Sudalins, Sudalins - Tirza right tributary in Gulbene district. Length 9 km. Swimming pool 147 km2. Sudaliņa flows from Sudalezers, flows into Tirza near Lejasciems. Most of the river basin is located in the Trapene Plain, but its eastern edge occupies the western slope of the Gulbene embankment. At the bottom of the river is the Lower Mill Dam and the reservoir. The largest tributary - Mudaža.

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