Hydrology, sediment transport and erosion in Longyeardalen (Research in Svalbard RiS ID 11641)

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The monitoring

The program runs in collaboration with Longyearbyen Lokalstyre and students from various Norwegian universities

The monitoring was initiated in 2018 and continues to run thanks to support of UNIS BSc course (AG221) and MSc program

The project includes:

1. Hydrological monitoring of Longyearelva (so far 2018 - 2022 and ongoing)

2. Investigation of suspended sediment and bedload transport in Longyearelva (so far in 2019, 2020, 2021)

3. Investigation of riverbed erosion (so far in 2019, 2020, 2021)

4. Identification and monitoring of geohazards in Longyeardalen

5. Investigation of erosion in Longyeardalen (so far in 2019, 2020, 2021, 2022)

6. Creation of 3D models (DEM) of Longyearelva as well as Larsbreen and Longyearbreen margins, moraines and their forefields

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Hydrology

A monitoring station is established every melt season since 2018 at the bridge on the north side of Longyearelva by the entrance to the fjord 

The station runs from the very beginning of snowmelt in May/June until the freeze-up in September/October.

In addition to runoff, hourly water quality is also monitored.

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Two UNIS and NTNU MSc students Lene Pallesen and Marthe Ottem getting ready to set up  monitoring station and start their MSc projects.

Sediment transport, bedload transport & Longyeardalen erosion

To know how much fine suspended sediments is being moved every summer by Longyearelva, automatic pump sampler is used to capture water in regular intervals.

After collection, the water is filtered and sediment dried and weighted. 

Knowing water discharge (runoff) allows to quantify daily sediment fluxes from Longyeardalen, as well as total annual sediment transport into Adventfjorden.

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Runoff and glacier recession
Key Results 

A rapid recession of all small size glaciers takes place across entire Svalbard. This is also the case for those draining into Longyeardalen, Longyearbreen, Larsbreen and Platåbreen (3D models of those glaciers are available through SvalDEM). 

2022 melt season in particular has been brutal for glaciers both in Svalbard and across the world, resulting in the record melt rates.

In the long term however, total amount of glacier meltwater draining the valley has been annually decreasing for the last decade, because too much ice has alredy melted and glaciers passed the peak water point (read more about it in SvalHydro Environmental report).

This trend is expected to continue. Yet, we need to pay attention on the amount of precipitation that can offset the lack of glacier melt and influence increased erosion in the valley.

 

As with any glacierised catchment in the High Arctic, hydrology in the valley can be divided into 3 parts.

 

  1. The beginning of the summer season is dominated by snowmelt, characterised by low discharge and sediment transport.

  2. The middle of the season is dominated by glacier ice melt, and high diurnal runoff fluctuations followed by high sediment load.

  3. When the summer ends, and glacier melt is nearing to the end, runoff drops and so does the sediment load.

 

This pattern however is being altered by the changing climatic conditions that influence the amount of rainfall (see e.g. Nowak and Hodson 2013). 

The Arctic is getting wetter, especially towards the end of summer, thus generating additional runoff, influencing sediment displacement as well as erosion within the entire valley (see SvalHydro).  

Erosion
Key Results 

The primary sources of sediment in Longyeardalen are the glaciers and their ice-cored moraines

The secondary sources are snow avalanches and rock glaciers located along the slopes of the valley.

 

When glaciers stop melting at the end of summer, and the active layer is thickest, sediments are supplied by the river bank erosion and thaw driven moraine slumps

 

Sediment movement varries daily in the summer, but largest fluctuations are observed towards the autumn. 

 

As in any glacierised catchment in Svalbard, there is a correlation of sediment transport with runoff in the summer that decreases in September/October. 

 

Pallesen MSc thesis (2022) shows that the total volume of sediment that has been removed by slumping in the moraines by 2021 is at least 2.8 ± 0.6 mln m3.

 

Furthermore, she noticed an acceleration in degradation over the past 10 years due to retrogressive behaviour of slumps in ice-cored moraines due to exposure to heat and water, and glaciofluvial erosion. This acceleration is promoted by an increase in active layer thickness due to warming. 

 

Pallesen shows that thaw-induced slumping is irregular and episodic with high hydrological connectivity in Longyeardalen.

However, magnitude and frequency of these sources is expected to increase with continued warming and increased rainfall. 

Thus we have to expect increased occurence of late season erosion in the valley 

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