The flood forecasting is one of the major activities undertaken by the Central Water Commission. Mahi Divion head quarter at Gandhinagar is assigned to provide flood forecasting in the inter-state river basins namely Mahi, Sabamati and Banas. Another Division, Tapi Division, situated at Surat is entrusted with flood forecasting in the Basins of river Tapi, Lower Narmada and Damanganga.
The following forecasts are issued:
Level forecast for 7 stations:
- Subhash Bridge-Ahmedabad (Sabarmati Basin)
- Wanakbori Weir (Mahi Basin)
- Surat (Tapi Basin)
- Garudeswar (Narmada Basin)
- Vapi (Damanganga Basin)
- Daman (Damanganga Basin)
Infow forecasts for 6 major reservoirs:
- Dharoi Dam (Sabarmati Basin)
- Kadana Dam (Mahi Basin)
- Dantiwada Dam (Banas Basin)
- Hatnur Dam (Tapi Basin)
- Ukai Dam (Tapi Basin)
- Madhuban Dam (Damanganga Basin)
Flood Forecasting Setup Under NTBO
Flood forecasting setup of CWC works under overall supervision of Member (RM), at national level, with head quarters at New Delhi. At regional level, flood forecasting operation are carried out under the overall guidance and direction of the Chief Engineer, Narmada Tapi Basin Organisation, CWC, Gandhinagar.
There are two subdivisions under the Hydrological Observation Circle under NTBO viz. Mahi division headquarters at Gandhinagar & Tapi division headquarter at Surat. Executive Engineers heading the divisions are the nodal officers for formulation of forecasts and the dissemination to various user agencies including local administration.
Executive Engineer, Mahi Division, Gandhinagar under supervision of Superintending Engineer, Hydrological Observation Circle, CWC, Gandhinagar has been entrusted with the work of issuing Inflow/ Level Forecasts on river Mahi, Sabarmati & Banas. The Mahi Division have four Sub Divisions located at Kadana, Himmatnagar, Palanpur & Ahmedabad to collect the hydro-metereological data for the formulation of flood forecasting. Executive engineer, Tapi Divison, under the supervision of Superintending Engineer, Hydrological Observation Circle, CWC, Gandhinagar has been entrusted with the work of issuing Inflow/ Level Forecasts on river Tapi, Damanganga & Lower Narmada. There are 5 subdivisions under the Tapi Division located at Surat, Bhusawal, Dhule, Bharuch & Silvasa, which assist Executive Engineer in Flood Forecasting Operations.
High Frequency & Very High Frequency Wireless sets are provided at these stations and in control rooms established at subdivisions & Divisions. Overall 67 sites are provided with wireless during flood season and Hydrological Observation Circle maintains a close liaison with civil authorities to communicate advance warning for appropriate mitigation measures. Recently telemetry systems has also been installed at 76 stations.
Inter-state meetings on the preparedness for monsoon and to ensure coordination among Government officers of Co-basin states are held before onset of monsoon. For year 2015, such meetings were held at Suart and Gandhinagar in May 2015. I addition, regualr interactions at various levels are also held to facilitate exchange of data and sharing information and proper coordination on data sharing arrangement during monsoon.
During monsoon, beginning from 1st June, 24X7 control rooms are also established at Divisional Headquarters (i.e. Gandhinagar & Surat). Similarly 24X7 control rooms are also established during monsoon at Sub-divisional Headquarters. The Mahi Division have been set up 32 nos. wireless stations & 5 seasonal wireless stations for collection and transmission of hydro-met data in river basins under 4 Sub divisions. Over all 67 wireless stations have been setup under Hyrological Observation Circle, Gandhinagar.
Steps Involved in Flood Forecasting
- Observation and Collection of hydrological and meteorological data
- Transmission and communication of data to the forecasting center (control room)
- Formulation of forecast
- Dissemination of forecasts and warning to the administrative and Engineering authorities of the state.
- Analysis of forecast versus actual observations and improvement of the models
The first step involved in the Flood Forecast system is observation of hydrological and meteorological data from various sites located in different parts of the basin. The various temporal data needed for FF are:
a) Meteorological data
- Wind velocities
In the above said 5 variables rainfall is the most important variable required. Requirement of other variables depends on the method that is used for FF.
b) Hydrological data
- River gauges
- River discharges
In Hydrological data, River gauge data is the most important for flood forecasting techniques.
Various systems used for data communication are a) Wireless Communication b) Landline Communication & Telemetry systems.
The wireless communication system essentially consists of both High Frequency (HF) and Very High Frequency (VHF) network. The VHF is generally used for short aerial distances upto maximum of 30 to 40 Kms. The HF network provides communication for long aerial distances of the order of 400 to 2000 K
Dissemination of Forecast
Dissemination of forecasts should be quick without loss of time. Hence it is made on top priority by Wireless/ Telephone/ E-mail or by giving 000 telegram/ or by sending special messenger to the Civil authorities as per the guidelines given in Flood Memorandum of State Government. In addition to dissemination of forecast to the user agencies, messages are conveyed to newspaper over phone if required by them.
The Flood Cell of Government of Gujarat, Gandhinagar is the main agency for monitoring the flood situation in rivers all over the State. It is responsible for collection of information on flood situation and dissemination of flood warning to the concerned local officers for taking precautionary measures in areas likely to be affected.The State Government has fixed different colour code signals to indicate about the gravity of the flood situation. The white signal is used for making alert, blue signal for readiness for evacuation and red signal for immediate evacuation in the affected areas.