Creating slope domain in LIGGGHTS

Hi,
I am about to make a simulation where the first part of the domain is nonsloping, but the second part of the of the domain should be sloping. It is a beach where the first part is at constant depth and then the sloped part, where the depth is decreasing until reaching the surface. Is it possible to make such a domain in LIGGGHTS?
I have attached a picture of the domain I want to create.

I have also tried to make a stl part of the surface, but somehow my particles does not "feel" the surface, so they just drop out of my domain. I have a liggghts_init and liggghts_resume file:

liggghts_init:
-------------------------------------------------------------------------
echo both
log ../DEM/log.liggghts
thermo_log ../DEM/post/thermo.txt

atom_style granular
atom_modify map array
communicate single vel yes

boundary f f f
newton off

units si

#region reg block -3.5 4.8 -0.22 0.54 0.0 0.1 units box # (M4)
region reg block -3.8 5.0 -0.3 0.8 -0.2 0.2 units box # (M4)

create_box 1 reg

neighbor 0.6 bin
neigh_modify delay 0 binsize 0.6

# Material properties required for granular pair styles

fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.3
fix m4 all property/global coefficientFriction peratomtypepair 1 0.5

# pair style
pair_style gran model hertz tangential history # Hertzian without cohesion
pair_coeff * *

# timestep, gravity
timestep 0.00001
fix gravi all gravity 9.81 vector 0.0 -1.0 0.0

# walls
#fix xwalls1 all wall/gran model hertz tangential history primitive type 1 xplane -3.5
#fix xwalls2 all wall/gran model hertz tangential history primitive type 1 xplane 4.8
#fix ywalls1 all wall/gran model hertz tangential history primitive type 1 yplane -0.22
#fix ywalls2 all wall/gran model hertz tangential history primitive type 1 yplane 0.5
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane 0.0
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 0.1

fix cad all mesh/surface file /work3/s165039/Forsberg/DEM/Ground2.stl type 1

#fix cad1 all wall/gran model hertz tangential history mesh n_meshes 1 meshes cad

#-------- NEW ---------
#Insertion place
create_atoms 1 single 0.0 -0.1 0.01 units box
create_atoms 1 single 0.0 -0.1 0.02 units box
create_atoms 1 single 0.0 -0.1 0.03 units box
create_atoms 1 single 0.0 -0.1 0.04 units box
create_atoms 1 single 0.0 -0.1 0.05 units box
create_atoms 1 single 0.0 -0.1 0.06 units box
create_atoms 1 single 1.0 -0.1 0.07 units box
create_atoms 1 single 2.0 -0.1 0.08 units box

#Particle properties

set atom 1 diameter 0.003 density 500 vx 0 vy 0 vz 0
set atom 2 diameter 0.003 density 920 vx 0 vy 0 vz 0
set atom 3 diameter 0.003 density 950 vx 0 vy 0 vz 0
set atom 4 diameter 0.003 density 1000 vx 0 vy 0 vz 0
set atom 5 diameter 0.003 density 1150 vx 0 vy 0 vz 0
set atom 6 diameter 0.003 density 1150 vx 0 vy 0 vz 0
set atom 7 diameter 0.003 density 1380 vx 0 vy 0 vz 0
set atom 8 diameter 0.003 density 1380 vx 0 vy 0 vz 0
#-------- NEW ---------

# apply nve integration to all particles that are inserted as single particles
fix integr all nve/sphere

# screen output
compute 1 all erotate/sphere
thermo_style custom step atoms ke c_1 vol
thermo 1000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes

# insert the first particles so that dump is not empty
dump dmpCAD all mesh/stl 5000 post/Ground*.stl cad
dump dmpParticle all custom 5000 post/dump*.liggghts_init id type type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius

run 0 upto

write_restart post/restart/liggghts.restart

------------------------------------------------------------

liggghts_resume:
-----------------------------------------------------------
echo both
log ../DEM/log.liggghts
thermo_log ../DEM/post/thermo.txt

atom_style granular
atom_modify map array
communicate single vel yes

boundary f f f
newton off

units si
processors 8 1 1

#read the restart file
read_restart ../DEM/post/restart/liggghts.restart

neighbor 0.6 bin
neigh_modify delay 0 binsize 0.6

#Material properties required for new pair styles

fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.3
fix m4 all property/global coefficientFriction peratomtypepair 1 0.5

#pair style
pair_style gran model hertz tangential history #Hertzian without cohesion
pair_coeff * *

#timestep, gravity
timestep 0.00001
fix gravi all gravity 9.81 vector 0.0 -1.0 0.0

# walls
#fix xwalls1 all wall/gran model hertz tangential history primitive type 1 xplane -3.5
#fix xwalls2 all wall/gran model hertz tangential history primitive type 1 xplane 4.8
#fix ywalls1 all wall/gran model hertz tangential history primitive type 1 yplane -0.22
#fix ywalls2 all wall/gran model hertz tangential history primitive type 1 yplane 2.0
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane 0.0
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 0.1

fix cad all mesh/surface file /work3/s165039/Forsberg/DEM/Ground2.stl type 1

#cfd coupling
fix cfd all couple/cfd couple_every 1 mpi
fix cfd2 all couple/cfd/force/implicit

#apply nve integration to all particles that are inserted as single particles
fix integr all nve/sphere

#center of mass
compute centerOfMass all com

#compute total dragforce
compute dragtotal all reduce sum f_dragforce[1] f_dragforce[2] f_dragforce[3]

#screen output
compute 1 all erotate/sphere
thermo_style custom step atoms ke c_1 vol c_centerOfMass[3] c_dragtotal[1] c_dragtotal[2] c_dragtotal[3]
thermo 1000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes

#insert the first particles so that dump is not empty
#dump myDump all stl 5000 post/dump_*.stl
dump dmpCAD all mesh/stl 5000 post/Ground*.stl cad
#run 1
dump dmpParticle all custom 5000 ../DEM/post/dump*.liggghts_resume id type type x y z vx vy vz fx fy fz f_dragforce[1] f_dragforce[2] f_dragforce[3] radius

run 1

Thanks in advance!

Cheers,
Jeppe