3.1.1 Basin-average statistics
The overall flood-related differences between scenarios with and without
re-infiltration are shown in Figure 3, calculated as basin-integral
change by averaging each metric over the whole grid cells that are wet
(water depth larger than 0.01 m). First, the differences are discernible
comparing the two, especially for the surface water volume ratio
(RV), which varies from 0.7 to 1. It suggests the
surface water with re-infiltration scheme could only account for 70% of
the condition without re-infiltration. There is also a 2.5-hr difference
in total inundation duration (D), meaning that ponding water retains 2.5
hours less on the surface for re-infiltration scheme. The total
inundation duration is an important factor for flood risk management
(Merz et al., 2010; Triet et al., 2020). Previous studies agree that the
re-infiltration results in a substantial reduction of river flow
discharge, which can be translated to flood depth (RH)
(Nahar et al., 2004; Woolhiser et al., 1996). For different conditions,
the antecedent soil moisture, as expected, exhibits the largest impact
on flood inundation dynamics when comparing the two scenarios. Lower
initial soil moisture leads to greater differences in flood depth
(RH), area (RF), volume
(RV), and dynamics. For instance, when the soil is
completely dry, the average flood depth (RH)/area
(RF)/volume (RV) of the re-infiltration
scheme only accounts for 85%/85%/67% of that of without the
re-infiltration scenario.
[INSERT FIGURE 3 HERE]
The initial inundation timing (Tinit) for
re-infiltration delays around 0.5 hours, and the total inundation
duration (D) is 2.5 hours less than the scenario without
re-infiltration. As soil gradually approaches saturation, the
differences diminish. Saturated hydraulic conductivity, Ksat, ranked as
the second most sensitive parameter during the test, exponentially
reduces flood depth/area/volume by 10%/7%/20% when its multiplier
increasing from 0.0 to 2.0. Furthermore, the differences of inundation
duration (D) range from 1.5 hours to 3.5 hours, making Ksat the most
influential parameter; however, the initial inundation timing is
relatively insensitive to it, as opposed to initial soil saturation
condition. This is due to the fact that Ksat only changes infiltration
flux along the way while exerting less impact on the initial inundation
timings. The infiltration parameter B, however, has the least impact on
the flood inundation dynamics among the three. These measures exhibit
the greatest changes at small B multipliers (0.1-0.3) and then level out
irrespective of increasing B multipliers. A plateau is reached because
of the constrain of the maximum infiltration capacity. In summary, this
sensitivity analysis tests our three main hypotheses, indicating the
non-negligible differences between the two schemes and how the soil type
and condition influence the results.