Changes in flood loads and reservoir levels, produced by climate change (CC), represent an increasing concern for dam safety managers and downstream populations, highlighting the need to define adaptation strategies based on the dam failure risk management framework. Currently, thousands of dams worldwide, varying in use, age, and maintenance, may represent a threat to downstream cities in the case of structural failure. Several studies relate the failure of dams to several issues in the spillway, which may be even more vulnerable in CC conditions. This study provides a review of dam safety threats due to CC and approaches for the design/redesign of the spillway to cope with CC. A general four-stage methodology is proposed: data gathering and hydro-climatic, hydrological, and hydraulic analyses. Afterward, this methodology is applied to the spillway design for the Sube y Baja dam in Ecuador. The Probable Maximum Precipitation (PMP) increases around 20% considering CC under the Representative Concentration Pathway 8.5. Such an increment derived a 25% increase in the spillway maximum flow. These results show that the non-stationary hydrological regimes related to CC require a revision of engineering design criteria for hydraulic structures in general, and call for a consensus on design variables under CC.

Obstruction of the racks in bottom intakes due to sediment wedged in the slit of the bars can significantly reduce diverted flow. Notwithstanding the design recommendations that are found in the literature, the problem of rack occlusion continues to occur in built structures. This work focuses on the clogging effects in the circular bars of a bottom rack system using gravels whose median diameter, d₅₀, is close to the spacing between the bars. An experimental campaign including 24 tests, each repeated time times, with six different longitudinal slopes from 0 to 35% and four different specific incoming flow rates, q₁, in the range of 0.115 to 0.198 m³/s/m, is presented. The results show the inefficiency of circular profiles in comparison with T-shaped bars. No important influence of rack slope is found that could help to reduce clogging. This works confirms the importance of the selection of bar profile to reduce maintenance labor. A comparison of results with previous works with gravel sediment in T-shaped bars is considered. A methodology to calculate the wetted rack length considering occlusion due to flow with sediment transport is proposed, and the results are compared with those in the bibliography.

A novel computational tool, DIMRACK, is presented for the design of the required length of bottom racks in intake systems. The users may consider clear water cases or the rack’s occlusion due to sediment transport in the river. The computational tool uses a methodology based on the experimental works undertaken at the Universidad Politécnica de Cartagena from 2010. This work also presents an extension of the methodology to cover a broad range of void ratios, bar profiles, slopes, and flow rates. Designing nomograms are also proposed. These are two diagrams to allow the approximate graphical computation of the rack length with clear water. In sediment transport cases, an occlusion factor is proposed, obtained from experimental gravel tests. This parameter enables an increment in the rack length due to occlusion, depending on the bar type. The results are compared with those proposed in classical technical manuals. Finally, the results have been compared with ten existing small hydropower plants’ bottom intake designs in Ecuador.

Flow over bottom racks is highly turbulent, three-dimensional and spatially varied. The design of bottom intake systems has mainly been studied in the laboratory. The comparison of existing experimental studies shows large deviations in the definition of design parameters such as wetted rack length. Each experimental study is limited to a single bar type or to a low range of void ratios, which makes it difficult to generalize the observed data. A combination of empirical, dimensional and inspectional analysis is presented as a useful tool to reduce the number of variables with influence in the design parameters, such as the wetted rack length or the mean discharge coefficient. This work includes a broad experimental campaign in which wetted rack length and mean discharge coefficient are characterized using five different bottom racks with different void ratios (area between bars divided by total area). T-shaped flat and circular bars are considered as well as five different longitudinal slopes. Empirical and inspectional analyses have allowed us to verify, in two different ways, the relation between wetted rack length and incoming flow through potential functions. The influence of the viscous forces has been studied as a function of the incoming flow. Similar results may be obtained when analysing the Froude number at the beginning of the rack, depending on the wetted rack length. A new formulation for calculating the mean discharge coefficient and wetted rack length is proposed.

Actualmente las presas están sujetas a nuevos escenarios como el sobrevertido por coronación o la rotura de la presa. En ciudades andinas que se encuentran por encima de los 2800 m.s.n.m. las condiciones topográficas, hidrológicas y geológicas son diferentes con otras regiones más planas. Este estudio plantea la simulación numérica en el software Iber de la rotura de una presa implantada en los andes centrales del Ecuador. Se analizará el tránsito de esta crecida hacia aguas abajo de la presa, a fin de identificar posibles zonas de afectación a la zona urbana e infraestructura civil considerando agua clara y agua clara con transporte de sedimentos. Además, se realizará un análisis de peligrosidad y grado de afectación utilizando dos códigos internacionales, los cuales son: el código español RD9/2008 y el código de la Agencia Federal para el manejo de Emergencias norteamericano FEMA. Los resultados obtenidos muestran similitud con otros estudios en cuanto al hidrograma de rotura con y sin sedimentos; adicionalmente se puede evidenciar las zonas de afectación y las diferencias de los códigos de peligrosidad analizados.