A prototype experiment of debris flow control with energy dissipation structures

Abstract

Large-volume debris flow events are defined when the volume of solid materials exceeds 1 million m 3 . Traditional engineering measures, such as check dams, diversion channels, and flumes, are effective for normal debris flow control but are not sufficient to control large-volume debris flows. Experiments were conducted with an artificial step-pool system on the new Wenjiagou Gully to mitigate large-volume debris flows. The old Wenjiagou Gully was buried by 81.6 million m 3 of loose solid material created by a landslide that was triggered by the Wenchuan earthquake on May 12, 2008. The new gully was formed during the scouring process caused by debris flows in 2008. Large-volume debris flows were initiated by rainstorm flood with high kinetic energy. The artificial step-pool system was constructed with huge and big boulders on the new Wenjiagou Gully in 2009. The step-pool system dissipated flow energy in steps and hydraulic jumps. Analysis proved that the step-pool system dissipated two-third of the kinetic energy of flow; thus, the critical discharge for triggering debris flow increased threefold. Due to the step-pool system maximized the flow resistance and protected the bed sediment and banks from erosion, the rainstorm floods in 2009 did not trigger debris flows. In 2010, the step-pool system was replaced with 20 check dams. Huge boulders were broken into small pieces of diameter less than 0.5 m and were used as building materials for the 20 dams. Without the protection of the step-pool system, a rainstorm flood scoured the base of the dams and caused failures for all of the 20 check dams in August 2010. The flow incised the gully bed by 50 m. The loose bank materials slid into the flow mixed with water and formed a large-volume debris flow with a volume of 4.5 million m 3 . Many houses were buried by the debris flow, and 12 people were killed. Comparison of the two strategies proved that energy dissipation structures are necessary for controlling large-volume debris flows. Check dams, if they are stable, may reduce the potential of bank failures and control debris flows. The step-pool system dissipates flow energy and control gully bed incision and bank failure. A combination of check dams and step-pool systems may be the most effective for mitigating debris flows.

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

“…When the water flows through a step-pool unit, the potential energy first transfers to kinetic energy, then to the turbulent energy, and finally is dissipated as heat (Wang et al, 2012). When the water flows through a step-pool unit, the potential energy first transfers to kinetic energy, then to the turbulent energy, and finally is dissipated as heat (Wang et al, 2012).…”

“…When the water flows through a step-pool unit, the potential energy first transfers to kinetic energy, then to the turbulent energy, and finally is dissipated as heat (Wang et al, 2012). Therefore, the energy dissipation ratio is related to bed stability and is a crucial parameter for effective riverbed consolidation by stabilization structures like step-pools (Wang et al, 2012). > 0.5) indicates that most of the potential energy at the step entrance is dissipated and thus, the flow velocity increase is largely limited and even negative sometimes.…”

“…For example, based on the comparison between a pre-and post-flood morphological survey for a 50-year reoccurrence flood, Molnar et al (2010) reported that over 60% of steps were reworked, destroyed or moved in Erlenbach, Switzerland. The failure or removal of step-pool sequences within a river reach may locally enhance river-bed erosion or incision (Molnar et al, 2010;Wang et al, 2012). Therefore, knowledge on the responses, stability and failure of step-pool features during exceptional flood events is important to provide new insight for application of step-pools to river restoration efforts (Turowski et al, 2009;Chartrand et al, 2011).…”

Effects of <i>Y</i>-type spillway lateral contraction ratios on debris-flowpatterns and scour features downriver of a check dam

“…Generally, different energy dissipaters such as the plunge pool (Pagliara et al, 2010;Duarte et al, 2015) or step-pool systems (Yu et al, 2007;Wang et al, 2009Wang et al, , 2012 are required to dissipate the kinetic energy of the surplus flow and prevent the dam foundation and riverbed from scouring when sudden changes to the channel slope occur. The energy dissipation process of the check dam was estimated using the Bernoulli Eq.…”

Early root development of field-grown poplar: effects of planting material and genotype

“…Methods to control various erosion types and processes comprise built structures (Gebrernichael et al 2005;Posthumus and De Graaff 2005;Yang et al 2009;Wang et al 2012) or the use of biological solutions, principally the establishment of a live vegetation cover (Zuazo and Pleguezuelo 2008;Stokes et al 2014). The choice of approach depends on factors such as the extent and severity of the erosion problem, initial and ongoing costs of implementation, anticipated maintenance requirements, and expected useful life of works.…”