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      Dear Guests   12/24/2016

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flood modeling

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Hi All,

I would like to model floods and evaluate damages it could have had on crops in a particular area. The problem is however, I do not have clue where to start and what processes are.

So far, the dataset I have :


- Digital Elevation Model (DEM)

- Land use map (with crop types)

- measure from gauge : water height (in meter) and debit (in cubic meter per second)


so, from there, where I am going, any other datasets needed?


Thank you

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so what software you prefer?


for hidrology modelling there are many software to make flood modelling


for me I will use HEC-HMS


the principle are :


1. DEM for topography measurement, so we can see the runoff fill the cavity or basin

2. Water height and debit to calculate the inflow to specified river/channel

3. overlay crop in to the dem to to measure the extents of specified crop that overflow by flood


you need another data too :

river morfology or maybe cross section from specified channel or river to calculate max capacity of the river/channel itself



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Thank you for the quick reply. I have ArcGIS in hand. Let me check HEC-HMS and will report back how I do. NOt very clear to me right now, how do you model which area gets flooded, since I think not every area under the waterheight will get flooded, only area close to the river/bassin, and even then, waterlevel is not getting as high as where the gauge is.


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If you want to model floods you will need two things:


Set up an hydrology model such as HEC-HMS to estimate your storm peak flow. Part of the model can be developed in GIS using ArcHydro and HEC-geoHMS. 

Then once peak flow is estimated, Create a HEC-RAS model and run a steady flow analysis to estimate flood depths and extents. Hydraulic model can be developed in GIS using HEC-geoRAS


These extensions are public domain and can be downloaded from the US Corps of Engineer webpage.


Datawise, for hydrology, you will at a minimum need a DEM, stream layer, landuse and soils.  Additionally, you will need rainfall data and flow data if you wish to calibrate the model.

                 for hydraulics, landuse, for mannings, DEM to delineate floodplain and cut model cross sections. However, a TIN is preferable to a DEM to extract the cross section profiles.

Edited by snoop

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I'm sorry for the extremely delayed answer but I just saw it.

Here's an alternative approach in case the requested clarification is still pending.


It all depends on the scale of implementation: Regional (smaller than 1/25.000, ie. 1/50.000 etc), Local (greater than 1/25.000, ie. 1/10.000, 1/5.000) or even site-specific (greater than 1/5.000, ie 1/2.500 ,1/1000 etc)

Data accuracy (especially regarding elevation) define in any cases the accuracy of outputs.

I would suggest a two step procedure: use morphological models to define "flood prone" areas; for instance the Topographic Wetness Index or TWI.


Beven, K. J., and M. J. Kirkby. "A physically based, variable contributing area model of basin hydrology/Un modèle à base physique de zone d'appel variable de l'hydrologie du bassin versant." Hydrological Sciences Journal 24.1 (1979): 43-69.

Sørensen, R., U. Zinko, and J. Seibert. "On the calculation of the topographic wetness index: evaluation of different methods based on field observations." Hydrology and Earth System Sciences Discussions 2.4 (2005): 1807-1834.

[12] Boehner, J., Koethe, R. Conrad, O., Gross, J., Ringeler, A., Selige, T.: Soil Regionalisation by Means of Terrain Analysis and Process Parameterisation. In: Micheli,E., Nachtergaele,F., Montanarella,L.[Ed.]: Soil Classification 2001. European Soil Bureau, Research Report No. 7, EUR 20398 EN, Luxembourg. pp.213-222, 2002

Manfreda S., Di Leo M., Sole A.: Detection of Flood-Prone Areas Using Digital Elevation Models. Journal of Hydrologic Engineering, 16 (10):781-790, 2011, (2011).

Rafael De Risi (2013): “A Probabilistic bi-scale framework for Urban Flood Risk Assessment, PhD Thesis, Dept. of Structures for Engineering and Architecture, University of Naples Federico II, p.198, Naples.

Papatheodorou K., Tzanou E., Ntouros K. "Flash Flood Hazard Prevention using Morphometric and Hydraulic models. An example implementation. "International Congress on “Green Infrastructure and Sustainable Socities/Cities” GreInSus’ 2014.

Maftei C., Papatheodorou K., Flash flood prone area assessment using geomorphologic and hydraulic models, Journal of Environmental Protection and Ecology (JEPE), Vol. 16(1), pp. 63-75, ISSN 1311-5065, 2015.


This procedure provides QUALITATIVE outputs; ie. consider the output as a map of the gradually flooded areas with increasing amounts of storm water. Data required include ONLY topography and the methodology provides reliable outputs with an accuracy relative to the input topographic data (the greater the scale the more accurate - but it's about defining susceptibility and NOT hazard).

In case topographic maps of a large scale (1/2.500 or greater....1/1000 etc) are not available, this stage will help you focus in specific "Flood Prone" areas where (2nd stage) you are going to need large scale topo maps, in order to assess flooding parameters (re- occurrence period, flood water flow velocity, flood extend and flood depth). All these parameters will help you define the level of damage in the area. Data requirements for this 2nd stage, which can be implemented using HEC-RAS, also include rainfall intensity (and manning coeffcients).


For the implementation, I would suggest using QGIS or ArcGIS for the 1st stage, since both include plug-ins to create HEC-RAS geometries (cross sections). To my opinion QGIS is far more efficient and stable.

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