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 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.

After clear-cutting & shrub removal the watershed cannot retain nutrients levels of NO 3 -, K +, and Ca ++ in streamwater draining experimental areas after clearcutting and shrub removal shaded area—after clear-cut Experimental studies on watersheds

P= precipitation (Vol /DA) /t R=runoff Vol/t P x DA = R Units L/t Units L/t * L 2 =L 3 /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 (L 2 ) gives Runoff (Volume/t or L 3 /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 (L 3 ). 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 L 3 /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 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 Location: Alberta Government > Environment > Water > Alberta River BasinsAlberta GovernmentEnvironmentWater 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 ) m 3 /s Watershed Area (km 2 ) * * * * * Slope = r—the runoff coefficient =0.030 m 3 /s per km 2 =0.95 m 3 /m 2 /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 10 7 s/yr]

Map of mean annual runoff (r) for Western Canada (mm) Averaged over the last 30 yr. 1000mm=1m 3 /m 2 of watershed each year or 1000 mm = m 3 /s per km 2 of watershed area