EVAPORATION AND ITS MEASUREMENT • Before rainfall reaches the outlet of a basin as runoff, certain demands of the catchment such as interception, depression storage and infiltration have to be met • Besides these, evaporation and transpiration processes transfer water to the atmosphere as water vapour • Evaporation from water bodies and the soil mass(…)

PROBABLE MAXIMUM PRECIPITATION (PMP) • PMP is used in the design of major hydraulic structures such as spillways in large dams • There appears to be a physical upper limit to the amount of precipitation that can occur over a given area in a given time • PMP – It is the greatest or the(…)

MEAN PRECIPITATION OVER AN AREA Raingauge – does point sampling of the areal distribution of a storm Hydrological Analysis – requires information on rainfall over an area, say, over a catchment Methods used to convert point rainfall values at different raingauge stations into an average value over a catchment include Arithmetical Mean Method Thiessen Polygon(…)

ANALYSIS OF RAINFALL DATA Before using rainfall records at a station for any analysis, the data has to be checked for Continuity Consistency Missing rainfall data can be estimated using the rainfall data at neighbouring stations. Estimation of Missing Rainfall Data • Required to find the missing annual precipitation at station X (not included in(…)

Design of Raingauge Networks Rainfall data is the most important and fundamental data required for all hydrological investigations. Catch area of a raingauge is very small compared to the aerial extent of a storm. Hence to get a representative picture of a storm over the entire drainage basin, the number of raingauges should be as(…)

Measurement of Precipitation Precipitation is expressed in terms of the vertical depth to which water from it would stand on a level surface area if all the water from it were collected on this surface. (the depth to which water would accumulate on the horizontal projection of the earth’s surface, if there were no losses(…)