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Large urban centers have begun to worry about the
sustainability of their water supplies Watershed
management has become an important issue.
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The water supply for the Toronto and surrounding
suburbs all comes from the Oak Ridges
moraine which is at under heavy pressure from
developers.
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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
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A Watershed is like a semi-funnel
P precipitation (Vol /DA) /t
Units L/t
P x DA R
Units L/t L2L3/t
Rrunoff Vol/t
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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)
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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 (Sunits 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.
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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(rDA)
(Precipitation Evapotranspiration) DA D
Storage
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Location Alberta Government gt Environment gt
Water gt Alberta River Basins
Alberta River Basins 1.Hay River 2.Peace/Slave 3.A
thabasca 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.c
fm
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The Watershed/Drainage basin
Smaller watersheds are nested subunits of larger
watersheds
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Watershed of High River Reservoir
The Watershed of the Oldman River
Little Bow River watershed
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Runoff (R ) from different sized watersheds
within the Oldman R watershed
Slope rthe runoff coefficient 0.030 m3/s per
km2 0.95 m3/m2/yr 0.95 m/yr
3.16 x 107 s/yr
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Castle River (Beaver Mines)


Oldman R at Waldrons
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Runoff (R ) m3/s
Waterton R (park gate)

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Castle River (Ranger stn)
Gold Cr.

600
800
200
400
Watershed Area (km2)
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Map of mean annual runoff (r) for Western
Canada (mm) Averaged over the last 30
yr. 1000mm1m3/m2 of watershed each year or
1000 mm 0.032 m3/s per km2 of watershed area