Hydrology, Floods and Droughts | Groundwater and Surface Water

Groundwater and surface water are two important components of the hydrologic system. One objective of hydrologic studies is to understand the spatial and temporal variations of water storage and movement. This article first presents an overview of the global distribution of water, the hydrologic cycle, and the water balance concept. It then describes the physical principles governing the movement of groundwater and surface water by focusing on the hydraulic gradient as the driving force for flow: Darcy's law for groundwater and Manning's equation for streams. Finally, applied aspects of hydrology are discussed as they relate to water contamination, land subsidence, hydrothermal fluids, and hydroseismicity.