However rare, dam breach occurrences are recently reported and associated with significant damage to life and property. The rupture of the structural dam wall generates severe flow rates that exceed spillway capacity consequently generating unprecedented flooding scenarios. The present research aims to assess the influence of the dam breach statistical configuration on the most relevant parameters to predict the rupture maximum discharge (RMD). McBreach© software was used to provide the necessary inputs for the operation of the HEC-RAS dam breach module. McBreach© automates the process of batch mode simulations providing a Monte Carlo approach to characterize the breach parameters stochastically. Thus, a sensitivity analysis was performed to identify the most influential breach parameters, followed by an uncertainty assessment regarding their statistical definition of the resultant RMD. Analysis showed that the overtopping failure mode discharges are most sensitive to the breach formation time (tf) parameter, followed by the final height breach (Inv) and the final width of the breach (B), which combined are responsible for 85% of the rupture’s maximum discharge. Further results indicated highly variable RMD magnitudes (up to 300%) depending on the breach parameter’s statistical definition (i.e., probability density function and associated statistical parameters). The latter significantly impacts the estimated flood risk associated with the breach, the flood zone delimitation, preparation of emergency action plans (EAP) and scaling of future dam projects. Consequently, there is a plausible need for additional investigations to reduce this uncertainty and, therefore, the risk associated with it.

The installation of hydroelectric plants has generated multiple environmental impacts on the world’s river systems. In central Chile, the impacts of hydroelectric reservoir operation have been documented in ecological and hydrologic regime terms. This investigation assesses the changes in channel morphology, vegetation distribution, and flows in the middle section of the Maule River during the period following the start-up of a hydroelectric plant. Changes in fluvial morphology (active area) and land cover are quantified using LANDSAT images, contrasted with a vegetation sampling and flow analysis. The results show a 12% decrease in active areas of the river, indicating a loss of geomorphological diversity. Within the active channel, there was a gradual increase in plant-covered surface area, which reached 159% between 1989 and 2018, mainly due to reductions in water (−61%), active bar (−35%), and bare soil surface areas (−29%). The changes were evident ten years after plant operations began and intensified during the period known as the megadrought in central Chile (2008–2018). The flow magnitudes present a decrease for exceedance probabilities (P) below 85% in the period after 1985, with a slight increase recorded for low flows (P > 85%). In the segments with superior stabilization, invasive species such as Acacia dealbata (silver wattle) predominated, which are specialists at taking advantage of disturbances to settle and stabilize active areas, narrowing the possibilities for morphological change.

Hydrodynamics are a major environmental factor on intertidal rocky shores. Morphological responses to this factor are expected to strongly influence spatial distribution of species across environmental gradients. We here analysed the shell phenotypic variability of the limpet Fissurella latimarginata using geometric morphometric analysis. The limpets were obtained from a sheltered intertidal coastal area and a wave-exposed environment. To determine whether the shell shape variation of the intertidal molluscs is linked to their resistance to differential intertidal wave exposure, mesocosm studies were developed in a hydraulic flume to explore the effects of hydrodynamic forces on this limpet species. A unidirectional current was used to test the impacts of step-by-step increased current flow velocities for each limpet. The phenotypic variability observed in the populations of F. latimarginata was associated with habitats characterized by contrasting wave exposure. Limpets from exposed environments showed a flattened, round to laterally wider and posteriorly narrower shell shape, larger foot and higher full limpet height, and were dislodged at higher velocities. A more laterally compressed and peaked shape was found in limpets from sheltered areas and these showed a lower resistance to wave action by dislodging at lower velocities.

The Bío Bío River is the second largest river in Chile considering both discharge and length. The Bío Bío River flows through the second most important economical centre in Chile and it has been recently classified as one of the world’s largest river systems strongly affected by fragmentation and change in flow regime, mainly due to hydropower and irrigation. The cities of Hualqui, Chiguayante, Concepción, Hualpén, and San Pedro de la Paz are located along the last 25 km of its course, and are exposed to a high flood risk due to a combination of increasing rainfall storms and the dams operation located in the upper basin. This work assessed several structural and non-structural flood defence alternatives for the lower 25 km of the river. A one-dimensional (1D) hydraulic model was used under different discharge scenarios. The results showed that storage areas and diversion canals located along the lower part of the Bío Bío River did not prove to be a suitable solution. Nevertheless, it was found that the most effective alternative implies a reservoir operation focused on storing the extra water produced by the incoming flood. Conclusions support the materialization of reservoir emergency operation protocols, as indicated in the Reglamento de Ley Nº20.304, approved by Decreto de Ley 138, Chile.

Accurate prediction of pollutant concentrations in a river course is of great importance in environmental management. Mathematical dispersion models are often used to predict the spatial distribution of substances to help achieve these objectives. In practice, these models use a dispersion coefficient as a calibration parameter that is calculated through either expensive field tracer experiments or through empirical equations available in the scientific literature. The latter are based on reach-averaged values obtained from laboratory flumes or simple river reaches, which often show great variability when applied to natural streams. These equations cannot directly account for mixing that relates specifically to spatial fluctuations of channel geometry and complex bed morphology. This study isolated the influence of mixing related to bed morphology and presented a means of calculating a predictive longitudinal mixing equation that directly accounted for pool-riffle sequences. As an example, a predictive equation was developed by means of a three-dimensional numerical model based on synthetically generated pool-riffle bathymetries. The predictive equation was validated with numerical experiments and field tracer studies. The resulting equation was shown to more accurately represent mixing across complex morphology than those relations selected from the literature.