Connections of a River - Connectivity
Vertical: Hyporheic zone
(pg 2 of 7)
Even in streams without substantial contribution
of groundwater there is an important exchange of
water between the stream and the sediments
underneath the stream. This area is known as the
The hyporheic zone runs parallel to the channel,
sometimes spreading out laterally for hundreds of
yards or even miles, depending on size of river,
breadth of floodplain, and porosity of sediments.
Oxygenated river water enters the hyporheic zone by
downwelling and seeps through the sediments below
the streambed, occasionally returning to the stream
channel by upwellings in the forms of springs.
Scientists only recently have realized the
importance of this zone. Its suitability for
organisms depends on interstices, or the spaces
between particles of sediment. Owing to the way
river sediments sort, particles get smaller as
depth increases. So most habitat lies no more than
a couple of feet beneath the channel.
But in large streams with porous substrates, the
hyporheic zone reaches deep below the streambed.
Researchers have found stoneflies more than 30 feet
deep in the floodplain of the Flathead River in
Montana, and more than a mile from the channel.
They concluded the biomass of the hyporheic zone
may exceed that of the river channel.