Freshwater Unit Groundwater Honors PDF

Freshwater Unit: Groundwater Water Cycle This unending circulation of Earth’s water supply. Infiltration The movement of surface water into rock or soil through cracks and pore spaces. Transpiration The process by which plants absorb water and release it into the atmosphere. Groundwater Water he...

Freshwater Unit: Groundwater Water Cycle This unending circulation of Earth’s water supply. Infiltration The movement of surface water into rock or soil through cracks and pore spaces. Transpiration The process by which plants absorb water and release it into the atmosphere. Groundwater Water held underground in pores or crevices in soil or rock. Aquifer Underground soil or rock through which groundwater can easily move. A permeable layer of rock and sediment that stores and carries groundwater in enough quantities to supply wells. Water Table The top of the water in the soil or rock. The surface below which the groundwater is saturated with water. Groundwater Water Table Zone of Aeration: the area below the surface that is above the water table, where the pores are not filled with water. Groundwater Water Table Zone of Saturation: the area below the water table, where the pores are filled with water.  Groundwater Water Table Aquiclude: a solid, impermeable area underlying or overlying an aquifer.  Groundwater Water Table Aquitard: impermeable beds that hinder or prevent groundwater movement. Porosity: Permeability: the percent of a the rate at which material’s volume water or other liquids that is pore space. pass through the pore spaces of a rock.  PERMEABILITY A high permeability corresponds to a high rate of infiltration Materials that do not allow water to pass through them are called IMPERMEABLE Specific Retention (Capillary Water): water that remains in the soil after water is drained out Specific Yield (Sy) Sy is defined as the proportion of water Sy = Vd / Vt occupying void spaces that drains under gravity. Vd = volume drained Because some water is Vt = volume total bound, or adsorbed, to the aquifer particles or fractures, the specific yield is always lower than the porosity Aquifer Underground soil or rock through which groundwater can easily move. A permeable layer of rock or sediment that stores and carries groundwater in enough quantities to supply wells.  What affects porosity, permeability, capillary water? High Quality Aquifer Characteristics High Porosity: More water stored High Permeability: water flows more quickly towards the well Low Capillary Water (Specific Retention): less water is retained (kept) in the sediment High Specific Yield: more water is able to come out of the aquifer.  Grain Size Sediment ranges in size from clay to boulders. Grain Size Effect Porosity: on Aquifer Unaffected by sediment size Characteristics Permeability: Increases with increasing sediment size Capillary Water: Decreases with increasing sediment size  Capillary Water: Adhesion and Cohesion Cohesion: Water is attracted to water. Adhesion: Water is attracted to other substances. Permeability A thin layer of water will always be vs. attracted to mineral grains. Pore Space The smaller the connections between Size the pore spaces, the harder it is for water to flow due to the layer of water attracted to the grains. Thus, coarse-grained (larger) sediments are usually more permeable than fine-grained (smaller) sediments, pebbles are more permeable than clays. Permeability Surface Area vs Particle Size Surface Area vs Grain Size Surface area increases as grain size decreases. There is more surface area for water to adhere to in smaller sediment.  Grain Sorting The grain sorting refers to the range of sediment sizes. Well sorted = small size range Poorly sorted = large size range  Grain Sorting Porosity: typically Effect on Aquifer lower for poorly sorted sediment. Characteristics Permeability: typically lower for poorly sorted sediment Capillary Water: typically higher for poorly sorted sediment Grain Packing (Overburden Stress) A measure of how close together the grains are, which is caused by weight of overlying materials pressing down.  Grain Packing Porosity: typically Effect on Aquifer higher for loosely packed sediment. Characteristics Permeability: typically higher for loosely packed sediment Capillary Water: if there is more sediment in the same volume capillary water increases  Grain Shape A measure of how spherical the sediment grains are. Angular Rounded Grain Shape on Porosity: typically Aquifer higher for more spherical grains. Characteristics Permeability: typically higher for more spherical grains Capillary Water: if there is more sediment in the same volume capillary water increases Unconfined Aquifer: Unconfined aquifers are those into which water seeps from the ground surface directly above the aquifer. Confined Aquifer: Confined aquifers are those in which an impermeable dirt/rock layer exists that prevents water from seeping into the aquifer from the ground surface located directly above. Well A hole drilled or bored into the earth to obtain water, petroleum, natural gas, brine, or sulfur. Recharge: the refilling of groundwater from the surface Recharge Area: a recharge area is the place where water is able to seep into the ground and refill an aquifer because no confining layer is present. Discharge: the movement of groundwater from the subsurface to the surface. Water Budget: water budgets account for the inputs, outputs, and changes in the amount of water of a system (e.g. aquifer, lake, etc.) by breaking the water cycle down into components. Water Budget = Input - Output Water Budget: water budgets account for the inputs, outputs, and changes in the amount of water of a system (e.g. aquifer, lake, etc.) by breaking the water cycle down into components. Water Budget = Input - Output Surplus: a surplus occurs when the inputs in the water budget of a system (e.g. lake) are greater than the outputs. Surplus = Input > Output Deficit: a deficit occurs when the outputs in the water budget of a system (e.g. lake) are greater than the inputs. Deficit = Output > Input Usage: When plants draw water from the soil at times when the need for moisture is greater than the rainfall. Groundwater Overdraft: Groundwater overdraft occurs when groundwater use exceeds the amount of recharge into an aquifer, which leads to a decline in groundwater level.1 Direct Impacts of Groundwater Overdraft1 Reduced water supply due to aquifer depletion or groundwater contamination Increased groundwater pumping costs, and the costs of well replacement or deepening Saltwater intrusion (if near the ocean) Indirect Impacts of Groundwater Overdraft1 Land subsidence and infrastructure damage Harm to groundwater-dependent ecosystems Economic losses from a more unreliable water supply Direct Impacts: Reduced Water Supply and Increased Cost Rural landowners and small-scale farmers are disproportionately affected by overdraft as they have fewer financial resources to dig new or deeper wells or diversify their water supply.1 Direct Impacts: Saltwater Intrusion Under natural conditions, the seaward movement of freshwater prevents saltwater from encroaching on freshwater coastal aquifers.1 Groundwater pumping can reduce freshwater flow toward coastal areas and cause saltwater to be drawn toward the freshwater zones of the aquifer.1 Direct Impacts: Saltwater Intrusion Saltwater intrusion is one of the main causes of groundwater quality degradation and a major challenge in the management of groundwater resources in coastal regions. Saltwater intrusion causes an increase of salt concentration in groundwater which places limitations on its uses. Excessive pumping always leads to a dramatic increase in saltwater intrusion.1 Indirect Impacts: Subsidence Indirect Impacts: Subsidence Land subsidence is a gradual settling or sudden sinking of the Earth's surface due to removal or displacement of subsurface earth materials.1 More than 80 percent of known land subsidence in the U.S. is a consequence of groundwater use, and is an often overlooked environmental consequence of our land and water-use practices.1 Indirect Impacts: Harm to groundwater-dependent ecosystems Groundwater dependent ecosystems (GDEs) are ecosystems which require access to groundwater on a permanent or intermittent basis to meet all or some of their water requirements so as to maintain their communities of plants and animals, ecological processes and ecosystem services.1 Indirect Impacts: Groundwater dependent ecosystems GDEs include aquifers, caves, lakes, palustrine wetlands, lacustrine wetlands, rivers and vegetation.