13.4 Results and Discussion
223
10, 16, 1989 and July 6, 1990, no tunnel flow was generated, though catchment outflow was observed. In medium storms, sediment contributions to the catchment by
the tunnel systems are often high such as on August 15, 1989 and July 30, 1990.
However, in heavy storms such as July 11, 26 and August 28, 1990, sediment contributions of tunnel flows fall off and are slightly higher than the proportion of tunnel
catchment areas to the catchment. In general, the pattern of sediment contribution is
quite similar to that of water discharge contribution (Zhu 1997).
13.5 Conclusions
A monitoring of tunnel flows was carried out in the Yangdaogou Catchment over the
1989 and 1990. Although tunnel flows were derived solely from the surface catchment via tunnel inlets, they did not simply mirror overland flow processes due to
instability within tunnel systems. Moreover, the peak sediment concentrations in the
tunnel flows were not distinctively higher than the peak channel flow concentrations
but considerably higher than those measured from the un-tunnelled hill slopes. In
general, no significant correlation between the flow discharges and sediment yields
could be found for the tunnel flows. Such an erratic relationship may be ascribed
to the influence of the variable sediment source area, the occurrences of collapses
within tunnel systems, and the initiation of new inlets. The temporal changes of sediment yield on an annual basis were very irregular and no seasonal trends might be
generalized for all tunnels. Based on the field monitoring data, about 43% of catchment runoff and 57% of catchment sediment were delivered by the tunnel systems.
These results clearly show that the tunnel system played a major hydrologic and
geomorphic role in the hilly loess region of the Western North China.
References
Boucher S C, Powell J M. 1994. Gullying and tunnel erosion in Victoria. Australian Geographical
Studies, 32(1): 17–26.
Bryan R B, Harvey L E. 1985. Observations on the geomorphologic significance of tunnel erosion
in a semi-arid ephemeral drainage system. Geografiska Annaler: Series A, Physical Geography,
67(3–4): 257–272.
Bryan R B, Jones J A A. 1997. The significance of soil piping processes: inventory and prospect.
Geomorphology, 20(3–4): 209–218.
Carey S K, Woo M K. 2000. The role of soil pipes as a slope runoff mechanism, Subarctic Yukon,
Canada. Journal of Hydrology, 233(1–4): 206–222.
Chen Y Z, Luk S H. 1989. Sediment sources and recent changes in the sediment load of the Yellow
River, China. Proceedings of 5th International Soil Conservation Conference, Bangkok: 313–323.
Crouch R J, McGarity J W, Storrier R R. 1986. Tunnel formation processes in the Riverina area of
NSW, Australia. Earth Surface Processes and Landforms, 11(2): 157–168.
223
10, 16, 1989 and July 6, 1990, no tunnel flow was generated, though catchment outflow was observed. In medium storms, sediment contributions to the catchment by
the tunnel systems are often high such as on August 15, 1989 and July 30, 1990.
However, in heavy storms such as July 11, 26 and August 28, 1990, sediment contributions of tunnel flows fall off and are slightly higher than the proportion of tunnel
catchment areas to the catchment. In general, the pattern of sediment contribution is
quite similar to that of water discharge contribution (Zhu 1997).
13.5 Conclusions
A monitoring of tunnel flows was carried out in the Yangdaogou Catchment over the
1989 and 1990. Although tunnel flows were derived solely from the surface catchment via tunnel inlets, they did not simply mirror overland flow processes due to
instability within tunnel systems. Moreover, the peak sediment concentrations in the
tunnel flows were not distinctively higher than the peak channel flow concentrations
but considerably higher than those measured from the un-tunnelled hill slopes. In
general, no significant correlation between the flow discharges and sediment yields
could be found for the tunnel flows. Such an erratic relationship may be ascribed
to the influence of the variable sediment source area, the occurrences of collapses
within tunnel systems, and the initiation of new inlets. The temporal changes of sediment yield on an annual basis were very irregular and no seasonal trends might be
generalized for all tunnels. Based on the field monitoring data, about 43% of catchment runoff and 57% of catchment sediment were delivered by the tunnel systems.
These results clearly show that the tunnel system played a major hydrologic and
geomorphic role in the hilly loess region of the Western North China.
References
Boucher S C, Powell J M. 1994. Gullying and tunnel erosion in Victoria. Australian Geographical
Studies, 32(1): 17–26.
Bryan R B, Harvey L E. 1985. Observations on the geomorphologic significance of tunnel erosion
in a semi-arid ephemeral drainage system. Geografiska Annaler: Series A, Physical Geography,
67(3–4): 257–272.
Bryan R B, Jones J A A. 1997. The significance of soil piping processes: inventory and prospect.
Geomorphology, 20(3–4): 209–218.
Carey S K, Woo M K. 2000. The role of soil pipes as a slope runoff mechanism, Subarctic Yukon,
Canada. Journal of Hydrology, 233(1–4): 206–222.
Chen Y Z, Luk S H. 1989. Sediment sources and recent changes in the sediment load of the Yellow
River, China. Proceedings of 5th International Soil Conservation Conference, Bangkok: 313–323.
Crouch R J, McGarity J W, Storrier R R. 1986. Tunnel formation processes in the Riverina area of
NSW, Australia. Earth Surface Processes and Landforms, 11(2): 157–168.