136
8 Sediment-Storage Effects of Check-Dam …
8.4.5 Relationship Between the Dam-Land Increase
and Erosion Reduction
Typically, the amount of gully erosion exceeds that of the interrill erosion. The gully
erosion would be alleviated if the gullies with serious gravity erosions become a flat
dam-land due to sediment deposition. As we know, soil erosions varied in different
regions in the small watershed. Erosion control could be improved when the area
with serious soil loss is controlled first. Compared with the order in Scheme A, the
order of building the check dams in Scheme B was “from the upper reaches to the
lower reaches” and “from the branch rill to the main gully”. Thus, soil loss in the
lower reaches of the main gully and branch rills with the most serious erosion was
not completely controlled, and enormous soil was lost. In this experiment, the sum
of sediment loss in the first two rainfall events was 60% of the total after 10 rainfall
events in Scheme B, while only 31% in Scheme A.
On the other hand, after the check dam system has been constructed, the soil was
retained in the upper reaches of the check dams, the dam-lands were enlarged, and the
gravity erosions on the gullies were reduced. Nevertheless, the forming rates of the
dam-land were different as different sequences of building dams were adopted even
though the antecedent land covers and check dams were the same. When the check
dams were built following Scheme A, all check-dams in the main gully were filled
after six rainfalls. In contrast, when the check dams were built following Scheme
B, Dam 1 was not filled after 10 rainfall events. Therefore, farming work would be
delayed and the economic benefit would be reduced due to the delayed formation of
the dam-land.
8.5 Conclusions
Hydro-sedimentologic balance is the most important element for realizing relative
stability and optimal planning of the check-dams, which means that soil and water
in the small watersheds controlled by the check-dams could be internally absorbed,
without the need of raising the height of the dam. Quantitative results from the
experiments indicate that the gullies could auto-stabilize themselves after the checkdams were built, as raising of the dam-land altitude became slower and the mean
gradient of the gully was kept at a constant. The experiments also show that the
sequence of constructing dams from the lower reaches to the upper reaches was
preferable, for less soil will be escaped from the catchment.
8 Sediment-Storage Effects of Check-Dam …
8.4.5 Relationship Between the Dam-Land Increase
and Erosion Reduction
Typically, the amount of gully erosion exceeds that of the interrill erosion. The gully
erosion would be alleviated if the gullies with serious gravity erosions become a flat
dam-land due to sediment deposition. As we know, soil erosions varied in different
regions in the small watershed. Erosion control could be improved when the area
with serious soil loss is controlled first. Compared with the order in Scheme A, the
order of building the check dams in Scheme B was “from the upper reaches to the
lower reaches” and “from the branch rill to the main gully”. Thus, soil loss in the
lower reaches of the main gully and branch rills with the most serious erosion was
not completely controlled, and enormous soil was lost. In this experiment, the sum
of sediment loss in the first two rainfall events was 60% of the total after 10 rainfall
events in Scheme B, while only 31% in Scheme A.
On the other hand, after the check dam system has been constructed, the soil was
retained in the upper reaches of the check dams, the dam-lands were enlarged, and the
gravity erosions on the gullies were reduced. Nevertheless, the forming rates of the
dam-land were different as different sequences of building dams were adopted even
though the antecedent land covers and check dams were the same. When the check
dams were built following Scheme A, all check-dams in the main gully were filled
after six rainfalls. In contrast, when the check dams were built following Scheme
B, Dam 1 was not filled after 10 rainfall events. Therefore, farming work would be
delayed and the economic benefit would be reduced due to the delayed formation of
the dam-land.
8.5 Conclusions
Hydro-sedimentologic balance is the most important element for realizing relative
stability and optimal planning of the check-dams, which means that soil and water
in the small watersheds controlled by the check-dams could be internally absorbed,
without the need of raising the height of the dam. Quantitative results from the
experiments indicate that the gullies could auto-stabilize themselves after the checkdams were built, as raising of the dam-land altitude became slower and the mean
gradient of the gully was kept at a constant. The experiments also show that the
sequence of constructing dams from the lower reaches to the upper reaches was
preferable, for less soil will be escaped from the catchment.