the great big gravel sponge operators manual. what’s groundwater? gw occupies the voids (pore...
TRANSCRIPT
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
Beaver Hills
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society
Landforms Emerge• After the ice melted and waters
drained, surficial geological features emerged over pre-existing 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
• It also influences how SW recharges GW aquifers through the sediment characteristics of surficial layers
Beaver Hills
Future valley
Gwynne channelSource: Godfrey, J.. 1993. Edmonton Beneath Our Feet.
Edmonton Geological Society
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
Beaver Hills
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 – hold much GW
• Smaller tributary pre-glacial stream valleys feed into the Beverly Valley from the BH
Beaver Hills
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society
Pre-glacialtributary
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 – hold much GW
• Smaller tributary pre-glacial stream valleys feed into the Beverly Valley from the BH
Beaver Hills
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society
Pre-glacialtributary
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 into underlying aquifers and preglacial valleys beyond its borders
Beaver Hills
Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society
Pre-glacialtributary