Fix reference and wording in model description

Corrected reference formatting and improved clarity in the marine-driven bed level change section.

Author: ssheminway

docs/user/model_description.rst

@@ -1150,7 +1150,7 @@ PLACEHOLDER
 Marine-driven Bed Level Change
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Bed-level change due to marine-driven dune erosion occurs when the total water level exceeds the based of the dune, or the dune toe :math:`\zToe` (``zToe``). See :ref:`Marine-driven Morphodynamics <Marine-driven Morphodynamics>` for more information. 
+Bed-level change due to marine-driven dune erosion occurs when the total water level exceeds the base of the dune, or the dune toe (``zToe``). See :ref:`marine-driven_morphodynamics` for more information.
 
 .. _groundwater-module:
 Groundwater Module (Hallin, 2023)
@@ -1419,6 +1419,7 @@ Avalanching
 
 PLACEHOLDER
 
+.. _marine-driven_morphodynamics
 Marine-driven Morphodynamics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^