～にわたって— Spanning the Whole Range

• 工事は三年間にわたって続けられた。

  Kōji wa sannenkan ni watatte tsuzukerareta.

  The construction continued over a period of three years.

  にわたって attaches to the span 三年間 and shows the work extended across that whole period.

• この地域は広範囲にわたる被害を受けた。

  Kono chiiki wa kōhan'i ni wataru higai o uketa.

  This area suffered damage spanning a wide range.

  にわたる directly modifies the noun 被害, describing damage that covers a broad scope.

• 調査は十日間にわたり行われた。

  Chōsa wa tōkakan ni watari okonawareta.

  The investigation was carried out over the course of ten days.

  にわたり is the formal written connective form, linking the span 十日間 to the action.

• ・Register: formal/written; common in news and reports.
• ・にわたって is adverbial (modifies a verb), にわたる is adnominal (modifies a noun).
• ・Pairs with spans, ranges, and quantities — not with a single point in time.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～にわたって is tested against.

• に際して — On the Occasion Of
• に先立って — Ahead of the Event
• につけ — At Every Turn
• ～たび(に) — Every Single Time
• ～あげく(に) — After All That, In the End
• ～折(に) — On the Occasion Of
• ～かと思うと／かと思ったら — No Sooner Than, Just When
• ～末(に)／の末(に) — After All Was Said and Done