SOME SUSPENDED SEDIMENT YIELDS FROM SOUTH ISLAND CATCHMENTS, NEW ZEALAND¹

Abstract

Estimates of specific annual suspended sediment yields, some of which rank among the highest reported in the world, are presented for 33 basins of South Island, New Zealand. Yield from each basin was determined by combining a suspended sediment concentration rating with the complete flow record of each catchment stream gaging station A multiple regression analysis between sediment yields and climatic, hydrologic and physiographic parameters of each basin demonstrates that most of the variance in yields is explained by catchment mean rainfall. Geology apparently has little influence on sediment yield as suspended sediment concentration ratings, from rivers draining catchments of differing lithology, and regolith, are indistinguishable. Specific suspended sediment yield prediction equations are given for four defined regions covering in area almost all South Island; and except for one area, feature rainfall as the principle independent variablc. Differences between regjons may be due to variations in intensity, frequency, and duration patterns of storms. It is proposed that a simple power law relationship between yield and rainfall provides useful suspended sediment yield estimates in mountainous regions of temperate maritime climate, provided catchments have not been modified extensively by man.

Sediment yield response to large storm events and forest harvesting, Motueka River, New Zealand

“…Griffiths & Glasby (1985) calculated the suspended sediment yield (SY) of the Motueka River to the coast at 277 t/km 2 /year. However, this estimate was based on a relationship between SY and rainfall derived from dominantly greywacke and schist catchments throughout the South Island (Griffiths 1981), and probably overestimated the yield. Mosley (1980), using the Griffiths (1981) method, suggested much of the yield is derived from the high-rainfall, steep terrain of the west-bank tributaries and estimated rates of 119 t/km 2 /year from the Dart River and 583 t/km 2 /year from the Wangapeka River.…”

Global evaluation of erosion rates in relation to tectonics

“…Most studies have concentrated on investigating controlling factors on a local scale and have come to a variety of conclusions regarding what most affects erosion rates ranging from precipitation (e.g., Galy and France-Lanord 2001;Griffiths 1979;Griffiths 1981) to mass wasting events (Hovius et al 1997) and lithology (Matsushi et al 2006). In addition, global data have been compiled with the intention of identifying the controlling factors of erosion rates.…”

Sediment production from forest roads in Queen Charlotte Forest and potential impact on marine water quality, Marlborough Sounds, New Zealand

“…However, annual sediment delivery rates based on estimates given by Griffiths (1981), Griffiths & Glasby (1985), and Cooper et al (1987) for rivers in the vicinity of the Sounds, and in the eastern foothills of the Southern Alps with similar topography and geology, range from 300 to as high as 600 tkm" 2 yr"…”