Sediment yield and transport: estimation and climate influence
Notice bibliographique
Résumé
Erosion, transfer and deposition of soil particles due to water and the impact of climate change on these physical processes have acquired a great importance during the last decades.Indeed, it is the subject of focused research in several fields of the earth sciences (such as hydrology, hydraulics, ecology, agriculture, geology, civil and environmental engineering, etc.), as the result of the continuous increase in hydrogeological risk in different geographical areas around the world, including Italy.Knowledge of the sediment volumes generated and transported by streams is useful, for example, for the successful design of hydraulic infrastructures, dams or reservoirs, for changes to forest waterways and terrain, for the land management and environment, etc. Sediment production at the catchment scale and solid transport in rivers can be assessed and quantified through mathematical and empirical models.Unfortunately, there is a shortage of gauged data regarding sediment fluxes and production at the catchment scale, because of topographical and pedological complexity and high spatial variability of all the hydrological characteristics.Another point that should be taken into account is the scarce availability of the appropriate equipment to make survey measurements.For these reasons, it is hard to implement monitoring techniques.However, in the absence of field data, major elements for land management, planning and protection include an estimate of soil loss and sediment yield and their comparison with other case studies.In the first part of this thesis project, a detailed sediment transport analysis in a reach of the Mimico Creek, which is located in Southern Ontario (Canada), was conducted by making use of the sediment transport investigations.A hydraulic model was developed and calibrated through the HEC-RAS software, by using the Wilcock and Crowe transport function, to a series of discharge events where in-situ bedload sampling occurred.Bedload samplings used in calibrating the transport model were limited by the orifice of the Helley-Smith bedload sampler (ranging between 0.5 mm and 32 mm).Calibration curves, that determine bed material transport rates as a function of the dimensionless reference shear stress, were created considering both step-wise discharge and unsteady flow simulations.The results of the calibrated model were used to calculate the mean travel distance of bed material: the goal was to compare the simulation results achieved to field observations, derived through the bed material particle tracking (RFID technique).The values achieved showed that the Wilcock and Crowe equation under-predicts the transport of the coarsest fractions in the bed load and that the travel distances calculated considering the BSTEM option (which also considers the presence of fine material from bank erosion) are longer.Finally, the travel distances of different grain sizes were estimated using the calibrated model results.The obtained values showed that particles have a steep reduction in travel distance with an increase in their size.Furthermore, transport distance values are higher for the flood events with higher peak discharges, generally in accordance with field measurements.The fractional transport distances of different grain classes estimated by using simulation results are lower than tracer surveys because in the field only the mobile particles were considered, Sediment yield and transport: estimation and climate influence PhD dissertation 1 ).The sediment yield for the rainfall event analysed was also estimated, using the MUSLE equation, for the 7 sub-basins identified in the Guerna catchment.The found values were used as input sediment load in the HEC-RAS model, that was developed for the Guerna Creek in order to simulate sediment transport.Wilcock and Crowe is the transport function that was chosen and the "Time-Area method" was adopted to create runoff hydrographs.The mean value of sediment discharge achieved is 6632 t/d and 66810 t/d, respectively at the upstream cross section and downstream cross section of the study reach.The downstream cross section is the Guerna watershed outlet, with an area of 30.9 km 2 .The upstream cross section is the outlet of its upstream sub-basin, with an area of 3 km 2 .Results are comparable to the measured value in the Rio Cordon catchment, a small mountain basin (5 km 2 ) in the northeastern Italian Alps with similar characteristics to the Guerna catchment: during an intensive flood event the sediment discharge recorded is 8040 t/d.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,002 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».