#35: Add trip_globe_shape to namelist

Part of JULES ticket #1374 this adds the namelist option trip_globe_shape which enables the user to change the shape of the earth in the UM-TRIP river routing model.

user_guide/doc/source/namelists/jules_rivers.nml.rst

@@ -179,7 +179,7 @@ River routing introduces two more grids to a JULES run: the river routing input
 
       The ratio of the actual to calculated river lengths in a river routing gridbox. See Oki et al. (1999). Oki & Sud (1998) called this the Meandering Ratio r_M and suggested an average global value of 1.4.
 
-.. nml:group:: TRIP parameters - used if :nml:mem:`i_river_vn` = ``1``
+.. nml:group:: TRIP parameters for UM-TRIP only - i.e. only used if :nml:mem:`i_river_vn` = ``1``
 
    .. nml:member:: lake_water_conserve_method
 
@@ -194,6 +194,18 @@ River routing introduces two more grids to a JULES run: the river routing input
       ``2``
           elake_surft: This is the lake evaporation component of fqw_surft. This avoids the impact that snow melt has on modifying fqw_surft.
 
+   .. nml:member:: trip_globe_shape
+
+      :type: integer
+      :default: 2
+
+      The shape of the Earth in the UM-TRIP river routing scheme.
+
+      ``1``
+          Spherical: Consistent with other component models (e.g. UM and NEMO) and is better at conserving water when passing water between these other models.
+
+      ``2``
+          Ellipsoidal: Closer to the actual shape of the Earth.
 
 .. seealso::
    References: