DFLOWZ Guide
Contents
1. Dipartimento di Scienze Biologiche Geologiche e Ambientali Universit di Bologna Italy DFLOWZ A free program to evaluate the area potentially inundated by a debris flow by Matteo Berti matteo berti unibo it Version 1 0 March 2014 Working Group Matteo Berti University of Bologna Italy Alessandro Simoni University of Bologna Italy Table of contents 1 2 3 4 5 6 IRtFOAUCtioni rr ee a cani Sori 3 Getting started acre lla 5 2 1 erz oap 3E p 5 2 2 The Graphical User IntetfaCce Lilli iii eat 6 2 3 Run a DFLOWZ analysis I 7 2 4 BEPCRUIdguIsb DR 7 2 5 Satmple datailes cote ome ERI ME IU ME 8 Theoretical background crinale Lean ER ai 9 Features and specifications eere iii 13 4 1 Digital Elevation Model 5 octets onde torem aon es setae rae een to enano 13 4 2 Flow esr 14 4 3 Debris o AT Tu EE 15 4 4 Cross SEC UONG oeiee 17 4 5 Analysis OptiOris i e bc E ai 18 4 5 1 Start deposition from a specified cross Section iii 18 4 5 2 Modify the channel flow area ii 19 4 5 3 Modify the DEM erectae e re ie tas Per abi 20 4 6 Showing results citet etes ee reete ecd ed E aae dee qu or vende dex esee dee E Pot cane 21 Release history ceteri etre ette tree e im iaia 23 iij 24 To download DFLOWZ and the electronic version of this user s manual please go to www bigea unibo it it ricerca2. Calculate button runs the analysis and shows the results on a new window Fig 4 6 The planimetric inundated area and the flow channel path are drawn on a low resolution contour map max 100x100 cells to speed up the display Section 1 Flooded Expected flow area m2 77 Computed flow area m2 77 DFLOWZ 1 0 Debris flow inundated area mE 2160 Debris flow volume m3 30000 Show cross section traces Expected inundated area m2 16413 2155 Computed inundated area m2 19704 2500 N 8 View section x 10 Elevation m N amp 2140 2135 2130 2125 1 n 1 4 80 Distance m Section 5 2060 Expected flow area m2 77 Computed flow area m2 79 E 7 pe 2 c B S 3 E S8 pi t w 5 Elevation m 6 488 6 49 6 492 Est coordinate m Fig 4 6 Sample results of DFLOWZ Planimetric inundated area left and cross sectional flow area for two selected profiles right The window provides a quick view of the results For a more accurate display click the Export grid button to save the inundated area in ASCII Grid format with the original DEM resolution The grid can be then opened using most GIS software and combined with other digital maps and georeferenced data The box Show cross section traces shows the profiles used in the analysis as said above the intersecting cross sections could be excluded
3. 1 Digital Elevation Model The DEM must include the active part of the fan that is the area where relatively recent deposition erosion and alluvial fan flooding have occurred This area typically contains the active debris flow channel which is the most probable path for future events Glade 2005 When the identification of active zones is difficult or when it is likely to have flow diversion from the active channel the entire fan area should be included in the DEM and different potential debris flow paths must be analyzed DFLOWZ is adapted to run with high resolution digital elevation models 1 to 3 m cell size such as those derived from airborne LiDAR data Care should be taken when using coarse resolution DEMs 10 m cell size or larger since the flow channel can be poorly represented and this will have important consequences on simulation results In general a smoothed topography will produce an inundation area which is wider and shorter than expected because a low resolution DEM underestimates the available area of the flow channel and the debris flow will inundate a large width to accomplish the theoretical value of A Fig 4 1 The main risk in these cases is to underestimate the runout distance and to spread the flow too much sideways DEMs often contain erroneous elevations referred to as sinks that are usually filled before hydrological modeling However some sinks may represent real surface depressions where the debri
4. by the analysis while the button Edit Figure allows users to customize the appearance of the map and to save it as image using the built in editing functions of Matlab Click on the listbox View section to see the inundated flow area in each cross section The cross sectional profile is shown on a separate chart with the flow area colored in red Fig 4 6 Interactive zoom and pan available as built in Matlab functions allow to check whether the model provides realistic results A careful check of each cross section is recommended in order to detect unexpected results related to particular topographic conditions 5 Release history Do not hesitate to contact the author matteo berti unibo it if you find any error and bug or if you have comments or suggestions to improve DFLOWZ We need your feedback Release Date Description 1 0 March 2014 First release of DFLOWZ 6 References Berti M Simoni A 2007 Prediction of debris flow inundation areas using empirical mobility relationships Geomorphology 90 144 161 doi 10 1016 j geomorph 2007 01 014 Berti M Simoni A 2014 DFLOWZ a free program to evaluate the area potentially inundated by a debris flow Computers amp Geosciences 67 14 23 Bianco G Franzi L 2000 Estimation of debris flow volumes from storm events In Debris flow Hazards Mitigation Mechanics Prediction and Assessment WieczorekGF NaeserND eds Balkema Rotterd
5. dflowz If you have questions about DFLOWZ or its use please contact Matteo Berti matteo berti unibo it 1 Introduction DFLOWZ is a free application that provides a preliminary evaluation of the area potentially inundated by a debris flow The method is based on the empirical statistical model originally proposed by Iverson et al 1998 to predict the runout length and the areas affected by lahars LAHARZ model DFLOWZ extends the Iverson s model to debris flow phenomena taking into account of the unconfined flow that occurs on a depositional fan Beside a digital elevation model DEM DFLOWZ has few input requirements debris flow volume and possible flow path The procedure is implemented in Matlab and a Graphical User Interface helps to visualize initial conditions flow propagation and final results Different hypothesis about the depositional behaviour of an event can be tested together with the possible effect of simple remedial measures Uncertainties associated to input parameters can be treated and their impact on results evaluated DFLOWZ is intended for students and practitioners who need a simple method for debris flow susceptibility mapping The method can be an alternative to more comprehensive numerical models when calibration data are not available or when a preliminary hazard analysis is required However it is essential to be aware that DFLOWZ is a simple geometrical model that does not reproduce the complex dy
6. used in the analysis can be conveniently stored in a data file A data file is a text file listing all the values used to run a simulation DFLOWZ creates a text file with dfz extension when the user click the Save button Alternatively the file can be created or modified with any convenient text editor Figure 2 2 shows the structure of a data file I Case 01 dfz Blocco note eai 9s File Modifica Formato Visualizza Digital Elevation Model ASCII raster format dem asc Flow channel path polyline shapefile channel shp Design debris flow volume m3 30000 confidence Intervals for the uncertainty parameters a and b 1 90 2 60 3 30 4 0 5 30 6 60 7 90 4 4 Comsutit ina cross sections method value method i user defined 2 automatic normal to channel 3 automatic parallel to slope value name of the shapefile for method 1 OR number of sections for methods 2 and 3 3 12 Interpolation technique for cross section drawing 1 linear 2 planar 1 Analysis option start deposition from section selected value selected 0 no i yes value number of the starting section used in the analysis put 1 if selected 0 0 1 Analysis option specify the area of the flow channel selected value selected 0 no 1 yes value name of the text file listing the x y A pairs where A is the flow area to be subtracted for each channel reach put NN if selected 0 O NN An
7. Ref 2010ES9BPY 005 Time space prediction of high impact landslides under the changing precipitation regimes 2 Getting started 2 1 Installing DFLOWZ DFLOWZ was developed in Matlab and compiled as a standalone application The application can run on any windows system without having Matlab or its auxiliary toolbox If you do not have Matlab installed on your computer release R2011b or higher download the Installation package with Matlab libraries 398 MB and save it on your computer in a separate folder The installation package contains e the DFLOWZ executable e four sample data files e the shared Matlab libraries Run the self extracting executable and follow the instructions displayed by the setup program The program will extract the DFLOWZ executable and the sample data files on the installation folder and it will run the Matlab Compiler Runtime MCR www mathworks com trademarks for a list of additional trademarks Other product or brand names may be trademarks or registered trademarks of their respective holders WARNING This program is protected by copyright law and international treaties Copyright 1984 2011 The MathWorks Inc Cancel P MATLAB Compiler Runtime Installer ol To install MATLAB Compiler Runtime 7 16 on your computer click Next MATLAB MATLAB and Simulink are registered trademarks of The MathWorks Inc Please see seriali ti ns R20llb MathWorks The MA
8. TLAB Compiler Runtime MCR is a standalone set of shared libraries that enables the components on computers that do not have MATLAB installed Once the installation is completed you can run the DFLOWZ executable execution of compiled MATLAB applications or If you have Matlab installed on your computer release R2011b or higher with the Statistics Toolbox just download the zip file 2 4 kB that contains the DFLOWZ executable and the sample data files Unzip the file and run the application 2 2 The Graphical User Interface The Graphical User Interface GUI of DFLOWZ is shown in Fig 2 1 r E onowzio arim DFLOWZ 1 0 A free program to evaluate the area potentially inundated by a debris flow r 1 Digital Elevation Model ASCII grid r 4 Cross sections Cross sections drawing User defined polylines shapefile r_ 2 Flow Channel polyline shape file LI Select file Automatic Normal to flow channel _ Automatic Parallel to the slope Number of sections 3 Design debris flow LI Volume m3 Options Confidence intervals for the prediction Interpolation algorithm DW X a V A relation 0 se b V B relation 0 r 5 Analysis Options 7 Start deposition from section E Modify the flow channel area i 7 Modify the DEM File name Path Open an exsisting datafile Plot the empirical scaling relatio
9. alysis option modify the DEM selected value selected 0 no i yes value name of the polygon shapefile put NN if selected 0 O NN Fig 2 2 Structure of a DFLOWZ data file Click the Open button to load the data file into the program 2 5 Sample data files Four sample data files are provided in the folder named Sample The files share the same digital elevation model dem asc flow channel path channel shp and design debris flow volume 30000 m but differ in other analysis parameters e Case Ol dfz is the data file used to generate Fig 4 6 which is Fig 9 in Berti and Simoni 2014 e Case 02 dfz uses the variables from case 1 but higher values of the confidence levels related to the two uncertainty parameters a and b see Berti and Simoni 2014 e Case 03 dfz uses the Modify the flow channel area option box 5 in Fig 2 1 to simulate an excavation of 30 m in the upper reach of the flow channel the values of the extra flow area are listed in the text file channel mod txt e Case 03 dfz uses the Modify the DEM option box 5 in Fig 2 1 to simulate the presence of a levee on the left side of the flow channel the shapefile levee shp contains the polygon to modify and the corresponding change in elevation 5 m stored in the attribute field ChangeEl Click the Open button to load a sample file for testing 3 Theoretical background A detailed description of the theory b
10. am 441 448 Ceriani M Crosta G Frattini P e Quattrini S 2000 Evaluation of hydrogeological hazard on alluvial fan Proc Int Symp INTERPRAEVENT 2000 Villach Band 2 213 225 D Agostino V Marchi L 2001 Debris flow magnitude in the Eastern Italian Alps data collection and analysis Physics and Chemistry of the Earth Part C 26 9 657 663 Hungr O Fell R Couture R Eberhardt E 2005 Landslide Risk Management Proceedings of the International Conference on Landslide Risk Management Vancouver Canada 31 May 3 June 2005 Taylor amp Francis 776 pp Hurlimann M Rickenmann D Medina V Bateman A 2008 Evaluation of approaches to calculate debris flow parameters for hazard assessment Engineering Geology 102 152 163 Iverson R M Schilling S P Vallance J W 1998 Objective delineation of lahar inundation hazard zones Geological Society of America Bulletin 110 972 984 Jakob M Hungr O 2005 Debris flow hazards and related phenomena Springer Chichester UK 798 pp Kronfellner Kraus G 1985 Quantitative estimation of torrent erosion In International Symposium on Erosion Debris Flow and Disaster Prevention Tsukuba Japan A Takei ed 107 110 Marchi L D Agostino V 2004 Estimation of debris flow magnitude in the Eastern Italian Alps Earth Surface Processes and Landforms 29 207 220 Scheidl C Rickenmann D 2010 Empirical relationships for debris flow mob
11. ath has a profound effect on the results because the flooded area always wanders around the predefined channel A proper definition of the potential flow path is therefore essential for meaningful results In most cases it is quite easy to identify the active debris flow channel on the fan by means of aerial photographs and field surveys The active channel is directly connected with the main feeder channel at the fan apex and it is usually characterized by fresh deposits scouring bare soil or scattered vegetation Hungr et al 2005 However when there is no morphological evidence of recent activity or there are no historical records of past events the choice of a likely debris flow pathway can be difficult In this case it is necessary to perform a sensitivity analysis to evaluate the effect of different flow paths on the inundated area The method proposed by Hurlimann et al 2008 is suitable to this purpose The method combines the D8 flow routing algorithm with a Monte Carlo random walk model to generate trajectories of debris flows that include the spreading effect around the steepest path Scheidl and Rickenmann 2010 implemented this method in their TopRunDF model The computed inundated area for each potential debris flow path can be then combined to obtain a hazard map showing the probability of each cell to be affected by a future debris flow given for example by the ratio of the times the cell has been flooded divided by th
12. cates the expected value of cross sectional flow area A left and planimetric inundated area B right for the selected debris flow volume 4 4 Cross sections DFLOWZ evaluates the inundated area B by connecting the inundation width W computed at each cross sectional profile Fig 3 2 The traces of the profiles can be defined manually or generated automatically by DFLOWZ see box 4 in the GUI Fig 2 1 In the first case the traces are manually drawn on a GIS software and imported in DFLOWZ as polyline shape file This option is useful when the topography is complex or irregular and a close control on the computational cross sections is needed More commonly the traces are generated automatically by specifying the number of sections and their direction normal to the flow channel or parallel to the slope Normal to flow channel means that each trace is drawn perpendicularly to the local direction of the flow channel parallel to the slope means that each trace is parallel to the local direction of the slope evaluated as the mean aspect of a 3x3 kernel centered at the intersection point between the channel and the profile Unless the flow channel cuts transversally the slope the differences between these two options are usually minor The traces are numbered consecutively from the first section upstream Before running the analysis is important to check the location of the traces Map button on the GUI Fig 2 1 to ensure the
13. correctness of the result Moreover since the number location and direction of the profiles affect to some extent the flooded area it is also important to evaluate the sensitivity of the analysis to such a factor Two methods of surface interpolation can be selected to generate the cross sectional profiles referred to as IDW and Planar in the GUI The IDW method Inverse Weighted Distance method Watson and Philip 1985 calculates the unknown elevation at each point of the profile as the average of the five neighbor cells weighted by their distance The Planar method approximates the ground surface of the nine cells around the point with a plane and computes the unknown elevation by planar fitting Planar method typically provides a smoother topographic profile It is common that two cross sections intersect near bends in the channel In this case DFLOWZ identifies the intersection point between the two lines and compares it with the inundated width computed for the downstream section Fig 4 3 if the inundated width exceeds the intersection point that is the debris flow would inundate an area already flooded the cross section is excluded by the analysis and the computation continues with the section downstream Fig 4 3b otherwise both sections are considered Fig 4 3a This control is necessary because the model assumes independent flooding of 2D profiles without interaction effects Fig 4 3 In case of intersect
14. e total number of simulations Such an analysis is also advisable when it is likely that the debris would divert from the active channel as a consequence of channel blockage or overbanking flow and flow downhill on the fan The probabilistic analysis of the multiple channel paths is not implemented in the current version of the program but it can be easily done by combining the results obtained with different channel paths 4 3 Debris flow volume The design debris flow should indicate the largest probable debris flow generated by hydrological events in the basin It is defined by a design volume V and by two uncertainty factors a and b see above Debris flow volume is here intended as the total amount of sediment organic material and water reaching the fan apex This volume is a function of the volume of the initiating failure or failures plus the volume entrained along the transport reach The estimate of debris flow magnitude is an essential step in the analysis since the extent of the flooded area mainly depends on the input volume Although different methods have been proposed in the literature to guess the potential debris flow volume Kronfellner Kraus 1985 Bianco and Franzi 2000 Ceriani et al 2000 D Agostino and Marchi 2001 Marchi and D Agostino 2004 Jakob and Hungr 2005 this estimate still remains a difficult task The main uncertainties are related to sediment availability expected water inflow effect of vegetatio
15. ehind DFLOWZ can be found in Berti and Simoni 2007 In this section we briefly outline the general principles of the model DFLOWZ extends to debris flows an empirical statistical model originally proposed by Iverson et al 1998 to predict the runout length and the areas affected by lahars LAHARZ model Both models are based on the simple observation that the larger the volume of the flow V the larger the cross sectional flow area A and the inundate planimetric area B The dependence V A and V B has been documented for different types of flow rock avalanches lahars debris flows and reported in form of two semi empirical scaling relationships Griswold and Iverson 2008 Scheidl and Rickenmann 2010 A k V 1a B k V 1b where k and k are dimensionless coefficients called mobility coefficients that vary with the flow type and 2 3 is a fixed exponent justified by geometric similarity Iverson et al 1998 Simoni et al 2011 combined the data of about 100 historical debris flows obtaining k 0 07 and k 18 Fig 3 1 These values can be considered of general validity for non volcanic debris flows since no systematic difference was found between datasets collected in different geological environments In reality the mobility of debris flows is certainly influenced by water content grain size distribution or debris availability but these differences are masked by the scatter of the data due to measur
16. ement uncertainties To account for the data dispersion around the regression lines Simoni et al 2011 proposed to include two uncertainty factors a and b in the scaling relations A a 0 07V 2a B b 18V 2b The parameters a and b indicate how the expected values of A and B differ from that predicted by the regression lines shown in Fig 3 1 The numerical values of a and b are plotted in the small insets of Fig 3 1 as a function of the confidence level of the prediction which measures the distance from the regression based upon the sample standard deviation and t statistic Weisberg 1985 10 is above the regression line 85 data 5 oat 4 Ga 10 FE pra E ee C 5 n d a 2 3 g 108 below the regression line i A 0 07V ma eee I NX 0 20 40 60 80 100 Pd oO Confidence level 279 95 ius 2 _ E se _ ossi o 10 n c N P de ne gle 79 P o no Vett o p o de Q S o 1 qo o 2 b 10 aere e I ed at _ 2 x90 E a 8 en s E 10 d goe 256 CO E a 10 vs i 0 10 10 10 10 104 10 10 10 108 3 Debris flow volume V m 10 above the regression line ge 115 data Uncertainty factor b x adi below the regression line P 0 1 99 0 20 40 60 80 100 ont Confidence level A 2 Planimetric area B m 3 A 10 10 10 103 104 10 10 107 108 Debris flow vo
17. es in order to perform this analysis easily The areas to modify can be digitized as a polygon layer on a GIS and saved as a shape file with the required change in elevation stored in an attribute field named ChangeFEl number data format values in meters DFLOWZ loads the polygon shape file and changes the elevations of grid cells inside the polygon according to the specified value Fig 4 5 A positive value will increase the elevation a negative value will lower the topography The data file Case 04 dfz provides a sample application of this option Modified DEM Original DEM ChangeE 0 ChangeEl lt 0 Original DEM Modified DEM Fig 4 5 The Modify the DEM option allows the user to simulate a positive ChangeEl gt 0 or negative ChangeEl lt 0 variation of the ground topography DFLOWZ reads the areas to modify from a polygons shapefile where ChangeEl is an attribute field When using these options it is essential to bear in mind that DFLOWZ is a simple geometrical model that does not reproduce the complex dynamics of debris flow channel interaction Therefore any simulation of debris flow countermeasures has to be carefully evaluated and the final design must always rely on detailed hydraulic modeling that account for flow velocity shear stress and pressure gradient For instance the possibility of structure damage failure and subsequent flow diversion is not considered in DFLOWZ 4 6 Showing results The
18. eter that should be chosen on the basis of a detailed geomorphological survey of the flow channel on the fan area This option allows to evaluate how the flooded area varies if some uncertainty still remains If not checked the program uses the default value of 1 and the deposition starts at the first upstream section 4 5 2 Modify the channel flow area The option Modify the channel flow area box 5 Fig 2 1 is designed to improve the analysis when the channel morphology is poorly represented in the DEM The influence of DEM resolution on debris flow routing is a well known problem e g Stolz and Huggel 2008 All the existing models are highly sensitive to the accuracy of topographic data and this also applies to simple methods like LAHARZ and DFLOWZ Stevens et al 2002 Berti and Simoni 2007 In particular results can be very inaccurate when the channel morphology is poorly represented in the DEM for instance because of a low spatial resolution Fig 4 4a or because the channel has been filled or excavated Fig 4 4b a Low resolution DEM Real topography Extra flow area A b Excavated channel Real topography gt Extra flow area A I Fig 4 4 The user can specify an extra flow area Ag along some stretches of the channel in order to account for a poor resolution of the DEM a or to roughly simulate a channel excavation b The extra flow values must be listed on a separated text file together with
19. g 3 1 The default values are 0 which correspond to a 1 and b 1 In this case A and B are estimated from the input volume V using the mean regression lines shown in Fig 3 1 The implicit assumption is that the mobility of debris flows in the study area is similar to that typically observed for subaerial debris flows By selecting for instance a confidence interval for b 90 we assume that the flow can be more mobile than the average and that the inundated area will be larger than usually is In the example shown in Fig 4 2 the user selected a 0 and b 60 then the expected values of A and B fall respectively on and above the corresponding regression lines Click on the Charts button of the GUI to see where the design flow plots with respect the two scaling relationships Simoni et al 2011 provide several indications on the selection of the uncertainty parameters a and b Scaling Charts meg X DFLOWZ 1 0 Empirical scaling relationships Debris flow volume m3 50000 Expected cross sectional flow area A 109 m2 Expected inundated area B 45684 m2 Log A m2 Log B m2 Log V m3 Log V m3 The red points indicate the expected cross flow area left and flooded area right for the design debris flow volume Points lies above or below the regression line depending on the selected Confidence Intervals for a and b Fig 4 2 Empirical scaling relationships implemented in DFLOWZ The red point indi
20. ility and deposition on fans Earth Surface Processes and Landforms 35 157 173 Schilling S P 1998 LAHARZ GIS programs for automated mapping of lahar inundation hazard zones U S Geological Survey Open File Report 98 638 80 pp Simoni A Mammoliti M Berti M 2011 Uncertainty of debris flow mobility relationships and its influence on the prediction of inundated areas Geomorphology 132 249 259 doi 10 1016 j geomorph 201 1 05 013 Stevens N F Manville V Heron D W 2002 The sensitivity of a volcanic flow model to digital elevation model accuracy experiments with digitised map contours and interferometric SAR at Ruapehu and Taranaki volcanoes New Zealand J Volcanol Geotherm Res 119 89 105 Stolz A Huggel C 2008 Debris flows in the Swiss National Park the influence of different flow models and varying DEM grid size in modelling results Landslides 5 311 319 Watson D Philip G 1985 A refinement of inverse distance weighted interpolation Geo Processing 2 315 327 Weisberg S 1985 Applied Linear Regression John Wiley amp Sons New York 344 pp
21. ing cross sections DFLOWZ checks if the intersection occurs along the inundated width or not In first case b the downstream section is omitted and the computation proceeds with the section further downstream In the second case a both the sections are maintained The sample file Case_01 dfz can be used to test the different options provided by DFLOWZ to draw cross sections Open the file choose an option and compare the inundated area in the different cases The Sample folder contains a shapefile with the traces of 14 user defined cross sections sections shp that must be loaded when the User defined option is selected 4 5 Analysis options Several options are available in DFLOWZ to take control of the analysis and possibly improve the representativeness of the prediction 4 5 1 Start deposition from a specified cross section The option Start deposition from section box 5 Fig 2 1 allows the user to evaluate the sensitivity of the results on the starting point of the deposition As said above the deposition starts at the first upstream section which is usually located at the fan apex In some cases however the flow channel is deeply incised in the upper part of the fan and the deposition may take place only from a point further downstream or the flow channel can be partially filled along its path and the deposition may start upstream the fan apex The starting point of deposition is an important input param
22. lume V m Fig 3 1 Empirical scaling relationships for debris flows from Simoni et al 2011 The dashed lines indicate the 95 prediction intervals Depending on the specific application the uncertainty factors a and b allow the user to obtain predictions of the best worst scenarios in terms of inundated and cross sectional areas as a function of the appropriate confidence level Also different combinations of a and b allow to reproduce different expected debris flow velocity and mobility whenever information on the flow behavior is available For instance one might expect that a dilute flow inundates a small cross sectional area a 1 because of its velocity and deposits over a large planimetric b gt 1 area because of its mobility Anyhow the rationale of such observations is rarely solid enough to base any prediction on and the statistic approach is preferable Equations 2a and 2b are implemented in DFLOWZ to predict the inundated area on a debris flow fan Input data are the debris flow volume V the uncertainty factors a and b the Digital Elevation Model DEM of the fan area the path of the flow channel and the traces of several representative cross sections For a given volume the model first computes the expected value of cross sectional A and planimetric B inundated area using equations 2a and 2b The flow area A is assumed to be constant for any location along the depositional reach and it is used to comp
23. n amount of sediment entrained along the channel bulking and to the fact that debris flow material deposited in previous surges or delivered by bank failure can be remobilized in subsequent surges In practice the estimate of the debris flow volume heavily relies on past observations and it is very difficult if historical data are not available DFLOWZ is computationally simple and it allows to perform a sensitivity analysis on the input volume quickly and easily Such a sensitivity analysis will detect the most significant zones of inundation from debris flows of various volumes thus providing a scenario map of flooding likelihood Of course additional information are required to convert any likelihood susceptibility map into a hazard map of debris flow flooding since flows with different volumes are characterized by different return periods which make larger flows less probable Once a design debris flow volume is selected the uncertainty factors a and b equations 2a and 2b can be varied to calibrate the expected flow area A and inundated area B according to the specific field conditions see section 2 For sake of clarity the possible values of a and b are reported as percentages in the two pull down menus Confidence interval for the predictions of the GUI Fig 2 1 The confidence intervals can be varied from 90 to 90 and the corresponding values of a and b are computed using the curves shown in the small insets in Fi
24. namics of debris flow channel interaction Therefore DFLOWZ cannot replace the existing numerical models that describe the physics of the phenomenon This user manual describes how to use DFLOWZ and the key features of the program Please refer to the reference papers listed below for details on the theory behind DFLOWZ as well as for the discussion of important issues such as choice of input parameters interpretation of the results and limitations of the method Reference papers Berti M Simoni A 2014 DFLOWZ a free program to evaluate the area potentially inundated by a debris flow Computers amp Geosciences 67 14 23 Simoni A Mammoliti M Berti M 2011 Uncertainty of debris flow mobility relationships and its influence on the prediction of inundated areas Geomorphology 132 249 259 doi 10 1016 j geomorph 2011 05 013 Berti M Simoni A 2007 Prediction of debris flow inundation areas using empirical mobility relationships Geomorphology 90 144 161 doi 10 1016 j geomorph 2007 01 014 Disclaimer DFLOWZ was developed for scientific purpose and it is free for non commercial users You are the sole responsible for your use of the program The author and the University of Bologna are not responsible for any damage however caused which results directly or indirectly from your use of DFLOWZ Acknowledgments This work was supported by the Italian Ministry of University and Scientific Research PRIN 2010 2011
25. nships Save the data Show DEM channel and sections i N Info Contact and dislaimer Calculate Compute the debris flow inundated area Fig 2 1 The DFLOWZ graphical user interface A short description of the GUI boxes is given below Box Description 1 Load the Digital Elevation Model of the area in ASCII grid format 2 Load the path of the flow channel in shp format 3 Define the design volume of the debris flow and uncertainty parameters of the volume area scaling relationships 4 Define the method used to draw the analysis cross sections see below 5 Analysis options used to 1 start the inundated area from a specified cross section 2 modify the channel geometry to account for excavated or filled areas 3 modify the DEM to simulate levees structures or retention basins 2 3 Runa DFLOWZ analysis To run a DFLOWZ analysis 1 Load the Digital elevation model of the study area as ASCII grid file 2 Load the path of flow channel as polyline shape file 3 Define the design debris flow volume in m and the uncertainty related to the volume area prediction confidence intervals of the scaling relationships 4 Choose the method to draw the analysis cross sections 5 Select an analysis option if needed 6 Click on the Calculate button to run the analysis A detailed description of these steps is reported in chapter 3 2 4 Data file structure The parameters
26. s can be trapped then reducing the flooded area The user must be aware of real topography to determine whether sinks in the DEM are errors or not The largest DEM array that can be loaded mainly depends on the system memory RAM plus swap file and operating system By assuming that no major processing are launched and that an unlimited memory is available the largest matrix size is about 1500 MB for 32 bit platforms and 16 GB for 64 bit platforms This roughly corresponds to a maximum DEM size of 14000x14000 cells or 46000x46000 cells respectively Input data file is an ASCII Grid 6 lines of header info followed by the elevation data compatible with most GIS software 30 a High resolution DEM 2 m cell size 25 Inundated width 19 m 20 DEM profile 10 Pai Real topography Height m a b Low resolution DEM 10 m cell size 25 4 Inundated width 28 m 20 E See 15 J o I 10 L 5 L 0 f 1 I 1 L 0 10 20 30 40 50 60 Distance m Fig 4 1 Effect of the DEM resolution of the inundated cross sectional width The inundated width tends to be larger for a low resolution channel profile b 4 2 Flow channel DFLOWZ calculates the deposition area by assuming a constant cross sectional flow area A which extends across a user specified channel path The path of the flow channel must be specified by a polyline shape file one single feature no attributes required The channel p
27. the channel coordinates To partially overcome this problem DFLOWZ allows the user to import an external text file which contains for each channel reach between points i and i 1 an extra flow area A in m not represented in the DEM Fig 4 4 A positive value of A will reduce the theoretical value of A on the selected channel reach while a negative value will increase it In the first case the inundated width will be smaller simulating the presence of a larger channel in the second case the inundated width will be larger simulating the presence of a smaller channel It is important to realize that A only affects the theoretical flow area A while B does not vary Therefore the planimetric inundated area will be narrower around the channel reaches with A gt 0 but it will extend longer downstream in order to attain the theoretical value of B This feature can be also used for a preliminary evaluation of debris flow countermeasures such as channel excavation or widening The data file Case 03 dfz provides a sample application of this option 4 5 3 Modify the DEM The Modify the DEM option allows to quickly modify the DEM and to evaluate its effect on the deposition patterns The DEM can be modified to generate 3D structures such as buildings or houses to improve the accuracy of the topography or to simulate the construction of channel levees or deflection walls DFLOWZ takes advantage of the Matlab s capability to read geodata fil
28. ute the inundated width along the profiles extracted by the DEM Fig 3 2 a Planimetric view b Cross sectional view Confined deposition section J i Debris flow volume V ATEEN 07 section i h 20 06 y Unconfined deposition W Fig 3 2 The planimetric inundated area a is estimated by interpolating the cross sectional inundation widths b computed on several cross sectional channel profiles The expected values of cross sectional flow area A and planimetric inundated area B are given by the two scaling relationships shown in Fig 3 1 The calculation starts with the first section upstream and proceeds downstream determining the inundation area between the sections The inundated area is progressively summed until it equals the expected value of B given by 2b The main difference between DFLOWZ and LAHARZ Iverson et al 1998 Schilling 1998 is that our model is designed to roughly simulate unconfined flow deposition When the flow exceeds the available channel area it is assumed that the debris deposits over the ground surface with a constant thickness A The thickness of unconfined flow is a function of debris flow volume and it is simply obtained by dividing V by the expected B A 0 06 V Fig 3 2 4 Features and specifications The Graphical User Interface of DFLOWZ Fig 2 1 is divided into five tasks which allow for the input of physical parameters and selection of run time options 4
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