Using 2d hydraulic modelling together with Structure-From- Motion (SFM) and You Tube videos to obtain indirect estimates of peak estimates of peak discharge and to assess the effects that changes in river bed conditions have on the discharge estimates.

Description: Despite the major damages caused by EL NINO South Oscillation (ENSO) rainfall events, there is a lack of discharge records of flash floods in one of Ecuador?s largest cities. As a response to that, in the present study the aim is to explore the use of an ensemble composed by 2d hydraulic modelling together with Structure-From-Motion (SFM) and YouTube videos to I) obtain reliable post-flood, indirect estimates of peak discharge for two ungauged ephemeral rivers, and to ii) assess the effects that changes in river bed conditions have on the discharge estimates of one of the rivers. To achieve this, besides the original river beds, scenarios of vegetation-removed and lowered/altered river bed bathymetry were created. Sub-metre- resolution DEMS of the river reaches were obtained using SFM techniques; the estimated ?observed? high water levels from YouTube videos were compared against several 2D hydraulic simulations to find the best fit at 0.22m (RMSE), -0.04m (ME) and 0.20m (MAE). Water velocity observations confirmed those discharge estimates. It is conclude that the ensemble can develop into a strong tool for indirect peak discharge estimates and, looking further, can become a tool of flood risk management.

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