Flood Hydraulic Analyses: a Case Study of Amik Plain, Turkey

water

Case Report Flood Hydraulic Analyses: A Case Study of Amik Plain, Turkey

Fatih Üne¸s 1, Yunus Ziya Kaya 2 , Hakan Varçin 1, Mustafa Demirci 1, Bestami Ta¸sar 1 and Martina Zelenakova 3,*

1 Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Iskenderun Technical University, Iskenderun 31200, Hatay, Turkey; [email protected] (F.Ü.); [email protected] (H.V.); [email protected] (M.D.); [email protected] (B.T.) 2 Civil Engineering Department, Faculty of Engineering, Osmaniye Korkut Ata University, Osmaniye 80100, Turkey; [email protected] 3 Institute of Environmental Engineering, Faculty of Civil Engineering, Technical, University of Košice, Vysokoškolská 4, 040 01 Košice, Slovakia * Correspondence: [email protected]

Received: 21 June 2020; Accepted: 16 July 2020; Published: 21 July 2020

Abstract: In recent years, significant flood events have occurred in various parts of the world. The most important reasons for these events are global warming and consequent imbalances in climate and rainfall regimes. Many studies are performed to prevent the loss of life and property caused by floods. Many methods have been developed to predict future floods and possible affected areas. Developing computer and numerical calculation methods gives opportunities to make simulations of flood hazards. One of the affected areas, which is also one of the world’s first residential districts at Hatay in Turkey, is the Amik Plain. In this study, the floods on the Amik Plain in Hatay province are analyzed. Hatay airport was also affected during floods since 2012 and serious material damage occurred. For this purpose, Google Earth Pro software was used to obtain maps of the basin where the airport is located and the rivers it contains. Afterwards, Hydrologic Engineering Center’s River Analysis System module (HEC-RAS) was used for the hydraulic and hydrological definitions of the river basin. The results of numerical models are presented as simulated maps.

Keywords: ﬂood; hazard; Amik plain; HEC-RAS; risk assessment

1. Introduction Flooding is a condition that causes water and soil environments to be disturbed in areas that are not normally submerged owing to increased flow and rising level in a stream. This situation may harm humans and animals and damage land and property near the river. In Turkey, 695 floods occurred from 1975 through 2010, causing great economic losses second only to earthquakes. A total of 634 people lost their lives in these floods, 810,000 hectares of land were left under water, and the total loss was 3.717 billion dollars. During this period, the distribution of flood losses by sectors was found to be 45% agricultural areas, 32% settlements and infrastructure, 7% portable goods and vehicles, 1% transportation, and 15% in other areas [1,2]. These stats show that flood is an extremely serious and important issue. In addition to saving many lives, the works to be done to predict floods and protect them from danger will contribute a lot to the national economy. The main purpose of this study is to investigate how vulnerable the Amik plain is against flood disasters using geographic information systems and HEC-RAS. Flood precautions and recreation studies are performed by state hydraulic works (DSI) in Turkey. State hydraulic works (DSI) is an institution responsible for the planning, management, development,

Water 2020, 12, 2070; doi:10.3390/w12072070 www.mdpi.com/journal/water Water 2020, 12, 2070 2 of 28 and operation of all water resources in the country. It is the responsibility of this institution to establish the flow rate values of the floods formed and the establishment of flow monitoring stations on the streams for the purpose of labor and to prepare reports of floods. Monitoring of floods occurring in the Amik plain started with four current observation stations established in 1956. These stations are located on Asi, Afrin, Karasu, and Büyük Asi in Antakya after the combination of these three branches. The first flood, after receiving current observations, occurred in 1956. In this first flood, the flow rate of Afrin was 464.0 m3/s, Karasu was 123.0 m3/s, and Asi was 274.0 m3/s. In the second flood event, which was occurred in March of 1969, the flow rate of Afrin channel was 710.0 m3/s, Karasu was 268.0 m3/s, and Asi was 167.0 m3/s. In the flood, 15,780.0 ha area was submerged. In April 1975, Asi River was at full capacity with 180.0 m3/s and the extra flow rate was discharged to Amik Plain as 50.0 m3/s. Approximately 1500.0 ha of cultivated land was submerged. Similar floods occurred in 1976, 1980, 1987, and 1998 and affected many agricultural lands. In Antakya flood, which occurred on 8–9May 2001, in the center of Antakya and Amik Plain, a total of 569.0 kg of precipitation fell in 48 h, with 137.0 kg in the first 24 h and 432.0 kg in the second 24 h. Considering that Hatay’s average rainfall for many years is 856.0 kg, the ratio of precipitation falling in 48 h to annual precipitation is 67%. This flood caused loss of life and property and the region was declared as a disaster area. In the floods that occurred in the Amik Plain in 2002 and 2003, large agricultural lands were flooded, and caused material damages. In this study, the flood that occurred in the Amik Plain between 27 January and 14 March 2012 is investigated. In the mentioned flood, an area of 13,000 hectares was affected and a total of 8465 ha of agricultural land, roads, bridges, settlements, and Hatay Airport was exposed to flood waters [3]. The floods listed above are repeated frequently and reach dangerous levels for the region. For this reason, it is extremely important to determine the size of the floods that may occur and the areas they affect. After the floods that occurred, DSI obtained the flow values from the flow monitoring stations on the rivers and made them into reports. For the examination of these reports, their discharge capacities were increased by enlarging the cross-sections of the streams for the protection from floods. Embankments have been made for the purpose of flood protection along the rivers. However, these precautions did not provide a definitive solution. Estimating the size of the floods that may occur and the areas they affect will make important contributions to the work to be done. However, this is a very difficult problem owing to the number of unpredictable parameters. Numerous methods have been developed recently to make calculations or estimations about the definition of flood areas. Zeleˇnáková et al. worked on a risk-based approach to flood modelling of Slatvinec stream [4]. Serencam studied the negative effects of possible floods in a specific part of Trabzon, Turkey [5]. Kowalczuk et al. used HEC-RAS software to simulate river flow [6]. Abd-Elhamid et al. researched flood prediction and mitigation for coastal tourism areas as a case study in Hurghada, Egypt [7]. Romali used a GIS-based approach for flood plain mapping in Segamat Town, Malaysia [8]. Ben Khalfallah et al. also used GIS tools and HEC-RAS software together to prepare a spatiotemporal flood plain map as a case study of the Majerda River, Tunisia [9]. In another GIS-based research project, Curebal et al. generated a model for flash floods in Keçidere, Turkey [10]. Oana-Elena et al. evaluated flood event susceptibility analyses on cultural heritage in Sucetiva, Romania [11], and Romanescu et al. prepared a case study of flood vulnerability assessment for Marginea village in Romania [12]. Natural disasters are defined as inevitable, irrepressible, irresistible events, but when anticipated, the amount of damage that may be generated can be reduced when suitable measures are taken. With this in mind, depending on the accuracy of the data used in the study, pre-modeling and simulating floods, demonstrating acceptable results modulated with structural or non-structural prevention measures, will minimize the losses [13–16]. Data such as discharge, land cross section, Manning coefficient, and topography scale are used for flood modeling in the present study. Various computer programs can be used for this purpose. One of them is the HEC-RAS program, which can be modeled for one-dimensional steady or unsteady flow. Water 2020, 12, 2070 3 of 28 Water 2020, 12, x FOR PEER REVIEW 3 of 30

951.1. Study Study Area Area 96 The Amik PlainPlain inin Hatay Hatay Province Province lies lies in south-eastin south-east Turkey Turkey with with the Kırıkhanthe Kırıkhan district district to the to north, the 97north, the Reyhanlı the Reyhanl districtı district to the to south, the south, the Syrian the Syrian border border to the to east,the east, and and the the Kırıkhan–Antakya Kırıkhan–Antakya road road to 98to the the west. west. 99 The Plain Plain also also includes includes a small a small piece piece of land of landon the on left the bank left of bank the Asi of River, the Asi on River,the Antakya- on the 100Reyhanl Antakya-Reyhanlıı road, extending road, extendingto the south. to theThe south.width of The the width Plain ofis approximately the Plain is approximately 36 km, the length 36 km, is 10140 the km, length and is the 40 km,elevation and the is elevationbetween 80 is betweenm and 250 80 m and[1]. 250The mAmik [1]. ThePlain’s Amik name Plain’s comes name from comes the 102natural from the Amik natural Lake, Amik which Lake, is shown which in is shownFigure 1. in As Figure the 1flood. As thearea flood and lake area level and lakein the level old inlake the were old 103very lake werevariable, very in variable, 1940, it was in 1940, designated it was designatedfor drying and for dryingflood protection and flood and protection Amik Lake and reclamation Amik Lake 104works. reclamation The Amik works. Lake The Drying Amik LakeTechnical Drying and Technical Economic and Feasibility Economic Report—Amik Feasibility Report—Amik Lake Project Lakewas 105prepared Project was in prepared1966 by IECO in 1966 (Inter bynational IECO (International Engineering Engineering Company). Company).The Karasu TheRiver, Karasu Afrin River, River, Afrin and 106Muratpa River, andşa Muratpa¸saflood flood canals were canals discharged were discharged through throughthe lake thebed lake to enable bed to enablethe canals the canalsto connect to connect with 107the with Small the Small Asi River, Asi River, and the and lake the lakewas dried was dried in 1972. in 1972. The flow The flowobservation observation station station located located on the on Asi the 108River Asi River and andits side its side arms arms recorded recorded flooding flooding between between January January and and March March 2012. 2012. Data Data relating relating to to this 109flood flood were complemented with records from the 1930 1930 Asi Asi River River E E¸srefiye,şrefiye, 1907 1907 Asi Asi River River Demirköprü, Demirköprü, 1101906 Afrin River Mü Mü¸srüflü,1905Karasuşrüflü, 1905Karasu River River Torun Torun Köpr Köprüsü,üsü, 1926 Küçükasi River River Hasanl Hasanlıı Bridge, Bridge, 111and 1908 Asi River Antakya flowflow observationobservation stations. The The map showing these observations and 112measuring stations is presented in Figure2 2[ 3[3].].

113 114 FigureFigure 1. PlainPlain location location and and the the lake lake area area before before it was dried [1]. [1].

115 The Amik Plain in the Mediterranean region of Hatay Province is a plain where floods have been 116experienced in various years. According to the data obtained from the Provincial Directorate of 117Agriculture, between 27 January and 14 March 2012, rainfall and sudden snow melting caused 118flooding over a 13,000 ha area on the Amik Plain. A total of 8465 ha of agricultural land, roads, 119bridges, settlements, and Hatay Airport runway and apron were exposed to flood waters. According 120to the reports of the Provincial Directorate of Agriculture, the flood damage observed in agricultural

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121lands cost 17,453,161 TL. The Asi River, Karasu stream, Afrin creek, Muratpasa channel, and Comba 122Waterchannel 2020 , were12, 2070 involved in the floods [3,17]. The flood hydrograph measured at the current4 of 28 123observation stations during this flooding is given in Figure 3.

124 125 Figure 2.2.Schematic Schematic representation representation of Asi of andAsi Küçükasi and Küçükasi Rivers, drainageRivers, drainage canals, and canals, current and observation current 126 stationsobservation [1,3]. stations [1,3].

The Amik Plain in the Mediterranean region of Hatay Province is a plain where floods have been experienced in various years. According to the data obtained from the Provincial Directorate of Agriculture, between 27 January and 14 March 2012, rainfall and sudden snow melting caused flooding over a 13,000 ha area on the Amik Plain. A total of 8465 ha of agricultural land, roads, bridges, settlements, and Hatay Airport runway and apron were exposed to flood waters. According to the reports of the Provincial Directorate of Agriculture, the flood damage observed in agricultural lands cost 17,453,161 TL. The Asi River, Karasu stream, Afrin creek, Muratpasa channel, and Comba channel were involved in the floods [3,17]. The flood hydrograph measured at the current observation stations during this flooding is given in Figure3.

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127127 128128 FigureFigureFigure 3. 3. 3. Observed ObservedObserved f loodflood ﬂood h hydrographydrograph hydrograph [ 1,[1,3]. [13,]3. ].

129129 AccordingAccordingAccording to to this, this, this, the the the highest highest highest hydrograph hydrograph hydrograph values values values are are are observed observed observed in in in the the the Afrin Afrin Afrin and and and Karasu Karasu Karasu channels. channels. channels. 130130 TheTheThe AmikAmik Amik PlainPlain Plain floodflood ﬂood lakelake lake elevationelevation elevation hydrographhydrograph hydrograph duringduring during thisthis this floodingflooding ﬂooding isis is givengiven given inin in Figure Figure Figure 4. 44. . 131131Accordingly, Accordingly, the the highest highest level levellevel was waswas measured measuredmeasured as asas 81.13 81.1381.13 m mm on onon 21 2121February2012.February February2012. 2012.

132132 133133 FigureFigureFigure 4. 4. 4.Amik AmikAmik Plain Plain Plain lake lake lake elevation elevation elevation hydrograph hydr hydrographograph during during during flooding flooding ﬂooding [ 1,[1,3]. [13,].3 ].

134134 FigureFigureFigure 5 55 sshows howsshows the the photographsphot photographsographs takentaken taken ofof of thethe the floods floods floods on on on 2 2 February2 February February 2012. 2012. 2012. The The The size size size and and and e ff effects ectseffects of of theof 135135the the flooding flooding flooding are are are clearly clearly clearly visible visible visible in in thein the the photographs. photographs. photographs. The The The apron apron apron project project project elevation elevation elevation and and and runway runway runway elevation elevation elevation of 136136of of the the the airport air airportport remained remained remained below below below the the the highest highest highest measured measured measured lake lake lake level. level. level.

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137

137138

138139 Figure 5. FloodFlood photos of flood flood in 2012 [ 1,1,3].3]. ( (aa) ) General General view view of of Amik Amik Plain Plain;; ( (b) Hatay Hatay airport during 140 the floodflood 2012;2012; (c) SpecificSpecific viewview ofof HatayHatay airportairport duringduring thethe floodflood 2012.2012. 139 Figure 5. Flood photos of flood in 2012 [1,3]. (a) General view of Amik Plain; (b) Hatay airport during 140141 the floodThe Amik 2012; ( Plainc) Specific is flooded flooded view of almost Hatay airportevery year during as thea result flood of2012 rainfall. . Similarly, Similarly, as a result of heavy 142rainfall in FebruaryFebruary 2019,2019, thethe waterwater levellevel increasedincreased and and caused caused the the Amik Amik Plain Plain to to be be flooded. flooded. Figure Figure6 141143 shows6 Theshows Amik the the situation Plainsituation is flooded of of the the Plain almostPlain in in 2019. every 2019. year as a result of rainfall. Similarly, as a result of heavy 142rainfall in February 2019, the water level increased and caused the Amik Plain to be flooded. Figure 1436 shows the situation of the Plain in 2019.

144 145 Figure 6. General view of Amik Plain after rainfall in 2019. 144 Figure 6. General view of Amik Plain after rainfall in 2019. 145 Figure 6. General view of Amik Plain after rainfall in 2019.

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2. Model and Application In this study, the HEC-RAS program was used to model flooding. HEC-RAS was developed in 1994 by USACE (United States Army Corps of Engineers). It uses the addition of a graphical user interface (GUI), which differs from the HEC-2 model in the 1970s, for modeling the water profile. The GUI is Windows-based, allowing the user to enter data, correct the entries, and display and get the output of the analysis in an easy format [18–21]. The flowchart showing the adopted methodology of theWater program 2020, 12, x is FOR shown PEER belowREVIEW (Figure 7). 8 of 30

171 172 Figure 7. Flow chart showing the methodology adopted.

1732.1. BasicThe Equations HEC-RAS for package Profile Calculation program can perform four different river analyses in one dimension. These include the following: 174 Water surface profiles are calculated from one section to another by the method named as the 1751.standard Calculation step method of regular based current on the water repeated surface solution profiles; of the energy equation. The energy equation 1762.can beVaried written flow as modeling;follows and given Figure 8: 3. Moving solid boundary sediment transport2 modeling; 2 훼2푉2 훼1푉1 4. Water quality analysis studies푧2 + 푌2 [21 +]. = 푧1 + 푌1 + + ℎ푒 (1) 2𝑔 2𝑔 For these four approaches, geometric data can be defined in the program and geometric and hydraulic calculations can be made. Regular uniform flow represents the current state in which the flow characteristics do not change depending on the location and time. The main characteristic of the slow changing flow is the slight changes in water depth and speed from one section to another. The HEC-RAS program can solve current problems with subcritical, supercritical, and both. One-dimensional energy equation is used by HEC-RAS to calculate water surface profiles. With this equation, the following variables are used, the friction coefficient in the Manning equation for energy

177

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losses, the kinetic energy correction coefficient for the change in velocity height owing to shrinkage and expansion changes, and the momentum equation where the water surface changes suddenly. In transitions from the river regime to the flood regime (hydraulic jump), the changes in the flow properties caused by the bridges and the analysis of the flow properties formed in the cross-sections of the rivers are also solved using these equations.

2.1. Basic Equations for Proﬁle Calculation Water surface proﬁles are calculated from one section to another by the method named as the standard step method based on the repeated solution of the energy equation. The energy equation can be written as follows and given Figure8:

α V 2 α V 2 z + Y + 2 2 = z + Y + 1 1 + he (1) 2 2 2g 1 1 2g 171

172 where z1, z2, main channelFigure bottom 7. Flow height chart (m); showingY1, Y the2, sectional methodology flow adopted. depth (m); V1, V2, mean velocity 2 (m/s); α1, α2,velocity coefficients; g, gravitational acceleration (m/s ); and he, energy loss height (m). 1732.1. The Basic energy Equations loss between for Profile two Calculation sections ( he) consists of friction loss and contraction or expansion loss. Energy head loss is defined by the following expression: 174 Water surface profiles are calculated from one section to another by the method named as the

175standard step method based on the repeated solution 2of the energy2 equation. The energy equation α2V2 α1V1 176can be written as follows and given Figurehe = LS 8f: + C (2) 2g − 2g 2 2 훼2푉2 훼1푉1 푧 + 푌 + = 푧 + 푌 + + ℎ푒 (1) where L, channel length; Sf,2 friction2 slope2𝑔 between1 two1 sections;2𝑔 and C, expansion or contraction loss coeﬃcient.

177 Figure 8. Representation of quantities in energy equations [21].

L channel length is calculated as follows:

L Q + L Q + L Q L = lob lob ch ch rob rob (3) Qlob + Qch + Qrob

where Llob, Lch, Lrob, flow way length, left flood plain, main channel, and right flood plain; Qlob, Qch, Qrob, mean discharge between sections, left flood channel, main channel, and right flood channel. Water 2020, 12, x FOR PEER REVIEW 9 of 30

178 Figure 8. representation of quantities in energy equations [21].

179where z1,z2, main channel bottom height (m); Y1, Y2, sectional flow depth (m); V1, V2, mean velocity 180(m/s); α1, α2,velocity coefficients; g, gravitational acceleration (m/s2); andhe, energy loss height (m).The 181e nergy loss between two sections (he)consists of friction loss and contraction or expansion loss. 182Energy head loss is defined by the following expression: 2 2 훼2푉2 훼1푉1 ℎ푒 = 퐿푆̅ + 퐶 | − | (2) 푓 2𝑔 2𝑔

183where L,channel length;Sf,friction slope between two sections; and C, expansion or contraction loss 184coefficient . 185 L channel length is calculated as follows:

퐿푙표푏푄̅푙표푏 + 퐿푐ℎ푄̅푐ℎ + 퐿푟표푏푄̅푟표푏 퐿 = (3) 푄̅푙표푏 + 푄̅푐ℎ + 푄̅푟표푏

186where Llob, Lch, Lrob,flow way length, left flood plain, main channel, and right flood plain; 187 Qlob, Qch, Qrob,mean discharge between sections, left flood channel, main channel, and right flood 188channel .

1892.2. Transmission Calculation of Section Subdivisions Water 2020, 12, 2070 9 of 28 190 In order to determine the total flow rate and velocity coefficient in a cross section, the cross 191section of the channel must be subdivided where the distributions are uniform. HEC-RAS considers 1922.2.the roughnessTransmission (n) Calculation changes onof Section main channelSubdivisions and flood channel to subdivide the cross sections as 193shown In order in Figure to determine 9.The transmission the total flow capacity rate and velocityfor each coefficient sub-region in a is cross calculated section, with the cross the sectionManning of 194theformula channel given must below. be subdivided where the distributions are uniform. HEC-RAS considers the roughness (n) changes on main channel and flood channel to subdivide1 the cross sections as shown in Figure9. 푄 = 퐾푆̅ 2 (4) The transmission capacity for each sub-region is calculated푓 with the Manning formula given below. 1 2 퐾 = 퐴푅13 (5) 푛 2 Q = KS f (4) 195where K,transmission capacity for each sub-region; n, Manning roughness coefficient for each 196 1 2 subregion; A, bottom sectional area; and R,bottomK = sectionAR 3 hydraulic radius. (5) 197 The program collects the transmission capacitiesn of subfields on the right and left coasts to 198wherecalculate K, transmissionthe total transmission capacity for capacity each sub-region; and the transmissionn, Manning roughness capacities coe of ﬃthecient main for channel, each subregion; which 199Aare , bottom usually sectional taken as area;a single and part.R, bottom section hydraulic radius.

200 201 Figure 9. DefinitionsDeﬁnitions of subsections of HEC-RASHEC-RAS [[21]21].. The program collects the transmission capacities of subﬁelds on the right and left coasts to calculate 2022.3. Head Loss Calculation the total transmission capacity and the transmission capacities of the main channel, which are usually taken as a single part.

2.3. Head Loss Calculation

In HEC-RAS, friction loss is calculated with the help of the friction gradient Sf and the length L, given by Equation (3). The friction slope (slope of the energy line) in each section is calculated from the Manning equation as follows. Q2 S = (6) f K

2.4. Determination of Contraction and Expansion Loss Contraction and expansion losses in HEC-RAS are calculated with the help of the following equation:

2 2 α2V2 α1V1 hce = C (7) 2g − 2g where C is the contraction or expansion coefficient. The software accepts that, if the speed load at the downstream is greater than that at the upstream, the expansion occurs when the speed load at the upstream is greater than at the downstream. Sample values for the C coefficient are given in Table1 below. The program tries to determine the water surface profile using the above equations with repeated solutions and limits the maximum number of iterations to 20 to balance the water surface. While the program uses the energy equation for regular currents, it uses the momentum equation in varied Water 2020, 12, x FOR PEER REVIEW 10 of 30

203 In HEC-RAS, friction loss is calculated with the help of the friction gradient Sf and the length L, 204given by Equation (3). The friction slope (slope of the energy line) in each section is calculated from 205the Manning equation as follows. 푄 2 푆 = ( ) (6) 푓 퐾

2062.4. Determination of Contraction and Expansion Loss 207 Contraction and expansion losses in HEC-RAS are calculated with the help of the following 208equation : 2 2 훼2푉2 훼1푉1 ℎ = 퐶 | − | (7) 푐푒 2𝑔 2𝑔

209w here C is the contraction or expansion coefficient. 210 The software accepts that, if the speed load at the downstream is greater than that at the 211upstream, the expansion occurs when the speed load at the upstream is greater than at the 212downstream. Sample values for the C coefficient are given in Table 1 below.

213 Table 1. Subcritical current contraction and expansion coefficients. Water 2020, 12, 2070 10 of 28 Transition Type Contraction Expansion No Transition Loss 0 0 flow. In many flow situations, there is a transition from supercritical to subcritical or to subcritical to Smooth Transition 0.1 0.3 supercritical. This situation occurs in sections, bridge structures, fall structures and sluices, and flow Bridge Transition 0.3 0.5 joints, which are important changes in channel slope. The momentum equation is derived from Sudden Transition 0.6 0.8 Newton’s second law of motion as follows and given Figure 10: 214 The program tries to determine the waterX surface profile using the above equations with 215repeated solutions and limits the maximum numberFx = ofma iterations to 20 to balance the water surface.(8) 216While the program uses the energy equation for regular currents, it uses the momentum equation in where F , force; m, mass; and a, acceleration. 217varied flow.x In many flow situations, there is a transition from supercritical to subcritical or to 218subcritical to supercritical.Table 1. ThisSubcritical situation current occurs contraction in sections, and expansion bridge structures, coefficients. fall structures and 219sluices, and flow joints, which are important changes in channel slope. The momentum equation is 220derived from Newton’s secondTransition law of motion Type as follows Contraction and given Expansion Figure 10: No Transition Loss 0 0 Smooth Transition∑ 퐹푥 = 푚푎0.1 0.3 (8) Bridge Transition 0.3 0.5 221w here Fx, force; m, mass; andSudden a, acceleration Transition. 0.6 0.8

222 Figure 10. Quantities in the momentum method [21]. 223 Figure 10.Quantities in the momentum method [21]. If we apply Newton’s second law of motion to the ﬂow segment between Sections1 and2, the momentum change in unit time can be written as follows:

P P + Wx F = Qρ∆Vx (9) 2 − 1 − f where P, 1 and 2 hydrostatic pressure force in cross sections; Wx, the x component of the weight force; Ff, friction loss between Sections1 and2; Q, discharge; ρ, speciﬁc mass of water; and ∆Vx, the change in velocity between points 1 and 2 in the x direction. After performing the necessary intermediate operations, the shape of the momentum equation used by the software can be obtained.

2 2 Q2 β2 A1 + A2 A1 + A2 Q1 β1 + AY2 + LSo LS f L = + AY1 (10) gA2 2 − 2 gA1

An important term used to determine the regime of the flow, that is, subcritical and supercritical flow in varied flows using the momentum equation, is the Froude number and is expressed as follows.

V Fr = p (11) gh

where V, flow velocity; g, gravity acceleration; and h, flow depth. If Fr = 1, it is defined as critical current, Fr < 1, it is defined as subcritical current, i.e., river regime, and if Fr > 1, it is defined as supercritical current, namely flood regime. Water 2020, 12, 2070 11 of 28

2.5. Manning Coefficient for Main Channel If the main channel roughness does not change, the section is not subdivided and the calculation is made by considering a single n value. If the main channel roughness is variable, HEC-RAS checks the compatibility of the roughness of the main channel sub-parts, and if necessary, calculates a single equivalent roughness coefficient of the entire section. It is important to determine the appropriate Manning coefficient for the accuracy of the calculated water surface profiles. Manning n value is highly variable and depends on many factors; surface roughness, plant properties, channel irregularity, channel horizontal slope, meandering, scouring and accumulation, obstacles, channel shape and size, flow, seasonal changes, temperature, hangers, and swabs. In the case in which there is water surface information of a cross section, the Manning value (n) can be calibrated. If there is no such information, similar current conditions or value obtained by experimental studies can be used for the n value. There are many sources for determining the value of Manning n for different channel properties. The broadest information for the value of “n” in streams and flood channels is given in Chow’s Open Channel Hydraulics (1959) [22]. The information from this book is given in Table2. The model can be calibrated with the n values of streams that are presented in the book and presented with pictures.

Table 2. Values for diﬀerent types of channels [22].

Type of Channel and Description Minimum Normal Maximum Natural streams-minor streams (top width at floodstage < 100 ft) 1. Main Channels a. clean, straight, full stage, no rifts or deep pools 0.025 0.030 0.033 b. same as above, but more stones and weeds 0.030 0.035 0.040 c. Clean, winding, some pools and shoals 0.033 0.040 0.045 d. same as above, but some weeds and stones 0.035 0.045 0.050 e. same as above, lower stages, more ineffective slopes and sections 0.040 0.048 0.055 f. same as "d" with more stones 0.045 0.050 0.060 g. sluggish reaches, weedy, deep pools 0.050 0.070 0.080 h. very weedy reaches, deep pools, or noodways with heavy stand 0.075 0.100 0.150 of timber and underbrush 2. Mountain streams, no vegetation in channel, banks usually steep, trees and brush along banks submerged at high stages a. bottom: gravels, cobbles, and lew boulders 0.030 0.040 0.050 b. bottom: cobbles with large boulders 0.040 0.050 0.070 3. Floodplains a. Pasture, no brush 1. short grass 0.025 0.030 0.035 2. high grass 0.030 0.035 0.050 b. Cultivated areas 1. no crop 0.020 0.030 0.040 2. mature row crops 0.025 0.035 0.045 3. mature field crops 0.030 0.040 0.050 c. Brush 1. scattered brush, heavy weeds 0.035 0.050 0.070 2. light brush and trees, [n winter 0.035 0.050 0.060 3. light brush and trees, in summer 0.040 0.060 0.080 4. medium to dense brush, in winter 0.045 0.070 0.110 5. medium to dense brush, in summer 0.070 0.100 0.160 d. Trees 1. dense willows, summer, straight 0.110 0.150 0.200 Water 2020, 12, 2070 12 of 28

2.6. HEC-RAS Software Buttons When the program is ﬁrst opened, the function of the buttons in the window is shown in Figure 11. ForWater more 2020, information, 12, x FOR PEER the REVIEW user’s guide can be read. 12 of 30

265 266 FigureFigure 11. 11.HEC-RASHEC-RAS mainmain buttonbutton barbar [[21]21].. 2.7. Creating Geometric Data In this study, the geometric model of the flooding, the maps of the Amik Plain, and the channels and rivers seen in Figure 12 were digitized as accurately as possible using the Google Earth software [23].Parts of the Küçükasi River (1050 m); Karasu River (8050 m); and the Comba, Muratpa¸sa, and Afrin channels (5100 m, 6550 m, and 6600 m, respectively) are modeled and a cross-section of every 50 m is formed. The drawing of the river network was created with the sections in the window that came in by clicking the Geometric Data icon in the main menu of HEC-RAS, shown in Figures 11 and 13. The HEC-RAS model of channels and cross-sections is presented in Figure 13. The lowest elevation levels in the numerical model were measured on the Küçükasi River +81 m, Karasu River +79 m, Afrin channel +79 m, and the Muratpasa and Comba channels +78 m. Afrin and Karasu are formed from two parts, considering the intersection points where the flow network was created. The sections of the flow paths were formed by entering data into the program similar to the cross-section values specified by the DSI in the flood report. Figure 14 shows these sections. There is a slope of 0.1% in the formed current networks. On the basis of the authors’ field observations, water organization reports, and Google Earth software, the authors saw that channels exist generally from natural soil, and that is why the Manning coefficient used for the study is considered as 0.042 for both sides of the channels and 0.032 for the bottom of channels. The Manning coefficient is selected in accordance with the regional conditions according to the information in Table2.

267 268 Figure 12. Screenshot of Hatay Airport from Google Earth [24].

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Water2652020 , 12, 2070 13 of 28 266 Figure 11.HEC-RAS main button bar [21].

267

268Water 2020, 12, x FOR PEERFigureFigure REVIEW 12. 12. Screenshot Screenshot ofof HatayHatay Airport Airport from from Google Google Earth Earth [24]. [24 ]. 13 of 30

269 270 FigureFigure 13. 13.Flood flood model created created in in HEC HEC-RAS-RAS program program..

271 The lowest elevation levels in the numerical model were measured on the Küçükasi River +81 272m, Karasu River +79 m, Afrin channel +79 m, and the Muratpasa and Comba channels +78 m. Afrin 273and Karasu are formed from two parts, considering the intersection points where the flow network 274was created. The sections of the flow paths were formed by entering data into the program similar to 275the cross-section values specified by the DSI in the flood report. Figure 14 shows these sections. There 276is a slope of 0.1% in the formed current networks. On the basis of the authors’ field observations, 277water organization reports, and Google Earth software, the authors saw that channels exist generally 278from natural soil, and that is why the Manning coefficient used for the study is considered as 0.042 279for both sides of the channels and 0.032 for the bottom of channels. The Manning coefficient is selected 280in accordance with the regional conditions according to the information in Table 2. 281

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283 284 FigureFigure 14. 14.SectionsSections created created in in the the HEC HEC-RAS-RAS program program:: (a (a) )Küçükasi Küçükasi river river;; (b (b) )Karasu Karasu river1 river1;; ( (cc)) Karasu Karasu 285 RiverRiver 2 2;; ( (dd)) Comba Comba channel channel;; ( (ee)) Muratpaşa Muratpa¸sachannel; channel; ( (ff)) Afrin Afrin channel1 channel1;; and and ( (gg)) Afrin Afrin channel 2 2..

2.8. Hydraulic Analysis 286 The steady flow icon is selected from the main bar and the window in Figure 15 appeared. After the geometric model was generated, the values measured at the flow observation stations during the flooding were entered into the program, as shown in Figure 15. These values were taken from the DSI flood report. On the basis of the available data, the model was run for steady flow conditions and the results were examined in accordance with this situation.

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2872.8 . Hydraulic Analysis 288 The steady flow icon is selected from the main bar and the window in Figure 15 appeared. After 289the geometric model was generated, the values measured at the flow observation stations during the 290flooding were entered into the program, as shown in Figure 15. These values were taken from the 291DSI Water flood2020, 12report., 2070 On the basis of the available data, the model was run for steady flow conditions15 and of 28 292the results were examined in accordance with this situation.

293

294 FigureFigure 15. 15. ProcessingProcessing of of flood ﬂood flows ﬂows into into the HEC HEC-RAS-RAS program program..

2953. Results Results 296 The results of the flow flow network were analyzed separately for each branch, and the following 3 297benefits benefits w wereere obtained. obtained. As As seen seen in in Figure Figure 16a 16,a,b,b, for for the the flow flow of ofQ Q= 216= 216 m3/s, m the/s, thefirst first (50 (50m) and m) andthe 298last the last(2750 (2750 m) sections m) sections of the of second the second part of part the of Karasu the Karasu river were river flooded were flooded about about2.5 m above 2.5 m the above upper the 299elevation upper elevation of the of channel. the channel. Figure Figure 16c,d 16 showc,d show perspective perspective views views of theof the flow flow from from two two sides sides for for all all 300sections. Figure Figure17a 17a–c–c graphically graphically show show the the change change in in the the Froude Froude number, number, speed speed,, and and water depth 301change along all sections for the second part of the Karasu river. When When the the graphs graphs are are examined, it is 302seen in Figure 17a17a t thathat the Froude number indicates that that the the flow flow is is sub sub-critical-critical across across all all sections, sections, 303that that is,is, forfor thethe standardstandard river river regime, regime, and and there there is is a slowa slow rise rise from from upstream upstream to downstream.to downstream. Figure Figure 17b 30417b indicates indicates a slow a slow increase increase in the in flowthe flow rate rate as well as well as in as the in Froudethe Froude number number plot. plot. Figure Figure 17c shows17c shows that 305that the water the water depth depth decreases decreases slowly slowly as the flow as the rate flow increases rate increasesfrom upstream from to upstream downstream. to downstream. Because the 306Because simulation the operates simulation in steady operates flow in conditions, steady flow the conditions, HEC-RAS program the HEC keeps-RAS programthe discharge keeps value the 307discharge constant, andvalue thus constant, water depthand thus decreases water de withpth increasing decreases velocitywith increasing values. velocity values. As seen in Figure 18, water depth is one meter above the first part of the Karasu river section (first 50 m) and is two meters above the second part (last 5250 m) of the Karasu river section. Figure 19 shows perspective views of the last four sections of the parts between 5100 and 5250 m. Figure 20a–c show the changes in the Froude number, velocity, and water depth along all the sections in the first part of the Karasu River. A similar situation is also observed in the second part of Karasu River. Froude number and velocity increase slowly, but the water depth decreases. Figure 21a,b relates to the Afrin channel analyses. It is understood from these figures that, when the discharge is Q = 256 m3/s, the water level is approximately two meters above the channel banks for the first part of the Afrin channel (first 50 m), and it is approximately three meters above the banks for the last 1250 m. Figure 22 shows a perspective view of the flow for all sections. Water 2020, 12, 2070 16 of 28 Water 2020, 12, x FOR PEER REVIEW 17 of 30

308 309 Figure 16. (a) Karasu River second part and Q = 216 m3/s discharge for the first (50 m) section; (b) Figure 16. (a) Karasu River second part and Q = 216 m3/s discharge for the ﬁrst (50 m) section; 310 Karasu River second part and Q = 216 m3/s discharge for the last 2750 m; (c)first perspective view for 3 (b) Karasu311 Riverall sections second; (d) second part perspective and Q = 216view mfor /alls dischargesections. for the last 2750 m; (c) ﬁrst perspective view Water 2020, 12, x FOR PEER REVIEW 18 of 30 for all sections; (d) second perspective view for all sections.

312 313Figure Figure 17. ( a17.) Graph(a) Graph of Froudeof Froude number number changechange across across all all sections sections for forthe theKarasu Karasu river riversecond second part part 314where where Q = 216 Q= 216 m3 /ms;3 (/sb; )(b velocity) velocity change change graph;graph; ( (cc)w) waterater depth depth change change graph graph..

315 As seen in Figure 18, water depth is one meter above the first part of the Karasu river section 316(first 50 m) and is two meters above the second part (last 5250 m) of the Karasu river section. Figure 31719 shows perspective views of the last four sections of the parts between 5100 and 5250 m.

318 319 Figure 18.(a) Karasu River first part and discharge Q = 216 m3/s for the first (50 m) section;(b) Karasu 320 River first part and discharge Q = 216 m3/s for the last (5250 m) section.

321

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312 313 Figure 17.(a) Graph of Froude number change across all sections for the Karasu river second part 314 where Q= 216 m3/s; (b) velocity change graph; (c)water depth change graph.

315 As seen in Figure 18, water depth is one meter above the first part of the Karasu river section 316(first 50 m) and is two meters above the second part (last 5250 m) of the Karasu river section. Figure Water 2020, 12, 2070 17 of 28 31719 shows perspective views of the last four sections of the parts between 5100 and 5250 m.

318 319 FigureFigure 18. 18.(a()a )Karasu Karasu River River first first part part and and discharge discharge Q Q = 216216 m m33/s/s for for the the first first (50 (50 m) m) section section;;( (bb)) Karasu Karasu Water 2020, 12, x FOR PEER REVIEW 3 19 of 30 320 RiverRiver first first part part and and discharge discharge Q Q = 216216 m m3/s/s for for the the last last (5250 (5250 m) m) section section..

321

322 Figure 19. Perspective view for sections 5100–5250 m for discharge Q = 216 m3/s in the Karasu River 323 Figure 19.Perspective view for sections 5100–5250 m for discharge Q = 216 m3/s in the Karasu River ﬁrst part. 324 first part. Changes in Froude number, velocity, and water depth are shown for the ﬁrst part of the Afrin 325 channelFigure and20 a– graphsc show relating the changes to them in arethe presentedFroude number, in Figure velocity 23. When, and thewater graphs depth are along examined, all the it is 326 sectionsseen that in the the first Froude part numberof the Karasu increases River. rapidly, A similar from asituation value of is about also 0.3observed upstream in the and second approaching part of 1.0 327 Karasu(critical River. value) Froude further number downstream. and velocity Similarly, increase the velocity slowly, valuebut the rises water to 4.5 depth m/s fromdecreases. 2 m/s. This change causes an increase in water depth of about 2 m.

328 329 Figure 20.(a)When the discharge is Q = 216 m3/s, the Froude number changes across all sections for 330 the first part of Karasu River;(b)velocity change graph;(c)water depth change graph.

331 Figure 21a,b relates to the Afrin channel analyses. It is understood from these figures that, when 332the discharge is Q =256 m3/s, the water level is approximately two meters above the channel banks

Water 2020, 12, x FOR PEER REVIEW 19 of 30

322

323 Figure 19.Perspective view for sections 5100–5250 m for discharge Q = 216 m3/s in the Karasu River 324 first part.

325 Figure20 a–c show the changes in the Froude number, velocity, and water depth along all the 326sections Water 2020 in, 12 the, 2070 first part of the Karasu River. A similar situation is also observed in the second par18 oft of 28 327Karasu River. Froude number and velocity increase slowly, but the water depth decreases.

Water 2020, 12, x FOR PEER REVIEW 20 of 30 328 3 333329for theFigureFigure first part 20. 20.(a (of)aWhen) the When Afrin the the discharge dischargechannel is(first isQ Q = =52160216 m m), m3 /s,and/ s,the theit Froudeis Froude approximately number number changes changes three acrossmeters across all all above sections sections the for forbanks 334330for thethethe last first ﬁrst 125 part part0 m of of. KarasuFigure Karasu River22 River; shows;(b (b)v)elocity velocitya perspective change change graph view graph;;( cof) (wc the)ater water flow depth depth for change all change sections. graph graph..

335 Figure 21. (a) Cross-section of the ﬁrst 50 m of the Afrin Channel and (b) cross-section of the last 1250m 336 Figure 21.(a) Cross-section of the first 50 m of the Afrin Channel and (b) cross-section of the last 1250m of the Afrin Channel, both at discharge Q = 256 m3/s. 337 of the Afrin Channel, both at discharge Q = 256 m3/s.

338 339 Figure 22.Afrin channel part one: perspective view for all sections.

340 Changes in Froude number, velocity, and water depth are shown for the first part of the Afrin 341channel and graphs relating to them are presented in Figure 23. When the graphs are examined, it is 342seen that the Froude number increases rapidly, from a value of about 0.3 upstream and approaching 3431.0 (critical value) further downstream. Similarly, the velocity value rises to 4.5 m/s from 2 m/s. This 344change causes an increase in water depth of about 2 m.

Water 2020, 12, x FOR PEER REVIEW 20 of 30

333for the first part of the Afrin channel (first 50 m), and it is approximately three meters above the banks 334for the last 1250 m. Figure 22 shows a perspective view of the flow for all sections.

335 336 Figure 21.(a) Cross-section of the first 50 m of the Afrin Channel and (b) cross-section of the last 1250m 337 of the Afrin Channel, both at discharge Q = 256 m3/s. Water 2020, 12, 2070 19 of 28

338 339 FigureFigure 22.22.AfrinAfrin channel channel part part one: one: perspective perspective view view for for all all sections sections.. Water 2020, 12, x FOR PEER REVIEW 21 of 30 340 Changes in Froude number, velocity, and water depth are shown for the first part of the Afrin 341channel and graphs relating to them are presented in Figure 23. When the graphs are examined, it is 342seen that the Froude number increases rapidly, from a value of about 0.3 upstream and approaching 3431.0 (critical value) further downstream. Similarly, the velocity value rises to 4.5 m/s from 2 m/s. This 344change causes an increase in water depth of about 2 m.

345 346 Figure 23. ((aa)) Froude Froude number number change change graph graph across across all sections for the the Afrin channel first first part when Q 3 347 = 256256 m m3/s/s;; ( (bb)) v velocityelocity change change graph graph;;(c ()cw) waterater depth depth graph graph.. Figure 24 shows that, at discharge Q = 256 m3/s in the Afrin channel second part, flooding occurs 348 Figure 24 shows that, at discharge Q = 256 m3/s in the Afrin channel second part, flooding occurs three meters above the channel section top height in the first 100 m and five meters above the channel 349three meters above the channel section top height in the first 100m and five meters above the channel section top height in the last 5300 m. Figure 25 shows perspective views of the last five sections between 350section top height in the last 5300m. Figure 25 shows perspective views of the last five sections 5100 and 5300 m. 351between 5100 and 5300 m.

352 353 Figure 24. (a) Afrin channel second part, section view for the first 100 m; (b) Afrin channel second 354 part, section view for the last 5300 m, both at discharge Q = 256 m3/s.

Water 2020, 12, x FOR PEER REVIEW 21 of 30

345 346 Figure 23. (a) Froude number change graph across all sections for the Afrin channel first part when Q 347 = 256 m3/s; (b) velocity change graph;(c)water depth graph.

348 Figure 24 shows that, at discharge Q = 256 m3/s in the Afrin channel second part, flooding occurs 349three meters above the channel section top height in the first 100m and five meters above the channel 350section top height in the last 5300m. Figure 25 shows perspective views of the last five sections 351between Water 2020 ,510012, 2070 and 5300 m. 20 of 28

352 353Water Figure2020Figure, 12 ,24. x FOR ((a)) AfrinPEER REVIEW channelchannel secondsecond part, part, section section view view for for the the ﬁrst first 100 10 m;0 (mb); Afrin(b) Afrin channel channel second second part,22 of 30 354 part,section section view view for the for last the 5300 last 530 m, both0 m, both at discharge at discharge Q = 256 Q = m 2563/s. m3/s.

355 356 FigureFigure 25. PerspectivePerspective view view for for sections sections 510 5100–53000–5300 m m at at discharge discharge Q Q == 256256 m m33/s/s in in the the Afrin Afrin channel channel 357 secondsecond part part..

358 FigureFigure 2266aa–c–cshow showss a a slow slow increase increase in in the the Froude Froude number number when when the the graphs graphs are are examined examined along along 359all all the the sections sections in in the the second second part part of of the the Afrin Afrin channel. channel. Likewise, Likewise, the the velocity velocity value value increases increases from from 1.5 360m/s 1.5 mto/ s2 tom/s. 2 m This/s. This increase increase causes causes a change a change in water in water depth depth of about of about 1.5 1.5m. m. In Figure 27a,b, at discharge Q = 128 m3/s, flooding occurs about three meters above the channel top level for the Muratpa¸sachannel first 50 m sections, and it is about four meters above the top level of the channel for the Muratpa¸sachannel last sections (6550 m). Figure 28 shows perspective views of the last four sections between 6400 and 6550 m. Figure 29a–c shows the changes in Froude number, velocity, and water depth along all sections in the Muratpa¸sachannel. When the graphs are examined, it is seen that the Froude number and the flow rate increase slowly as in the Afrin channel. This change causes an increase in water depth of about 1 m.

361 362 Figure 26. (a) Froude number change graph for all sections of the second part of the Afrin channel 363 when Q = 256 m3/s; (b)velocity change graph;(c)water depth change graph.

364 In Figure 27a,b, at discharge Q = 128m3/s, flooding occurs about three meters above the channel 365top level for the Muratpaşa channel first 50 m sections, and it is about four meters above the top level 366of the channel for the Muratpaşa channel last sections (6550 m). Figure 28 shows perspective views 367of the last four sections between 6400 and 6550 m.

Water 2020, 12, x FOR PEER REVIEW 22 of 30

355 356 Figure 25.Perspective view for sections 5100–5300 m at discharge Q = 256 m3/s in the Afrin channel 357 second part.

358 Figure 26a–cshows a slow increase in the Froude number when the graphs are examined along

359all Water the2020 sections, 12, 2070 in the second part of the Afrin channel. Likewise, the velocity value increases from21 of 1.5 28 360m/s to 2 m/s. This increase causes a change in water depth of about 1.5 m.

361 362 Figure 26. ((aa)) Froude number change graph graph for for all sections of the second part of the Afrin channel when Q = 256 m33/s; (b) velocity change graph; (c) water depth change graph. 363Water when2020, 12 Q, x= FOR256 mPEER/s; (REVIEWb)velocity change graph;(c)water depth change graph. 23 of 30

368 369 Figure 27. ((aa)) The The first ﬁrst (50 (50 m) m) cross cross-section-section in in the the Muratpaşa Muratpa¸sachannel; channel; (b)t thehe last last (655 (65500 m m)) crosssection crosssection 370 inin the the Muratpaşa Muratpa¸sachannel, channel, both at flow ﬂow rate Q = 128128 m m33/s/s..

371 372 Figure 28. Perspective view for sections 6400–6550m at discharge Q = 128 m3/s in the Muratpaşa 373 channel.

374 Figure 29a–cshows the changes in Froude number, velocity, and water depth along all sections 375in the Muratpaşa channel. When the graphs are examined, it is seen that the Froude number and the 376flow rate increase slowly as in the Afrin channel. This change causes an increase in water depth of 377about 1 m.

Water 2020, 12, x FOR PEER REVIEW 23 of 30

368 369 Figure 27. (a) The first (50 m) cross-section in the Muratpaşa channel; (b)the last (6550 m) crosssection 370 in the Muratpaşa channel, both at flow rate Q = 128 m3/s. Water 2020, 12, 2070 22 of 28

371 3 372Water 2020Figure, 12 28., 28.x FORPerspective Perspective PEER REVIEW view view for for sections sections 6400–6550 6400–6550m m at discharge at discharge Q = 128 Q m = 128/s in m the3/s Muratpa¸sachannel. in the Muratpaşa24 of 30 373 channel.

378 3 379 Figure 29. ((aa)) Froude Froude number number change change graph across all sections at discharge Q = 128 m 3/s/s in in Muratpaşa Muratpa¸sa 380 channelchannel;; ( b)) v velocityelocity change graph graph;; ( c) w waterater depth change graph.graph.

3 381 Figure 30aa,b,b showsshows that,that, at discharge QQ == 121288m m3/s,/s, flooding flooding occurs occurs two two meters meters above above the the Comba Comba 382channel top level for the first first 5050m m section, section, and and ten ten meters meters above above the the channel channel top top level level for for the the 510 51000 m 383section. Figure Figure 3131 showsshows perspective perspective views views of of the last five five sections between 4900 and 5100 m. Figure 32a–c shows graphically the changes in Froude number, velocity, and water depth along all sections in the Comba channel. When the graphs are analyzed, it is seen that the Froude number increases rapidly from the upstream part with a value of 0.2 and approaches the critical value of 1.0 in the downstream part. Likewise, the velocity increases from 2 m/s and reaches 6 m/s. This rapid increase causes a change in water depth of about 7 m.

384 385 Figure 30. (a) Cross-sectional view of Comba channel first 50 m; (b) cross-sectional view of Comba 386 channel last 5100 m, both at discharge Q = 128 m3/s.

Water 2020, 12, x FOR PEER REVIEW 24 of 30

378 379 Figure 29. (a) Froude number change graph across all sections at discharge Q = 128 m3/s in Muratpaşa 380 channel; (b) velocity change graph; (c) water depth change graph.

381 Figure 30a,b shows that, at discharge Q = 128m3/s, flooding occurs two meters above the Comba 382Waterchannel 2020 top, 12, 2070level for the first 50m section, and ten meters above the channel top level for the 510230 of m 28 383section. Figure 31 shows perspective views of the last five sections between 4900 and 5100 m.

384

385Water 2020Figure, 12, x 30. FOR (a PEER)) Cross Cross-sectional REVIEW-sectional view view of of Comba Comba channel channel first ﬁrst 5 500 m m;; ( (bb)) c cross-sectionalross-sectional view view of of Comba Comba25 of 30 386 channel last 510 51000 m m,, both at discharge Q = 128128 m m33/s/s..

387 388 FigureFigure 31. 31.PerspectivePerspective view view for for sections sections 6400 6400–6550–6550 m min inComba Comba channel channel at atdischarge discharge Q Q= =128128 m m3/s.3 /s.

3 389 FigureIn Figure 32a –33c showsa,b, now graphically at the flow the rate changes Q = 472 in m Froude/s, it can number, be observed velocity, that and the water first (0 depth m) section along of 390all the sections Küçükasi in the River Comba was approximatelychannel. When 1.5 the m graphs below theare topanalyzed, elevation it is of seen the channel,that the Froude and there number was no 391increases flood in rapidly this part. from Flooding the upstream occurred part about with 0.3 am valu abovee of the0.2 topand level approaches of the channel the critical in the value last 5100of 1.0 m 392in section. the downstream Figure 34 showspart. Likewise, perspective the views velocity of theincreases last five from sections 2 m/s between and reaches 800 m 6 and m/s. 1000 This m. rapid 393increase Figure causes 35 a–ca change shows in graphically water depth the of changes about 7 in m. Froude number, velocity, and water depth along all sections in the Küçükasi River. While the Froude number is about 0.3 in the upstream part, it increases rapidly and reaches the critical value 1.0 further downstream. In the same way, the velocity value rises from 2.5 m/s to 6 m/s. This increase leads to a change in water depth of about 3 m. When the flood water levels found by means of the HEC-RAS program are examined, it is seen that the values are much higher than the land elevation (78 m–81 m) of the region. The digital elevation model (DEM) map relating to Hatay region is used to mark the flood area, and it is presented in Figure 36[24].

394 395 Figure 32. (a) Froude number change graph across all sections in Comba channel at discharge Q = 128 396 m3/s; (b)velocity change graph;(c)water depth change graph.

397 In Figure 33a,b, now at the flow rate Q = 472 m3/s, it can be observed that the first (0 m) section 398of the Küçükasi River was approximately 1.5 m below the top elevation of the channel, and there was

Water 2020, 12, x FOR PEER REVIEW 25 of 30

387 388 Figure 31.Perspective view for sections 6400–6550 m in Comba channel at discharge Q = 128 m3/s.

389 Figure32a–c shows graphically the changes in Froude number, velocity, and water depth along 390all sections in the Comba channel. When the graphs are analyzed, it is seen that the Froude number 391increases rapidly from the upstream part with a value of 0.2 and approaches the critical value of 1.0 392in the downstream part. Likewise, the velocity increases from 2 m/s and reaches 6 m/s. This rapid Water 2020, 12, 2070 24 of 28 393increase causes a change in water depth of about 7 m.

Water 2020, 12, x FOR PEER REVIEW 26 of 30 394 399no flood in this part. Flooding occurred about 0.3 m above the top level of the channel in the last 5100 395 FigureFigure 32. 32. (a)( aFroude) Froude number number change change graph graph across across all sections all sections in Comba in Comba channel channel at discharge at discharge Q = 128 400 3 396 m section.mQ3/=s;128 ( bFigure)v melocity/s; 3 (b4 )change shows velocity graph perspective change;(c)w graph;ater views depth (c) water ofchange the depth last graph changefive. sect graph.ions between 800 m and 1000 m.

401 402 FigureFigure 33. ((aa)) First First (0 (0 m) m) cross cross-section-section in in Küçükasi Küçükasi River River;; ( (bb)) l lastast (100 (10000 m m)) cross cross-section-section in in Küçükasi Küçükasi 403 river,river, both at discharge Q = 472472 m m33/s/s..

404 405 Figure 34.Perspective view for sections between 800m and 1000m in Küçükasi river at discharge Q = 406 472 m3/s.

407 Figure 35a–c shows graphically the changes in Froude number, velocity, and water depth along 408all sections in the Küçükasi River. While the Froude number is about 0.3 in the upstream part, it 409increases rapidly and reaches the critical value 1.0 further downstream. In the same way, the velocity 410value rises from 2.5 m/s to 6 m/s. This increase leads to a change in water depth of about 3 m.

Water 2020, 12, x FOR PEER REVIEW 26 of 30

399no flood in this part. Flooding occurred about 0.3 m above the top level of the channel in the last 5100 400m section. Figure 34 shows perspective views of the last five sections between 800 m and 1000 m.

401 402 Figure 33. (a) First (0 m) cross-section in Küçükasi River; (b) last (1000 m) cross-section in Küçükasi 403Water 2020river,, 12 both, 2070 at discharge Q = 472 m3/s. 25 of 28

404 405 FigureFigure 34.34.PerspectivePerspective view view for for sections sections between between 80 8000m mand and 100 10000m in m Küçükasi in Küçükasi river river at discharge at discharge Q = Water 2020, 12, x FOR3 PEER REVIEW 27 of 30 406 Q472= 472m3/s m. /s.

411 412 Figure 35. 35. ((aa)) FroudeFroude number number change change graph graph for for the the Küçükasi Küçükasi river river at the at the discharge discharge Q = Q472 = m4723/s; 413 (mb3)/s velocity;(b)velocity change change graph; graph (c) water;(c)water depth depth change change graph. graph.

414 When the flood water levels found by means of the HEC-RAS program are examined, it is seen 415that the values are much higher than the land elevation (78m–81m) of the region. The digital elevation 416model (DEM) map relating to Hatay region is used to mark the flood area, and it is presented in 417Figure 36[24]. 418 The potential danger zone is obtained with reference to the natural elevations of the plain. 419According to the ESRI results, it is possible to see that a huge part of the plain including Hatay airport 420and agricultural areas are at risk of flooding.

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421 422 FigureFigure 36. 36.MarkedMarked ﬂoodflood areaarea usingusing digitaldigital elevation elevation 3D 3D model model map map of of Hatay Hatay [[2244].].

4234. ConclusionsThe potential danger zone is obtained with reference to the natural elevations of the plain. According to the ESRI results, it is possible to see that a huge part of the plain including Hatay airport 424and agriculturalAmik plain areas is originally are at risk a region of flooding. consisting of artificially dried natural lakes and swamps under 425the control of local government. This area was considered as an agricultural area and improved. At 4264.an Conclusions advanced stage, an airport was built in part of the plain in line with demands and research. 427However , in recent years, both agricultural fields and the airport have faced flooding events under Amik plain is originally a region consisting of artificially dried natural lakes and swamps under 428climatic effects. With this study, the flood capacity of the artificial channels and the affected area was the control of local government. This area was considered as an agricultural area and improved. 429analyzed using HEC-RAS software(developed by U.S. Army Corps of Engineers Hydrologic At an advanced stage, an airport was built in part of the plain in line with demands and research. 430Engineering Center-HEC ). However, in recent years, both agricultural fields and the airport have faced flooding events under 431 In this case study, in order to understand the water level of Hatay’s Amik Plain during the flood, climatic effects. With this study, the flood capacity of the artificial channels and the affected area 432all important flow networks were examined together, and the effect of the flood was investigated. was analyzed using HEC-RAS software (developed by U.S. Army Corps of Engineers Hydrologic 433The results of the study are as follows. Engineering Center-HEC). 434 By examining the hydraulic conditions of each channel and river branch, it is seen that the 435sections of Muratpaşa, Comba channels, and Afrin River should be increased. The presented

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In this case study, in order to understand the water level of Hatay’s Amik Plain during the flood, all important flow networks were examined together, and the effect of the flood was investigated. The results of the study are as follows. By examining the hydraulic conditions of each channel and river branch, it is seen that the sections of Muratpa¸sa,Comba channels, and Afrin River should be increased. The presented hydraulic modeling method is sufficient to ensure flood safety, but it must be done before proposing the flood protection structure. The highest flood value was found in the smallest channel Comba. As Hatay airport is close to this channel, necessary measures should be taken against high flood conditions in and around the airport. Considering this situation, it has been determined that it is appropriate to re-plan the Comba drainage channel. According to the data obtained from the previous studies and model results of Amik Plain and changes in water level, it is seen that more measures should be taken during floods. It is concluded that the capacities of measured excessive discharge values, Muratpa¸sa,Comba channels, and Afrin river sections are not sufficient to carry these discharge values directly to Küçükasi River. According to the evaluation of the results obtained in this study and the similar studies presented here, the flood risk of the area is expected to increase day by day with the influence of changing climate conditions. Depending on the changing climatic conditions, Amik Plain’s research on the relationship between precipitation and discharge will help engineers to design optimum channels that represent measures against possible floods in the future.

Author Contributions: Conceptualization, F.Ü. and B.T.; compiling data, Y.Z.K.; formal analysis, M.D.; funding acquisition, M.D.; investigation, H.V.; methodology, H.V.; project administration, M.Z.; resources, M.D.; software, Y.Z.K.; supervision, F.Ü., B.T., M.Z., and F.Ü.; validation, F.Ü.; visualization, Y.Z.K.; writing—original draft preparation, Y.Z.K. and H.V.; writing—review and editing, M.Z. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: Authors would like to thank the General Directorate for State Hydraulic Works (DSI) for sharing their measurements. This work was supported by the project of the Ministry of Education of the Slovak Republic VEGA 1/0308/20: Mitigation of hydrological hazards—floods and droughts—by exploring extreme hydroclimatic phenomena in river basins and the project of the Slovak Research and Development Agency APVV-18-0360: Active hybrid infrastructure towards a sponge city. Conflicts of Interest: The authors declare no conflict of interest.

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