Abstract from: Historical survey of the River Conon
RC Johnson and MD Cranstoun, Mountain Environments: November 2000

 Keywords: Conon, floodplain habitats, hydro-schemes, floodbanks, hydrology, floods

1. The floodplain of the River Conon is a residual alluvial woodland site, which has been incorporated into the Wet Woods LIFE Project run by the Caledonian Partnership. The river catchment has undergone numerous artificial modifications affecting the naturalness of the river and its floodplain. These modifications include the construction of upstream reservoirs for hydro-power generation, floodbanks to prevent flooding of the riparian areas and drainage of the floodplain and surrounding hills for improved arable farming, grazing and commercial forestry.
2. Flow data from the River Conon catchment were collated to describe any hydrological changes which occurred over the period of record. Since 1829 flood events causing inundation of the Conon floodplain occurred approximately once every 10 years both prior to and following the construction of the hydroelectric scheme. This suggests that the hydroelectric scheme has not altered the frequency of the higher magnitude floods however the increase in flood frequency in the 1980s and 1990s is not evident in the flood chronology and could be attributable to the hydroelectric scheme.
3. The flood embankments confine the mean annual flood on the Conon however the largest flood events still inundate the floodplain. If the flood banks were removed then the Conon floodplain would be subjected to more frequent flooding.
4. Changes in the habitat mosaic below Dunglass Island are dominated by the expansion of woodland closely related to the river, either in strips along the river bank or on the stable sediment deposits forming islands.
5. From the information collected in this study it is clear that there are likely to have been several significant changes in the hydrological regime of the River Conon and the adjacent floodplain.
   These changes include:
   
• The Blackwater total flow is significantly reduced due to water transfers, this will affect the river habitat at Contin Island which will be drier throughout the year;
• The Conon total flow at Moy Bridge is likely to be enhanced by the water transfer from the Orrin, this will increase the wetness of the habitats between Moy Bridge and the Orrin confluence;
• The Conon and Blackwater summer flood flows are reduced, this will result in the river and river-estuary habitats being drier in summer;
• The major winter floods on the Conon and Blackwater are unchanged and so the resulting inundation of all habitats will be unaffected;
• The medium flood events on the Blackwater are unchanged and so the inundation of Contin Island will be unaffected;
• The medium events on the Conon are attenuated with a reduced peak flow hence all river habitats below Moy Bridge will be drier.