This document discusses soil moisture and groundwater recharge. It defines key terms like the vadose zone, porosity, water content, and capillary fringe. It describes how soil moisture is measured and influenced by precipitation and evapotranspiration. The unsaturated zone allows infiltration of water according to Darcy's law. Water table recharge occurs when infiltrating water reaches the capillary fringe and displaces air, causing the water table to rise. The rate of recharge depends on factors like the thickness of the unsaturated zone and vertical hydraulic conductivity.

1. Al-Azhar University-Gaza
Master Program of Water and Environmental
Science
Soil Moisture and
Groundwater Recharge
prepared by
Safaa A. EL Derawi

2.  Introduction
The uppermost layer of the earth may contain a three phase
system of material:
 solid
 liquid
 gaseous

3. The earth layer that
contain the three phase
system is called the:
vadose zone also know
as zone of aeration, and
unsaturated zone .

4. Porosity and water content of soil

5.  Porosity

6.  The void ratio of the soil
is the ratio of volume of the voids to the volume of the solids.

7. V= Vv + Vs ,
n= Vv/V
n= Vv / Vv +Vs
divide by Vs
V= Vv + Vs ,
e= Vv/Vs
e= Vv / V - Vv
divide by V

8.  The gravimetric water content
 The volumetric water content
 The saturation ratio

9. Bulk Soil = Particle volume + pore volume
 The dry bulk density :
 The particle density:

10.  Porosity can be calculated in practice:

11. Soil Water Measurement
Measures mass water content
 Take field samples
 weigh(Wm)
 oven dry at 105 C
 weigh ( Ws) until a constant mass is
obtained Ww=Wm-Ws
Gravimetric water content = Wm-Ws / Ws
and Vw = (Wm - Ws / w )/V
Volumatric water content =Vw/V

13. Electrical Resistance Blocks & Meters

14.  Capillarity and the capillary fringe
Capillary forces :
The forces acting on soil
moisture in the
unsaturated zone,
attributable to molecular
attraction between soil
particles and water.

15. The capillary rise in cm is :
Capillary Rise

16. Capillary fringe :

17. The zone of aeration is best defined as the zone where the
soil moisture is under tension

18.  Pore-water tension in the vadoes zone
 Fluid pressures in the vadose zone are negative
 The negative pressure head is measured in the field
with a tensiometer

19. Tensiometer for Measuring Soil Water Potential
Water Reservoir
Variable Tube Length (12 in- 48 in)
Based on Root Zone Depth
Porous Ceramic Tip
Vacuum Gauge (0-100 centibar)

20.  soil water
is the water in the vadoes zone, that is available to
growing plants.

21. Soil moisture depend on:
1.
Change in the amount
of precipitation.
2.
Change in the amount
of evapotranspiration

22. Types of soil water

24. Field Capacity - Wilting Point

26.  Theory of Unsaturated Flow
The infiltration of water into the unsaturated can be
considered in terms of:
 Gravity potential, Z
 Moisture potential, ψ

27. Darcy’s law is valid for flow in the unsaturated zone.
Is not constant ,
content
is a function of the volumetric water

28. Idealized curves showing relationships of volumetric water
content, hydraulic conductivity, and soil-moisture head

29.  Water-Table Recharge
When the front of
infiltrating water reaches
the capillary fringe, it
displaces air in the pore
spaces and cause the water
table to rise.

30. Rate of Recharge
The rate of water-table recharge depends on:
1. Thickness of the unsaturated zone
(The thinner zone, the faster rise of water table)
2. The vertical unsaturated hydraulic conductivity
3. The permeability .
May generate a localized ground-water mound