Hyporheic zone

The hyporheic zone is the region of sediment and porous space beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water. The flow dynamics and behavior in this zone (termed hyporheic flow or underflow) is recognized to be important for surface water/groundwater interactions, as well as fish spawning, among other processes.[1] As an innovative urban water management practice, the hyporheic zone can be designed by engineers and actively managed for improvements in both water quality and riparian habitat.[2]

The assemblage of organisms which inhabits this zone are called hyporheos.

The term hyporheic was originally coined by Traian Orghidan[3] in 1959 by combining two Greek words: hypo (below) and rheos (flow).

Hyporheic Zone and Hydrology

The hyporheic zone is the area of rapid exchange, where water is moved into and out of the stream bed and carries dissolved gas and solutes, contaminants, microorganisms and particles with it [4]. Depending on the underlying geology and topography, the hyporheic zone can be only several centimeters deep, or extend up to 10s of meters laterally or deep.

The conceptual framework of the hyporheic zone as both a mixing and storage zone are integral to the study of hydrology. The first key concept related to the hyporheic zone is that of residence time; water in the channel moves at a much faster rate compared to the hyporheic zone, so this flow of slower water effectively increases the water residence time within the stream channel. Water residence times influence nutrient and carbon processing rates. Longer residence times promote dissolved solute retention, which can be later released back into the channel, delaying or attenuating the signals produced by the stream channel [5].

The other key concept is that of hyporheic exchange [6][7], or the speed at which water enters or leaves the subsurface zone. Stream water enters the hyporheic zone temporarily, but eventually the stream water reenters the surface channel or contributes to groundwater storage. The rate of hyporheic exchange is influenced by streambed structure, with shorter water flow paths created by streambed roughness [8][9]. Longer flowpaths are induced by geomorphic features, such as stream meander patterns, pool-riffle sequences, large woody debris dams, and other features.

The hyporheic zone and its interactions influence the volume of stream water that is moved downstream. Gaining reaches indicate that groundwater is discharged into the stream as water moves downstream, so that the volume of water in the main channel increases from upstream to downstream. Conversely, when water infiltrates into the groundwater zone resulting in a net loss of surface water, the stream reach is considered to be "losing" water.

Studying the Hyporheic Zone

A stream or river ecosystem is more than just the flowing water that can be seen on the surface: rivers are connected to the adjacent riparian areas [10]. Therefore, streams and rivers include the dynamic hyporheic zone that lies below and lateral to the main channel. Because the hyporheic zone lies underneath the surface water, it can be difficult to identify, quantify, and observe. However, the hyporheic zone is a zone of biological and physical activity, and therefore has functional significance for stream and river ecosystems [11]. Research scientists use tools such as wells and piezometers, conservative and reactive tracers [12], and transport models that account for advection and dispersion of water in both the stream channel and the subsurface [13]. These tools can be used independently to study water movement through the hyporheic zone and to the stream channel, but are often complimentary for a more accurate picture of water dynamics in the channel as a whole.

Biogeochemical Significance

The hyporheic zone is an ecotone between the stream and subsurface: it is a dynamic area of mixing between surface water and groundwater at the sediment-water interface. From a biogeochemical perspective, groundwater is often low in dissolved oxygen but carries dissolved nutrients. Conversely, stream water from the main channel contains higher dissolved oxygen and lower nutrients. This creates a biogeochemical gradient, which can exist at varying depths depending on the extent of the hyporheic zone. Often, the hyporheic zone is dominated by heterotrophic microorganisms that process the dissolved nutrients exchanged at this interface.


  1. Lewandowski, Jörg (2019). "Is the hyporheic zone relevant beyond the scientific community?". Water. 11 (11): 2230. doi:10.3390/w11112230.
  2. Lawrence, J.E.; M. Skold; F.A. Hussain; D. Silverman; V.H. Resh; D.L. Sedlak; R.G. Luthy; J.E. McCray (14 August 2013). "Hyporheic Zone in Urban Streams: A Review and Opportunities for Enhancing Water Quality and Improving Aquatic Habitat by Active Management". Environmental Engineering Science. 47 (8): 480–501. doi:10.1089/ees.2012.0235.
  3. Orghidan, T. (1959). "Ein neuer Lebensraum des unterirdischen Wassers: Der hyporheische Biotop". Archiv für Hydrobiologie. 55: 392–414.
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  7. Bencala, Kenneth E. (2006), "Hyporheic Exchange Flows", Encyclopedia of Hydrological Sciences, American Cancer Society, doi:10.1002/0470848944.hsa126, ISBN 9780470848944
  8. Kasahara, Tamao; Wondzell, Steven M. (2003). "Geomorphic controls on hyporheic exchange flow in mountain streams". Water Resources Research. 39 (1): SBH 3–1–SBH 3-14. doi:10.1029/2002WR001386. ISSN 1944-7973.
  9. Harvey, Judson W.; Bencala, Kenneth E. (1993). "The Effect of streambed topography on surface-subsurface water exchange in mountain catchments". Water Resources Research. 29 (1): 89–98. doi:10.1029/92WR01960. ISSN 1944-7973.
  10. "An ecosystem perspective of alluvial rivers: connectivity and the hyporheic corridor | Scinapse | Academic search engine for paper". Scinapse. Retrieved 2019-03-15.
  11. Boulton, Andrew J.; Findlay, Stuart; Marmonier, Pierre; Stanley, Emily H.; Valett, H. Maurice (1998-11-01). "The functional significance of the hyporheic zone in streams and rivers". Annual Review of Ecology and Systematics. 29 (1): 59–81. doi:10.1146/annurev.ecolsys.29.1.59. ISSN 0066-4162.
  12. Mulholland, Patrick J.; Tank, Jennifer L.; Sanzone, Diane M.; Wollheim, Wilfred M.; Peterson, Bruce J.; Webster, Jackson R.; Meyer, Judy L. (2000). "Nitrogen Cycling in a Forest Stream Determined by a 15n Tracer Addition". Ecological Monographs. 70 (3): 471–493. doi:10.1890/0012-9615(2000)070[0471:NCIAFS]2.0.CO;2. hdl:10919/46856. ISSN 1557-7015.
  13. Bencala, Kenneth E.; Walters, Roy A. (1983). "Simulation of solute transport in a mountain pool-and-riffle stream: A transient storage model". Water Resources Research. 19 (3): 718–724. doi:10.1029/WR019i003p00718. hdl:2027/uc1.31210024756569. ISSN 1944-7973.

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