THE HYDROLOGIC CYCLE 2 GROUNDWATER The Hydrologic Cycle
- Slides: 20
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
The Groundwater System Gaining Streams Losing Streams
The Water Table Mirrors Surface Topography
Groundwater Flows From High Pressure To Low Pressure Areas
Usually, this means Down Gradient
So, To Understand Groundwater Flow We Need To Know: 1) Depth of the water table. 2) Gradient (slope) of the water table. 3) Characteristics of the rocks that the groundwater is traveling through.
Depth and Gradient: Gradient determines the direction of groundwater flow.
Gradient = (h 1 - h 2)/L Where: h 1 and h 2 are the elevations of the water table at two locations, and L is the horizontal distance between them h 1 h 2
Rock Characteristics: 1) Porosity – How much water the rock will hold. 2) Permeability – The ability of a rock to transmit water. Depends on size and connectivity of pores.
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 Low Clay Shale Solid Limestone Sandstone Fractured Limestone Gravels & Sands High
The first person to study these characteristics of the groundwater system was a geologist named Henri Darcy noted that the velocity of groundwater flow was proportional to the gradient of the water table. 1) V α (h 1 - h 2)/L but we need to account for permeability 2) V = k (h 1 - h 2)/L where k is a permeability variable, and 3) Q (discharge) = Ak (h 1 - h 2)/L where A is a measure of cross sectional area
Darcy’ Law Q (discharge) = Ak (h 1 - h 2)/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.
Problem 1) 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? 2) 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?
1) Gradient = (h 1 - h 2)/L = 500’ – 300’/2000’ = 0. 1 2) Velocity = k (h 1 - h 2)/L = 0. 01 ft/day x 0. 1 =. 001 ft/day 3) Q = Ak (h 1 - h 2)/L = 40’ x. 05 x. 001 =. 08 ft 3/day
2) Groundwater Contamination Human activity Produces Many Sources of Waste!
Contaminant Plume
Contaminant Plume in Map View
- Water cycle the hydrologic cycle
- How does groundwater rejoin the water cycle
- Hydrograph
- Hydrologic losses
- Objectiveable
- Hydrologic engineering center
- River analysis system
- Storage equation
- Continuity equation hydraulics
- Difference between reservoir routing and channel routing
- Hydrologic engineering center
- Hydrologic abstractions
- Hydrologic engineering center
- Hydrologic routing
- Hydrologic routing and hydraulic routing
- Water budget equation
- بئر ارتوازي
- Is groundwater a renewable or nonrenewable resource
- Groundwater flow net
- Groundwater erosion and deposition
- Groundwater true/false quiz answers