The effect of channel bed infiltration on flood wave progression in ephemeral systems

One of the most catastrophic natural hazards around the world is flooding, as they were constantly associated with very high levels of damage. This natural hazard is reported to have a greater reoccurring possibility in recent times. However, flooding in arid and semi-arid climates has received a relatively limited attention in the literature, which means there is a scarcity in data and understanding relating to floods and hydrological processes in arid and semi-arid areas. Such processes include ephemeral river systems, flash flooding, high channel infiltrations and high evaporation rates. Therefore, the aim of this research is focused on studying the effect of channel bed infiltration on flood wave progression in ephemeral systems, where this process is most important. This investigation can lead to a more profound understanding of the flood wave progression, and hence, can support conducting more robust flood risk assessments in both, temporal and spatial terms. Additionally, this realization of ephemeral systems can be essential for local authorities to make highly informed predictions of flood warning systems, effective emergency response, and resilience measures. In order to achieve this aim, a Green-Ampt infiltration model was implemented within the LISFLOOD-FP hydrodynamic model. The evaluation of the effectiveness of the updated version of the hydrodynamic model was assessed through 4 testing levels of increasing complexity. The case study of the area has been chosen for this research, due to several occurrence of flood that hit the city of Hafr Al-Batin, which caused numerous losses in human life, damage to the public and private properties. Various model scenarios were constructed for the ephemeral wadi system upstream of Hafr Al-Batin, which including different infiltration process representations (none, steady state and variable) and these were used to evaluate the importance of infiltration on the flood wave characteristics. The outcome of this research shows that the Infiltration losses have significant implications on the flood wave propagation characteristics in ephemeral river systems. These includes the extent of the flooded area, the water volume and the flow travel time. These were demonstrated in the study catchment area of Wadi Al Batin in Saudi Arabia. The conclusion from this study is that applying the spatial variable Green-Ampt infiltration losses is necessary in ephemeral systems and will provide more robust hydrodynamic modelling for use in the flood risk assessments in these systems.