## 4 Results
### Testing Possible Future Variations in the Fraser River Delta  
Perhaps one of the most exciting capacities of forward stratigraphic modelling applications in modern environments is to test and predict changes in future morphological and stratigraphic architecture. In this study, a future model in one step (S3) is created by presuming no changes in today's input variations (Figure 3M-S). Then, we also test how the delta can evolve if sediment supply and water discharge values change over time. In this test, sand distribution maps were plotted to represent the evolution of the delta (Figure 5). Erosion maps were also plotted and compared to visualize under which conditions the delta might become unstable (Figure 6). The results of these tests show that if the sediment supply gradually increases while the water discharge gradually decreases, the majority of the sediments will not reach offshore and will be trapped at the river mouth, creating a bulge inland (Figure 5). In this scenario, only a slight erosion is observed in the distal parts of the prodelta (Figure 6). In contrast, when sediment supply gradually decreases while water discharge increases, delta progradation slows significantly, and local or regional erosion takes place (Figure 6). Erosion first starts in the upper delta plain and gradually affects the entire delta as the discharge rate increase and sediment supply decrease (Figure 6). Erosion results in exposure of underlying sand-rich delta plain and delta front deposits (Figure 5). When both sediment supply and water discharge increase, the delta shows progradation in all directions offshore, with little or no erosion (Figures 5 and 6). In this scenario, erosion occurs when discharge is more than 6750 m\({}^{3}\)/s and sediment supply is less than 13,500 km\({}^{3}\)/Ma (Figure 6). These results can play a critical role when further modifications on the river (such as placing a dam) are considered.  
In addition to variations in sediment supply and water discharge, a possible sea level variation is also tested in this study. The effect of sea level variations in coastal areas is a global issue due to several reasons, such as global warming and anthropogenic influence. The Fraser River Delta may also face this issue, due to the fact that parts of the delta plain show noticeable subsidence, possibly resulting in a 2 m increase in the next 100 years [33; 40]. In Dionisos software, testing variations over 100 years is not possible; however, if one considers that this relative sea level increase will remain constant in the next modelling time step, it is possible to test how stratigraphic architecture can respond to such variation. Therefore, a 100 m relative sea level increase is tested, maintaining all other parameters similar to step 2 (Figure 7). The results show a dramatic shift in the evolution of the delta: from an overall prograding system to a retrograding system (Figure 7). Sediments during this scenario deposit mostly on the Boundary Bay area, but a clear backstepping deposition is also visible on the delta plain (Figure 7). The majority of the sand accumulates on the upper delta plain (Figure 7A), while silty deposits show uniform distribution throughout the delta (Figure 7B) and shale unit deposits predominate the prodelta (Figure 7C). Water discharge shows a southward deflection towards Boundary Bay (Figure 7D), similar to step 3. No negative effect in terms of delta stability (e.g., major erosion) is observed, but it cannot be ruled out that if this scenario takes place wave erosion can be a major concern on the delta plain, resulting in a wave ravinement-like surface.  
Figure 5: Hypothetical delta evolution in the next 5000 years with variant sediment supply and water discharge values. Please note that the block diagram in the center (S3) represents no changes in sediment supply and water discharge values (similar parameters used in S2).  
Figure 6: Results showing erosion rate (m/MA) maps in the next 5000 years with variant sediment supply and water discharge values.