Topic 3, Subtopic A of Review Handbook or Chapter 10 of Earth Science Book. 97% of Earth s water is found as saltwater in Earth s oceans.

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1 Topic 3, Subtopic A of Review Handbook or Chapter 10 of Earth Science Book Groundwater 97% of Earth s water is found as saltwater in Earth s oceans. That leaves only 3% for freshwater! But 90% of the freshwater is frozen in the icecaps! So only a very small percentage of Earth s water is available in fresh liquid form to be used by humans and other land-dwellers. Freshwater is stored in two ways: 1. lakes, streams, and rivers 2. underground in pore spaces of soil, rock and other Earth materials. Sources of Groundwater Groundwater=water stored within the materials below Earth s surface. Evaporation from the oceans and seas is the ultimate source of all surface water and groundwater. Hydrologic Cycle (aka: The Water Cycle) 1. Water evaporates into the atmosphere 2. Clouds form from condensation of water vapor 3. Water falls as precipitation back to the surface 4. The cycle repeats Infiltration=water that soaks into the ground through tiny openings (pore spaces) 1

2 Factors Influencing Infiltration vs Runoff: 1. Porosity & Permeability a. porosity=how big/many are the spaces packing larger size particles greater porosity sorting better sorted more porous shape rounded gives more pore space, angular gives less b. permeability=material s ability to allow fluids to pass through it large connected pores means more fluid can pass through permeable examples=sandstone, limestone, and bedrock with lots of cracks impermeable examples= silt, clay, shale and other fine-grained materials 2. Saturation and Rate of Precipitation a. If the ground is saturated new water cannot enter the ground instead it becomes runoff. b. Rate of precipitation light gentle rains allow water to soak in or infiltrate if the ground is permeable and not already saturated heavy precipitation is less likely to sink in if the ground is impermeable or saturated. 3. Slope of the Land a. Precipitation falling on slopes infiltrates less than precipitation on flat ground. b. If the ground is on a steep slope it flows down the surface rather than sinking in. 4. Vegetation a. More vegetation means greater infiltration plants catch the water and allow it to trickle into the ground. b. Little to no vegetation rain falls more forcefully, ground packs together and lessens porosity c. vegetation on slopes decreases the runoff and increases infiltration 5. Land Use a. installing concrete and/or asphalt for roads and buildings decreases infiltration b. Farming can reduce infiltration if land is left with no vegetation. c. Livestock remove vegetation and compact the soil decreasing infiltration. 2

3 Distribution of Groundwater Groundwater is not evenly distributed below Earth s surface. Zone of Saturation=where groundwater completely fills in the pore spaces of a material Zone of Aeration=area above zone of saturation that is moist but pore spaces are mostly filled with air. Water Table=boundary between the zone of aeration and zone of saturation Water Table fluctuates depending on local conditions. 1. stream valleys-water table is located within a few meters of the surface 2. swampy areas-water table is almost at the Earth s surface 3. hilltops or arid regions-water table can be very deep 10-hundreds of meters or more beneath the surface 4. During drought conditions the water table lowers. The water table follows the topography of an area. Capillarity=tendency of water to be drawn upward from the water table due to surface tension plants are able to draw water from the soil due to capillarity smaller pore spaces means greater capillarity so fine grained soils hold more water than coarse grained soils. 3

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