Create Rectangular Cavity

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1

I need to create this model as shown below by using the FORTRAN compiler 1= layer one 2= layer tow 3= cavity (rectangular cavity)

program Make_2D_Model
	implicit none
	 integer :: width,length,Area
     integer:: i,j,nx,nz 
     integer :: idepth
 character*1,allocatable,dimension(:,:) :: icode
nx=1000  
nz=500
idepth=100
width = 30
length=20
Area = 600
	allocate(icode(1:nx,1:nz))	
	do i=1,nx
		do j=1,nz
			if(j<=idepth)then
				icode(i,j)='1'
			elseif(j>idepth)then
				icode(i,j)='3'		
            endif
		enddo
    enddo

    do i=1,nx
        do j=1,nz
            if  (width*length)<=Area then
                icode(i,j)='2'
            endif
        enddo
    enddo
open(2012,file='model.txt',status='unknown')
		do j=1,nz
			write(2012,1000)(icode(i,j),i=1,nx)
		enddo
	close(2012)
	1000 format(<nx>a1)
    end program Make_2D_Model