def reduce_dam(grand_proc, new_class):
    """ Creates a collapsed main use category that lumps dams
    listed as Recreation, Fisheries, and Other into a generic "Other expanded"
    class. 
    
    Parameters
    -----------
    grand_proc : geodataframe
        Processed geodataframe to add new column
        
    new_class : string
        Name of new dam main use column to be created
    
    Returns
    --------
    grand_proc :geodataframe
        The geodataframe with the added newly created column
    """
    grand_proc[new_class]=grand_proc['MAIN_USE']
    grand_proc.loc[(grand_proc['MAIN_USE'] == 'Recreation') |
                         (grand_proc['MAIN_USE'] == 'Fisheries') |
                         (grand_proc['MAIN_USE'] == 'Other'), 'MAIN_RED'] = 'Other expanded'
    
    return grand_proc