After national isolation the family continued to have control over transportation in the Katsura-gawa River and established the Suminokura Yakusho Office at every key port of the river lower than the present-day Seki, Nantan City.
鎖国以後も桂川水運の管理を任され、現在の南丹市世木より下流の、桂川の重要な港には角倉役所が置かれた。