diff --git a/src/create_surfaces.f90 b/src/create_surfaces.f90
index 3ffd5e63781dd9dd5087b1c3132ca7898022ea0f..1f4833b556818f4315a722786b644d468ab897df 100644
--- a/src/create_surfaces.f90
+++ b/src/create_surfaces.f90
@@ -557,9 +557,10 @@ select case(surface_type)
         ! a sinus, 
         ! sp01 is the z level
         ! sp02 is the wavelength 
-        ! sp03 is the amplitude 
+        ! sp03 is the amplitude
+        ! sp04 is the phase
         do i=1,ns
-           z(i)=sp01+sp03*sin(x(i)*2.d0*pi/sp02)
+           z(i)=sp01+sp03*sin(x(i)*2.d0*pi/sp02+sp04)
         end do
    case (7)
         ! a noisy surface, 
@@ -583,9 +584,10 @@ select case(surface_type)
         ! a cosinus, 
         ! sp01 is the z level
         ! sp02 is the wavelength 
-        ! sp03 is the amplitude 
+        ! sp03 is the amplitude
+        ! sp04 is the phase
         do i=1,ns
-           z(i)=sp01+sp03*cos(x(i)*2.d0*pi/sp02)
+           z(i)=sp01+sp03*cos(x(i)*2.d0*pi/sp02+sp04)
         end do
    case (10)
         ! a 2D embankment