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6 AUTOMATIC HYDROLOGICAL OBSERVATIONSThese are same of the factors which must be considered in the colder partsof the world. Similarly, extremely hot, arid or humid climates give rise to theirown peculiar sets of instrumentation problems. In all extreme climotes, on analysisshould be mode of the conditions which would affect the operation of proposed outomaticequipment. A valuable aid in this regard is the experience which has beengained by users of various types of : automatic equipment in similar location••Discussion with these people or reference to the literature may eliminate costlyerrors in the choice of instruments.The characteristics of the terrain in the immediote vicinity of the observingstation play an important role in the selection of equipment. For example, itwould be extremely costly to build wells to house water-level recorders near riverswhere waier-level fluctuations are quite large and the river banks are mostly bedrock.Wells will also be impractical where the river transports great amounts of sedimentwhich will continually block intake pipes. In these cases, a float-type gauge wouldnot be practical and instruments using the hydrostatic principle for detecting waterlevelchonges should be used.On the other hand, for rivers having moving beds, it mightany instrument having the detecting section in the stream itself ascarried away. An installation using a well and a float-type gaugepractical.be unwise to useit might bewould be moreFactors such as the geology of the local terrain and the presence of excessvegetation will affect the selection of the type of installation. Many instruments,in order to operate properly, have to be level, in which case the foundation of theshelter may have to be foirly elaborate in order to ensure that the structure is notaffected by changes in temperature, erosion or plant growth.In mountainous areas the installation of radio relay stations may be necessaryto provide for the transmission of the data. The initial and mointenance costs may bea significant factor in a decision on automation.Other conditionsIn urban and in certain remote areas, the problem of vandals can beserious and often may necessitate the use of special housing and equipment.addition, wherever possible, exterior portions of any installation should beto avoid tampering.veryInburiedWhen considering sites in inaccessible areas, difficulties and cost of transportation,in some cases, exclude the use of heavy equipment. In these c~ses, boththe type of installation and the instruments themselves should b: chosen w~th dueconsideration to weight and possible difficulties in tronsportat~on.
AUTOMATION OF OBSERVING STATIONS7Animals may prave to be a problem in certain areas and, if so, suitableprotection should be included in the installations.1.3.2Many of the installations which will be considered in connexion with theautomation of hydrological obser/otions will imply the use of electric power forsensor purposes, chart movement, heating or data transmission. This is one of themost important and sometimes most difficult considerotions in the choice of equipment.If power is available locally, the choice will be relatively simple but, even so, astandby system of batteries may be necessary. This will be the case when, forexample, the observations are being used for flood forecasting and where, duringextreme floods, power lines could often be broken. In order to assure uninterruptedobservation of data during these critical periods, a standby battery system isessential.If no commercial power is available other sources such as wind-generators,fuel-driven generatars and batteries should be considered. As a first step, a carefulevaluation of the energy consumption of the observation system should be made.ObviouslYt continuous transmission of data will appreciably increase the power consumption.As the use of more sophisticated power supplies, such as generators,involves the possibility of mechanical failure, it is generally preferable, whereverpossible, to employ low-consumption equipment which would permit the use of batteries.The batteries should be carefully chosen to ensure reliable operation under differentclimatic conditions, especially in extremely hot or cold temperatures. Rechargeablebatteries usually involve a large initial expenditure as well as relatively frequentinspections. For most recording instruments, non-rechargeable batteries are available,if required, which guarantee approximately two years of operation beforereplacement.At present, it is very difficult to obtain recording and transmitting equipmentas well as power supplies which will completely answer 011 the problemsencountered at ony one site. It should be understood by the network planner thatlocal modifications will almost invariably be nec~ssary to meet the particularcombination of problems arising from both local conditions and power demands.1.3.3As hydrological observing stations are installed primarily to obtain data tohelp ensure proper use of water resources, it is evident that the accuracy of themeasurements should meet the standards of those who use the information. Cost ofequipment usually varies directly with its accuracy. Therefore, excessive demandsover and above the accuracy needed by the data users would, in effect l be a waste offinancial resources. This is elso true when the G~curacy demanded from one part ofan observation programme is out of proportion with the results obtained in the overallprogramme.During the design of an observing proglomme it is therefore obvious that astudy should be made regarding the accurocy needed by the users, both present and
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Page 12 and 13: 2AUTOMATIC HYDROLOGICAL OBSERVATION
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Page 57 and 58: ANN E X 1QUESTIONNAIRE ON HYDROMETE
Page 59 and 60: ANN E X 2LIST OF INSTRUMENTS OF PRO
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