In the Aggadah of Rav Yeva Saba we have learnt why Vav-Dalet are included in Yud. And he answers, the plant of the garden, which is Zeir Anpin, is called Vav. There is another garden called Dalet. That Dalet, which is Malchut, is watered by Vav, which is Zeir Anpin. This is the meaning of the verse, “And a river went out of Eden to water the garden.” Who is Eden – it is the highest Chochmah and it is Yud. It waters the garden, which is Vav, which is Zeir Anpin. “And from thence it was parted and became four heads” (Ibid.): this refers to Dalet, that is, Malchut. And everything is included in Yud.