Baseflow

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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]

Contents

Importance

Baseflow is important for sustaining human centers of population and ecosystems. This is especially true for 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 species are more adept at surviving in low flow conditions than introduced species.

Geology

Baseflow is derived from bedrock water storage near surface valley soils and riparian zones. Water percolates to groundwater and then flows to a body of water . Baseflow depletion curve is the declining of baseflow/groundwater and soil reserves. [2] The volume and rate of water moving as baseflow can be affected by macropores, 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 hydrograph occurs from baseflow, and what portion occurs from overland flow. Common methods include using isotope tracing and the software program HYSEP, among others.

Anthropogenic effects

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. [11] 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 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

Related Research Articles

<span class="mw-page-title-main">Hydrology</span> Science of the movement, distribution, and quality of water on Earth and other planets

Hydrology is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydrologist. Hydrologists are scientists studying earth or environmental science, civil or environmental engineering, and physical geography. Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation, natural disasters, and water management.

<span class="mw-page-title-main">Aquifer</span> Underground layer of water-bearing permeable rock

An aquifer is an underground layer of water-bearing material, consisting of permeable or fractured rock, or of unconsolidated materials. Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could lead to the formation of a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.

Surface-water hydrology is the sub-field of hydrology concerned with above-earth water, in contrast to groundwater hydrology that deals with water below the surface of the Earth. Its applications include rainfall and runoff, the routes that surface water takes, and the occurrence of floods and droughts. Surface-water hydrology is used to predict the effects of water constructions such as dams and canals. It considers the layout of the watershed, geology, soils, vegetation, nutrients, energy and wildlife. Modelled aspects include precipitation, the interception of rain water by vegetation or artificial structures, evaporation, the runoff function and the soil-surface system itself.

<span class="mw-page-title-main">Hydrograph</span>

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 . Hydrographs often relate changes of precipitation to changes in discharge over time. It can also refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network. Graphs are commonly used in the design of sewerage, more specifically, the design of surface water sewerage systems and combined sewers.

In hydrology, discharge is the volumetric flow rate of a stream. It equals the product of average flow velocity and the cross-sectional area. It includes any suspended solids, dissolved chemicals, or biologic material in addition to the water itself. Terms may vary between disciplines. For example, a fluvial hydrologist studying natural river systems may define discharge as streamflow, whereas an engineer operating a reservoir system may equate it with outflow, contrasted with inflow.

In hydrology, there are two similar but distinct definitions in use for the word drawdown:

<span class="mw-page-title-main">Ecohydrology</span>

Ecohydrology is an interdisciplinary scientific field studying the interactions between water and ecological systems. It is considered a sub discipline of hydrology, with an ecological focus. These interactions may take place within water bodies, such as rivers and lakes, or on land, in forests, deserts, and other terrestrial ecosystems. Areas of research in ecohydrology include transpiration and plant water use, adaption of organisms to their water environment, influence of vegetation and benthic plants on stream flow and function, and feedbacks between ecological processes, the soil carbon sponge and the hydrological cycle.

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<span class="mw-page-title-main">Infiltration (hydrology)</span> Process by which water on the ground surface enters the soil

Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meters per day but can also be measured in other units of distance over time if necessary. The infiltration capacity decreases as the soil moisture content of soils surface layers increases. If the precipitation rate exceeds the infiltration rate, runoff will usually occur unless there is some physical barrier.

The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) is a dynamic rainfall–runoff–subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas.

Runoff is the flow of water across the earth, and is a major component in the hydrological cycle. Runoff that flows over land before reaching a watercourse is referred to as surface runoff or overland flow. Once in a watercourse, runoff is referred to as streamflow, channel runoff, or river runoff. Urban runoff is surface runoff created by urbanization.

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 runoff component, the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.

<span class="mw-page-title-main">Hydrological transport model</span>

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<span class="mw-page-title-main">Groundwater recharge</span> Groundwater that recharges an aquifer

Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally and through anthropogenic processes, where rainwater and or reclaimed water is routed to the subsurface.

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<span class="mw-page-title-main">Runoff model (reservoir)</span> Type of water motion

A runoff models or rainfall-runoff model describes how rainfall is converted into runoff in a drainage basin. More precisely, it produces a surface runoff hydrograph in response to a rainfall event, represented by and input as a hyetograph. Rainfall-runoff models need to be calibrated before they can be used.

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Baseflow residence time is a parameter useful in describing the mixing of waters from the infiltration of precipitation and pre-event groundwater in a watershed. It describes the average amount of time that water within the transient water supply resides in a watershed. Many methods of determining baseflow residence time have been developed, mostly involving mathematical models using a convolution integral approach with isotopic or chemical data as the input. Other methods that do not require such extensive and expensive data collection include Brutsaert and Nieber, which uses aquifer parameters as inputs, and Vitvar et al., which uses the stream flow hydrograph to determine baseflow recession parameters.

<span class="mw-page-title-main">Catchment hydrology</span> Hydrology of drainage basins

Catchment hydrology is the study of hydrology in drainage basins. Catchments are areas of land where runoff collects to a specific zone. This movement is caused by water moving from areas of high energy to low energy due to the influence of gravity. Catchments often do not last for long periods of time as the water evaporates, drains into the soil, or is consumed by animals.

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. ↑ Ward, Andy and Trimble, Stanley (2003). Environmental Hydrology, Second Edition. CRC Press. ISBN   978-1-4200-5661-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. ↑ R., Bierman, Paul (2013-12-27). Key concepts in geomorphology. Montgomery, David R., 1961-, University of Vermont., University of Washington. New York, NY. ISBN   9781429238601. OCLC   868029499.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link)
  4. 1 2 Mount, Jeffrey F. (1995). California rivers and streams : the conflict between fluvial process and land use. Berkeley: University of California Press. ISBN   9780520916937. OCLC   42330977.
  5. ↑ Glynn, Pierre D.; Plummer, L. Niel (2005-03-01). "Geochemistry and the understanding of ground-water systems". Hydrogeology Journal. 13 (1): 263–287. Bibcode:2005HydJ...13..263G. doi:10.1007/s10040-004-0429-y. ISSN   1431-2174. S2CID   129716764.
  6. ↑ O'Keeffe, Jay (2009). "Sustaining river ecosystems: balancing use and protection". Progress in Physical Geography: Earth and Environment. 33 (3): 339–357. doi:10.1177/0309133309342645. 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. ↑ Bloomfield, J.P.; Allen, D.J.; Griffiths, K.J. (2009-06-30). "Examining geological controls on baseflow index (BFI) using regression analysis: An illustration from the Thames Basin, UK" (PDF). Journal of Hydrology. 373 (1–2): 164–176. Bibcode:2009JHyd..373..164B. doi:10.1016/j.jhydrol.2009.04.025. ISSN   0022-1694.
  9. ↑ Posavec, Kristijan; Bacani, Andrea; Nakic, Zoran (2006-05-26). "A Visual Basic Spreadsheet Macro for Recession Curve Analysis". Ground Water. 44 (5): 060526082055001––. doi:10.1111/j.1745-6584.2006.00226.x. ISSN   0017-467X. PMID   16961500. S2CID   12485813.
  10. ↑ Vitvar; et al. (2002). "Estimation of baseflow residence times in watersheds from the runoff hydrograph recession: method and application in the Neversink watershed, Catskill Mountains, New York" (PDF). Hydrol. Processes. 16 (9): 1871–1877. Bibcode:2002HyPr...16.1871V. doi:10.1002/hyp.5027. S2CID   28833693. Archived from the original (PDF) on 2016-03-03. Retrieved 2009-07-10.
  11. 1 2 Price, Katie (2011). "Effects of watershed topography, soils, land use, and climate on baseflow hydrology in humid regions: A review". Progress in Physical Geography. 35 (4): 465–492. doi:10.1177/0309133311402714. S2CID   7544941.
  12. ↑ "HydroOffice | Tool | BFI+". hydrooffice.org. Retrieved 2023-05-19.
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