SOME SUSPENDED SEDIMENT YIELDS FROM SOUTH ISLAND CATCHMENTS, NEW ZEALAND

Abstract. Soil erosion rates on plots of waste rock at Ranger uranium mine and basin sediment yields have been measured for over 30 years in Magela Creek in northern Australia. Soil erosion rates on chlorite schist waste rock are higher than for mica schist and weathering is also much faster. Sediment yields are low but are further reduced by sediment trapping effects of flood plains, floodouts, billabongs and extensive wetlands. Suspended sediment yields exceed bedload yields in this deeply weathered, tropical landscape, but the amount of sand transported greatly exceeds that of silt and clay. Nevertheless, sand is totally stored above the topographic base level. Longitudinal continuity of sediment transport is not maintained. As a result, suspended sediment and bedload do not move progressively from the summit to the sea along Magela Creek and lower Magela Creek wetlands trap about 90.5% of the total sediment load input.

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Suspended sediment and discharge dynamics across multiple spatial and temporal scales in a glaciated alpine environment: the case of the upper Ötztal, Austria

10.5194/egusphere-egu21-9575 ◽

2021 ◽

Author(s):

Lena Katharina Schmidt ◽

Till Francke ◽

Theresa Blume ◽

Johannes Schöber ◽

Daniel Pfurtscheller ◽

...

Keyword(s):

Suspended Sediment ◽

Temporal Dynamics ◽

Management Strategies ◽

Transient State ◽

Data Availability ◽

Spatial And Temporal Scales ◽

Sediment Yields ◽

Catchment Areas ◽

Suspended Sediment Concentrations ◽

Alpine Catchments

High alpine areas are affected disproportionately by global warming and are thus found to be in a transient state. This causes accelerating glacial retreat, which can have severe impacts on discharge and potentially sediment dynamics. Possible effects include changes in water quantities and hydrograph timing as well as changing sediment source areas and the associated magnitude and timing of transport capacities. In turn, the resulting changes in water and sediment supplies and timing have the potential to severely impact downstream ecosystems and infrastructure.An essential step towards estimating the effects of future changes and developing sustainable management strategies is to quantify the behavior in the past and present. We therefore used the excellent data availability of discharge and suspended sediment concentrations in our study area in the upper &#214;tztal in Tyrol, Austria, to make such an assessment. We study discharge and suspended sediment concentrations, which have been monitored at three gauges and for a minimum of seven years in the case of the youngest gauge. The resulting nested catchment setup, with catchment sizes ranging between 98 km&#178; and 785 km&#178;, allows us to learn about discharge and sediment fluxes and their spatial distribution, thus allowing us to quantify the relative importance of the glaciated areas as compared to the lower-lying catchment areas. It also allows us to study the temporal dynamics, such as the seasonal timing of the peaks and their interannual differences. In turn, the nested catchments allows us to investigate the spatial variability of these temporal dynamics. &#160;The results confirm the high specific sediment yields for alpine catchments in the order of 10&#179; t/km&#178; per year and higher yields in areas with higher glacier cover as well as a very pronounced seasonality.

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Sediment Load and Suspended Sediment Concentration Prediction

Soil and Water Research ◽

10.17221/6502-swr ◽

2013 ◽

Vol 1 (No. 1) ◽

pp. 23-31 ◽

Cited By ~ 2

Author(s):

Bečvář Martin

Keyword(s):

Suspended Sediment ◽

Sediment Yield ◽

Suspended Sediment Concentration ◽

Sediment Load ◽

Sediment Concentration ◽

River Basins ◽

River Systems ◽

Sediment Yields ◽

Suspended Sediment Concentrations ◽

Annual Sediment

Sediment is a natural component of riverine environments and its presence in river systems is essential. However, in many ways and many places river systems and the landscape have been strongly affected by human activities which have destroyed naturally balanced sediment supply and sediment transport within catchments. As a consequence a number of severe environmental problems and failures have been identified, in particular the link between sediments and chemicals is crucial and has become a subject of major scientific interest. Sediment load and sediment concentration are therefore highly important variables that may play a key role in environment quality assessment and help to evaluate the extent of potential adverse impacts. This paper introduces a methodology to predict sediment loads and suspended sediment concentrations (SSC) in large European river basins. The methodology was developed within an MSc research study that was conducted in order to improve sediment modelling in the GREAT-ER point source pollution river modelling package. Currently GREAT-ER uses suspended sediment concentration of 15 mg/l for all rivers in Europe which is an obvious oversimplification. The basic principle of the methodology to predict sediment concentration is to estimate annual sediment load at the point of interest and the amount of water that transports it. The amount of transported material is then redistributed in that corresponding water volume (using the flow characteristic) which determines sediment concentrations. Across the continent, 44 river basins belonging to major European rivers were investigated. Suspended sediment concentration data were collected from various European basins in order to obtain observed sediment yields. These were then compared against the traditional empiric sediment yield estimators. Three good approaches for sediment yield prediction were introduced based on the comparison. The three approaches were applied to predict annual sediment yields which were consequently translated into suspended sediment concentrations. SSC were predicted at 47 locations widely distributed around Europe. The verification of the methodology was carried out using data from the Czech Republic. Observed SSC were compared against the predicted ones which validated the methodology for SSC prediction.

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Large-scale mass-wasting processes following the 232 CE Hatepe Eruption of Taupo Volcano, New Zealand - Sedimentary features and dispersal of reworked Taupo Ignimbrite in the Ongarue River valley

10.5194/egusphere-egu2020-11852 ◽

2020 ◽

Author(s):

Anke Verena Zernack ◽

Jonathan Noel Procter

Keyword(s):

New Zealand ◽

Large Scale ◽

Basal Layer ◽

Source Area ◽

Field Studies ◽

Mass Wasting ◽

Sedimentary Characteristics ◽

Sediment Yields ◽

Fluvial Sedimentation ◽

Taupo Volcano

The 232 CE Hatepe Eruption of Taupo Volcano, New Zealand (also referred to as Taupo Eruption), was one of the most violent and complex silicic eruptions worldwide in the last 5,000 years. The pyroclastic sequence was subdivided into 7 distinct stratigraphic units that reflect diverse eruption mechanisms with pumice fallout unit 5 (Taupo Plinian) and unit 6 (Taupo Ignimbrite) contributing the largest volumes, an estimated 5.8 km3 and 12.1 km3 DRE respectively. The non-welded Taupo Ignimbrite was emplaced by a highly energetic flow over a near-circular area of 20,000 km2 around the vent, reaching distances of 80&#177;10 km. It consists of an irregular basal layer and a thicker pumice-dominated main unit containing varying proportions of pumice clasts, vitric ash and dense components, overlain by a thin co-ignimbrite ash bed. The main ignimbrite unit shows two distinct facies, a landscape-mantling veneer deposit that gradually decreases from 10 m proximal thickness to 15-30 cm distally and a more voluminous, up to 70-m thick valley-ponded ignimbrite that filled depressions and smoothed out the landscape.The sudden influx of vast volumes of loose pyroclastic material choked the drainage systems around the volcano, resulting in a large-scale geomorphic and sedimentary response. While previous work focused on major river catchments north to southeast of the volcano, we aim at characterising and quantifying landscape adjustment and remobilisation processes to the west, using stratigraphic, sedimentologic and geomorphic field studies of the volcaniclastic sequences along the Ongarue and Whanganui River valleys. Our working hypothesis involves a four-stage landscape response model based on previously described mass-wasting processes in the aftermath of large explosive eruptions: 1) large-scale remobilisation of ignimbrite veneer material from sloping surfaces by series of debris and hyperconcentrated flows, emplacing lahar deposits across the ignimbrite dispersal area and beyond, 2) cutting of steep channels into valley-ponded ignimbrite and resedimentation as lahar deposits downstream, 3) gradual widening of channels leading to establishment of an active channel with adjacent floodplains as sediment yields decrease and the landscape restabilises, represented by normal stream flow and flood deposits in the ignimbrite dispersal area and a shift from lahar to fluvial- dominated sequences downstream, and 4) return to pre-eruption sediment yields resulting in further downward incision to the original bedrock channel bed and prevailing fluvial sedimentation processes with remnants of primary and reworked deposits preserved as terraces along the valley walls.Here we present initial results on the stratigraphy of the volcaniclastic sequence and the sedimentary characteristics and dispersal of the identified lithofacies associations, which range from debris-flow and hyperconcentrated-flow to pumiceous fluvial deposits. Tempo-spatial variations in deposit characteristics are due to differences in source material, flow type, and nature of the source area and depositional environment.

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