L11 - Groundwater Hydrology

define permeability

measure of the soil's ability to permit fluid to flow through its pores or voids

does loose soil have high or low permeability?

high permeability

does dense soil have high or low permeability?

low permeability

define porosity

- the ratio of the volume of voids to the total volume

- n = (V_v)/(V_t)

- 0 < n < 1

define specific yield

drainable porosity from effective pores

define specific retention

porosity from non-effective pores

subsurface storage is proportional to ...

porosity

what is the formula for total watershed storage?

n * h (A_out + A_in)/2

what does porosity depend on?

- packing of grains

- different packings cause differing void space

- less void space = more porous

what happens to energy during water flow?

- energy is dissipated in overcoming the soil resistance

- water loses energy as it flows through soil

what is hydraulic head?

total hydraulic head = elevation head + pressure head

define pressure head

- corresponds to the height to which fluid rises above point of interest, when opposed by air pressure

Define elevation head

- corresponds to the elevation of the point of interest

what is fluid potential?

- the energy per unit mass of fluid

- fluid potential = gravity * height

define head

elevation above a datum to which water rises

what is hydraulic head in a standard water body?

it is the same everywhere

define piezometer

measures head adjacent to well screen (where it is in hydraulic contact with the formation)

define equipotential line

a line along which the hyradulic head is constant

define piezometric surface/equipotential surface

- a two-dimensional version of equipotential liens

- similar to a topographic map

- hydraulic head is plotted instead of elevation

define streamline

- shows the direction of groundwater flow

- streamlines are perpendicular to equipotential lines

define hydraulic gradient

hydraulic gradient = difference in total head/distance between points A and B

the hydraulic graident is a proxy for energy difference and is the driving force that causes groundwater to move in the direction of maximum decreasing total head