210
13 Tunnel Flow and Erosion Processes …
studies have been conducted in semiarid or arid areas. Moreover, these field programs were often designed to monitor hydrological responses of pipe-flow to natural
rainstorms. The pipe-flow erosion processes and their relationship to hydrological
processes are still not fully understood. The relative significance of surface and
subsurface erosion in hillslope sediment delivery, and the overall contributions of
subsurface erosion to basin sediment yield are largely unknown in many parts of the
world.
This chapter describes the field monitoring program conducted on the Loess
Plateau (Zhu 1997, 2003, 2006, 2012; Zhu et al. 2000, 2002). Tunnel systems on
the Loess Plateau of China are among the largest and most complicated ones in the
world. Tunnel erosion and its controlling factors have been intermittently discussed
by several people (Wang 1989; Zhu 1958; Thorp 1936; Fuller 1922), but mainly at
qualitative level. Since 1989, an intensive field study has been conducted in Yangdaogou, a small catchment in western Shanxi Province. Sediment and runoff processes
of tunnel flows have been monitored at the tunnel outlets over a two-year period and
the tunnel systems have been repeatedly surveyed in the study catchment. The field
study methods, hydrological and sediment processes of tunnel flows, significance of
tunnel erosion in the catchment are discussed in the following sections.
13.2 Characteristics of the Wangjiagou Catchment
The study was conducted in the hilly-gully sub-region of the Loess Plateau. The field
experiment site, Yangdaogou, is one of the sub-watershed in the Wangjiagou Catchment, with the area of 0.203 km
2 (Fig. 13.1). Wangjiagou is a long-term experimental
watershed run by the Shanxi Institute of Soil and Water Conservation (SISWC). The
study site is situated in the silty loess zone (Chen and Luk 1989). Vertically, loess
consists of the upper Pleistocene Malan Loess, the Mid Pleistocene Lishi Loess, and
the Lower Pleistocene Wucheng Loess (Liu 1964).
The climate of the study site is semiarid temperate with a mean annual precipitation of 500 mm or so, among which over 70% falls in the summer monsoon season
(June to September). Both overland and tunnel flows occur only in a few summer
storms (Zhang et al. 1992; Luk 1991). A long term rainfall record shows that the
mean event precipitation of runoff-generating storms was 21.5 mm and the mean
maximum 30-min rainfall intensity was 19.2 mm/h with a mean duration of 3.35 h
(SISWC 1982).
Topographically, the hill slopes in Yangdaogou are characterized by gentle upper
slopes of <5°, intermediate to steep middle slopes of up to 25°, and very steep lower
slopes of >30°. The upper and middle slopes are mainly comprised of the croplands,
while the lower slopes were bush-lands or barren valley slopes.
13 Tunnel Flow and Erosion Processes …
studies have been conducted in semiarid or arid areas. Moreover, these field programs were often designed to monitor hydrological responses of pipe-flow to natural
rainstorms. The pipe-flow erosion processes and their relationship to hydrological
processes are still not fully understood. The relative significance of surface and
subsurface erosion in hillslope sediment delivery, and the overall contributions of
subsurface erosion to basin sediment yield are largely unknown in many parts of the
world.
This chapter describes the field monitoring program conducted on the Loess
Plateau (Zhu 1997, 2003, 2006, 2012; Zhu et al. 2000, 2002). Tunnel systems on
the Loess Plateau of China are among the largest and most complicated ones in the
world. Tunnel erosion and its controlling factors have been intermittently discussed
by several people (Wang 1989; Zhu 1958; Thorp 1936; Fuller 1922), but mainly at
qualitative level. Since 1989, an intensive field study has been conducted in Yangdaogou, a small catchment in western Shanxi Province. Sediment and runoff processes
of tunnel flows have been monitored at the tunnel outlets over a two-year period and
the tunnel systems have been repeatedly surveyed in the study catchment. The field
study methods, hydrological and sediment processes of tunnel flows, significance of
tunnel erosion in the catchment are discussed in the following sections.
13.2 Characteristics of the Wangjiagou Catchment
The study was conducted in the hilly-gully sub-region of the Loess Plateau. The field
experiment site, Yangdaogou, is one of the sub-watershed in the Wangjiagou Catchment, with the area of 0.203 km
2 (Fig. 13.1). Wangjiagou is a long-term experimental
watershed run by the Shanxi Institute of Soil and Water Conservation (SISWC). The
study site is situated in the silty loess zone (Chen and Luk 1989). Vertically, loess
consists of the upper Pleistocene Malan Loess, the Mid Pleistocene Lishi Loess, and
the Lower Pleistocene Wucheng Loess (Liu 1964).
The climate of the study site is semiarid temperate with a mean annual precipitation of 500 mm or so, among which over 70% falls in the summer monsoon season
(June to September). Both overland and tunnel flows occur only in a few summer
storms (Zhang et al. 1992; Luk 1991). A long term rainfall record shows that the
mean event precipitation of runoff-generating storms was 21.5 mm and the mean
maximum 30-min rainfall intensity was 19.2 mm/h with a mean duration of 3.35 h
(SISWC 1982).
Topographically, the hill slopes in Yangdaogou are characterized by gentle upper
slopes of <5°, intermediate to steep middle slopes of up to 25°, and very steep lower
slopes of >30°. The upper and middle slopes are mainly comprised of the croplands,
while the lower slopes were bush-lands or barren valley slopes.