It rises at Cwm y Saeson, and flows east past Cefn Llech to Sychnant, where it is joined by the Full Brook. Here it turns north past the ford at Rhyd Myheryn at Glanyrafon, receiving the Rhydyclwydau Brook on the right bank. The old track bed of the Mid-Wales Railway follows the course of the Dulas from this point, through the valley towards Llanidloes railway station.[1] The Dulas continues flowing north-west past the village of Tylwch beyond which it forms a narrow rocky gorge, which has been used by whitewater kayakers, although fallen trees across the gorge are a reported hazard.[2] At Rhos-y-pentref, where the river is measured, it is joined by Nant Gynwydd, and is crossed by the A470 road. Turning north once more, the river passes Upper Glandulas where it meets its last tributary the Afon Brochan, before joining the Severn to the south-west of Llanidloes at Felindre.[1]
The flow of the Dulas has been measured at a flume, in the lower reaches at Rhos-y-pentref since 1969. This long-term record shows that the catchment of Шаблон:Convert to the gauging station yielded an average flow of Шаблон:Convert.[3] The highest river level recorded at the station occurred in October 1998 with a height of Шаблон:Convert through the flume, giving a corresponding flow of Шаблон:Convert.[4]
The Dulas catchment upstream of the station has a substantial average annual rainfall of Шаблон:Convert and a maximum altitude of Шаблон:Convert at Crugyn Llwyd hill on the eastern edge of the watershed, near to the Pegwn Mawr windfarm. Land use within the basin is described as "mainly pasture, forest and moorland".[5]
