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 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 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 channel Source: Godfrey, J 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 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 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 Edmonton Beneath Our Feet. Edmonton Geological Society Pre-glacial tributary

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 Edmonton Beneath Our Feet. Edmonton Geological Society Pre-glacial tributary

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 Edmonton Beneath Our Feet. Edmonton Geological Society Pre-glacial tributary