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Ground Water Basics continued. Aridic arid climate, usually dry, irrigation required for crop production. Ustic—semiarid climate, rainfall during a growing season. Xeric—semiarid climate, Mediterranean climate, cool, moist winters, dry summers, dryland crop possible from stored soil water.
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Aridic arid climate, usually dry, irrigation required for crop production. • Ustic—semiarid climate, rainfall during a growing season. • Xeric—semiarid climate, Mediterranean climate, cool, moist winters, dry summers, • dryland crop possible from stored soil water. • Udic—humid climate, usually moist, generally irrigation not required for crop • production. • Perudic—precipitation exceeds evapotranspiration in all months, but soil is not • saturated for long periods. • Aquic—soil saturated long enough to cause anaerobic conditions
Types of Porous Media Isotropic Anisotropic Homogeneous Heterogeneous
Layered media (horizontal conductivity) Q4 Q3 Q2 Q1 Q = Q1 + Q2 + Q3 + Q4 K2 b2 Flow K1 b1
Layered media(vertical conductivity) R4 Q4 Flow R3 Q3 K2 b2 R2 K1 b1 Q2 Controls flow R1 Q1 Q ≈ Q1 ≈ Q2 ≈ Q3 ≈ Q4 The overall resistance is controlled by the largest resistance: The hydraulic resistance is b/K R = R1 + R2 + R3 + R4
Aquifers • Lithologic unit or collection of units capable of yielding water to wells • Confined aquifer bounded by confining beds • Unconfined or water table aquifer bounded by water table • Perched aquifers
Transmissivity • T = Kb gpd/ft, ft2/d, m2/d
Schematic T2 (or K2) b2 (or h2) i = 2 k2 d2 T1 b1 i = 1 k1 d1
T2 (or K2) k2 T1 k1 Pumped Aquifer Heads b2 (or h2) i = 2 d2 b1 i = 1 d1
T2 (or K2) k2 T1 k1 Heads h2 - h1 b2 (or h2) h2 i = 2 d2 h1 b1 i = 1 d1
LeakanceLeakage coefficient, resistance (inverse) • Leakance • From below: • From above:
T2 (or K2) k2 T1 k1 Flows h2 h2 - h1 b2 (or h2) h1 i = 2 d2 qv b1 i = 1 d1