Bedload dynamics and associated snowmelt influence in mountainous and semiarid alluvial rivers

Moñino

2018

Hydrological Processes

Self Cite

Soil loss, fluvial erosion, and sedimentation are major problems in semi‐arid environments due to the high associated costs of decreasing services such as provisioning and regulating water resources. The objective of this research is to analyse sediment yield in a mountainous semi‐arid basin, paying special attention to the sources of sediment, the associated uncertainties, and the transport processes involved. The segregation hypothesis along a reservoir of the sediment coming from hillslopes or fluvial systems is also evaluated. For this purpose, bottom‐set and deltaic deposits of a reservoir (110 hm3) in southern Spain have been measured and compared with basin erosion and fluvial transport monitoring over a 12‐year period. The volume of sediment stored at the bottomset of the reservoir shows a relative match with parametric predictions based on the Revised Universal Soil Loss Equation/Modified Universal Soil Loss Equation hillslope models and rating curves, estimated as being between 7 and 13 t·ha−1·year−1. Similarly, the measured volume of deltaic deposit fits the average value of stochastic simulations from different bedload transport equations. These contributions represent 50–65% of the total volume measured regarding suspended sediment inputs, way above that described in previous works. This highlights the importance of considering bedload when estimating the useful life of reservoirs in semi‐arid environments. The major differences in sediment grain size between hillslopes and river systems, and the size fractions measured along the reservoir, support the assertion of segregation hypothesis. Nonetheless, based on the processes observed and the uncertainty related to modelling, that assertion has to be taken with caution. At basin scale, a specific sediment yield of between 19 and 24 t·ha−1·year−1 has been estimated, which includes hillslopes and fluvial contributions. This rate is in the range of sediment yield reported for Mediterranean mountain areas of a torrential character. The pulse‐like nature of the system and the spatial heterogeneity of fluvial and hillslope erosion rates points out the importance of considering mid to long‐term and process‐based approaches and emphasizes the limitations of annual estimations for management purposes.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Study Sitementioning

confidence: 99%

Section: Study Sitementioning

confidence: 99%

Section: Study Sitementioning

confidence: 99%

See 3 more Smart Citations

Sediment yield and transport process assessment from reservoir monitoring in a semi‐arid mountainous river

Moñino

2018

Hydrological Processes

Self Cite

Impact of river regulation on a Mediterranean delta: Assessment of managed versus unmanaged scenarios

Bergillos

Rodríguez-Delgado

Water Resources Research

et al. 2016

This work addresses the effects of the construction of a reservoir 19 km from the mouth on the dynamics of the Guadalfeo delta (southern Spain), a Mediterranean delta in a semiarid and high‐mountain basin. The sediment volume transported as bed load and accumulated in the delta was estimated under two scenarios by means of a calibrated hydrological model: a managed scenario, considering the flows drained by the dam, and an unmanaged scenario, considering the absence of such infrastructure. Bathymetric and topographic measurements were analyzed and correlated with the fluvial and maritime forcing agents. Results indicate that the reservoir has significantly modified the dynamics downstream: the coast has lost almost 0.3 hm3 of sediments since the entry into operation of the dam, generating a 1.4 km coastline retreat around the mouth, with a maximum retreat of 87 m (92% of the initial). The beach profile decreased by up to 820 m2, whereas the average decrease around the mouth was equal to 214 m2. Under unmanaged conditions, more than 2 hm3 of bed load would have reached the coast. Based on the results, three new management scenarios of flows drained by the dam, in combination with bypassed sediment from the reservoir, were proposed to prevent more severe consequences in the delta and the silting of the reservoir. The proposed methodology for new management scenarios can be extended to other worldwide deltas, especially to those in semiarid and Mediterranean basins, and it represents an advanced tool for decision making.

Hydro‐meteorological drivers influencing suspended sediment transport and yield in a semi‐arid mountainous basin

Earth Surf Processes Landf

Moñino

2020

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Understanding erosion and sediment transport dynamics is key for sustainable water resources management. The objective of this research was to assess suspended sediment responses, identifying relationships with hydro‐meteorological drivers, sediment sources and connectivity in a mountainous semi‐arid basin. With this purpose, suspended sediment concentrations of 12 events were measured by automatic sampling and classified based on six descriptors of hydro‐meteorological drivers, their related rating curves and hysteresis loop behaviour, and distribution of precipitation, snowfall and snowmelt. Comparison with sediment transport and yield along the river, previously reported, was also performed. The results allowed us to distinguish up to three types of events with different erosive responses, comparable with other Mediterranean environments and snowmelt‐driven basins. Events classified as type I and II were closely linked to snow processes. Those classified as type III presented higher sediment yield and negligible influence of snow processes. The analysis of rating curves and hysteresis loops confirmed the identified transport responses. Type I and II events, with clockwise behaviour, were related to in‐channel sediment storage. Type III events, with predominantly counter‐clockwise behaviour, were related to hillslope erosion processes of gullying and landslides. The sediment connectivity analysed highlights the role of vegetation cover and land uses, and its sensitivity in high mountainous environments, which fits with the observed sediment transport at the study site. The volume of sediment trapped in the bottomset area of a reservoir downstream was related to type I events (more frequent and of greater magnitude). However, spatial distribution and frequency of type III events are likely to become more relevant under future climate scenarios due to their high sensitivity to hydro‐meteorological drivers. These results highlight the vulnerability of high mountainous areas on erosive dynamics and justify long‐term monitoring as hotspots of future challenge for water resource management. © 2020 John Wiley & Sons, Ltd.