Talk:River Avon, Warwickshire

message: Having discovered with other British river articles that the reference used to provide their lengths appears to be especially inaccurate, I had a look at the Warks Avon and have found, by making my own measurements, that it is between 170k and 175km in length, significantly in excess of the 137km figure given by Owen 2005 which has been cited to date. This figure of mine is clearly original research so cannot be entered into the article but it does flag up the need for a search for a reliable accurate length. At this length, it seems likely that the Warks Avon is the longest tributary river in Britain, ranking 7th in the list of longest GB rivers in its own right - unless further reassessments of other rivers show otherwise! Incidentally Britannica gives a figure of 154km which is closer. Does anyone own a copy of 'Owen 2005' - I don't - does it say on what basis river lengths are asserted? cheers Geopersona (talk) 12:06, 6 February 2021 (UTC)
replies: text: Hi Geopersona I have checked my copy of Owen et al 2005, the Longest rivers in Britain is Appendix 2 on page 232, which gives 136.7 km /85 miles as per the article. The source for the table is given as The Guinness Book of Answers (9th edition) 1993. In the past I did try to search for an online copy of the 9th edition, but didn't have much luck - but it can be bought for a few quid if needed...Jokulhlaup (talk) 14:50, 7 February 2021 (UTC)

text: Hmm, as I think my bank balance will stand it - but not sure if my bookcase will, I have ordered a copy of the 9th edition, hopefully it will gives us a firm source for these figures...Jokulhlaup (talk) 15:15, 7 February 2021 (UTC)
replies: text: Thanks Jokulhlaup - let us all know if it turns up anything interesting. Myself, I've been looked at more major UK river lengths since - entirely unreferenced ones this time - and they too have been significantly under-measured. Shame that a reputable body like OS doesn't publish such data, based on accurate surveys, which of course they possess. cheers Geopersona (talk) 19:33, 7 February 2021 (UTC)
replies: text: Geopersona The Guinness Book of Answers (9th edition) 1993 shows on page 711 a table of the Longest Rivers of the United Kingdom, which is similar to the info in Owen et al. It gives the same length for the Avon as 136.7 km /85 miles. The table is prefaced by the following - "Specially compiled maps issued by the Ordnance Survey in the second half of the last century are still the authority for the length of the rivers in the United Kingdom. It should be noted that these measurements are strictly for the course of the river bearing one name; thus for example, where the principal headstream has a different name its additional length is ignored - unless otherwise indicated." So it seems special maps were drawn up between 1850-1899 by the OS exactly as you wished for - what a strange coincidence. A quick search on google didn't throw up anything obvious - but at least we now know where this info was coming from...Jokulhlaup (talk) 10:26, 15 February 2021 (UTC)
replies: text: Good work Jokulhlaup - I can follow that up with some OS map specialists with whom I'm in contact - more light may yet be shed! Geopersona (talk) 19:53, 15 February 2021 (UTC)

text: I have further info from an authoritative source who I expect will not mind me conveying to you his belief that the maps are probably those at the 10-mile (1:633,600) scale compiled in the late 1860s for a royal commission on water supply . . . presumably this one (119) at https://www.british-history.ac.uk/office-holders/vol9/pp62-91#h2-0027 and this: https://d29jwmc6w46mhx.cloudfront.net/images/12590_1H.jpg?mtime=20200726130104&focal=none If you try to extract the length of a river from a map at that scale, you will inevitably get something that is hopelessly short of an accurate figure. I'll see if I can track down copies.  thanks Geopersona (talk) 08:43, 16 February 2021 (UTC)
thread_title:  Length of the river