Samenvatting

Before finalizing the design plans for the Seawater Reverse Osmosis (SWRO) plant in Jubail, Saudi Arabia, requested by IDOM’s client, a flood risk analysis of the site is required.
Within this flood risk analysis, the impacts on the SWRO site will be simulated during a rainfall event with a return period of 100 years. This impact will be considered based on three different scenarios:
the scenario not considering climate change, the scenario considering the most likely climate change scenario (SSP2-4.5) and its effects on a T100 rainfall event, and the scenario considering the most
extreme climate change scenario (SSP3-7.0) and its effects on a T100 rainfall event. Based on the results, the client will determine if flood measures are required to be included in the design.

To simulate the impacts, two main analyses have been conducted.
The first is a hydrological analysis. Within this analysis, the movement of water during a T100 rainfall event was studied. This was done by defining the drainage network, calculating the concentration
time, constructing the hyetographs (for all scenarios), estimating the amount of runoff by defining the curve number (CN), and defining the initial abstraction, impervious area, and lag time. Resulting in a
HEC-HMS basin model from which hydrometeorological models were extracted at the junction point that will serve as the inlet to the research area for the simulated floods.
The second analysis is a hydraulic analysis. Within this analysis, the flood depth, velocity, and hazard levels were defined by HEC-RAS flood simulations within the project area.

Finally, based on the present risks/hazards shown within the HEC-RAS flood simulations, an analysis of possible adaptation measures has been conducted. From this analysis, one ´´best-fit´´ measure is
proposed based on a multi-criteria analysis. This part of the report serves an advisory purpose and is meant to create awareness for the client about the possibilities beyond mitigation measures to reduce flood risks on the site.