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Le Cong Thanh Director National Center for Hydrometeorological Forecasting (HMF) Hydrology n 1991, the flash Service of Vietnam (HMS) occurred very I suddenly, and the people of Son La still remember the horrible Vaisala Automatic Systems in Vietnam events. Formidable flows of muddy water destroyed every- thing in their path. During our first survey trip to Son La, one AutomaticAutomatic FloodFlood AlertAlert local resident told us: “It was terrible. We just watched the water rising higher and higher; SystemSystem ProtectsProtects thethe our house, our gardens disap- peared. Nothing was left but mud, everywhere. I didn’t even know where my relatives were.” PeoplePeople ofof SonSon LaLa The damage would not have been so severe, and thousands of lives could have been saved, if the flood had been predicted and announced to the residents of Son La. Realizing the need for timely flood prediction, the Hydrology & Meteorology Service of Vietnam (HMS) had feasibility studies conducted by its experts, and took a decision to design and deploy the first automatic flood reporting sys- tem in the province of Son La.

Reliability a key criterion

The first requirements of the system were simplicity and reli- ability, as HMS experts set out to define and create a basic sys- tem design. The project was di- vided into two phases for smooth implementation, as in- stallation of hardware is possi- ble in this area only during the dry seasons. In its system spec- ification, HMS suggested that automatic data acquisition sta-

The province of Son La, which is located in a mountainous area of Northwest Vietnam, suf- fered a sudden in 1991. Taking peo- ple by surprise, the flood claimed the lives of many families. In order to prevent catastrophes like this, the Hydrology & Meteorology Service of Vietnam (HMS) has designed and installed an automatic system. Vaisala MILOS500 Data Processing and Collection Systems form the core of the system.

Mountains characterize the landscape of Son La province, making it susceptible to .

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tions be installed in the river- Vaisala MILOS Data on a PC with serial connec- heads of the river system basin Collection Platform tions. A communication link in Son La. A key concern in selected between HMS headquarters in the design was the fact that the Hanoi and the MILOS System stations must be self-contained, After tenders, HMS selected in Son La town was installed via solar-powered and automated. Vaisala as the manufacturer of a dial-up line. The Vietnamese Unmanned operation is essen- the remote and central stations Graphical User Interface was tial in Son La, because some 80 for the flood alert system in very helpful for the users of the per cent of the province’s area Son La. Vaisala’s expertise in system. is covered by mountains. manufacturing sensors and Moreover, as transportation data acquisition systems, and Flood monitoring and energy supply systems are its worldwide quality-proven remote stations not sufficiently developed to installations, were key factors form a functioning infrastruc- in the selection. But, above all, The flood alert system obtains Repeater stations were installed on ture, this set special require- Vaisala systems met the de- measurement data at carefully top of the obstructing mountains to ments for power supply solu- manding design criteria. The selected sites where five remote make sure that signals from the end tions. central system, based on the measuring stations, consisting of stations reach the central station. Vaisala MILOS500 platform, Vaisala MAWS301 Automatic A demanding was installed in the office of the Weather Stations, provide im- environment for Hydrology & Meteorology portant information on the con- communications design Station - a subsidiary of HMS ditions. There are 6 remote sta- Increased safety in the town of Son La. The tions for water level measure- Each data acquisition remote MILOS500 at the Central Data ment and 8 remote stations fpr Even though it took quite a lot station was defined to consist Collection Station polls mea- both water level and precipita- of hard work and effort to set of sensors to measure rainfall surement data from each re- tion measurements. These sta- up the first automatic flood and water pressure, which mote station, calculates data tions are all solar-powered. alerting system, HMS is very would then be converted into averages, checks it against pre- Average 10-minute values happy with the results. After water level. The measured data set limits and issues alarms. are calculated and transmitted the first phase was finished, all would be collected in a data Moreover, the MILOS stores to the central station. In this the raw data could be retrieved processing unit (DPU) within the data. application, cumulative values either from the Central Station the remote station and then Thanks to the simple data in- provide valuable information in Son La or from the Control transferred to a central station terface, open architecture and on the development trends. PC in Hanoi. The data is then in Son La town. The only ade- excellent documentation of All the remote stations are further processed and evaluat- quate means of communica- MILOS500, it took no more solar powered and transmit ed by the software to issue tions between the remote sta- than four weeks for the IT ex- data with an UHF Transceiver. alarms and other reports. On tions and the central station perts of HMS to successfully Four UHF repeater stations the basis of the acquired data, was radio transmission. develop the software to control ensure that data communica- experts estimate that, with this Therefore, each of the remote the whole system. This tions also function in difficult system, a flash flood similar to stations would be equipped Windows-based software is run locations. that of 1991 could be predicted with a wireless modem to trans- and alerts sent to local authori- fer the collected data, pre- ties 5 to 8 hours in advance. processed into a proper format This is sufficient to organize by the station’s DPU. evacuation and to take neces- Extensive joint efforts were sary action to prevent damage. made by HMS experts to draft The province of Son La will out the frequency plan for the be fully protected against end-stations. The objective was floods after the second phase of to eliminate any eventual cross- the project. Additionally, HMS interference between the radio of Vietnam will further invest paths. At some specific sites, in automatic alert systems that mountains could act as an ob- will be installed in river basins struction to the antenna beam in other flood-endangered re- and could deflect the radio gions in Vietnam. paths. The solution for this was to install a repeater on top of the obstructing mountain, whereby the radio signal transmitted from an end-station would be re- ceived by the repeater and then re-transmitted to the central sta- tion at a different frequency. The final frequency plan, which had Remote stations, been optimized both for its consisting of Vaisala costs and reliability, was then MAWS301 Automatic submitted to the Vietnam Radio Weather Stations, provide Frequency Department for ap- important information on proval. the conditions.

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