OK, bit by bit the details behind your question are unfolding. Itzi is an excellent flood simulation modeling program. To run it you must begin with an elevation raster, a DEM. Do you have a DEM raster covering your watershed?
Have you followed the steps in the Itzi wiki page?
Next, the example in those docs refers to a single rain map (with uniform precipitation over the watershed). The time steps in the tutorial simulation are 5 seconds, over a period of 2 hours (24 time steps). In your case, as I pointed out in the comments, you have a huge number of rainfall measurements: IIUC, you have rainrate every 1/4 second for 15 hours. So that's 4x60x60x15 = 216,000 total measurements (!). What do you intend to do with that data? Perhaps aggregate to hourly rainfall, then create 15 hourly raster maps, each with a uniform rain rate over your watershed. Then define a STRDS in GRASS from those 15 rainfall rasters and use that as input to Itzi...
If this is your plan, then:
- You need to be working in a projected LOCATION (required by Itzi), NOT long/lat
- You need a DEM as pointed out in the Itzi docs
- I assume you have a polygon of the watershed, already imported into GRASS
So the steps would be:
g.region -ap vect=<watershed_polygon>
# For each of the 15 hourly aggregated rainfall values:
r.mapcalc "rain_hr1 = <rainrall_at_hour1>" # Note the space surrounding the '=' sign
r.mapcalc "rain_hr2 = <rainfall_at_hour2>"
# Create a STRDS
t.create type=strds temporaltype=relative output=rain_strds semantictype=mean title="Rain STRDS" description="Rain STRDS"
t.register -i type=raster input=rain_strds maps=`g.list raster pattern="rain_hr*" separator=comma` start="2020-10-10" increment="1 days"
Now you should have enough to get started with Itzi.