Baseflow (also called drought flow, groundwater recession flow, low flow, low-water flow, low-water discharge and sustained or fair-weather runoff) is the portion of the

streamflow Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle. It is one component of the movement of water from the land to waterbodies, the other component being surface runoff. Wate ...

that is sustained between precipitation events, fed to streams by delayed pathways. It should not be confused with

groundwater flow Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

. Fair weather flow is also called base flow.

Importance

Baseflow is important for sustaining human centers of population and

ecosystems An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

. This is especially true for watersheds that do not rely on

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many par ...

. Different ecological processes will occur at different parts of the

hydrograph A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs). It can als ...

. During the baseflow ascending limb, there is frequently more stream area and

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

available for water-dependent species, spawning

salmon Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus '' Oncorhy ...

for example. During the recession limb which in California is from May to October, there is increasingly less stream area,

indigenous Indigenous may refer to: *Indigenous peoples *Indigenous (ecology), presence in a region as the result of only natural processes, with no human intervention *Indigenous (band), an American blues-rock band *Indigenous (horse), a Hong Kong racehorse ...

species are more adept at surviving in low flow conditions than

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...

Geology

Baseflow is derived from bedrock

water storage Water storage is a broad term referring to storage of both potable water for consumption, and non potable water for use in agriculture. In both developing countries and some developed countries found in tropical climates, there is a need to store p ...

near surface

valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

s and

riparian zone A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...

s. Water percolates to

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

and then flows to a

body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such a ...

^. Baseflow depletion curve is the declining of baseflow/groundwater and soil reserves. The volume and rate of water moving as baseflow can be affected by

macropore In soil, macropores are defined as cavities that are larger than 75 μm. Functionally, pores of this size host preferential soil solution flow and rapid transport of solutes and colloids. Macropores increase the hydraulic conductivity of soil ...

micropores A microporous material is a material containing pores with diameters less than 2 nm. Examples of microporous materials include zeolites and metal-organic frameworks. Porous materials are classified into several kinds by their size. The recom ...

, and other fractured conditions in the soil and shallow

geomorphic Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...

features. Infiltration to recharge subsurface storage increases baseflow. Evapotranspiration reduces baseflow because trees absorb water from the ground. In the fall baseflow can increase before it starts to rain because the trees drop their leaves and stop drinking as much water.

River incision River incision is the narrow erosion caused by a river or stream that is far from its base level. River incision is common after tectonic uplift of the landscape. Incision by multiple rivers result in a dissected landscape, for example a dissected ...

can decrease the baseflow by lowering the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

and

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...

. Good baseflow is connected to surface water that is located in permeable, soluble, or highly fractured bedrock. Bad baseflow is in

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

line or massive bedrock with minor fracturing and doesn't store water. Losing reaches is when the water flow decreases as it travels downstream and is fracturing deeper than surface water or in karst geology because limestone and dolomite high storage. Gaining reaches is when flow increases as it travels downstream. Gaining reaches are common in humid mountainous regions where the water table is above the surface water and the water flows from high head to low head following

Darcy's law Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of ...

Measurement

Methods for identifying baseflow sources and residence/transit time include using

solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent ...

and tracers. Solutes that originate in distinct areas of the watershed can be used to source baseflow-geochemical signatures. Tracers may be inserted into different parts of the watershed to identify flow paths and transit times. Methods for summarizing baseflow from an existing streamflow record include event based low flow statistics, flow duration curve, metrics that explain proportioning of baseflow to total flow, and the baseflow recession curve which can be used on ungauged streams based on empirical relationship between watershed characteristics and baseflow at gauged sites. Certain parameters of baseflow, such as the

mean residence time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...

and the baseflow recession curve, can be useful in describing the mixing of waters (such as from precipitation and groundwater) and the level of groundwater contribution to streamflow in catchments. Baseflow separation is often used to determine what portion of a streamflow

occurs from baseflow, and what portion occurs from

overland flow Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the s ...

. Common methods include using isotope tracing and the software progra
HYSEP
among others.

Anthropogenic effects

Anthropogenic effects to baseflow include

forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. ...

urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

, and

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

Forest cover Forest cover is the amount of forest that covers a particular area of land. It may be measured as relative (in percent) or absolute (in square kilometres/square miles). Around a third of the world's surface is covered with forest, with closed-canop ...

has high infiltration and recharge because of tree roots. Removal of forest cover can cause a short-term increase in mean flow and baseflow because there is less interception and

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...

. Urbanization includes a re-organization of surface and subsurface pathways so that water is flushed through catchments because of reduced hydraulic resistance,

Manning's n The Manning formula or Manning's equation is an empirical formula estimating the average velocity of a liquid flowing in a conduit that does not completely enclose the liquid, i.e., open channel flow. However, this equation is also used for calculat ...

, channels and impervious surfaces which decreases infiltration. In urban areas water is often imported from outside the watershed from deep wells and

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

s. The pipes that transport the water often leak 20-25% to the subsurface which can actually increase baseflow. Agriculture can lower baseflow if water diverted from stream for irrigation, or can raise baseflow if water is used from a different watershed. Pastures can increase compaction and reduce organic matter with reduces infiltration and baseflow.

References

{{Authority control Hydrology Limnology

Importance

Geology

Measurement

Anthropogenic effects

See also

References