Hydrology is concerned with water of the Earth in all its states, their occurrences, distribution, and circulation through the unending hydrologic cycle of precipitation, consequent runoff, stream flow, infiltration and storage, eventual evaporation, and reprecipitation. Water exists on the earth in gaseous form, liquid, and solid forms, and is circulated among the different parts of the Earth mainly by solar energy and planetary forces. Hydrological cycle is referred to as the circulation of water from the sea to the land through the atmosphere back to the sea often with delays through process like precipitation, interception, runoff, infiltration, percolation, ground water storage, evaporation, and transpiration and also water that returns to the atmosphere without reaching the sea. A flood is an unusually high stage in a river, normally the level at which the river overflows its banks and inundates the adjoining area.