Otra (vassdrag 021): longitudinal profile and candidate natural migration barriers

Screening test of the method, 2026-10-08. Mouth (Kristiansand) to the upstream end of the NVE Elvenett line in Agder, km along the Elvenett centre line. Primary elevation = Kartverket bare-earth DTM (1 m, NN2000), sampled every 5 m.

Read this first. Everything below is a screening signal from elevation data, not a verified barrier list: no field check, no fish data. The DTM shows the water surface at the date of the laser survey; falls are detected from height steps only. The Otra is one of the most regulated rivers in Norway: most large steps are dams and power stations (grey), and only 5 dams are mapped in OpenStreetMap, so "natural candidate" may still hide an unmapped weir or intake. NB: the Otra is vassdrag 021 in NVE data (019 is Topdalselva).
Drag on the chart to zoom, double-click to reset, wheel = zoom.
DTM filtered (primary) DTM raw FKB vector Z (where polygons exist) lake / reservoir natural candidate, drop ≥3 m in 10 m natural candidate, 2-3 m 1.5-2 m or cascade (small fish, check) regulation (dam / power station, not natural)
Click a barrier on the chart, the map or in the table.
💬 Innspill