I am working on flood plain analysis. I have completed all the process of the DEM generation, contour interpolation. Sink fill processing of the DEM.
Now two things i need a clarification
1. I am interested to get a flood extent in 1 D. For this purpose i need to give input to the model. So the data i need to add to this I want elaboration.
2. Shall I use HEC RAS for this and if that is the case what type of the data will be needed for input.
Please specify
The 1D hydraulic modelling is in deed carried out with HEC-RAS. For this purpose, just as any other 1D hydraulic modell you need to input cross section of the river. For this you have to possibilities; either you extract cross sections from a DEM or you have field measurements of your cross sections. Let me now elaborate on the first one.
For preparing geometric data (that is cross section data) there is a GIS extension called HEC-GeoRAS wich works with ArcGIS. This one allows you to define and extract cross sections and other pertinent information like river bank boundaries for example. This may become a long tedious work, but a necessary one wich will save you the manual input of geometry data within HEC-RAS, as you export directly from ArcGIS to HEC-RAS by using the HEC-GeoRAS extension.
If you do not have ArcGIS, you can use any other GIS software to define and extract cross sectional data, but you are going to find the way to define your whole geometry within HEC-RAS.
One observation though, cross sectional data from DEM should in principle only be used for the flood plain since DEM usually do not represent river channel geometry well; the cell resolution usually is to low and the elevation of the channel is usually that of the water surface and not that of the channel bottom. So be carefull about this.
Second option is to have field data from your river and this you can enter manually into HEC-RAS. By the way HEC-RAS comes with an almost self explanatory manual, wich should guide you through the process.
Then under ideal conditions you should have field data for your river tied up to flood plain data from your DEM.
Then you have to have an idea of the boundary conditions regarding the flow in the river. For a river stretch somewhat away from the ocean and not affected by dams, you can safely assume uniform flow conditions (normal flow) at the inlet and outlet of your river stretch.
At last you will need river discharge for different recurrance probabilities, wich you should have previously stablished through hydrological analysis. At this point it is important to define what information is important for you. If you just want to delimit flood plains you can do a steady flow simulation with your peak discharge. If you want to estimate flood travel time, flood wave attenuation and so on, then you need to carry out an unsteady flow simulation with a hydrograph. As a side note, the unsteady flow simulation is not so straight forward, since the numerical solutions do not converge so easily. Meaning you have to manipulate your geomtrical data until the solutions converge and then you have to judge if your results are maningfull.
For a steady flow simulation, running the model is quite a straight forward issue, the actual work is getting the data ready.
Once this is finished you can export a Raster map of the water elevation to ArcGIS and the Flood = WaterElevation - DEM. So wherever the Water Elevation is larger than the DEM, you will have a flood. Being that this is a 1D modell you will probably have to manually correct many strange issues, such as isolated water ponds which are not connected to the river therefore raising the question where the water came from. Simplest solution you connect the pond to the river and define by hand this additional flood area.
Hope it helps and again, referr to the manuals, they are quite practical.
Go and see the technical article published by the team including Herve Piegay in the journal Geomorphology in 2015. They have done a toolbox for ArcGIS that should help you do that.
Otherwise look at the "Tools in Geomorphology" by M. Kondolf and H. Piegay.
dear gomez i saw the ebook but only sample chapter is avaliable . can u help me out please.
Dear Amol,
You would have to wait, I am out station in the field until mid january... but if you still need it by then, contact me again, I will send you an electronic copy.
Dear recently I am working on Arc GIS for the preparation of map of ground water quality
I am of the opinion of Rafael Anleu. for more information contact:
[email protected], [email protected], [email protected], [email protected] (my PhD).
They can help you
I think that Rafael Anleu gave you a brief overview of what you have to do in order to do the Flood plain mapping using Arcgis and HEC RAS!
Dear pawar,
you can follow this article:
https://www.researchgate.net/publication/294089869_Assessing_flood_inundation_extent_and_landscape_vulnerability_to_flood_using_geospatial_technology_A_study_of_Malda_district_of_West_Bengal_India
Article Assessing flood inundation extent and landscape vulnerabilit...
Dear pawar,
the main data you need are the geometric data like the cross-sections of the main channel or river, also you need the roughness manning coefficient for left and right of floodplain. It is very important to know the boundary conditions that include the discharge hydrograph in upstream and water level hydrograph or rating curve for downstream. It is necessary to see the manual of HEC-RAS,
www.hec.usace.army.mil/software/hec-ras/.../HEC-RAS_4.1_Users_Manual.pdf
http://hmf.enseeiht.fr/travaux/projnum/content/2011-g3/1-modeliser-une-riviere-avec-hec-ras
dear all,
we are working in Arc gis, hecras and water quality analysis ... if you need any type of guidance please contact 9765006651, email: [email protected]
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