WATERSHED
Canan Cengiz
Faculty of Forestry, Department of Landscape
Architecture, Bartın University, Bartın, Turkey
Synonyms
Drainage basin
Definition
A watershed is an area of land that drains into a given
stream, river, lake, or wetland. The shape and size of
watersheds vary. They have no county, state, and national
boundaries (URL, 1).
Description
An area of land that drains into a given stream, river, lake,
or wetland is called a watershed. Surface water run-off
along with discharged groundwater merge with streams
during their transport and eventually intertwine at the
intersection of their valleys. Great rivers are formed by
the intersection of large watersheds which then flow into
estuaries and oceans (Otto et al., 2004).
Watersheds are geohydrologic basins defined in terms
of the boundaries of their water catchment area. They are
almost always drained by river courses. All land, water,
and biotic resources within their hydrologic boundaries
are included in the watersheds which behave as ecological
entities. Similar to islands, the boundaries of a watershed
can also be marked, and its components can be interlinked.
While water is the common factor, other aspects of
individiual watersheds such as geology and vegetation
modulate the quality and quantity of the water flow. Each
watershed can be divided into interconnected tributaries.
The changes that occur in some cases may not be significant; however, in other cases, drastic changes may occur
(Clark, 1996).
Rivers are linked in a watershed (Otto et al., 2004). The
land drained by a river and its creeks is part of a watershed
(Smardon et al., 1995). A channel network resembling the
branches of a tree forms when smaller streams come
together in a watershed generating a drainage network.
A drainage basin is where water is fed to the drainage network, and the main channel size, along with its flow rate,
increases in proportion with the size of the drainage basin
(Marsh, 2010).
Bibliography
Clark, J. C., 1996. Coastal Zone Management Handbook. Boca
Raton: Lewis Publishers.
Marsh, W. M., 2010. Landscape Planning: Environmental Applications, 5th edn. Hoboken: Wiley.
Otto, B., McCormick, K., and Leccese, M., 2004. Ecological Riverfront Design: Restoring Rivers, Connecting Communities. Chicago: American Planning Association, Planning Advisory
Service Report Number, pp. 518–519.
Smardon, R. C., Felleman, J. P., and Senecah, S., 1995. Protecting
Floodplain Resources: A Guidebook for Communities. Washington, DC: Federal Interagency Floodplain Management Task
Force, FEMA publication number 268.
URL, 1. http://water.epa.gov/type/watersheds/whatis.cfm. Accessed
15 June 2013.
WAVE-DRIVEN SEDIMENT RESUSPENSION
Malcolm O. Green
Coastal and Estuarine Physical Processes, NIWA
(National Institute of Water and Atmospheric Research),
Hamilton, New Zealand
Definition
Sediment resuspension occurs when sediment is raised
from the bed into the water column by fluid forces, including those exerted by waves. This entry discusses sediment
resuspension by waves (see Sediment Transport).
Description
Field and modelling studies have firmly established that
gravity waves in estuaries are capable of resuspending
bed sediments (e.g., Ward et al. (1984), Schoellhamer
(1995), de Jonge and van Beusekom (1995), Green
et al. (1997), Carniello et al. (2005), Talke and Stacey
(2008)), and this includes very small waves, less than
20 cm high (Anderson, 1972; Dyer et al., 2000; Uncles
and Stephens, 2010; Green, 2011). Unlike tidal currents,
which are periodic, waves occur episodically, and the
corresponding episodic sediment resuspension adds to or
even masks any periodic resuspension driven by tidal
currents. For example, Green et al. (1997) described
a New Zealand mesotidal intertidal flat where
resuspension was entirely due to episodically occurring
waves; Christie et al. (1999) reported an order-ofmagnitude increase in suspended-sediment concentration
(SSC) during storms compared to during fair weather on
an intertidal flat in the Humber Estuary (UK); Ralston
and Stacey (2007) described how SSC on an intertidal flat
in San Francisco Bay drops rapidly as winds and waves
abate.
Sediment resuspension can be meaningfully divided
between that caused by waves and that caused by currents
(see “Tidal Hydrodynamics”). The latter includes currents
driven by tides, gravitational circulation, and wind. Waves
may be generated locally by wind acting on the fetch
inside the estuary basin, or they may have been formed
in the ocean and propagated into the estuary (de Lange
and Healy, 1990; Wright et al., 1992; Talke and Stacey,
2003). Waves and currents vary on different timescales:
whereas periods of locally generated waves are 0.5–5 s
and ocean-wave periods may exceed 20 s, currents vary
on timescales of tens of minutes to hours. Hence, for the
same free-stream current speed, the wave benthic
734
WATERSHED
Canan Cengiz
Faculty of Forestry, Department of Landscape
Architecture, Bartın University, Bartın, Turkey
Synonyms
Drainage basin
Definition
A watershed is an area of land that drains into a given
stream, river, lake, or wetland. The shape and size of
watersheds vary. They have no county, state, and national
boundaries (URL, 1).
Description
An area of land that drains into a given stream, river, lake,
or wetland is called a watershed. Surface water run-off
along with discharged groundwater merge with streams
during their transport and eventually intertwine at the
intersection of their valleys. Great rivers are formed by
the intersection of large watersheds which then flow into
estuaries and oceans (Otto et al., 2004).
Watersheds are geohydrologic basins defined in terms
of the boundaries of their water catchment area. They are
almost always drained by river courses. All land, water,
and biotic resources within their hydrologic boundaries
are included in the watersheds which behave as ecological
entities. Similar to islands, the boundaries of a watershed
can also be marked, and its components can be interlinked.
While water is the common factor, other aspects of
individiual watersheds such as geology and vegetation
modulate the quality and quantity of the water flow. Each
watershed can be divided into interconnected tributaries.
The changes that occur in some cases may not be significant; however, in other cases, drastic changes may occur
(Clark, 1996).
Rivers are linked in a watershed (Otto et al., 2004). The
land drained by a river and its creeks is part of a watershed
(Smardon et al., 1995). A channel network resembling the
branches of a tree forms when smaller streams come
together in a watershed generating a drainage network.
A drainage basin is where water is fed to the drainage network, and the main channel size, along with its flow rate,
increases in proportion with the size of the drainage basin
(Marsh, 2010).
Bibliography
Clark, J. C., 1996. Coastal Zone Management Handbook. Boca
Raton: Lewis Publishers.
Marsh, W. M., 2010. Landscape Planning: Environmental Applications, 5th edn. Hoboken: Wiley.
Otto, B., McCormick, K., and Leccese, M., 2004. Ecological Riverfront Design: Restoring Rivers, Connecting Communities. Chicago: American Planning Association, Planning Advisory
Service Report Number, pp. 518–519.
Smardon, R. C., Felleman, J. P., and Senecah, S., 1995. Protecting
Floodplain Resources: A Guidebook for Communities. Washington, DC: Federal Interagency Floodplain Management Task
Force, FEMA publication number 268.
URL, 1. http://water.epa.gov/type/watersheds/whatis.cfm. Accessed
15 June 2013.
WAVE-DRIVEN SEDIMENT RESUSPENSION
Malcolm O. Green
Coastal and Estuarine Physical Processes, NIWA
(National Institute of Water and Atmospheric Research),
Hamilton, New Zealand
Definition
Sediment resuspension occurs when sediment is raised
from the bed into the water column by fluid forces, including those exerted by waves. This entry discusses sediment
resuspension by waves (see Sediment Transport).
Description
Field and modelling studies have firmly established that
gravity waves in estuaries are capable of resuspending
bed sediments (e.g., Ward et al. (1984), Schoellhamer
(1995), de Jonge and van Beusekom (1995), Green
et al. (1997), Carniello et al. (2005), Talke and Stacey
(2008)), and this includes very small waves, less than
20 cm high (Anderson, 1972; Dyer et al., 2000; Uncles
and Stephens, 2010; Green, 2011). Unlike tidal currents,
which are periodic, waves occur episodically, and the
corresponding episodic sediment resuspension adds to or
even masks any periodic resuspension driven by tidal
currents. For example, Green et al. (1997) described
a New Zealand mesotidal intertidal flat where
resuspension was entirely due to episodically occurring
waves; Christie et al. (1999) reported an order-ofmagnitude increase in suspended-sediment concentration
(SSC) during storms compared to during fair weather on
an intertidal flat in the Humber Estuary (UK); Ralston
and Stacey (2007) described how SSC on an intertidal flat
in San Francisco Bay drops rapidly as winds and waves
abate.
Sediment resuspension can be meaningfully divided
between that caused by waves and that caused by currents
(see “Tidal Hydrodynamics”). The latter includes currents
driven by tides, gravitational circulation, and wind. Waves
may be generated locally by wind acting on the fetch
inside the estuary basin, or they may have been formed
in the ocean and propagated into the estuary (de Lange
and Healy, 1990; Wright et al., 1992; Talke and Stacey,
2003). Waves and currents vary on different timescales:
whereas periods of locally generated waves are 0.5–5 s
and ocean-wave periods may exceed 20 s, currents vary
on timescales of tens of minutes to hours. Hence, for the
same free-stream current speed, the wave benthic
734
WATERSHED