7.4 Results and Discussion
107
Jing and Zheng (2004) and Li (1997) have reported that surface runoff retained by
the structure measures of soil and water conservation, was often consumed by local
humans and animals in the small watersheds of the upper reaches, which would result
in a decrease of the total runoff, and even lead to a cutoff of the lower Yellow River.
However, in this research, an assessment of regional soil and water loss has indicated
the successfulness of the conservation efforts by quantifying the contribution of
improved land cover to potential erosion reduction. The notable difference has been
obtained in the TRE for water and that for soil in the same practice. It has been
shown in Table 7.1 that the former was much smaller than the later. The result of
relatively small TRE for water in this study testified that the conservation practices
worked better in retaining sediment than in reducing runoff from the Loess Plateau.
On the other hand, because of the accumulation of silt in the Yellow River channel,
water has to be used for flushing out the sediments deposited on the channel bed and
transporting them to where it needed or into the Bohai Sea (Yu 2006). Thus water
for sluicing the soil could be put into other uses in the lower reaches of the Yellow
River in virtue of the conservation practices on the Loess Plateau.
From what has been discussed above, we may safely draw the conclusion that soil
and water conservation practices will not aggravate the shortage of water resources,
either in the local catchment or in the Yellow River. Upon the present condition,
negative effects of the conservation practice are not noteworthy.
7.4.5 Role of Check Dam in Reducing Soil and Water Loss
Soil conservation measures should be selected referring to many factors, such as soil
types, topographical conditions, hydrological processes, land uses and land management practices (Shen et al. 2010). In accordance with the specific circumstance
of the Loess Plateau, the emphasis of conservation may be slope control or gully
control, and planting or structure practice, but which one is more effective in preventing the sediment poured into the Yellow River from this area, is still in dispute. In
semiarid Tunisia, more emphases have been imposed on terracing than gully control
(Bouchnak et al. 2009). While in the Three Gorges Reservoir Area of southern China,
hedgerows were the best way for soil erosion control, followed by stone dike terraces
and soil dike terraces (Shen et al. 2010). Yet, in any case, the suitable vegetative cover
was a primary consideration for soil and water conservation (Mohammad and Adam
2010). For instance, in the Upper Min River watershed of Southwest China, vegetation played a crucial role in protecting soil from erosion loss (Zhou et al. 2008), and
in the Ziwuling region of the Loess Plateau, vegetation was regarded as a key factor
affecting soil erosion (Zheng et al. 2006).
However, most regions of the Loess Plateau are short of water and thus unsuitable
for planting. Control of soil and water erosion on the Loess Plateau by planting alone
has been proved unsuccessful in recent decades (Xu et al. 2004). Trees are difficult to
survive owing to the arid climate and barren soil, and even if they are alive, most of
them will not grow strong enough to control soil and water losses. As revealed in this
107
Jing and Zheng (2004) and Li (1997) have reported that surface runoff retained by
the structure measures of soil and water conservation, was often consumed by local
humans and animals in the small watersheds of the upper reaches, which would result
in a decrease of the total runoff, and even lead to a cutoff of the lower Yellow River.
However, in this research, an assessment of regional soil and water loss has indicated
the successfulness of the conservation efforts by quantifying the contribution of
improved land cover to potential erosion reduction. The notable difference has been
obtained in the TRE for water and that for soil in the same practice. It has been
shown in Table 7.1 that the former was much smaller than the later. The result of
relatively small TRE for water in this study testified that the conservation practices
worked better in retaining sediment than in reducing runoff from the Loess Plateau.
On the other hand, because of the accumulation of silt in the Yellow River channel,
water has to be used for flushing out the sediments deposited on the channel bed and
transporting them to where it needed or into the Bohai Sea (Yu 2006). Thus water
for sluicing the soil could be put into other uses in the lower reaches of the Yellow
River in virtue of the conservation practices on the Loess Plateau.
From what has been discussed above, we may safely draw the conclusion that soil
and water conservation practices will not aggravate the shortage of water resources,
either in the local catchment or in the Yellow River. Upon the present condition,
negative effects of the conservation practice are not noteworthy.
7.4.5 Role of Check Dam in Reducing Soil and Water Loss
Soil conservation measures should be selected referring to many factors, such as soil
types, topographical conditions, hydrological processes, land uses and land management practices (Shen et al. 2010). In accordance with the specific circumstance
of the Loess Plateau, the emphasis of conservation may be slope control or gully
control, and planting or structure practice, but which one is more effective in preventing the sediment poured into the Yellow River from this area, is still in dispute. In
semiarid Tunisia, more emphases have been imposed on terracing than gully control
(Bouchnak et al. 2009). While in the Three Gorges Reservoir Area of southern China,
hedgerows were the best way for soil erosion control, followed by stone dike terraces
and soil dike terraces (Shen et al. 2010). Yet, in any case, the suitable vegetative cover
was a primary consideration for soil and water conservation (Mohammad and Adam
2010). For instance, in the Upper Min River watershed of Southwest China, vegetation played a crucial role in protecting soil from erosion loss (Zhou et al. 2008), and
in the Ziwuling region of the Loess Plateau, vegetation was regarded as a key factor
affecting soil erosion (Zheng et al. 2006).
However, most regions of the Loess Plateau are short of water and thus unsuitable
for planting. Control of soil and water erosion on the Loess Plateau by planting alone
has been proved unsuccessful in recent decades (Xu et al. 2004). Trees are difficult to
survive owing to the arid climate and barren soil, and even if they are alive, most of
them will not grow strong enough to control soil and water losses. As revealed in this