The Great Big Gravel Sponge

1. The Great Big Gravel Sponge Operators Manual

3. 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

4. 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

5. Landforms Emerge Beaver Hills • 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 Future valley Gwynne channel Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society

6. 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

7. …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

8. 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 Pre-glacial tributary Beaver Hills Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society

9. 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 Pre-glacial tributary Beaver Hills Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society

10. 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

11. 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!

12. 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 Pre-glacial tributary Beaver Hills Source: Godfrey, J.. 1993. Edmonton Beneath Our Feet. Edmonton Geological Society