Rationality in pier geometry of Kintaikyo Bridge from viewpoint of river engineering

The Kintaikyo Bridge, with its elegant wooden arches, has a unique pier shape and continues to be loved by residents and visitors alike. Although this bridge is an active footbridge and an important landscape element along with the Nishikigawa River and its river beach, the rationality or irrationality of the shape of its piers remains unknown. This paper is intended to clarify the river engineering characteristics of the piers for the first time by conducting 1/129 scale hydraulic model experiments. The shapes tested were a perfect spindle shape (which has been adopted as a common theory for many years) and a reconstructed current shape based on the spindle shape, and for comparison, an oval and a non-regular hexagon shape with the same width and area. The current shape, along with the spindle shape, suppressed the water level rise around the pier more than the others. As for the riverbed fluctuation, the current shape slightly increased the scour more than the others, but it also maximized the sedimentation around the scoured part. In other words, the current shape has the potential to facilitate the procurement of sediment for post-flood restoration. In addition, the current shape overwhelmingly reduced the statistical dispersion associated with the experiment, suggesting that it stabilizes the trend of riverbed fluctuation even during actual floods. Based on the results, the future conservation of the Kintaikyo Bridge was also discussed.

Induced micro seismicity due to raising mine water level in former coal mines in the eastern Ruhr area (Germany)

<p><strong>FloodRisk</strong> is an interdisciplinary project focusing on the effects of mine water level rise in abandoned coal mine regions in Germany. Such effects are heterogeneous ground uplift, stress changes due to the change in pore pressure and the reactivation of potential faults. One of the most directly measurable effects is certainly the induced micro seismicity. It is known from previous studies that the flooding of old mines can lead to a renewed increase level in induced micro seismicity in these regions.<br>In this study  the relationship between mine water rise, fluid-induced stress changes and induced seismicity in the Haus Aden dewatering area in the eastern Ruhr area (Germany) will be investigated in more detail. <br>For this purpose, we operate a network of currently 21 short period seismic stations in the region of the former "Bergwerk Ost" colliery, which had the highest seismicity rate in the Ruhr area during active underground coal mining. This network is still to be expanded to cover the entire water drainage area, about 30 Raspberry Shake sensors are waiting for the possibility of installation. <br>Nevertheless, the existing network registered almost 1000 induced micro seismic events in a magnitude range from -0.7 up to 2.6 M<sub>Lv</sub>. Many of these events are  spatially clustered and some show quite high waveform similarity. This allows relative localisation  and can increase the accuracy of the location. The depth location of the earthquakes, within the limits of localisation accuracy, agrees very well with the distribution of seismicity at the time of active mining. The spatial distribution so far seems to be limited by a large inactive transverse fault in the west. It needs to be clarified what influence this fault has on the propagation of mine water in the  underground.<br>The measured temporal trend of the mine water level, after pumps were shut down in mid-2019, shows a strong correlation with the temporal evolution of the observed micro seismicity. In the first  months after the pumps are switched off, the water levels at the observation points rise only slowly and isolated microseismic events occur again. In November 2019, the rise in water levels doubled and at the same time, the strongest induced event in the measurement period was recorded with a magnitude of 2.6 M<sub>Lv</sub>. In the following months, the seismicity rate ranged from 8 to 34 events above 0.5 M<sub>Lv</sub> per month, some of which were felt. A structural geological 3D subsurface model is developed to help to understand the distribution of induced seismicity and the role of the raising mine water level.</p>

High-resolution, large-scale laboratory measurements of a sandy beach and dynamic cobble berm revetment

High quality laboratory measurements of nearshore waves and morphology change at, or near prototype-scale are essential to support new understanding of coastal processes and enable the development and validation of predictive models. The DynaRev experiment was completed at the GWK large wave flume over 8 weeks during 2017 to investigate the response of a sandy beach to water level rise and varying wave conditions with and without a dynamic cobble berm revetment, as well as the resilience of the revetment itself. A large array of instrumentation was used throughout the experiment to capture: (1) wave transformation from intermediate water depths to the runup limit at high spatio-temporal resolution, (2) beach profile change including wave-by-wave changes in the swash zone, (3) detailed hydro and morphodynamic measurements around a developing and a translating sandbar.

Mechanisms of Flood-Induced Levee Breaching in Marumori Town during the 2019 Hagibis Typhoon

Typhoon Hagibis, which occurred at the beginning of October 2019, was one of the largest and most powerful tropical cyclones and was considered to be the most devastating typhoon to hit Japan in recorded history. Extreme heavy rainfall caused massive impacts to Japan in general and to Marumori Town, Miyagi Prefecture in particular. In the present study, the detailed flood characteristics at Marumori Town were investigated by using field observation and numerical simulations. The obtained data immediately after the flood has clearly shown that most levee breaches were caused by the water overflow on the river embankment at the constriction areas such as the tributaries’ junction and the intersection of the river embankment. Numerical simulations were performed to investigate the mechanism of levee breaching in Marumori Town. According to the simulation results, the flooding water from the upstream levee breach locations flowed into the paddy field area and caused the levee to breach at the river embankment interaction in the downstream area. A new levee breach criterion in terms of overflow depth and its duration on the river embankment was proposed. In addition, a sensitivity analysis was also performed to understand the effect of the backwater and phase lag of water level rise between the mainstream and tributaries. Although there have been many studies on flood disasters, the typhoon’s flood-induced disasters on the river and coastal infrastructures have still remained a big challenge. The present study outcomes provide useful information not only to understand how the river embankment of tributaries is vulnerable to water level rise, but also to support the river authorities to prepare better mitigation plans for future flood disasters.

To issue of gorges and ice jams in the Kuban river basin

Purpose: analysis of quantitative indicators of actual сongestion and ice jams in the Kuban river basin with subsequent intra-basin zoning of the parameters studied. Materials and Methods: data from hydrometeorological observations of ice phenomena were used. The summary calculation of the quantitative indicators of gorges and ice jams along the river Kuban, as well as for each basin of tributaries of the first order was carried out. Results: as a result of the analysis, it was found that the cases of maximum ice jams above the “0” graph in the river Kuban basin were observed more often than the maximum gorge rises. On the river Kuban the number of jams was 90, gorges – 64; in the river Belaya basin number of jamming phenomena was 96, gorges – 9; in the river Laba basin – 43 ice jams and 18 gorges; on the river Pshish the number of jams – 31, gorges – 6; in the river basin Urup the number of jams is 10, and the number of gorges is 20; the river Bolshoi Zelenchuk basin has 25 jams, and 5 gorges. The maximum rise in the water level during jams was 248 cm on the river Pshish at the Bzhedukhovskaya gauging station. The highest water level during gorge events was also recorded on the river Pshish in the aul Teuchezhkhabl and amounted to 386 cm. Most of the recorded cases of water level rise in the presence of gorge phenomena occur at the end of December and the second decade of February. There are no observational series of gorge events at most gauging stations, but, according to available data, most gorge events occur at the end of January and the second decade of February. Conclusions: gorges and ice jams are very dangerous natural phenomena and therefore require promptness and accuracy of forecasting. The solution of such problems is impossible without a network of hydrological posts and observation points, which is currently underdeveloped. Therefore, thickening and improving the existing observational network is one of the main solutions to this issue.

IMPROVING THE EFFICIENCY OF THE STORAGE FLOOD MONITORING SYSTEMS

The effectiveness of monitoring systems for runoff floods is determined by the amount of time required to implement preventive measures in order to reduce the severity of potential losses and to adequately assess the degree of threat. The three-level model of the degree of hydrological threat adopted in the Roshydromet system – the normal mode, the mode of an adverse event (AE) and the mode of a hazardous event (AE), does not make it possible to ensure preventive measures. With the rapid development of the flood, the time of the water level rise between the AE and OI marks is often no more than 10-15 minutes, which is insufficient to ensure preventive measures. The transition to a five-level model for describing the degree of hydrological threat, based on GOST 22.3.13-2018 (ISO 22324: 2015) and providing, in addition to assessing the degree of threat in the notation of Roshydromet, two modes: a mode of increased attention and a mode of potential danger, allows on the basis of an ultra-short-term flood forecast runoff nature to provide a lead time of 2–6 hours to assess the degree of hydrological threat. In the existing flood monitoring system, the degree of hydrological threat is determined for the places where hydrological posts are installed, which are often located outside of settlements. It is proposed to introduce the concept of a zone of potential hydrological threat (ZPHU), for which the degree of threat is determined by calculation. Various approaches to the implementation of ultra-short-term flood forecasting taking into account the formation model of the precipitation field are considered.