Whilst searching for something else I found some images of Warwickslade Cutting Railway. Warwickslade Cutting was a straight drainage ditch dug circa 1850 in the New forest. In 2009, The Forestry Commission decided to fill it in and replace it with a meandering stream, presumably to benefit wildlife. A light railway was used to assist in this work to allow working in all conditions, prevent too much erosion, and reduce emissions.
The 'loco' is a Boxer Mini-Skid, and the track panels appear to use cylindrical rails. It's difficult to tell if it's standard or narrow gauge, but it looks fairly broad. Obviously modelling it accurately would require some challenging scratchbuilding, but kits could but used to build a narrow gauge interpretation. In in O scale KBscale track and rolling stock could be used, or Nigel Lawton's range could be used in 009 with modified N gauge setrack used to represent the track panels. Operationally it would be fairly dull, though in O scale a working digger might be a possibility.
More pictures can be found on Geograph and Wikimedia Commons
Broad gauge rail - still in use!
11 hours ago