NAME

       r.lake  - Fills lake at given point to given level.

KEYWORDS

       raster, hydrology, hazard, flood

SYNOPSIS

       r.lake
       r.lake --help
       r.lake  [-no]  elevation=name  water_level=float   [lake=name]    [coordinates=east,north]    [seed=name]
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -n
           Use negative depth values for lake raster map

       -o
           Overwrite seed map with result (lake) map

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       elevation=name [required]
           Name of input elevation raster map

       water_level=float [required]
           Water level

       lake=name
           Name for output raster map

       coordinates=east,north
           Seed point coordinates
           Either this coordinates pair or a seed map have to be specified

       seed=name
           Input raster map with given starting point(s) (at least 1 cell > 0)
           Either this parameter or a coordinates pair have to be specified

DESCRIPTION

       The module fills a lake to a target water level from a given start point. The user can  think  of  it  as
       r.grow  with  additional  checks  for  elevation.  The  resulting  raster  map contains cells with values
       representing lake depth and NULL for all other cells beyond the lake. Lake depth is reported relative  to
       specified water level (specified level = 0 depth).

       This  module  uses a 3x3 moving window approach to find all cells that match three criteria and to define
       the lake:

           •   cells are below the specified elevation (i.e., water level);

           •   cells are connected with an initial cell (seed or coordinates pair value);

           •   cells are not NULL or masked.

       The water level must be in DEM units.

NOTES

       The seed (starting) point can be a raster map with at least one cell value greater than zero, or  a  seed
       point  can  be  specified  as  an E, N coordinate pair. If the seed is specified as a coordinate pair, an
       additional check is done to make sure that the target water level is above the level of the DEM.  When  a
       raster  map  is  used as a seed, however, no such checks are done.  Specifying a target water level below
       surface represented by DEM will result in an empty map. Note: a raster lake map created in a previous run
       can also be used as a seed map for a new run to simulate rising water levels.

       The  module  will create a new map (lake=foo) or can be set to replace the input (seed=bar) map if the -o
       flag is used.  The user can use -o flag to create animations of rising water level  without  producing  a
       separate  map  for  each  frame.   An initial seed map must be created to start the sequence, and will be
       overwritten during subsequent runs with resulting water levels maps (i.e., a single file serves for  both
       input and output).

       Negative  output  (the -n flag) is useful for visualisations in NVIZ.  It equals the mapcalc’s expression
       "negative = 0 - positive".

   r.mapcalc equivalent - for GRASS hackers
       This module was initially created as a script using r.mapcalc.  This had some limitations - it  was  slow
       and  no  checks  where done to find out required iteration count. The shell script code (using r.mapcalc)
       used in the original script is shown below:
       ${seedmap} = if( ${dem}, \
       if( if( isnull(${seedmap}),0,${seedmap}>0), ${wlevel}-${dem}, \
        if( \
         if(isnull(${seedmap}[-1,0]),0, ${seedmap}[-1,0]>0 && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[-1,1]),0, ${seedmap}[-1,1]>0 && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[0,1]), 0, ${seedmap}[0,1]>0  && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[1,1]), 0, ${seedmap}[1,1]>0  && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[1,0]), 0, ${seedmap}[1,0]>0  && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[1,-1]),0, ${seedmap}[1,-1]>0 && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[0,-1]),0, ${seedmap}[0,-1]>0 && ${wlevel}>${dem}) ||\
         if(isnull(${seedmap}[-1,-1]),0, ${seedmap}[-1,-1]>0 && ${wlevel}>${dem}),\
        ${wlevel}-${dem}, null() )))

       The ${seedmap} variable is replaced by seed map names, ${dem} with  DEM  map  name,  and  ${wlevel}  with
       target  water  level. To get single water level, this code block is called with same level numerous times
       (in a loop) as the lake grows by single cells during single run.

KNOWN ISSUES

           •   The entire map is loaded into RAM.

           •   A completely negative seed map will not work! At least one cell must have a  value  >  0.  Output
               from r.lake -n cannot be used as input in the next run.

EXAMPLE

       Example of small flooding along a street (North Carolina sample dataset):
       g.region raster=elev_lid792_1m -p
       # water accumulation next to street dam
       r.lake elev_lid792_1m coordinates=638759.3,220264.1 water_level=113.4 lake=flooding
       # draw resulting lake map over shaded terrain map
       r.relief input=elev_lid792_1m output=elev_lid792_1m_shade
       d.rast elev_lid792_1m_shade
       d.rast flooding
       d.vect streets_wake

       Small flooding along a street (r.lake, using Lidar 1m DEM)

SEE ALSO

        r.mapcalc, r.grow, r.plane

AUTHOR

       Maris Nartiss (maris.nartiss gmail.com)

SOURCE CODE

       Available at: r.lake source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual