Carrying out repairs to the banks
of the River Teviot along Duke Street in Hawick – 1890
Flood causes in the Scottish Borders
Records of flooding in the Teviot catchment extend back into history and show that floods can be caused by summer thunderstorms, winter rain or snow melt and can be so severe that they result in extensive impacts to communities. In recent years, flooding in the catchment has been thoroughly reported and records show that there have been numerous occasions when the river has overtopped its banks causing damage to agricultural land, blocking roads, destroying walls and inundating urban areas, including the town of Hawick.
The main cause of these floods appears to have been climatic however it has also been suggested that there could be additional causes with land use changes, industrialization and housing developments possibly increasing runoff rates, reducing flood water storage and enhancing flood peaks. It has also been suggested that flooding in Hawick, as with other parts of the UK, has become more frequent and severe – possibly related to climatic change.
Centuries of industrial, agricultural and forestry development in the Teviot catchment have left a legacy of river and drainage engineering works. Within the town of Hawick, the Teviot and Slitrig rivers are confined within large masonry walls, factories and mills have been built along the river banks, channels and bridges have been built over the rivers and urban drains feed directly into the rivers.
Upstream of Hawick, despite the low intensity of land use, the land drainage and river characteristics have been significantly altered. Hillslope drainage was undertaken in plantation forest, field drains and stone culverts were constructed to improve grasslands and wetlands drained to expand grazing land. In the river systems there are numerous cases of straightened and diverted small watercourses, meanders in the larger rivers have been artificially cut-off and bank protection works carried out. In addition estates would remove fallen trees from river channels, sediments would be excavated to provide materials for road construction, river banks protected to reduce erosion and after major floods debris was removed from the rivers.
The traditional practices of draining land and altering river channels have shaped the Teviot catchment and have had huge consequences for the river regimes, including flood flows. Around the middle of the 19th century, during a significant phase of agricultural drainage, complaints began to be registered about the effect of land drainage on patterns of flow in the Tweed. Floods were noted to be more severe and of shorter duration, a trend attributed to speeding up of runoff by the new drains and lack of buffering by wetlands. In 1836, one local claimed that “a little summer flood which took a fortnight or three weeks to run off previous now completely run out in 8 hours”.
There was a particularly significant increase in the amount of drainage following the Land Drainage Act of 1847, which provided government subsidies for land drainage. By the start of the 20th century, most of the agricultural land in the Borders was drained, prompting this quote from 1912: “many of the small burns, which are now roaring floods in time of rain and nearly dried up in drought, used, before hills were drained, to carry a steady volume of water all year round”.
A second phase of intense drainage started around the middle of the 20th century, this time brought about by an escalating forestry industry. Ground preparation was carried out before planting and included the ploughing of hillslopes, creation of cut-off drains and construction of hill roads. Trees were then densely planted to create “blanket” forests, although most of the Borders forests retained narrow un-planted strips along watercourses. The ground preparation probably increased the runoff rates in storm conditions for several years until the artificial drains became overgrown or in-filled with tree debris. Recent anecdotal evidence from other plantation forests now suggests that these types of drains can remain in-active for many years until a major storm impacts the area when they can once again become active and increase runoff rates.
The outcome of these land use changes in the Teviot catchment is likely to be a more ‘flashy’ catchment more susceptible to serious flooding, due to a combination of a decreased storage of water through the catchment, increased hillslope runoff rates and increased flow rates in watercourses.