Browsing by Author "Dodamani, B M."

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Characterization Of Historical and Future Hydrometeorological Droughts in an Indian Tropical River Basin
(National Institute of Technology Karnataka, Surathkal, 2020) Pathak, Abhishek A.; Dodamani, B M.
Drought is acknowledged as a significant natural disaster which leads to food, fodder, and water shortages along with destruction of vital ecological system. Drought is a transient recurring sinister disaster, which originates from the lack of precipitation and further creeps into different subdivisions of hydrological cycle causing adverse effects on agricultural and its allied sector. Combination of these leads to economic losses and several damage to living organisms. Identifying and quantifying drought characteristics of a region is must to understand the behavior of drought and its profound impacts on society, economy, and environment. Along with the historical knowledge, comprehensive overview of future drought projections is a vital step in ensuring future water and food security. The present study focuses on characterizing different hydrometeorological droughts in the historical and future climate of an agrarian Indian river basin. The specific objectives of the study are 1) To investigate annual and seasonal trends of hydro meteorological variables, over the study area. 2) Assessment and comparison of Meteorological, Hydrological and Agricultural drought characteristics with multiple indices 3) To explore the applicability of copulas theory for joint modeling of drought characteristics 4) Characterization of future hydro-climatic droughts. The study was implemented in the Ghataprabha river basin, being one among the potential lands for agriculture in the basin of river Krishna. Firstly, the basin has been categorized in to humid, sub humid and semiarid region based on Aridity Index. Similarly, groundwater well of the study area are grouped in to different clusters using hierarchical and non-hierarchical clustering methods The annual and seasonal trend analysis of different hydrometeorological variables are carried out using Mann-Kendall trend test and the magnitude of the trend was estimated using the Sen’s Slope Estimator. A non-significant decreasing trends in both rainfall and rainy days was observed in semiarid region during monsoon period. Significant increasing trend in mean temperature was observed for all the stations and for all the seasons with the average magnitude of 0.2⁰ C per decade. Along with the mean temperature, annual andseasonal PET trends were also increasing for all the stations but are significant only in semiarid region with the average increase of 3.5mm per decade. The trends in annual streamflow of the basin are decreasing with magnitude of 574.25 cumecs/year, whereas, no significant trends were observed in the reservoir levels. The trend analysis of the groundwater levels of different clusters, revealed that annual water level in the 81% of the wells of cluster 2 and 47% of the total wells of the study area are significantly declining. The hydrometeorological droughts assessment with different indices portrayed significant number of droughts in the past. The RDI and SPI are behaving similarly in all the stations whereas, significant discrepancies was observed between SPI/RDI and SPEI. The hydrological drought assessed with SDI followed similar pattern with SRSI whereas it showed significant divergence with meteorological droughts. Similarly, Agricultural drought derived through VCI followed similar pattern of SPI-6 in comparison with SPI-3. A teleconnection between meteorological drought and groundwater drought was observed along with the crucial role of underlying hydrogeological characteristics. Joint modelling of hydrometeorological drought characteristics and regional bivariate frequency analysis was carried out by employing Archimedean copula. An attempt has also been made to characterize drought in multivariate perspective by developing Standardized Hydro Meteorological drought Index. From the results of bivariate frequency analysis of meteorological drought, it was observed that, droughts of high severity with prolonged duration are frequent in semiarid region compared to humid and sub-humid regions. The joint probability of hydrological drought conveyed drought of smaller duration or severity are more prominent in the basin whereas joint return periods of groundwater drought is high in the well of cluster 2. The developed SHMI considers combined effects of precipitation and streamflow to picturize a near realistic drought scenario of the basin. The future hydrometeorological drought characteristics were assessed by different RCMs. The different bias correction methods were applied to rainfall and temperature to raw RCMs and observed that CNRM-CM5 with LS bias correction method performed better for correcting the rainfall and VS is proved to be superior for correcting the temperature projections. The trend analysis carried out for the future hydrometeorological variable showed significant decreasing trends in annual and post monsoon season whereas temperature trend is increasing significantly with the rise of 0.150 C per decade. The future hydro-meteorological drought characteristics revealed that the basin will experience more number of droughts compared to the past and it can be attributed to decreasing rainfall trend and significant rise in temperature of the basin. In this study, an attempt has been made to characterize future and historical hydrometeorological droughts comprehensively. The outcome of the study will be helpful to design proactive drought mitigation and preparedness strategies for upcoming drought and it also provides a framework to evaluate the drought risks at other parts of the world.
Shoreline Dynamics In Response To River Sediment: A Case Study
(National Institute of Technology Karnataka, Surathkal, 2020) Yadav, Arunkumar.; Dodamani, B M.; Dwarakish, G S.
The coastal zone of Karwar is acquiring increasing importance due to its rich ocean resources and favorable conditions for the development of port-based industries, defense activity, tourism, fisheries, and small scale industries. Rivers and its networks are the major sources of the sediments, which supplies to the coast. These sediments are responsible for beach nourishment and shoreline configuration. The present study is carried out with a view to study the long-term shoreline configuration with the response to pre-construction dam and post-construction of the dam, to study the seasonal variation on shoreline configuration, to investigate the change in Kali estuary to assess the impact of the dam on sediment yield, To understand the sediment dynamics of beach face sand using granulometric method and To quantify the seasonal coastal process in terms of beach sand volume. These objectives are addressed using various conventional data, related tools, and freely available satellite data. Kali river basin, Aghanashini river basin, Karwar coast and Aghanashini coast along the west coast of India is the study area. There are five dams constructed across the Kali river basin for hydel power purposes. The presence of these reservoirs regulates stream flow and thus sediment load in the basin. However, the free flow of water across the catchment of the Aghanashini river leads to the unobstructed or natural passage of sediments and sediment budget to the downstream and the river mouth, as the catchment is not disturbed by the reservoir. Survey of India toposheet was used to prepare the base map. A conceptual, continuoustime and semi-distributed, SWAT2012 (Soil and Water Assessment Tool) model was selected for the sediment yield analysis. Dam location and dam discharge data were one of the major inputs for the model to estimate the sediment yield. Simulated and observed values of runoff are compared, and calibration and validation were done for the basins using SWAT CUP. The long-term shoreline configuration was carried out using LANDSAT satellite products only. The predominant direction of sediment transport was determined by drawing sediment trend matrices based on the statisticalviii parameters of beach face sediments. To understand the change in Kali estuary a portion of Devabag beach, satellite data were used for the duration from 1975 to 2018. The Total Station survey was carried for Ravindranath Tagore beach and Devabagh beach of Karwar coast, including a seasonal wise profile survey and cross-section survey during 2017. Based on the present analysis of sediment yield, it is concluded that the Sediment yield obtained at the catchment outlet was 1.39t/ha/year and 4.58t/ha/year for the Kali river and Aghanasini river basins respectively. It was observed that the decline in sediment load in the Kali river basin compared to the Aghanashini river basin indicates that the influence of reservoir operation on streamflow and sediment yield. The analysis to study the long-term shoreline configuration with the response to the pre-construction dam and post-construction of the dam, shows that shoreline of the Karwar coast was having accretion and later, it is turned in to erosion zone due to postconstruction of the dam. It shows the importance of natural river flow. Shoreline change analysis on the Aghanashini coast shows the accretion zone due to the natural flow of the Aghanashini river to the coast. The study estuary change shows that for the period of 1975 to 2018 northern part of the estuary has lost area and construction of seawall was revealed from ground truth data. Beach profile studies by total station on Ravindranath Tagore beach reveals that beach profile changes according to the season. The volume of sand is decreased during the pre-monsoon season and increased during the post-monsoon season. The accuracy of all the results can be increased by an increase in a number of inputs in the case of SWAT tool, the accuracy of results obtained from the satellite can be increased by higher resolution data. From the study, it is concluded that the river and its network are the major sources for the sediment supply to the coast. Sediment is one of the major factors for beach nourishment. Dam influences the flow of the river and its network and reduces sediment supply to the coast. A natural flow of the river and natural supply of river sediment enhances the beach nourishment and maintains the equilibrium of sediment budget to the coast.