Hydraulic Head

Hydraulic Head Measure of the potential energy available for

flow in groundwater. Indicated by the water level in a monitoring

well (piezometer). Total hydraulic head is a combination of

gravitational potential energy and fluid pressure energy.

Hydraulic head is measured using small monitoring wells (piezometer wells).

Head is measured as DTW (depth to water), which is then subtracted from the elevation of the well head.

Datum (sea level)

Hydraulic Head

Depth to water (dtw)

Elevation of well head (e)

Elevation Head(z)

Pressure Head(hp) ht = hp + zTotal Head

(ht)

ht = e - dtw

Point water pressure head vs.Fresh water pressure head

Point water head: the actual measured hydraulic head.

Fresh water head: the equivalent hydraulic head that would be observed if the well was filled with fresh water.

If the aquifer contains fresh water, the two are the same.

Fresh

Brackish

Saline

Point water heads

Apparent hydraulic gradient

Fresh

Brackish

Saline

Fresh water heads

Actual hydraulic gradient

Groundwater contours = equipotential / potentiometric contours

Groundwater flow lines cross equipotential lines at 90.

Groundwater flows from high to low equipotential.

Groundwater divide - barrier to flow created by water table ridge (recharge) or gaining stream valley (discharge).

Groundwater Divide

Equipotential contour lines: cross section view All points along the same equipotential line have equal value of

hydraulic head. Hydraulic head = elevation of intersection of water table and

potentiometric contour.

252015

Equipotential contour values

252015

30

Discharge

RechargeFlow lines and Recharge / Discharge

25

Hp=30

HT = 25Hp = 30z = -5

25

HT = 10Hp = 20z = -10

Well 1

Well 2Well 3

3-Point Problem The hydraulic gradient across a local area of an aquifer can be determined if

three values of hydraulic head are known.

h=40 h=30 h=35

3-Point Problem

N

100 meters

h=40m

h=30m

h=35m

3-Point Problem

N

100 meters

h=40m

h=30m

h=35m

dh=5

dh=5

dh=10

3-Point Problem

N

100 meters

h=40m

h=30m

h=35m

dh=5

dh=5

dh=10

3-Point Problem

N

100 meters

h=40m

h=30m

h=35m

32

34

36

38

3132

3433

36373839

3-Point Problem

N

100 meters

h=40m

h=30m

h=35m

32

34

36

38

3132

3433

36373839