A Study On The Hydrological Cycle

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II. Literature survey A. The Hydrological Cycle The central focus of any hydro-meteorological study is the hydrological cycle shown in Figure 2.1. The hydrological cycle has no beginning or end and its many processes occur continuously (Chow et al., 1988). In describing the cycle, the water evaporates from ocean and land surface to become part of atmosphere; water vapour is transported and lifted in the atmosphere until it condenses and precipitates on the land or the oceans. Precipitated water may be intercepted by vegetation, becomes overland flow over the ground surface, infiltrate into the ground, flow through the soil as subsurface flow and discharges into streams as surface runoff. The infiltrated water may percolate deeper to recharge groundwater, later emerging as spring and seeping into streams to form surface runoff and finally flowing into the sea or evaporating into the atmosphere as the hydrological cycle continues. Figure 2.1 Elements of the hydrologic cycle (freeze and cherry 1979) It is noted that though the concept of the cycle seems simple, the phenomena are enormously complex and intricate. It is not just one large cycle but it is rather composed of many interrelated cycles of continental, regional and local extent. The major achievement and objectives of the rainfall runoff modelling is thus to study a part (section) of the hydrological cycle, namely the land phase of the hydrological cycle on a catchment scale. Then the problem becomes to express the
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