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Journal of Civil Engineering and Technology (JCIET) Volume 4, Issue 2, July-December 2017, pp. 1–12, Article ID: JCIET_04_02_001

Available online at http: //www.iaeme.com/jciet/issues.asp?JType=JCIET&VType=4&IType=2

ISSN Print: 2347-4203 and ISSN Online: 2347-4211

© IAEME Publication Scopus Indexed

FLOOD ROUTING FOR A SPECIFIC

ORIENTATION OF PLANNED DEVELOPMENTS

FOR AL-SHAMIYA RIVER IN IRAQ AS CASE

STUDY

Imad Habeeb Obead

Asst. Prof, Civil Engineering Department,

College of Engineering-University of Babylon, Hilla-Iraq

Aliaa Adnan Khodaier

M.Sc. Graduate Student-Civil Engineering

Department-College of Engineering-University of Babylon, Hilla-Iraq

ABSTRACT

Flood routing in branched rivers is an important issue in open channel hydraulic.

Consequently, in this work the simulation of flood waves was performed in Al-Shamiya

branched River, a fully hydraulic approach was involved by solving the Saint Venant

equations using a four-point implicit finite difference scheme as a numerical method.

HEC-RAS software was used to conduct the solution of flood routing problem, the

hydraulic model of Al-Shamiya river included a main channel with total of 12 cross

sections for main channel. The model was calibrated Manning's roughness coefficient

adopted herein of (n=0.04) led to the best agreement between the calculated and

observed data for the Al-Shamiya river in study area for main reach, also the time

weighting factor was (θ=1). The present results indicate that the proposed hydraulic

control approach was by deepening the reach by (0.42 m) and modifying the side slopes

by (5:1, and 7:1) respectively for control section, or constructing compound section by

adding extended berms with filling embankments.

Key words: Flood Routing; Saint Venant Equations; Hydraulic Control; Al-Shamiya

River.

Cite this Article: Imad Habeeb Obead and Aliaa Adnan Khodaier, Flood Routing For

A Specific Orientation of Planned Developments For Al-Shamiya River In Iraq As Case

Study, Journal of Civil Engineering and Technology, 4(2), 2017, pp. 1–12.

//www.iaeme.com/jciet/issues.asp?JType=JCIET&VType=4&IType=2

Imad Habeeb Obead and Aliaa Adnan Khodaier


1. HYDRAULIC ROUTING METHODOLOGY

Hydraulic flood routing approaches employ conventional Saint Venant equations with both

continuity and momentum equations. The continuity equation is [1]:

�� + ��

�� = ±q (1)

and the momentum equation is:

�� + �

� ��.�� + g. A ��

� + S�� = 0 (2)

in which Q is the flow rate; A is the cross-section area; q is lateral inflow/outflow per unit

length; and h is the head of water:

h= z+y, where y is the water depth, and z is the elevation of the river bed bottom above an

arbitrary datum such as mean sea level. x is the distance along the channel; Sf is the friction

slope; and g is the gravitational acceleration; β momentum correction coefficient; and (t) is

time. Equations 1 and 2 represent a system of nonlinear hyperbolic partial differential

equations, for which analytical solutions can only be obtained under certain linearization

assumptions for simple channel geometries and boundary conditions [2].

2. NUMERICAL SOLUTION METHOD

In this research, the weighted four-point implicit finite difference method is selected to solve a

Saint Venant equations for its versatility and computing efficiency. The numerical method was

performed to the Al-Shamiya branched River at the reach from Shamiya Barrage with reach

length of 31.517 Km. to conduct analysis of the following parameters: maximum flood wave

discharge, maximum flood wave elevation, and time of arrival of flood wave to a major section

along the river in a case study as shown in figure (1).

Figure (1) Schematic diagram of the Al-Shamiya branched river

The reach was divided into (55) cross sections, the location of the cross-sections on Shatt-

AL-Shamiya and the lengths of sub reaches were illustrated in Table (1) below.

Flood Routing For A Specific Orientation of Planned Developments For Al-Shamiya River In Iraq As

Case Study


Table (1) Location of the cross-sections along AL-Shamiya river [4]

Section No. Station Location (km) Sub-reach Length (m)

1 0+00 1455

5 1+455

10 4+309 3177

15 7+486

20 11+013 3586

25 14+599

30 17+389 4067

35 21+456

40 24+568 3112

45 26+795

50 29+386 2131

55 31+517

The approximations of the derivatives and constant terms in the four point weighted

difference scheme were performed as follows:

(1) The space derivative of Saint-Venant equations approximated as:

�� = � ��

∆��/� + (1 − �) �� ∆��/� (3)

�%�� = � %��%��

∆��/� + (1 − �) %�� %��∆��/� (4)

�� &.��

' � = �(

()*+.,�- .��

�� (()*+.,�

- .��

∆��/� + (1 − �)(

()*+.,�- .��

� � (()*+.,�

- .��

∆��/� (5)

(2) The time derivatives in Saint-Venant equations (Continuity) were approximated as:

�'�/ = '��'��

0∆/� + '��'��0∆/� (6)

��/ = ��

0∆/� + ��0∆/� (7)

The friction slope Sf is modeled with Manning’s formula:

12 = 13 = ��4�'�56/7 (8)

Where; Sο is the channel bed slope; n is the Manning coefficient, and R is the hydraulic

radius(R=A/P), in which P is the wetted perimeter as shown in figure (2).

Figure (2) Definition sketch of the wetted perimeter P, wetted area A, and top width T of an open

channel cross section



There are other ways of representing the Saint-Venant equations which were based upon

the same hypothesis but expressed in terms of different set of dependent variables. Hence, the

water depth (y) in Eq. (2) can be replaced by the water surface elevation (h), The derivative of

(h) with respect to the longitudinal axis (x) along the channel yields:

�%�� = �8

�� + �9�� (9)

Since[�9�� = −1;];

�%�� = �8

�� − 1; (10)

Therefore; the momentum equation can be now expressed in term of (h) by using Eq. (10)

in Eq. (2). Finally, neglecting lateral seepage and lateral overland flow per channel length (q),

the constant terms were approximated as:

12)=>?/0 = 4@��@�'̅�5@6/7 (11)

B@= = ��>��0 (12)

C̅= = '�>'��0 (13)

D@= = '̅�E@� = '̅�

F@� (14)

G@= = F�>F��0 (15)

Substituting the necessary terms in the continuity equation yields:

'��'��0∆/� + '��'��0∆/� + � ��

∆��/� + (1 − �) �� ∆��/� = 0 (16)

Multiplying Eq.(16) by (∆xi+1/2) to take the following form:

�HB=>?I>? − B=I>?J + +(1 − �)HB=>?I − B=IJ + ∆��/�0∆/� KHC=>?I>? + C=I>? − C=>?I − C=IJL = 0 (17)

Again, substituting the necessary terms in the momentum equation and by multiplying this

equation with (∆xi+1/2),which yields:

∆��/�0∆/� KB=>?I>? + B=I>? − B=>?I − B=IL + � M(NB0 C⁄ )=>?I>? − (NB0 C⁄ )=I>? + PC̅=I>?(ℎ=>?I>? − ℎ=I>? +

∆R=>�� . 12=>?/0

I>? )T + (1 − �) U(NB0 C⁄ )=>?I − (NB0 C⁄ )=I + PC̅=I V ℎ=>?I + ℎ=I + ∆R=>�� . 12=>�

�I WX = 0

(18)

The terms with subscript (j) in continuity and momentum equations are known either from

initial conditions or from the solution of Saint-Venant equations at the previous time step. Since

cross sectional area (A) and channel top width (B) are functions of water surface elevation (h),

the only unknown terms in these equations are discharge (Q) and water surface elevation (h) at

the (j+1)th time step at nodes (i) and (i+1) [figure 3]. Therefore, there are only four unknowns

in these equations. All remaining terms are either constants or are functions of these unknowns.

As there are N-1 grids in a time line, a total of [2×(N-1)] equations were formed for one

time line between the upstream and downstream boundary. There are two unknowns (Q and h)

in each of the N nodes giving a total of 2N unknown along each time line. The system of 2(N-

1) equations with 2N unknown require two additional equations to be determinate. These two

additional equations are supplied by the upstream and downstream boundary conditions. The


Case Study


resulting system of 2N non-linear equations with 2N unknowns was commonly solved by the

Newton-Raphson iterative technique to handle the non-linearity in the equations [3].

Figure (3) Finite difference discretization of (x-t) solution plane representing 1-D flow domain with

respect to time

4. CASE STUDY

The study area adopted herein is Shatt AL-Shamiya. It was part of Euphrates river in Iraq, the

upstream boundary of our study begin from Shamiya Barrage with reach length of 31.517 Km

and an average bed slope range of (7-12cm/km), in which a part of AL-Kifil/AL-Shanafia

irrigation project. The designed discharge for the barrage is 1200 m3/sec, with upstream level

of 23 m.a.s.l., the Barrage consists of radial steel gates, hydroelectric power plant, and

navigation lock. The downstream of the study area was bounded by Al Khwarneq barrage which

is similar to the Shamiya barrage, but its consist of 5 slots. Table 2 includes all the available

hydraulic and spatial information for AL-Shamiya Barrage [4].

Table (2) Hydraulic characteristics for Al-Shamiya barrage

5. RESULTS AND DISCUSSION

In the present work, hydraulic model was developed using HEC-RAS Version 4.1, which

performed unsteady flow analysis for networked channels. The observed flow hydrograph

accompanying to the steady state flow in control section upstream at the head regulator of Al-

Shamiya River was shown in figure (4). The downstream condition used herein considered at

the downstream end of the Al-Shamiya river observed stages hydrograph shown in figure (5).

Details Value

Location Euphrates river/Iraq

No. and Dimension of slots 6 gates of (6.3×12) m

The radius of radial gates 10.5 m

Methods of gates operation Manually/Electrically

Maximum designed discharge 1200 m3/sec

Maximum designed level U/S 23.5 m.a.s.l.

Normal operation discharge U/S 50-200 m3/s

Barrage sill level D/S 16.5 m.a.s.l.

Hydroelectric power 6 MW



Figure (4) Inflow hydrograph for upstream boundary (station No. 1) [after (QWRD), 2016]

Figure (5) Stage hydrograph in downstream boundary (station No.55) [after (QWRD, 2016]

Hydraulic approach involves complex numerical equations with high accuracy however

using a lot of data, especially physical data and river specifications. In the study area, the routed

flood hydrograph produced by the Saint Venant model with an acceptable accuracy in flood

routing required parameters which based on the calibration process performed previously by

researchers, such as time step period (∆t = 1 day), Manning’s coefficient (n =0.04), and finite

difference weighing factor(θ=1).

5.1. Steady State Flow Scenario

According to the Directorate of Water Resources in Qadisiyah Governorate/Iraq, the steady

discharge was (70 m3/sec), the water surface elevation compared to both bank elevations and

full bank elevations per each investigated sections along the reach were shown in figure (6)

below.

Figure (6) Variation of river bank, full bank and water surface elevations for all investigated sections

along the study reach for steady flow

The bank-full discharge at a river cross section is the flow which just fills the channel to the

tops of the banks. Such a discharge therefore marks the condition of incipient flooding [5]. As

illustrated from figure (6), almost all sections along reach were sufficient to hold a steady


Case Study


discharge. The last Two section (No.50, and 55) were approaches to critical case with maximum

differences in elevations of (0.63m and 0.53 m) respectively. Figures (7, 8, and 9) were

demonstrated the differences between full-bank and flow water elevations for upstream,

downstream control sections and critical cross-section pointed in station No. (50).

Figure (7) Control section (No.1) in Al-Shamiya barrage for steady discharge scenario

Figure (8) Section (No.50) along Al-Shamiya reach for steady discharge scenario

Figure (9) Control section (No.55) for steady discharge scenario

The deficiency in the riverbank's holding capacity corresponding bank-full levels suggested

by author, which can be written as:

YZ = [1 − �\]�8^\] �_ × 100% = [1 − ∆bcde.

\] _ × 100% (19)

Where; ηD is the deficiency of riverbank's holding capacity, YB is the bank-full elevation

(m), and yn is the normal depth for a specified discharge in a channel (m).Table (3) demonstrated

the deficiencies of each section along the reach.

Table (3) Deficiency of riverbank's holding capacity for different channel sections

Section No. ∆∆∆∆Elev.(m) ηηηηD %

1 6.48 73.6

5 1.81 90.3

10 1.7 90.8

15 1.62 91.1

20 1.57 91.3



Section No. ∆∆∆∆Elev.(m) ηηηηD %

25 1.5 91.6

30 1.45 91.8

35 1.35 92.2

40 1.21 92.9

45 1.06 93.6

50 0.63 95.9

55 6.93 67.8

If the peak discharge exceeds the riverbank’s holding capacity, then water would be spread

out into the floodplain. Consequently, the more hazard or insufficient section were pointed from

section No. (5) to section No. (50).

5.2. Flood Propagation Scenario

The flood wave propagated downstream reach based on existing cross sections was produced,

the flood discharge was (200m3/sec), the water surface level versus the bank elevations and full

bank elevations per each investigated sections along the reach were shown in figure (10). The

simulation results illustrated that most of the cross sections were breached except of the control

section No. (1), whereas the downstream control section (No.55) has reached a critical state.

Figure (10) Variation of river bank, full bank and water surface elevations for all investigated sections

along the study reach for flood scenario

As shown in figure (10), all sections along reach were breached under the flood discharge

of (200 m3/sec), except section No. (1), the maximum differences in elevation were occurred

for sections No. (1) of (2.71 m and 1.75 m) for both bank-full and normal bank elevations

respectively. Figure (11) shows the difference between full-bank and flood water elevations for

downstream control sections in station No. (55).

Figure (11) Control downstream section (No.55) for flood scenario


Case Study


5.3. Hydraulic Control along Reach

5.3.1. Deepening Critical Sections along the Reach

One of the specified development plan of Al-Shamiya reach involves increasing its lower bound

normal operation upstream discharge from (20 m3/sec) to (75 m3/sec). Figure (12) shows the

critical section corresponding this state of operation, with the most appropriated trapezoidal

section containing the entire existing flow area prior to hydraulic control process. The

inclination angle of left side slope of trapezoidal section is (θ1= 83.3ο), while the inclination

angle of right side slope of trapezoidal section is (θ2=78.7ο), the bed width is (B= 51.6 m), and

the depth of water about (2 m).

Figure (12) Critical section corresponding steady state flow of (75 m3/sec)

To make control on the reach considered in present work, different values of bed levels for

critical cross section No. (50) can be taken and used in the HEC-RAS. Herein, the value was

less than the values of the existing bed levels by (∆=1.047-0.63=0.417m), thus the bed level

was( 12.933 m)and corresponding elevation of flow water was obtained to be (14.41

m).Consequently, the riverbank holding capacity improved by decreasing ηD from 95.9% to

94.1%.

5.3.2 Modifying Channel side slope (H: V)

For practical purposes and implementation requirements, a proper side slope was considered to

be in convenient with downstream control section No. (55) as a sufficient section for steady

flow condition. Figure (13) shows the improved section No. (50) with a combination of

increment in flow depth, and side slopes (, where left side slope of (5:1) and right side slope of

(7:1) respectively.

Figure (13) Improved trapezoidal cross section for steady flow condition

The hydraulic and geometric properties of both existing irregular section and most

appropriated trapezoidal cross section were given in table (4).



Table (4) Hydraulic and geometric properties for critical section (No.50) with hydraulic control

5.4. Hydraulic Geometry Due to Flood Flow

By performing HEC-RAS run for flood flow condition for (16 days) and with fixing all the

values of the other parameters, it was found that the flood water level would be (22.02 m.a.s.l.)

in section No. (50) at the beginning of the twelfth day, as shown in figure (14) below.

Figure (14) Obtained stage elevation hydrographs (m.a.s.l.) for different time steps (∆t) during flood

period in critical section No. (50)

Thus, the hydraulic control of breached sections along reach (among many possible options)

will be based on enlarge the improved trapezoidal section shown in figure (13) above to hold

the exceed water quantity produced by flood wave. Otherwise, it would create back water effect

that may endanger the surroundings of the reach. The extra flow area was provided to new

section by mean of fill embankment along the critical sections (from No.5 to No. 50) to provide

berm. The berm was provided in such a way that the bed line and bank line were maintained

parallel:

Gf = g(h2 − hi)g × j? (20)

In which; Bw is the berm width (m), Zf is the fill side slope, Zc is the cut side slope, and d1

is the full bank depth (m). For channels with silt laden water, the actual capacity of the channel

is worked out with 2:1 side slopes in filling, i.e., Zf =2.

Let Bw1 is left side berm width:

Gf? = |(2 − 5)| × 1.98 = 5.94 q

Then, the left side berm width = 6.0 m

Let Bw2 is right side berm width:

Gf0 = |(2 − 7)| × 1.98 = 9.90 q

Section

No.

Cross section

Shape

Full-bank

depth(m)

Water

depth(m)

Wetted

Perimeter P(m)

Flow Area

A(m2)

Hydraulic

Radius

R(m)

Remarks

50

Irregular 1.98 1.98 77.47 101.56 1.31 Non-sufficient

Trapezoidal

(depth increment ) 2.397 1.48 78.67 112.82 1.43 Sufficient, non-applicable

Trapezoidal

(combination) 2.897* 1.30 75.68 199.78 1.66 Sufficient, and applicable

55 Irregular 7.49 1.06 174.08 894.5 5.45 Sufficient for steady and

flood conditions

* with free-board of (0.5m)


Case Study


Then, the right side berm width = 10.0 m. therefore, and to approve the implementation

requirements, using the same side berm width of (10.0m). Let the full depth of channel section

is (Df), thus:

Df = flood water level-channel bed level = 22.02-13.35= 8.67 m.

A schematic compound cross section for modified section No.50 of full bank flow condition

was shown in figure (15) below. Some comparative characteristics for sections along studied

reach were summarized in table (5) below.

Figure (15) A typical schematic of improved cross-section (not to scale)

Table 5 Characteristics of breached sections and improved one along studied reach for flood condition

Section No. Flow Area (m2) Wetted perimeter P(m) Hydraulic radius R(m)

5-45* 817.58 127.90 6.40

50 874.20 128.0 6.83

* values are averages for hydraulic parameters.

5.5 Conclusions

From the point of view hydraulic, the relevant treatments of study problem, can be summarized:

• The results obtained herein illustrated that the most applicable hydraulic treatment, would be

deepening the reach by about (0.42m) and modifying exist side slopes of critical cross section

by (5:1, and 7:1) respectively to be sufficient to steady flow conditions (long return period).

• Operating the reach such that the (75 m3/sec) discharge will produce a water level downstream

the AL-Shamiya reach of (14.41 m) at km (29.386).

• Alternative treatment for flood flow (of short return period) scenario was proposed by presented

a compound section adding extended berms and extra flow area to previous cross section by

using fill embankments.



REFERENCES

[1] Chanson, H., (2004), Environmental Hydraulics of Open Channel Flows, Elsevier

Butterworth Heinemann, Linacre House, Jordan Hill, Oxford.UK.

[2] Orouji, H., Haddad, O. B., Mehdipour, E. F., and Marino, M. A., (2012), Flood routing in

branched river by genetic programming, Water Management, Proceedings of the Institution

of Civil Engineers, ICE Publishing, http://dx.doi.org/10.1680/wama.12.00006.

[3] Chow, V. T., Maidment, D. R., and Mays, L. M., (1988), Applied Hydrology, McGraw-

Hill, Inc.

[4] QWRD (Qadisiya Water Resource Directorate, Ministry of Water Resources, Iraq.), (2016),

“Report about Shatt Al-Shamyia.

[5] Kalpalatha.Ganamala and P. Sundar Kumar, A Case Study on Flood Frequency Analysis,

International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 1762-1767.

[6] Rituparna Choudhury, B.M. Patil, Vipin Chandra, Uday B. Patil and T. Nagendra,

Assessment of Flood Mitigation Measure For Mithi River – A Case Study, International

Journal of Civil Engineering and Technology, 7(3), 2016, pp. 56–66.

[7] Williams, G. P., (1978), Bank-Full Discharge of Rivers, Water Resources Research,

Volume 14 (6).

[8] Chow, V. T., (1959), Open-Channel Hydraulics, McGraw-Hill Book Company.

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