1. Al-Azhar University-Gaza
Master Program of Water and Environmental
Science

2. I. Introduction
A. Diagram
“ the water table is a subdued replica of the surface topography”
A ground water basin is defined volume of subsurface through
which ground water flows from areas where the water
table is recharged to location where ground water
discharge occurs.

3. Regional groundwater flow
- Simple flow nets provide basis for understanding regional groundwater
flow
- flow patterns are dictated by the variation in the shape of the basin and
water table, and spatial patterns of hydraulic conductivity
Discharge area - water is crossing the water table upwards into
unsaturated zone, land surface, or base of some surface water body

4. Natural basin yield - average rate of discharge from a hill slope
or basin in the
absence of anthropogenic disturbances
- water table is usually at or near the surface at the discharge
area and are usually the
sites of lakes, marshes, etc.
- the line separating recharge from discharge areas is called the
hinge line of (or midline

5. Effect of Basin aspect Ratio
-basin shape exerts influence over the groundwater flow pattern
- the basin aspect ratio (length to depth) is one measure of basin
shape
-two basins of identical length but different depths will have
different natural basin yields
- the deeper basin will have a higher yield because there is more
cross-sectional area to pass the water through

6. - the depth of the basin will also affect the pattern of flow
- in deep basins vertical hydraulic gradient’s exist over a large
portion of the basin
- and shallower basins flow is essentially horizontal over most of a
basin
Effect of topography
-Complex land-surface topography should produce complex
water-table topography

8. -similarly local flow systems are superimposed on top of regional
flow systems
-independently these flow systems appear similar but on different
scales
-local vs. regional is subjective, but regional is usually considered
to recharge at a basin divide and discharge at a valley bottom
-local flow system water has less of a residence time underground
and therefore less interaction with geology
-local flow system water temperatures close to mean annual
surface, more active in hydrologic cycle

9. -spring flows from local systems is more variable than regional
-intermediate flow systems have at least one local flow system between their
recharge and discharge areas
-for shallow basins the regional system may exist but may be attenuation to as a
result of the dominant influence of local flow systems

10. Stagnation points

11. II. Groundwater Flow Patterns

12. II. Groundwater Flow Patterns
GW Divide

13. II. Groundwater Flow Patterns
Discharge Zone
Recharge Zone
GW Divide
Hinge Line
Discharge Zone

14. III. Piezometer Patterns

15. IV.
Effects of Topography
Toth systems of flow
local
intermediate
regional

16. IV.
Effects of Topography

17. IV.
Effects of Topography

18. V. Flow System Mapping
(recharge and discharge zones)

19. V. Flow System Mapping
A.
(recharge and discharge zones)
Topography

20. V. Flow System Mapping
A.
B.
(recharge and discharge zones)
Topography
Piezometer Trends

21. V. Flow System Mapping
A.
B.
C.
(recharge and discharge zones)
Topography
Piezometer Trends
Hydrochemical Trends

22. V. Flow System Mapping
A.
B.
C.
D.
(recharge and discharge zones)
Topography
Piezometer Trends
Hydrochemical Trends
Environmental Isotopes

23. V. Flow System Mapping
A.
B.
C.
D.
E.
(recharge and discharge zones)
Topography
Piezometer Trends
Hydrochemical Trends
Environmental Isotopes
Soil, Vegetation and Land Surface Features

25. Groundwater-Lake/Wetland interactions
-hydrologic regime of a Lake is strongly influenced by
the regional groundwater flow system in which it sets
- large permanent lakes almost always discharge areas
for regional groundwater systems
- small permanent lakes in upland portions of
watersheds usually discharge areas for local or
intermediate flow systems
-where water table elevations are higher than Lake
levels on all sides, recharge-lake only possible if high
permeability at depth

28. Groundwater that is “noncyclical”
- some groundwater by and large does not take part in flow
systems:
connate water: Water which was deposited, by geological
means, simultaneously with the surrounding rock formations
and held without flow.
- This water usually occurs deep in the earth, and is high in
mineral content due to long contact with rock.
connate water and fossil water often get interchanged
- some definitions have connate water as any water that is
out of contact with the surface for a long time
magmatic water: may contain water that was subducted
previously and juvenile water

29. VI. Salt Water Encroachment
A. The problem

30. VI. Salt Water Encroachment
B. Possible Solutions
1. modification of pumping pattern

31. VI. Salt Water Encroachment
B. Possible Solutions
2. artificial recharge

32. 3. pumping troughs

33. 4. freshwater ridge (injection barrier)

34. 5. subsurface barrier

35. VI. Salt Water Encroachment
B. Possible Solutions
1. modification of pumping pattern
2. artificial recharge
3. pumping troughs
4. freshwater ridge (injection barrier)
5. subsurface barrier

38. Quantitative Interpretation of Regional Flow Systems (how much
recharge/discharge)
-using flow net construction we can calculate rates are
recharge and discharge throughout the basin profile
Recharge-discharge profiles
-can be created above flow nets
-also a good way of checking flow that construction since in
steady state recharge must equal discharge
- 3-D maps possible as well