DESCRIPTION
r.inund.fluv - This command allows to obtain a
fluvial potentially inundation map given a high-resolution DTM of
the area surrounding the river and a water surface profile
calculated through an 1-D hydrodinamic model.
The implemented
procedure has innovating characteristics; even if it remains
substantially one-dimensional, it takes into account the
two-dimensionality of territory and inundation phenomena, adducing
hypotheses that let to correct many errors typical of
one-dimensional usually employed procedure. With respect to a
two-dimensional model, it has advantage that it needs a lower
computational effort, that allows to apply it to river reaches very
long (of the order of 100km).
The single phases in which the
procedure is divided, are here summarized, even if the whole
procedure is excecuted automatically.
- In the first phase,
the value of water level in the nearest point of fluvial axis is
assigned to each pixel of terrain, through the creation of Thiessen
polygons (r.surf.idw setting
npoints=1) (at the resolution res_B). Then the
procedure makes a comparison between elevation of each pixel and
water level, and defines pixels characterized by elevation lower
than water level, at hazard.
- In the second phase, the
procedure removes all the areas previously defined at hazard but not
connected with the river axis, i.e. surrounded by terrain not at
hazard, neglecting infiltration or underground rivers (v.select).
- In the third phase, the
hypotesis is that water diffuses from river to the surrounding areas
only in direction perpendicular to the river axis. Through an
implemented fortran code (clean_inundation.f90), the
procedure individuates the pixels, considered at hazard at the end
of phase 2, inundated for sure by water; hence it dries the ones,
considered at hazard at the end of phase 2, not reached by water
because protected by levees or small hills posed along the
perpedicular path between the pixel and the river axis (at the
resolution res_C).
- In the fourth phase, the
hypothesis is that water, outside the main channel, moves along the
maximum terrain slope direction. First, through an implemented
fortran code (find_main_channel.f90), the procedure
individuates the "boundaries" of the main channel. Then, through an
implemented fortran code (2d_path.f90), the procedure
individuates the water path outside the main channel along the
maximum terrain slope direction (at the resolution res_C).
Finally, through an implemented fortran code (
correction_from_path.f90), the procedure individuates the
pixels, dried at the end of phase 3, connected to a water path, and
defines them at hazard (at the resolution res_B).
- In
the fifth and last phase, the final potentially inundated map is
defined as sum of areas at hazard in the third and fourth phases.
Use
Requested input and output:
The command requires some input:
1 - a Digital Terrain Model (DTM, DEM or DSM) of the area surrounding the river; an high-resolution DTM (e.g. 5 x 5 m or higher) is required to describe levees and other human infrastructures on the floodplain.
2 - an ASCII file describing the water surface profile along the channel axis, in this format (e.g.):
411815.62874469644 4944870.642304279 197. 104
411848.8162966241 4944958.868788462 196.96 103.933*
411882.0010118869 4945047.096337882 196.89 103.866*
411915.188102181 4945135.322989558 196.82 103.8*
...
3 - a vector line describing the river axis from upstream to dowstream.
The output are:
4 - the fluvial potentially inundation map;
5 - the area in doubt, i.e. areas which could be at flooding hazard because of their elevation, but aren't defined at hazard at the end of the procedure.
WARNING -
The original resolution of DTM must be high. If the pixel dimension is greater than 5 m, the command informs the user with a warning message; however the procedure runs.
Optional input and output:
The command has some input parameters that the user can choose in the Optional parameters & maps interface. They refer to intermediate phases of the procedure, described in detail in reference.
1b - It's possible to set another water surface profile associated with a return period of 100 years or greater, from which the procedure starts to find automatically the "boundaries" of main channel. The file format is as mentioned above for the input file 2.
2b - It's possible to set a delta_z different from the default value (0.5 m), as the step with which the procedure increases the water level inside the main channel, to find automatically the "boundaries" of main channel itself.
3b - It's possible to set a delta_x different from the default value (1.5*DTM_resolution in meters), i.e. the threshold value of the distance between the points individuated on a bank in two consecutive steps, to exceed so that the procedure may define the "boundary" of main channel in a pixel between such two points.
4b - The user may view the "boundaries" of main channel, to verify the working of the procedure, especially if delta_z and delta_x were setted different from the default values.
5b - 6b - The procedure performs some calculations using resolution different from the DTM one. The default values of 10 and 20 meters, used in different steps of the procedure, are a compromise between computational speed and consistency of output map. It's suggested that only the expert user modifies such values.
7b - The user can view a vector point map of the water surface profile along the river axis.
AUTHORS
Roberto Marzocchi, GTER s.r.l., Genoa, Italy e-mail
Bianca Federici, University of Genoa, Italy e-mail
Domenico Sguerso, University of Genoa, Italy e-mail
REFERENCES
- Federici B. & Sguerso D. (2007). Procedura automatica per la creazione di mappe di potenziale inondazione fluviale. Bollettino SIFET, n. 4.
- Marzocchi R., Federici B., Sguerso D. (2008). Procedura automatica per la creazione di mappe di potenziale inondazione fluviale in GRASS: il modulo r.inund.fluv. Under revision for the pubblication on Atti del IX Meeting degli Utenti Italiani di GRASS - GFOSS.
- Pdf presentation of the work at the "IX Meeting degli Utenti Italiani di GRASS - GFOSS":
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