[c]Aquifer characteristics
Introduction:-
The hydraulic parameters T, S, and K have been determined by many authors (Hussein, 1975, Alsheikh, 2002).But the calculation of these parameters during this study aims to show the impact of high dam constructed at 3.2km upstream from the upper gate. This is also calibrated by continuous measurements of water level at well52.
Table (6) Fig (4.3)
To achieve these goals the pumping test carried out at well80,51 and 50 tables (1,2, and 3).
Methods of interpretation:-
The analysis of pumping test data is usually achieved by the application of formulae, representing various methods of variable accuracy a scale which can be used in the computation of the hydraulic properties of the aquifer systems.
These methods include:-
The Thies graphical solution method which is based on the non equilibrium equation.
S=(Q/4πt) W(u)………………………………………………………………………….1
U=(r²S/4Tt)…………………………………………………………………………………2
Where s is the draw down in meters, s=h0-h different in head (m). Q is the discharge rate in m³/day, T is the transmissivity in m²/day. S is the storage coefficient (dimensionless) and r is the distance between pumped well and observation well in (m).
By a log –log plot of w(u) along the y- axis and 1/u along the x- axis commonly called Thies standard curve- Thies standard curve which result from the plotting of the values w(u), u. The field data plotted as along the x- axis, and draw down along the y- axis, which called the field curve Fig( ). The procedure of matching of the Thies standard curve (theoretical curves), field curve is knowned as the data analysis. The data analysis may be done by either manually or by computer- aided program. In this study the data analysis done by computer.
2 – Recently, Neumam (1975) developed a new equation for unconfined aquifer, which properly treats the of the storage, and avoids the error arising from this problem. The draw down in this formula is given by:
S= (Q/4πT) W(UA, UB, β)…………………………………………………………………..3
Where, w (UA, UB, β) is the unconfined well function UA (type A curve for early time) ,when water is released from the storage, UB (type B curve for later time).
Β= r²kv/b²kh………………………………………………………………………………………4
Where kv is the vertical hydraulic conductivity, kh is the horizontal hydraulic conductivity in m/day, b is the thickness of the aquifer.
Kv= (βb²hk)/r²……………………………………………………………………………………5
3 Hantush (1964 and1962) method, which over comes the partial penetration.
ho- h= (Q/4πТ) w (u, r/B), u= r²S/4Tt. B= (Tb/k)½.
Table (4): shows the result of pumping test data.
Well No Methods Theis Hantush Neuman
Para meters T m²/d Km/d S T m²/d Km/d S T m²/d Km/d S
50 49.39 2.69 0.604 41.62 2.08 0.604 24.94 1.24 0.60
51 93.82 4.69 0.81 79.07 3.95 0.82 64.60 3.23 0.82
80 156.76 7.84 0.07 126.58 6.33 0.042 76.57 3.83 0.42
-Discussion of the Results:-
After the precise matching of the field and master curves, the hydraulic parameters T,S &K are tabulated in table (4) .However, the values of the transmisstivity obtained by Neumann’s method is taken for any evaluation because , this method is applied for unconfined aquifer .
The storativity
-Water Level Fluctuation:-
Short-term fluctuation was observed in well No.52which was equipped with an automatic water level records. Water level in Khor Arbaat begins to rrise in July or august in response to the recharge from the base flow through the upper gate or direct infiltration from the rainfall during the floods.
Water levels c continue to rise throughout the year and they are reached their maximum level in august or September. They are usually decline after the peak of the floods die out.
The water level reached its lowest value in April or May fig( ). Water level reached its lowest value in April or May Fig ( ) .water level date is sh0wn in table( ) The measurement over the period 2002,2003and 2004 is done respectively after the construction of the dam in which the decline in water level during these years is 1.2,1.05 and 1.2m respectively .
Table ( ) shown the average month values of well 52.
Years month 2002 2003 2004
Jan. 9.76 9.82 9.38
Feb. 9.79 9.93 9.93
Mar. 9.80 10.10 9.39
Apr. 9.98 10.20 9.43
May. 10.16 10.31 9.50
June. 10.01 10.36 9.66
Jul. 9.80 10.39 10
Aug. 9.82 9.76 10.21
Type equation here. Sep. 9.29 9.25 10.36
Oct. 10.02 9.39 9.89
Nov. 9.93 9.57 9.89
Des. 9.98 9.42 9.93
The Hydraulic gradient:-
It’s importance that has been affected in ground water flow, its different values along the Khor, extent. The gradient can be calculated from formula:
I= Δh/L
Where:
Δh: different water level values between two wells
L: the distance between two point (wells).
From fig( ) and Table ( ) the gradients values are 0.005 at upper gate, 0.008 at the middle 0.007 at lower gate.
Table :shows the content of hydraulic gradients measurements
Well No Contour line S.W.L Water level from a.s.l
37 145 11.40 133.6
38 140 9.33 130.77
50 135 10.67 124.33
58 137 8.09 128.91
13 118 5.5 112.5
11 112 6.3 105.7[/left][/b][/color]