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Groundwater modeling of harrir plain and mirawa valley in Shaqlawa-Harrir Basins, Kurdistan region, Iraq

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With the increase in population and establishment of agricultural and industrial projects, the utilization of groundwater became more important for Kurdistan region. The increased demand for water in Kurdistan for different purposes has led to an increased consumption of groundwater from the aquifers. A three-dimensional finite-difference groundwater flow model using Visual MODFLOW was developed to investigate the change in hydrogeological conditions and to simulate the properties of the flow system under different stress scenarios for the unconfined aquifer of Harrir plain in Harrir basin and the semi-confined aquifer of Mirawa valley in Shaqlawa basin. The plain of Harrir contains two sedimentary formations of Pleistocene and Pliocene age. The aquifer is underlain by massive beds of claystone and sandstone of Miocene age. Mirawa valley consists of Pliocene and Miocene formations which were used as upper layer and Eocene formation as lower layer for modeling. The two-layer model was calibrated under steady state conditions using hydraulic parameters obtained from observation and pumping wells. The calibrated model succeeds in producing groundwater head distribution in steady state and good accordance to observed data. The standard error was estimated as 1.06 m and 2.24 m, and the normalized root mean square error (NRMSE) are 2.6 % and 2.46% for Harrir and Mirawa respectively. By increasing the pumping rate to 200% and 400% for the pumping wells, the head decreased about 6 m and 18 m in Harrir plain, and about 1 m and 2 m in Mirawa valley respectively.
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1
Groundwater Modeling of Harrir plain and
Mirawa valley in Shaqlawa-Harrir basins,
Kurdistan Region, Iraq
Seeyan, Shwan Hydrogeology Institute, TU-Bergakademie Freiberg; Johanna-
Römer-Str. 13, 09599 Freiberg, Germany,
shwanom2003@yahoo.com
Merkel, Broder Hydrogeology Institute, TU-Bergakademie Freiberg; Gustav-
Zeuner-Str. 12, 09599 Freiberg, Germany,
merkel@geo.tu-freiberg.de
With the increase in population and establishment of agricultural and industrial projects, the utilization
of groundwater became more important for Kurdistan region. The increased demand for water in
Kurdistan for different purposes has led to an increased consumption of groundwater from the
aquifers. A three-dimensional finite-difference groundwater flow model using Visual MODFLOW
was developed to investigate the change in hydrogeological conditions and to simulate the properties
of the flow system under different stress scenarios for the unconfined aquifer of Harrir plain in Harrir
basin and the semi-confined aquifer of Mirawa valley in Shaqlawa basin.
The plain of Harrir contains two sedimentary formations of Pleistocene and Pliocene age. The aquifer
is underlain by massive beds of claystone and sandstone of Miocene age. Mirawa valley consists of
Pliocene and Miocene formations which were used as upper layer and Eocene formation as lower
layer for modeling. The two-layer model was calibrated under steady state conditions using hydraulic
parameters obtained from observation and pumping wells. The calibrated model succeeds in producing
groundwater head distribution in steady state and good accordance to observed data. The standard
error was estimated as 1.06 m and 2.24 m, and the normalized root mean square error (NRMSE) are
2.6 % and 2.46% for Harrir and Mirawa respectively. By increasing the pumping rate to 200% and
400% for the pumping wells, the head decreased about 6 m and 18 m in Harrir plain, and about 1 m
and 2 m in Mirawa valley respectively.
Keywords: Groundwater model, Visual MODFLOW, Steady state, Kurdistan Region
1 Introduction
Numerical modeling is an important method for managing groundwater resources and predicting
future responses for different aquifer systems and various formations. The modular finite-difference
groundwater flow model (MODFLOW) is a program used for simulating groundwater flow systems
(McDonald and Harbaugh 1988; Harbaugh and McDonald 1996). Direct approach of designing
MODFLOW finite difference model is less intuitive, specifically for complex boundary conditions.
Therefore, a MODFLOW model can be developed either using a grid or conceptual model approach
(Sohrabi et al. 2013). A groundwater model is a mathematical representation of ground water systems
and comprises suppositions and facilitation made for various specific purposes. It is developed for the
analysis of hydrogeological processes of flow, transport, and transformation, and has many specific
applications (Kumar 2013).
Groundwater models can be used to test different conceptual models and estimate hydraulic
parameters. They can be used as well for water resource management and to predict how the aquifer
might respond to changes in pumping, hydraulic properties and climate change (Yaouti et al. 2008).
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Groundwater in Shaqlawa-Harrir Basin represents a significant main water resource and an important
source of fresh water; therefore it is important to study the groundwater systems in order to maintain
this vital source and to get necessary information for studying flow system and hydraulic parameters
of this area. The main objective of this article is to study the groundwater processes of the
hydrogeological system of Harrir unconfined aquifer (porous aquifer) and Mirawa semi-confined
aquifer (karst-fractured aquifer); two of the most important groundwater resources for domestic and
agricultural sectors in Kurdistan Region. The model can be used to predict future groundwater flow
conditions, estimate the hydraulic response of an aquifer, and to predict the pumping rate needed to
monitor the well discharge; therefore it can be used to predict water availability and sustainability in
the area.
2 Material and Method
2.1 Modeled area description
Shaqlawa-Harrir basin located in northeast of Erbil City, covers an area of about 1150 km2. Harrir
plain located in center of Harrir basin lies between longitude (44 8' 2.4"; 44 26' 20.4") and latitude
(36 36' 7.2"; 36 26' 31.2") bounded by Greater Zab River in north, Harrir anticline in east, and
Khatibian mountain in southwest. Mirawa valley located in southeastern part of Shaqlawa basin lies
between longitude (44 12' 28.8; 44 30' 18") and latitude (36 30' 25.2"; 36 17' 45.6") surrounded by
Safin anticline in southwest, Shakrok anticline in west, Khatibian mountain in northwest (Fig. 1). The
modeled area covers 181 km2 of Harrir basin and 92 km2 of Shaqlawa basin.
2.2 Geological and hydrogeological setting
The groundwater reservoir of Harrir plain consists of an unconfined aquifer characterized by the
presence of Quaternary deposits (10 m thickness), the permeable Pliocene Bai Hassan and Muqdadeya
formations (including thick sandstone, siltstone and conglomerate) and an impervious substratum of
Fatha Formation of Miocene age which represent aquiclude (including sandstone, claystone, limestone
and rare evaporite). Mirawa valley consists of semi-confined aquifer characterized by three layers;
first layer comprises of Quaternary deposits and Muqdadeya formation, second layer consists of Injana
and Fatha formations and third layer represent PilaSpi formation of Middle-Late Eocene age
(including dolomitic limestone overlain by recrystallized and chalky limestone) which characterizes a
fractured aquifer with a substratum of Gercus formation (including red mudstone, sandstone, shale and
few conglomerate) of Eocene age (Fig. 2).
2.3 Data collection
The geological and hydrogeological input data for groundwater aquifers’ modeling include
information on surface and subsurface geology water table, precipitation, evapotranspiration, pumped
abstraction, stream flows, boundary condition, and hydraulic properties. Hydrogeological properties
include geological formations, lithological descriptions and a topographic map with observation wells
and boreholes location. Physical parameters include the aquifer thickness, hydraulic conductivity,
recharge, specific yield, and pumping rates of wells. Thirteen observation wells with three pumping
wells were used for Harrir plain modeling, and nine observation wells with five pumping wells were
used for Mirawa valley modeling (Tabs. 1 & 2).
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Fig. 1: Location Map of Kurdistan Region, Shaqlawa-Harrir Basin, Harrir Plain and Mirawa Valley
with digital terrain model showing the elevation of the study area, A-B for cross section.
A
B
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Fig. 2: Geological cross section (A-B) of Shaqlawa-Harrir basin showing the formations and
corresponding aquifers (adopted from Seeyan and Merkel 2014).
Tab. 1: Observation wells used for modeling in Mirawa Valley, UTM (WGS-84) coordination system
Well No. Well Name Easting Northing Elevation
(m) a.s.l Water table
(m) a.s.l
W-1 Bawyan 444936 4041578 651 466
W-2 Barbian 429517 4053458 472 378
W-3 Qandil 426356 4053458 360 335
W-4 Qura Bag 423239 4051304 350 315
W-5 Harash 426842 4049420 435 389
W-6 Kani Khazal 428404 4048388 440 403
W-7 Basermay Kon 443207 4038657 645 470
W-8 Harir Extinguish 441106 4046032 600 450
W-9 Badel-1 434237 4047114 445 410
W-10 Baren-2 437737 4041614 514 435
W-11 Kuba 429116 4046402 455 416
W-12 Kebur 430723 4046385 450 418
W-13 Chamasur 433337 4044484 520 424
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Tab. 2: Observation wells used for modeling in Mirawa Valley, UTM (WGS-84) coordination system
Well No. Well Name Easting Northing Elevation
(m) a.s.l Water table
(m) a.s.l
W-1 Sarkand Khaylani 432636 4037449 725 670
W-2 Mawarani Kon 435948 4035378 796 718
W-3 Mawaran 450222 4020810 1005 959
W-4 Haji Bayz 439755 4030445 897 820
W-5 Qarata Sor 441274 4029473 892 845
W-6 Mirawa 442360 4032279 888 828
W-7 Rasan Project 452088 4020409 1019 960
W-8 Aqubani Khwaru-2 448617 4023034 981 948
W-9 Aqubani khwaru-1 445167 4025534 985 925
2.4 Hydraulic properties of the aquifers
Physical properties of the aquifer can be estimated from single well test (Kruseman and de Ridder
1994; Dellur 1999; Schaaf 2004). Hydraulic properties of the two modeled areas were obtained from
the data of pumping test for three wells in Harrir plain and five wells in Mirawa valley by using the
software Aquifer Test. The parameters obtained comprise transmissivity (T), hydraulic conductivity
(K), specific yield (Sy) and storage coefficient (S). Theis and Numan methods were used to determine
hydraulic conductivity, transmissivity, and Storage coefficient (Tab. 3).
Water recharge and discharge from an aquifer represents a change in the storage volume within a
confined aquifer by changing the pressure head. For unconfined aquifers the storage coefficient is
simply expressed by the product of the volume of aquifer lying between the water table at the
beginning and at the end of period of time and the average specific yield of the formation (Todd
2005).
2.5 Specific yield
The quantity of water that a unit volume of the aquifer will yield when drained by gravity is called its
specific yield. The part of the water that is retained in the aquifer mass is held against water that a unit
volume of aquifer retains when subjected to gravity drainage is called its fractions or percentages. The
sum of the specific yield and specific retention equals the porosity of the aquifer. Specific yield is
calculated by:
  Wy
V1
Where: Sy is specific yield, Wy is water spent size (m3), and V is the total volume (m3)
The specific yield was calculated in the study area according to (Johnson 1955):
  Saturatedthicknessb
1000 2
Saturated thickness (m) determined by the geological profile of the wells (Figs. 3 a, b).
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Tab. 3: Hydraulic parameters estimated from pumping well test according to Theis and Numan by
using Aquifer Test program, and specific yield according to Johnson for Harrir Plain and Mirawa Valley.
Pumping
Well No.
Methods
Theis Numan
Johnson
Hydraulic
conductivi-
ty (K) m/d
Transmissivi-
ty (T) m2/d
Storage
coeffi-
cient (S)
Hydraulic
conductivity
(K) m/d
Transmissiv-
ity (T) m2/d
Storage
coeffi-
cient (S)
Specific
Yield
(Sy) %
Harir P.W-1 0.0136 65.7 0.0021 0.0149 65.2 0.0025 0.08
Harir P.W-2 0.0254 76.83 0.0049 0.0298 76.8 0.0081 0.085
Harir P.W-3 0.0521 84.2 0.018 0.063 83.89 0.027 0.14
Mirawa P.W-1 0.0134 13.4 0.00108 0.0156 13.4 0.00126 0.085
Mirawa P.W-2 0.0245 307 0.00569 0.0301 312 0.00875 0.079
Mirawa P.W-3 0.0842 1.19 0.02 0.089 1.19 0.031 0.069
Mirawa P.W-4 0.2946 3.27 0.107 0.317 3.8 0.115 0.11
Mirawa P.W-5 0.6402 99.5 0.5 0.7321 149 0.53 0.098
2.6 Specific capacity
Specific capacity is a measure of the productivity of a well and the value of discharge available for a
unit drawdown. The specific capacity values are not constant for wells in unconfined aquifers, because
an increase in drawdown at the same time decreases the water saturated thickness of the aquifer.
(Fetter 1994) defined the specific capacity as the discharge of the well over drawdown:
  Q
S3
where Sc is specific capacity in m2/day, Q is rate of discharge (m3/day), and S is drawdown (m).
According to (Al-Sawaf 1977) the specific capacity can be calculated using the formula:
  HQ
TD  SWLS4
where Sc is specific capacity in m2/day, Q is rate of discharge (m3/day), H is saturated thickness (m),
TD is total depth (m), SWL is static water level (m), and S is drawdown (m).
The difference between the two methods is using saturated thickness in second method, which is less
than the total depth penetrated by the well (Tab. 4).
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
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Tab. 4: Specific capacity of the pumping wells in Harri and Mirawa according to Fetter and Al-Sawaf
Well No. H (m) SWL (m) Q (m3/day) S (m) TD (m) Sc (Fetter) m2/day Sc (Al-Sawaf) m2/day
Harir P.W-1 81 16.78 648 16 153 40.5 24.1
Harir P.W-2 100 15 479.5 7 171 68.5 43.9
Harir P.W-3 158 34 207.4 6 253 34.6 24.9
Mirawa P.W-1 70 29 304.2 10 123 30.4 22.7
Mirawa P.W-2 66 77 518.5 20 121 25.9 38. 9
Mirawa P.W-3 42 10.5 298.1 70 145 4.3 1.3
Mirawa P.W-4 110 110 207.4 45 216 4.6 4.8
Mirawa P.W-5 98 52 583.3 7 107 83.3 148.5
2.7 Recharge
Recharge in the study area was calculated by three methods: water balance, water table fluctuation
(WTF), and chloride mass balance (CMB). The average groundwater recharge value produced based
on these three methods is 50.9, 114.5, and 87.4 mm/year respectively (Seeyan and Merkel 2015). The
average recharge estimation of the three methods for the two modeled areas is 94.3 mm/year.
2.8 Conceptual modeling
The first step in groundwater modeling is to establish the modeling purpose and to formulate the
conceptual view of the groundwater system. The adequacy of the groundwater system conceptual view
dictates the resulting groundwater models’ performances. A conceptual model is a simplified
representation of reality with a focus on the geological and hydrogeological conditions. Construction
of a conceptual model includes the definition of the basin boundaries, aquifers recharge, and discharge
sources (Anderson and Woessner 1992).
In Harrir plain, groundwater system is conceptualized as a single unconfined (porous) aquifer consist-
ing of two areas having different hydrogeological properties: the alluvial deposits and Tertiary
formations (Bai Hassan and Muqdadeya Formation).
Mirawa Valley is conceptualized as two hydrogeological layers of semi-confined (karst-fractured)
aquifer: the upper layer is represented by quaternary (Alluvial deposits) and Tertiary (Bai Hassn,
Muqdadeya, and Fatha) Formations, and the lower layer is represented by Eocene (PilaSpi) Formation.
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Fig. 3a: Lithological profile of two pumping wells; Harrir P.W-3 and Mirawa P.W-4 (Fn.: Formation,
A.D: Alluvial Deposits, P.W: Pumping well)
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
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Fig. 3b: Lithological profile of the pumping wells in Harrir plain and Mirawa valley (Fn.: Formation,
A.D: Alluvial Deposits, P.W: Pumping well)
2.9 Numerical Model
The finite-difference was designed with 100 x 100 m for each cell and 95 rows and 94 columns for
Harrir plain and 90 rows and 84 columns for Mirawa valley.
2.9.1 Boundary conditions
Definition of proper boundary conditions is the most important step for constructing a groundwater
model. Three types of boundary conditions (BC) were used for both models:
First: no flow BC
Second: River boundary conditions representing Greater Zab River, Harash River, and Mawaran
River. The rivers setting are shown in Tab. 5.
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The conductivity of the riverbed was assumed as 1.0E-6 m/s for Greater Zab and Harash Rivers, and
1.0E-5 m/s for Mawaran River; this riverbed conductivity was assumed to be valid for the entire river.
Third: at Harrir plain a first order (pressure head) boundary condition was set to 480 m in southeast-
ern part, and for Mirawa valley set to 940 m in southeastern part of the model area.
Groundwater recharge for the uppermost shallow aquifer was defined as flow BC with 94.3 mm/year
for the whole model area (Figs. 4 and 5).
Tab. 5: Rivers boundary conditions for both model areas
Rivers Model area Water Table
(m) a.s.l River bed
(m) a.s.l River bed thickness
(m) Width of River
(m)
Greater Zab Start point in E part 350 345 4 10
End point in W part 310 305 4 10
Harash Start point in NW part 356 350 0.3 4
End point in SE part 500 496 0.2 2
Mawaran Start point in NW part 645.2 644.4 0.4 6
End point in SE part 1060.5 1060 0.1 2
2.9.2 Hydrodynamic characterization
Estimation of the hydraulic conductivity and specific storage of the unconfined aquifer system of
Harrir plain and semi-confined aquifer system of Mirawa valley were obtained from the analysis of
pumping tests that were carried out in the boreholes in Harrir plain and Mirawa valley. The Neuman
and Theis methods were applied to obtain the values of hydraulic conductivity, coefficient storage, and
the ratio of horizontal and vertical hydraulic conductivity. The measured hydraulic conductivity values
(Kv) in Harrir plain range from 1.57*10-7 to 6.03*10-7 m/s (with an average of 3.5*10-6 for Kx,y and
3.5*10-7 for Kz), and for Mirawa valley ranges from 1.55*10-7 to 7.41*10-6 m/s (with an average value
of 4.7*10-5 for Kx,y and 4.7*10-6 for Kz). The other parameters like total porosity, effective porosity,
specific storage, and the specific yield were used as default parameters.
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
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Fig. 4: Harrir plain area, observation wells (brown-white point) with boundary conditions; rivers BC
(blue line), first order (pressure head) BC (red line), and no flow BC (light green area)
Fig. 5: Mirawa valley area, observation wells (brown-white point) with boundary conditions; rivers BC
(blue line), first order (pressure head) BC (red line), and no flow BC (light green area)
N
N
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3 Results and Discussion
3.1 Model calibration
The average groundwater head observations in thirteen observation wells in Harrir plain and nine
observation wells in Mirawa valley were compared to the simulated groundwater heads.
The calibrations were performed manually by changing hydraulic conductivity with running the model
several times using different hydraulic conductivities. The final hydraulic conductivity were used for
calibration is 3.5*10-7 for Harrir plain model, and 4.7*10-6 for Mirawa valley model. Standard error for
the model, normalized root mean square (NRMS), and correlation coefficient for both model was
estimated (Tab. 6 and Fig. 6).
Table 6: Statistics of calibration under steady state flow condition for both modeled area
Parameters Harrir Plain Mirawa Valley
Standard error of the estimate (m) 1.06 2.24
Root mean square (m) 4.03 7.13
Normalized RMS (%) 2.6 2.46
Correlation coefficient 0.99 0.99
Maximum residual (m) 8.3 at Well no. 4 -12.26 at Well no. 9
Minimum Residual (m) -0.004 at Well no. 5 -1.62 at Well no. 1
Residual mean (m) 1.68 -3.27
Abs. residual mean (m) 3.02 6.48
Fig. 6: Comparison of measured and simulated groundwater heads (m a.s.l) under steady state
calibration flow; A- for Harrir plain and B- for Mirawa valley.
A B
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3.2 Model results
Groundwater head simulation of Harrir plain shows that the equipotential head started from the highest
level in the southeastern part at about 480 m a.s.l and decreasing to the center of the plain at about 60
m a.s.l and then decreases to the Greater Zab river direction in northwest to an elevation of 80 m a.s.l.
According to the shape and patterns of groundwater potentials, an important source of the groundwater
input to the aquifer is from Harrir Mountain in the southeastern and Shakrok anticline in the south-
western part of the plain (Fig. 7).
The contour lines clearly show that the Greater Zab River drains the shallow groundwater. In Mirawa
valley, groundwater head starts from the southeastern part of the valley and decreases towards the
northwest of the valley from 940 m to 640 m a.s.l. The most important groundwater input source to
aquifer in Mirawa valley is Safin anticline and Pirmam Mountain in southwest, and Shakrok anticline
in southeast (Fig. 8). On contrary to the Harrir plain aquifer for the Mirawa valley aquifer only a minor
relationship between groundwater and the corresponding river can be seen, this could be either due to
drainage system or because of groundwater pumping. The flow direction is from southeastern part to
the Greater Zab River in northeastern part.
Fig. 7: Groundwater head equipotential (black line) and flow directions (red arrows) in Harrir plain,
contour interval is 20 m, UTM WGS-84 coordination system.
N
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Fig. 8: Groundwater head equipotential (black line) and flow directions (red arrows) in Mirawa valley,
contour interval is 40 m, UTM WGS-84 coordination system
3.3 Model prediction
The drawdown was calculated for the wells during increasing recharge rate from 94.3 mm/year to
%200 and %400 for both modeled areas under steady state flow condition; which shows that the
drawdown increases toward the rivers and decreases towards the mountain (Figs. 9a and 9b). The head
of pumping well was calculated by increasing pumping rate in the pumping wells to %200 and %400
for both modeled areas, which shows that the head decreases by increasing the pumping rate (Tab. 7
and Figs. 10a and 10b).
The decreasing of well head by increasing pumping rate is higher in Harrir plain due to the shallower
water table in porous aquifer and because the wells penetrates quaternary and tertiary deposits while
the wells in Mirawa valley penetrates PilaSpi formation in karst-fractured aquifer.
4 Conclusions
The present study provides the first interpretation of the regional-scale hydrogeological modeling of
regional groundwater flow in the Shaqlawa-Harrir basin, Kurdistan region under steady conditions.
Both calibrated models succeed in producing groundwater head distribution in steady state and the
model show good agreement between observed and calculated water levels.
N
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
15
Table 7: Head change in the pumping wells during increasing pumping rate to %200 and %400
Pumping Wells Discharge
or Pumping
rate (m3/d)
Well head
(m) a.s.l
Increasing pumping
rate Well head in m after
increasing pumping rate
200% 400% 200% 400%
Harrir P.W-1 518.4 367.3 1036.8 2073.6 362.2 351.5
Harrir P.W-2 670 416.3 1340 2680 409.3 394.6
Harrir P.W-3 846.7 464.5 1693.4 3386.8 458.7 446.7
Mirawa P.W-1 345.6 669.7 691.2 1382.4 669.5 669.3
Mirawa P.W-2 648 725 1296 2592 724.7 724.1
Mirawa P.W-3 518.4 832.2 1036.8 2073.6 831.8 831.5
Mirawa P.W-4 950.4 946.7 1900.8 3801.6 945.6 943.5
Mirawa P.W-5 578.9 953.6 1157.8 2315.6 952.5 950.5
Freiberg Online Geoscience Vol 39, 2015
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Fig. 10a: Drawdown differences by increasing recharge rate for Harrir plain, contour interval is 20 m
for 200% increased recharge and 30 m for 400% increased recharge.
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
17
Fig. 10b: Drawdown differences by increasing recharge rate for Mirawa valley, contour interval is 50 m
Freiberg Online Geoscience Vol 39, 2015
18
Fig. 11a: Head equipotential differences by increasing pumping rate in the pumping wells for Harrir
plain, contour interval is 20 m
Seeyan, Shwan Groundwater modeling for Shaqlawa-Harrir basins, Kurdistan Region, Iraq
19
Fig. 11b: Head equipotential differences by increasing pumping rate in the pumping wells for Mirawa
valley, contour interval is 50 m
Freiberg Online Geoscience Vol 39, 2015
20
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