Shinano River Research Articles

Analyzing the heavy rainfall event of July 2011 in Niigata using ground, satellite and radar rainfalls

In recent years the application of radar and satellite precipitation observations has become increasingly useful in poorly gauged areas. However, understanding the relationships between these data sources and ground observations is vital to correct the datasets and improve their application in hydrological studies. In this study we analyzed the spatial and temporal relationships between Global Satellite Mapping of Precipitation-Near Real Time (GSMaP_NRT) data set with radar and ground observations at downstream of Shinano River, Japan. GSMap_NRT observation showed better relationship with ground observations for longer-duration observations (eg. 3, 6, 12 and 18 hours) than hourly observations. The GSMap_NRT showed excellent relationship with ground rainfall at satellite observation time compared to non-observation time. Comparison of radar observations at various time scales and spatial resolutions showed that radar estimates at smaller-time-interval ratio and lower-spatial-scale ratio are better than longer-time-interval ratio and higher-spatial-scale ratio. We also observed that radar precipitation estimate well-represent the areal averaged precipitation of ground observations. Results from this study showed that radar precipitation estimates could serve as very important input to improve merging of ground and satellite precipitation as well satellite rainfall improvement systems.

Strategic Siting of Hydroelectric Power Plants to Power Railway Operations with Renewable Energy

The present study explores the strategic siting of hydroelectric power plants, focusing on the Miyanaka Intake Dam (MID) and Shinano River Hydroelectric Power Station (SHP). Built in 1939 to support Tokyo’s railway electrification, these facilities demonstrate the complexities of balancing renewable energy production with ecological conservation. Despite the high costs and energy losses associated with transmitting power from the Sea of Japan side, the SHP has effectively powered Tokyo’s rail system for over 80 years, owing to advanced transmission technologies and the region’s abundant water resources. However, river-crossing structures such as dams disrupt fish migration and habitats, necessitating the implementation of fishways. The MID fishway, continually improved since its construction, emphasizes the importance of integrating ecological considerations into hydropower projects. Our findings highlight the higher power generation efficiency on the Sea of Japan side and stress the need for careful site selection to ensure sustainable hydroelectric power while preserving river ecosystems. In conclusion, hydropower sites should be chosen based on both environmental impacts and future development potential to maintain the ecological balance and support long-term renewable energy goals.

Enhancing Runoff Simulation Using BTOP-LSTM Hybrid Model in the Shinano River Basin

Runoff simulation is an ongoing challenge in the field of hydrology. Process-based (PB) hydrological models often gain unsatisfactory simulation accuracy due to incomplete physical process representations. While the deep learning (DL) models demonstrate their capacity to grasp intricate hydrological response processes, they still face constraints pertaining to the representative training data and comprehensive hydrological observations. In order to provide unobservable hydrological variables from the PB model to the DL model, this study constructed hybrid models by feeding the output variables of the PB model (BTOP) into the DL model (LSTM) as additional input features. These variables underwent feature dimensionality reduction using the feature selection method (Pearson Correlation Coefficient, PCC) and the feature extraction method (Principal Component Analysis, PCA) before input into LSTM. The results showed that the standalone LSTM performed well across the basin, with NSE values all exceeding 0.70. The hybrid models enhanced the simulation performance of the standalone LSTM. The NSE values increased from 0.75 to nearly 0.80 in a sub-basin. Lastly, if the BTOP output is directly fed into LSTM without feature dimensionality reduction, the model’s accuracy significantly decreases due to noise interference. The NSE value decreased by 0.09 compared to the standalone LSTM in a sub-basin. The results demonstrated the effectiveness of PCC and PCA in removing redundant information within hydrological variables. These findings provide new insights into incorporating physical information into LSTM and constructing hybrid models.

Accumulation of thick fluvial sediments in the Shinano River incised-valley fills: implications for sequence stratigraphy and alluvial architecture

ABSTRACTThe relationship between fluvial systems and base-level changes, controlled mainly by sea-level fluctuations and tectonic activity, on time scales of 103–104 years, is important for evaluating and improving nonmarine sequence stratigraphy and numerical and physical alluvial architecture models. However, there are not enough quantitative data available from field studies, especially for periods of rapid base-level rise. The Echigo Plain, Japan, is a fluvial–coastal lowland where the tidal range is very small and where a very deep valley was incised by the Shinano River during the latest Pleistocene. The depth of the incised valley near the shoreline, 160 m below mean sea level, is greater than the amount of sea-level fall during the Last Glacial Maximum (LGM) because of tectonic subsidence. We studied an approximately 100-m-long borehole sediment core obtained from the landward part of the plain, where thick fluvial deposits have accumulated since the LGM. Sediment facies, diatom assemblages, sulfur content, carbon to sulfur ratios, and radiocarbon age dates indicate that most of the core sediments were deposited in a fluvial environment during the past 12 kyr. Sediment accumulation rates were 10–15 m/kyr between 12 and 8 cal kyr BP, and relatively low (less than 5 m/kyr) subsequently, mainly because of glacio-eustatic sea-level rise. The timing of the reduction in the accumulation rate is one possible indicator of the position of the maximum-flooding surface in a sequence composed only of fluvial sediments. The presence of many thin layers of very fine to fine-grained sand (20–80 cm thick), interpreted as crevasse-splay deposits, that formed between 11 and 8 cal kyr BP, when the base level was rising rapidly, implies that crevasse-splay deposits are characteristic of aggrading fluvial sediments and the transgressive systems tract in nonmarine sequence stratigraphy. Tectonic subsidence at approximately 2 m/kyr has contributed markedly to the larger accumulation rate of fluvial sediments of the highstand systems tract on the Echigo Plain, compared with rates in other fluvial–coastal lowlands, since 5–6 cal kyr BP, when the eustatic sea-level rise had mostly ceased.

Unravelling and improving the potential of global discharge reanalysis dataset in streamflow estimation in ungauged basins

Mastery in forecasting the streamflow is of great importance in environmental and sustainability research. Although many global-scale reanalysis products provide a new way to overcome the lack of streamflow records in ungauged basins, streamflow estimation through hydrological models remains a great challenge mostly due to inevitable biases. In this study, we developed a novel bias-correction system equipped with the proposed Piecewise Random Forest (P-RF) model to improve the potential of GloFAS-ERA5 (GloFAS), a global-scale river discharge reanalysis product, as a calibration benchmark for building hydrological models in ungauged basins. Considering three ungauged scenarios, several cases of temporal, spatial, and spatiotemporal bias-corrections were implemented with a total of 13 river gauges located in the Min River Basin in China, and the Fuji River Basin and the Shinano River Basin in Japan. Then, the well-improved GloFAS discharge was applied for the calibration of the Block-wise use of the TOPMODEL (BTOP) model to evaluate its performance in substituting the discharge observations. The results show that: (1) the bias-correction system performs better on the temporal scale, which applies to ungauged basins lacking long-term continuous observations; (2) the integrity and adequacy of the samples used for training the P-RF model have a significant impact on the spatial and spatiotemporal bias-corrections, and they can be reliably estimated by the proposed metric, Ratio of the Valid samples' Proportion; and (3) the statistical metric differences between the simulated discharges obtained by the calibrated BTOP model using observations and GloFAS discharge, are reduced by 25%–50% through the bias-correction.

INVESTIGATION OF RIVER STRUCTURES DAMAGED AT CHIKUMA RIVER DUE TO TYPHOON NO. 19, OCTOBER 2019

Typhoon 19, which landed on the Japanese Islands on October 12, 2019, brought record-breaking heavy rain to the Kanto-Koshin and Tohoku regions. In the Chikuma River basin of the Shinano River system, severe damage to bridges and large-scale inundation occured due to a levee breach occurred. On October 23 and 24, 2019, about 10 days after the disaster, we carried out a field survey at the damaged sites of river structures in the Chikuma River. The investigation techniques used field exploration and aerial photography by Unmanned Aerial Vehicle (UAV). This paper reports the damage situations obtained from the field survey at the sites where the abutment backfills were washed away and the levee breach occurred. It also cites issues for future consideration.

Differences in regulation of planktonic and epilithic biofilm bacterial production in the middle reaches of a temperate river

To clarify the governing factors of planktonic and epilithic bacterial production (BP) and to quantify their relative contributions to the carbon cycle, we investigated the seasonal variation and regulatory factors of planktonic and epilithic BP in the middle reaches of the Shinano River, Japan, ecosystem from February 2019 to May 2020. Sampling was conducted at 3 stations: upper stream riffle, upper stream pool, and lower stream riffle, where current velocity, water depth, and bed shear stress were distinct. Planktonic and biofilm BP ranged from 5.5 to 466 mgC m-3 d-1 and 2.9 to 132 mgC m-2 d-1, respectively, showing clear seasonal variation. Biofilm BP was higher in the upper stream riffle than at the other stations, where no spatial variation in planktonic BP was observed. Generalized linear models suggest that BP was primarily regulated by water temperature. Additionally, planktonic BP was significantly correlated with dissolved organic carbon, suggesting carbon limitation. Biofilm BP showed no evidence of resource limitation (nutrients and organic matter), but was significantly explained by current velocity and station. The results suggest that although seasonality is dominant in biofilm BP variation, spatial differences are significant within the seasonal variability. Moreover, current velocity and bottom shear stress related to local geomorphologies such as riffles and pools affect substrate supply rate and biofilm formation processes, regulating biofilm BP variation. This study demonstrated different regulatory factors of planktonic and biofilm BP in the middle reaches of a temperate river.

Adaptive management of vegetation in the fishway for fish runs and habitat in Miyanaka Intake-Dam on the Shinano River.

Adaptive management of vegetation in the fishway for fish runs and habitat in Miyanaka Intake-Dam on the Shinano River.

TSUNAMI RISK ASSESSMENT OF NIIGATA CITY ACCOUNTING FOR SOIL LIQUEFACTION AND SNOW MELT

Tsunami risk assessment was conducted for Niigata City, one of the largest cities facing Japan Sea. Niigata City is known as historical port town developed on a low land formed as the delta by the Shinano River and the Agano River. The city is therefore vulnerable for soil liquefaction. In 1964, the city was devastated by a large earthquake in which soil liquefaction and tsunami worsened the damage. In addition, because of the heavy snowfall in winter, like many coastal cities on the Japan Sea side, the water level rise in the Shinano River in the snow-melt season appears to increase the flooding risk of the harbor area. The harbor is protected by a 4 km long breakwater. This study aims to investigate the tsunami risk of the Niigata City considering the collapse of the infrastructures, the soil liquefaction and the tsunami invasion to rivers in the snow-melt period.Recorded Presentation from the vICCE (YouTube Link): https://www.youtube.com/watch?v=hiBabxOE1Nc

Seasonal trends of density, biomass, and secondary production of Antocha sp. （Diptera:Tipulidae） in relation to summer floods in the middle reaches of the Shinano River

Seasonal trends of density, biomass, and secondary production of Antocha sp. （Diptera:Tipulidae） in relation to summer floods in the middle reaches of the Shinano River

Development of Aerial Space Time Volume Velocimetry for Measuring Surface Velocity Vector Distribution from UAV

Due to the remarkable development of unmanned aerial vehicle (UAV) in recent years, its application in river engineering increases widely mainly for the measurement of ground topography such as by the technique Structure from Motion (SfM) using a series of high-resolution static images. However, although UAV usually installed a high density video camera, the use of the movie is limited just for watching and observing the geometrical feature of the ground. In the light of such a present status, the authors have developed an aerial space-time image velocimetry (STIV) technique to measure streamwise river surface velocity distributions. However, as STIV is insensitive to the change of flow direction, the aerial space-time volume velocimetry (STVV) technique, which is an extension of STIV, was developed in this research. STVV examines the change of volumetric texture within a space-time volume (STV) instead of examining the change of image intensity on a line segment as in STIV. The performance of STVV was investigated during the measurement of snowmelt flood of the Shinano River by comparing it with those obtained by the other techniques such as STIV, LSPIV and ADCP. It was made clear the aerial STVV has a great advantage over the existing image-based techniques.

<b>Annual Behavior of Pesticides in River Waters in Niigata Prefecture </b>

We studied variations in annual pesticide concentrations in two rivers in the Niigata Prefecture from April 2012 to March 2014 using GC/MS and LC/MS. Of the 83 pesticides targeted, 38 were detected in the Shin River and 25 in the Shinano River. Herbicides used mainly in paddy fields were detected more frequently, and at higher concentrations, than fungicides and insecticides. Although the pesticide concentrations in the Shin River were higher than those in the Shinano River, most pesticides were detected around the farming season for both the rivers. A small number of herbicides used only in paddy fields were detected in both rivers in winter. In this study, all pesticide concentrations were under their corresponding standard criteria.

Influence of Seasonal Pumping on Groundwater Sources and Flow System, Nagaoka Plain, Japan.

Intensive groundwater development in the urban area of the Nagaoka Plain, Japan, has induced changes in the pH and saturation index of calcite in groundwater. To account for these chemical changes, it is important to determine seasonal variations of recharge and the groundwater flow system in the aquifer. This study identified the sources and flow system of groundwater in this urban area by a comprehensive method using stable isotope data and a numerical groundwater model of the Nagaoka Plain. Stable isotope evidence shows that the groundwater is recharged by meteoric water originating from low-elevation areas rather than the mountains surrounding the plain. The water table in the study area is drawn down during the winter and recovers in the other seasons. Numerical modeling shows that discharge occurs primarily along the Shinano River during the recovery period, whereas discharge is centered in urbanized areas during the drawdown period, when a conical depression of the water table stimulates recharge from the immediate area. These results are indications of a local groundwater flow system, with its recharge area between the Shinano River and the urban areas, which is governed by intensive seasonal groundwater extraction.

信濃川中流域にみられる更新世中期〜後期の赤色風化 : 赤色土の高度分布について(29.第四紀地質)

信濃川中流域にみられる更新世中期〜後期の赤色風化 : 赤色土の高度分布について(29.第四紀地質)

Influence of deposition in dam reservoir on the deep marine hemipelagic environment off Niigata, central Japan

It has been well known that dam construction on rivers can cause a decrease in sediment supply and serious coastal erosion, while influence of dams on the sedimentary environment beyond the coastal area has not been well known. The mass accumulation rate (MAR) in the hemipelagic environment (500–700 m water depth) off Niigata, central Japan since the early half of the twentieth century was obtained from core samples, based on excess 210Pb activity. Decreases in MAR during the mid-twentieth century were recognized in several core samples located northern off the Agano and Shinano river mouths. Using the CIC model, combining correction for the influence of surface bioturbation based on the ratio of MARs, decreases in MAR were estimated as occurring during 1959–1964 and 1949–1955. These dates correspond with construction of the Okutadami dam (1956–1961), possessing the largest capacity and reservoir sediment volume of 3.9 × 107 m3 in the Agano and Shinano river systems. The other core located NW off the Agano river mouth showed constant MAR through the mid-twentieth century. A synchronicity of huge dam construction and decrease in MAR in deep marine environment, the similarity between silt–clay-sized grain size of dam reservoir sediment and that seen in the hemipelagic environment, and horizontal distribution of decreasing MAR in cores according to north–northeastward sediment transport on shelf, makes it reasonable to interpret that the decrease in MAR in hemipelagic environment was caused by entrapment of silt–clay grains in the huge dam reservoir.

Downstream drift of suspended matter and macroinvertebrates swept by a riverbed leveling work in the middle reaches of the Shinano River Japan

Downstream drift of suspended matter and macroinvertebrates swept by a riverbed leveling work in the middle reaches of the Shinano River Japan

<strong>Flight density of the aquatic insect fauna over the water surface in the middle reaches of the Shinano River, Japan, mainly among caddisflies (Trichoptera)</strong>

We focused on the relative number of flying adult caddisflies on the river surface captured by sticky board traps with the aim of elucidating differences in the distribution pattern of caddisfly larvae along the slope in the middle reaches of the Shinano River. The individual number of adult caddisflies caught increased from April and decreased from October. Even in the same middle reaches of a river, there was a large difference geographically in the species captured. Hydroptila sp. was caught mainly downstream of the Taishyobashi Bridge, Psychomyia acutipennis (Ulmer 1908) in the vicinity of the Taishyobashi Bridge, and Stenopsyche marmorata Navás 1920 upstream of the Awasabashi Bridge. It is known that the slope of the Shinano River bed suddenly becomes less and the flow rate slower in the area from the Taishyobashi Bridge to the Awasabashi Bridge, and it was shown that the species composition and number of aquatic insects caught changes with the change in the slope of the river bed.

Characterization of Seismic Levee Fragility Using Field Performance Data

We characterize the seismic fragility of levees along the Shinano River system in Japan using field performance data from two M 6.6 shallow crustal earthquakes. Levee damage is quantified based on crack depth, crack width, and crest subsidence for 3,318 levee segments each 50 m long. Variables considered for possible correlation to damage include peak ground velocity ( PGV), geomorphology, groundwater elevation, and levee geometry. Seismic levee fragility is expressed as the probability of exceeding a damage level conditioned on PGV alone and PGV in combination with other predictive variables. The probability of damage (at any level) monotonically increases from effectively zero for PGV < 14 cm/s to approximately 0.5 for PGV ≈ 80 cm/s. Of the additional parameters considered, groundwater elevation relative to the levee base most significantly affects fragility functions, increasing and decreasing failure probabilities (relative to the PGV-only function) for shallow and deep groundwater conditions, respectively.

Research on cavity formation below Ohkozu old movable weir in the Shinano River

Research on cavity formation below Ohkozu old movable weir in the Shinano River

In-situ loading test of wooden pile at Shinano River Ohkouzu old movable weir and discussion on foundation design

In-situ loading test of wooden pile at Shinano River Ohkouzu old movable weir and discussion on foundation design