Groundwater P = Q + ET + G +  S

Floridan Aquifer Extent

Hydrologic Horizons PressureTension θ pwp < θ < n θ fc < θ < n θ = n

Geologic Profiles (Stratigraphy)

Confinement

Transmissivity How much water can be moved horizontally –Function of thickness and K sat –Good measure of well productivity –Floridan is the most transmissive aquifer in the world

Loss of Potential

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

Gainesville’s Well Field Also Lake City Jasper Geology Land use Conservation Easement

Murphree Wellfield Cone of Depression 1988 (Observed)2010 (Predicted)

How to make a sinkhole Pray for lots of Rain Suck a lot of water

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.

Groundwater and Wetlands

Invasion Fire Subsidence Degraded wildlife habitat

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 Q groundwater = K A ΔH/L Darcy’s Law Darcy’s law can calculate vertical leakage through a clay layer AND lateral flow through a seepage face. Q is water crossing the defined area of the boundary in m 3 /day

K is hydraulic conductivity, or the capacity of the media to transmit water Most meaningful as saturated hydraulic conductivity K sat (m/day). Why? Q= K A ΔH/L

Measuring Ksat Constant Head Method –Constant depth of water (~50mm) on top of a saturated soil column with known dimensions (diameter, length) –Outflow volume collected over a period of time (e.g., 5 hrs) –Darcy’s Law to solve for Ksat

Measuring Ksat Hvorslev Method –Field measurement in screened wells K only determined minutes H/H o t 37 Log scale Linear scale H/H o =.37 casing Gravel pack Screen LeLe L e /R must be >8 R high K material r

Approximate K sat and Uses Ksat (cm/h)Comments 36 Beach sand/Golf Course Greens 18 Very sandy soils, cannot filter pollutants 1.8 Suitable for most agricultural, recreational, and urban uses 0.18 Clayey, Too slow for most uses <3.6 x Extremely slow; good if compacted material is needed

ΔH is the difference in H between two points Water flows from high ψ total to low ψ total (could be “up”) PointψGψGψPψPH A B C H = Ψ gravity + Ψ pressure H = level of water in an open well above some datum H A = ? H B = ? ΔH = ? Flow Direction?!?

D? ΔH? Direction?

ΔH AD? Dir? ΔH BF? Dir? ΔH AF? Dir? ΔH/L BF?

Q=K A ΔH/L K?A?ΔH?L? Vertical leakage problem Ksat=0.001m/d Watershed=100 ha Datum

Q = K * A * ΔH/L K = m/d A = 100ha = 1,000,000 m 2 ΔH = 5-3 = 2m L = 2m Q = 0.001m/d x 1,000,000m 2 x 2m / 2m Q = 1,000 m 3 /day or 365,000 m 3 /year Q surface depth = 365,000 m 3 / 1,000,000 m 2 = 0.365m

Q=K A ΔH/L K=0.1m/d A=100m x 50m =5,000m 2 Δ H=108m-105m =3m L=1,000m Qm 3 /d= 0.1m/d * 5,000m 2 *0.003 = 1.5m 3 /d Lateral leakage problem

Groundwater Flowpaths at Streams

Groundwater Discharges

Groundwater Flowpaths

Next Time… Soil Water Storage