Hydrology and ocean science

Hydraulic control

Hydraulic control is the condition in stratified or open-channel flow where long waves cannot travel upstream, typically at a sill crest, governing exchange through straits and fjords.

Hydraulic geometry

Hydraulic geometry is an empirical method in fluvial geomorphology expressing a river channel's width, depth, and velocity as power functions of discharge, introduced by Leopold and Maddock in 1953.

Hydraulic head

Hydraulic head, also called piezometric head, is a measure of the total energy that moves ground water through an aquifer, expressed as a height above a datum.

Hydraulic tomography

Hydraulic tomography is an aquifer characterization method that maps spatially varying hydraulic conductivity and storage by inverting head responses from sequential pumping or injection tests.

Hydrobiologia

Hydrobiologia is a peer-reviewed scientific journal of aquatic sciences published by Springer since 1948, covering the biology of freshwater and marine environments from molecular to ecosystem level.

Hydrodynamic dispersion is the spreading and mixing of a solute as it moves through porous media, combining mechanical dispersion with molecular diffusion, and widening contaminant plumes in aquifers.

Hydrograph separation

Hydrograph separation is a hydrology method that splits a streamflow hydrograph into baseflow and quickflow, using graphical, digital-filter, or tracer mass-balance techniques to quantify how catchments generate runoff.

Hydrographer of the Navy

The Hydrographer of the Navy is the senior Royal Navy officer heading Britain's naval hydrographic effort, overseeing Admiralty charts since the office was created in 1795.

Hydrographic office

A hydrographic office is a national agency responsible for surveying a country's waters and producing the nautical charts, tide tables, and Notices to Mariners that ships need to navigate safely.

Hydrographic survey

Hydrographic survey is the measurement of water depth and seafloor features to produce bathymetric models and nautical charts, using single-beam and multibeam echo sounders, airborne LiDAR, and satellite-derived bathymetry.

Hydrography

Hydrography is the applied science of measuring and describing the physical features of oceans, seas, coastal waters, lakes, and rivers, chiefly to chart hazards and support safe navigation.

Oct 21, 2026

Hydrologic balance

Hydrologic balance (water balance): accounting where storage change equals precipitation minus evapotranspiration and runoff; basis of catchment hydrology, the Budyko framework, and water balance models.

Hydrological model

A hydrological model, also called a hydrological transport model, is a mathematical representation of water movement in a catchment, supporting flood forecasting and water resource management.

Hydrology

Hydrology, or hydrologic science, is the science of Earth's water, studying its occurrence, movement, and properties through the water cycle, from precipitation and runoff to evaporation.

Hydrophytic vegetation

Hydrophytic vegetation, also called hydrophytes, is the plant life of areas where saturated soils control which species grow, and one of three wetland delineation criteria.

HydroSHEDS

HydroSHEDS is a free suite of global hydrographic datasets, including catchment boundaries, river networks, and lakes, derived from satellite elevation data and initiated by World Wildlife Fund US in 2006.

Hydrosphere

The hydrosphere is all of Earth's water in liquid and solid form at and beneath the surface, including oceans, rivers, lakes, groundwater, glaciers, and ice sheets.

Hydrothermal circulation

Hydrothermal circulation: seawater moving through oceanic crust, driven by thermal gradients, exchanging heat and chemicals; accounts for 20–25% of Earth's heat loss and sustains chemosynthetic vent ecosystems discovered in 1977.

Hydrothermal vent

A hydrothermal vent, also known as a deep-sea vent, is a seafloor opening where seawater heated by magma reemerges as mineral-rich fluid, discovered near the Galápagos Islands in 1977.

HyMeX

HyMeX, the Hydrological Cycle in the Mediterranean Experiment, was a 10-year international research program from 2010 to 2020 studying the Mediterranean water cycle, especially heavy precipitation, flash floods, and droughts.

HYPE (hydrological model)

HYPE (HYdrological Predictions for the Environment) is a semi-distributed catchment model simulating water flow and nutrients, developed at SMHI in Sweden and applied operationally there since 2008.

Hypolimnion

The hypolimnion is the cold, dense bottom layer of a stratified lake, lying beneath the thermocline and cut off from atmospheric oxygen during summer stratification.

Hyporheic zone

The hyporheic zone is the porous region of a stream bed and banks where surface water and shallow groundwater mix, a subsurface environment distinct from both.

Ice cover dynamics

Ice cover dynamics is the study of the seasonal cycle of freezing, thickening, and thawing on lakes, summarized by ice phenology and used to track climate change.

Ice floe

An ice floe is a flat piece of sea ice 65 feet (20 m) or more across that floats freely, drifting with winds and currents in the polar pack.

Ice lens

An ice lens is a layer of nearly pure ice that forms in freezing soil as water migrates to the freezing front, causing frost heave.

Ice shelf collapse

Ice shelf collapse is the rapid disintegration of a floating Antarctic ice shelf into thousands of small icebergs, as with Larsen A in 1995 and Larsen B in 2002.

Ice-jam flood

An ice-jam flood is a flood caused by an accumulation of river ice that blocks the channel, producing water depths two to three times higher than open-water floods at the same flow.

Ice-Tethered Profiler

The Ice-Tethered Profiler (ITP) is an autonomous oceanographic instrument developed at Woods Hole that profiles the upper ocean beneath drifting Arctic sea ice and transmits data via satellite.