The local scour and sediment deposition at a bridge pier during flood waves is analyzed to investigate the effects of different flow and sediment regimes (regulated and unregulated discharges with or without excess sediment supply). Concurrent field measurements of scour and streamflow were performed during 6 days at the Rapel Bridge, over the Rapel River (mean annual discharge, $\mathrm{QMA}=172{\mathrm{m}}^3/\mathrm{s}$ ), located in Central Chile (71°44’9” W, 33°56’22” S). During the measurements, river discharge was regulated by the operation of a hydropower plant, located 24 km upstream of the bridge, which follows a daily hydropeaking scheme. A simple mathematical model of scour and deposition is proposed, and field measurements are used to estimate optimal model parameters and to evaluate model performance. The model was applied to pre- and postdam scenarios to compare expected scour caused by a natural flow regime and by hydropeaking considering different excess sediment supply. Results show that the ultrasonic scour sensor is reliable for real scour monitoring under the presented field conditions. A single and easy-to-perform measurement of scour evolution during one flood was enough for estimation of optimal model parameters. The calibrated model reproduced measured scour and deposition in a verification case with high precision, i.e., root mean square error, $\mathrm{RMSE}=0.023\mathrm{m}$ and Nash-Sutcliffe efficiency, $\mathrm{NSE}=0.96$ . The model application showed that scour and deposition are very sensitive to the excess sediment supply. After two years, scour in the predam scenario resulted higher than in the postdam scenario when equilibrium conditions or no sediment deposition occurred. In case of equilibrium conditions and excess sediment supply deposition occurred during the falling limb of floods producing important refilling of the scour hole. However, floods’ high peak-discharges and excess sediment supply produced high scour depths of comparable magnitude as those after the two years hydrograph, which occurred only briefly around the peak discharges before sediment deposition, illustrating the complex interactions between flow and sediment in time, with important consequences for monitoring of bridge pier scour in the field and for forensic analyses.

A multidisciplinary approach is followed for analysis of the effect of changes in land use patterns on the hydrologic response of the Vergara watershed (4340 km²) located in central Chile. Probable future land use scenarios were generated using heuristic rules and logistic regression models, in order to identify and represent the main pressure on the watershed, namely forestation of extensive areas used for agriculture with rapid growing exotic species. The hydrologic response of the watershed was computed with a physically based distributed precipitation-runoff model, which was calibrated and validated for the current period. Results show that mean annual discharge increase with agricultural land use and diminish with introduced forest coverage. Thus, forestation of areas with introduced species like Pinus radiata and Eucalyptus globulus might be regulated in order to protect the water resources of the watershed.

The focus is on the application of the SWAT model for the Lonquimay River basin (Central Chilean Andes), a small sub-basin of the Biobío, in which snow accumulation and snowmelt dynamics play an important role. In the absence of local measurements of snow coverage, remotely-sensed snow cover information (MODIS) was combined with discharge time series in order to validate the model representation of stream hydrology and spatial snow cover extent. The results showed satisfactory to good general model performance in terms of representation of long-term or annual mean discharge at the basin outlet, as well as a reasonably good description of snow cover extent under most circumstances. The case study also provides an example quantitative indication of how well a model may perform under limited availability of input meteorological data. In the current work, the MODIS snow products were used for validation purposes only. The future inclusion of MODIS information directly into the model calibration proce... Résumé Cet article porte sur l'application du modèle SWAT au bassin versant de la Rivière Lonquimay (Andes Chiliennes Centrales), petit sous-bassin de celui du Biobío, au sein duquel la dynamique d'accumulation et de fonte nivales jouent un rôle important. En l'absence de mesures locales de la couverture neigeuse, des informations relatives au manteau neigeux obtenues par télédétection (MODIS) ont été combinées avec des séries temporelles de débit afin de valider la modélisation de l'hydrologie liquide et de la distribution spatiale du manteau neigeux. Les résultats montrent des performances générales de modélisation satisfaisantes à bonnes en termes de représentation du débit à long terme ou moyen annuel à l'exutoire du bassin, ainsi qu'une description raisonnablement bonne du manteau neigeux dans la plupart des circonstances. L'étude de cas fournit également un exemple d'estimation quantitative des performances qu'un modèle peut avoir en cas de données météorologiques peu disponibles. Dans cette étude, ...

Inland water is fundamental for the conservation of flora and fauna and is a source of drinking water for humans; therefore, monitoring its quality and ascertaining its status is essential for making decisions in water resources management. As traditional measuring methods present limitations in monitoring with high spatial and temporal coverage, using satellite images to have greater control over lake observation can be a handy tool and have satisfactory results. The study of chlorophyll-a (Chl-a) has been widely used to ascertain the quality of the inland aquatic environment using remote sensing, but in general, it depends on the local conditions of the water body. In this study, the suitability of the Sentinel-2 MSI sensor for Chl-a estimation in a lake in south-central Chile is tested. An empirical approach is proposed, applying multiple linear regressions, comparing the efficiency and performance with L1C and L2A products, separating the equations constructed with spring-summer and fall-winter data, and restricting Chl-a ranges to those measured in the field to generate these regressions. The algorithms combining spectral bans proved to have a good correlation with Chl-a measured in the field, generally resulting in R² greater than 0.87 and RMSE and MAE with errors less than 6 μg L⁻¹. The spatial distribution of Chl-a concentrations at the study site was obtained based on the proposed equations.