## 5 Discussion  
The simulated Fraser River Delta, particularly its evolution and programation rate, is similar to what has been documented in the literature, e.g., [10; 50] suggesting that the majority of the input parameters used in this study were predicted accurately. Diffusion coefficients adopted from other studies were documented to work correctly, because other input parameters used in this study are real-time or close to real values. Although each parameter played a critical role in the model, sediment supply and water discharge values were the main controlling mechanisms. Today's known values and available data (e.g., paleobathymetry, river discharge, and sediment supply) were enough to successfully simulate the overall stratigraphic architecture, shoreline morphology, and delta progradation, particularly in S2 (Figure 3G-L). However, some parameters were modified in S1, considering changes in paleodepositional conditions. Today's sediment supply and water discharge values were observed to be too low to replicate the progradation of the delta in the first 5000 years to fill up the accommodation space (Table 1 and Figure 3A,B). Following several attempts, it was realized that the river discharge and sediment supply values during S1 must have been slightly higher than today's values (Table 1). Given that the Fraser River Delta is a post-glacial setting, the higher values suggest rapid melting of glaciers, increasing both sediment supply and water discharge. Similar variations have been documented in other deltas located in high latitude areas, e.g., [51]. Today, the Fraser Delta experiences similar yearly low and high sediment supply and water discharge values in winter and summer, respectively. During the summer  
Figure 7: (**A–D**) Modelling results representing the effects of a hypothetical 100 m relative sea level increase in the next 5000 years. It should be noted that in this model, only the sea level curve was introduced to the model; other parameters remain similar to step 2 (Figure 3G–L and Table 1). season, both values are significantly higher due to melting of accumulated snow, while they are lower when snow accumulates in highland areas [32; 52]. The two sea-level variation scenarios displayed dramatic differences in delta progradation. A constant sea level (zero fluctuation) successfully created the delta progradation up to its today's limits. However, a 12 m sea level increase failed to generate a realistic model. When a 12 m sea level increase was used, sediments were trapped in the delta plain region, and delta progradation stopped short of today's delta limits, despite countless attempts to change and test variations in parameters (e.g., sediment supply and diffusion coefficients). Although this observation may suggest that the Fraser Delta has not experienced major sea level fluctuations, it should be noted that there are other parameters that may have contributed to delta progradation. For example, the net northward sediment transportation due to strong tidal currents [21; 25] or deep-water renewal events, bringing external sediments into the Fraser basin [23], may have played a role in supplying additional sediments to the delta. If these processes were sufficient, the delta progradation could reach to its current limits under a 12 m sea level increase. Unfortunately, testing these processes is beyond the current capacity of the software. Perhaps one of the most important parameters to validate the delta evolution between a real system and a modelled system is the progradation rate. The Fraser River Delta's progradation rate has previously been documented, based on the sedimentological record [11; 13; 15; 50]. The model successfully created a similar progradation rate in two steps (Figure 3). The simulated first and second steps displayed 15 km and 9 km (cumulative: \(\sim\)24 km) progradation, respectively (Figure 3). Water discharge data show pathways for major channels.