Gubash Azhikodan
@tmu.ac.jp
Assistant Professor, Department of Civil and Environmental Engineering, Faculty of Urban Environmental Sciences
Tokyo Metropolitan University
EDUCATION
Ph. D. in Engineering, Tokyo Metropolitan University, Japan
M. Tech in Water Management, IIT Kharagpur, India
B. Tech in Agricultural Engineering, Kerala Agricultural University, India
RESEARCH, TEACHING, or OTHER INTERESTS
Environmental Science, Aquatic Science, Civil and Structural Engineering, Oceanography
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
K. Vidyalashmi, Megha Chandana L, J.S. Nandana, Gubash Azhikodan, K L Priya, Katsuhide Yokoyama, and Suresh Kumar Paramasivam
Elsevier BV
Nay Oo HLAING, Gubash AZHIKODAN, and Katsuhide YOKOYAMA
Japan Society of Civil Engineers
Pan Ei PHYU, Gubash AZHIKODAN, and Katsuhide YOKOYAMA
Japan Society of Civil Engineers
Megha R. Raj, K. Krishnapriya, N. Hisana, K. L. Priya, and Gubash Azhikodan
Springer Nature Singapore
Lett Wai Nwe, Katsuhide Yokoyama, and Gubash Azhikodan
Elsevier BV
Gubash Azhikodan, Nay Oo Hlaing, Katsuhide Yokoyama, and Masashi Kodama
Elsevier BV
Kirana Somsook, Gubash Azhikodan, Maurice A. Duka, and Katsuhide Yokoyama
Elsevier BV
Lett Wai Nwe, Gubash Azhikodan, Katsuhide Yokoyama, and Masashi Kodama
Elsevier BV
Gubash Azhikodan and Katsuhide Yokoyama
Elsevier BV
Joan Cecilia Casila, Gubash Azhikodan, and Katsuhide Yokoyama
Elsevier BV
Saritha Padiyedath Gopalan, Akira Kawamura, Hideo Amaguchi, and Gubash Azhikodan
Springer Science and Business Media LLC
Nagendram Veerapaga, Tetsuya Shintani, Gubash Azhikodan, and Katsuhide Yokoyama
Springer Singapore
In order to discuss the variation of salinity intrusion and mixing types in terms of estuary length, width, depth, and bathymetry, a total of 31 numerical experiments were carried out with a conceptual estuary by using a three-dimensional hydrodynamic simulator, Fantom-Refined. Since sand bars are formed in a river channel, and cyclic variation of the river bed height is found in longitudinal direction, sinusoidal wavy shapes were considered for rough bottom cases to represent the river bed with four different wave amplitudes (0.1, 0.2, 0.3 and 0.4 m) and wavelengths (350, 700, 1400 and 2800 m). In the cases of constant tidal range and discharge with the flat bottom, salinity intrusion length was decreased with increase in estuary length, and mixing condition was changed from salt wedge to well mixed type. On the other hand, salinity intrusion length was increased with increase in width of the channel under constant discharge. Further, the salinity mixing condition was changed from well mixed to salt wedge with the increase in depth of the channel. The salinity intrusion length was increased in the case of funnel shaped estuary when compared with the rectangular shaped estuary. Wavy bottom of the channel had less intrusion length compared with the flat bottom of the constant tidal range and discharge as the bottom friction reduced the velocity of the gravitational flow as well as enhanced vertical mixing. For the constant wavelength, the salinity intrusion length was decreased with increase in wave amplitude. On the other hand, for constant wave amplitude, the salinity intrusion length was increased with increase in wavelength.
Gubash Azhikodan, Kirana Somsook, and Katsuhide Yokoyama
Springer Singapore
Saritha Padiyedath Gopalan, Akira Kawamura, Hideo Amaguchi, Tadakatsu Takasaki, and Gubash Azhikodan
Elsevier BV
Gubash Azhikodan and Katsuhide Yokoyama
Elsevier BV
Nagendram Veerapaga, Gubash Azhikodan, Tetsuya Shintani, Naoya Iwamoto, and Katsuhide Yokoyama
Elsevier BV
SARITHA PADIYEDATH GOPALAN, AKIRA KAWAMURA, HIDEO AMAGUCHI, and GUBASH AZHIKODAN
The International Association for Hydro-Environment Engineering and Research (IAHR)
Predictions made by the rainfall-runoff models are inherently uncertain in nature and it is very vital that these models should undergo vigorous calibration and uncertainty analysis. Recent researches relating to hydrologic model uncertainty mostly refers to the identification of parameter uncertainty. The quantitative evaluation of parameter uncertainty of rainfall-runoff models is very important especially in urban watersheds due to the high flood risk in these areas. Therefore, this study aims to analyze the parameter uncertainty of an urban specific rainfall-runoff model, urban storage function (USF) model, using the simplified jackknife approach and its effect on the model simulations. The use of jackknife procedure, a resampling technique, to assess the parameter uncertainty of rainfall-runoff models appear not to have been tried before. The standard rainfall-runoff-model calibration procedure is applied by treating as missing each block of the model residuals to the objective function with a block length of 50. In this study, we scrupulously evaluated the uncertainty of USF model parameters by estimating the 95% confidence interval (CI) of parameters and identified the parameters from the highest to the least uncertainties. Further, the effect of parameter uncertainty on the model simulation uncertainty was investigated by computing 95% CI of the simulated discharge series. The results revealed that the model was able to bracket only 43% of the observations, on average, within the confidence band which further disclosed that the parameter uncertainty has a great impact on the USF model simulation uncertainty.
Saritha Padiyedath Gopalan, Akira Kawamura, Tadakatsu Takasaki, Hideo Amaguchi, and Gubash Azhikodan
Elsevier BV
Gubash Azhikodan and Katsuhide Yokoyama
Elsevier BV
Gubash Azhikodan and Katsuhide Yokoyama
Elsevier BV
Gubash Azhikodan and Katsuhide Yokoyama
Coastal Education and Research Foundation
ABSTRACT Azhikodan, G. and Yokoyama, K., 2015. Temporal and spatial variation of mixing and movement of suspended sediment in the macrotidal Chikugo River estuary. The effect of mixing on the movement of the estuarine turbidity maximum (ETM) was examined in the highly turbid Chikugo River estuary, Japan, in consideration of four significant issues: semidiurnal and semilunar tidal variations, spatial distribution, and synchronism of data acquisition. Vertical profiles of salinity and turbidity were measured for 2 weeks at 1 km intervals from the river mouth (0 km) to 17 km upstream, with a short duration for every cruise. Spring-neap transition and the spatial variation of mixing, and suspended sediment concentration (SSC) was found during the semilunar tidal cycle. The estuary gradually changed from a vertically well-mixed condition during spring tide to a stratified condition during the neap tide via a partially mixed condition during the intermediate half tides. The relationship between the flow ratio and the SSC showed that ETM growth was dominated by both tidal forcing and freshwater flow. SSC was high when the salinity was 0.5 practical salinity units (psu) in the upper estuary and 10 psu in the lower estuary. For the same mixing strength (MS), SSC in the lower estuary was greater than that in the upper estuary. Based on flow ratio, salinity, and MS, the occurrence of the ETM and its development at the macrotidal estuary was a consequence of three processes: bed-sediment erosion by seawater in the lower estuary, sediment transport in the estuarine channel by the tidal current and freshwater flow, and sediment accumulation at the salinity front in the upper estuary.
RECENT SCHOLAR PUBLICATIONS
MOST CITED SCHOLAR PUBLICATIONS
GRANT DETAILS
1. PI of the sponsored project entitled “Analysis of Morphodynamic Evolution in a Meandering Estuarine Channel in the Context of Climate Change”, Japan Society for the Promotion of Science (JSPS), 4,160,000 JPY, 04/2020-03/2024.
2. PI of the sponsored project entitled "Comparative study of hydrodynamic processes in large and small estuaries", Tokyo Metropolitan University Grant-in-Aid for Scientific Research Challenge Support (Basic Research - B), 2,000,000 JPY, 04/2024-03/2025.
3. Co-PI of the sponsored project entitled “Prevention of water pollution caused by the floating waste disposal from megacities in the context of global warming and COVID-19 lockdowns”, Tokyo Metropolitan Government (TMG), 45,000,000 JPY, 04/2022-03/2025. Co-investigators (Katsuhide Yokoyama (PI), Yoshiyuki Imamura, Masayuki Kawahigashi, Yasuhiro Arai, Hiroshi Sakai, Tetsuya Shintani, Hideo Amaguchi).
4. PI of the sponsored project entitled “International comparative study on hydrodynamic processes in Asian estuaries”, Tokyo Metropolitan University (Promotion of Internationalization), 800,000 JPY, 04/2023-03/2024.
5. PI of the sponsored project entitled “International comparative study on hydrodynamic processes in Asian estuaries”, Tokyo Metropolitan University (Promotion of Internationalization), 600,000 JPY, 04/2022-03/2023.