G Density driven flow

Question 1

specific gravity equations

Answer 1

=density of seawater/density of pure water

Question 2

seawater density

Answer 2

1025 kgm-3

Question 3

freshwater density

Answer 3

1000 kgm-3

Question 4

major control on density is

Answer 4

salinity

Question 5

pressure with depth equation

Answer 5

=P0+densitygchange in z

Question 6

transition zone (between saline and fresh) towards the coast gets

Answer 6

broader towards the coast

Question 7

equivalent freshwater head equation

Answer 7

=density saline/density fresh *Zs

Question 8

dupuit approximation

Answer 8

assume horizontal flow in thin aquifers

Question 9

why is dupuit approximation invalid close to the coast

Answer 9

proportional to distance from the coast so if it is zero then equation doesn’t work (can’t square root zero)

Question 10

coastal aquifer management

Answer 10

extraction of fresh waters and saline upconing
extraction of cooling water or brackish groundwater for desalinisation
injection of waste water

Question 11

sea water intrusion cause

Answer 11

pumping lowers the water table so the interface between saline and fresh moves inland until new equilibrium is reached

Question 12

if volume pumped>replenishment

Answer 12

no equilibrium can be established and sea water will encroach until the aquifer is all saline

Question 13

management after seawater intrusion

Answer 13

reduce extraction, change pumping location
import fresh water or extract saline water

Question 14

scavenger wells

Answer 14

simultaneous pumping of both fresh and saline groundwaters from wells at different depths reduces mixing

Question 15

Skimming wells

Answer 15

pump the freshwater at shallow depth and run under a steady state where the flow rate does not draw the saline water up high enough into the well screen