http://www.catskillaccommodations.com/maps/images/ny100b.gif

Large urban centers have begun to worry about the sustainability of their water supplies

Watershed management has become an important issue.

The water supply for the Toronto and surrounding suburbs all comes from the Oak Ridges morainewhich 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 mapand calculating stream discharge & velocity

The temporal variability of stream flow

Stream order within a watershed

P= precipitation(Vol /DA) /t

R=runoffVol/t

P x DA = R

Units L/t

Units L/t * L2=L3/t

A Watershed is like a semi-funnel

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)

The hydrological balance equation

PA EA

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 - S = 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 S are L3/t.

The hydrological balance equation Runoff(r*DA)= (Precipitation – Evapotranspiration) *DA – Storage

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.

Alberta River Basins1.Hay River2.Peace/Slave3.Athabasca4.Beaver5.North Saskatchewan6.Red Deer7.Bow8.Oldman9.South Saskatchewan10.Milk

Location: Alberta Government > Environment > Water > Alberta River Basins

http://www3.gov.ab.ca/env/water/basins/BasinForm.cfm

The watershed/Drainage basin is the key management unit

The Watershed/Drainage basin

Smaller watersheds are nested subunits of larger watersheds

x

The Watershed of the Oldman River

Little Bow River watershed

Watershed of High River Reservoir

Runoff (R )m3/s

Watershed Area (km2)

10

20

30

200 400 600 800

**

*

*

*

Slope = r—the runoff coefficient=0.030 m3/s per km2

=0.95 m3/m2/yr=0.95 m/yr Castle River (Beaver Mines)

Castle River (Ranger stn)

Oldman R at Waldrons

Waterton R (park gate)

Gold Cr.

Runoff (R ) from different sized watersheds within the Oldman R watershed

[3.16 x 107 s/yr]

Map of mean annual runoff (r) forWestern Canada(mm)Averaged over the last 30 yr.

1000mm=1m3/m2 of watershed each year

or

1000 mm = 0.032 m3/sper km2 of watershed area