Continued from previous lecture

Aquifers are the major topics in Hydrogeology

- you MUST understand Darcy's law (in theory and math)
- be able to calculate hydraulic head

Hydraulic Conductivity

- ease of flow of water through subsurface
- similar to permeability but related to geologic fluid AND structure (eg. water and sandstone; oil and shale)
- NAPL- non-aqueous phase liquids

Intrinsic Permeability vs. Hydraulic Conductivity

- hydraulic conductivity equation: K=k(pg/mu)
- K- hydraulic conductivity, k- permeability
- p-

Measuring these in the lab: at least four diff ways

Transmissivity (another aquifer property)

- the total amount of water that can be transmitted horizontally through a geologic unit's single unit width (1 unit length, not 2 or 3)
- T=KB, T- transmissivity, K- hydraulic conductivity, B-
- definition is based on Darcy's Law

Specific Storage (another aquifer property)

- super duper important
- aka elastic storage coefficient
- the vol of water an aquifer releases/produces from storage (fully saturated): per unit vol per unit decline in hydraulic head
- insert specific storage equation here
- hydraulic head measured in length, Ss measured in vol like ac ft or ft cubed
- it's caused by pressure changes, water moves from higher hydraulic head to lower
- water and rocks have elastic properties
- as pressure increases, more space becomes avilable for water due to expanding pore space and contracting geologic unit
- as pressure decreases, less space becomes available for water due to expansion of water molecules
- material and water compete for space

- water and rocks have elastic properties

Storativity (ditto)

- amount of water expelled per unit surface area per unit change in hydraulic head
- S=bS
_{s} - storativity is different for confined and unconfined aquifers, due to specific yeild's relation to storativity
- Confined
- aquifer is always saturated
- Ss less than .005

- Unconfined
- saturation varies, therefore thickness of aquifer varies:: always fluctuating
- groundwater drainage is much more important here
- S=S
_{y}+ h(S_{s}) - Ss between .02 to .3
- highly dependent on grain size

- Confined

Lecture Notes 5

all about flow

isotropic similar to homogeneous, isotropic is about permeability in 3 directions

anisotropic similar to heterogeneous

generally, vertical and horizontal permeability are very idfferent

generally, vertical hydrulic conducivity is 10% of horizontal

you can have a homogenous structure that is anisotropic

aquifers are naturally heterogeneous

for aquifers with layers, we use the average hydraulic conductivity

- insert avg horizontal hydr conductivity formula, can be used with any number of layers

Potentiometer Surface

From physical geology labs: contours and elevations (topographic maps)

Potentiometer = total hydraulic head (instead of elevation)

Map that shows flow direction of groundwater or other fluids

- made of equipotential lines (instead of contour lines) that are generally parallel to eachother
- flow lines are perpindicular to equipotential lines
- when three wells form a right triangle, we can calc hydraulic gradient exactly
- insert super complicated formula here for Grad h=

Specific Discharge or Darcy's flux

Q/A = k (hydraulic gradient) or Q/A = k (dh/dl)

Flow Lines aka Flow Nets

shows the paths that gw takes through an aquifer

- solid lines show flow direction
- dashed lines show hydraulic gradient markers
- assumptions:
- aquifer is homogenous, isotropic and fully saturated (never happens in real life)
- Darcy's law is valid, flow is laminar

- Flow Net Theory
- ?

- total flow can be calc from these maps
- insert formulas here
- and here
- there might be more
- but we don't have to know them
- just the theories they support

- Seepage Under Dams
- many diff types