Large urban centers have
begun to worry about the
sustainability of their water
supplies
Watershed management has
become an important issue.
http://www.catskillaccommodations.com/maps/images/ny100b.gif
The water supply for the
Toronto and surrounding
suburbs all comes from
the Oak Ridges moraine
which is at under heavy
pressure from developers.
The watershed concept
Quantitative analysis of stream flow
The water balance equation
Alberta watersheds
The runoff coefficient, and runoff maps
Measuring the area of watersheds on a topographical map
and calculating stream discharge & velocity
The temporal variability of stream flow
Stream order within a watershed
The Hubbard Brook Watershed in the
Appalachian mountains (New
Hampshire) supports a rich Maple/Beech
regrowth forest
Experimental Watersheds
where effects of various
harvest regimes and
methods on nutrient cycling
are being studied
Mirror Lake alongside Highway
93
A watershed is the entire drainage
basin of a stream or river, from
which all surface runoff and
groundwater leaves at a single
point.
Experimental studies on watersheds
shaded area—after clear-cut
•After clear-cutting & shrub
removal the watershed cannot
retain nutrients
•levels of NO3-, K+, and Ca++ in
streamwater draining
experimental areas after
clearcutting and shrub removal
A Watershed is like a semi-funnel
P= precipitation
(Vol /DA) /t
Units L/t
P x DA = R
Units L/t * L2=L3/t
R=runoff
Vol/t
The hydrological balance equation
EA
PA
To allow for both precipitation and
evapotranspiration from the watershed we
have
(P-E)DA = R
Where P an E have the same units (L/t).
When multiplied by DA (L2) gives Runoff
(Volume/t or L3/t)
Almost immediately after it stops raining on the
funnel, water stops pouring out the spout.
Imagine if that the surface of the funnel is lined with a
sponge.
Water would tend to seep to the bottom of the sponge
and trickle out the spout for some time even after it
stopped raining.
Hydrologists refer to the water in the “sponge” as
storage (S—units volume (L3).
We can now write the equation as
(P-E)DA - DS = R
This equation indicates that there need not be an
instantaneous runoff response to changes in P-E
because the storage capacity of the watershed can
change.
The units of each term including DS are L3/t.
What watershed processes contribute to
storage?
The volume bound up in the various pools of
the watershed
Snow, glaciers, wetlands, lakes, streams
rivers, groundwater, soil and plants
Each of these pools gain water from
precipitation and give up water to surface
runoff
The flows in and out of these pools are measured in Volume/t, as a changes in
the volume of each pool.
The hydrological balance equation
Runoff(r*DA)= (Precipitation – Evapotranspiration) *DA – D Storage
Location: Alberta Government > Environment > Water > Alberta River Basins
Alberta River Basins
1.Hay River
2.Peace/Slave
3.Athabasca
4.Beaver
5.North Saskatchewan
6.Red Deer
7.Bow
8.Oldman
9.South Saskatchewan
10.Milk
The watershed/Drainage basin is
the key management unit
http://www3.gov.ab.ca/env/water/basins/BasinForm.cfm
The Watershed/Drainage basin
Smaller watersheds are nested subunits of larger watersheds
x
Watershed of
High River Reservoir
The Watershed of the
Oldman River
Little Bow River watershed
Runoff (R ) from different sized watersheds within the Oldman R watershed
Slope = r—the runoff coefficient
[3.16 x 107 s/yr]
3
2
=0.030 m /s per km
=0.95 m3/m2/yr
=0.95 m/yr
Castle River (Beaver Mines)
30
*
20
*
Runoff (R )
m3/s
*
Oldman R at Waldrons
Waterton R (park gate)
*
10
Castle River (Ranger stn)
Gold Cr.
*
200
600
400
Watershed Area (km2)
800
Map of mean annual runoff (r)
for
Western Canada
(mm)
Averaged over the last 30 yr.
1000mm=1m3/m2 of watershed
each year
or
1000 mm = 0.032 m3/s
per km2 of watershed area