1.Since the 1950s, the various countries have constructed many fishways .
自上世纪50年代以来，世界各国建筑了许多鱼道。
2.Thus a study is undertaken to explore the extent of severity of this flow so that designer can keep in mind in designing these fishways .
因此，我们着手研究了它的严重性以便设计者在设计鱼道时能考虑这些因素。