r.in.gdal -e d23720312400go20040824.asc out=wilmington_dem20ft -o
    g.region rast=wilmington_dem20ft -p
    r.colors wilmington_dem20ft co=elevation
    r.shaded.relief wilmington_dem20ft shade=wilmington_dem20ftsh
    r.lake wilmington_dem20ft wl=06 xy=2322000,142000 lake=flood_06ft
    r.lake wilmington_dem20ft wl=10 xy=2322000,142000 lake=flood_10ft
    r.lake wilmington_dem20ft wl=15 xy=2322000,142000 lake=flood_15ft
    r.lake wilmington_dem20ft wl=16 xy=2322000,142000 lake=flood_16ft
    r.lake wilmington_dem20ft wl=17 xy=2322000,142000 lake=flood_17ft
    r.lake wilmington_dem20ft wl=18 xy=2322000,142000 lake=flood_18ft
    r.lake wilmington_dem20ft wl=20 xy=2322000,142000 lake=flood_20ft
    r.lake wilmington_dem20ft wl=30 xy=2322000,142000 lake=flood_30ft

if the stream in the SE corner does not have a flood protection you may need to put one seed into the stream
and have water spread from the main channel and the stream

r.lake wilmington_dem20ft wl=15 xy=2328750,140500 lake=flood3_15ft
r.lake wilmington_dem20ft wl=15 xy=2322000,142000 lake=flood_15ft

    wxnviz wilmington_dem20ft
   use the flood outputs as color 

it also works well in 2d over the shaded relief, you can make it slightly transparent

 v.in.ascii be3720312400go20040820.txt out=be_pts fs=, skip=1 x=1 y=2 z=3
 g.region res=6 -pa
 v.surf.rst -z be_pts elev=dem_be_6 npmin=120
 r.lake dem_be_6 wl=15 xy=2328750,140500 lake=flood_r6_15ft --o
 r.lake dem_be_6 wl=15 xy=2322000,142000 lake=flood_r6c_15ft
 r.lake dem_be_6 wl=17 xy=2322000,142000 lake=flood_r6c_17ft
 r.shaded.relief dem_be_6 shade=dem_be_6shade