Date of Award

1971

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

L. Clayton

Abstract

The Cass River drainage basin is in the Southern Alps in the central part of the South Island of New Zealand. The Alps are composed of complexly folded greywacke which is still actively rising. The basin has been modified by several glacial advances during Pleistocene time.

The Cass basin has a temperate climate characterized by a steep precipitation gradient. Its vegetation includes plants of the forest grassland, shrubland, swamp, rock, and river-bed associations.

The Cass basin may be divided into four geomorphic areas: bedrock areas, high-angle fans, moderate-angle fans, and a low-angle fan. The bedrock areas consist of fractured greywacke; the high-angle fans are active talus cones; the moderate-angle fans are inactive fans preserved from the last glacial advance; and the low-angle fans are active alluvial fans.

A single large groundwater flow system occurs in the low-angle fan and in the moderate-angle fans in the Cass basin. Small flow systems occur in high-angle fans along the sides of the basin. Sediment movement is highest in areas of positive groundwater pressure and lowest in areas of negative groundwater pressure.

Computer programs were used to handle the data from the quantitative sediment and hydrologic studies. The quantitative sediment studies of the basin were inconclusive because of the extreme variability of the sediment.

Three types of channels occur in the basin: confined bedload channels, unconfined bedload channels, and suspended-load channels. The confined and unconfined bedload channels are adjusted to transport a maximum of bedload sediment. The width of the confined bedload channels is limited by independent variables other than sediment load. The suspended-load rivers are adjusted to carry a maximum of suspended sediment.

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