ISO 18365:2013 pdf free

ISO 18365:2013 pdf free.Hydrometry一Selection, establishment and operation of a gauging station
The site selected for determination of stage shall be selected according to the purpose for which the readings are required. Accessibility of the site and the availability of an observer if the gauge is to be non-recording are important criteria as is the availability of an appropriate power supply and data communication capabilities if the gauge is to be recording.
Gauges on lakes and reservoirs are normally located near the outlet, but shall be located sufficiently far away from the zone where an increase in velocity causes a drawdown in water level. Gauges on large bodies of water shall also be located so as to reduce the effect of strong winds which may cause misleading data which may not be representative of the body of water being measured. Hydraulic conditions (preferably a sufficiently long uniform stretch of water channel with uniform bed topography) are important factors in site selection in open channels, particularly where water levels may later be used in the computation of discharge. To ensure repeatability of the readings, ideally a bed or channel control shall be present, which itself shall be stable and sensitive to changes in the level of the water. For the purpose of monitoring water levels e.g. for flood warning purposes, this may not be a strict requirement.
A list of potential sites shall be established with their advantages and disadvantages identified. Site selection can then be made according to the criteria identified in Clause 4. The establishment of the gauge zero shall be chosen so as to avoid negative readings. Thus it shall be set well below the level of the control feature. This zero point shall be correlated with a national datum through a station benchmark and should be checked annually with respect to this benchmark. This will ensure that, should loss or damage to the reference gauge occur, it can be replaced at exactly the same level.
The benchmark itself shall be checked regularly in order to confirm that it still represents the national datum. The frequency of such checks shall be dependent on local soil dynamics.ISO 18365 pdf download.