Journal Articles
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Item Surfzone Wave Characteristics during Flood Tide on the Central West Coast of India(World Scientific Publishing Co. Pte Ltd michael.wagreich@univie.ac.at, 2015) Seelam, J.K.; Jishad, M.; Yadhunath, E.M.; C, C.; Gowthaman, R.; Pednekar, P.S.; Luis, R.; Mehra, P.Surfzone wave characteristics, measured using a wave and tide gauge (WTG) during a flood tide, were studied at three different beaches having different nearshore slopes. The spectral wave characteristics viz., wave-height and mean wave period were estimated considering different sample sizes. Inter-comparisons of wave climate between each of three beaches for a similar tide level are presented. The wave-height and mean wave period values obtained from the wave analysis for each of the record using waves by wave method show that surfzone wave-height increased with time during a flood tide and the mean wave period decreased with time up to mid tide and then increased during the rest of the measurement period at Keri and Miramar beaches. At Candolim, the reversing trend of mean wave period increase is observed to occur much before reaching the mid tide level. The surfzone waves during a flood tide indicated that the wave-heights increased with time while the mean wave period showed a decreasing trend in general. The variation of breaker index showed a decreasing trend from low tide to high tide ranging between 0.45 and 0.23. The surf similarity parameter estimated corroborates with the visual observations. © 2015 World Scientific Publishing Company.Item Hierarchical clustering approaches for flood assessment using multi-sensor satellite images(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) Senthilnath, J.; Shreyas, P.B.; Rajendra, R.; Sundaram, S.; Kulkarni, S.; Benediktsson, J.A.In this paper, hierarchical clustering methods are used on synthetic aperture radar (SAR) (during the flood) and LISS-III (before the flood) data to analyse damage caused by floods. The flooded and non-flooded regions are extracted from the SAR image while different land cover regions are extracted from the LISS-III image. Initially, the Bayesian information criterion (BIC) is implemented to obtain the constraints for the number of clusters. The optimal cluster centres are then computed using hierarchical clustering approach (i.e. cluster splitting and merging techniques). The cluster splitting techniques such as Iterative Self-Organising Data Technique (ISODATA), Mean Shift Clustering (MSC), Niche Genetic Algorithm (NGA) and Niche Particle Swarm Optimisation (NPSO) were applied on SAR and LISS-III data. The cluster centres obtained from these algorithms are used to group similar data points by using merging method into their respective classes. Further, the results obtained for each method are overlaid to analyse the individual land cover region that is affected by floods. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.Item Laboratory investigations of wave attenuation by simulated vegetation of varying densities(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) John, B.M.; Shirlal, K.G.; Rao, S.Coastal communities across the world are facing the need to adapt to rising sea levels, an increase in the frequency of natural hazards like storm surges, cyclones, tsunamis, and an increase in beach erosion. This present-day scenario calls for a sustainable, environment-friendly, and cost efficient solution for coastal protection. Under these circumstances, the role of vegetation in providing ecosystem services to coastal populations is becoming increasingly prominent. This work presents the results of an experimental study carried out with simulated rigid submerged and emergent vegetation meadows of varying plant densities in a wave flume 50 m long, 0.71 m wide and 1.1 m deep. The material used for modeling the vegetation is nylon. The tests are carried out with regular waves for water depths of 0.40 and 0.45 m, and wave periods 1.4–2 s at an interval of 0.2 s. Five different wave heights ranging from 0.08 to 0.16 m at an interval of 0.02 m are generated. Measurements of wave heights at different locations indicate an exponential decay in wave height along the vegetation meadow which leads to wave attenuation and confirms that vegetation can be a viable option for coastal protection. © 2017, © 2017 Indian Society for Hydraulics.Item Copula-Based Frequency and Coincidence Risk Analysis of Floods in Tropical-Seasonal Rivers(American Society of Civil Engineers (ASCE), 2021) Muthuvel, D.; Mahesha, A.The conventional method of univariate flood frequency analysis based solely on peak flow (Q) overlooks the influence of other characteristic flood variables, such as the accumulated volume (V) of the flood and the duration (D) of flood events. A copula-based multivariate model that represents the joint behavior of these dependent flood variables could aid in computing joint return periods of flood events in tropical, seasonal rivers of India. In connection with the potential locations of high flood risk among west-flowing rivers, multivariate flood frequency analysis was performed on the Bharatapuzha, Periyar, and Chaliyar Rivers of the state of Kerala, India. A comparison of univariate return periods with multivariate return periods reveals that the intersection of flood variables corresponding to a 20-year univariate return period yields a trivariate return period of 91 years at Bharatapuzha and 144 years at Periyar and Chaliyar. The return period by the union of such flood variables is 10 years. The choice of flood variables and their combination depend on the problem at hand. Additionally, basinwise confluence flood frequency models are built with the peak flow at each stream as the random variables show their spatial interdependencies using conditional probabilities and return periods. The copula-based flood coincidence risk model captures the temporal aspect of the co-occurrence of flood peaks in a basin's streams. The co-occurrence of annual flood peaks between the stream pairs of the Bharatapuzha, Periyar, and Muvathapuzha basins is the highest toward the end of July with probabilities of approximately 2.2×10-4 (at the Kumbidi and Mankara stations), 3×10-4, and 1×10-3, respectively. A trio of copula-based multivariate flood frequency, confluence flood frequency, and flood coincidence risk models could be used to design safe and economic hydrologic infrastructure. © 2021 American Society of Civil Engineers.Item Flood susceptibility modeling based on morphometric parameters in Upper Awash River basin, Ethiopia using geospatial techniques(Springer Science and Business Media Deutschland GmbH, 2022) Tola, S.Y.; Shetty, A.The hydrological response, such as direct surface runoff, is linked to the characteristics of the watershed. Evaluation and knowledge of geomorphometric parameters in relation to floods and the identification of specific flood-prone sites in the basin are critical for mitigation measures. Despite advancements in geospatial tools, the utilization of geospatial data in many river basins prone to flooding and erosion is minimal. Morphometric aspects: linear, areal, and relief analysis of the Upper Awash River basin were performed in four subbasins to better understand the hydrological signatures behaviour. The topographic wetness index (TWI) and topographic position index (TPI) were also used to determine the extent of inundation. The aggregated parameters revealed that SB-1 is highly susceptible to flooding, SB-3 and SB-4 are moderately susceptible, and SB-2 is low. However, based on the geomorphologic instantaneous unit hydrograph, SB-2 and SB-4 demonstrated rapid response and a high flood generating potential. The degree of susceptibility was determined by incorporating the TWI and TPI through overlay analysis. Overall, the Upper Awash River basin accounts for 23%, 42%, and 36% of the total bay has been classified as high, medium, and low flood-prone, respectively. According to the study, topographic indices (TWI and TPI) are critical attributes that show specific flood potential areas and inundation extents in addition to morphometric parameter-based flood susceptibility analysis. The analysis provided input for holistic water and soil erosion management by providing the hydrological behaviour of the stream, geomorphological characteristics, basin responsiveness, and stream power to flood potential and denudation characteristics in the subbasins. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Effect of Flash Flood and Weather Changes on Unconfined Compressive Strength of Cement- and Fly Ash-Stabilized Black Cotton Soil Used as Road Materials(Springer, 2023) Chethan, B.A.; Ravi Shankar, A.U.Stabilized soil naturally undergoes variation in moisture content and temperature during seasonal weather changes. In this investigation, the influence of these weather changes on unconfined compressive strength (UCS) of black cotton (BC) soil stabilized with ordinary Portland cement (43 grade) and class F fly ash was studied. Cement dosage was varied from 3 to 10%, along with different combined dosages of (cement + fly ash) (where fly ash < 32%) for stabilizing various mixes. The UCS specimens were cured for 0 (immediately after preparation) 3, 7, 28, 60, and 90 days in a desiccator and subsequently submerged for 24 h in water to ensure saturation. The flash flood effect was evaluated in terms of strength reduction by correlating UCS of saturated specimens (UCSs) with UCS of desiccator-cured specimens. The stabilized materials’ resistance to wetting–drying (WD), freezing–thawing (FT) durability tests and subsequent UCS retained over time were determined. The UCS values increased substantially at higher cement and fly ash contents and with the curing period, whereas a notable reduction in UCSs values was observed for saturated samples. However, the samples with high cement and fly ash contents exhibited low moisture susceptibility with lesser strength reduction. The UCS and UCSs values are linearly correlated with R2 values > 0.9. All the specimens were intact with improved volume stability at higher cement and fly ash dosages during saturation and drying. Mixes with high cement and fly ash dosages shown improved resistance to WD cycles, whereas at a low dosage, most of the mixes failed during the second wetting cycle due to a drastic absorption of water after the first drying cycle. All FT specimens were intact with considerable strength retained after 12 cycles exhibiting a minimal mass loss. The formation of hydration products has justified the strength gain as observed from scanning electron microscope (SEM) images, energy dispersive X-Ray analysis (EDAX), and X-ray diffraction (XRD) plots. © 2021, The Author(s), under exclusive licence to Chinese Society of Pavement Engineering.Item Dual attention guided deep encoder-decoder network for change analysis in land use/land cover for Dakshina Kannada District, Karnataka, India(Springer Science and Business Media Deutschland GmbH, 2023) Naik, N.; Chandrasekaran, K.; Sundaram, V.M.; Prabhavathy, P.The Earth is frequently changed by natural occurrences and human actions that have threatened our environment to a certain extent. Therefore, accurate and timely monitoring of transformations at the surface of the Earth is crucial for precisely facing their harmful effects and consequences. This paper aims to perform a change detection (CD) analysis and assessment of the Dakshina Kannada region, being one of the coastal districts of Karnataka, India. The spatial and temporal variations in land use and land cover (LULC) are being monitored and examined from the data received as LULC maps from the National Remote Sensing Agency, Indian Space Research Organization, India. The time-series data from advanced wide-field sensor (AWiFS) Resourcesat2 satellite as LULC maps (1:250k) are analyzed using a deep learning approach with an encoder–decoder architecture with dual-attention modules for the change analysis. The model provides an overall accuracy and meanIOU(intersection over union) of 94.11% and 74.1%. The LULC maps from 2005 to 2018 (13 years) are utilized to decide the variations in the LULC, including urban development, agricultural variations, vegetation dynamics, forest areas, barren land, littoral swamp, and water bodies, current fallow, etc. The multiclass area-wise changes in terms of percentage show a decline in most LULC classes, which raises a point of concern for the environmental safety of the considered area, which is highly exposed to coastal flooding due to increased urbanization. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Runoff retention characteristics of forested and deforested catchments: an analysis using a spatially lumped model(Taylor and Francis Ltd., 2023) Sreejith, K.S.; Varaparambil, P.This study investigates the runoff characteristics of forested and deforested catchments using the Soil Conservation Services–curve number (SCS-CN) model from the perspective of the Kerala floods in 2018 and 2019. The forested and deforested catchments chosen for the study are the drainage area of the Kakkayam Dam and Punoor River respectively of Kozhikode District, Kerala. The study used input variables such as rainfall, land use/land cover (LU/LC) and soil data to estimate the runoff depth from these catchments during the floods in 2018 and 2019 using the SCS-CN model. Here, the hydrological response of these catchments is examined by different scenarios of rainfall and LU/LC change. It is found that the deforested catchment generates more runoff compared to the forested catchment under identical rainfall conditions. However, the study shows that, the runoff depth in the deforested catchment is expected to reduce if certain portion of plantations and barren land converts into the forest cover. The ability of runoff retention of the forested catchment is expected to lose if the forest-covered land is utilized for the plantation activities. © 2023 Indian Society for Hydraulics.Item Quantification of change in land cover and rainfall variability impact on flood hydrology using a hydrological model in the Ethiopian river basin(Springer Science and Business Media Deutschland GmbH, 2023) Tola, S.Y.; Shetty, A.Changes in land cover and climate are the dominant factors that significantly impact the hydrological process. However, the impact on flood response behaviour varies spatiotemporally. This study quantitatively assessed the effects of individual and coupled changes in land cover and climate on peak and high flows in the upstream and downstream parts of the Upper Awash River basin. Two time periods were chosen for comparison: baseline (1988–2001) and evaluation (2002–2015). The Soil Water and Assessment Tool (SWAT) was used to estimate the impact of these changes. The model satisfactorily simulated daily and extreme flows. The evaluation of annual maximal discharge variability between 1985 and 2015 at upstream and downstream stations showed significant positive and insignificant negative trends, respectively. However, the sub-basin’s annual wet day rainfall (PRCPTOT) showed a downward trend. The annual maximal discharge–PRCPTOT relationship was significant during the baseline but later had no significance. The SWAT model showed that the main factor that affected the changes in upstream flow was the land cover change, increasing peak and high flow by 38.69% and 11.95%, respectively, compared to the baseline period. However, combined changes resulted in downstream peak and high flow reductions of 19.55% and 50.33%, respectively. As a result, changes in flood characteristics are strong functions of land cover, especially in the upstream sub-basin and land cover and climate in the downstream sub-basin. Overall, the impact of changes in the cropland-dominated basin was noticeably different. The study assists water resource managers in understanding the causes of hydrological dynamics and developing mitigation strategies. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Recent Changes in Hydrometeorological Extremes in the Bilate River Basin of Rift Valley, Ethiopia(American Society of Civil Engineers (ASCE), 2023) Lambe, B.T.; Kundapura, S.The hydroclimatic extremes such as floods and droughts have been causing damage and losses with rising frequency than ever before. The human-induced and internal climate variability create extreme events and local hydrometeorological changes influencing climate-sensitive sectors. This research is aimed at analyzing the recent changes in the hydrometeorological extremes using indices over the Bilate basin in Ethiopia. Mann-Kendall and Sen's slope estimator were used to examine changes in hydrometeorological extreme indices. The rainy days' rate of change falls between þ10.64 mm in the downstream to −10.67 mm in the upstream north. The wet day rainfall and heavy rainfall day indices were stronger in the basin's southwest, implying more likely flood events. The consecutive dry days show a rising tendency with more variability, while the consecutive wet days show no trend with less variability. The change point analysis revealed inconsistencies for the majority of the extreme indices. The stations' average warmest nights and days significantly increased at a rate of 0.0358°C and 0.0320°C per annum, respectively. The coldest nights in most of the stations show a significant and negligible rise in the basin while on the coldest days more than half of the stations declining. The peak flow in the annual and seasonal time series shows a rising trend and a dominant rise in most low flow indices, which possibly flashes downstream flooding. The global and local climate anomalies revealed a weak correlation, but with overlap of wet and drought years. Basin water resource plans may benefit from identified overlap cross of threshold years for improved flood control and drought monitoring. © 2018 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.