XF 1.4 Directing to Portal Page

I would like to redirect my main domain from the forum index page to the portal page. My index page is www.rivalforums.com .

The portal page URL is rivalforums.com/index.php?portal/

How do I change the .htaccess file to redirect to the portal? I have tried DirectoryIndex index.php?portal/ but it still goes to the forum index.

Thanks for any help!