Suspended sediment and discharge dynamics in a glacierized alpine environment: Identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria

Climatic changes are expected to fundamentally alter discharge and sediment dynamics in glaciated high alpine areas, e.g. through glacier retreat, prolonged snow-free periods and more frequent intense rainfall events in summer. However, how exactly these hydrological changes will affect sediment dynamics is not yet known. In the present study, we aim to pinpoint areas and processes most relevant to recent sediment and discharge dynamics on different spatial and temporal scales in the Ötztal Alpine Region in Tyrol, Austria. Therefore, we analyze observed discharge and relatively long suspended sediment time series of up to 15 years from three gauges in a nested catchment setup. The catchments range from 100 to almost 800 km2 in size with 10 to 30 % glacier cover and span an elevation range of 930 to 3772 m a.s.l.. The investigation of satellite-based snow cover maps, glacier inventories, mass balances and precipitation data complement the analysis. Our results indicate that mean annual specific discharge and suspended sediment fluxes are highest in the most glaciated sub-catchment and both fluxes correlate significantly with annual glacier mass balances. Furthermore, both discharge and suspended sediment loads show a distinct seasonality with low values during winter and high values during summer. However, the spring onset of sediment transport is almost synchronous at the three gauges, contrary to the spring rise in discharge, which occurs earlier further downstream. A spatio-temporal analysis of snow cover evolution indicates that the spring increase in sediment fluxes at all gauges coincides with the onset of snow melt above 2500 m elevation. Zones above this elevation include glacier tongues and recently deglaciated areas, which seem to be crucial for the sediment dynamics in the catchment. Precipitation events in summer were associated with peak sediment concentrations and fluxes, but on average accounted for only 21 % of the annual sediment yields of the years 2011 to 2020. We conclude that glaciers and the areas above 2500 m elevation play a dominant role for discharge and sediment dynamics in the Ötztal area, while precipitation events play a secondary role. Our study extends the scientific knowledge on current hydro-sedimentological changes in glaciated high alpine areas and provides a baseline for investigations on projected future changes in hydro-sedimentological system dynamics.

Catchment Sediment Dynamics and the Role of Deep-Seated Landslide-Dams; Waipaoa Catchment, Raukumara Peninsula, New Zealand

<p>Sediment volumes retained by landslide-dams of the Waipaoa are small at 1.85x10⁶m³ compared to the 24.5km³ (Marden et al., 2008b) of sediment eroded in the landscape since the last glacial maximum. Landslide-dams do however represent a major perturbation to sediment transport, although due to their mainly short life span this disruption is discontinuous representing a pulsing in the transport network. The objective of this study is to investigate the sedimentary dynamics of the Waipaoa catchment by providing insights into the role that deep-seated landslides play and asks the questions: What is the impact on sediment transport imposed by the landslide-dams of the Waipaoa catchment? and; What do the sediments impounded in landslide-dammed lakes tell us about catchment sediment dynamics through time? The Waipaoa River on the East Cape of New Zealand‘s North Island delivers volumes of sediment to the coast which are considered high by global standards. Catchment erosion is controlled by soft marine sediments, combined with a history of tectonic fracturing and frequent intense rain storms. Erosion events are driven by intense cyclonic systems rain storms which deliver ≥200mm/24hr rainfall and induce catchment wide gully erosion as well as shallow surficial landslides. Under current land covers gully erosion provides the dominant source of sediments, with high degrees of slope channel coupling and steep gradient river profiles providing for efficient delivery to the coast. Offshore in the Poverty Bay, sediments delivered by the Waipaoa River show considerable variability over a range of temporal scales. Valley slopes within the Waipaoa catchment are also susceptible to large deep-seated landslide failures, with movement depths greater than 5 metres often on internal structural failure planes. These large slope movements can be produced by both extreme storm events (≥300mm/24hr) which occur on a return periods of 1 in 5 years and seismic ground shaking of 1 in 1000-2000 years. Where these large events block channels and are able to persist for long periods, sediments accumulated upstream to provide a unique record of the catchments sedimentary history. There have been some 1100 historic large scale features which have been identified within the Waipaoa region, with this study selecting seven that have shown evidence of channel blockage. The project aims to provide insights into the age of a sample of deep-seated landslides that have dammed channels to determine how long landslide-dams survive in the landscape and quantify the volumes of sediment they have trapped. Further, the project aims to determine what the spatial and temporal distribution of these blockages has meant to sediment delivery and whether there have been changes in sediment dynamics in their upper catchments over time. The project uses the detailed mapping of the trapped body of sediments, GIS modelling of the palaeo and present landscapes and age control determinations provided by tephra and 14C dating to provide both volumes and rates of sediment delivery.</p>

Catchment Sediment Dynamics and the Role of Deep-Seated Landslide-Dams; Waipaoa Catchment, Raukumara Peninsula, New Zealand

<p>Sediment volumes retained by landslide-dams of the Waipaoa are small at 1.85x10⁶m³ compared to the 24.5km³ (Marden et al., 2008b) of sediment eroded in the landscape since the last glacial maximum. Landslide-dams do however represent a major perturbation to sediment transport, although due to their mainly short life span this disruption is discontinuous representing a pulsing in the transport network. The objective of this study is to investigate the sedimentary dynamics of the Waipaoa catchment by providing insights into the role that deep-seated landslides play and asks the questions: What is the impact on sediment transport imposed by the landslide-dams of the Waipaoa catchment? and; What do the sediments impounded in landslide-dammed lakes tell us about catchment sediment dynamics through time? The Waipaoa River on the East Cape of New Zealand‘s North Island delivers volumes of sediment to the coast which are considered high by global standards. Catchment erosion is controlled by soft marine sediments, combined with a history of tectonic fracturing and frequent intense rain storms. Erosion events are driven by intense cyclonic systems rain storms which deliver ≥200mm/24hr rainfall and induce catchment wide gully erosion as well as shallow surficial landslides. Under current land covers gully erosion provides the dominant source of sediments, with high degrees of slope channel coupling and steep gradient river profiles providing for efficient delivery to the coast. Offshore in the Poverty Bay, sediments delivered by the Waipaoa River show considerable variability over a range of temporal scales. Valley slopes within the Waipaoa catchment are also susceptible to large deep-seated landslide failures, with movement depths greater than 5 metres often on internal structural failure planes. These large slope movements can be produced by both extreme storm events (≥300mm/24hr) which occur on a return periods of 1 in 5 years and seismic ground shaking of 1 in 1000-2000 years. Where these large events block channels and are able to persist for long periods, sediments accumulated upstream to provide a unique record of the catchments sedimentary history. There have been some 1100 historic large scale features which have been identified within the Waipaoa region, with this study selecting seven that have shown evidence of channel blockage. The project aims to provide insights into the age of a sample of deep-seated landslides that have dammed channels to determine how long landslide-dams survive in the landscape and quantify the volumes of sediment they have trapped. Further, the project aims to determine what the spatial and temporal distribution of these blockages has meant to sediment delivery and whether there have been changes in sediment dynamics in their upper catchments over time. The project uses the detailed mapping of the trapped body of sediments, GIS modelling of the palaeo and present landscapes and age control determinations provided by tephra and 14C dating to provide both volumes and rates of sediment delivery.</p>