Q. What is Crest gauges explain?
In case of bridges, it is sometimes necessary to observe high flood levels rather than daily gauges to ensure that minimum clearance is not encroached upon. Very high peaks may occur any time during day and night. Unless recorder type gauges are installed it is difficult to obtain peak gauge data. Devices called crest gauges are useful to record peak flood levels under such conditions.
A simple crest gauge consists of bottles fixed to a staff gauge. Another version is an empty pipe with inside staff gauge on which peak water level is marked by granulated cork powder deposited inside the pipe. One more type of crest gauge has a float moving inside a transparent tube, the float being prevented from moving down with receding water level by means of a rubber skirt attached to it. Another simple device is to paint stripes on the staff gauge by yellow dextrine powder which leaves a high water mark when it gets dissolved in water. Details of such peak water levels over a period of years collected at the -bridge site will help in flood frequency studies.