graddata = graddata[[1]];
data = data[[1]];
iF = Interpolation[
   graddata /. {a_, b_, c_} :> {a + RandomReal[10^-10*{-1, 1}],
      b + RandomReal[10^-10*{-1, 1}], c}, InterpolationOrder -> 1];
ListPlot3D[data, MeshFunctions -> {Function[{x, y, z}, iF[x, y]]},
 Mesh -> {5}, MeshStyle -> Directive[Red, Thick]]