The Great Big Gravel Sponge
Operators Manual
What’s Groundwater?
• GW occupies the voids (pore spaces and fractures) in
rocks and deposits below the water table.
• The water table generally parallels the surface contours,
with hilly gradients.
• Usually the water table is deeper in uplands and shallow
in low-lying areas (lakes, wetlands) – except in areas of
high relief relative to the adjacent plains, like the Beaver
Hills area
• GW moves very slowly through the surficial geological
deposits (by percolation), directed by gravity downward
or downhill (where a water table gradient exists)
• As a result, it can flow deeper underground, or laterally
(e.g. toward deep riverbeds like the NSR)
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
Glacial Retreat
• Retreat of the last glacier
created – literally – the
groundwork for future
landforms in the Edmonton
region
• Glacial Lake Edmonton
collected the meltwater left
behind during the retreat of the
main glacier –
• Lake was created by flooding
of a pre-glacial river valley
(Empress Formation)
• The stagnant ice east of the
lake formed the Beaver Hills,
depositing hummocky mounds
of gravel and glacial till
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
Beaver Hills
Landforms Emerge
• After the ice melted and waters
drained, surficial geological
features emerged over preexisting geological features
(like the Empress Formation).
• Later, those soils and
vegetation established over
these features, but the
underlying geology shapes the
terrain and produces the
physical landforms we see
today
Future
• It also influences how SW
valley
recharges GW aquifers
through the sediment
characteristics of surficial
Gwynne
layers
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
channel
Beaver Hills
And Over Time…
• … our present landscape evolved.
• With glacial till of varying composition (clay, sands,
gravels) and permeability over Cretaceous formations
that now form our main GW aquifers
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
…And Left the
Great Big Gravel Sponge
• The sandstone
formations formed
during the Cretaceous
period are porous –
and so can hold GW
• 2 key bedrock
aquifers in the
Edmonton area:
– Belly River Formation
– Lower Horseshoe
Canyon Formation
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
Beaver
Hills
Great Big Gravel Sponge
• The other main
aquifer in our area are
the pre-glacial valleys
of the Empress
Formation – filled with
sands and gravels –
Pre-glacial
hold much GW
tributary
• Smaller tributary preglacial stream valleys Beaver
feed into the Beverly Hills
Valley from the BH
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
Great Big Gravel Sponge
• The other main
aquifer in our area are
the pre-glacial valleys
of the Empress
Formation – filled with
sands and gravels –
Pre-glacial
hold much GW
tributary
• Smaller tributary preglacial stream valleys Beaver
feed into the Beverly Hills
Valley from the BH
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
Lower Horseshoe Canyon
Formation
• Deposited in a swampy delta sometimes flooded
by sea
– Contains numerous coal seams, which are fractured
in places – holds GW (particularly abundant under
Cooking Lake Moraine)
– Upper part, of non-bentonitic sandstone also porous –
holds GW (main supply for Calmar, Millet area)
• Water in these aquifers captured during
Cretaceous period
– Brackish – poor water quality
– Recharged slowly by SW – through the overlying
sediments
Beaver Hills GW Flow
• Glacial till includes rock flour (now clay), plus
pebbles, gravels, cobble – leaky sieve
• Higher permeability than Glacial Lake Edmonton
– tight clay
• The hummocks of the BH formed by deposits of
glacial till – relatively permeable in places
• Water table lies about 150 m above the NSR in
the BH – close to ground surface (BH’s rise
about 60 m above surrounding plains!)
• Combination of surficial sediments and water
table position – great for recharge/discharge!
Great Big Gravel Sponge
• BH plays a key role in
regional water cycle –
from precipitation, to
percolation into
surficial sediments
Pre-glacial
into underlying
tributary
aquifers and
preglacial valleys
Beaver
Hills
beyond its borders
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society