Baseflow: Difference between revisions

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{{Short description|Stream flow between precipitation events}}

'''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]] that is sustained between precipitation events, fed to streams by delayed pathways. It should not be confused with [[groundwater flow]]. Fair weather flow is also called base flow.<ref>{{cite journalbook

|author= Kendall and McDonnell

|year= 1998

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== Importance ==

Baseflow is important for sustaining human [[Center of population|centers of population]] and [[Ecosystem|ecosystemsecosystem]]s. This is especially true for [[Drainage basin|watersheds]] that do not rely on [[snowmelt]]. Different ecological processes will occur at different parts of the [[hydrograph]]. During the baseflow ascending limb, there is frequently more [[stream]] area and [[habitat]] available for water-dependent species, spawning [[salmon]] for example. During the recession limb which in California is from May to October, there is increasingly less stream area, [[Indigenous (ecology)|indigenous]] species are more adept at surviving in low flow conditions than [[introduced species]].

== Geology ==

Baseflow is derived from [[bedrock]] [[water storage]] near surface [[valley]] [[soil]]s and [[riparian zone]]s. Water [[Percolation|percolates]] to [[groundwater]] and then flows to a [[body of water]]^. Baseflow depletion curve is the declining of baseflow/groundwater and soil reserves.<ref>{{Cite book|title=Environmental Hydrology, Second Edition|lastlast1=Ward,|first1= Andy and |last2=Trimble,|first2= Stanley|publisher=CRC Press|year=2003|isbn=978-1-4200-5661-7}}</ref> The volume and rate of water moving as baseflow can be affected by [[macropore]]s, [[micropores]], and other fractured conditions in the soil and shallow [[Geomorphology|geomorphic]] 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.<ref>{{Cite book|title=Key concepts in geomorphology|last=R.Bierman|first=Bierman, Paul R.|others=Montgomery, David R., 1961-, |publisher=University of Vermont., University of Washington.|isbn=9781429238601|___location=New York, NY|oclc=868029499|date = 2013-12-27}}</ref> [[River incision]] can decrease the baseflow by lowering the [[water table]] and [[aquifer]].<ref name=":1">{{Cite book|title=California rivers and streams : the conflict between fluvial process and land use|author=Mount, Jeffrey F.|date=1995|publisher=University of California Press|isbn=9780520916937|___location=Berkeley|oclc=42330977}}</ref>

Good baseflow is connected to surface water that is located in permeable, soluble, or highly fractured bedrock. Bad baseflow is in [[crystal]]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]].<ref name=":1" />

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Methods for identifying baseflow sources and residence/transit time include using [[solutes]] and [[Flow tracer|tracer]]s. 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.<ref>{{Cite journal|last1=Glynn|first1=Pierre D.|last2=Plummer|first2=L. Niel|date=2005-03-01|title=Geochemistry and the understanding of ground-water systems|journal=Hydrogeology Journal|language=en|volume=13|issue=1|pages=263–287|doi=10.1007/s10040-004-0429-y|bibcode=2005HydJ...13..263G|s2cid=129716764|issn=1431-2174}}</ref>

Methods for summarizing baseflow from an existing streamflow record include event based low flow statistics,<ref>{{Cite journal|last=O'Keeffe|first=Jay|date=2009|title=Sustaining river ecosystems: balancing use and protection|journal=Progress in Physical Geography: Earth and Environment|volume=33|issue=3|pages=339–357|doi=10.1177/0309133309342645|bibcode=2009PrPG...33..339O |s2cid=131587514}}</ref> flow duration curve,<ref>{{Cite book|title=Handbook of Hydrology|lastlast1=Stedinger,|first1= JR,|last2= Vogel,|first2= RM, and |last3=Foufoula-Georgiou,|first3= E|publisher=McGraw-Hill|year=1993}}</ref> metrics that explain proportioning of baseflow to total flow,<ref>{{Cite journal|date=2009-06-30|title=Examining geological controls on baseflow index (BFI) using regression analysis: An illustration from the Thames Basin, UK|journal=Journal of Hydrology|language=en|volume=373|issue=1–2|pages=164–176|doi=10.1016/j.jhydrol.2009.04.025|issn=0022-1694|last1=Bloomfield|first1=J.P.|last2=Allen|first2=D.J.|last3=Griffiths|first3=K.J.|bibcode=2009JHyd..373..164B|url=http://nora.nerc.ac.uk/id/eprint/7510/1/Bloomfield%20Allen%20Griffiths%202009.pdf}}</ref> and the baseflow recession curve which can be used on ungauged streams based on empirical relationship between watershed characteristics and baseflow at gauged sites.<ref>{{Cite journal|last1=Posavec|first1=Kristijan|last2=Bacani|first2=Andrea|last3=Nakic|first3=Zoran|date=2006-05-26|title=A Visual Basic Spreadsheet Macro for Recession Curve Analysis|journal=Ground Water|volume=44|language=en|issue=5|pages=060526082055001––|doi=10.1111/j.1745-6584.2006.00226.x|pmid=16961500|bibcode=2006GrWat..44..764P |s2cid=12485813 |issn=0017-467X}}</ref>

Certain parameters of baseflow, such as the [[Mean baseflow residence time|mean residence time]] 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.<ref>{{cite journal|author=Vitvar|display-authors=etal|year=2002|title=Estimation of baseflow residence times in watersheds from the runoff hydrograph recession: method and application in the Neversink watershed, Catskill Mountains, New York|url=http://www.cof.orst.edu/cof/fe/watershd/pdf/2002/Vitvar_et_al_2002.pdf|journal=Hydrol. Processes|volume=16|issue=9|pages=1871–1877|doi=10.1002/hyp.5027|bibcode=2002HyPr...16.1871V|s2cid=28833693 |access-date=2009-07-10|archive-date=2016-03-03|archive-url=https://web.archive.org/web/20160303185145/http://www.cof.orst.edu/cof/fe/watershd/pdf/2002/Vitvar_et_al_2002.pdf|url-status=dead}}</ref>

Baseflow separation is often used to determine what portion of a streamflow [[hydrograph]] occurs from baseflow, and what portion occurs from [[overland flow]]. Common methods include using [[Isotope hydrology|isotope tracing]] and the software program [https://water.usgs.gov/software/HYSEP/ HYSEP], among others.

== Anthropogenic effects ==

[[Human impact on the environment|Anthropogenic]] effects to baseflow include [[forestry]], [[urbanization]], and [[agriculture]]. [[Forest cover]] 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]].<ref name=":0">{{Cite journal|last=Price|first=Katie|date=2011|title=Effects of watershed topography, soils, land use, and climate on baseflow hydrology in humid regions: A review|journal=Progress in Physical Geography|volume=35|issue=4|pages=465–492|doi=10.1177/0309133311402714|bibcode=2011PrPG...35..465P |s2cid=7544941}}</ref> 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]], channels and impervious surfaces which decreases infiltration. In urban areas water is often imported from outside the watershed from deep wells and [[reservoir]]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.<ref name=":0" />

==See also==