[Metqeu]

Hello,
I am trying to create mesh using blockMesh for a 2D wave tank. This particular geometry has a beach and a simple coastal defense structure. I would like to refine the cells around the free surface at y = 0 (vertical coordinate range is from -0.5 to 0.5m).
The blockMesh directory below shows what I have done so far.
The problem with it is that it grades each block at 50% of its height, and because this geometry has variable height along the x direction, then the refinement is no longer at y = 0, but it shifts upwards (because of the sloped beach).
Is there a way to grade this mesh along a constant horizontal line?

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.OpenFOAM.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
  // back face
(0 -0.5 -0.1)             //0
(8.33 -0.5 -0.1)          //1
(16.455 -0.09375 -0.1)    //2
(16.9144 0.117 -0.1)      //3
(17.1144 0.117 -0.1)      //4
(17.378 0 -0.1)           //5
(20 0 -0.1)               //6
(20 0.5 -0.1)             //7
(17.378 0.5 -0.1)         //8
(17.1144 0.5 -0.1)        //9
(16.9144 0.5 -0.1)        //10
(16.455 0.5 -0.1)         //11
(8.33 0.5 -0.1)           //12
(0 0.5 -0.1)              //13

(0 -0.5 0.1)             //14
(8.33 -0.5 0.1)          //15
(16.455 -0.09375 0.1)    //16
(16.9144 0.117 0.1)      //17
(17.1144 0.117 0.1)      //18
(17.378 0 0.1)           //19
(20 0 0.1)               //20
(20 0.5 0.1)             //21
(17.378 0.5 0.1)         //22
(17.1144 0.5 0.1)        //23
(16.9144 0.5 0.1)        //24
(16.455 0.5 0.1)         //25
(8.33 0.5 0.1)           //26
(0 0.5 0.1)              //27
);

blocks
(
  hex (0 1 12 13 14 15 26 27) ( 740 90 1 ) simpleGrading
  (
    1
    (
      (0.5 0.5 0.33) 
      (0.5 0.5 3)    
    )
    1
  )
//2
  hex (1 2 11 12 15 16 25 26) ( 722 90 1 ) simpleGrading
  (
    1
    (
      (0.5 0.5 0.33)    
      (0.5 0.5 3)    
    )
    1
  )
//3
  hex (2 3 10 11 16 17 24 25) ( 41 90 1 ) simpleGrading
  (
    1
    (
      (0.5 0.5 0.33)    
      (0.5 0.5 3)    
    )
    1
  )
  //4
  hex (3 4 9 10 17 18 23 24) ( 18 90 1 ) simpleGrading
  (
    1
    (
      (0.5 0.5 0.33)   
      (0.5 0.5 3)    
    )
    1
  )
//5
  hex (4 5 8 9 18 19 22 23) ( 23 90 1 ) simpleGrading
  (
    1
    (
      (0.5 0.5 0.33)     
      (0.5 0.5 3)    
    )
    1
  )
//6
hex (5 6 7 8 19 20 21 22) ( 233 90 1 ) simpleGrading
(
  1
  (
    (0.5 0.5 0.33)    
    (0.5 0.5 3)    
  )
  1
)
);


edges
(
);

patches
(
    patch inlet
    (
      (27 13 0 14)
    )
    wall bottom
    (
      (14 0 1 15)
      (15 1 2 16)
      (16 2 3 17)
      (17 3 4 18)
      (18 4 5 19)
      (19 5 6 20)
    )
    patch outlet
    (
      (7 21 20 6)
    )

    patch atmosphere
    (
      (13 12 26 27)
      (12 11 25 26)
      (11 10 24 25)
      (10 9 23 24)
      (9 8 22 23)
      (8 7 21 22)
    )

    empty frontBack
    (
      (13 12 1 0)
      (12 11 2 1)
      (11 10 3 2)
      (10 9 4 3)
      (9 8 5 4)
      (8 7 6 5)
      (27 14 15 26)
      (26 15 16 25)
      (25 16 17 24)
      (24 17 18 23)
      (23 18 19 22)
      (22 19 20 21)
    )
);

mergePatchPairs
(
);

// ************************************************************************* //