Groundwater

Proportion that groundwater makes of freshwater

30.1%

Porportion of rainwater that infiltrates/percolates

10%

infiltration

Downward entry of water into soil

Percolation

Downward movement of water in soil

Water table

Upper boundary of an aquifer

recharge

precipitation - runoff - evapotranspiration

residence time

average time a substance remains in a resevoir

scale of groundwater resevoir time

1000s of years

aquifer

body of permable rock that can hold water underlain by an impermable material

confined vs unconfined aquifer

confined is sandwiched between impermable layers / unconfined does not have an impermable upper boundary

cause of artisan wells

confined aquifers being pressurised and then being drilled into

porosity

sum of all void spaces in a rock

what controls porosity

• grain shape + packing

• grain-size distribution

• degree of compaction

• degree of cementation

average porosity

10-60%

when considering change in groundwater, what are the only variables that can be measured

precipitation and runoff

hydraulic gradient

difference in hydraulic head per unit distance, dh/dl

flow rate, Q (K,A, dh/dl)

Q = -KA dh/dl

specific discharge, q (Q, A)

q = Q/A

hydraulic conducticity, K, in term fo solid and liquid properties

K = Cd² (ro*g/µ)

permability, k (C, d)

k = Cd²

transmissivity

permability across the depth of an aquifer

assumption about water flow

laminar flow

how to determine whether water flow is laminar or turbulent

Reynolds number, Re = ro*v*d / µ, <10 = laminar, >10 = turbulent

effect of decreasing grain size of hydraulic gradient

decreases as smaller grains increases SA which increases frictional resistance

within a lattice where does water flow the fastest

between grains

average velocity of groundwater

v = q/n

potentio/piezometric surface

level water would rise to if unconfined due to pressure

equipotential lines

lines of equal pressure in the groundwater system

how does water flow compared to EP lines

perpendicular

Use of Thiem eqn

to calculate K of a confined aquifer based on well discharge and drawdown