Changing URLS: from a short well optimised URL to a longer one – What's the traffic risk

[moge]

I'm working with a client who has a website that is relatively well optimised, thought it has a pretty flat structure and a lot of top level pages.

They've invested in their content over the years and managed to rank well for key search terms.

They're currently in the process of changing CMS and as a result of new folder structuring in the CMS the URLs for some pages look to have significantly changed.

E.g Existing URL is: website.com/grampians-luxury-accommodation which ranked quite well for luxury accommodation grampians

New URL when site is launched on new CMS would be website.com/destinations/victoria/grampians

My feeling is that the client is going to lose out on a bit of traffic as a result of this. I'm looking for information or ways or case studies to demonstrate the degree of risk, and to help make a recommendation to mitigate risk.

[Hurf]

There's some good news about 301 redirects that you may have missed: Since early/mid 2016, changing the directory structure (alone) and creating 301 redirects isn't going to (or shouldn't) cause any loss in PageRank.

The fact that 301s generally resulted in a loss of around 15% of PageRank (which was confirmed by Matt Cutts in 2013: https://www.youtube.com/watch?v=Filv4pP-1nw) is simply no longer the case.

Sceptical? So was I. Read on...

In February 2016, Google Web Trend Analyst, John Mueller confirmed this:

Q. Do I lose "link juice" from the redirects?

A. No, for 301 or 302 redirects from HTTP to HTTPS no PageRank is lost.

(Source: https://plus.google.com/+JohnMueller/posts/PY1xCWbeDVC)

Further, Google's Gary Illyes confirmed this in July 2016, on twitter: 
"30x redirects don't lose PageRank anymore."
(Source: https://twitter.com/methode/status/757923179641839616?ref_src=twsrc%5Etfw)

(Bear in mind, PR is not the only ranking signal.)

So, changing URLs for SEO purposes, including "Improving directory/subfolder structure" is considered less risky now that 301 redirects preserve PageRank (as long as the content and structure remains the same).

There's a great article on the subject of 301 redirect rules: "301 Redirects Rules Change: What You Need to Know for SEO" here: https://moz.com/blog/301-redirection-rules-for-seo

Remember: For this to work out for you, the content of the page at the receiving end of the 301 needs to match the original source as closely as possible.

Good luck!

[moge]

Thanks James, appreciate the speedy response. I found huge amounts of information on URL structure, but many varying points of view and nothing I could relate specifically to the situation.

The site does have a good amount of content for each state and region landing page – which are all top level in the current flat structure at the moment.

There are over 100 different regions, so I did feel that there would be value in the directory that the digital agency had recommended, but also felt there is a risk (large) of traffic loss introducing the new sub-directory / hierarchical structure. General rule of thumb being 15% PR loss for any URL changes...

So I'm trying to do a bit of a risk / benefit analysis – what the client may lose in traffic initially, will they gain back overtime.