Environmental Engineering Reference
In-Depth Information
The artificial step-pool system provided stable habitat, therefore, some aquatic plant species colonized
the stream bed, which made the stream green, as shown in Fig. 11.58. Under natural conditions before the
artificial step-pool system was installed, the main species of benthic invertebrates sampled in the Diaoga
River were Hydropsychidae, Baetidae, and Haliplidae . After the artificial step-pool system was installed,
the dominant species were Baetidae, Simuliidae, and Hydropsychidae. Some species, such as Caenis,
Perlidae, and Limnephilidae, which were not found in the stream before the artificial step-pool system
was installed, colonized the habitat. Baetidae species feed mostly by scraping algae and fine particulate
detritus from solid surfaces (Gui, 1994). Simuliidae often develop in running-water habitat and play an
important role in the diets of other aquatic organisms, such as fish P (Peter and Wang 1994). Hydropsychidae
feeds by collecting organic detritus from running water (Glenn, 1994). The change of taxa richness and
abundance of the dominant benthic invertebrates indicates that the aquatic habitat environment was more
favorable to invertebrate development. Hence, the aquatic ecosystem of the experimental reach had been
improved.
Fig. 11.58
The stream became green two years after the artificial step-pool system was installed
Artificial step-pool systems have been used for ecological restoration in many streams. However, the
experiment on the Diaoga River was perhaps the first time a system was used integrating incision control,
hazard mitigation, and ecology restoration. An artificial step-pool system on a mountain stream represents a
return toward a more 'natural' condition that previously had a relatively heterogeneous physical structure
that had been transformed to more homogenous conditions in response to accelerated rates of sediment
flux induced by incision and land-use changes (Fryirs and Brierley, 2009). Alterations to the physical
structure of the river modified process-forms relationships and associated sedimentation patterns,
enhancing retention of pools along the study reach. Enhancement of physical conditions is a critical step
in improving ecological relationships along the river (Brierley and Fryirs, 2008). Creation of step-pool
sequences resulted in greater heterogeneity in the physical river structure, thereby providing multiple
habitats for different species. This, in turn, resulted in obvious ecological improvements. Aquatic biodiversity
has increased, with more species of benthic macro-invertebrates observed following construction of step-
pools.
11.3.2
Debris Flow Control With Artificial Step-Pool System
11.3.2.1 Wenjiagou Landslide and Debris Flow in 2008
Artificial step-pool systems may also used to stabilize new drainage systems on landslides and control
debris flows. The Wenjiagou Landslide, which was triggered by the Wenchuan Earthquake on May 12,
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