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THE HYDROLOGIC CYCLE 2: GROUNDWATER

THE HYDROLOGIC CYCLE 2: GROUNDWATER. The Hydrologic Cycle - Fresh Water Storage Reservoir % of Total Fresh Water Glaciers (Frozen) 76% Groundwater 22% Rivers & Lakes < 2% Groundwater – largest liquid fresh water storage reservoir. The Groundwater System.

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THE HYDROLOGIC CYCLE 2: GROUNDWATER

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  1. THE HYDROLOGIC CYCLE 2: GROUNDWATER

  2. The Hydrologic Cycle - Fresh Water Storage Reservoir % of Total Fresh Water Glaciers (Frozen) 76% Groundwater 22% Rivers & Lakes < 2% Groundwater – largest liquid fresh water storage reservoir.

  3. The Groundwater System

  4. The Groundwater System Gaining Streams Losing Streams

  5. The Water Table Mirrors Surface Topography

  6. Groundwater Flows From High Pressure To Low Pressure Areas

  7. Usually, this means Down Gradient

  8. So, To Understand Groundwater • Flow We Need To Know: • Depth of the water table. • Gradient (slope) of the water • table. • 3) Characteristics of the rocks • that the groundwater is • traveling through.

  9. Depth and Gradient: Gradient determines the direction of groundwater flow.

  10. Gradient = (h1- h2)/L Where:h1and h2 are the elevations of the water table at two locations, and L is the horizontal distance between them h1 h2

  11. Rock Characteristics: • Porosity – How much water the rock will hold. • Permeability – The ability of a rock to transmit water. Depends on size and connectivity of pores.

  12. Low Porosity A) Sediments Soil 55% by volume Clay 45 Sand 35 Gravel 20 B) Rocks Shale 5% Limestone 5 Sandstone 15 Granite 1 Fractured Limestone 20 Permeability Clay Shale Solid Limestone Sandstone Fractured Limestone Gravels & Sands High

  13. The first person to study these characteristics of the groundwater system was a geologist named Henri Darcy. • Darcy noted that the velocity of groundwater flow was proportional to the gradient of the water table. • 1) V α (h1- h2)/L but we need to account for permeability • V = k (h1- h2)/L where k is a permeability variable, and • Q (discharge) = Ak (h1- h2)/L where A is a measure • of cross sectional area

  14. Darcy’ Law Q (discharge) = Ak (h1- h2)/L = AV Pore Remember, when calculating cross – sectional area the water is only flowing through the open pores (unlike a river channel). So A (area) =width X depth X porosity.

  15. Problem • What is the gradient of the water table whose elevation is 500’ at well 1, 300’ at well 2, and the wells are 2000’ apart? • If the aquifer has a width of 40 feet, and a depth of 40 feet, a porosity of 5%, and a k = 0.01 ft/day, what is the groundwater velocity and discharge?

  16. 1) Gradient = (h1- h2)/L = 500’ – 300’/2000’ = 0.1 2) Velocity= k (h1- h2)/L = 0.01ft/day x 0.1 = .001ft/day 3)Q = Ak (h1- h2)/L = 40’ x 40’ x .05 x .001 = .08 ft3/day

  17. 2) Groundwater Contamination Human activity Produces Many Sources of Waste!

  18. Contaminant Plume

  19. Contaminant Plume in Map View

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