| Check dam system plays an important role in the ecological construction of soil and water conservation in the Loess Plateau. Scientific understanding the impact of check dam system on the runoff and sediment process in a watershed is important for the safe operation of check dam system and maintain ecological security in the Loess Plateau. The present study selected Wangmaogou watershed, in the Suide county, Shaanxi province, as research subject. Based on statistical analysis, prototype observation and numerical simulation, etc, we evaluated the characteristics of soil moisture distribution in dam land, analyzed the regulation effect of check dam system on gully erosion dynamic process and illustrated the mechanism of runoff regulation, and sediment reduction of check dam system.The main conclusions were as follows:(1) The hierarchical deposition structure of dam land had an obvious effect on water migration, which caused a layered distribution of soil moisture. The spatial distribution of soil moisture on the surface of dam land (0-20 cm) belonged to moderate variation. The average soill moisture content in 0-240 cm soil layers ranged from 9.92% to 23.70%, which decreased first and then increased with soil depth. The soil moisture had an obvious layered distribution in the profile, and the soil moisture in each layer in dam head were significantly higher than that in dam middle and dam tail, which belonged to moderate variation with time. The MIKE SHE model fairly simulated the layered distribution of soil moisture in dam land. Among the layered soil structure of dam land, the sediment layer of coarse texture acted as the barrier function while that of fine texture as the aquifer function whose moisture content was significantly higher than that of coarse sediment.(2) Based on the hydrological model coupled of MIKE SHE and MIKE 11, the flood process of a single rainstorm in a small watershed in the Loess Plateau was beautifully simulated. The results showed that the construction of check dam system desreased flood peak and flood volum by 65.34% and 58.67%, respectively. And the flood process were flatten. The construction of key dam, medium dam and small dam decreased the flood peak by 27.28%,33.39%, and 40.13%, respectively, and decreased flood volume by 2.18%, 27.08%, and 44.89%,respectively. The series,parallel and hybrid connection of check dam system decreased flood peak and flood volume by 64.30%, 75.38%, 83.31% and 37.52%, 50.88%, 52.68%, respectively.The dam construction changed the flood duration. The key dam and medium dam increased flood duration, while the small dam desreased it. Parallel connection of dam system had no impact on the flood peak time, while the series and hybrid connection of dam system delayed the flood peak for 10 min.The series connection of dam system reduced the flood duration,while the parallel and hybrid connection of dam system increased it.(3) The construction of check dam system obviously changed the hydrodynamic process in front and behind the dam,which reduced the runoff erosion power. The hydrodynamic parameters, such as velocity, shear force, power of runoff, and unit flow power were all reduced sharply in front of the dam due to the construction of different types of dam. Howerver,different check dam system had different impact on the hydrodynamic process behind the dam,and key dam had relatively less reduction on the hydrodynamic parameters. Dam system construction also changed the distribution of erosion dynamics of the channel, which reached the maximum at basin outlet without dam, while the minimum after dam system constructed and that the other dam system layouts were between these two conditions. Different cascade modes of dam system had different regulating effects on the erosion dynamics. The series,parallel and hybrid connection of dam system reduced the maximum flow rate by 57.83%,69.40%, and 78.35%, the maximum runoff shear stress was reduced by 82.23%, 90.64%, and 95.32%, and the maximum runoff power reduced by 92.50%, 97.14%, 98.99% in the basin outlet, respectively. And the hybrid dam system connection had the largest reduction effect.(4) The dam system construction significantly changed the runoff erosion power and reduced the sediment discharge of the basin. When there was no dam in the channel, the runoff erosion power of multiple branch ditches were greater than that of the main channel, which maintained basically unchanged, and ranged from 2×10m4/(s.km2) to 5×10-4m4/(s.km2) along the channel. After the dam system constructed, however, the runoff erosion power of the whole basin notablely reduced and that of the main channel decreased first and then increased from the upstream to the downstream. Compared with the no dam basin, the construction of key dam,medium dam and small dam decreased the sediment modulus by 24.74%, 47.11%, and 64.11%,respectively. And the small dam had the largest reduction effect. While, after the construction of check dam system, the sediment modulus decreased most, that was reached to 83.92%. |
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