I've recently been lucky enough to spend quite a bit of time undertaking a review of flood history in my home catchment, Strathglass, for a local flood risk project. It's an interesting glen to look at flood risk in as while it has historically been subject to some significant flooding (from an impact point of view), the hydrological data related to fluvial flooding is relatively sparse, primarily as the main flow gauges are highly impacted by large reservoirs upstream and so are not classed as suitable for peak flow analysis.
Therefore, while my 'go-to' plan might normally be a look at high flow data from the nearest gauge(s), in this case it wasn't possible. In some ways, this forced me to look a little further, and perhaps identify an even richer source of flood risk information. In this case, one of my sources was a book published in 1895 titled 'Memorable Floods in the Highlands during the Nineteenth Century with some accounts of the great frost of 1895'. This little gem contains some detailed information on flood impacts from some significant flooding that occurred during the 1800's in the Highlands. A future post will look at this in a bit more detail as the book provides an important record of the flood regime pre-hydro in the straths.
What interests me in relation to Natural Flood Management is primarily the observations by the author surrounding the impact of runoff changes as a result of land-use. For example:
'Of course, a great change had taken place in the condition of the country within the previous 25 or 30 years. In the western watershed, the land had been so improved for sheep and other farming purposes, that the water that used to collect in pools and marshes was drained off rapidly into the rivers and lakes, which rose suddenly, and sought an impetuous exit by the streams which received their superfluidity.'
And also..
'and as long as the mountain sides continue to be occupied by sheep, deer, and grouse, instead of trees, these occasions will always be liable to eclipse each other in their sadness and consequent results. In the olden days, when Strathfarrar, Glen Cannich and Glen Affric were rich in timber, and nature was more left to accomplish its own drainage, a flood of such impetuosity of 1892 was almost impossible. There might have been quite as great a snowstorm, and quite as sudden a melting of the snow in former times, but the rivers were then slower in their risings and fallings, and though more prolonged, the floods thus inflicted less damage. The amount of water which careered seawards in January 1892, in a compression of three days would probably have been spread over a week. Those who remember the flood of 1849 and subsequent events of that kind, never saw the Beauly rise with such startling rapidity as it did on this occasion; and this must remain, as we have said, the characteristic of such visitations so long as the mountains are bare, with tree forests disappearing, and man ever moving in the direction of getting quickly rid of the earths superfluous moisture.'
Remember this was published in 1895. My first observation is probably one of slight sadness that modern science and engineering reports tend to discourage the use of such poetic language in reporting! However, while Natural Flood Management as a term is fairly recently coined, the idea that upland land management might impact on runoff is clearly not new. In an age of modelling, monitoring and data analysis it can often be easy to dismiss such accounts, especially given the tendency to use dramatic language. At the time of these events, the population was generally less mobile than we are today and probably often had a much greater connection to the land through work and subsistence. So it's not too much of a stretch of the imagination to believe that local folk would have had a reasonably intuitive understanding of runoff processes through observation (potentially a better understanding than many of us today). I'm yet to find an older reference for someone espousing the value of trees and natural vegetation cover, so perhaps the author is one of the founding enthusiasts of NFM?
Future work will look at trying to georeference historical OS maps against those showing modern day tree cover in order to put the authors comments into some context. Strathglass today contains quite a reasonable tree cover, albeit a significant proportion of it is short-rotation commercial conifer woodland which is in the process of being felled.
Nairne, D. (1895) Memorable Floods in the Highlands during the Nineteenth Century with some accounts of the great frost of 1895. The Northern Counties Printing and Publishing Company Limited.