Flood Risk Map

[StratosVasilakos]

Hi there,

I'm doing a flood risk map of an area and I want to create a DTM to see if there'll be a possible flood. I've gathered all of my data with

SmartNet and Total Station and I have a dataset of 3D coordinates. I'm not so sure how to create a DTM but once I do that how can I tell

if there'll be a flood in the area?


Thank you very much,

Stratos Vasilakos
University of Glasgow.

[neilo_brien]

To identify a community's flood risk you have to calculate statistical data for river flow, storm tides, hydrologic/hydraulic analyses, and rainfall and topographic surveys. Then use this data to create the flood hazard maps that outline your community's different flood risk areas.

[StratosVasilakos]

Hi Neil,

thank you very much. The only data that I have are the ones from the survey that I did

with GPS and Total Station. I don't have access to any other kind data. Someone told

I can do the flood risk map just with the DTM or using ArcHydro tools.

[MattMead]

1) You can either convert your points to a TIN and then the TIN to DEM conversion(all in 3dAnalyst toolbox) or you can use one of the interpolate to Raster methods in Spatial Analyst.

2)The DTM would only be the terrain that you would compare to the water surface elevations to determine if the area is inside the floodplain or not.  If you want to calculate the flood risk, ie the percent chance that any particular location will flood in a given year, it requires several flood profiles from known return intervals(ex, 500yr=0.2%, 100yr=1%, 50yr=2% etc) like the other person said.  FEMA is developing Risk MAP(Mappings, assessment and planning) to do just this, but it does not appear that their guidance documents are publicly available yet.

To calculate the water surface elevations you need a hydraulic model(ex. HEC-RAS) to calculate the flood elevations, and a hydrologic model(HEC-HMS) to calculate the flow rates that go into the hydraulic model.  From what I understand ArcHydro is only for delineating the watersheds...someone else can tell you more.  I did some quick googling and found a powerpoint presentation that seems to imply that it has a hydrologic model built in.  MBoucher21 seems to be the go to guy for Arc Hydro help here so maybe he will stop by and help you on that.

If you do need to expand your dataset, http://floods.jrc.ec.europa.eu/ has a fair bit of information on who is in charge of what data.  Its been a couple years since I had to go there for a project so I'm not sure where anything is unfortunately.  I do seem to recall getting the impression that most of the data(including stream models) were created by government agencies as opposed to private companies so you may be able to freely request additional data.  I'm in the US though, so I honestly have no idea how the EU handles survey data.  Any idea if there is an overall keeper of data like the USGS is here in the US?

If you can get a hold of LISFLOOD model http://floods.jrc.ec.europa.eu/lisflood-model.html it looks like it might be exactly what you need.

Best of luck.

[StratosVasilakos]

Hi Matt,

lots of information there! Thank you very much! The problem is that I don't have access to other kinds of data
except the ones from the survey I did. So, I have a file of X, Y, Z coordinates and from these I have to create a
DTM. My supervisor told me I can do the flood map only with the DTM or I can take a look at ArcHydro Tools which
I did but I don't understand how they work, plus I think I need data for rainfall etc for those tools to work.

[MattMead]

Yes, you will definitely need rainfall data for any sort of hydrology project.  From some googling, it looks like the Met Office might be your best bet as to who to contact to get such information.  http://www.metoffice.gov.uk/climate/uk/ws/  Are they the UK equivalent of the US's NOAA(National Oceanic and Atmospheric Administration=keepers of all things weather related)?  It looks like you can get the 30-year average RF here: http://www.metoffice.gov.uk/climate/uk/averages/ but it looks like that is monthly totals and not any specific storm/return interval event.  Still, probably worth checking out the Met Office.

As for your supervisor saying all you need is the terrain....double check with them? 

Slightly random question, is this stream based flooding or local flooding(undersized pipe/poor drainage/etc)?

Also,did you do the survey yourself or was the data given to you by your supervisor?  The reason I ask is because if you didnt do it yourself is it possible that some of the survey points are "high water marks" that denote the peak of the flood extents?  If so, the elevations of such points would give you the flood elevations that you need to compare to your terrain data.  That is the only way I can think of that you can determine what floods or not with just the survey data that you have.

[StratosVasilakos]

Hi Matt,

once again thank you very much! I searched all the sources you told me but I can't find something suitable
for my area. I did the survey and I know that the resulting DTM will not be very good because there were
parts of the river not accessible so...
There was a exercise I did with elevation data of an area, shapefiles for buildings and roads and then into ArcScene
tried to show a possible flood.
I'm very frustrated because I don't know what to do!

Regards,

Stratos

[DarrochKaye]

Rainfall data is collected by the Scottish Environment Protection Agency (SEPA) and dependent on your exact location, it should be in 15min intervals and should be available through the Freedom of Information Act.