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32 AUTOMATIC HYDROLOGICAL OBSERVATIONS(iv)(v)(vi)(vii)(viii)(ix)(x)The whole measurement cycle is 5 minutes.The measurement frequency may be varied by an aperatar and may be performedon-an hourly, two-hourly, or once or twice a day basis.The accuracy· of measurements:Water-level ± (1-2) cm.Water temperature t0.2°C.from the auto­Hydrological sensors may be at a distance of up to 2 000 mmation unit.The automation unit operates satisfactorily at temperatures from _35 0 C to+35 0 C and an air humidity up to 98 per.·cent; the ·puncher at temperaturesfr~m 0 to 30 0 t and an air humidity up ~o 70 per cent.The dimensions and the weight of the automation unit are 850 x 500 x 400 mmand 95 kg, respectively.The AHRS automation unit is installed in a shelter for protection against_9t~ospher~c influences (rain, wind, etc.).3.4 Example IV (U.S.S.R.). Mudflow radio warner (MRW)IntroductionSudden temporary torrents appear in mountainous regions as a result ofheavy rain storms i snow melt and flushins from glacial, moraine-dammed lakes, causingmudflows which are a dangerous phenomenon inflicting heavy damage and casualties.Protection against mudflows has been a matter of great concern. Variousprecautions are taken for this purpose in the areas where mudflows are likely tooccur: mud dams and chutes are erected, special mud flow watch and warning servicesare established, etc.The mudflow radio warner is intended to warn, with on ample time margin, thepopulation and authorities of mountain and sub-mountain regions of the formation andpassage of a mudflow registered by special sensors installed .in. a mountain riverbasin. Besides that, the MRW provides for remote supervision of river water-level,and the sharp fluctuations which often indicate a mudflow formation. For thispurpose the mud flow warner contains two sensors, one for water-level and one for mudflow.The MRW is based on the principle of . a signal frequency selection. Aspecific audio frequency is assigned to each of the three elements under study (thefirst water-level, the second water-level and the mudflow). The audio frequencydiscriminated by appropriate devices turns on the warning system.The MRWsystem includes transmitting and receiving stations.A transmitting statian (the system usuallystations) is established in a mountain river basin,incorporates several broadcastingin tributDries and in major