Útstreymi

Utstreymi is an Icelandic noun meaning the act or rate of flowing outward from a system. In hydrology it refers to discharge, the volume of water that leaves a river, lake, or reservoir per unit time, commonly expressed as cubic meters per second (m3/s). It is a key component of the water balance and is influenced by precipitation, snowmelt, groundwater discharge, evaporation, and human management such as dam releases. The term covers natural outflows at river mouths, springs, and groundwater seeps, as well as engineered outflows through spillways or turbines in hydroelectric facilities. The opposite concept is innstreymi, the inflow of water into a system.

Measurement and modelling: Outflow is typically measured with stream gauges or inferred from hydraulic models. In reservoirs, controlling útstreymi allows flood mitigation, water supply regulation, and ecological considerations. In estuaries, outflow interacts with tidal inflow and saline intrusion, affecting nutrient transport and sediment deposition.

Terminology and usage: The word is formed from út- meaning out and streymi meaning flow, and is commonly used in Icelandic hydrology, environmental science, and engineering literature. In broader contexts, útstreymi can describe the outflow of other substances, such as pollutants or nutrients, from a system. Related terms include innstreymi (inflow) and discharge, which are integral to understanding water balance and environmental management.