GSC1620 Chapter 11

1. GSC1620 Chapter 11 Resources Overview and Water as a Resource

2. Resources (Background) • Earth resource – any valuable or useful commodity extracted from the Earth • Resources can be classified into various categories including: reserves, subeconomic resources, hypothetical resources, and speculative resources • Reserves – identified resources that are profitable to extract

3. Resources • Subeconomic resources – identified resources that are currently unprofitable to remove • Note: the classification of resources as reserves or subeconomic resources can change if the commodity price fluctuates significantly

4. Resources • Hypothetical Resources – resources hypothesized to exist because resources of that type have been found in the same general area and geological setting (gold “rush” mentality) • Speculative Resources – resources that are speculated to exist even though resources of that type haven’t been found in that area (see review figure)

6. Resources • Resources can also be classified as renewable and nonrenewable • Renewable resources are replaceable on a human time scale while nonrenewable resources are not • What is an example of a renewable and a nonrenewable resource?

7. Water as a Resource

8. Water as a Resource • Obviously no society can prosper without a reliable source of fresh water • Fresh, potable water has become a precious commodity in many parts of the world, here in the U.S. there are many legal battles raging, especially in the West, over water usage rights

9. Water as a Resource • Remember, the surface and subsurface waters of Earth are part of the hydrologic cycle (see figure) • We’ll initially focus on groundwaters since they constitute such a large percentage of our liquid freshwater resource (see figures)

10. Hydrologic cycle – powered by solar energy, the continual circulation of Earth’s water through the atmospheric, surface, and subsurface reservoirs.

11. Groundwaters constitute about 95% of Earth’s liquid freshwater resources! About half of the US population relies on groundwater for drinking water!

12. Groundwater • The origin of groundwater is water that infiltrates the surface; however, not all subsurface water is termed groundwater • Groundwater is defined as subsurface water present in the saturated zone - here all the pore spaces between adjacent rock and sediment particles are saturated with water (see figure)

14. Groundwater • Groundwater moves due to the influence of gravity and the pressure from the weight of the overlying rock and sediment (squeezed sponge analogy) • Therefore, groundwater moves toward zones of lower pressure (i.e., the surface) (see slides)

17. Groundwater • As you’re seeing the groundwater and surface water systems (streams, lakes, wetlands) are typically intimately connected • Today, many scientists are advising that we consider these as one resource system • Why? Think of the practical and environmental applications when viewing the next slide.

19. Oakland Press June 12, 2005

20. Brochure distributed in 2005 by the Brandon Township Phase II Stormwater Management Education Group

21. Oakland Press 7/26/07

23. Future Concern?

24. Groundwater • Significant quantities of groundwater are found only in sediments or rocks that are sufficiently porous and permeable (How would you define these terms?) • Porosity – the percentage of void (open) space a substance contains • Permeability – a measure of how readily a substance transmits fluids

25. Groundwater • Aquifers - rock or sediment bodies that absorb and transmit water very effectively • Aquicludes - rock or sediment bodies that absorb and transmit water very poorly • Aquitards – rock or sediment bodies with properties between those of an aquifer and aquiclude • See the following table and try to discern the best aquifer material

27. Groundwater Accumulation • Sediments like sands and gravels (which typically underlie the surface soils in southeast MI to maximum depths of 400 ft) typically make good aquifers • ~97% of Oakland County wells terminate into sand/gravel aquifers

28. Groundwater Accumulation • Rocks like limestone and poorly cemented sandstones typically make good aquifers • Clay sediments, sedimentary rocks like shale and nearly all igneous and metamorphic rocks are aquicludes except under rare circumstances (see slides)

29. fractures e.g., granite

30. Groundwater • Deep (hundreds of feet) accumulations of groundwaters may have taken thousands of years to accumulate; significant volumes of groundwater are not typically found below about 2300 feet (see slide) Why?

32. Groundwater Flow Rates • Groundwater flow rates depend on two factors: 1) the permeability of the rock or sediment, and 2) the slope of the water table (tilt of the rock or sediment body to the ground surface) • Groundwater flow rates vary widely from a few inches a year in impermeable materials to perhaps 500 – 10000 ft/day in very porous and permeable materials (e.g., some gravels) (see figure) (water-table slope)

33. Groundwater • On the average, groundwaters flow a few inches to about a foot per day; remember this is a gross average

34. Artesian Springs • An artesian system requires a confined aquifer (an aquifer directly overlain and underlain by low-permeability rocks) to form and is defined as a system where the water rises under its own pressure (no pumping required) past the top of the aquifer (see slide)

36. Geologic Work of Groundwater • Certain rocks (e.g., limestone) are prone to slow dissolution by slightly acidic groundwaters – what is the primary acid? • The dissolving of these rocks may lead to the formation of caverns/caves, sinkholes and other unique features often called “karst topography”(see slides)

37. Acidic soil water Limestone or similarly soluble bedrock Caverns exposed when water table lowers

38. Cavern deposits of precipitated rock (usually limestone)

40. Geologic Work of Groundwater • Sinkholes – depressions formed by the collapse of the ground surface into an underlying void (cavern) • Sinkholes vary in size and are fairly common in areas underlain by cavernous limestone • Think about the potential hazards (obvious and nonapparent) of sinkholes as we view the following slides

46. Geologic Work of Groundwater • Karst topography – landscape, predominantly formed by the dissolution of soluble bedrock like limestone, that typically hosts sinkholes, sinking (disappearing) streams, and caverns/caves (see slide)

47. Approximately 25% of the world’s population lives atop karst topography!

48. Consequences of Groundwater Withdrawal • If groundwater is removed faster than it is replenished the water table lowers, but not uniformly as one may think • Cone of depression – a cone-shaped drawdown in the water table immediately adjacent to a pumping well (see slide) • Possible consequences: negative impact on the water levels in nearby wells and ground subsidence (see slides)