 |
| Titel |
Dynamics of bedload size and rate during snow and glacier melting in a high-gradient Andean stream |
| VerfasserIn |
Luca Mao, Ricardo Carrillo |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132639
|
| Publikation (Nr.) |
 EGU/EGU2016-13165.pdf |
|
|
|
|
|
| Zusammenfassung |
| The evaluation and prediction of coarse sediment movement and transport is crucial for
understanding and predicting fluvial morphodynamics, and for designing flood hazard
mitigation structures and stream habitat restoration. At the scale of single flood event, the
relationship between water discharge (Q) and bedload rate (Qs) often reveals hysteretic loops.
If Qs peaks before Q the hysteresis is clockwise and this suggests a condition of
unlimited sediment supply. In contrast, counterclockwise hysteresis would suggest
limited sediment supply conditions. Understanding the direction and magnitude of
hysteresis at the single flood event can thus reveal the sediment availability. Also,
interpreting temporal trend of hysteresis could be used to infer the dynamics of
sediment sources. This work is focused in the temporal trend of hysteresis pattern of
bedload transport in a small (27 km2) glaciarized catchment in the Andes of central
Chile (Estero Morales) from 2014 to 2015. Bedload is measured using a 0.5 m long
Japanese acoustic pipe sensor fixed on the channel bed, which register the intensity of
impulses generated by the impact of sediments on the sensor. Based on flume and field
measurements, the sensor was calibrated as to provide intensity of transported sediments.
Also, direct bedload samplings were taken within a range of 0.01 – 1000 g s-1 m-1)
sediment transport rates, and allowed to assess median and maximum grain size of
transported sediments. The analysis reveals that hysteresis at the scale of single
flood tends to be clockwise during snowmelt and early glaciermelting, whereas
counterclockwise hysteresis is dominant during the late glaciermelting. Also, bedload
transport rates and grain size of transported sediments reduces progressively from
early to late glaciermelting. Interestingly, direct bedload samplings revealed that
grain size of transported sediments tends to exhibit a counterclockwise hysteresis
when the sediment transport is clockwise. Thus during the snowmelt and early
glaciermelting, sediment availability appears to be unlimited and hysteresis can be
ascribed to pulses of sediments coming from the proglacial area. Instead, as the
glaciermelting season progresses, sediment availability decreases probably due to the
progressive exhaustion of sediments stored in the channel bed, and counterclockwise
hysteresis can be ascribed to changes in the organization of the surface sediments at the
scale of clusters. Results highlight the complex relationships between dynamics
of sediment sources at the basin scale and changes in channel sediment storage
overtime, resulting in abrupt changes in rate and size of sediment transport. Long-term
assessment of these dynamics using indirect methods to assess bedload transport can
provide important insights for understanding probable trajectories of morphological
evolution of glacierized streams which are subject to rapid environmental changes. This
research is being developed within the framework of Project FONDECYT 1130378. |
|
|
|
|
|
|