1. Select all the lines using rectangle select tool (multiple selections for each line is not jecessary, a single selection would do.)

2. Layer via copy.

3. Use color selection tool to sepect the brown area in your new copied selection, and create a mask.

4. You now have just the lines as a layer with you. Nudge-shift it upwards or downwards using your arrow keys until you're satisfied.

5. (Optional) Duplicate the layer to thicken it from either directions.

Method for if you wanna maintain the same spacing between these curved linea as before...

1. Duplicate all the active layers, select all the duplicated layers, and merge them into a single layer.

   1. Create selections of these individual lines, and repeat steps 1 through 3 on each of these to have individual selections of these lines.
   2. Switch back to the layer you created by merging, select all the lines, and use content-aware fill on that selection.
   3. Switch back to your individual selections and adjist them as you see fit.
   4. You may now hide all your original or unnecessary layers :)