Experimental study on blocking and self-cleaning behaviors of beam dam in debris flow hazard mitigation

Abstract

Blocking is one of the important features when a beam dam intercepts debris flow, while self-cleaning is another when managing suspended debris flow. Both features determine the debris flow control benefits of beam dam but the latter often is not considered in practical engineering design. In this paper, a series of specially designed flume experiments were done to simulate blocking and self-cleaning processes. The blocking ratio and deposition features were measured to contrast the blocking and self-cleaning performance before and after artificial self-cleaning. The experimental results reveal that the beam dam net opening, particle diameter of sediment, sediment concentration, and gradient of the channel are the main factors affecting blocking performance. A new criterion of blocking performance of beam dams that considers the interaction of multiple factors and can provide guidance to practical project design is proposed. For all three types of blocking, sediment deposited upstream of a beam dam can be effectively transported downstream by erosion from post-debris-flow floods, Self-cleaning performance is most efficient for temporary blocking, followed by partial-blocking, and total-blocking. The efficiency of self-cleaning largely depends on the change of the sediment deposit due to erosion. Finally, a discussion is given for the optimal design of an open-type check dam and the feasibility of synergistic effects of self-cleaning in combination with artificial cleaning. Some supporting artificial silt-cleaning should be implemented in practice. A beam dam will, thus, have more storage capacity with which to control the next debris flow event.

Introduction

Debris flows are geomorphic processes or violent natural disasters of multiphase movement due to gravity in mountainous areas (Fei and Shu, 2004, Iverson, 1997). Check dams, which are one of the most effective counter measures for debris flow hazard mitigation, can be distinguished as closed-type and open-type. The former is commonly used to stabilize the gully bed and bank slopes, whereas the latter is mainly used to trap and regulate sediment of debris flows (Fei and Shu, 2004, Li, 1997). Some open-type check dams, such as beam dams (Chen et al., 2006, Cui, 2005, Cui et al., 2007), slot-check dam (Chen et al., 2014, Zou et al., 2014, Zou and Chen, 2015) have performed well in Wenchuan earthquake area and scenic spots. There have also been successful precedents in debris flows mitigation along railways ( Fei & Shu, 2004; Li, 1997; Shen & Wang, 1996). At present some linear projects still pass through areas where mountainous hazards frequently occur: e.g., there are thousands debris flow gullies along the Sichuan-Tibet Highway (Zhao, 1993). Further, the Sichuan-Tibet railway project which is under construction, also facing with increasingly serious issues of mountainous hazards. Thus, open-type check dams will frequently be applied in these areas. To meet design requirements, some qualitative and quantitative experimental and numerical research (Itoh et al., 2013, Lin et al., 2011, Michele and Arrmanini, 2000, Mizuno et al., 2001, Takahashi et al., 2010, Watanbe et al., 1980, Zou and Chen, 2015) have been done for various open-type check dams. Additionally, D'Agostino et al. (2000), Wu and Chang (2002), Nakatani et al., 2007, Nakatani et al., 2008, Maricar and Hashimoto (2014), and Schwindt et al. (2015) did a series of researches which focused on other aspects of a check dam, such as the trapping of driftwood with an open-type check dam.

A blockade forms when trapping debris flow with an open-type check dam. The blockade forms in opening of the check dam due to the deposition large gravel particles in the debris flow, and the subsequently transported sediment deposits upstream. Self-cleaning is a phenomenon in which sediment deposited upstream of a check dam is eroded by perennial flow or post-debris-flow floods whereby storage capacity is recovered automatically. A considerable number of studies have been done to investigate blocking behavior at open-type check dams using experimental, numerical and mathematical methods (Han, 2007, Maricar, 2012, Michele et al., 2005, Mizuyama et al., 1995, Satofuka and Mizuyama, 2006, Shibuya et al., 2012, Takahashi et al., 2001, You, 2001, Zhao, 2013), however, few studies have paid attention to self-cleaning (Piton and Recking, 2015, Shrestha et al., 2008, Wu and Chang, 2002).

To demonstrate the blocking and self-cleaning behaviors of beam dams, an experimental study was done at the Key Laboratory of Mountain Hazards and Earth Surface Process (KLMHESP), Chinese Academy of Sciences (CAS). According to the available research methods, the characteristics of blocking and self-cleaning of beam dams were analyzed, including the critical blocking criterion and the self-cleaning performance for different blocking-types under erosion from post-debris-flow floods (PDFF). These experimental results may provide a technological basis for an optimal design of a beam dam so that it will provide a better service for disaster prevention and mitigation.