SedimentaryStudy of QarranquRiver Using Hec-Ras - · PDF fileIntl. Res. J. Appl. Basic. Sci....

International Research Journal of Applied and Basic Sciences © 2013 Available online at www.irjabs.com ISSN 2251-838X / Vol, 4 (11):3582-3591 Science Explorer Publications

SedimentaryStudy of QarranquRiver Using Hec-Ras

JafarChapokpour*1 and Rasoul Daneshfaraz2

1. Member of university of Maragheh, Maragheh, Iran

2. Assistant Professor of Civil Department, University Of Maragheh, Iran *Corresponding Author’s email:[email protected], [email protected]

ABSTRACT:Hec-Ras is an applied software package for simulation of river network in steady and unsteady flow regime. The sediment transport simulation is also added in 4.1 version. The goal of this paper is to investigate application and verification of it in transport modeling of rivers of East Azarbayjan province in Iran. For river network simulation, coupled use of ARCGIS,Hec-GeoRas and Hec-Ras modelswere used in Qarranquriver and tried to verify the model simulation with field survey. Due to the bed material and other characteristics of mentioned river and on the base of previous studies, the Laursen transport equation with Toffaleti fall velocity equation was applied in the simulation. At the end, different types of outputs resulted in both tabular and graphical moodsand the depositional and erosional processes of river network interoperated using effective indices like velocity, shear stress and bed level changes. It was found that the general of trend of transport activities could be verified by field survey but the magnitudes of them did not confirmed which reply high dependency of model to the selection of transport relationships. Keywords: River Network, Sediment Transport, Hec-Ras, Hec-Georas

INTRODUCTION

The goal of sedimentary researches Sedimentary studieshave important rolein the river training affairs.Identification of sedimentation mechanisms is useful manner for offering training switches. Additionally these mechanisms are also important in the reduction of dam reserves capacity, bridge hydraulics, prediction of morphological changes of river and the other structures which are built inline or laterally in the rivers. Sediment transport rate is dependent on various variables such as physiographic characteristics of river basin, bed and flood plain materials of river, stream power and hydraulic characteristics of river. Since the types of erosional and sedimentation processes in bed and bank of rivers are different therefore it is needed to exhibit the type and rate of mentioned mechanisms for training activities. The location of field study QarranquRiver is one of main branches of QizoulozanRiver which is sourced from SahandMountain in east Azarbayjan province of Iran. This river collects other floods of basin in its path and other rivers like KalaganChay, SaraskandChay, ShorChay,QalaJougChay, ShaharChay and AydoghmoushChayareconnected to it in its path towards downstream of basin. Finally, at the outletof basin after collecting other subsidiary floods in vicinity of Mianeh town, it connects to the QizoulOzanRiver. The total area of basin is 821 square kilometers and the length of Main River is 155 kilometers. In the Fig. 1 the location of field study showed at the East Azarbayjan province of Iran (Qarranqu river report, 2011).

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Intl. Res. J. Appl. Basic. Sci. Vol., 4 (11), 3582-3591, 2013

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Figure 1. Location of field study in and East Azarbayjan provinceof Iran

Introducing of reaches of Qarranqu River In this study, only 24 kilometers of river selected for modeling and field survey which is divided to 3 reaches. First reach located between downstream of Sahand Dam to junction of Kalgan river. Second reach is confined between Kalgan junction to junction of Shorchay and the third stream located between Shorchay junction and Khorasanak rail station. Figs of 2, 3 and 4 are the satellite images of mentioned reaches (Qarranqu river report, 2011).

Figure 2. First study reach from UTM of X=667695 , Y=4141997 to X=676430, Y=4142270


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Figure 3. Second study reach from UTM of X=676430 , Y=4142270 to X=681772, Y= 4139651

Figure 4. 3rd study reach from UTM of X=681772, Y=4139651 to X=687714, Y=4138947

MATERIALS AND METHODS Determination of erosional and depositional reaches using sediment transport model Using of mathematical models is a favorable method for estimation of transport rate through the river. These models are capable to simulate changes in bed and bank elevation during floods in various seasons of year. Since determination of transport rate and morphological changes are very important, use of mathematical models are necessary here. There are different models in sediment transport studies such as HEC-RAS 4.1 ،GSTARS2 ،SEDFLOW ،MIKE11 ،MOBED ،FLUVIALand TABS-2. Some of them become Commercial and were used several times in different projects around the world. In Table 1, characteristics of mentioned models and the advantages of them indicated(Guide Line for Erosion and Sedimentation Studies, 2007). Because of capability, background and accessibility in Iran, the HEC-RAS4.1 model which is developed by US Army Corps of engineersis used in this study. It uses direct step by step method for calculation of water surface profile and for calculating of sediment transport rate,it uses number ofsemi theoreticaland empirical methods.

RESULTS AND DISCUSSION

The sediment transport results of model For transport simulation, after consulting with other engineers and referring to the background of these type studies in Iran, it was decided to use discharges with return period of 25 year. Also in model simulation the Laursen transport relation with Toffaleti fall velocity equation were usedon the base of study of Akbari et al. (2010). Akbarzadeh et al. (2010), in their research on sediment trapping of dam reservoir also used from Toffaleti fall velocity equation and found favorable results. The maximum erosion depth along the river was imposed 5m and any minimum erosion depth was not imposed to the model. Also all width of cross section imagined to be erosional. One of important factors in transport formulas is to enter bed gradation carefully. In this study sampling and sieve gradation from river bed material accomplished and the results entered to the model.All of available sediment


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boundary conditions were rating curves therefore tried to enter them into the model in four sections along this river. Ultimately a plan designed for transport simulation with one geometry file, one quasi unsteady file, one sediment data file and the flood forced to river with 7 days duration. After model running different types of outputs in tabular and graphical moods gained and the propagation of flood along the river plan and cross sections exhibited. In addition there are some other indices for estimation of intensity of erosion or aggradation along the river such as shear stress, flow velocity and mass changes. By precision to their variation and magnitudes a hydraulic engineer can say which reach is risky to sedimentation or erosion.

Table 1. Characteristics of available sediment transport models and their advantages

Model name HEC-RAS GSTARS2 MOBED SEFLOW MIKE11

Dimension of model 1D Semi 2D 1D 1D 1D

Type of flow steady unsteady Quasi unsteady

Steady Quasi unsteady

unsteady

unsteady

steady unsteady

Flow regime subcritical supercritical mixed

subcritical supercritical

subcritical subcritical subcritical supercritical

Sediment particle type Cohesion lesscohesive

Cohesion lesscohesive

Cohesion less Cohesion less Cohesion lesscohesive

Number of available methods in model

7 11 1 3 5

Capability for simulation of effects of hydraulic structures

y y y y y

The Country which model is developed in it

America America Canada Nederland Denmark

Steps for simulation of Qarranqu river in HEC-RAS model is outlined as below: Preparation of river plan and it’s main and sub main branches Surveying of cross sections and hydraulic structures in the river Preparations of input file and input data Collection of discharge or other types of flow data Model calibration Interpretation of results Since the digital maps were existed from bed and banks of river with scale of 1/1000 and the GIS modeling software like ARC-GIS was accessible, for creation of cross section information, the connection between HEC-RAS model and ARC-GIS was done using HEC-GEORAS which is developed by US army corps of engineers also. Sediment Modeling using HEC-RAS Sediment transport modeling is notoriously difficult. The data utilized to predict bed change is fundamentally uncertain and the theory employed is empirical and highly sensitive to a wide array of physical variables. However, with good data, a skilled modeler can utilize a calibrated sediment model to predict regional, long term trends that can inform planning decisions and can be used to evaluate project alternatives(Hydraulic Reference Manual of Hec-Ras,2010). Quasi-Unsteady Flow Before HEC-RAS can compute the sediment transport, the river hydraulics must first be determined. The quasi-unsteady flow assumption approximates a continuous hydrograph with a series of discrete steady flow profiles. For each record in the flow series, flow remains constant over a specified time window for transport(Hydraulic Reference Manual of Hec-Ras,2010). Sediment Continuity The HEC-RAS sediment routing routines solve the sediment continuity equation also known as the Exner equation (1):

�1 − ��

��=

��

�� (1)

Where: �: Channel width, �: Channel elevation, ��: Active layer porosity, �: Time, �: Distance, Q�: Transport sediment load.

This equation simply states that the change of sediment volume in a control volume (e.g. aggradation or degradation) is equal to the difference between the inflowing and outflowing loads (Fig.5).


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The sediment continuity equation is solved by computing a sediment transport capacity through the control volume associated with each cross section. This capacity is compared to the sediment supply entering the control volume. If capacity is greater than supply there is a sediment deficit which is satisfied by eroding bed sediments. If supply exceeds capacity there is a sediment surplus causing material to deposit(Hydraulic Reference Manual of Hec-Ras,2010).

Figure 5. Schematic of the control volume used by Hec –Ras for sediment calculation(Hydraulic Reference Manual of Hec-Ras,2010).

Computing Transport Capacity The right hand side of the continuity equation is the sediment gradient across the control volume comparing the sediment inflow with the sediment outflow. Sediment inflow is simply the sediment entering the control volume from the upstream control volume(s) and any local sources (lateral sediment inflows). The maximum amount of sediment that can leave the control volume, however, is a function of the amount of sediment that the water can move. This is referred to as the sediment transport capacity, and it is computed for each control volume for each bed mixing time step(Hydraulic Reference Manual of Hec-Ras,2010). Sediment transport results are strongly dependent on whichtransport function is selected. The range of assumptions, hydraulic conditions and grain sizes for which each method was developed should be reviewed carefully and then the method should be selected(User’s Manual of Hec-Ras,2010). The locations for discharge changes in Qarranquriver model For hydraulic and sediment transport simulation of river, hydrological study is needed. Since this study is accomplished previously.Therefore the locations for discharge changes and the magnitude of themare indicated as Table. 2.

Table 2. The location and magnitudes of discharge changes with different return periods (cms) Location of discharge changes

Location of cross section for discharge change (m) in Hec-RAS

Return period (year)

2 5 10 25 50 100 200 Before connection ofKalaganchay

23988-13988 64.4 105 135.2 170.6 203.5 248.6 288.5

After connection of Kalaganchay

13788 87.3 142.2 183.3 231.3 275.8 336.9 391

After connection of Shorchay

5600 103.1 168.1 216.6 273.3 325.9 398.1 462

After connection of Saraskandchay

2200 112 182.5 235.1 296.7 353.8 432.2 501.6

Figs.6 and 7 show variation of flow velocity and bed shear stress along the river during mentioned flood.


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Increase in both of them consequences to erosion and decrease of them results tosedimentation of river. The maximum computed flow velocity is about 3 m/s with 27 pa shear stress. But an average computed velocity is about 1.3 m/s with 8 pa shear stress. As is found, the maximum risky position in QarranquRiver is the zone around Railway Bridge which because of decrease in river width, the magnitude of velocity and shear stress increased and dominant scouring imposed to bridge piers. Additionally in this position there is another entrance flood from ShorchayRiver which enhanced sedimentation in this junction. These mixed effects of scouring and sedimentation shows the necessity of training works there.

Figure 6. Variation of flow velocity during flood with return period of 25 year along river

Figure 7. Variation of shear stress during flood with return period of 25 year along river The Figs. 8and9are the samples of plan variation in flow velocity and flood propagation along the river. By precision to these Figs it is obvious that in the regions with wide flood propagation the training works are necessary

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and establishment of any installations needs to training affairs. As is illustrated in Fig. 9, the specified railway bridge zone has maximum velocity magnitudes resulting maximum scouring around it.

Figure 8.Flood propagation and variation of flow velocityin the zone upstream of autobahn intersection with river

Figure 9.Flood propagation and variation of flow velocityaround Railway Bridge

Figure10 shows intermittent variation in mass changes in both positive and negative direction along river which exhibits intermittent happening of both erosional and depositional processessuch as during flood in some cross sections firstly degradation happens and then the state changes to aggradation.

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Figure 10.Mass changes during flood with return period of 25 year along the river

Figure11 shows the magnitudes of bed level changes in Qarranquriver during flood. As is illustrated, the intermittent occurrences of erosion and sedimentation are observed in all reaches of the river. The maximum depth of erosion in these reaches is about 57cm and the maximum deposition is about 10cm in wide regions of river. As is found, alongall of three reaches depositional activities are dominant.

Figure 11.Bed level variation (cm) during flood with return period of 25 year Observed general erosional and sedimentation actions in the river reaches During floods, the bed and bank material of river erodes and general erosion happens but it is obvious that the decreasing of bed elevation in mentioned condition is temporal. And by changes in hydraulic conditions of river, sedimentation of bed and bank happens. This phenomenon is also called general sedimentation. Totally the occurrence of flood causes general erosion in upstream and general deposition in downstream of river reaches. Sometimes both of themhappen during a one flood intermittently (Guide Line for Erosion and Sedimentation Studies, 2007).

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As itwas observed in field survey, at downstream of river connection with Tabriz-Zanjan Autobahn, there are general depositional regions because of large width of river which causes in decrease of flow velocity and flood distribution (Figure12).

Figure 12. The general sedimentation zone at downstream of Autobahn, located in UTM of X=680303, Y=4142346

Local deposition and scour Local scour always happens around bridge piers, river bends, levee foundation and downstream of structures and obstructions which is built in the river. Normally the height of local scour is more than general erosion therefore dimensions of scour hole are very important in the structure stability. Figs. 13 and 14 shows the samples of local scour in foundation of training wall and laterally junction to mentioned river respectively.

Figure 13. The local scour zone at the foundation of

training wall

Figure 14. The local scour zone at river junction

Local sedimentation mostly occurs inside of river bends, river junctions, upstream of bridges, diversion dams or other hydraulic structures. Because of meander nature of Qarranqu river, local sedimentation observed in most length of river creating some problems in flow intakes. By surveying along river, it was observed that there is some trained reaches by levee and groyen. Some of these groyens is built recently and the effect of deposition and scouring around them is not evident yet. Deposited islands are one of usual bed form in gravel Bed Rivers that is generated by effect of sedimentation in middle of river cross section and is observed in some reaches. Generally it could be mention that because of existence of density currents during the floods in this river, potential of risky local deposition upstream of old bridges exists but the most important disturbing action in the bed and bank of Qarranqu river is sand and gravel mining. This action disturbs the hydraulics and morphological process of river and caused deposition/erosion in some reaches (Guide Line for Erosion and Sedimentation Studies, 2007).


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In this river most of erosional and depositional processes could be observed but the erosional processes are dominant. In some reaches of river when the discharge of river decreases, the flow concentrates to small channels inside the river bed therefore braided mood of river could be observed. Another notable observation was the creation of new gardens along the river bed by farmers which imposes disturbances to river hydraulic and effected on sedimentaryprocesses of river. Some customaryintakes are also built by farmers of river vicinity which become out of use because of sedimentation and erosional processes of disturbing factors in up and downstream of river. As the erosional processes increases in the river, the water surface elevation decreases and the water supplying intakes gets out of use. On the other hand by deposition at entrance region of intake, it gets useless again.

CONCLUSION HEC-RAS is integratedmulti-purposingsoftware package which extended for use in hydraulically and environmentally aspects of river system. The simulation of flow and hydraulic structures were used previously in rivers of East Azarbayjan Province but sediment transport simulation was not accomplished in the rivers of mentioned areaby this model yet. The coupled simulation was accomplished with Hec-Ras, Hec- GeoRas and ARC GIS software. Due to the previous investigations on different available empirical and semi theoretical transport equation, the Laursen transport relationship combined with Toffaleti fall velocity equation were used.It was found that the general trend of river in sedimentaryactivities could be interpreted with model but real magnitude and rate of it is highly dependent to selection of transport formula. Alsothe mass change results showed an intermittent variation in bed changes in both positive and negative directions which reply intermittent changes in both erosional and depositional processes but as is found by model results and field survey, depositional activities are dominant in study reaches of river.

REFERENCES Akbari M, Maghrebi M, Tarom.2010. “The investigation on combination of different sediment transport relationships with fall velocity formula for

prediction of bedform changes in the rivers”5th National Congress of civil engineering, Semnan, Iran. Akbarzade N, Goreishi SH, Majdzade MR. 2010. “The investigation on sediment trapping of ShahidAbbaspourdam using empirical relationships

and Hec-Ras model”5th National Congress of civil engineering, Semnan, Iran Department of water engineeringstandards.2007. “Guide Line for Erosion and Sedimentation Studies in River Training” S.N: 383, Tehran, Iran. Iranian Water Resources Association.2011.“Erosional and depositional processes of Qarranqu river”, East Azarbayjan Water Resources

Association, Tabriz, Iran. US Army Corps of Engineers.2010.“Hydraulic Reference Manual of Hec-Ras, 4.1 Version” Hydrologic Engineering Center (HEC), 609 Second

Street, Davis, CA 95616-4687. US Army Corps of Engineers.2010.“User’s Manual of Hec-Ras, 4.1 Version” Hydrologic Engineering Center(HEC), 609 Second Street, Davis,

CA 95616-4687.

SedimentaryStudy of QarranquRiver Using Hec-Ras - · PDF fileIntl. Res. J. Appl. Basic. Sci....

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