The impact of landslides on sediment yield, South Westland, New Zealand

Sediment yields in the Southern Alps of New Zealand are among the highest in the world due to high annual precipitation, rapid uplift, weak bedrock and episodic earthquakes. Two neighbouring watersheds, those of the Poerua and Waitangitaona rivers, were studied to determine the impact landslides have on sediment yield. Both watersheds have been recently disturbed by landslides, 1) a large rock avalanche from Mt. Adams in the Poerua River watershed and 2) a failing slope known as the “Gaunt Creek slip” in the Waitangitaona watershed. I conducted a ground penetrating radar survey of the lower Waitangitaona River valley and a dGPS topographic survey of the lower Poerua River valley to determine average sediment yields on different timescales. The estimated sediment yields, which are among the highest in the world, are controlled by differences in the time, size, and character of the landslides that have perturbed the fluvial system.