The application of hydrologic and hydrodynamic models in flash flood hazard assessment is mainly limited by the availability of robust monitoring systems and long-term hydro-meteorological observations. Nevertheless, several studies have demonstrated that coupled modeling approaches based on event sampling (short-term observations) may cope with the lack of observed input data. This study evaluated the use of storm events and flood-survey reports to develop and validate a modeling framework for flash flood hazard assessment in data-scarce watersheds. Specifically, we coupled the hydrologic modeling system (HEC-HMS) and the Nays2Dflood hydrodynamic solver to simulate the system response to several storm events including one, equivalent in magnitude to a 500-year event, that flooded the City of Tena (Ecuador) on 2 September, 2017. Results from the coupled approach showed satisfactory model performance in simulating streamflow and water depths (0.40 ≤ Nash-Sutcliffe coefficient ≤ 0.95; −3.67% ≤ Percent Bias ≤ 23.4%) in six of the eight evaluated events, and a good agreement between simulated and surveyed flooded areas (Fit Index = 0.8) after the 500-year storm. The proposed methodology can be used by modelers and decision-makers for flood impact assessment in data-scarce watersheds and as a starting point for the establishment of flood forecasting systems to lessen the impacts of flood events at the local scale.

Riparian vegetation is widely promoted as a nature-based solution (NbS) for flood regulation, yet its hydraulic effects within compound-channel systems remain insufficiently understood. This study evaluated how floodplain land-use/cover change modified flood hydraulics along the Tena–Pano river corridor in Ecuador. A coupled hydrological–hydrodynamic modelling framework was used to simulate base, forest, and agriculture scenarios under floods with return periods of 2, 10, and 100 years. Hydraulic responses of the main channel and floodplain were evaluated along the study reach. Forest cover increased mean maximum water depth by 4.72–6.99% and reduced mean maximum flow velocity by 2.31–5.35%, whereas agriculture reduced depth by 3.89–5.96% and increased velocity by 4.68–10.47%. At the downstream cross-section, changes in peak discharge remained comparatively limited, ranging from −6.05% to 1.17%, while peak depth increased by up to 11.77% and peak velocity decreased by up to 14.03% under forest conditions. Significant differences among scenarios were detected for discharge, water depth, and flow velocity (p < 0.05). Median absolute changes in flood intensity were consistently greater in the main channel, where they were 1.6–3.2 times as large as those in the floodplain. Factorial decomposition further showed that flow velocity accounted for 61.03–67.00% of the changes in flood intensity within the channel and 68.94–73.49% within the floodplain. These results demonstrate that floodplain land-use/cover change generates stronger hydraulic responses within the main channel than in the floodplain itself, primarily through velocity-driven changes in flood intensity. Potential implications of general scour in the main channel are also discussed.

Peri-urban Amazonian rivers are increasingly affected by interacting pressures associated with recreational use, land-cover change, water-quality degradation, and flood exposure, requiring integrated approaches to support environmental management. This study developed a multi-indicator environmental assessment of the Tena River (Ecuador), informed by sociohydrological concepts. Flood exposure was evaluated using outputs from a TETIS–Iber hydrological–hydraulic modeling framework previously calibrated and validated for the Tena River basin. Simulated inundation scenarios for 2-, 10-, and 100-year return periods were analyzed at the Puente Ikiam and Tazayaku recreational sites. Riparian vegetation dynamics were evaluated using PlanetScope-derived NDVI (2016–2024), recreational water quality was assessed according to Ecuadorian Ministerial Agreement AM 097-A, and community perception was characterized through surveys and participatory mapping. Hydraulic simulations identified increasing water depths and inundation extents with increasing return periods, while NDVI analysis revealed a decline in dense riparian vegetation between 2016 and 2024. Water-quality monitoring showed episodic fecal coliform exceedances at urban recreational sites, and community responses highlighted strong concern about river degradation but limited collective environmental action. Rather than developing a fully coupled sociohydrological model, this study integrates hydrological, ecological, and social evidence within a sociohydrological framework to identify priority areas for flood-risk management, riparian restoration, water-quality protection, and participatory governance in an urban Amazonian river.