force the jquary change function

I'm working on a mysql/php form. I am repopulating the form on page load.  My question is how do I force the change function in the ajax function, which is used in a dependent select box.

 The Ajax script is:

<script type="text/javascript">// Dynamic Support Select based on Depth
           $(document).ready(function(){
                     $("#Depth").change(function(){
                     var depth=$("#Depth").val();
                     $.ajax({
                        type:"post",
                        url:"support_get.php",
                        data:"depth="+depth,
                        success:function(data){
                              $("#A_Sup").html(data);
                                            $("#B_Sup").html(data);
                        }      
                     });
            
               });
           });
            
      </script>


The function to repopulate the page steps through the form setting values based on saved values in the mysql table. I was setting the value of 'Depth' and then trying to trigger as follows, but it doesn't fire. ???


      form1.Depth.value="<?php echo $row_Quote['Depth']; ?>";

      $("Depth").trigger("change");
            
      setSelectedIndex_val(document.getElementById("A_Sup"),"<?php echo $row_Quote['A_Sup']; ?>");
      setSelectedIndex_val(document.getElementById("B_Sup"),"<?php echo $row_Quote['B_Sup']; ?>");