I am redesigning a gallery which has several different pages and want to make it just one page. I would take the content from each existing page and add it to this one page. I would use 301 re-directs to direct traffic from the old pages to the one page. Would this hurt the keyword rankings for the pages I will be redirecting at all? I have read initially traffic will change, bit then it should be back to normal after a few weeks once everything is indexed. My client needs some reassurance his current traffic won't be affected.
301 redirect is one of the most SEO-friendly redirects. It basically (and theoretically) tells the crawling robot that:
This page has moved permanently to this other page. So please from now on change your indices and preserved rankings to this new page.
Look what Google thinks about 301 redirects here.