Water is Earth’s most critical fluid in environmental processes and human life. When discussing stormwater management it is important to distinguish between hydrology and hydraulics. Some aspects of hydrology involve hydraulics but, in general, the two are very different. Here’s how to understand these differences.
What is hydrology?
Hydrology is the study of the circulation of water and its constituents through the hydrologic cycle or the quantification of flows that are ultimately produced by precipitation. It deals with precipitation (rain, snow, sleet, hail, etc.), evaporation, infiltration, groundwater flow, surface runoff, streamflow, and the transport of substances dissolved or suspended in flowing water. In the field of stormwater engineering, hydrology typically refers to the rate of precipitation, the quantity of water, the rate of surface runoff, and the timing of its arrival at a point of interest.
What is hydraulics?
Alternatively, the term hydraulics is defined as the study of the mechanical behavior (movement/flow) of water in physical systems (Henry M. Morris and James M. Wiggert). In engineering terms, hydraulics analyzes how surface and/or subsurface flows move from one point to the next. A hydraulic analysis is used to evaluate flow in rivers, streams, storm drain networks, water aqueducts, water lines, sewers, etc.
As you can see, though hydrologic and hydraulic processes are interdependent, they are distinctly different.