1- Introduction: 
 

Gaza Strip (Figure 1) like some other parts of
the Middle East countries has a distinct and
serious deficit in water. Currently, there is a water shortage problem for most
of the Gaza
Strip’s residents. Further more it is forecasted that the quantity of available
water, which is already scarce, may drop to incompatible levels with un
acceptable standard of living, public health, social and economic development in
the region.

Every aquifer has its own physical parameters, as
Porosity (E), Transmissivity (T), and Storage Coefficient (S), these physical
parameters control the fluids passage through the aquifer. To study any
aquifer, we must calculate the aquifer physical parameters.

 

The aim of this research is to find some physical
characteristics for the Coastal Plain Aquifer in Gaza Strip, as values for Transmissivity (T)
and Storage Coefficient (S), Permeability, and Porosity. So we can solve the
quantity shortage problem in Gaza
Strip and calculation the amount of stored water in the aquifer

 

 

 

 

 

 

2. Methodology

A number of pumping and observation wells (Figure 2)
were selected to perform some pumping and analysis tests, to find some physical
parameters for the Coastal Plain Aquifer in Gaza Strip, these wells were spread
over the entire Gaza Strip.

 

A- Analysis and Evaluation of Field Pumping Tests:

 

Gaza Strip was divided to five locations
according to the availability of pumping water wells as well as the observation
wells. These locations are Beit Lahia, Beit Hanoun, Gaza City,
Khan Younis, and Rafah. All the wells in these five localities are pumping
wells, which supply water for domestic consumption and most of them mainly pump
water about 24 hours daily.

 

The pumping tests were carried out continuously for
period about (18-36) hours. The results of pumping tests may not be very
accurate because: first, pumping tests will be run for short period  due to the needy water for domestic use and
in the same time they can not stop supplying water to houses for longer time.
Second, the interference of the drawdown in the pumping wells with the near by
agricultural wells which are in use during the pumping tests.

 

Pumping
Test Results :

The results of long term pumping test and
step-discharge-pumping test in the study area are tabulated in appendix
No-1.  These results were drawn
graphically on a semi-log paper, and various equations were applied. See
Appendix-2. The following Table 4-1 shows the values of transmissivity and
storage coefficient of the coastal plain aquifer .

 

 

 

 

Table -1, Results of some pumping test
calculations, for the values of (S), and (T).

 

 

It is noticed, there are some results described as out
of ranges, because the duration of pumping may be is not enough, and the pumped
wells are close to some agricultural wells which were in use during the pumping
operation, that affects the water level readings.

 

From Table -1, the values of S for all the tested wells are in the
range (0.00017- 0.052) in pumping, and as (0.0367 – 9.4) in the recovery case.
And for T, it is in the range (1062 – 19533) m²/day for pumping, and as (973-
21198) m²/day for recovery.

 

B. Permeability (k):

 

There are a number of different methods for
permeability measurements. Among these are methods are the following:  There is ring infiltrometer (consists of a
pipe or a ring) which is simple method. It is straightforward way to conduct
infiltration test. The water flow through the soil inside the infiltrometer
pipe is pure vertical, while the flow under the bottom of the pipe is
3-dimensional. For a coarse soil most of the flow is vertical, as the capillary
forces of such a soil are not very strong. The larger the pipe diameter, the
larger portion of the flow is pure vertical. For a very large pipe almost all
flow is vertical.

 

      Some field tests for permeability  carried out in different locations in Gaza
Strip and the average values were found as:

 

1.  The average k value for the  infiltration field tests is:

       k 
= (7.6 + 6.3 + 8.2 + 6.06) x10^-6  
/4 =   7.04   x 10^{-6 m / sec.}

                

2. From both laboratory soil tests and the
field infiltration tests, we find  the
permeability value represents (or very close to) the standard value for the
silty sand material, which actually represent the study area.

C. Porosity:

 

It is defined as the percentage of the voids which
exist between the soil or rock particles, to its total volume. The porosity
value normally varies between 35 – 55 %. 

Soil samples at different depths (0.0 – 95.0 cm), were taken  to perform: mechanical analysis, density, bulk
density, and then find  porosity value
for these samples. The results of these tests and calculations are shown in
Table 4-2:

 

Table 4-2, Porosity value for soil samples

 

First : Southern Area

Mechanical Analysis

<!--[if !supportLists]-->·       
<!--[endif]-->( Khan Younis)

 

% passing sieves
Description	#4	#10	#30	#40	#60	#100	#200
Sample –1	99.6	99.5	99.4	98.3	53.7	--	1.1
Sample –2	97.5	96.3	94.6	87.7	42.5	--	11.2

<!--[if !supportLists]-->·       
<!--[endif]-->(Meraj)

 

% passing sieves
Sieve No.	3/8	#4	8#	#16	#30	#50	#100	200#
Sieve Opening Size(mm)	9.5	4.8	2.4	1.2	0.6	0.3	0.15	0.075
% Passing	100.0	99.6	99.5	99.4	99.3	87.3	49.9	32.5

 

Water
Content As Received 2.90 %       Bulk
Density         1.519 g/cm³.

Sand Content                                 67.50%       Specific Gravity             2.574.

 

Second : Gaza Area

Mechanical Analysis

 

% passing sieves
Sieve No.	3/8	#4	#8	#16	#30	#50	100#	#200
Sieve opening Size(mm)	9.5	4.8	2.4	1.2	0.6	0.3	0.15.	0.075
% Passing	99.1	98.7	98.5	98.4	96.9	28.1	6.6	5.4

 

Water
Content as Received 3.80%          Bulk
Density         1.667 
g / cm³.

Sand Content                               94.60%           Specific Gravity         2.537

 

 

Third : Northern Area

 

Mechanical Analysis

 

 

Soil Physical Properties

 

 

Porosity %

37.162

37.331

37.751

 

From the above tables, the porosity for the top soil in the study
area, is varied between 37.16 – 37.75 %.

 

D. Soil:

 

Sieve analysis and soil classification, were carried
on  soil 
samples from Khan Younis, Meraj (southern Gaza Strip area),  samples from Gaza city area, and from Jabalia (northern
Gaza Strip area),  see Appendix - 3. All
the results for these samples showed that, most of the study area is covered
with sand mixed with some silt or clay. From Appendix - 3.  and some information, it is  concluded that, all the study area has no
outcrops neither from igneous rocks, nor from metamorphic rocks. But it has
classtic (sedimentary) rocks and mainly composed of sand with some fines as
silt or/ and clay. Silt and clay content generally increases with distance from
the coast toward east.