Annan Fishery Management Plan - RAFTS

River Annan DSFB Fisheries Management Plan 2009 – 20142 Annan Catchment Characteristics2.1 Physical Characteristics2.1.1 Annan TopographyRepeated glaciations throughout the last 2 million years have resulted in gentlyrounded plateaux and convex summits dissected by incised valleys and ravinesin the upland part of the catchment. The middle section is generally flat or gentlyundulating and consists of flood plains through which the catchment watersmeander (SNH). The lower reaches increase in gradient again to the sea (Fig 2.1a).2.1.2 Annan GeologyThe oldest rocks which dominate the geology of the area derive from ancientmuds, silts and sands laid down over 420 million years ago. Around 400 millionyears ago, the two land masses either side of the long disappeared LapetusOcean met in a continental collision known as the Caledonian Orogeny (ScottishGeology website) to form the mountain chain that formed the foundation of thesouthern uplands. Fossils crucial to interpreting the boundary between theOrdovician and Silurian periods have been found at Dobbs Linn in the Moffat Hills(SNH).The lower ground is mostly covered by drift deposits, comprising till, sand andgravel, from the last ice sheet. Gorse covered knolls are evident where olderrocks are exposed through the more recent glacial deposits (SNH).The buffering capacity of such as magnesium and carboniferous limestonesmean that the Annan catchment is largely protected from the ravages ofacidification with any problems being mainly localised events.7