Collaborative Research - Sediment Production and Alluvial Buffering in a Steepland River Basin: Waipaoa River Basin, New Zealand

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

In comparison with the area they drain, small steepland rivers supply a disproportionate amount of sediment to Earth's oceans. The major rivers draining the East Coast, North Island, New Zealand, for example, generate some 55 Megatonnes of suspended sediment annually, which amounts to about 0.3% of the total global suspended sediment input to the ocean from only 0.0033% of Earth's total land area. It is presumed that steepland rivers, like the Waipaoa, convey a high percentage of the sediment generated by erosion within their drainage basins directly to the ocean. So that the effects of climate, vegetation, and land use change that have occurred in the last 10,000 years should be readily apparent in the depositional record. However, except when the Waipaoa River basin was deforested by European settlers in the past 200 years, high-resolution cores suggest there has been comparatively little variation in sedimentation rates on the adjacent continental shelf. Thus, it is hypothesized that, in the Waipaoa River basin, variations in hillslope sediment production are buffered by floodplain storage, as opposed to being observed directly as changes in fluvial sediment yield. To provide information on long-term trends and patterns in sediment production that are a response to climatic and anthropogenic change, field survey, coring, and analyses of the cosmogenic nuclides produced in rock and soil will be used to define rates and patterns of surface erosion in the headwaters of the Waipaoa River basin and deposition on the Poverty Bay Flats. This information, in conjunction with hydrological data and information about the past climate derived from lake sediment cores, will help define the input parameters for a numerical model that will be used to recreate river discharge and sediment load records for the past several thousand years. Previous studies have provided information on long-term trends and patterns in sediment production and yield that are a response to climatic and anthropogenic change, but the inability to link process and response continues to limit our understanding of how fluvial systems respond to environmental change. Understanding how rates of erosion and sediment discharge to the ocean vary over time is necessary to assess the effectiveness of sustainable land management strategies and the effect human activities have on landscapes. Studying the Waipaoa River basin, an area where rates of geomorphic activity rank amongst the highest recorded globally, will permit direct links to be established between process and response, and thus help answer one of the fundamental questions in fluvial geomorphology and sediment transport; that is, "how sensitive is the fluvial system to environmental change?"