Horizontal ridge rupture
Horizontal ridge rupture or breaching is a common concern in Northeast
China, as erosive storms can occur in summer with short duration but
high intensity; these storms often coincide with snowmelt runoff in
spring (Li et al., 2016; Lu et al., 2016; Xu et al., 2018). Contour
ridge stability is mainly related to ridge geometry, sloping land
microtopography, soil physical properties of the ridge body, and
rainfall characteristics (Liu et al., 2014a).
Generally, Hr can increase water infiltration before breaching (Liu et
al., 2015; USDA-ARS, 2008, 2013) and lead to abundant sediment storage
(Xu et al., 2018). The time of ridge rupture shortened with higher
rainfall intensity as previous studies (Liu et al., 2015; Liu et al.,
2014a; Liu et al., 2014b; Xu et al., 2018). The result of extremely high
runoff and soil loss rates after rupture (Figure 4 and 5) was like the
relationship between the peaks of runoff and sediment and ridge failure
(Liu et al., 2015; Liu et al., 2014b; Xu et al., 2018). Averaged peak
runoff and soil loss rates after ridge failure were 9.33- and 36.67-fold
larger than their prior neighboring points, respectively (Figure 6 and
7). The ratio of peak sediment rate to base sediment rate under Hr in
this study ranged from 13.84 to 94.70 g L-1. The
varied range differed but included previous results reported by Liu et
al. (2014b) and Xu et al. (2018). Our study showed that contour ridges
ruptured at 50 mm h-1 were not in agreement with the
results of Xu et al. (2018), possibly because of the differences in
ridge geometry characteristics, such as ridge height. Liu et al. (2014b)
suggested that increasing ridge height might be useful to prevent
horizontal ridge failure and decrease soil loss hazard risk, according
to enhanced water storage capacity.
Our study illustrated that mulching could not always avoid ridge rupture
but can significantly postpone the collapse time of ridge failure
(Figure 6 and 7), possibly because mulching improves soil properties
(Kader et al., 2017; Kurothe et al., 2014; Prosdocimi et al., 2016a, b)
and, therefore, alters runoff and soil erosion characteristics (Gholami
et al., 2013).