Baseflow

Source: Wikipedia, the free encyclopedia.

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.[1]

Importance

Baseflow is important for sustaining human

indigenous species are more adept at surviving in low flow conditions than introduced species
.

Geology

Baseflow is derived from

micropores, and other fractured conditions in the soil and shallow 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.[3] River incision can decrease the baseflow by lowering the water table and aquifer.[4]

Good baseflow is connected to surface water that is located in permeable, soluble, or highly fractured bedrock. Bad baseflow is in crystalline 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.[4]

Measurement

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

solutes 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.[5]

Methods for summarizing baseflow from an existing streamflow record include event based low flow statistics,[6] flow duration curve,[7] metrics that explain proportioning of baseflow to total flow,[8] and the baseflow recession curve which can be used on ungauged streams based on empirical relationship between watershed characteristics and baseflow at gauged sites.[9]

Certain parameters of baseflow, such as the

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.[10]

Baseflow separation is often used to determine what portion of a streamflow

overland flow. Common methods include using isotope tracing and the software program HYSEP
, among others.

Anthropogenic effects

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 reservoirs. 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.[11]

Analysis software

BFI+ Software for baseflow separation from a hydrogram. It was developed for baseflow separation from daily or weekly time series of river discharges. The program includes a choice of 11 methods for separation. It includes methods such as local minimum, fixed interval or sliding interval methods; and also methods of recursive digital filters.[12]

See also

References

  1. ^ Kendall and McDonnell (1998). "Isotope Tracers in Catchment Hydrology". Elsevier. Archived from the original on July 5, 2008. Retrieved July 10, 2009. {{cite journal}}: Cite journal requires |journal= (help)
  2. ISBN 978-1-4200-5661-7.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  3. OCLC 868029499.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link
    )
  4. ^
    OCLC 42330977
    .
  5. S2CID 129716764
    .
  6. S2CID 131587514
    .
  7. ^ Stedinger, JR, Vogel, RM, and Foufoula-Georgiou, E (1993). Handbook of Hydrology. McGraw-Hill.{{cite book}}: CS1 maint: multiple names: authors list (link)
  8. ISSN 0022-1694
    .
  9. S2CID 12485813
    .
  10. S2CID 28833693. Archived from the original
    (PDF) on 2016-03-03. Retrieved 2009-07-10.
  11. ^
    S2CID 7544941
    .
  12. ^ "HydroOffice | Tool | BFI+". hydrooffice.org. Retrieved 2023-05-19.
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