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MIKE FLOOD 1D-2D MODELLING

1. 10 20 25 30 15 M21 Cells j Figure 38 Floodplain Demonstration Diagram of MIKE FLOOD Links The upstream discharge hydrographs for the river and tributary and the downstream water level boundary condition which is tidal are shown below Upstream Discharge LU DU LEN Bud Du c UL LOL LENE DIEU LU LO DE ED ul 2000 08 23 Wi 05 25 Lt 06 30 Oa Figure 39 Floodplain Demonstration Boundary Conditions Model results showing water surface contours and velocity vectors near the peak of the flood event are presented in Figure 40 The time series plots in Figure 41 show water levels E MIKE FLOOD 1D 2D MODELLING immediately upstream and downstream of the road embankment and water level difference across the road embankment Also shown is discharge through the main river channel and through each culvert The model results show that for this particular flood event there is a peak 0 36 m head drop across the road embankment However the peak head drop at the peak of the flood is 0 16 m Peak discharge through the main river channel is 44 2 m s which is much higher than the culvert flows of 1 7 m s and 3 8 m s If this model was intended to investigate the hydraulic impacts of the road embankment a model of the existing situation no road could also be performed Comparing model results with and without the road embankment could give an indication of the likely impacts Also the perf
2. 1200 1200 1100 1100 1000 1000 I 900 900 800 800 700 700 600 600 Ib 500 H Water Depth m m 500 BE Above 0 6337 CO a Bo C 0 5193 0 5574 EN xo e 4 PS 04049 0 4431 A a E Ux EN 02906 0 3287 00 ee m CT 01762 0 2143 p m CT 01381 0 1762 0 0 09996 01381 Below 0 09998 Undefined value 0 200 400 600 0 200 400 600 01 01 03 01 20 00 Time step 8 of 100 01 01 03 16 40 00 Time step 10D of 100 Figure 15 Lateral Link Test 1 Results Water Depth and Velocity There is a distinct difference in flow patterns between the left and right basins Using MIKE VIEW look at the longitudinal profile of the upstream branch 44 DHI Water amp Environment EXAMPLES meter Water Level 1 1 2003 16 09 50 1 07 0 97 0 8 0 7 3 0 67 0 57 0 47 0 3 d 0 2 0 17 0 0 7 0 0 50 0 100 0 150 0 200 0 250 0 300 0 350 0 400 0 450 0 500 0 550 0 1 8 4 Water Level Ge 5 See 1 13 T 2 45 Ss Discharge n 3 s LATMe1 0 1100 600 0 650 0 700 0 750 0 800 0 850 0 900 0 950 0 1000 0 1050 0 1100 0 meter Figure 16 Lateral Link Test 1 Results Water Level and Flow Profile C 100 0 Similarly the lateral discharges can also be presented tick the Lateral Inflows button in the Additional Output Menu in HD Parameters me Water Level 1 1 2003 16 09 Water Level 45 1 27 o o o 4 g E 117 o ees p 1 0 T 0 97
3. The extrapolation factor is not applied for lateral links or for structure links For more information see the scientific documentation Hydrodynamics Standard Links 3 2 5 Add Replace Momentum Terms Mom _ Addi Replace Link type Location Fact Ext Fact Mom Structured This option is available for structure links e Ifthe momentum terms are replaced flow conditions calculated in MIKE 11 overwrite flow conditions in the MIKE 21 cell e H momentum terms are added the flow conditions calculated in MIKE 11 are added to the flow conditions in the MIKE 21 cell To illustrate consider a situation where a weir structure in MIKE 11 represents a road embankment in a MIKE 21 grid similar to that shown in Figure 3 The MIKE 11 structure flow would replace the MIKE 21 flow conditions Next consider the same situation except with a culvert located under a section of the road The culvert structure would be modelled in MIKE 11 in a separate branch to the weir and added to the flow conditions in the MIKE 21 cells As long as this culvert structure link is listed in the coupling file after the weir structure link both weir and culvert flow would be included in MIKE 2 Consider a third possibility where the road embankment is instead simulated as normal MIKE 21 cells This is a reasonable practice the upwinding facility automatically implemented in MIKE 2 has been shown to simulate weir flow well In this situation th
4. Bottom Left Cell Right Cell momentum equation of o left cell Water depth in right M21 cell linked to right M11 h point Water depth in left M21 cell linked to left M11 h point oO _ h q h M11 Branch Figure 7 Structure Link Diagram As shown the momentum equation from the MIKE 11 q point replaces the x momentum equation of the left MIKE 21 cell This is the only thing that is modified within MIKE 21 Note that the link is directional so the following situation can occur Valid locations of right top M21 link cell M11 momentum equation is distributed into the x and y momentum equations of left M21 cell Figure 8 Structure Link Directional Link 34 MIKE FLOOD 1D 2D MODELLING This second case raises the question of where the right side of the link should be located in MIKE 21 The main requirement is that the left or bottom MIKE 21 cell of the structure link must be adjacent to the right or top MIKE 21 cell Therefore valid locations are directly to the right directly above or one diagonal cell to the top right For example if the start of the structure link is at coordinates 10 12 valid locations for end of the link are 11 12 10 13 and 11 13 Choice of this location will depend upon which cell is considered to be best representative of the water level at that particular structure If the MIKE 11 momentum equation replaces the MIKE 21 momentum equation the implicit terms for t
5. Also contour plots of concentration in the MIKE 21 domain are shown at two instances LLLI JL LL H PD RDA B d x pollutant EN Above 93 33 P 85 67 93 33 LJ EJ E E 4 E E LT amp LT E E E EI a E E E Li LJ E E W Ld E i i a E E Ll LJ LJ LJ LJ LI L3 E E E E E R ET E E E LT il E E E E E LJ LJ P N k HE Below 0 IT undefined Value D 200 400 600 D 200 400 600 01 01 03 01 20 00 Time step 8 of 100 01 01 03 16 40 00 Time step 100 of 100 Figure 22 Lateral Link Test 1 Results Concentration pollutant HE Above PS 86 67 80 aon mw C co 7 CO m m 2 93 33 93 33 86 67 80 73 33 66 67 0 Undefined Value 8 3 48 E MIKE FLOOD 1D 2D MODELLING Lateral Link 2 This is a test to ensure that the structure equation in the lateral link is consistent with that in a standard MIKE 11 simulation The first test is a simple MIKE FLOOD model that has a MIKE 11 branch linked to a MIKE 21 basin using a standard link MIKE 11 Branch Weir Type 1 Standard Link 1000 600 600 400 200 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Figure 23 Lateral Link Test 2 Standard Link Layout The MIKE 11 branch is 1000 m long with a uniform cross section of width 500 and bed level 0 m The MIKE 21 basin is also 500 m wide with a bed level of 0 m and is 1000 m long Grid spacing is 100 m The MIKE 11 branch has a weir located near the
6. 0 5155 0 5318 06 6153 Haliw 06 Urdesried sale B127 300 EE 3r 2000 3r 2200 37 2400 37 2500 37 2800 373000 373200 CES 13 3000 Time step 27 ol 27 Figure 40 Floodplain Demonstration Water Surface and Velocities near peak of flood 60 DHI Water amp Environment EXAMPLES 1 4 Water Level Upstream of Road Max 1 22 1 2 Water Level Downstream of Road Max 1 06 1 06 at Peak U S Water Level e Head Drop Across Road Max 0 36 0 16 at Peak U S Water Level Water Level m o o o A o e ho 0 2 22 05 21 00 23 05 09 00 23 05 21 00 24 05 09 00 24 05 21 00 50 e Discharge in Main River Channel Max 45 i 44 2 43 9 at Peak U S Water Level 40 Discharge in Culvert 1 North Side Max gt 1 7 1 7 at Peak U S Water Level 35 d s Discharge in Culvert 2 South Side Max j 1 3 8 3 8 at Peak U S Water Level 30 25 20 Discharge m3 s 22 05 21 00 23 05 09 00 23 05 21 00 24 05 09 00 24 05 21 00 Figure 41 Floodplain Demonstration Results Water Levels and Flows at Road Embankment
7. 0 87 es jose Hi o iD o o 250 450 0 77 0 67 0 57 0 47 0 3 d 0 27 0 17 0 0 0 0 50 0 100 0 150 0 200 0 250 0 300 0 350 0 400 0 450 0 500 0 550 0 Lateral Inflow M21 650 LATM21 0 1100 600 0 650 0 700 0 Figure 17 Lateral Link Test 1 Results Lateral Flow Profile Last but not least a check of the mass in the system can be made by comparing the total discharge into the model the upstream inflow from the upstream branch with the discharge out of the model from the downstream branches As shown 100 m s enters from upstream Approximately 50 m s 49 96 m s through the left branch and 50 04 m s through the right flows out of each downstream branch m 3 s Discharge 4 0 2 0 F 0 0 2 0 4 0 Discharge nv 3 s o ire E E Q zd Q Te D F N KO m o e ro D be 750 0 800 0 850 0 900 0 950 0 1000 0 1050 0 1100 0 meter Time Series Discharge 10 07 95 0 90 0 7 85 0 80 0 75 07 70 0 65 0 60 0 55 0 50 0 45 0 00 00 00 1 1 2003 01 00 00 02 00 00 03 00 00 04 00 00 05 00 00 06 00 00 Figure 18 Lateral Link Test 1 Results Time Series of Discharge harge LATM21 25 00 LM21 475 00 zb RM21 475 00 MIKE FLOOD 1D 2D MODELLING For comparison the same setup has been done using M
8. 21 cell specified as a zero flow link in the x direction will have zero flow passing across the right side of the cell Similarly a zero flow link in the y direction will have zero flow passing across the top of the cell The zero flow links were developed to complement the lateral flow links To ensure that floodplain flow in MIKE 21 does not travel directly across a river to the opposite side of the floodplain without passing through MIKE 11 zero flow links are inserted to block MIKE 21 flows An alternative to using the zero flow links is to apply land cells which depending upon grid resolution may not be appropriate Another useful application of zero flow links is to represent narrow blockages on a floodplain such as roads and levees Rather than using a string of land cells a string of zero flow cells can be used Standard Link QH Extrapolation The standard link uses a predictor term that modifies flow from MIKE 11 This is required to establish a value in MIKE 21 that is consistent with the time centring differences in the MIKE 11 and MIKE 21 solutions The extrapolation factor controls this predictor An alternative method to this is the QH extrapolation standard link This link uses the implicit terms from MIKE 11 to produce a QH relationship through the link In this way the predictor from MIKE 11 is in fact the slope of the QH curve In practice there appears to be very little difference between the two standard link methods
9. E Lateral links can switch direction when the difference in water levels between MIKE 11 and MIKE 21 is similar To avoid this use the Depth Tolerance factor Using the highest HGH structure source type is usually the most convenient method This picks the highest resolution of points MIKE 21 cells or MIKE 11 h points then assigns bed levels using the highest values from the MIKE 21 cells and MIKE 11 points If available external input from a GIS could be used to extract more detailed bank line information To view the lateral flows in the MIKE 11 results file tick the Lateral Links option in the Additional Output menu of the HD Parameter File HD11 Structure Links The structure links are implicit This means that a simulation that uses these links will be more stable than the explicit links and simulations can be performed using longer timesteps In the structure links MIKE 11 lags one timestep behind MIKE 21 Thus the displayed value of flow in the q point of the MIKE 11 branch may not necessarily be the flow through the MIKE 21 cell It is recommended that for structure links the MIKE 21 results be interrogated rather than the MIKE 11 results A structure link entry is required for both the inlet location and the outlet location The locations of the locations must be defined as either Top Right or Bottom Left The Bottom Left cell is the one that will be modified in MIKE 21 depending on the direction of the l
10. It is possible that the QH extrapolation is marginally more stable however tests show that while results using this method remain stable at higher timesteps accuracy of the solution at these high timesteps rapidly deteriorates It is recommended that this link type be used with caution It may be useful in cases where the last q point in the MIKE 11 branch is a structure it is this situation where the extrapolation factor cannot be applied Finally note that this link type requires a land cell immediately behind the link cell to maintain stability Going Further The next generation of MIKE FLOOD will continue to improve and expand on the linkage and structure capabilities DHI Water amp Environment APPLICATION DETAILS E 3 APPLICATION DETAILS Any combination of links can be used in a MIKE FLOOD simulation All the information relating to the MIKE FLOOD links is contained in one file the coupling file file extension COUPLE The MIKEI1 and MIKE21 simulation files do not contain any information relating specifically to the links except for e A dummy source sink entry must be included in the MIKE21 setup if using MIKE FLOOD e A dummy water level boundary condition must be applied at each link point in MIKE 11 The exceptions are lateral links and zero flow links which do not need this The coupling file interface is arranged as shown MIKE FLOOD Definition Standard Structure Link Options Lat
11. Leg m u ef Zoe E 21550 xo TT sf Vui Sa LE u u E soi M TT ef Vases GH Estep L D L u a u ESCH Mede Cede Leg i ei u M ud KOD m1 Fg GH Een Leg Cat r mM SD teu lee Branmavi L ul SEI it ia ie Ce rn a SH Eum Lin T ei ee 46 n HS EE frak SA r ca D ipii MEE EE 2 2m m 2H 7 z ZX EL T 5 3001 l Le ig i f LE HOA 12 59 ai nuoto 13 29 AD DOC Figure 12 Standing Wave Test Results Water Level Profiles 2 MIKE FLOOD 1D 2D MODELLING While it is difficult to examine the individual curves the plots shown above demonstrate that the various link types are performing satisfactorily See the examples provided for further interrogation 42 DHI Water amp Environment EXAMPLES e ll 8 2 Lateral Link 1 This is a test to assess the performance of the lateral links and to illustrate their implementation The test represents an inflow channel with overtopping onto a broad flat basin or floodplain as shown Inflow Hydrograph An inflow hydrograph discharges into the upstream MIKE 11 river branch Flow spills over the banks of the river channel and into the MIKE 21 basins The left and right basins are separated by land Two downstream MIKE 11 branches are connected to the end of the left and right basins Water level boundary conditions are applied to the downstream branches A closed boundary is applied to the downstream end of the upstream river branch The MIKE 11 network
12. Notice that there is a slight variation in flow distributions in the laterally linked case the variations are shown by the velocity vectors in the link cells 50 E MIKE FLOOD 1D 2D MODELLING 1000 500 500 1000 1500 2000 01 01 90 20 20 00 Time step 100 of 100 Figure 27 Lateral Link Test 2 Results Standard Link 1000 500 500 1000 1500 2000 01 01 90 20 20 00 Time step 100 of 100 Figure 28 Lateral Link Test 2 Results Lateral Link DHI Water amp Environment 8 4 EXAMPLES e ll Flow Direction This test was initially designed to test links applied in a direction that is not aligned with the MIKE 21 grid However it evolved into a demonstration of all the link types available in MIKE FLOOD The test consists of a square MIKE 21 basin with a variety of MIKE 11 branches discharging flow into it The branches are aligned at different angles to the MIKE 21 grid and consist of standard and lateral links In the centre of the basin is a lateral link that drains the basin Using the zero flow links the bottom right corner has been isolated from the rest of the basin except for two structure links on each side The structure links are connected to 3 point MIKE 11 branches with a weir Some of the link cells in MIKE 21 are completely surrounded by wet cells Others have land cells or alternatively zero flow links inserted behind the link cells The MIKE 21 grid size is 10 m and the initial water level is 1 m A
13. column is bed level Table 2 Format of External QH File HQH file is a comment marker as many comment lines as desired 53 can be included in this file 0 0 SE 5 ig Line 1 Number of upstream levels rows nr and number 1 0 0 3 0 3 0 3 of downstream levels columns nc space delimited 2 0 0 4 0 5 0 7 Line 2 List of nc values of downstream levels space 3 0 0 9 1 9 2 9 delimited 5 0 10 0 20 0 50 0 i Line 3 onwards nr lines List of nc 1 values of upstream level then nc values of discharge space delimited Notes If QHTABLE levels are water level If QDTABLE levels are water depth If CELLTOCELL discharge is flow per unit width At present upstream and downstream changes depending upon flow direction This feature can be improved if considered useful contact DHI for more information DHI Water amp Environment 4 1 4 2 4 3 4 4 RUNNING MIKE FLOOD RECOMMENDED STEPS RUNNING MIKE FLOOD RECOMMENDED STEPS Errors and inconsistencies in a model setup will occur While every effort has been made to produce clear error messages it can be difficult to keep track of all components in the model setup To ensure that errors are minimised we recommend following a clear step by step procedure to develop and run MIKE FLOOD Define model layout A MIKE FLOOD model is often a compromise between model resolution grid size and computational time required for a simulation No
14. performed easily but it is still the modeller who decides how best to design the integrated model This manual will help you to make the decisions on how best to create a MIKE FLOOD simulation 6 DHI Water amp Environment GENERAL DESCRIPTION E 2 GENERAL DESCRIPTION At present there are six different types of MIKE FLOOD linkage available 2 1 Standard Link This is the standard linkage in MIKE FLOOD where one or more MIKE21 cells are linked to the end of a MIKEII branch This type of link is useful for connecting a detailed MIKE 21 grid into a broader MIKE 11 network or to connect an internal structure or feature inside a MIKE 21 grid The link is explicit see the scientific documentation for a full description Potential applications are shown Standard Link Connecting a detailed MII structure within a M21 grid m M E MII Be ha ec AE Work M Fi ne T em Standard Link Connecting a broad MII network to a detailed M21 Fre Figure 1 Application of Standard Links E MIKE FLOOD 1D 2D MODELLING 2 2 Lateral Link A lateral link allows a string of MIKE21 cells to be laterally linked to a given reach in MIKE 11 either a section of a branch or an entire branch Flow through the lateral link is calculated using a structure equation or a QH table This type of link is particularly useful for simulating overflow from a river channel onto a floodplain where flow over the river levee is calculated using a weir eq
15. the highest resolution The structure bed levels are the highest of the MIKE 11 bank markers and the MIKE 21 cells e EXT Information is read from an external ASCII file The HGH source type is the default 3 3 6 Depth Tolerance In a similar way to wetting and drying in MIKE 21 a lateral link can rapidly switch between being inactive zero flow to active flowing The depth tolerance factor is used to avoid this 3 3 7 Structure Coefficients Coefficients controlling flow through the link structure include the weir coefficient default 1 838 the weir exponent coefficient default 2 1 5 the Manning s n friction coefficient and the form loss coefficient Note that friction can be included in the weir equations see the scientific documentation for more information 20 E MIKE FLOOD 1D 2D MODELLING 3 3 8 External Files External Files Geometry OH Table geom txt Ea qhtab txt IL Il If the structure source is EXT an external file is specified If the structure type requires a QH table to be read a qh external file is specified The formats of both files are shown in Table 1 and Table 2 Table 1 Format of External Structure File External file from GIS is a comment marker as many comment lines as desired 4 can be included in this file 0 0 2 0 100 0 0 0 Line 1 Number of entries 500 0 0 0 Line 2 onwards column entries space delimited first 1000 0 2 0 column is chainage second
16. 1 with friction term included DHI Water amp Environment APPLICATION DETAILS e WEIR2H MIKE 11 Weir Formula 2 Honma with friction term included e OHTABLE A QH table is used read in from an external file Note that if using a CELLTOCELL method the Q in the QH table is the flow per unit width e QDTABLE A QH table is used except that water depth above the structure invert is used rather than water level This could be useful if using a CELLTOCELL method with different bed levels in each cell but similar flow characteristics This is read in from an external file 2 e FORMLOSS Standard velocity head form loss equation Ah G V SA g The form loss coefficient can include a friction component The WEIRI type is the default See the Scientific Documentation for more information 3 3 5 Structure Source The structure source determines where the structure geometry information comes from e MII Structure points are defined at each MIKE11 computation h point The cross section left or right bank markers marker 1 or marker 3 are extracted from the cross section database and used as the link structure bed levels Bank levels at h points without a cross section are interpolated e M21 Structure points are defined at each MIKE21 cell Bed levels from MIKE21 cells are used as the structure bed levels e HGH Structure points are defined at either each MIKE 11 computational h point or each MIKE 21 cell whichever has
17. 1s AC 0QC 2 av 9t Ox ox Ox where C is concentration D dispersion coefficient A cross sectional area K linear decay C the source sink concentration and q lateral inflow AKC C q For zero flow links no advection will occur across the link due to the zero flow specification and dispersion is turned off 7 6 36 MIKE FLOOD 1D 2D MODELLING Flow Distribution by Depth Flow is distributed according to the Chezy equation for resistance Q ACVRS where Q Flow A Area width depth 2 w h C Chezy coefficient R Hydraulic radius approx depth h and S slope Rearranging this equation gives Q whCh gt gy wos Thus proportionality can be derived between flow and water depth h O AE Flow is then distributed across a number n of MIKE 21 cells For each cell count i1 1 n the distributed flow Q is calculated from the total flow Qror hib Q Qro gt hib i l DHI Water amp Environment 7 7 SCIENTIFIC BACKGROUND LAA Inclusion of Friction Term in Weir Formulae 1 and 2 Honma The equation for the Weir Formula 1 is i 0 385 h Q wCh 1 5 1 where w width C weir coefficient 1 838 k exponential coefficient 1 5 h depth of water above weir level upstream Haus Hw and h depth of water above weir level downstream Has Hy This equation is actually a free overflow term wCh combined with a sc
18. F SE s HE SEES SEES SEEST TESTET TET TESTET TTT TTT M ea TEE TEE E a E TT EEN iit DEET TEE e a M ee r Pe o A EE EH ersten Water Level Gel o 400 200 200 400 600 Cross section X data meter Figure 33 Floodplain Flow Test Typical Cross section The total length is 10000 m The river has a uniform slope of 1 1000 the bed of the main river channel upstream is 10 m and the bed downstream is 0 m To each of these setups an upstream flow hydrograph is applied which has a peak discharge of 2000 m s A downstream water depth of 4 m is maintained 12 00 TE OUI XY DO DO OU 0400 oo 1200 15 00 1349 01 01 LIZ Figure 34 Floodplain Flow Test Upstream Hydrograph The water level at the upstream end of each of the four models is presented NI NI Vater Level MIKE FLOOD Water Level MIKE 11 Single Channel Water Level MIKE 11 th Link Channels Water Level MIKE 21 Water Level m ER o co c5 NI 10 1 01 08 00 1 01 12 00 1 01 16 00 1 01 20 00 2 01 00 00 2 01 04 00 2 01 08 00 2 01 12 00 2 01 16 00 2 01 20 00 Figure 35 Floodplain Flow Test Results Upstream Water Level Further the discharge at the downstream ends of each model is presented with the upstream hydrograph DHI Water amp Environment EXAMPLES e ll Discharge MIKE FLO
19. H Extrapolation link type e alOcell 1000 m wide setup of the same test case e a MIKE 11 model of the entire test no MIKE FLOOD link and e aMIKE 21 model of the entire test no MIKE FLOOD link The setup StandingWavew couple is as shown DHI Water amp Environment EXAMPLES e ll Standard Link 1 Cell Wide QH Extrap Link 1 Cell Wide Standard Link Ba 10 Cells Wide QH Extrap T ME d 10 Cells Wide 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 Figure 11 Standing Wave Test Layout 2 Thus size separate tests are included in this single MIKE FLOOD setup The results are shown as water level profiles at various timesteps H ger Depths mg Wali E ai ede Pi Crip IL var D EH SE ats id Ve Sexe iF uj u11 a jede aa I MFE F ut sd Ande GH Etat bes ve e Viale MS Car el Vive aes baw e SE PL M1 med Mat st MT ad vue GH Ear MEE DAH e iiia Mrt Ce Wide Seer mr Cui T m UE t 4 y Wa FL re b Web Cael teg ME rech een OH n 266 T WH MEE Ci at Cal rm Slender RUE SO uit Sume Dari Eid 1 ieee Dt Met ME EE zb z08 2M r 205 zm 204 2541 HM in LA 202 E E ETTE 308 F 3 L1 I z 0 43 2m E i E piii 18 EH EE un um Lai T tied EE H IR 200 i H IOC 2000 GO AD 500 Boo rrr mood NS FEST Dette DOS 119000 DOC Deo 1727 3CEDO DOG H ia Dep ry 35b Tu 1 s Voie GH Ets
20. IKE 11 For the MIKE 11 setup the left and right basins are represented using branches Flow from the upstream branch to the basins occurs through two additional branches with cross sections representing the bank levels The MIKE 11 test has been combined with the original MIKE FLOOD application see mf2 couple 1500 The MIKE 11 test has two branches representing lateral 1400 flow aligned equally at the centre of the upstream en branch Comparison of discharges from the downstream a branches for the MIKE FLOOD and MIKE 11 tests are um presented below 1000 B Lateral x Branches Im 3 s Time Series Discharge 2 re is d as weirs TEMA 47500 em RM11 475 00 500 400 301 A0 100 o id 100 42 WI ii E 1 1 2003 gi HE v NE v u JU EL BU SEU IAU Tau i i Figure 20 Lateral Link Test 1 Results Time Series of Figure 19 Lateral Link Test 1 Layout 2 Discharge 2 Both the MIKE FLOOD and MIKE 11 simulations preserve mass with the amount of flow leaving the system exactly the same as the amount entering However the MIKE FLOOD and MIKE 1 simulations each give different distributions between the left and right banks There are several possible reasons for this e MIKE FLOOD accounts for the water level gradient in the channel This increases the accuracy of overbank flow calculations e MIKE FLOOD calculates weir flow across each calc
21. IKE 11 and MIKE 21 The predictor assumes that the flow between the last two cross sections in MIKE 11 before the coupling is based on normal bed resistance flow e no structures If there is a structure in the previous q point before the coupling point set the extrapolation factor 0 or consider using a structure link Note that this may affect stability of the link MIKE FLOOD computes discharge from MIKE 11 and distributes it to the associated point s in MIKE 21 If the link in MIKE 21 consists of more points the discharge is distributed uniformly to all points If the depth distribution flag is used flow is distributed according to water depth in each individual cell If the time step in MIKE 11 is a multiple of the time step in MIKE 21 an interpolated discharge is transferred to MIKE 21 The discharge from MIKE 11 influences the continuity equation as well as the momentum equation The direction of the flow is derived from comparison of the orientation of the MIKE 21 grid and the direction of the MIKE 11 branch MIKE FLOOD computes the water level from the link point area in MIKE 21 and assigns it to the associated boundary point in MIKE 11 If the MIKE 21 link consists of more points the average value from these points is transferred to MIKE 11 In general more than one linked MIKE 21 grid point will tend to smooth and stabilise a coupling Lateral Links When performing initial tests with MIKE 11 with no MIKE FLOOD links do you ge
22. KE 11 boundary point Note that this is not necessarily the upstream chainage in the branch it may well be the downstream chainage the label US refers to lateral link specifications only The same boundary 14 E MIKE FLOOD 1D 2D MODELLING location should exist in the MIKE 11 boundary file bnd11 and be defined as a water level boundary in the initial MIKE 11 set up This boundary condition specification is only to maintain consistency between MIKE FLOOD and MIKE 11 it will be overwritten by information from the link during simulation Furthermore if performing an AD simulation then an open concentration boundary should be specified not the Time Series dependent option e If using a lateral link M11 river name is the MIKE 11 branch with the link US M11 chainage and DS M11 chainage define the upper and lower extents of the lateral link so all MIKE 11 calculation points between the specified chainages will be linked to MIKE 21 Unlike the standard links no further adjustments need to be made to the MIKE 11 boundary definitions e Forzero flow links no MIKE 11 information is required M11 River M11 Chainage M i Area name Ho us DS 8 branchi 10 000 D 1t 3 1 7 MIKE 21 Area Number This option is available for applications with nested MIKE 21 grids The default value for no nested grids is 1 3 1 8 MIKE 21 Coordinates There is a separate table available to enter a list of coordinates RE defining t
23. KE 11 network must be described in the same UTM metric grid as the MIKE 21 bathymetry file e The type of result data to display contours and or vectors is selected in Result Viewer Projects Active View Settings On line animation as well as production of videos can be done Time series can be extracted by using the time series button at the upper toolbar to the right Use double click on the left mouse button to select a point graphically and display the time series in a separate window Use Ctrl Left click to select more points graphically and display all the time series in a separate window by use Ctrl Double Left mouse click 6 6 1 24 MIKE FLOOD 1D 2D MODELLING TIPS AND TROUBLESHOOTING General Considerations File Layout MIKE FLOOD Release 2003 is designed so that all information relating to MIKE FLOOD is stored in the coupling file The MIKE 11 and MIKE 21 simulation files are standard which means that MIKE 11 and MIKE 21 can be run separately Initial Conditions To obtain a stable MIKE FLOOD simulation it is important that the hydraulic conditions are in dynamic equilibrium at the link point In simplest terms make sure that the initial water levels in MIKE 11 and MIKE 21 are the same Alternatively hotstart files in the MIKE 11 and the MIKE 21 setup could be used Boundaries MIKE FLOOD linkages in MIKE 21 do not necessarily need to be aligned with the MIKE 21 grid This is different to the restric
24. MIKE FLOOD 1D 2D MODELLING User Manual DHI Software 2003 MIKE FLOOD 1D 2D MODELLING DHI Water amp Environment Agern All 11 DK 2970 Hersholm Denmark Tel 45 4516 9200 Fax 45 4516 9292 E mail dhi dhi dk Web www dhi dk Latest Revision May 2003 MIKE FLOOD User Manual doc CFN DHI Water amp Environment CONTENTS CONTENTS 1 INTRODUCTION cinse nananana aT AEAN Heu Ka era aene reg 5 1 1 General Approach to Modelling with MIKE FLOOD 5 2 GENERAL DESCRIPTION eere rennen nennen nnne nnn nnn nnn 7 te Eet E lui 7 22 LAS En EE 8 29 EIERE nk mplielb ee ee 9 2 4 Zero Flow Link Gand 10 2 5 Standard Link QH Extrapolation ecce 10 2 0 COMO FURER ELE 10 3 APPLICATION DET AUS iiiicaicisecseccccceteacicedvesvetscdwateouasespeensestetcenietesaetiete 11 3d DEMIO a E a 12 Skt MIKE 2T FIENI ME ron EE 12 39 1 2 MIKE 11 File Name oo re t o o a heler 12 Selo NEE eege 12 SN MENS 13 Su SE OUP IAN TND Ea at ne ineo eN ED adem x Rn eh Rt deo oO Re 13 3 1 6 MIKE 11 River Name and Chainag ccccccccccsseeeeeeseeeeeeeeeeeeeens 13 31 7 MIKE 21 Area NUMBE EE 14 218 MIKE 21 Coordinates 25520 ES Ea ae 14 3 2 Options for Standard Structure Links eeeeeseeeeseeeeeeeeeene 15 Sie ENK Eege 15 32a dE m tmm 15 322 MEM enn NEE 15 sos UG ee dun ee eg 16 3 2 5 Add Replace
25. Momentum Terms ccccssececeeeeeceeeeeeseeeeeeeeeesaes 16 Ou Ree el Ur EE 17 DHI Water amp Environment i li E MIKE FLOOD 1D 2D MODELLING 3 2 7 Activation Depth Minimum and Maximum 17 3 9 Options for Lateral LINKS iti eos e econ beo ee 18 CPC MEE IV OC c 18 392 SIDS OR IAIV SL EE 18 J99 METRO WEE 18 994 GEERT Type ae eenegen 18 3390 3Slr ciufe SOUICE eneen een 19 330 Depi FoleratiGQ uii eet po Rao eater Ier eis Dat peti Rae 19 3 3 7 Structure Coefficients nennen nnn nnns 19 SEO E a e ERE LT UI 20 RUNNING MIKE FLOOD RECOMMENDED STEPS 21 Z1 3deunemodellayOUU 5e anti a SEES ESS ERE DEER RES 21 4 2 Setup and Run MIKE 11 Model 21 4 3 Setup and Run MIKE 21 Model 21 AA Setup MIKE TLEOODJ iuiisetitketeri EE 21 45 Run MIKE FLEOOD Simulation esensia Soest eu etae suo ta ue vade nur vanis ene 22 PRE AND POST PROCESSINQ 1 KEREN K KREE KREE n uuu 23 TIPS AND TROUBLESHOOTING 1 eee 24 6 1 General Considerations nennen nnn nnns 24 MEME el TEILS 25 68 Standard NI cO UR 26 P MEN E Eesbech 26 6 5 SIRUCTUNE LINKS enee 27 ob cHMECA Co FIOWLINKS NEU Tem 27 SCIENTIFIC BACKGROUND eee eee 29 7 1 Hydrodynamics Standard Links essere 29 7 2 Hydrodynamics Lateral Umke 30 DHI Water amp Environment CONTENTS LAA 7 3 Hydrodynamics Structure Links ccccseeceecsseeee
26. OD Discharge MIKE 11 Single Channel Discharge MIKE 11 ith Link Channels Discharge MIKE 21 Discharge Upstream CJ 2 o 3 ki E a 40 WU VM 1 01 08 00 1 01 12 00 1 01 16 00 1 01 20 00 2 01 00 00 2 01 04 00 2 01 08 00 2 01 12 00 2 01 16 00 Figure 36 Floodplain Flow Test Results Downstream Discharge For each test case the upstream water levels are reasonably consistent with the other However the MIKE 21 simulation predicts a higher water level suggesting more losses along the length of the model The downstream discharges are also reasonably consistent although again the MIKE 21 simulation and to a lesser extent the MIKE FLOOD simulation have a reduced more dampened discharge peak This again suggests more losses in the model A possible reason for this variation in model predictions between MIKE 11 and MIKE 21 could be due to wetting and drying in MIKE 21 8 7 58 E MIKE FLOOD 1D 2D MODELLING Floodplain Demonstration This example is available as a demonstration model to illustrate a real application of MIKE FLOOD The application consists of a flood simulation through a river system The area of interest is at a confluence with a tributary where a road embankment has been proposed Culverts under the road are located on each side of the river The river system is represented in MIKE 11 A MIKE 21 grid is inserted into the broader MIKE 2 network to represent floodplain flow as shown in Figur
27. This means that for the majority of MIKE FLOOD applications a constant eddy viscosity formulation should be applied For overland flow conditions it is unlikely that eddy viscosity will have a major effect on model predictions friction will dominate However for flow in and around structures the value of eddy viscosity can have a significant effect upon predictions Caution is advised in such cases Additional Options Additional options can be specified in the MIKE 21 parameter file In the couple file the entry M21 Run Info contains four variables e Link typeis 1 for MIKE 11 and 2 for MOUSE e Debug type is 0 for none and 1 2 or 3 for debug output If debug type 3 then only Courant number warnings are printed in the log file e M21 timestep factor is usually 1 DHI Water amp Environment 6 2 TIPS AND TROUBLESHOOTING e MIT ad conversion factor is usually 1 0 Incoming MIKE 11 AD concentrations are divided by this value in MIKE 21 The option M21 struc dirtol applies a tolerance to linkage directions This can be used to force flow directions in MIKE 21 to be either horizontal or vertical Stability The MIKE 11 and MIKE 21 manuals contain information on stability in numerical modelling The comments made are equally applicable for MIKE FLOOD Most issues relating to stability in MIKE FLOOD occur in the links themselves and in the wetting and drying in MIKE 21 In numerical solution of both is explicit and th
28. aling term for submergence that approaches 0 as h approaches h The equation for the Weir Formula 2 Honma is EPA Q wCh Ah GEN o 54c J h h The first equation is free overflow identical to Formula 1 with free overflow while the second is for submerged conditions Both equations are derived from the equation for form loss across a structure where 2 y nere 28 If a friction loss is added this becomes 2 Ah C4 F 2g where 2gLn F D 7 he Cr Friction coefficient L length of structure and n Manning s number Expanding w l1 28 vinh deg This equation is similar in form to Weir Formulae 1 and 2 for free overflow except that the weir coefficient is replaced 38 MIKE FLOOD 1D 2D MODELLING Assuming that the entrance exit losses G are the same a new weir coefficient C can be derived from the original coefficient C and the additional friction So the existing equations for weir flow calculations can be used except that the weir coefficient is modified according to This equation is applied to the weir calculations in the lateral link specifications DHI Water amp Environment EXAMPLES e ll 8 EXAMPLES The examples presented below are designed to test the operation of the new features of MIKE FLOOD and to demonstrate the use of these features Most are available with the DHI software release version 2003 in the Examples folder Oth
29. ayout The width of the basin is 100 m and the mean water depth is 2 0 m The bed resistance is C 50 mie An initial disturbance of the water surface is imposed corresponding to a sinusoidal variation of range 0 10 m The basin is described using MIKE FLOOD 4 km is described in MIKE 11 and 4 km is described in MIKE 21 In both models the longitudinal grid spacing is 100 m MIKE FLOOD simulates the transfer of mass as well as momentum between the 1D MIKE 11 model and the 2D MIKE 21 model The water level at different times after start of the simulation is depicted below MIKE 11 m MIKE 11 m MIKE 11 m rs MIKE 21 m MIKE 21 m MIKE 21 m Standing Wave Test Standing Wave Test Standing biu Test m o a N o a Water level m hv o e Water level m N o e o j Water level m co a co a Z TT irri rs i i at rrr rrr ret Ve Ae ie RE T I T4T13T711T a ae a ae ae a a a ae a a a a a a ee a a TTT a ae rT rt 0 2000 4000 6000 0 2000 4000 6000 0 2000 4000 6000 Distance m istance m istance m 01 01 90 12 00 00 000 01 01 90 12 23 20 000 01 01 90 14 53 20 000 Figure 10 Standing Wave Test Results Water Level Profiles The files required to setup and run this example are available These files take this example further than presented here with tests using e the standard link type e the Q
30. be important For lateral links try to make the structure resolution the same as or finer than the MIKE 11 dx and the MIKE 21 grid size the HGH structure source option is recommended Lateral links can switch direction when the difference in water levels between MIKE 11 and MIKE 21 is similar To avoid this use the depth tolerance factor Also consider using a friction coefficient in the links it is considered physically correct in situations with vegetation on the river levees and improves link stability If modelling a simple structure between adjacent MIKE 21 cells the implicit structure link is significantly more stable than a standard link Stability in a link is improved if flow is continuous in one direction only through the link for example cascading flow over a weir Other adjustments such as increasing friction and or eddy viscosity can be used to improve stability However such adjustments can compromise model performance 6 3 6 4 26 MIKE FLOOD 1D 2D MODELLING Standard Links The end of branches in MIKE 11 that connect to MIKE 21 must have a water level boundary specified This is a dummy boundary specification for initialisation purposes and will not affect the MIKE FLOOD simulation Link points in MIKE21 can be dry initially and can wet or dry during a simulation A predictor extrapolation factor is applied for obtaining proper time centring of the values that are exchanged between M
31. ce oet Tot Weir C Fric n FLC Geometry e OH Table E Lateral Right Cellto Cell wer HH 1 838 0 050 Lateral Left Cellto Cell wer HGH 5 o 1 838 0 050 SS 3 3 1 Link Type This is carried over from the previous Definition menu and cannot be edited 3 3 2 Side of River Side of river defines whether the lateral link is a link on the left bank or the right bank of the river channel Link type xi Side e Left bank is equivalent to Marker 1 in the MIKE 11 cross Latera Left 7 section editor Right e Right bank is equivalent to Marker 3 in the MIKE 11 cross section editor 3 3 3 Method Mit Structure Link type Side Method Type Source Pept Ta i Weir Fric n Lateral Fight Cell to Cell Weir HGH 1 838 0 050 The structure method defines the method by which flow is distributed between MIKE 11 and MIKE 21 e The CELLTOCELL method performs a flow calculation for each individual point in the defined structure Each calculated flow is then redistributed to MIKE 21 and MIKE 11 This means that the number of MIKE 11 points doesn t necessarily have to match the number of MIKE 21 cells e The SIMPLE method performs a single calculation of flow then distributes that flow to each MIKE 21 cell and or MIKE 11 computation h point The CelltoCell method is the default 3 3 4 Structure Type The structure type defines the type of flow calculation to be performed e WEIRI MIKE 11 Weir Formula
32. constant discharge of 10 m s is applied to the upstream end of each branch and the timestep in both MIKE 11 and MIKE 21 is 2S 550 Standard Links 500 450 EE E CC DSDS ait ESTA T St E E Ki EE E e 153 e E Bi ss A LY RBS LINE 4 3 PA Dp Jd Tu HHHH EI Ir E E EX E d ITT ttt tt ttt PET TT 400 Lateral Links 350 Ree a RRS ESS WE E a E a EI a L E E a L ahaa E Ex SECH 300 250 200 CTT CEET he Standard Links E FEHE StructureLinks BRRSSS HHHHHHHHHHHHHHHHHRIE BE Samm GK fel EA IS d dq ET FE EA SS q EJ E BES SP ELI LL LULA EE LED 34 d LE ELI ESL por EVES CEs ese 150 100 LITLILELII TIT AJ ABRMSEILLLLITELEILITLFTITILETIETSM 1 50 E FESTE Jp E m pup PELL Pe E SERRE TILLLEFISI p gg dg gu EIE 0 PA Standard Links 100 150 200 250 300 350 400 450 500 550 Figure 29 Flow Direction Test Layout E MIKE FLOOD 1D 2D MODELLING The HD simulation run to steady state conditions is presented below H Water Depth m m B Above 1 494 BE 1 487 1 494 EJ 1 481 1 487 53 1 475 1 481 1 469 1 475 1 462 1 469 1 456 1 462 1 45 1 456 1 444 1 45 1 438 1 444 1 431 1 438 1 425 1 431 1 419 1 425 1 413 1 419 1 406 1 413 1 4 1 406 1 394 14 1 388 1 394 1 381 1 388 1 375 1 381 1 368 1 375 1 362 1 369 1 356 1 362 1 35 1 356 50 100 150 200 250 300 350 400 450 500 550 01 01 90 12 33 20 Time s
33. e 37 Downstream Water Level SEE Culverts 8128600 8128600 3 8128400 3 8128300 38 Eon 8128200 8128100 8128000 8127900 8127800 8127700 4 8127600 3 8127500 T us H YEN 5 81274004 Proposed Road 8127304 Embankment AREER FERNE bome OM 8127200 T een Ze BELL Pee gees S Dons y EN E er gt z e S a zi 1 e 4 4 i d 8127100 a Upstream Discharge zu d 8127000 8126900 e 8126800 4 8126700 E 372500 373000 373500 374000 371500 372000 Figure 37 Floodplain Demonstration Layout A 5 s timestep is used in the simulation and the MIKE 21 grid size is 30 m The model has been developed with the following MIKE FLOOD links e lateral links between the main river channel and floodplain and the tributary and floodplain e zero flow links along the centre line of the river channel to ensure that water flows from one side of the floodplain to the other via the main channel e similarly zero flow links along the centre line of the tributary e zero flow links defining the road embankment assuming that the road does not overtop e implicit structure links for flow through the culverts A diagram illustrating the locations of the links is shown DHI Water amp Environment EXAMPLES d X Lateral Link Right Bank Lateral Link Left Bank X Implicit Structure Links Zero Flow Links X or Y 25 Bi BEI 20 SR x x X ES J SR M21 Cells k a
34. e dominant constraint is the timestep The explicit links Standard and Lateral are explicit The numerical design of the links however means that the local Courant conditions inside the linked cells h points cannot exceed 2 it is normally 1 This is important to remember unlike a standard MIKE 11 or MIKE 21 simulation which are semi implicit if the local Courant number Cr is 2 00001 the model will blow up The local Courant number is defined as C vot ed Jat deem where v velocity g gravity d 2 water depth At timestep and Ax grid spacing Another important factor relating to stability is wetting and drying although there have been improvements in this area To some extent this can be a model design issue and adjustments can be made to improve stability For example make troublesome link points fully wet if possible or reduce the timestep increase the MIKE 21 grid size decreasing the Courant number can minimise the impact of other sources of instability Including a depth dependence to the link which will reduce the flow rate in shallow cells relative to deeper cells within the link may also help See the description above in Section 6 1 MIKE 11 pertaining to use of the DELTA coefficient in MIKE 11 to dampen potential instabilities In most cases increasing DELTA to say 0 85 will not adversely affect model predictions Set the momentum factor 0 0 in links where momentum conservation is unlikely to
35. e weir structure in MIKE 11 would not be required and the culvert structure flows would be added to the MIKE 21 cells DHI Water amp Environment APPLICATION DETAILS E Note the add replace options mean that the order in which structure links are listed in the couple file will affect the model behaviour By specifying Replace in a link all previous link inflows from previous links will be overwritten 3 2 6 Depth SED Dept ACUSIMEN Depth Activation Activation Adjst Depth min Depthi max If depth adjustment is active flow through a link is distributed into the MIKE 21 cells according to the water depth in those MIKE 21 cells This is considered appropriate for links on natural terrain or channels but may not always be applicable for structures 3 2 7 Activation Depth Minimum and Maximum The activation depth is valid only for the zero flow XFLOW 0 and YFLOW 0 links If specified then these links will be turned off once the activation depth is reached A maximum and minimum value is available to gradually apply the flow conditions over a range to minimise instabilities Note that the usefulness of this feature is uncertain If the minimum and maximum values are set to zero the activation depth facility is inactive 3 3 18 E MIKE FLOOD 1D 2D MODELLING Options for Lateral Links The options listed in this menu are only relevant for lateral links Link type Structure emails Files Side Method Type Sour
36. eceeeeeeceeeeeeeaeeeseeeeeeeeeens 33 7 4 Hydrodynamics Zero Flow Umks ccccseececeeeeeeceeeeeseeeeeeeeesaeeeseeeeesenees 35 7 5 JAdVOCIIOn DISDOFSIOFPIs sc eost idu du tst a ute iie tu ee 35 7 6 Flow Distribution Dy DODITI uror iri pueda Eau paga Pesaro Ex a parva oa ERR EET E Dann 36 7 7 J nclusion of Friction Term in Weir Formulae 1 and 2 Honma 37 8 EXAMPLES rsum a a 39 E WE ae e BEER 40 8 2 ikateral LNK WE 43 cnc MEN Ee E in 48 E Ee de e ee EE 51 6 5 jmplicitStr elure LINK TEST seio renee ee 54 EN Ge elei ln Re EE 55 8 7 Floodplain Demonstraton senest kk skt ERE SEERE nen 58 TABLES Table 1 Format of External Structure File ccccscccsccscsccsccccccccccsccccccccccccccccccccccccccscccees 20 Table 2 Format of External QH File eene eee eee eue o eee en eden ane aine aa erae a n aano n aane aae aano serra nna ao poae 20 FIGURES Figure 1 Application of Standard Links sccccsssssssccccccccscssssssssssssscssscccccccsscssssssseeeeeees 7 Figure 2 Application of Lateral Links eee eee ee eee eee eere eee eee ee eene eene eese asses EEN 8 Figure 3 Application of Structure Links ce eere e e e eee eee eee eee eaae eese eee EEN 9 Figure 4 Lateral Link Definition of Internal Structures ecce eee e e e eee eren 30 Figure 5 Lateral Link Interpolation of Water L
37. ection Test Results Concentration ecce eee e eere e eene eee eene ue 53 Figure 32 Floodplain Flow Test Layout cccccccccsssssssssssssssccsccccccccsscccccsssssssssssscccccsssssees 55 Figure 33 Floodplain Flow Test Typical Cross section cccccccccsssssssssssssssssssssccccccsessees 56 Figure 34 Floodplain Flow Test Upstream Hydrograph ssssssscssssssssssscccccecesescees 56 Figure 35 Floodplain Flow Test Results Upstream Water Level 56 Figure 36 Floodplain Flow Test Results Downstream Discharge 57 Figure 37 Floodplain Demonstration Layout scccccccssssssssssccccccssssssccccscccsssssscccsscssssscees 58 Figure 38 Floodplain Demonstration Diagram of MIKE FLOOD Links 59 Figure 39 Floodplain Demonstration Boundary Conditions sscccccccsssssssscsccccsscsssees 59 Figure 40 Floodplain Demonstration Water Surface and Velocities near peak of flood 60 Figure 41 Floodplain Demonstration Results Water Levels and Flows at Road Embankment eege H 61 DHI Water amp Environment INTRODUCTION e ll 1 INTRODUCTION MIKE FLOOD is a tool that integrates the one dimensional model MIKE 11 and the two dimensional model MIKE 21 into a single dynamically coupled modelling system Using a coupled approach enables the best featu
38. eral Link Options The Definition menu contains information on the simulation files used in MIKE FLOOD and the general linkage definitions Additional options for the various link types are contained in Standard Structure Link Options and Lateral Link Options E MIKE FLOOD 1D 2D MODELLING 3 1 12 Definition Mike 21 File Name Data projects MIKE_FLOOD test direction_test m21ad M21 Edit M21 input MIKE 11 File Name Data projects MIKE_FLOOD test direction_test m1ladsim11 Edit M11 input Number of links f n ES Link fane Coupling M11 River M11 Chainage M21 Area Ho of M21 M 1 Coord 1 type name Zoe Ho Cells 1 x 1 XFLOW 0 1 11 os 31 39 2 YFLOW 0 1 16 f2 32 40 3 Standard E HD and AD branch1 85 000 1 1 ERE 33 41 4 XFLOVY 0 1 17 4 34 42 5 YFLOVY 0 1 26 5 40 43 6 Standard E HD and AD branchs 165 000 1 2 6 41 44 pem Standard E HD and AD branch3 30 000 1 2 y E E 8 Standard E HD and AD branch 350 000 1 1 E 4 45 g Lateral HD and AD branch 0 000 100 000 1 10 4 46 10 Lateral HD and AD branch8 0 000 165 000 1 14 7 47 11 Standard E HD and 4D branch2 90 000 1 2 7 48 12 Standard E HD and amp D branche 130 000 1 13 13 Standard E HD and amp D branch4 160 000 1 1 3 1 1 MIKE 21 File Name A complete MIKE 21 setup should be established and tested prior to setting up MIKE FLOOD The MIKE 21 setup is defined in the usual way using MIKE ZERO The path and file name of the res
39. ere the internal structure locations differ from the MIKE 21 cell locations and the MIKE 11 h point locations As shown water levels are interpolated from the MIKE 21 cells and the MIKE 11 h points to the specific internal structure locations DHI Water amp Environment SCIENTIFIC BACKGROUND E Linked M21 Lateral Linked M11 cells Structure h points be Interpolated levels can overlap but distance dependence minimises inconsistencies r ff Water levels to structure interpolated from relative locations of M11 h points M21 cells and internal structures Interpolation is distance dependent Figure 5 Lateral Link Interpolation of Water Levels Using the calculated width and bed level and interpolated water levels the flow across each internal structure is calculated using a standard structure equation These structure equations weir type 1 or 2 are the same equations used in MIKE 11 The flow from each internal structure is then distributed to from the MIKE 11 h points and MIKE 21 cells This is done by determining the range of influence that each internal structure has upon each linked MIKE 11 h point and MIKE 21 cell As shown in Figure 6 if MIKE 11 h points lie within the range of influence of a given internal structure flow is distributed across those points according to water depths in each point If no MIKE 11 h points lie within the range of influence flow is distributed to the nearest upstream and downstream po
40. erwise check www dhisoftware com where the input files can be downloaded Various MIKE ZERO tools can be used to view the results including the Result Viewer MIKE VIEW not in MIKE ZERO Plot Composer and the time series profile series and grid series editors A brief outline of the examples 1s provided e Standing wave examines momentum transfer through standard links e ateral link test 1 investigates lateral link flow over a bank of varying bed levels and includes an AD component e Lateral link test 2 investigates lateral link flow and compares results to a standard MIKE 11 weir e Flow direction test examines flow directions through various links e Implicit structure link examines the structure link and compares performance to the standard link and MIKE 11 e Floodplain flow examines the transition from in bank to floodplain flow in a simplified setup e Floodplain demonstration demonstration of a real floodplain application Note The MIKE FLOOD interface uses a full file path specification including folder location directory for the linked MIKE 11 and MIKE 21 files If a problem occurs when running the examples check that the MIKE 11 and MIKE 21 files name boxes in the Definition menu have the correct file path for your system setup 8 1 40 E MIKE FLOOD 1D 2D MODELLING Standing Wave Consider an 8 km long basin closed at both ends MIKE 11 Branch MIKE 21 Basin M Figure 9 Standing Wave Test L
41. evels ccce ecce e eene eee eee eene 31 Figure 6 Lateral Link Interpolation of Flows cccccccccsssssssssssssssssssssscscccccsssssssseeeeeees 32 Pisure 7 Structure Link Diagram 05e EE 33 Figure 8 Structure Link Directional Link eee e eere eee eee eee eene eee eese sssssuus 33 Figure 9 Standing Wave Test Layout xcscssccscdsescssccssscessscecscscssncecccosessnscescsssadovessvcced osdoccesed vcossees 40 Figure 10 Standing Wave Test Results Water Level Profiles 40 DHI Water amp Environment UI iv MIKE FLOOD 1D 2D MODELLING Figure 11 Standing Wave Test Layout 2 4 oieeeeeecocesessuee vagos eeepas s CES 41 Figure 12 Standing Wave Test Results Water Level Profiles 2 41 Figure 13 Lateral Link Test 1 Layout un ccoeseetise cetus iste siesta epo e e enero eee o dc Epi pena e oe b penu ere paa ecu 43 Figure 14 Lateral Link Test 1 Left and Right Bank Levels eeeeeee 43 Figure 15 Lateral Link Test 1 Results Water Depth and Velocity 44 Figure 16 Lateral Link Test 1 Results Water Level and Flow Profile 45 Figure 17 Lateral Link Test 1 Results Lateral Flow Profile 45 Figure 18 Lateral Link Test 1 Re
42. hannel in MIKE 11 and flow between them in MIKE FLOOD The test consists of four separate setups e MIKE FLOOD river channel modelled in MIKE 11 floodplains in MIKE 21 connected with MIKE FLOOD lateral links mf couple e MIKE 11 single branch for main channel and floodplains mf couple e MIKE 11 separate main channel and floodplain branches interconnected by link channels mf couple e MIKE 21 both river channel and floodplains modelled in MIKE 21 m21a M21 M11 Branch with M11 Single Branch MF Lateral Links Upstream Flow Bes 10000 Hydrograph 6000 Ve MII Branch with M11 Link Channels to Floodplain Branches 5000 EISE 8000 M21 Grid 50 m 3000 6000 2000 5000 M21 Grid 50 m with upstream and downstream channels 1 1000 cell width 4000 Bathymetry m BH Above 14 13 14 0 3000 12 13 11 12 10 11 eo net e CH 1000 5000 2000 1000 NI CO Ze Cn C HH OO D RO GAP Cn C CO m m zT o 3000 Downstream Fixed 0 1000 2000 3000 4000 25 1275 Water Level Figure 32 Flooaplain Flow Test Layout E MIKE FLOOD 1D 2D MODELLING Each test represents the same geometry consisting of a 50 m wide 5 m deep channel On each side of the channel is a 50 m wide levee Beyond the levees the floodplains are initially 1 m below the levees and rise laterally by 1 m over a distance of 250 m A typical cross section is shown meter 8 0
43. he MIKE 21 cells The linked cells can be horizontal vertical or any other alignment Remember that if using a lateral link the cells should be in the same sequence as increasing chainage specified in MIKE 11 Li DHI Water amp Environment APPLICATION DETAILS E 3 2 Options for Standard Structure Links The options listed here are only applicable for Standard and Structure links Es d Ee Depth Activation Activation Link type Location Ext Fact Mom Adjat Depthimin Depthimax 43 xrow o 0 000 0 000 2 YFL 0 000 0 000 3 Standard E 1 000 1 500 4 XFLOWEO 0 000 0 000 5 vrLOw n 0 000 0 000 B Standard E 1 000 1 500 T Standard E 1 000 1 500 8 Standard E 1 000 1 500 g Lateral 10 Lateral 11 Standard E 1 000 1 500 12 Standard E 1 000 1 500 13 Standard E 1 000 1 500 14 structure Dottomd eft Replace 15 Structurerl Top Right Replace 16 structure Bottom L eft Ada 17 Structurerl TaopiRight Add 3 2 1 Link Type Link type Location Structure TopRigt ll Zap This is carried over from the previous Definition menu and cannot be edited 3 2 2 Location Two links are required for a structure link one for the left or bottom cell and another for the top or right cell These linked links can only be one horizontal or vertical cell apart Define each end of the paired links with bottom left or top right 3 2 3 Mom Fact E
44. he momentum equation within the MIKE 21 cell are replaced Adjustments need to be made for link direction 0 and conversion from discharge Q to flux q Q A A grid spacing For the momentum equation in the x direction n l n l n l __ Gy au bydja cyaft dyn SES duu COSO M21 A Dan bui m Cy COSO M21 A pm duu cos M21 If the terms are added for example if the structure link represents a structure flowing under the existing MIKE 21 topography further adjustments are made to ensure consistency between the MIKE 11 and MIKE 21 terms Again for the x direction n4l n l n l __ g ayah byuag Ce zit dyn dun Ayr Tt DA M11 DA bun M 21 M 21 b M11 M 21 M 21 Dun The same adjustments apply for the y direction momentum equation except a sine direction adjustment is made rather than a cosine adjustment Note that the implicit terms from MIKE 11 used are from the MIKE 11 solution at the previous timestep In most applications where flow conditions vary quite slowly relative to the timestep this is not a problem It may become a problem if rapid and relevant changes do occur over a timestep Also the displayed value of flow in the q point of the MIKE 11 branch may not DHI Water amp Environment 7 4 7 9 SCIENTIFIC BACKGROUND a necessarily be the flow through the MIKE 21 cell It is recommended that the MIKE 21 results are interrogated in this case rather than the MIKE 11
45. ikely that standard spreadsheets EXCEL would also be useful for data management Links to external programs are available at present through MIKE ZERO Linkage properties can be imported into MIKE FLOOD either through an external ASCII file XYZ files from a GIS or by cutting and pasting into the MIKE FLOOD interface Further development of useful tools for MIKE FLOOD is under way Contact DHI for the latest progress or check the DHI web site to download new programs The results from MIKE FLOOD water levels discharges fluxes AD components etc can be viewed using the Result Viewer Plot Composer and Data Viewer MIKE 21 and MIKE VIEW MIKE 11 Also MIKE ZERO allows MIKE 21 result files to be exported to an ARC GIS ASCII input file The recommended tool to use 1s the Result Viewer which is activated from MIKE ZERO File New Result Viewer The viewer can present 1D 2D and 3D results from different DHI Software models at the same time including res11 result files from MIKEII and dfs2 results files from MIKE 21 e New files are added to the Result Viewer project by using Result Viewer Projects Add files to project and press the new page icon to the right B The File Type is a scroll down menu where the result file is chosen e The work area is defined under Result Viewer Projects Work Area e In order to display the results together the two models need to be based on the same geo reference Thus the MI
46. ines v e Can model very long or complicated river systems with little computational effort Y e Can model one dimensional channel flow accurately v e Can be easily linked to rainfall and runoff programs v MIKE FLOOD 1D 2D MODELLING Can simulate high velocity supercritical flow conditions v Is one dimensional so two dimensional effects such as cross channel momentum not possible X Overland flow is difficult to model if uncertain of flowpaths X Requires more conceptualisation of flow conditions and more approximations X Cannot easily simulate a coastal situation X Similarly consider MIKE 21 Two dimensional means more accuracy and better resolution v Two dimensional so overland flow can be simulated more accurately also has efficient flooding and drying facility v Fixed grid means less flexibility with resolving features X Nested grid option means more flexibility with resolving features v Can simulate high velocity supercritical flow conditions v Can simulate a coastal situation Y Requires more computational effort X Can be difficult to model narrow channels and flow paths particularly if diagonal to flow X MIKE 21 boundaries must be aligned with the grid horizontal or vertical X Consider which of these features are most desirable for your application How can you integrate MIKE 11 and MIKE 21 to best utilise the best features while minimising the bad features MIKE FLOOD enables this integration to be
47. ink the x momentum to the right of the cell and or the y momentum to the top of the cell terms will be modified The MIKE 21 cells that define the inlet and outlet of the structure link must be adjacent to each other For example if the inlet cell is 5 10 then the outlet cell can be 5 11 6 10 or 6 11 However more than one MIKE 21 cell can be specified and a list of cells can be in any direction or alignment The MIKE 11 branch that defines the structure link can only be a 3 point branch one h point at the inlet one h point at the outlet and one q point connecting them The q point can have as many parallel structures as are needed or can have no structures it can simply be a cross section There is an option to add or replace momentum terms If the momentum terms are replaced the flow conditions calculated in MIKE 11 overwrite flow conditions in the MIKE 21 cell If the momentum terms are added the flow conditions calculated in MIKE 11 are added to the flow conditions in the MIKE 21 cell Zero Flow Links A single link can be used to specify all XFLOW 0 cells in a MIKE 21 grid The same applies for the YFLOW 0 cells Note that at this stage the convective terms in the surrounding cells are not adjusted which means that some inconsistencies are possible Please contact DHI if problems occur With regard to activation depth the idea is that for most flooding conditions there will be left bank floodplain flow in ba
48. ints using a distance dependent interpolation The same applies for MIKE 21 cells SS 32 MIKE FLOOD 1D 2D MODELLING M11 branch with h points Single h point lies within No h points lie within internal structure influence interpolate flow into two nearest h points distance Internal structures 4 5 CT i E f 4 mE Three h points lie N j i i i j within internal VBS structure influence Lo distribute flow to each depth dependent Method of flow j distribution into M21 cells p M NE i same as for M11 i A Figure 6 Lateral Link Interpolation of Flows This approach allows a high level of flexibility when designing the lateral link However it is likely that a similar distribution of MIKE 11 h points MIKE 21 cells and internal structures will produce the most accurate solution DHI Water amp Environment SCIENTIFIC BACKGROUND 7 3 Hydrodynamics Structure Links The structure link takes the implicit terms describing momentum through a 3 point MIKE 11 branch and uses them to replace or modify the implicit terms describing momentum across the face of a MIKE 21 cell In this way the flow properties from one MIKE 21 cell to another are modified to represent a structure Consider the following diagram M11 momentum equation replaces or modifies M21
49. ld already have the components ready for running the MIKE FLOOD model This step is to create the MIKE FLOOD couple file and define the links to be applied 4 5 22 MIKE FLOOD 1D 2D MODELLING Run MIKE FLOOD Simulation Note that the standard links and the lateral links are explicit Courant conditions cannot exceed 2 It is this initial simulation where the Courant conditions are likely to be encountered and any stability problems relating to the links will occur Do not be surprised if several adjustments of the links need to be made at this stage or that the timestep required is much shorter than you expected Check some of the tips available in this document see Tips and Troubleshooting Once an initial MIKE FLOOD simulation has been completed the modeller should have a good appreciation of the model layout and its various components and be aware of the potential problems that may crop up in subsequent simulations and analyses DHI Water amp Environment PRE AND POST PROCESSING e ll 5 PRE AND POST PROCESSING It is envisaged that much of the pre and post processing of MIKE FLOOD will be done in a GIS The GIS provides superior tools for the management and storage of large amounts of data which is required for many floodplain applications However many GIS do not have specialised tools suitable for modelling time series analysis grid editing etc so MIKE ZERO has its place in the modelling method Also it is l
50. link chainage 850 m This weir has a height of 2 2 m and is 500 m wide A weir formula 1 is applied The second test aims to replicate the first except using a lateral link rather than a standard link The MIKE 11 branch branchl is the same as the first test except it is truncated at the weir location at chainage 800 m where another branch latb is attached This branch has a length of 500 m and the left banks of the cross sections have a bed level of 2 2 m The lateral link connects this branch to the MIKE 21 basin A weir formula 1 is applied in the lateral link MIKE 11 Branches MIKE 21 Grid M11 branch connection b Lateral MNA 1000 800 600 400 200 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Figure 24 Lateral Link Test 2 Lateral Link Layout The initial water level and the downstream water level at the MIKE 21 boundary is 2 m so water depth is 2 m in the upstream branch and in the MIKE 21 grid The simulations are performed using a timestep of 30 s explicit Courant conditions The upstream flow boundary in MIKE 11 gradually rises from 0 m s to 100 m s and remains steady at this flow rate The resulting water level at the upstream end of the MIKE 11 branch and the discharge at the downstream end are presented below DHI Water amp Environment EXAMPLES e ll 2 55 Water Level m N zech ol Water Level Upstream Standard Link Value at End of Simulation 2 43 N e e Wate
51. nk channel flow and right bank floodplain flow The interactions between these three will be governed by the MIKE FLOOD links However water depths could increase until the interactions between the separate flowpaths are no longer relevant At this stage a MIKE 21 simulation without the MIKE FLOOD links would be more accurate By using the activation depth to switch on MIKE 21 flows across a river channel MIKE FLOOD 1D 2D MODELLING this could be done Note that this feature has not been thoroughly investigated mainly because we re not sure how useful it is Please contact DHI if you do feel this feature could be of benefit to you 28 DHI Water amp Environment SCIENTIFIC BACKGROUND 7 1 SCIENTIFIC BACKGROUND The scientific backgrounds of MIKE 11 and MIKE 21 are also applicable for MIKE FLOOD Hydrodynamics Standard Links Discharge is extracted from the MIKE 11 boundary the first Q point and imposed in MIKE 21 in a similar way as a MIKE 21 source discharge The discharge is centred at timestep n l The discharge from MIKE 11 has an impact on the continuity equation as well as the momentum equation in MIKE 21 as with a normal source discharge see MIKE 21 scientific documentation MIKE 11 requires a water level boundary from MIKE 21 at time step n 1 in order to step from time step n to n 1 Therefore MIKE 21 will always be one time step ahead of MIKE 11 Thus in order to provide a discharge to MIKE 21 at time ste
52. ntrance and exit losses can be represented to some extent by turbulence and eddy viscosity losses that occur upstream and downstream of the structure These losses depend upon grid size and eddy viscosity values in MIKE 21 Difficulties arise when using MIKE FLOOD because the entrance and exit losses can be represented both in MIKE 21 and MIKE 11 This can create an overestimation of structure losses which can result in a larger than expected head loss across a structure To account for this the entrance and exit losses in the MIKE 11 structure equations should be reduced The question is how much these values should be adjusted and the answer often depends upon choice of MIKE 21 grid size eddy viscosity parameter and what type of structure is being applied This test is designed to investigate the representation of structure losses in MIKE 21 and how various parameters can effect these losses While these tests won t answer all questions relating to this subject it highlights potential problems that may be encountered when using MIKE FLOOD Note At present this test is still being developed Please check the web site www dhisoftware com for latest updates DHI Water amp Environment EXAMPLES e ll 8 6 Floodplain Flow This is another test of the lateral links It compares model performance over a broad floodplain application This is a simplified representation of a typical lateral link application floodplain in MIKE 21 river c
53. or the top or right cell These linked links can only be one horizontal and or vertical cell apart For zero flow links XFLOW 0 and YFLOW 0 a link is a list of cells in MIKE 21 There is no corresponding reference to the MIKE 11 simulation Note that the number of links is not the total number of MIKE 21 cells connected to MIKE 11 calculation points To demonstrate the setup shown in Figure 1 has five links although each link contains several MIKE 21 cells There are two links shown in Figure 2 one for the left bank lateral flow and another for the right bank lateral flow Figure 3 has two links one upstream of the road and the other downstream of the road 3 1 4 Link Type The link type defines the type of link Standard Link type 1 xrLow si wie 2 standard E Ici 3 Lateral Structure Implicit EUM E SEL OW E XFLOW 0 ENZ YFLOW 0 Standard iaHExt Standard QH Extrap disabled at present 3 1 5 Coupling Type The coupling type can be Coupling HD only the link will only transfer hydrodynamic information type requires HD simulation defined in MIKE 11 and MIKE 21 HD only AD only the link will only transfer advection dispersion information requires AD simulation defined in MIKE 11 and MIKE 21 HD and AD 3 1 6 MIKE 11 River Name and Chainage If using a standard or structure link M11 river name is the MIKE 11 branch with the link and 1 US M11 chainage is the chainage of the MI
54. ormance of the culverts could be assessed maybe more are needed Note that this is a demonstration model not a real example Other modelling considerations that could be of relevance in this example include e The MIKE 21 grid does not cover the entire floodplain width e The proposed road crosses over the main channel Any hydraulic effects bridge structure or pier losses created by this situation are ignored e The roughness parameter on the floodplain has been set to a constant value of M 20 The roughness may actually be varying spatially particularly 1f there are a range of land use patterns e The upstream and downstream MIKE 11 branches only represent the main channel They do not include the floodplains Eivsfacie Eliecaliari rri Abowe 1284 1208 1 284 BTA T 1 2852 1 282 1336 13252 1 72 1 238 12705 31 7 13809 1205 ifs 11858 1357 1373 1 141 y 157 1325 1 3141 B127300 F Lins 1125 1003 1109 LOTT 1002 v cd 1061 1077 2127800 1045 108 103 1045 1014 102 Uri 1014 0 9918 0 9977 A177700 e Ki 1885685 5918 1 95 0 9559 0 53341 0 95 BE 0 5102 0 0341 N 00023 03182 8127600 a 0 8064 0 0023 0 8705 8 RSA 0 8545 amp 705 i 0 0388 0 8585 ai 27500 P 0 8227 0 8386 0 0088 0 8227 0 7909 0 PO pre 0 7909 EL OFFS el 0 7432 0 7581 02273 07432 0414 0 7273 5355 0 7114 0 6785 0 6855 0 6636 METIS 0 6477 0 6036 0 6318 Q amp A47TT
55. p n a predictor is applied in MIKE 11 to estimate the discharge Q given the computed discharges Q and water levels H at timestep n 0Q oH Q JO g g dt Ox A C PR where t is the time x is the length A is the cross section area C is the Chezy resistance number and R is the hydraulic radius The gradient in water level is at the last Q point in MIKE 11 The calculated time derivative of discharge is transferred to MIKE 21 together with the discharge at time n in order to predict the discharge at a later time step n 2 The predictor assumes that the convective acceleration terms in the last grid point in MIKE 11 are negligible Furthermore it assumes that normal bed resistance represented by a Chezy or Manning number controls the flow Thus a structure in the last Q grid point in MIKE 11 before a link to MIKE 21 should either be avoided or the predictor removed see Extrapolation Factor Ext Fact Alternatively remove the predictor and an extra cross section between a structure and a link to MIKE 21 or try the structure link 7 2 30 MIKE FLOOD 1D 2D MODELLING Hydrodynamics Lateral Links For lateral links flow from MIKE 11 is via a lateral boundary which is then applied into MIKE 2 via a source and vice versa The lateral link varies from the standard source sinks in the following ways 1 Flow through the link is dependent upon a structure equation and water level
56. r Level Upstream Lateral Link Value at End of Simulation 2 44 1 95 11 45 12 45 13 45 14 45 15 45 16 45 17 45 18 45 19 45 20 45 21 45 Figure 25 Lateral Link Test 2 Results Time Series of Water Level 120 e e e Discharge m3 s o e A e Discharge in Upstream Branch Standard Link Value at End of Simulation 100 0 Discharge in Upstream Branch Lateral Link Value at End of Simulation 100 0 Downstream Discharge from MIKE 21 Standard Link Value at End of Simulation 100 0 N e Downstream Discharge from MIKE 21 Lateral Link Value at End of Simulation 100 0 0 11 45 12 45 13 45 14 45 15 45 16 45 17 45 18 45 19 45 20 45 21 45 Figure 26 Lateral Link Test 2 Results Time Series of Discharge There is a slight variation in water levels as the discharge increases but the steady state levels are similar for both simulations 2 43 m and 2 44 m These variations may be due to the missing momentum transfer across the lateral links Steady state discharge is the same for both simulations 100 m s indicating that mass is conserved through the links Notice the oscillations in the discharge at the downstream end of the MIKE 21 basin This is a result of reflections in the MIKE 21 model created as the initial wave front produced by the rising discharge enters the MIKE 21 domain The water level contours and current vectors in MIKE 21 for each simulation are presented below
57. res of both MIKE 11 and MIKE 21 to be utilised whilst at the same time avoiding many of the limitations of resolution and accuracy encountered when using MIKE 11 or MIKE 21 separately Special features of MIKE FLOOD include e Momentum preservation through links e Lateral links enabling simulation of overbank flow from river channel to floodplain e Comprehensive hydraulic structures package e Specialist implicit structure links e GIS integration e Links possible along any alignment in MIKE 21 not just horizontally or vertically e A graphical user interface standard MIKE ZERO allowing for easy data input and output as well as data preparation and analysis e A thorough on line help system user manual and technical reference documentation e Support and continuing commitment from DHI Water and Environment There are many advantages to using MIKE FLOOD and many model applications can be improved through its use including e Floodplain applications e Storm surge studies e Urban drainage e Dambreak e Hydraulic design of structures e Broad scale estuarine applications 1 1 General Approach to Modelling with MIKE FLOOD Consider the two modelling systems that are integrated MIKE 11 and MIKE 21 By combining the two the modeller can choose the best features of both and make the best model with these features For instance consider the following abilities and limitations of MIKE 11 e Has comprehensive and proven structure rout
58. results Hydrodynamics Zero Flow Links If the link type is a XFLOW 0 link the x direction momentum across the right face of the MIKE 21 cell is set so that q 0 This is done by modifying the implicit terms n l n l n l __ du zt byuag Cy hi dy Ayr Cyr Ayr 9 x Dui Similarly if a YFLOW 0 link the y direction momentum across the top face of the MIKE 21 cell is set to q 0 Advection Dispersion Concentrations of AD components are transferred explicitly between MIKE 11 and MIKE 21 depending on the direction of the flow For standard links with flow from MIKE 11 to MIKE 21 the concentration of the AD component is imposed as with a standard MIKE 21 source i e as a flux of mass into the MIKE 21points oV Cee 4 x 7 d Cy When flow is going from MIKE 21 to MIKE 11 the modification to the AD equation in MIKE 2 is n A oV i Cuz P Q s d f E M21 The corresponding boundary condition in MIKE 11 can be either a transport boundary or a concentration boundary as usual Furthermore a mixing coefficient can be defined as normal For lateral links the mass of the AD component being transferred is calculated from the lateral discharge and the concentration in MIKE 11 or MIKE 21 depending upon flow direction This is then applied as a source or sink term in the branches and cells The source term into MIKE 21 is as for the standard links For MIKE 11 the one dimensional advection dispersion equation
59. rn The zero flow links are also zero concentration links the plot above demonstrates that the zero flow links are a barrier to advection and dispersion Finally a check of mass conservation in the model is made With 8 separate inflow branches the total flow rate into the system is 80 m s The resulting discharge through the draining lateral link in the centre of the basin is shown below At the completion of the simulation the flow rate shown in MIKE VIEW at the last point in the lateral flow branch is 77 m s While this may appear to be a mass loss error in fact it is a minor presentation bug caused by having a lateral link at the last h point in the branch The discharge presented in MIKE VIEW is at the last q point As lateral flows are added to the h points this means that the flow rate of 77 m s does not include an additional 3 m s entering the last h point To check this rerun this simulation with the lateral link connected between chainage 20 to 100 m on the MIKE 11 branch branch9 The discharge at the last point will then be presented as 80 mie indicating that mass is preserved 8 5 54 E MIKE FLOOD 1D 2D MODELLING Implicit Structure Link Test Structures are an important feature of any river and floodplain model Applying structures into a one dimensional model MIKE 11 uses established structure flow equations that generally consist of a given entrance loss structure loss and exit loss In a two dimensional model e
60. s in MIKE 11 and MIKE 21 2 Flow through the link is distributed into several MIKE 11 h points and several MIKE 21 cells 3 The lateral links do not guarantee momentum conservation A structure is required to calculate the flow between MIKE 11 and MIKE 21 This structure is typically a weir that represents overtopping of a riverbank or levee The geometry of the structure can be determined from MIKE 11 bank markers MIKE 21 cell bed levels a combination of the highest of each or from an external file With a CELLTOCELL method the structure geometry is subdivided into a series of internal structures Each internal structure has a bed level and a width determined from the resolution of points defined along the structure Consider the schematic diagram below of a structure defined from MIKE 11 h points Extent of Lateral Link structure e ee i O MIKE 11 Internal Structure e E e Branch defined with a single e p ranc H point bed level and a width 4 Mon E H points Figure 4 Lateral Link Definition of Internal Structures The internal structures are defined so that all of the information available 1n the structure geometry is utilised During computation each internal structure is assigned a water level from MIKE 11 and from MIKE 21 These values are found by interpolating levels at existing calculation points onto the internal structures Consider the schematic diagram below Figure 5 of an externally defined structure wh
61. sults Time Series of Discharge 45 Figure 19 Lateral Link Test 1 Layout 2 1 6 eeeses eese sto eren poenas a asa eaa tepore nean aree aab peeEe doe 46 Figure 20 Lateral Link Test 1 Results Time Series of Discharge 2 46 Figure 21 Lateral Link Test 1 Results Time Series of Concentration 47 Figure 22 Lateral Link Test 1 Results Concentration eee e ecce eere eee ee eene enun 47 Figure 23 Lateral Link Test 2 Standard Link Layout c ccce rece eene eene eene 48 Figure 24 Lateral Link Test 2 Lateral Link Layout ee eee e eee ee eee eene e eeu uu 48 Figure 25 Lateral Link Test 2 Results Time Series of Water Level 49 Figure 26 Lateral Link Test 2 Results Time Series of Discharge 49 Figure 27 Lateral Link Test 2 Results Standard Link eere eere eene 50 Figure 28 Lateral Link Test 2 Results Lateral Link ccce eere eee eee ee eene enun 50 Figure 29 Flow Direction Test Layout ccccccccsssssssssssssssssssscssccccccccsssscssessssssssssscccccossssees 51 Figure 30 Flow Direction Test Results Water Depth and Velocity 32 Figure 31 Flow Dir
62. t the error message Error no 25 At the h point the water depth greater than 4 times max depth This can occur if the bank markers in the cross sections which will be laterally linked to MIKE 21 are low To avoid this message the MIKE11 INI file HD entry WL EXCEEDANCE FACTOR should be set to a higher value A high resolution of MIKE 11 grid points improves model stability Use the CELLTOCELL method for lateral flows The WEIRI and WEIR2H types are linked to the MIKE 11 structure routines They include drowned conditions and simulate lateral flows accurately The FORMLOSS method is straightforward If these methods are not sufficiently detailed then an external QHTABLE type is available H is considered to be water level either at the MIKE11 h point or the MIKE21 cell Otherwise QDTABLE uses water level structure depth Also if a CELLTOCELL method is applied then Q is flow per unit width Bed friction can be included in the weir calculation see the Scientific Background While this is normally uncommon for in channel structures riverbank overflow can often occur across reasonable distance the levee width and through thick vegetation Rather than estimating a new weir coefficient to account for this specification of a friction term may be a desirable alternative The length of the link used in this calculation is determined from the MIKE 21 cell size DHI Water amp Environment 6 5 6 6 TIPS AND TROUBLESHOOTING
63. te that computational time is mostly influenced by the total number of wet computational points that occur over an entire simulation This means that a flood simulation with a short duration sharp peaked hydrograph will use much less computational effort compared to a long duration flat peaked flood event Consider this when deciding on grid resolution Other things to consider include e The 1D model extent e The 2D model extent e Where model boundaries will be located remember that often a MIKE FLOOD link is more flexible than applying a boundary condition directly in MIKE 21 e The alignment of the 2D grid this may depend upon the alignment of main channels floodplain features etc e The type of links to be used Setup and Run MIKE 11 Model MIKE FLOOD is a combination of MIKE 11 and MIKE 21 Setup MIKE 11 and MIKE 21 separately then join them together using MIKE FLOOD It should be possible to completely define the MIKE 11 model that will be linked in MIKE FLOOD This should be done to ensure that no errors exist in the MIKE 11 model While the results of the simulation will not be correct they may provide an indication of potential problems Setup and Run MIKE 21 Model As for the MIKE 11 setup ensure no errors exist in the MIKE 21 definition files Run the simulation and ensure that the results are reasonable Setup MIKE FLOOD The model layout should already be decided upon and the MIKE 11 and MIKE 21 models shou
64. tep 1000 of 1000 Figure 30 Flow Direction Test Results Water Depth and Velocity As shown the direction of flow discharging from each linkage point is consistent with the branch alignment The link points that have land or zero flow links behind them show slightly different flow patterns As a result of the zero flow links water levels in the bottom right corner are lower than the rest of the model This is driving flow through the structure links An AD simulation was also performed Initial concentration was set to zero and inflows apply a conservative concentration of 100 The contour plot below shows results 52 DHI Water amp Environment EXAMPLES e ll Graphical Items Color point 550 XX Width point 500 450 400 350 300 pollutant H E Above 100 B oer 100 E 91 39 957 J 87 08 91 39 82 78 87 09 78 48 82 78 23 74 17 78 48 33 68 87 74 17 Pl 65 57 69 87 IB 61 26 65 57 IB 56 96 61 26 IBN 52 65 56 96 BN 48 35 52 65 EN 44 04 48 35 ES 39 74 44 04 BE 35 43 39 74 B 31 13 35 43 HE 26 83 31 13 B 22 52 26 93 mH 18 22 22 52 HE 13 91 18 22 E 98 609 13 91 FT 5 304 9 609 WH 1 5 304 IT Below 1 undefined Value 250 200 150 100 50 50 100 150 200 250 300 350 400 450 500 550 01 01 90 15 20 00 Time step 50 of 83 Figure 31 Flow Direction Test Results Concentration The flow directions from the links create a slight whirlpool patte
65. tions imposed on boundary locations in MIKE 21 Utilise this feature for any MIKE 21 simulation Wetting and Drying Any link can be initially dry or can dry at any time in the simulation If a link is completely dry flow will be added to the dry MIKE 21 cells until cell water depth is above the cutoff flooding depth Then the cell will become an active wet point Timestep The timestep in the two models can be different MIKE 11 time step a multiple of the MIKE 21 time step although it is recommended to use the same time step to avoid mass errors MIKE 11 The DELTA coefficient dampens high frequency oscillations from a MIKEII simulation The frequency of the dampened oscillations depends upon the timestep and the value of DELTA Note that the timestep for a typical MIKE FLOOD application is relatively small which means that increasing DELTA is unlikely to have a significant effect upon the accuracy of model predictions Therefore increasing the DELTA parameter is therefore a very useful feature for eliminating minor wobbles and potential instabilities from a simulation See the MIKE 11 Scientific Documentation for a more detailed description MIKE 21 The default value for land in a MIKE 21 bathymetry is 10 If a floodplain model has bed elevations higher than this ensure that the bathymetry file has this specified MIKE 21 For applications with significant wetting and drying the Smagorinsky eddy viscosity formulation should not be used
66. uation An example is shown Specify flow over either left K QO right banks vn P BE EEN 2 Y MII Network Lateral Link Lateral weir flow from river channel M11 to floodplain M21 Link from every h point in branch to every linked M21 cell Figure 2 Application of Lateral Links 8 DHI Water amp Environment GENERAL DESCRIPTION Ss 2 3 Structure Link Implicit The structure link is the first of a series of new developments planned for MIKE FLOOD The structure link takes the flow terms from a structure in MIKE 11 and inserts them directly into the momentum equations of MIKE 21 This is fully implicit so should not affect timestep considerations in MIKE 21 The structure link is useful for simulating structures within a MIKE 21 model The link consists of a 3 point MIKE 11 branch upstream cross section structure downstream cross section the flow terms of which are applied to the right or top of a MIKE 21 cell or group of cells An example is shown n 11 Branch with structure one or more defined at q point Structure Link Flow over road is modelled using MII hqh branch representing a structure s implicitly inserted into M21 flow equations Flow conditions from M11 can either replace flow in M21 or be added to existing M21 flow Figure 3 Application of Structure Links 2 4 2 5 2 6 10 MIKE FLOOD 1D 2D MODELLING Zero Flow Link X and Y A MIKE
67. ulation point 20 in total whereas the MIKE 11 simulation calculates weir flow at one calculation point e tis possible that additional losses from 2D effects such as eddy formations in MIKE 21 are contributing to the lateral link structure losses This may create a variation between a MIKE 11 prediction and the MIKE FLOOD prediction The findings of this test show that the lateral links are mass preserving and behave as expected Further the test highlights the importance of using lateral links in situations where there is a significant water level gradient in the in bank river channel Finally an AD simulation is added to the test To do this add the AD computation to MIKE 11 and MIKE 21 then set the MIKE FLOOD Coupling Type to be HD and AD 46 DHI Water amp Environment EXAMPLES Ss The time series plot displays pollutant concentrations entering the upstream boundary and flowing out the two downstream boundaries mu g m 3 Time Series Concentration 100000000 0 90000000 0 80000000 0 70000000 0 60000000 0 50000000 0 40000000 0 30000000 0 20000000 0 10000000 0 0 0 T 02 00 00 04 00 00 06 00 00 08 00 00 10 00 00 12 00 00 14 00 00 16 00 00 1 1 2003 Figure 21 Lateral Link Test 1 Results Time Series of Concentration Concentration LATM21 0 00 POLLUTANT 9 LM21 500 00 POLLUTANT e RM21 500 00 POLLUTANT
68. ulting MIKE 21 File Name m21 is provided in this menu Mike 21 File Mame Data projects MIKE_FLOOD test direction_test m21 adhe Edit Mz1 input A button allows for browsing the parameter file Furthermore the Edit M21 input button allows for opening the existing MIKE 21 parameter file for further editing 3 1 2 MIKE 11 File Name A complete MIKE 11 setup also should be established and tested As with MIKE 21 this is done in the usual way using MIKE ZERO The path and file name of the MIKE 11 File Name sim11 is provided in this menu Mike 21 File Mame AData projects MIKE_FLOOD Westydirection jet ad M 1 Edit M21 input A button allows for browsing the parameter file Furthermore the Edit M11 input button allows for opening the existing MIKE 11 simulation file for further editing 3 1 3 Number of Links Number of links 1 i DHI Water amp Environment APPLICATION DETAILS E The Number of links can be found as follows For standard links a link 1s the connection between the end of a MIKE 11 branch and a series of MIKE 21 cells For lateral links a link 1s the connection between one MIKE 11 river reach within one branch and a series of MIKE 21 cells For structure links a link 1s the connection between the end of a MIKE 11 branch and a series of MIKE 21 cells same as a standard link However two links are required for each structure link one for the left or bottom cell and another f
69. uses a 50 m spacing between h points and the MIKE 21 grid has a spacing of 50 m A simulation timestep of 15 s is used The links at the downstream end of the MIKE 21 basin are standard links The main interest in this test however is the lateral links The left bank of the upstream branch chainage 100 m to 1100 m is connected to the MIKE 21 cells in the right basin 7 31 to 7 11 The right bank is connected to the left basin 5 31 to 5 11 F ixed d s water levels Figure 13 Lateral Link Test 1 Layout The left and right bank markers of the branch are defined by a sinusoidal curve as shown 4 Left Bank Right Bank Bank Level m 0 100 200 300 400 500 600 700 800 900 1000 1100 Chainage 0 1100 m Figure 14 Lateral Link Test 1 Left and Right Bank Levels E MIKE FLOOD 1D 2D MODELLING Lateral flow spilling out of the river channel into the basin will be distributed across the length of the branch depending upon the bank levels the water level profile along the branch and the flow distribution will vary between the left and right sides of the river The MIKE FLOOD couple file is mf couple Run this simulation then inspect results using the Result Viewer in MIKE ZERO Contours of water depth and vectors of velocity at two instances in the simulation are shown below 1600 Graphical Items 1500 Color point il gt lt Width point d i 1500 1500 1400 1400 1300 1300
70. we Mom Link type Location Fact Ext Fact Etandarai E 1 000 1 500 j This is an abbreviation for Momentum Factor The Momentum Factor is applied to the momentum terms in MIKE21 for standard links A value of 1 means full momentum transfer through the link while a value of 0 means that momentum transfer is not guaranteed 16 E MIKE FLOOD 1D 2D MODELLING Note that even if the factor is set to 0 the source term applied to the continuity equation still creates some momentum While this is sufficient in cases where conservation is not critical such as over weir structures or for very large MIKE 21 cell size relative to the MIKE 11 flow capacity it will not be accurate enough for all cases On the other hand in some instances model stability may be improved by removing the momentum terms Momentum is disabled for the lateral links in MIKE 11 because of the conceptual difficulties associated with lateral flows in a 1D model For the structure links momentum is preserved via the implicit terms and this parameter is not applicable 3 2 4 Ext Fact This 1s an abbreviation for Extrapolation Factor For standard links the extrapolation factor has a default value of 1 5 This factor controls the time predictor in MIKE 11 which establishes MIKE 21 link values for the next timestep If factor is set to zero the same value at n 1 will be used as at n Note f the last q point in the linked branch is a structure this factor must be set to zero

MIKE FLOOD 1D-2D MODELLING

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