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2AUTOMATIC HYDROLOGICAL OBSERVATIONS1.2Reasons for introducing automation1.2.1The primary reason for changing to, or increasing the degree of, Qutomationin a data callection network is the need to improve the quality, quantity and/ortimely receipt of the data. Most present day hydrological networks were developedin response to particular, localized problems or scientific interests and not with aspecific objective of satisfying the future requirements for all hydrological purposes.Many networks depend on manual, in-situ observations by observers. This isa slow and laborious way of collecting data. Consequently, there is often inadequatespatial information for those areas where observers are not readily available. Datafrom such networks are sufficient for simple general hydrological resource studies,but are of only limited value for project planning and operation. In most cases thedata collection programme does not meet the requirements for timely preparation andissuing of·hydrolagical forecasts and warnings or for synoptic monitoring.As the demands for hydrological planning and forecasting services increase,the agency or agencies responsible for providing such services will be faced with adecision on the need for modernizing the data collection network.1.2.2 Manual versus automaticIt is often frustrating to maintain a network of stations manned by observerswhen there may be a serious need to change to an automoted system. Changingobservers to improve the quality and/or reliability of reporting is a continualproblem. Although the trend for people to be more mobile has resulted in more frequentchanges in observers than has been possible in the' past, it is becomingincreasingly difficult to obtain observers who are willing to make measurements onweekends. Moreover, there is a steady rise in the cost of observers, their recruitmentand training and the processing of data collected from hydrological networksmanned by observers.Although such factors may make a change to a more· fully automated systemappear attractive lthere are problems and costs associated with automated systemsthat should be carefully evaluated before a final decision is taken. A cost/benefitapproach should be the primary basis for such a decision. It is, however, extremelydifficult to determine the actual value of either the old or new system or even thecomparative figures. This is especially true when the data are utilized for severalpurposes and costs must be allocated accordingly. In addition to cost comparisons,the following questions should be given careful consideration.(a)(b)(c)Is there a real need to improve the quality of the data?Is there a real need to increase the quantity of data(i.e. improve the areal coverage)?Is there a real need to reduce the time required forreceipt of data?
AUTOMATION OF OBSERVING STATIONS3In considering the above questions it should be recognized thot the problem is adynamic one. Rapid chonges in the field of hydrology, instrumentation and means oftransmission of data as well as in the demand for services make it imperative thatanticipated future conditions be given proper evaluation.The automation of data collection systems may reduce or eliminate most humanobservational errors. However, this advontage moy be offset by the introduction ofinaccuracies caused by instability in the sensing, recording or transmission system.Errors resulting from such instability in electronic systems may be much moredifficult to identify and correct than the human ones and quolity control of dot~then becomes highly dependent upon the quolity of maintenance.A distinct advantage in most automated systems is the continuous recordingcompared to the point measurements obtained by manual observations. For example,continuous flow hydrographs, required for mony hydrologicol analyses, permit thedetermination of maximum and minimum values, which are essential for the developmentand application of mathematical and physical hydrological models that are now incommon use.The quality of the data may be improved by data collection techniques otherthan the automation of the present system. Remote sensing technology moy providemeans to obtain acceptable areal averages for certain elements. Many such improvedtechniques ore now being developed ond these should be evoluated for the present andfuture requirements before automation of a point measurement network is undertaken.One of the most obvious advantages of automation is the obility to obtoindata for locations where observers are not available. However, this should not be abasis for a decision· to automate the entire network. From a cost consideration themost valuable data collection programme may be one in which automation is used foronly a portion of the area or for only those areas for which data are required on a"real time" basis.The rapid advancement that is taking place in the fields of instrumentationand data transmission may provide ways and means for improved collection of data inthe near future that would be of great use, at less overall cost than those atpresent in use. Information on considerations that should be given to selection ofa transmission sy~tem is given in Chapter 2.Careful consideration should be given to the possible advantages to begoined by automating only that portion of the . system required for present andforeseeable needs. However, the initial plans for any automatic system shouldinclude provisions for expansion and for the incorporation of neW technology wheneverpossible. Since the demands for improved data, quality and quantity, normallyincrease with time, a constant effort must be devoted to improve instrumentation.
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