Complex sentence: What is now known as the "Sumida River" was previously the path of the Ara-kawa, however towards the end of the Meiji era work was carried out to divert the main flow of the Ara-kawa to prevent flooding.
Split into simpler sentences: What is now known as the "Sumida River" was previously the path of the Ara-kawa. However, towards the end of the Meiji era work was carried out to divert the main flow of the Ara-kawa to prevent flooding.