Yamakawa wa ki no ha nagarezu asaki se o sekeba fuchi to zo aki wa naru ran - Shui Wakashu(English Translation & Meaning)

山河はきのはながれず浅き瀬を
堰けば淵とぞ秋はなるらん

Roma-ji: Yamakawa wa ki no ha nagarezu asaki se o sekeba fuchi to zo aki wa naru ran
English Translation: In the mountain stream
the fallen leaves do not flow,
and the shallow rapids
they dam, and so into pools
in autumn the stream must turn.
Meaning: In the mountain stream the leaves do not flow away but dam the shallows, and so in autumn it must become deep pools.
Commentary: Book Seven Names of Things 368

Headnote: "Hagi no hana (bush clover flowers)"
The poet surmises that because the leaves in the mountain stream do not flow away but dam the shallows, in autumn the stream must turn into deep pools. Imagining how piled-up fallen leaves change the shape of the stream, the poem hides the name "hagi no hana" given in the headnote in the run of sounds "ha ki no ha na" from the first to the second line. The headnote names the thing hidden in the poem.
Tadamine, that is, Mibu no Tadamine, was one of the compilers of the Kokinshū and the father of Mibu no Tadami, and he is counted among the Thirty-Six Immortal Poets.
Harumichi no Tsuraki's autumn poem in the Kokinshū, "Yamagawa ni kaze no kaketaru shigarami wa nagare mo aenu momiji narikeri," also sings of autumn leaves heaped in a mountain stream and unable to flow.

First line, "yamakawa wa," means "the stream flowing among the mountains."
Second line, "ki no ha nagarezu," means "the leaves do not flow." With "wa" at the end of the first line, it hides the name "hagi no hana."
Third line, "asaki se o," means "the shallow rapids."
Fourth line, "sekeba fuchi to zo," means "since they dam them, into pools," the perfective form with "ba" expressing a reason, strengthened by the particle "zo."
Final line, "aki wa naru ran," means "in autumn it must become," with "ran" an auxiliary of present conjecture, resolving "zo" in its attributive form.
Author: Mibu no Tadamine
Source: Shui Wakashu
Prev Poem: Shiratsuyu no kakaru ga yagate kiezaraba kusaba zo tama no kushige naramashi
Next Poem: Takitsuse no naka ni tama tsumu shiranami wa nagaruru mizu o o ni zo nukikeru