A level forecast is considered reasonably accurate if the difference between the forecast and the corresponding actual observed river level lies within+/- 15 cm.

• Inflow forecast – variation of inflow volume within +/-20% is considered acceptable.

• Level forecast reliable to an extent of 95%

• Inflow forecast reliable to an extent of 96%

 

Standard Operating Procedure (SOP) for Flood Forecasting & Warning

• Nomination of Nodal Officers of CWC for interaction with the Nodal Officers of concerned State Governments before monsoon every year.

• Gearing up of flood forecasting network before monsoon every year.

• Operation of Divisional Flood Control Room during monsoon every year

• Operation of Central Flood Control Room (CFCR) during monsoon every year.

• 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.

• Sending flood alerts through SMS on Mobile Phones to the concerned officers of State/ Central Government during high and unprecedented flood situations for issuing alerts and electronic messaging in the event of disaster situations.

 

Major Flood Prone Basins

Ganga, Brahmaputra & Mahanadi Basin are major flood basins in India

• Brahmaputra basin

• Inundation

• Bank erosion

• Flash floods (including flows from Bhutan & China)

• Ganga basin

• Inundation

• Bank erosion

• Water logging/drainage congestion

• Floods from Nepal

• Mahanadi basin

• Inundation

• Water logging/drainage congestion

 

Forecasting Schedule

• Major rivers (Travel time >24 hours)

Forecasts are being formulated based on 0800 hrs./ 0900 hrs. water level data and issued once in a day at 1000 hrs. with advance warning time from 24 hrs. to 36 hrs.

• Medium rivers (Travel time 12-24 hours)

Forecasts are being formulated based on 0600 hrs. and 1800 hrs. water level data and issued twice in a day at 0700 hrs. and 1900 hrs. with advance warning time from 12 hrs to 24 hrs

• Flashy rivers (Travel time < 12 hours)

Forecasts are being formulated based on any main hr. water level data and issued multiple times (more than twice) in a day with advance warning time less than 12 hrs.

 

Flood forecasting cooperation with other countries

Co-operation with Bangladesh

• India shares transmission of water level, discharge of rivers and rainfall data with Bangladesh during monsoon season since 1972.

• Water level, weather report and discharge data of Farakka on Ganga,  Pandu , Goalpara & Dhubri on Brahmaputra, Silchar on Barak river and Tista on Damohani river twice daily (0800 hrs. and 2000 hrs).

• Rainfall data at Jalpaiguri, Coochbehar, Siliguri, Dhubri, Goalpara, Silchar, Tura and Agartalla at 0800 hrs

• Water level at Kailashahar on Manu river, Amarpur on Gumti river, Badarpurghat on Barak river, Gazaldoba on Tista river, NH-31 on Jaldhaka (Dharla) and Ghughumari on Torsa (Dudkhkumar) thrice a day at 0900, 1300 and 1800 hrs throughout flood season.

Co-operation with China

• Data of 3 stations namely Yanghen, Nugesha and Nuxia on Siang river located in China are being received twice a day at 0530 hrs. and 1730 hrs. since 2002.

• Data are used for formulation of flood forecast and shared with the Govt. of Arunachal Pradesh & Assam.

Co-operation with Bhutan

• A scheme to carry out Hydro-meteorological observations in Bhutan on the rivers common to India and Bhutan.

• A network 35 nos. of hydro-meteorological /meteorological stations maintained by Royal Govt. of Bhutan.

• A Joint Expert Team (JET) consisting of officials from the Government of India and Royal Government of Bhutan has been constituted to review the progress.

Co-operation with Pakistan

• Exchange of flood data between India and Pakistan for rivers in India Water Treaty of 1960

• Inflows, outflows and levels of Pong reservoir on the Beas, and Bhakra reservoir on the Sutlej main

• A flood warning cell is operated round the clock in the Indus wing during monsoon. The frequency of flood warning messages varies as hourly/ 3 hourly/ 6 hourly etc. depending on the magnitude of floods.

Co-operation with Nepal

• 42 hydro-meteorological stations in Nepal territory, share data with Bihar & U.P.

• Joint Task Force (JTF) and Committee on Flood Forecasting (CFF) recommended 47 stations against 42 existing stations for improving the existing flood forecasting scheme.