Big Boulders Research Articles

Northeastern coast of Lake Baikal as a habitat of baikal seal <i>Pusa sibirica</i> in the summer period

Filling of the rookeries of baikal seal Pusa sibirica on the northeastern coast of Lake Baikal is surveyed instrumentally for the first time within the boundaries of protected area. The main coastal haulouts of the species are located in this area, so all places suitable by their lithological parameters for the seals rookeries were examined to assess intensity of their use in modern conditions of anthropogenic impact. In total, ≈ 246 km of the coastline were traced, including 170 km surveyed with unmanned aerial vehicle DJI (in 317 minutes) and visual observations on the rest of the coast with binoculars and ground photo- and video-recording. Only 9 % of the surveyed coastline (> 21 km) is suitable for rookeries, located mainly in the northern part of the area. Unfavorable lithological properties (sands, sandy pebbles, small stones, rocks) prevail on the other part of the coast, though many places (usually big boulders) are available for small rookeries there, too. Currently all these places are almost never used by seals, except of short, sporadic haulouts, mainly in June, immediately after complete disappearance of the floating ice. The main reason why the animals leave their traditional rookeries in this area in July-August is an intensive anthropogenic load, in particular at the places where the largest rookeries existed previously, as the bays Frolikha, Ayaya, Khakusy, capes Khaman-Kit, Pongonye, and some others. The leaving of rookeries contradicts to increasing needs of seals for a solid substrate to complete their molt in conditions of climate warming. Possibly, the threat of losing the northeastern coast as a summer habitat for a significant part of the baikal seal population is underestimated.

Preliminary assessment of the impact of Hurricane Iota on coral reefs in Providencia and Santa Catalina Islands

Hurricanes are important natural destructive forces for coral reefs that can change the structural component of the habitat. On November 16th, 2020, the hurricane Iota passed ~10 km north of the islands of Providencia and Santa Catalina with sustained winds of a category 5 hurricane. The purpose of this study was to document the magnitude of the impact on coral reefs around the islands two weeks after the hit, as part of the “Operación Cangrejo Negro”. Visual assessments were performed at 11 representative coral reef formations between 2 and 17 m depth. Estimates of the impact were evaluated within an approximate area of 200 m2, which was categorized with score values ranging from 0 to 5 according to the level of damage. Preliminary estimates at coral reef formations indicated impact in 72 % of the stations surveyed, concentrated mainly on shallow areas (5-7 m). Approximately 45 % of the sites had low to low-medium damage and 27 % showed medium to moderate damage with high variability between and within stations. From this preliminary assessment we conclude that the impact was widespread along the island on shallow areas structured by big boulders of Orbicella spp., mainly related to colony-level damage with less reef structural damage

The Artistic Exploration of Balbir Singh Katt: An Introduction

Balbir Singh Katt, an eminent Indian stone carver of the modern era has always been credited for enrichment of the institutionalized ethos of monumental sculptures with a purified connotation tuned to post-colonial eclecticism. More than three decades (1970’s to 2000) during his career spanning, it was indeed amazing to see that how he continued his ‘sustained interest in handling large blocks’ invariably big boulders while many of his contemporaries preferred to do small or portable pieces for practical exigencies. This study investigates his artistic works and life in the domain of contemporary Indian Art. Through adopting qualitative research tools this paper explores in his artistic output in the context of monumental sculpture in public space in India.

Classification of underwater photogrammetry data for temperate benthic rocky reef mapping

The fine characterization of the substrate is a baseline to thoroughly investigate the relations between organisms and their biotopes. Cutting edge spatial technologies now provide access to accurate information on biotopes and biocenoses both in terrestrial and in marine environments. Photogrammetry is one of them and has recently been applied in submarine environments especially in shallow clear water. In this study, we investigated the potential of photogrammetry to characterise benthic habitats in turbid environments. Although more challenging, turbid environments are more frequent in temperate marine coastal areas. We selected two rocky sites in the bay of Saint-Malo (Brittany, France), differentiated by their level of turbidity, one being a marine site exposed to natural tides (Buharats), while the other (Bizeux) is subjected to both natural tides and artificial currents created by the functioning of a hydroelectric dam. The different substrates observed were classified into eight classes at a centimetre resolution using photogrammetry-based spatial and multispectral predictors. The spatial benthic terrain predictors were derived from a digital surface model (DSM) at various spatial scales, and the multispectral predictors were retrieved from the red-green-blue (RGB, natural colours) orthomosaic imagery. An overall classification was computed for Buharats and Bizeux, with accuracies of 84.76% and 79.54% respectively, revealing a good quality of the substrate classification. The combination of RGB, DSM, and several spatial benthic terrain variables, with a pixel resolution of 5 and 10 mm, and a kernel size of 30, 60 and 90 pixels leads to the best benthic substrate classification (highest overall accuracy). At the class scale, producer's (PA) and user's (UA) accuracy showed that big boulders and field material were correctly distinguished. Small boulders and cobbles, having similar sizes, showed the lowest classification performances. This classification methodology provides new perspectives for mesoscale (100 m2 to 1 km2) semi-automatic mapping of the fine resolution (1 cm) relationship between benthic organisms and their substrate.

Paleo-sea levels, Late-Holocene evolution, and a new interpretation of the boulders at the Rocas Atoll, southwestern Equatorial Atlantic

Rocas Atoll is a remote place and the only atoll in the southwestern Atlantic Ocean. This study presents new paleo-sea level reconstructions and a new interpretation on former ones. The new data indicate that sea level was higher at the Late-Holocene than it is at present and that the hydrodynamic factors overlap with sea-level changes, precluding more precise paleo-sea level reconstructions. According to previous works, the Rocas Atoll presents one of the most conspicuous paleo-sea level indicators, represented by reef remains. But, in this paper, these supposedly reef remains are reinterpreted as algal-reef boulders detached from the atoll reef-front by high-wave energy events and deposited over the reef rim, where they remain detached or are cemented and, sometimes, mushroom shaped. It is considered that the bigger boulders may have been deposited in their current position by the cumulative effects of past energetic wave events. Furthermore, the use of beachrocks as paleo-sea level indicators in former studies is discussed, leading to the conclusion that they actually indicate beach progradation and lateral accretion resulting from a positive sand budget. Finally, a schematic morphological evolution of the atoll during the Late-Holocene is proposed. At the atoll, leveling with RTK and imagery with laser scanner were collected, and eleven radiocarbon ages were measured by accelerator mass spectrometry (AMS).

Building on Hope

As we begin a new year—AWWA's 140th, by the way—I cannot help but feel hopeful. Even though there isn't a true bright line between years and we still need to wear masks to protect each other's health (at least as 2021 begins), I feel hope. From time to time I have been known to say, “The world is run by those who show up.” The last time I publicly used that phrase was at the Young Professionals Summit last February. The point I make with this phrase is that if you want to change the world for the better, you must engage in the solution—you must show up. From the number of tweets, it appears the phrase and the concept resonate with the young professional audience. That, too, provides hope. Almost seven years ago, AWWA, Engineers Without Borders USA, and the American Society of Civil Engineers banded together to create Community Engineering Corps (CECorps). CECorps’ noble mission is to bring underserved communities and volunteers together to advance local engineering solutions. Learn about the Community Engineering Corps at www.CommunityEngineeringCorps.org. Every year, CECorps “shows up” to change the world for the better. While the technical support CECorps provides to underserved communities is critical, the magic of CECorps is the power of hope its volunteers bring to the communities they serve. Two recent examples show how CECorps helped with water infrastructure solutions. The Culver Lake Water Company—despite the implication of its name—depends on a single well (not a lake) as its water supply. The well is situated in a 1910 concrete structure. The system was challenged in meeting New Jersey regulatory standards, and the company lacked the necessary engineering analysis and funding to address the infrastructure issues until a small team of CECorps volunteers from AWWA's New Jersey Section stepped in to help. Today, equipped with a detailed report and analysis from the CECorps team, Culver Lake Water Company has a clear path for financing and improving its system. In Seattle, the educational opportunities at Nathan Hale High School include a commercial-sized greenhouse and a half-acre school garden—known as the Nathan Hale Urban Farm. The educational idea is to provide students with hands-on experiences that connect them to the earth, the food they eat, and their community. With the program's introduction came increased water demand for the school and the need for a better water solution. CECorps volunteers provided a preliminary design and concept for a rainwater collection system to supply the garden with water. The preliminary design and concept were used as part of a grant application which, along with additional assistance from the CECorps team, successfully led to a finished project for the school. CECorps’ core values require it to go beyond the technical projects, knowledge-sharing, and providing hope to these communities and groups. CECorps members also are committed to addressing infrastructure challenges in a socially responsible way. This includes promoting solutions that improve equity in access to public infrastructure, considering the needs of diverse populations, and engaging volunteers who reflect the communities helped by CECorps. In 2020, in support of advancing social responsibility, CECorps entered into a cooperative agreement with the National Society of Black Engineers (NSBE). NSBE is a 45-year-old, student-governed, nonprofit organization. Cementing this collaboration is the fact that NSBE's mission also envisions hope for a better world. NSBE's mission is to increase the number of culturally responsible Black engineers who excel academically, succeed professionally, and have a positive impact on the community. Even with great partners like NSBE, CECorps may not solve all the infrastructure challenges for all the underserved communities; but that will not stop us from showing up, providing hope, and solving what we can where we can. Steve Barr, who leads AWWA's CECorps work, puts it this way: “Solving these infrastructure challenges sometimes seems like pushing a big boulder uphill, but through CECorps I see the passion AWWA members have to help those who need help the most. I like showing up for that. It gives me hope.” It is a new year, so if you'd like to become a volunteer for CECorps, contact Steve Barr at sbarr@awwa.org to learn about how you or your section can get involved.

Slope Instability at Nablus-Al Bathan Road, Palestinian Territories (Causes, Analysis and Remedy Measurements)

Nablus-Al Bathan Road which connects Nablus City and Jordan Valley in the West Bank of Palestinian Territories, was widened, reconstructed and rehabilitated in 2009, however, between 2010 and 2012 road defects at several locations were observed. To fix these defects especially at station 2 + 100 of the road, soil replacement in the body of the road and big boulders to support the edge of the road were used. Unfortunately, large settlement occurred in the part of the road under maintenance and more sliding and slope instability occurred in the road at station 2+ 100 during the remedial measures. Studies were carried out to find the causes of this problem. These included surveying of the area, geotechnical studies (making trial pits, performing geophysical seismic exploration and digging out several boreholes), in addition to slope stability analysis. It was found that the main causes of landslides were types of soils at the site, high slopes, groundwater recharged from rainfall and changing of weights (cut and fill). Remedy measures were suggested to overcome sliding problem based on available resources and local technology.

Estimating the blast sill thickness using changepoint analysis of MWD data

Measurement while drilling (MWD) data are collected during production drilling in the open pit operation in question. On every bench in the open pit, a fractured marble zone (sill) is left on top of the hard and un-fractured marble to facilitate subsequent loading and transportation. The boreholes are drilled through this sill and then continue into the solid marble. The varying sill thicknesses cause challenges in the charging and blasting processes since charging the sill can cause fly-rocks and failing to charge enough can result in big boulders that need to be reduced in size through a cost- and time-consuming hammering process. If the sill thickness in each borehole is known, borehole specific charging depths can be developed. This paper shows how a step-wise changepoint analysis on MWD data can be used to estimate sill thicknesses. The estimated sill thicknesses are compared with optical televiewer (OTV) images to validate the predictions. Principal component analysis is used to create variables which gradually explain a decreasing amount of the variances in the data. The study concludes that a mean and variance-based changepoint analysis on the first principal component (PC1) can detect the sill thicknesses with a correlation coefficient equal to 0.98 and sum of squared deviation 0.12 from actual sill thickness. The PC1 is mainly (46% of the variance) described by rotation pressure, feed pressure and dampening pressure, indicating that the variations in these three variables are most important when studying high contrast physical and mechanical differences in rocks.

Laboratory investigation for development of local scour depth model for varying shapes of obstruction

This paper reports the effect of the shape of obstruction on local scour depth. Laboratory experiments were conducted on a tilting glass flume to study scour phenomenon around five obstructions of different shapes. Obstructions studied were chosen keeping in view not only the bridge piers but also some other structures, like obstructions in the flow channels, e.g., a jetty, big boulder, any building in the coastal area, etc. Maximum local equilibrium scour, a dependent parameter, was studied as a function of flow parameters and shape parameters of the obstruction. A model was developed for the maximum local scour depth estimation in which maximum local scour depth (ds) is a function of Froude number (Fr), flow depth (y) and shape factor (Sf). The experimental findings depict a considerable effect of the shape of obstruction on the local scour depth.

Laboratory investigation for development of local scour depth model for varying shapes of obstruction

This paper reports the effect of the shape of obstruction on local scour depth. Laboratory experiments were conducted on a tilting glass flume to study scour phenomenon around five obstructions of different shapes. Obstructions studied were chosen keeping in view not only the bridge piers but also some other structures, like obstructions in the flow channels, e.g., a jetty, big boulder, any building in the coastal area, etc. Maximum local equilibrium scour, a dependent parameter, was studied as a function of flow parameters and shape parameters of the obstruction. A model was developed for the maximum local scour depth estimation in which maximum local scour depth (ds) is a function of Froude number (Fr), flow depth (y) and shape factor (Sf). The experimental findings depict a considerable effect of the shape of obstruction on the local scour depth.

Interaction of two-phase debris flow with obstacles

Landslides, debris avalanches and flows are common events in mountainous regions, causing tremendous damages to people and infrastructures. Their dynamics are substantially affected and altered by obstacles such as trees, big boulders and civil structures on their way. Appropriately designed and optimally installed obstacles, including braking mounds, catching or deflecting dams, in the flow path can drastically change the flow dynamics by deflecting, re-directing or stopping the debris mass. Such structures can substantially reduce the kinetic energy of the flow and associated risks. So, a proper understanding of the flow-obstacle-interaction is required to construct adequate defense structures. Here, we simulate a two-phase debris flow as a mixture of solid particles and viscous fluid down an inclined surface with tetrahedral obstacles of different dimensions, numbers and orientations. This is achieved by employing a physically-based general quasi-three dimensional two-phase mass flow model (Pudasaini, 2012) consisting of a set of non-linear and coupled partial differential equations representing mass and momentum conservations for both the solid- and fluid-phases. Simulations on mass flows are performed with a high-resolution and efficient numerical scheme that is capable of capturing rapid and detailed dynamics, including the strongly re-directed flow with multiple stream lines, mass arrest, strong shock waves and debris-vacuum generation and flow pattern formations, as the rapidly cascading mass suddenly encounters the obstacles. The estimated impact pressure is useful for designing the defense structures. The solid and fluid phases show fundamentally different interactions with obstacles, flow spreading and dispersions, and run-out dynamics and deposition. The observations are in line with natural debris flows and experiments. Our understanding of the complex interactions of real two-phase mass flows with multiple obstacles helps us to plan defense structures and constitute advanced and physics-based engineering solutions for the prevention and mitigation of risks caused by different gravitational mass flows.

Geomorphological and spectrophotometric analysis of Seth's circular niches on comet 67P/Churyumov–Gerasimenko using OSIRIS images

We provide a detailed geomorphological and spectrophotometric analysis of the circular niches located on the Seth region of 67P using OSIRIS images. The features can be related to landslide events that occurred on 67P and shaped its surface, as the recent Aswan cliff collapse detected in the same region. We therefore provide an analysis of the area pre- and post-perihelion suggesting that no specific changes have been observed. To assess this, after performing a geomorphological map of the area that allows us to identify different terrain units, we computed the boulders cumulative size frequency distribution (SFD) of the niches, before and after the perihelion passage. The niches SFDs are characterized by a similar trend with two different power-law indices within the same deposit: lower power-law value (between −2.3 and −2.7) for boulders smaller than 5 m and steeper power-law value (between −4.7 and −5.0) for boulders larger than 5 m. These trends suggest that smaller boulders have evolved and progressively have been depleted (lower power-law index), while bigger boulders are more representative of the event that generated the deposit and are less degraded. Then, we perform the spectrophotometric analysis of this region comparing pre- and post-perihelion results. We found colour changes within the area, in particular brighter patches related to the presence of exposed water ice mixed to the refractory materials have been detected in the post-perihelion images.

The golden thread: educator connectivity as a central pillar in the development of creativity through childhood education. An Irish life history study

This paper presents the narratives of five creative Irish Adults who contributed to the study by sharing their childhood education experiences. The five participants are all of different ages and occupations. All identify themselves as highly creative people and all worked with me over the course of this study to identify how this creativity developed within their engagement with the Irish childhood education system. All excelled with higher education and they share a high degree of success within their careers. Between them, they express their creativity across five key genres. These are: Science, Engineering, The Arts, Entrepreneurship and Social Entrepreneurship. Well-developed themes were analysed to identify interrelationships which formed a theoretical framework of core concepts that demonstrate what holds great importance in the lives of these participants for the development of their creativity during childhood education in Ireland. A clear theme of this study was that of connectivity. Connections and relationships matter greatly. The creative journey is joyful and clear where children experience a positive connection with their educator. Conversely, the creative journey is stymied by a lack of connection or by a negative connection. These stand in the way of creative growth, like a big boulder on the child's developmental path. This paper showcases, through the stories of these five research participants, how creativity development is affected by the connection between the child and their educator.

Collision and gravitational reaccumulation: Possible formation mechanism of the asteroid Itokawa

Aims. We investigate the possibility that the observed sea-otter shape of the asteroid Itokawa, associated with the presence of big boulders on its surface, originates from the reaccumulation process that may have formed this asteroid, assuming that it consists of reaccumulated fragments from a catastrophically disrupted parent body.Methods. We computed the gravitational phase of an asteroid disruption, during which fragments can reaccumulate and form aggregates, using a version of the N -body code pkdgrav that includes a model of rigid aggregates. This new model allows the formation of non-idealized rubble piles as a result of reaccumulation that are made up of irregular, competent pieces. Shape and spin information of reaccumulated bodies are thus preserved by allowing fragments to stick on contact (and optionally bounce or cause further fragmentation, depending on user-selectable parameters), instead of merging into growing spheres. Results. We find that the reaccumulation process of an asteroid disruption can produce aggregates whose form is similar to that of Itokawa, and can lead to the deposit of big boulders on the surface, as observed on Itokawa.

TERRESTRIAL LASER SCANNING FOR COASTAL GEOMORPHOLOGIC RESEARCH IN WESTERN GREECE

Abstract. We used terrestrial laser scanning (TLS) for (i) accurate volume estimations of dislocated boulders moved by high-energy impacts and for (ii) monitoring of annual coastal changes. In this contribution, we present three selected sites in Western Greece that were surveyed during a time span of four years (2008-2011). The Riegl LMS-Z420i laser scanner was used in combination with a precise DGPS system (Topcon HiPer Pro). Each scan position and a further target were recorded for georeferencing and merging of the point clouds. For the annual detection of changes, reference points for the base station of the DGPS system were marked. Our studies show that TLS is capable to accurately estimate volumes of boulders, which were dislocated and deposited inland from the littoral zone. The mass of each boulder was calculated from this 3D-reconstructed volume and according density data. The masses turned out to be considerably smaller than common estimated masses based on tape-measurements and according density approximations. The accurate mass data was incorporated into wave transport equations, which estimate wave velocities of high-energy impacts. As expected, these show smaller wave velocities, due to the incorporated smaller mass. Furthermore, TLS is capable to monitor annual changes on coastal areas. The changes are detected by comparing high resolution digital elevation models from every year. On a beach site, larger areas of sea-weed and sandy sediments are eroded. In contrast, bigger gravel with 30-50 cm diameter was accumulated. At the other area with bigger boulders and a different coastal configuration only slightly differences were detectable. In low-lying coastal areas and along recent beaches, post-processing of point clouds turned out to be more difficult, due to noise effects by water and shadowing effects. However, our studies show that the application of TLS in different littoral settings is an appropriate and promising tool. The combination of both instruments worked well and the annual positioning procedure with own survey point is precose for this purpose.

Off-Site Construction in Saudi Arabia: The Way Forward

Off-site construction, which gained prominence in the last quarter of the previous century, is the form of construction in which the intent is to move some of the effort that goes into construction from the construction site into the controlled environment of a manufacturing facility (Arif and Egbu 2010). Gibb (2001) traced the history of off-site construction as far back as 1851; however, Arif (2009) actually goes one step further and argues that the use of big boulders instead of smaller bricks in pyramids is no different from using prefabricated wall panels. Humanity has always looked for better ways of building faster, and the use of precut rocks and boulders leveraged the opportunity to fill large volumes of pyramid structures more quickly (Arif and Egbu 2010). The benefits of off-site construction have been well-documented in the literature. Gibb and Isack (2003) classified the benefits into five major categories: time, quality, cost, productivity, and people. Arif and Egbu (2010) identified off-site as a construction paradigm that can address the housing shortage in the future. However, there are some major challenges associated with the implementation of off-site construction. Pan et al. (2007) documented the barriers to the implementation of off-site construction. The most important five barriers identified by Pan et al. (2007) are higher capital cost, difficulties in achieving economies of scale, complexity of interfacing between systems, inability to freeze the design early on, and the nature of the planning system. Saudi Arabia, the world’s largest oil producer, has seen an economic boom in the previous five years, owing to high oil prices. Oil and gas exports have increased from 70.7 billion USD in 2001 to 205 billion USD in 2007 (Tabata 2009). This economic growth has resulted in significant economic activities being undertaken in the kingdom. However, the construction projects being performed are fraught with delays and inefficiencies (Alkharashi and Skitmore 2009). One documented benefit of off-site construction is productivity, leading to a higher speed of construction. To assess the issues with the implementation of off-site construction in Saudi Arabia, a workshop was organized in Jeddah in November 2010. There were 20 attendees in the workshop; all were project managers, either in government organizations or private construction companies. The objectives of the workshop were 1. To introduce the benefits and challenges associated with offsite construction to the audience. 2. To document the perceptions associated with off-site construction in the construction industry in Saudi Arabia. 3. To identify the major barriers to the implementation of off-site construction in Saudi Arabia. 4. To propose a way forward in implementing off-site construction in Saudi Arabia. Workshop Execution

Distribution and status of the freshwater pearl mussel Margaritifera margaritifera in northern Fennoscandia

The present distribution and status of the freshwater pearl mussel (Margaritifera margaritifera) was investigated in the northern cross-border areas of Sweden, Norway, Russia, and Finland in the period of 2003–2007. Location of the populations was done in two steps, first by gathering all the existing data from earlier studies, historical pearl fishing, and from local people through interviews. After this preliminary data collection, the populations were located more precisely by field studies. The results of the investigations varied depending on the catchment area. Abundant and viable populations were found in some of the catchments, while in the others M. margaritifera had disappeared or were near extinction. Besides the absence or low densities of host fish, other threats to M. margaritifera in these vast and remote areas are ground preparation as part of the felling operations, ditching of forests and bogs, building of forest roads, and mining. During the field surveys, the mussels were found in habitats not reported earlier, e.g., in rivers totally covered by big boulders, on the roots of the water plants, and in extremely shallow brooks.

A quasi-experimental setting of coarse clast transport by the 2010 Chile tsunami (Bucalemu, Central Chile)

On 27th February, 2010 a M W 8.8 earthquake occurred in central Chile, causing a tsunami that severely affected the central Chilean coast. In this study we present sedimentological data of the 2010 Chile tsunami from the coastal town of Bucalemu in Central Chile. The tsunami deposited both fine grained sediments as well as cobbles and boulders. The location offers a quasi-experimental setting for coarse clast transport because an artificial pile of cobbles and boulders was piled there for construction purposes some days before the tsunami. Therefore, the pre-tsunami transport setting and transport distances are well defined. Additionally, a local flow depth of ca. 2 m and flow speed of ca. 5.6 m/s are deduced from eyewitness reports and video recordings. The cobbles and boulders have been transported up to 155 m from the pile in landward direction. The size of the quarried clasts was restricted to max. 0.3 m 3 and 720 kg. Bigger boulders were not available at the location, even though calculations show that the tsunami would have been capable to transport them. Calculations of flow speeds required for the initialization of transport in different modes, such as sliding, rolling or saltation, indicate that all clasts that were moved by the tsunami in landward direction, were entrained by the flow given a minimum observed speed of 5.6 m/s, with 65% being transported by rolling and 35% by saltation. The transported clasts are arranged in three groups positioned in morphological depressions on the coastal plain. A landward fining trend is not present. The arrangement of clasts originating from a pile and being deposited in distinctive groups, entails that the landward transport of cobbles and boulders is a function of repeated entrainment, transport and deposition by several waves of the tsunami wave train. Consequently, we interpret the clast distribution as a result of a combination of the number of individual waves of the tsunami wave train, their respective energies, the local topography, and the pre-transport setting of a clast pile which releases wedged clasts with each successive wave.

A prototype experiment of debris flow control with energy dissipation structures

Large-volume debris flow events are defined when the volume of solid materials exceeds 1 million m3. 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 m3 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 m3. 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.

Spatial analysis of rockfall activity, bounce heights and geomorphic changes over the last 50 years – A case study using dendrogeomorphology

Tree-ring series have been used to reconstruct 50 years of rockfall behavior on a slope near Saas Balen (Swiss Alps). A total of 796 cores and 141 cross sections from 191 severely injured conifer trees ( Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra L.), combined with a series of aerial photographs, were used to investigate the evolution of the forest stand so as (i) to reconstruct past rockfall rates; (ii) to analyze the spatial behavior of maximum bounce heights; and (iii) to analyze the spatial comportment of rockfall activity over the last five decades. Tree-ring analysis permitted the reconstruction of the age distribution at the study site; results were in perfect agreement with the afforestation process shown in the aerial photographs. The oldest are located in the lower, central part of the study site; the youngest individuals at its uppermost lateral boundaries. Reconstructed rockfall rates reveal strong interannual variations and single event years with increased activity, namely in 1960/1961 and 1995. Spatial analysis of the maximum bounce heights indicate highest values at the lateral boundaries and lowest heights in the lower central part of the forest stand, where a big boulder seems to shield trees growing below it. The spatial analysis of past rockfall activity shows high active zones at the uppermost north-facing boundaries of the forest and least active zones in the lowermost central part of the studied stand. The high rockfall activity at the slope is expressed by a mean rockfall rate of > 1 event m − 1 y − 1 .