「おりる」＆「くだる」 - They share the same basic meaning "go down", "get down". That's why they share the same kanji, "下(under)". - 「くだる」: go down - 「おりる」：go down caferully/slowly/intentionally. ＊＊＊　例文： - 馬をおりる - 霜(frost)がおりる - 勝負をおりる（stop playing game) - 電車をおりる - 認可がおりる - 川をくだる 「おりる」 is more widely used than 「くだる」 They are almost always not interexchangeable. ＊＊＊＊ -　おりる：The desitination, where you land on, is important -　くだる：Process of going down/or action of going down itself is important. OK:階段をおりたら右に曲がってください。 NG:階段をくだったら右に曲がってください。

I want to say that the difference between 下る and 降りる are only different for more context-heavy situations, as jisho.org describes 下る not only holding the same meaning as 降りる, but also holds "to pass time" and "to surrender" versus 降りる using "to dismount (eg from a horse)" and "to form mist or fog".