Groundwater P = Q + ET + G + S. Floridan Aquifer Extent.
Post on 17-Dec-2015
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Transmissivity
• How much water can be moved horizontally– Function of thickness
and Ksat
– Good measure of well productivity
– Floridan is the most transmissive aquifer in the world
Potentiometric Surface
• Elevation of “free water surface”
• Where this surface and the ground intersect (and there’s no confinement) water seeps
Relevant Questions
• Where is the water going?– Potentiometric (piezometric) surface
• How much water is moving? How quickly?– Potentiometric surface and Darcys Law
• What level of natural assimilation is occuring?– Water quality modeling
Drilling and pumping
Developed into a hole 300ft deep and
300ft wide
Hundreds of sinkholes developed over a
period of 6 hours.
Freeze Protection• To protect strawberry yield during a January
freeze in 2010, ~ 2 billion gallons per day of water pumped over a 5 day period. Voila.
Artesian Springs• Where a confining layer exists, there may be a
pressure potential in the aquifer HIGHER than the gravity potential of the surface.
• When tapped, water flows upwards
Soil water movement across a watershed boundary.
P=Q+ET+G+ΔS
Qgroundwater= K A ΔH/L
Darcy’s Law
Darcy’s law is mostly used to calculate vertical leakage through a clay layer, but may also be used to calculate lateral flow.
Q is water crossing the defined area of the boundary in m3/day
K is hydraulic conductivityMost meaningful as saturated hydraulic conductivity Ksat (m/day). Why?
Q= K A ΔH/L
ΔH is the difference in H between two points
Water flows from high ψtotal to low ψtotal (could be “up”)
Point ψG ψP H
A
B
C
H = Ψgravity + Ψpressure
H = level of water in an open well above some datum
HA = ? HB = ? ΔH = ?
Flow Direction?!?
Q = K * A * ΔH/L
K = 0.001 m/d
A = 100ha = 1,000,000 m2
ΔH = 5-3 = 2m
L = 2m
Q = 0.001m/d x 1,000,000m2 x 2m / 2m
Q = 1,000 m3/day or 365,000 m3/year
Q surface depth = 365,000 m3 / 1,000,000 m2= 0.365m
Q=K A ΔH/L
K=0.1m/d
A=100m x 50m=5,000m2
ΔH=108m-105m=3m
L=1,000m
Qm3/d= 0.1m/d * 5,000m2 *0.003 = 1.5m3/d
Lateral leakage problem
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