渠

Top-left water radical — three drops, the side-form of 水. Indexes 渠 in the watercourse family alongside 河 river, 江 large river, 沟 ditch, 池 pool. Anchors the meaning: a canal is an artificial channel for moving water across land.

Top-right 巨 — originally a carpenter's measuring square, later 'huge.' Supplies the phonetic frame: jù shifting to qú via well-attested initial alternation. Same phonetic in 距 distance, 拒 to refuse, 苣 a plant. Hints faintly that a canal is a measured, engineered cut through the land.

Bottom 木 — a tree pictograph, four strokes branching from a central trunk. In 渠 it represents the wooden lining or planking used to reinforce a canal's walls. Together the three pieces 'water + measure + wood' picture an engineered, plank-lined waterway — the original sense of a man-made canal.