It's here, https://goo.gl/60NMb9. Judging by googles (probably highly inaccurate) it's 70m long! It's also a confluence (meeting) of the two rivers underground. The stretch along the back of Wickes is pretty interesting too, but I'd not like to enter that one walking upstream, much easier to walk down to it. The pictured section however, has a lot of different access points which are all pretty easy!
Again, if you need anything else let me know, sounds like you have an interesting job/lifestyle!
Sorry for the resurrection, but I've been looking at some old maps and trying to work out where the Holme Brook joins the River Hipper. Not sure why Google Maps labels the downstream part as Holme Brook as I would have thought it was the Hipper downstream of the confluence. From the aerial view it looks as though the two rivers meet somewhere under Boythorpe Road.