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Hydrologic interactions between streams and their subsurface hyporheic zones


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Title: Hydrologic interactions between streams and their subsurface hyporheic zones

Hydrologic interactions between streamsand their
subsurface hyporheic zones
CENTRAL QUESTIONWhat is the hyporheic zone?
  • It derives from the Greek meaning under (hypo)
    the current or flow (rheo).

The hyporheic zone
is a portion of the groundwater interface in
streams where a mixture of surface water
groundwater can be found (Bencala 1993)
The hyporheic zone
  • In the bed and banks of streams, water and
    solutes can exchange in both directions across
    the streambed. This process, termed hyporheic
    exchange, creates subsurface environments that
    have variable proportions of water from ground
    water and surface water.

Figure from Winter et al. 2000
The hyporheic zone
  • The bi-directional exchange of water mixes water
    solutes from surface and subsurface
    environments. An empirical perspective from
    hydrologists recognizes a hyporheic zone as the
    subsurface zone receiving at least 10 of water
    by input from the stream (gt10 channel water).

Definition after Triska et al. 1989. Figure from
Winter et al. 2000
Some important concepts
  • Length and timescale of the interaction help to
    distinguish hyporheic exchange from the much
    larger (and longer term) channel and groundwater

Figure from Winter et al. 2000
Some important concepts
  • Hyporheic flowpaths leave and return to the
    stream many times within a single study reach
    the exchange of surface water back and forth
    between the active channel and the subsurface is
    rapid. Within several kilometers, stream water
    in relatively small channels is often completely
    exchanged with the porewater of the hyporheic
  • This repeatedly brings stream water into close
    with geochemically and microbially active

Figure from Harvey Wagner 2000
Chemical gradients at the interface
Steep concentration gradients in dissolved
constituents exist at the groundwater/surface
water interface, due to mixing of
chemically-different waters and chemical
Zonation of metabolic activity in hyporheic zone
  • Hydrologic exchange regulates sources of
    oxygen, carbon, nutrients to organisms and
  • This directly controls trophic structure and
    primary productivity in streams

  • Hydrologic fluxes potentially can enhance
    ecosystem production on both sides of the
    groundwater/surface water interface, by supplying
    solutes that are needed in biological metabolism.

hyporheic zone is important to aquatic biota
  • The term hyporheic zone was originally used by
    Orghidan (1959), who described the interface as a
    new groundwater environment containing
    distinctive biota. Higher than expected
    abundances of aquatic insects were found in
    sediments where concentrations of oxygen were

hyporheic zone can be a source of
nutrientsexample from Sycamore Creek, Alaska
  • In a study of the ecology of Sycamore Creek near
    Phoenix Arizona, hydrologic exchange fosters
    recovery of desert stream ecosystems following
    storms, by stimulating recycling of the nutrients
    from buried organic matter.

hyporheic zone at Sycamore Creek, Arizona
Photo courtesy of Stuart Fisher, Arizona State
Following a storm, oxygen advection into
hyporheic zone stimulates aerobic decomposition
of buried algae. Released nutrients are
delivered to the surface channel by return flows
from hyporheic flow paths. Nitrate in surface
channel stimulates new primary productivity by
After Valett et al. 1994
Abundance of algae in streambed sediments, as
indicated by concentration of chlorophyll a, was
markedly greater in areas of upwelling (where
groundwater moved upward through the sediments)
than in areas of downwelling.
After Valett et al. 1994
Hyporheic zone under and adjacent to stream with
active exchange of water
In dry valley streams the hyporheic zone is
observed as a wetted zone adjacent to stream
Dry valley streams flow through porous alluvium
with high rates of hyporheic exchange.
Experimental enrichment with nitrate and
phosphate 1.5 hrs
Sampling Green Creek during experiment
Stream algal mats win! Added nutrients are taken
up and do not reach the lake.
hyporheic zone feedbacks to terrestrial
landscapeexample from southeast Alaska
  • Pacific salmon spend most of their lives growing
    at sea before returning to fresh water to spawn
    and die in their natal streams, carrying
    marine-derived nitrogen in their body tissues.
    Returning salmon provide a seasonal food source
    for birds mammals, and nutrients from decaying
    salmon carcasses are incorporated into freshwater
    biota at various trophic levels.
  • From this nutrient subsidy, growth rates are
    significantly increased in trees near spawning
  • MDN be transferred from spawning streams to
    riparian forests by flooding which deposits
    salmon carcasses on stream banks through the
    transfer of dissolved nutrients from spawning by
    hyporheic exchange.

Shading DOC. inputs Sediment, nutrient
filtration Bank stabilization
Flooding Bank erosion Sediment deposition
MDN fertilization of riparian vegetation
Enhanced riparian growth Changes in spp.
composition, diversity, soil chemistry
Materials carried downstream
MDN carried upstream
Slide courtesy of Bob Naiman, University of
Where does hyporheic exchange take place?example
from southwest Alaska
  • Lateral nutrient transfers occur in the hyporheic
    zone in adjacent riparian floodplains along
    spawning reaches.
  • Hyporheic storage re-release of MDN is an
    important mechanism by which nutrients are
    retained over winter within stream ecosystems and
    subsequently made available to primary producers
    the following growing season.

hydraulic head gradients in a well network
Slide courtesy of Tom OKeefe Rick Edwards,
University of Washington
DO gradients illustrating hyporheic exchange
Slide courtesy of Tom OKeefe Rick Edwards,
University of Washington
Photo courtesy of Bob Naiman, University of
Loss of water from stream reach to the hyporheic
zone commonly related to meanders in streambed
Figure from Winter et al. 2000
Where does hyporheic exchange take place? example
from St. Kevin Gulch, CO
Inflow of water from the hyporheic zone to the
stream was greatest at the downstream end of
After Harvey Bencala, 1993
Stream water flows into the subsurface beneath
and to the side of steep sections of streams
(riffles), ground water enters streams most
readily at the upstream end of deep pools
From Harvey Bencala, 1993
important points about controls on where
hyporheic exchange takes place
  • Hyporheic exchange caused to a large extent by
    the irregular topography of the streambed, which
    creates pools riffles characteristic of
    mountain streams.
  • Channel irregularity is an important control on
    the location of groundwater inflow to streams and
    on the size of the hyporheic zone in mountain
    streams because changes in slope determine the
    length depth of hyporheic flow paths.

Harvey Bencala, 1993
Loss of water from stream reach to the hyporheic
zone commonly related to abrupt changes in slope
of the streambed
Figure from Winter et al. 2000
How extensive can a hyporheic zone be?
  • Depending on the type of sediment in the
    streambed and banks, the variability in slope of
    the streambed, and the hydraulic gradients in the
    adjacent ground-water system, the hyporheic zone
    can be as much as several feet in depth and
    hundreds of feet in width.
  • The dimensions of the hyporheic zone generally
    increase with increasing width of the stream and
    permeability of streambed sediments.

Example of large hyporheic zone Willamette
River, OR
  • A large, 9th order stream with permeable,
    coarse-grained, alluvial deposits in the channel
  • HZ width hundreds of m
  • Nitrogen coming in from regional groundwater was
    removed in the HZ
  • HZ gains/losses in flow over reaches of 1-2 km
    were on the order of 5 of streamflow

CENTRAL QUESTIONWhat are some common methods
used to quantify hyporheic flowpaths?
Subsurface measurements in piezometers
Water levels in piezometers are located at the
water table. This level is a measure of the
hydraulic head, or potential at that point.
upwelling downwelling can be inferred with
piezometer monitoring data
Vertical flow direction
Horizontal flow direction
Hydrometric measurements at Rio Calavares, NM
Photo courtesy of Michelle Baker, Utah State
Injection transport of a solute tracer in the
  • A tracer is released, and measurements of its
    passage are made at a location downstream. What
    will a graph of tracer concentration over time
    look like at the downstream monitoring point?

Injection transport of a solute tracer in the
  • The concentration will rise, reach a plateau,
    and then decline as the pulse passes the point of
    monitoring. The solute disperses from its point
    of release due to the force of the current
    (advection) and diffusion and turbulent mixing
    throughout the stream.

(No Transcript)
Dye tracer illustrates water storage at channel
margins 1) sides are initially dye-free
Photo courtesy of Jud Harvey, USGS, Reston, VA
Dye tracer illustrates water storage at channel
margins2) all parts of channel have dye
Photo courtesy of Jud Harvey, USGS, Reston, VA
Dye tracer illustrates water storage at channel
margins 3) sides retain dye longer than center
Photo courtesy of Jud Harvey, USGS, Reston, VA
Transient Storage the temporary retention of
solutes in slowly moving or stationary water, and
the eventual movement of solutes and water back
into the stream channel.
  • Five storage zones observed in a small mountain
    stream (Bencala Walters 1983)
  • turbulent eddies generated by large-scale bottom
  • large but slowly moving recirculating zones along
    the sides of pools
  • small but rapidly recirculating zones behind flow
    obstructions, especially in riffles
  • side pockets
  • flow in and out of beds of coarse substrate.

modelling the injection transport of a solute
tracer in the stream
  • As a first approximation, this curve can be
    achieved with a basic equation describing
    advection dispersion, taking into account
    stream dimensions water velocity.
  • Change in solute concentration over time
  • ? C / ? t - U ? C / ? x D ? 2 C / ? x2
  • 1st term describes downstream advection and is
    proportional to water velocity, u.
  • 2nd term describes mixing of the solute randomly
    throughout the mass according to a dispersion
    coefficient D

modelling the injection transport of a solute
tracer in the stream
  • More complicated models are needed to account
    for additional variables such as groundwater and
    tributary inputs, channel storage and subsurface
  • Inclusion of terms for transient storage is
    necessary for the description of solute dynamics
    in small streams and their hyporheic zones.

OTIS One-dimensional Transport with Inflow and
StorageConceptual Model (OTIS, Runkel
1998)Represents stream transport, inflow,
outflow, exchange
modelling the injection transport of a solute
tracer in the stream
  • Passage of a the tracer, including transient
    storage is given by
  • ? C/ ? t -U ? C/ ? x D ? 2/C/ ? x2 a(Cs -
  • ? Cs/ ? t - a A/As (Cs C)
  • Where As is the cross-sectional area of a
    hypothetical storage zone. The rate of
    dispersion of solute in or out of this zone is
    proportional to the difference between solute
    concentration in the storage zone (Cs) and the
    water column (C) and an exchange coefficient (a).

  • Adding a transient storage term permits the
    model to account for significant features of the
    of a solute pulse that the earlier equation is
    unable to mimic. Specifically, measured passage
    of a tracer pulse usually shows the rising
    shoulder of the actual pulse to be more gradual
    and the descending tail to be prolonged relative
    to the symmetrical curve generated by the earlier

  • The storage zone component of the model is an
    abstraction. In contrast to cross-sectional area
    (A) of the stream channel, which can be measured
    directly, storage zone area (As) is determined by
    fitting the model to observed solute dynamics.
  • Nonethelesss, storage zones exist and are
  • Model estimates of As provide a useful index of
    the size of the transient storage effect.


These models are empirically useful descriptions
of observed dynamics, in which transient storage
clearly takes place. Example Rhodamine WT
tracer Experiment in Clackamas River, OR (Laenen
Risley 1997). Downstream data are better when
simulated with hyporheic exchange considered in
the modeling.
Hyporheic zone as a sink for nutrientsExample
w/ modelling to interpret field datafrom Little
Lost Man Creek, CA
  • A study of a coastal mountain stream in northern
    California indicated that transport of dissolved
    oxygen, dissolved carbon, and dissolved nitrogen
    in stream water into the hyporheic zone
    stimulated uptake of nitrogen by microbes and
    algae attached to sediment.
  • A model simulation of nitrogen uptake indicated
    that both the physical process of water exchange
    between the stream and the hyporheic zone and the
    biological uptake of nitrate in the hyporheic
    zone affected the concentration of dissolved
    nitrogen in the stream.

Kim et al. 1992
Nitrate injected into stream was stored and taken
up by algae and microbes in the hyporheic zone.
After Kim et al. 1992
Channel friction factor 8gds/u2 (where g is
gravitational acceleration, d is stream depth, s
is streambed slope, and u is stream velocity).
The ratio of storage zone area to stream cross
sectional area As/A exhibits a strong positive
relation with channel friction factor. (From
Harvey Wagner 2000)
  • Bencala K (1993). A perspective on
    stream-catchment connections. Journal of the
    North American Benthological Society 12(1)44-47.
  • Eagleson PS (2002). Ecohydrology Darwinian
    expression of vegetation form and function.
    Cambridge University Press, 443pp.
  • Harvey JW KE Bencala (1993). The effect of
    streambed topography on surface-subsurface water
    exchange in mountain catchments. Water Resources
    Research 29(1)89-98.
  • Harvey JW BJ Wagner (2000). Quantifying
    hydrologic interactions between streams and their
    subsurface hyporheic zones. pp. 3-44 in JB
    Jones PJ Mulholland, eds., Streams and Ground
    Waters. Academic Press.
  • Helfield JM RJ Naiman (2001). Effects of
    salmon-derived nitrogen on riparian forest growth
    and implications for stream productivity.
    Ecology 82(9)2403-2409.
  • Hinkle SR, JH Duff, FJ Triska, A Laenen, EB
    Gates, KE Bencala, DE Wentz, SR Silva (2001).
    Linking hyporheic flow and nitrogen cycling near
    the Willamette River a large river in Oregon,
    USA. Journal of Hydrology 244157-180.
  • Nuttle WK (2002) Eco-hydrologys past and future
    in focus. Eos 83(7 May) 205.
  • OKeefe TC RT Edwards (2002). Evidence for
    hyporheic transfer and removal of marine-derived
    nutrients in a sockeye stream in southwest
    Alaska. American Fisheries Society Symposium
  • Valett HM, SG Fisher, NB Grimm, P Camill
    (1994). Vertical hydrologic exchange and ecologic
    stability of a desert stream ecosystem. Ecology
  • Rodriguez-Iturbe I (2000). Ecohydrology a
    hydrologic perspective of climatesoilvegetation
    dynamics. Water Resources Research 3639.
  • Runkel (1998). One-dimensional transport with
    inflow and storage (OTIS) A solute transport
    model for streams and rivers. US Geological
    Survey, Water Resources Investigations Report
  • Triska FJ, VC Kennedy, RJ Avanzino, GW Zellweger,
    KE Bencala (1989). Retention and
    transportation of nutrients in a third-order
    stream in northwestern California hyporheic
    processes. Ecology 701893-1905.
  • Kim BKA, AP Jackman, FJ Triska (1992).
    Modeling biotic uptake by periphyton and
    transient hyporheic storage of nitrate in a
    natural stream. Water Resources Research 28(10)
  • Winter TC, JW Harvey, OL Franke, WM Alley
    (1998). Ground water and surface water A single
    resource. US Geological Survey, Circular 1139,
    87 pp.
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