*3.4. Model Parameter Dependence on Catchment Characteristics*

Figure 6a plots log α against the log of the catchment area, showing that there is an increase in α with area for smaller catchments. For catchments with areas of approximately 100 km<sup>2</sup> and larger, a limited dependence on the area is observed. Although no clear dependency of α on climatic condition was observed, it is notable that similar values of α, from 10 to 20, were observed in five catchments, four (Galabre, Bès, Ribera Salada, Isabena) in Mediterranean mountainous and one (Carapelle) in Mediterranean climate, regardless of catchment area. These five catchments are located around the Mediterranean Sea with Mediterranean-type climate, where climate and bedrock show similarities (for instance, limestone is present in many areas), except for Carapelle (a clayey-loamy dominated watershed). Relatively larger values of α (>100) were observed for the five largest catchments (i.e., Owenabue, Bandon, Hopland, Guerneville, and Meuse). The catchment data that could be analyzed thus far are limited, but it is encouraging that the filtration parameter is reasonably consistent, with area dependency and with similarity between sites of similar catchment area, among a wide range of catchments. Unlike the filtration parameter (α), the bed erosion parameter (β) values varied within a narrow range of 2.4 to 5.3 in the 13 catchments without notable dependency on catchment area or other environmental characteristics (Figure 6b).


**Table 3.** Model validation results.

**Figure 5.** Model validation output for (**a**) the Ribera Salada from 1 November 2007 to 30 October 2008, (**b**) the Isabena from 1 October 2010 to 30 September 2012, and (**c**) the Meuse River from 1 October 2000 to 30 November 2010. The dashed magenta line represents the storage capacity of the sediment bed for fine sediments, Mcap[Q(t)], and the dotted black line represents the mass of fine sediments stored in the sediment bed, M(t). The black line with triangles represents the observed cumulative mass of fine sediments released from the sediment bed by the first i flood events (Ai,obs) and the red line with circles represents the modeled cumulative mass of sediments released for the first i flood events (Ai,model).

**Figure 6.** Model parameter dependency on the catchment area. (**a**) the relationship between α and the catchment area and (**b**) the relationship between β and the catchment area.
