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1. The formula of Engelund and Hansen can be written for transport without pores as C u s 0 054 gAD3 05 0 05 E JEC A Da in which us shear velocity u Ag C m s Dso median grain size of bed material m UNESCO IHE frr Institute for Water Education SOBEK DELFT HYDRAULICS Engelund and Hansen is valid for situations in which w 1 0 19 lt Dso lt 0 93 mm and 0 07 lt 0 lt 6 in which is the fall velocity The formula of Meyer Peter and M ller is defined as s 8 D gA u0 0 047 in which D mean grain size of bed m u tipple factor C Coo Coo grain roughness 18 log 124 Doo It is valid for situations in which w a gt 1 D gt 0 4 mm and u0 lt 0 2 To obtain the sediment transport rate including pores it is necessary to multiply the equations above with a factor 1 1 2 in which e is the porosity of the bed in the order of 0 4 Output of sediment transport rates from SOBEK RE is presented as transport including pores e Bed level For the bed level the sediment transport balance in SOBEK is used for the total cross section 1A oe l e amp in which A area of cross section m S sediment transport through a cross section m s E fraction of potes For a constant width this equation reduces to l e Y amp in which 2 bed level m D sediment transport per unit width excluding pore
2. 1 en k 5 no measures e Compute the morphological behaviour with bifurcation relationships in which amp equals 5 reference setting and 1 Compare the results Side channel and dredging separately use k 5 e Change the SOBEK input to compute the effects of these measutes e Can you explain the short and long term effects of both measures separately e Change the locations of the measures in upstream and downstream direction What is the effect of the location on the morphological behaviour 15 UNESCO IHE frr Institute for Water Education SOBEK DELFT HYDRAULICS Both measures simultaneously use k 5 e Simulate the morphological behaviour for both measures simultaneously Use the settings of the locations as given in Table 2 e What is your advice about the morphological effects e Where would you locate the side channel Why e Assume that you get more money to do some extra research What would you investigate to obtain more reliable results het 6 62 m he2 6 36 m z 1 38 m z 6 36 le2 9 96 10 5 j Z 1 64 m lei 1 104 Ls 50 000 m i 11250000m Branch 3 he1 6 62 m he3 9 54 m z 1 64m i1 1 104 z 9 54 m 2 4 56m ie3 9 96105 16
3. SOBEK RE exercises Handout February 2007 UNESCO IHE frr Institute for Water Education SOBEK DELFT HYDRAULICS Chapter 1 Introduction 1 1 Introduction This is the user manual for the exercises of the River Systems amp River Dynamics Module 5 course at the Unesco IHE The main goal of these exercises is to get experience with morphological modelling The one dimensional SOBEK RE modelling system is used for this exercise This system has been developed by WL Delft Hydraulics and Rijkswaterstaat RIZA and is used for understanding and predicting river behaviour More information can be found at www sobek nl Note this exetcise has been designed and applied at the Delft University of Technology part of the course CT5311 on River Dynamics 1 2 Contents Chapter 2 gives a short introduction into SOBEK RE The set up of a new model is discussed in Chapter 3 This knowledge is needed for both exercises The two exercises are presented in Chapters 4 and 5 respectively The first one Local shoal can be considered as a basic introduction to the modelling system and the type of morphological processes that are reproduced You have to do all model steps bathymetry boundaries runs interpretation of the results etc The second exercise Bifurcation is more complex The schematisation of this exercise will be made available to you You have to analyse the effects of management strategies on the morphological behavi
4. 2 2 9 ga Hs soo 0 2 a xX A ox CRA in which Q discharge m s t time s x distance m dg Boussinesq coefficient A cross section with flow m A total cross section m g acceleration due to gravity m s h water level m UNESCO IHE fr Institute for Water Education SOBEK DELFT HYDRAULICS C Ch zy coefficient m 2 s R hydraulic radius m wW flow width m Note that in a situation with steady uniform flow the water depth approaches the normal depth value The normal depth follows from equation 2 by eliminating the accelaration and convection terms and replacing the surface slope 0 0x by the bed slope m m 3 2 W C i n The flow velocity z then follows from the continuity equation Q W ubs e Sediment transport A sediment transport formula can be selected for instance Engelund Hansen or Meyer Peter M ller Often sediment transport formulas can be rewritten as a power law of the flow velocity s au 3 in which 5 sediment transport per unit width excluding pores m s coefficient m gt s exponent representing the degree of nonlinearity current velocity m s a b u In transport formulas in SOBEK the Shields parameter is often the governing parameter It is defined as 2 a nm C AD AD in which D characteristic grain size of bed material m A relative density of sediment for sand A 1 65 0 Shields parameter
5. Sobek Case Manager Figure 1 Graphical User Interface of SOBEK RE e SOBEK RIVER is the new version of SOBEK capable of simulating 1D channel flow and 2D flooding It is part of the new product line of SOBEK which integrates all modules in a GIS environment Although it is more user friendly and more flexible than the SOBEK RE it does not yet contain an easy to use morphological module Therefore SOBEK RE is chosen as tool for this exercise UNESCO IHE fr Institute for Water Education 1e 13 DELFT HYDRAULICS ScaNetter Delft Hydraulics network ntw E jgix SF Slo Edt view Select Options Tools Help m neg QQxOR NES s mer v Metwoi Cross sections Type Y Z Profile z Define dimensions Cross section 2001 114020110 14 Li 500 Edit Table Use Ground L a E Uee Bruni Layer Edi Serene oniSuface id T d a Figure 2 Graphical User Interface of SOBEK RIVER GIS based RR Link 2 2 Hardware Sobek can be used on a PC with MS Windows For normal applications SOBEK needs at least a Pentium II processor or higher The PC version can only be used with a hardware key Unauthorized use is not possible 2 3 Equations e Water motion In Sobek the one dimensional mass balance and momentum balance for water motion are solved Without wind and density differences these equations read t 2 zs 0 1 2 2
6. conditions Specify the boundary conditions for water flow and morphology You can also specify lateral discharges dredging etc Although a river without tidal influence only needs a condition for the bed level or the sediment transport at the inflow boundary SOBEK also requires a boundary condition at the outflow boundaries Set the sediment transport rate at this boundary at zero e Initial Conditions Specify initial conditions and grain sizes Note that if a sediment transport formula is selected see later SOBEK will only ask for the grain size required by that particular formula Otherwise all grain sizes Dss Dso Dm and Doo are required 3 2 5 Numerical grid To generate a grid with constant mesh size it is necessary to specify the grid size distance and generate a grid 3 2 6 Runtime data Time Parameters Specify the begin and end time note the format and the time step UNESCO IHE Tr Institute for Water Education ie 2144 DELFT HYDRAULICS Numerical Parameters Change the calculation mode into Steady for quasi steady simulations F x F t reports Specify the parameters and time steps for your output If you change the simulation time or computational time step you should probably also change the output time step etc The output time step indicates the number of computational time steps after which output is written to file and is therefore not ex
7. in the near future S he asks your advice for this river problem 4 2 Information The situation after the landslide is as follows longitudinal bed level profile The sand of the shoal is equal to the sand of the rest of the river bed Discharge Q 1000 m s Width B 200m Slope i 104 Ch zy roughness C 50 m 2 s Grain size D50 0 2 mm wss0 0 04 m s 11 UNESCO IHE fr Institute for Water Education ie 2144 DELFT HYDRAULICS 4 3 Analytical exercises e Calculate the equilbrium water depth and the flow velocity in the undisturbed river section e Choose a transport formula Engelund Hansen of Meyer Peter M ller and give a motivation Calculate the annual sediment load s m s Compute the propagation velocity of a bed disturbance Choose the spatial step Ax Choose the time step Az Choose the simulation period Information in the the book Principles of River Engineering Jansen et al 1979 4 4 Simulations with SOBEK Simulate the problem with the SOBEK software 4 5 Exercises e How many equations does SOBEK solve dynamically e Which model variables are computed dynamically in SOBEK e Which initial and boundary conditions are needed for your simulation e Draw the propagation velocity of the top of the shoal as a function of time Is the numerical propagation velocity equal to the an
8. alytical propagation velocity Why e Does the shape of the shoal change in time Why e Simulate the same problem for median grain sizes of 0 4 mm and 0 1 mm twice and half the reference value Use the same transport formula What is the sensitivity of the propagation velocity of the shoal when you increase or decrease the median grain size Can you explain this by using the transport formula 12 Lake with constant water level Chapter 5 5 1 Problem definition Branch 2 UNESCO IHE frr Institute for Water Education Bifurcation Branch 1 Tie ae arae Pec Optional side channel River discharge x A river splits into two branches before debouching into a lake with a constant water level In this river system two types of measures are being considered The first type regards four options of dredging to improve navigation either by one time deepening options B1 and B2 or by continuous sediment withdrawal options B3 and B4 The second type of measures regards four options of side channels for purposes of nature rehabilitation It is assumed that the side channels convey only water and do not extract any sediment from the main river All options of dredging and side channels are summarized in Table 1 Table 1 Dredging D1 one time deepening in upper Branch 2 1 m lowering of bed level over reach between 0 and 25 km from bifurcation D2 one time deepening in lower Branch 2 1 m lowering of bed level ov
9. e from the lowest point in the CfOSS section Define the cross section of the river Start with the level width table by clicking on tabulated see Figure 2 e lt CrossSections gt cross section location and height Define the location and the reference level of the cross section Determine first how many locations must be given and if you would use a slope slope is only necessaty if SOBEK cannot determine the slope from interpolation between two cross sections on a branch The reference level is used to determine the height of a cross section relative to a reference level only if the height had not been set yet relative to this reference in descriptions gt Each river branch must have at least one cross section at a certain distance from the begin node with a specified height More than one cross section should be defined in a river branch if the cross sections are not uniform or if the slope is not uniform see figure 4 UNESCO IHE frr Institute for Water Education SOBEK DELFT HYDRAULICS R Cross section 1 z axis Cross section 2 Zeross1 Zeross2 Ynodel Reference level x ax z 0 Figure 4 Definition of cross sections 3 2 3 Friction Define the roughness predictor Give values for flow and reverse flow Although the river flow in a situation without tidal influence has always the same direction the roughness must be given for both directions 3 2 4 Conditions e Boundary
10. er reach between 25 and 50 km from bifurcation D3 continuous sediment withdrawal from upper Branch 3 0 001 m3 s at 5 km from bifurcation D4 Continuous sediment withdrawal from middle part of Branch 3 0 001 m3 s at 15 km from bifurcation Options of dredging and side channels Side channel 51 100 ni s discharge from Branch 2 teach between 10 and 20 km from bifurcation 52 150 m s discharge from Branch 2 teach between 20 and 30 km from bifurcation 53 200 m s discharge from Branch 3 teach between 5 and 15 km from bifurcation 54 100 m s discharge from Branch 3 teach between 15 and 25 km from bifurcation As a tivet engineer you are asked to advise about the short term effects of these measures fitst weeks after implementation as well as the long term morphological effects 50 year 13 UNESCO IHE Tr Institute for Water Education SOBEK DELFT HYDRAULICS You only need to analyse one combination of a dredging option D and a side channel option S Please select two options from Table 1 5 2 Data The model is already available at your computer The input has been based on the data and calculations below Data B 300m Li 50 km ij 1 10 C 50 m 2 s B2 150m La 50 km C2 50 m 2 s B5 100 m Ls 50 km C3 50 m 2 s At the upstream boundary the discharge is constant and equal to 2500 m s The median grain size is equal to 0 3 mm for the enti
11. our of the river 1 3 Information For questions please contact e dr ir Kees Sloff WL Delft Hydraulics phone 015 2858585 kees sloff wldelft nl UNESCO IHE Institute for Water Education DELFT HYDRAULICS Chapter 2 Description of SOBEK 2 1 Introduction SOBEK is a one dimensional modelling system for open channel networks It can be used to simulate unsteady and steady flow uniform and graded sediment transport morphology salt intrusion and water quality SOBEK is developed by WL DELFT HYDRAULICS and Rijkswaterstaat RIZA Rijksinstituut voor Zoetwaterbeheer en Afvalwaterbehandeling in The Netherlands Presently there are two versions for river applications e SOBEK RE the original version to be used for this SOBEK Exercise in which RE refers to Rivers and Estuaries This version was developed in the period between 1995 and 2000 and temained unaltered since then SOBEK RE is still used for the morphological model but will be replaced in the future by SOBEK RIVER Eie View Operations Help Edit View Layer 2 Topography Cross Sections Structures Friction Conditions Initial Conditions Meteo Data Dispersion Grid Definition Run Time Data Transport Formula 67 Reading Transport layer file lt C SOBEK MODEL NEWTUTOR SBK WORK DEFTRN 1 gt 68 Model Sobek 2 x style read No unrecoverable errors while parsing the model input 69 Composing model for display 70 Done
12. pressed in a time unit such as hours 3 2 7 Transport formula Choose a sediment transport formula which is suitable for your problem 3 2 8 Validation Once all the input has been specified the model input can be validated by using Operations and Validate model If all data are correct you can leave the Model schematisation and go to Hydraulic computation 3 3 Hydraulic computation Start the simulation in the box Hydraulic computation When an error occuts go back to Model schematisation to check your input When the computation does not give error messages go to Hydraulic Results to interpret the numerical results 3 4 Hydraulic results The results of the computations can be visualized by clicking the box Hydraulic results First select an output file e g the flow output or the morphology output Then make graphs of the most important variables e g the bed level development and the current velocity The parameters can be plotted in time as well as space The graphs can be printed or copied to other applications 10 UNESCO IHE frr Institute for Water Education ie 2144 DELFT HYDRAULICS Chapter 4 Local shoal 4 1 Problem description An alluvial river section has a length of 10 km After heavy rains sand from a nearby hill slides down into the river and forms a local shoal This shoal makes navigation more difficult The river manager would like to know how this shoal will develop
13. re area The equilibrium situation for Branch 1 can be easily calculated from the parameter values given above Q Buh Bh CVRi 6 This gives 2 ha al 2 6 62 m BC Ri R 6 34 m Please recall that there are eight unknown variables downstream of the bifurcation four at each branch i e equilibrtum depth slope discharge and sediment transport rate Eight equations are needed to solve these variables They are given in Equations 7 to 14 below Water motion 11 Q B Ch Rhi 7 i Q B Ch Ri 8 14 UNESCO IHE Tr Institute for Water Education Sediment transport S B mC R2i2 9 S BymC R2 10 Continuity equations sediment transport discharge and water level Si S 58 11 Q 0 Q 12 i is 13 A bifurcation relationship or nodal point relation is needed for the sediment transport distribution at the bifurcation 4 2 2 14 5 B Q For a stable solution i e both branches open amp must be larger than z 3 Here amp 5 is used By iteration the solution can be found Table 2 Table 2 Solution of the bifurcation problem Parameter Branch 1 Branch 2 Branch 3 O m3 s 2500 1152 62 1347 38 S 102 m5 s 1 483 0 604 0 879 6 359 9 539 i 10 4 0 996 0 996 The equilibrium situation is illustrated on the last page of this manual Choose the grid size and the time step while considering the Courant conditions 5 3 Computations Bifurcation k
14. s m s For these balance equations de Vries 1965 has shown that small scale disturbances propagate in flow direction with a speed v following from the method of characteristics uw 1 Fr where y aide z ps5 and c in m s h in which b power of transport formula see equation 3 Fr Froude number z y gh UNESCO IHE frr Institute for Water Education Chapter 3 Model set up 3 1 Starting SOBEK Sobek has been installed on the network Start the SOBEK software and open a new project and save this project directly with a new name e g ex1 Then open the empty case and save this case with a new name e g ex1 You see three yellow boxes at the left hand side Model schematisation Hydraulic computation Hydraulic results These boxes can be entered by clicking on them Each box is discussed separately in the next subsections The other boxes on the screen are not used during these exercises 3 2 Model schematisation 3 2 1 Model attributes When building a new model go first to Model Attributes under File On this screen parts of SOBEK can be activitated for the current case For case Local shoal River Water Flow Sediment Transport and Morphology Besides the geographical area must be specified in this window Choose a sufficiently large area for your model Specify the Geographical Area of the river in X and Y coordinates Then the model schematisation itself sho
15. uld be specified in the Select Layer window at the right hand side The following parts are important for this exercise 3 2 2 Nodes branches and cross sections Mind the difference between nodes branches and cross sections e A node is only used for an internal bifurcation or confluence or an external boundary These nodes are defined in the horizontal plane and only have an x and y coordinate e Between two nodes a branch is defined It represents the actual river channel between bifurcations confluences or boundaries Many models consist of one branch only e Cross sections are defined to prescribe the varying bed levels and widths of the cross sectional profile along a branch or river UNESCO IHE fr Institute for Water Education SOBEK QN eee dp ecd DELFT HYDRAULICS e lt Topography gt Defining nodes and branches with these nodes and the branches the topography in the horizontal plane is defined see Figure 3 Nodes gt Specify the nodes of the river by giving a name and the coordinates in X and Y Branches gt Specify the branches of the river by giving a begin and end node Branch 1 Node1 0 0 Node 2 x1 Y1 X2 y2 Ynode4 Ynode2 y axis Ynodel X axis Xnodel Xnode4 Xnode3 Figure 3 Definitions of nodes and branches Thereafter the cross section must be defined The definition is split into two parts e lt Definitions gt cross section shape width versus distanc

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