Key Definitions in Hydrology and Physical Geography
Glossary of Hydrological and Geographical Terms
River Basin (Drainage Basin)
A river basin, also known as a drainage basin, is the entire land area or region drained by a river and its tributaries. All precipitation within this area flows into the same river system.
Watershed (Drainage Divide)
A watershed, or drainage divide, is the high ground or ridge that separates two adjacent river basins, directing water to different river systems.
River Network
A river network illustrates the interconnected system of a main river and its tributaries, showing how they converge and drain a specific geographical area. Its formation is influenced by the geological structure of the region.
Riverbed (Channel)
The riverbed, or channel, is the physical space occupied by the flowing waters of a river. It defines the path and boundaries within which the water circulates during normal flow conditions, before flooding occurs.
Water Infiltration
Water infiltration refers to the downward movement of water from the surface into the soil and rock layers. This process is crucial for groundwater recharge and is often associated with the leaching of minerals within the rock.
Underground Water (Groundwater)
Underground water, commonly known as groundwater, is water that exists beneath the Earth’s surface in soil pore spaces and in the fractures of rock formations. It often flows through permeable layers, such as limestone aquifers.
Aquifer
An aquifer is an underground layer of water-bearing permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted. Many aquifers, particularly in regions like Spain, face issues of overexploitation.
Water Table
The water table is the upper surface of the zone of saturation, where the pores and fractures of the ground are saturated with water. Its depth varies, and it is the level at which groundwater can be accessed by wells.
River Capacity (Flow Measurement)
River capacity refers to the volume of water a river channel can hold or transport. Its measurement is typically conducted at gauging stations, where instruments record water levels and flow rates to assess the river’s discharge and overall capacity.
Flow Rate (Discharge)
Flow rate, or discharge, is the volume of water passing a given point in a river per unit of time, typically measured in cubic meters per second. It can be calculated over long periods to determine a river’s regime, including absolute flow, average flow, and peak flow.
Flood (Flash Flood)
A flood, or flash flood, is a rapid and often violent increase in the volume of water in a river or drainage basin, leading to the inundation of normally dry land. These events can be catastrophic and often occur during periods of intense rainfall, such as in autumn.
Inundation (Flooding)
Inundation refers to the process where an area is covered with an extraordinary amount of water, typically from a river overflowing its banks or from heavy rainfall. These events can be unusual and often have catastrophic consequences.
Low Flow (Drought Period)
Low flow, or estiaje, describes the period when a river or lake experiences its minimum water levels and discharge. This typically occurs during dry seasons or drought periods.
Torrent (Stream Course)
A torrent is a fast-flowing, impetuous, and often violent stream of water, typically found in mountainous regions. Its course is characterized by rapid flow, especially during heavy rainfall events.
Canyon (Gorge)
A canyon, or gorge, is a deep, narrow valley with steep sides, often carved by a river. These formations are common in limestone regions, where the erosive power of water can create impressive geological features, sometimes leading to the collapse of underground galleries.
River Terrace
A river terrace is a flat, step-like landform found along the sides of a river valley, representing an old floodplain or riverbed that has been abandoned as the river incised its channel deeper. They are formed by cycles of deposition and erosion, often indicating changes in river flow or base level.
Ria
A ria is a submerged river valley, typically found along coastlines, formed when a river valley is flooded by the sea due to a rise in sea level or a subsidence of the land. They are common features of the Galician coast in Spain, often associated with tectonic activity and the development of Atlantic rivers.
Delta
A delta is a landform that forms at the mouth of a river, where the river’s current slows down upon entering a larger body of water (like a sea or lake). This reduction in velocity causes the river to deposit its sediment load, creating a triangular or fan-shaped alluvial accumulation. Deltas are less common in seas with strong tides, such as the Mediterranean, compared to those with weaker tides.
Wadi
A wadi is a natural riverbed or valley, typically found in arid or semi-arid regions, that remains dry except during periods of heavy rainfall. When rain occurs, wadis can experience sudden, powerful flash floods, making them characteristic features of desert climates.
River Regime
A river regime describes the annual pattern of variations in a river’s flow, indicating periods of high water (floods) and low water (droughts). It is influenced by factors such as precipitation, snowmelt, and human activities.
Estuary
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries are typically flooded by high tides and are often found at the mouths of rivers.
Marsh
A marsh is a wetland area, typically low-lying and often near sea level, that is frequently flooded by tides or river waters. Characterized by herbaceous vegetation, marshes are vital habitats for migratory birds and are often protected under conventions like RAMSAR.
Lagoon (Albufeira)
A lagoon is a shallow body of water separated from a larger body of water (like the sea) by a narrow landform, such as a barrier island or a sandbar (a littoral cordon). While often beneficial for agriculture, many lagoons are ecologically sensitive and face environmental threats.
Tide
A tide refers to the regular and cyclic rise and fall of sea levels, primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun. Atlantic tides are generally much stronger than those in the Mediterranean Sea, where they are often negligible.
Tombolo
A tombolo is a depositional landform, typically a sand or shingle bar, that connects an island to the mainland or to another island. These natural formations are often utilized for coastal development and urban centers.
Bioclimatic Relations
Bioclimatic relations involve the direct interactions and dependencies between climate conditions and the biological communities (flora and fauna) that inhabit and respond to those specific climatic environments.
Biomass
Biomass refers to the total amount of organic matter present in a given area or ecosystem. It includes phytomass (plant matter) and zoomass (animal matter). Biomass is considered an ecological alternative energy source, though its production and pricing are distinct from conventional agricultural commodities.
Ecosystem
An ecosystem is a biological community of interacting organisms and their physical environment. It encompasses all living creatures and the non-living elements with which they interact.
Climax Vegetation
Climax vegetation represents the final, stable stage of ecological succession in a given environment. It is a biological community that has reached equilibrium with its environmental conditions, demonstrating maximum biological development and ecological potential for that specific climate and soil type.
Endemic Species
An endemic species is a species of plant or animal that is native to and restricted to a particular geographical region. It is found exclusively in that specific area and nowhere else in the world, even if other areas have similar environmental conditions.
Conifer Forests
Conifer forests are typically found in continental cold climates. These forests are characterized by coniferous trees (e.g., pines, spruces, firs) that generally retain their needles year-round, giving them a green appearance even in winter. Their fruits are typically cones.