My client needs maps that show flooded areas above a specified elevation
based on precipitation rate and time. I can approximate precip rates based
on daily measures at nearby weather stations and can assume saturated soils.
The topography is flat: 0-3% slope is the characteristics of this soil map
unit, and the ~40 ha area is essentially flat.
Precipitation flows off this land through an under-road culvert with a
known invert elevation. If the culvert is blocked he needs to know the area
inundated with a given precipitation rate for a specified time (e.g., one
day).
I've looked at the hydrologic models and don't see any that appear to
provide answers to this question. It's not landscape level analyses, nor are
there any defined stream channels, or noticeable slopes. r.lake shows
inundated areas at specified water heights above a given elevation, but
this is independent of precipitation rates and time.
Laurent's Itzi model calculates accumulation at various elevations for
a specified precipitation rate and time, yet I'm not seeing how to use this
if there is blocked at a specified coordinate along the drainage path.
The h_max output map of Itzï will correspond to the maximum water
level reached during the simulation.
To simulate the blockage, you might need to change the DEM locally.
But in the case of a under-road culvert, just leaving the measured
elevation of the road might be enough. The water will accumulate
behind the road until it overtops it (or the rain stops).
If you use direct rainfall, all the cells in the h_max map will appear
wet (although with very small depth). You will need to clean up the
map using r.mapcalc to keep only the cells with a water depth above a
threshold of your choice.
My client needs maps that show flooded areas above a specified elevation
based on precipitation rate and time. I can approximate precip rates based
on daily measures at nearby weather stations and can assume saturated soils.
The topography is flat: 0-3% slope is the characteristics of this soil map
unit, and the ~40 ha area is essentially flat.
Precipitation flows off this land through an under-road culvert with a
known invert elevation. If the culvert is blocked he needs to know the area
inundated with a given precipitation rate for a specified time (e.g., one
day).
I've looked at the hydrologic models and don't see any that appear to
provide answers to this question. It's not landscape level analyses, nor are
there any defined stream channels, or noticeable slopes. r.lake shows
inundated areas at specified water heights above a given elevation, but
this is independent of precipitation rates and time.
Laurent's Itzi model calculates accumulation at various elevations for
a specified precipitation rate and time, yet I'm not seeing how to use this
if there is blocked at a specified coordinate along the drainage path.
The h_max output map of Itzï will correspond to the maximum water level
reached during the simulation.
Laurent,
I did this to reveal water accumulation with un-blocked flows and did not
see how to modify it to show blocked flow accumulations.
To simulate the blockage, you might need to change the DEM locally. But in
the case of a under-road culvert, just leaving the measured elevation of
the road might be enough.
I'll need to experiment with this to understand how to 'leave the road
elevation' when the culvert's blocked. Perhaps increasing the DEM of all
cells to that of the road elevation will do it.
If you use direct rainfall, all the cells in the h_max map will appear wet
(although with very small depth). You will need to clean up the map using
r.mapcalc to keep only the cells with a water depth above a threshold of
your choice.
Don't completely understand this now; thinking about it and trying various
simulations will probably help.
The h_max output map of Itzï will correspond to the maximum water level
reached during the simulation.
Laurent,
I did this to reveal water accumulation with un-blocked flows and did not
see how to modify it to show blocked flow accumulations.
To simulate the blockage, you might need to change the DEM locally. But in
the case of a under-road culvert, just leaving the measured elevation of
the road might be enough.
I'll need to experiment with this to understand how to 'leave the road
elevation' when the culvert's blocked. Perhaps increasing the DEM of all
cells to that of the road elevation will do it.
Culverts usually don't appear on a raster DEM.
For instance, if you use LiDAR DEM, you will have only the elevation
of the road surface. Even bridges might appear as a dam on LiDAR data.
Itzï is not yet able to simulate pipe flow. To model a functioning
culvert, you will need to lower locally the DEM to let the flow pass.
Therefore, I'm not totally sure to understand how you modelled the
functioning culvert without changing the DEM.
But basically, yes, you need to have a DEM showing the actual
elevation of the road surface.
If you use direct rainfall, all the cells in the h_max map will appear wet
(although with very small depth). You will need to clean up the map using
r.mapcalc to keep only the cells with a water depth above a threshold of
your choice.
Don't completely understand this now; thinking about it and trying various
simulations will probably help.
Culverts usually don't appear on a raster DEM. For instance, if you use
LiDAR DEM, you will have only the elevation of the road surface.
Laurent,
The culvert is below the road surface and about 60cm above the bottom of
the roadside swale.
To model a functioning culvert, you will need to lower locally the DEM to
let the flow pass. Therefore, I'm not totally sure to understand how you
modelled the functioning culvert without changing the DEM.
I'm re-running the analyses taking a slightly different approach and will
carefully modify the DEM so the cells with the culvert (in- and outflow)
have the appropriate elevations.
If I correctly recall reading the Itzi technical information I can
generate time series. I'll re-read everything and figure out how to model
the flows given daily precipitation rates (mm/hr for each day) over a three
week period, with saturated soils from antecedent precipitation.