The physically-based hydrodynamic model can simulate the water flow dynamics of a stream network against time varying boundary conditions that can be implemented for the case of Ichamati River. Such river models are often an important component of flood forecasting, tidal fluctuation system that forecasts river levels in flood prone regions of the middle stream of Ichamati river. The measurements of river bed depth/slope, water quality (river cross section), floodplain mapping and boundary condition flow are essential for the set up of a river model. But one can use proxy approaches relying mostly on remote sensing data from space platforms for the purpose. In this study, we set up the one dimensional river analysis system (RAS) model of the hydrologic engineering center (HEC) over the stream network of the Ichamati river basins. Good quality in situ measurements of river hydraulics (cross section, slope, flow) were available only for the upstream and middle stream flood prone region of the basin. The de-siltation of the stretch of Ichamati river under survey i.e. middle part showed impacts which were positive in ways more than one. The river velocity in the top strata is 0.3 m/s from model and the river regained its ecological flow. Also, the increased salinity of the river helped in cultivation of different species of fishes, which are socio economically relevant in the adjoining areas. Due to the increased capacity of the channel in the middle part possibility of flood has also decreased. The total volume of silt accumulated has been estimated 277,589.92 m3. The rate of sedimentation was then calculated and found to be 16,328.82 m3/month silt deposition during monsoon and 11,109 m3 silt deposition during non monsoon period. It may be concluded that out of 6 % annual silt deposition, 5 % silt deposition took place during the month between June and October and 1 % silt deposition during the month between November and May. Silt excavation along 20 km stretch of Ichamati river showed distinct rejuvenation of the river stretch. The program of silt excavation along other stretches of river Ichamati study area would certainly bring positive impact on the river ecology and environment. Ecological flow needs to be maintained in rivers in the upstream due to chocking the silt deposition. Ecological flow in Ichamati river is absent in many stretches of the river due to heavy silt deposition.

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Estimation of hydrodynamic pattern change of Ichamati River using HEC RAS model, West Bengal, India

The spatial mapping of flood menace extents is crucial for the effective and competent enactment of risk-lessening strategy. We focused on geographical pattern and variation in flood-affected villages in Bongaon sadar sub-division, West Bengal, India, during the period between 1996 and 2016. To appraise the indigenous smoothing and dissimilarity of flood-affected/non-affected villages, GIS-based Voronoi statistics were used. Inverse distance weighting (IDW) is used to interpolate and predict the pattern of flood-affected/non-affected zones across the sub-division. Moran’s I index statistics was considered to appraise spatial auto-correlation among the flood affected and non-affected villages. Getis-OrdGi*(d) statistics was employed to recognize the flood hotspot and cold spot areas within the study site. The higher magnitude of Moran’s I was calculated as 1999–2001, 2004, 2011, 2013, 2015, and 2016. The high Z score was recorded in 1996–1999, 2001–2003, 2011, 2013, and 2014 indicated a spatial clustering of flood-affected villages. The predictive map derived through IDW showed that 7.76% (64.59 km2) area comes under very high threat zones of flood, followed by 16.27% as high risk, 24.49% as medium risk, 23.97% as low risk, and 27.51% as very low risk. This study determines the solicitation of GIS-based prophecy for the impost of revelation mapping, so as to define the latitudinal extent and frequency of areas where most affected villages are located and potential risk areas.

Assessment of flood hotspot at a village level using GIS-based spatial statistical techniques

The study was carried out to assess some physico-chemical water quality parameters and pollution scenario of the Ichamati river. Water samples were collected from nine different selected stations at origin of the river Majhdia to Taki end portion of the Ichamati river during the pre-monsoon, monsoon and post-monsoon periods. A seasonal variation in these parameters was observed throughout the study period and monthly comparisons were made as monsoon, pre-monsoon and post-monsoon. The results of the present investigation was undertaken to asses seasonal and spatial variation in pH, Electrical Conductivity, Turbidity, Salinity, Chlorophyll, DO and Water Temperature are compared with literature values and investigation reveals that there is a fluctuation in the physico-chemical characters of the water, this will be due to ebb and flow and change in the temperature and salinity as season changes. All parameters except turbidity and conductivity have shown high concentration in pre-monsoon-monsoon and post-monsoon, overall the concentration of water quality parameters were governed by flushing of rainfall, river water flow, sea water intrusion runoff from agricultural fields. Turbidity content in the study area was higher because the Ichamati river is dynamic zone of lower stretch. This river only depends on upper stretch rainy season rain water; no tidal fluctuation but lower stretch of the river is high tidal fluctuation the salinity is must high then upper stretch the value of Salinity 3–8.5 ppm that the parallely fluctuation the huge amount of sediment continuing; the turbidity is very high 600–700 NTU.

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Water quality modeling for seasonal fluctuation of Ichamati river, West Bengal, India

Evolution of river course and morphometric features of the River Ganga: A case study of up and downstream of Farakka Barrage

Since the period of human civilization, the hydrological and morphological characteristics of most of the rivers have been intensively modified by human interferences. In this context, the Ichamati River is one of the worst affected distributary channels flowing on the lower Gangetic delta of South Bengal. This tidally active river is streaming on the most densely inhabited district (North 24 Parganas) of West Bengal. The river is gradually decaying over time due to direct and indirect human activities on and along the river. Therefore, the prime aim of this research study is to explain the temporal change of the channel behaviour, especially fluvio-morphological characteristics of the river during 1976–2016. The present study also highlights location-specific causal factors liable for the downstream modification of the channel behaviour. In this research study, channel migration, erosion rate, bank vulnerability zone and channel planform pattern have been assessed using Landsat images of 1976, 1996 and 2016 in remote sensing and GIS environment. Besides, an intensive field survey was conducted for cross-sectional survey of the river. Primary data were gathered from brick kilns through a questionnaire survey for the estimation of sediment extraction rate from the river to prepare the sediment-water budget of the river. This study reveals that the morphological characteristics of Ichamati River have been modified at the human–nature interface and continuous siltation causes gradual upliftment of the riverbed. The channel is gradually narrowing and decaying over time. This study is helpful to understand the current status of the river and helps river scientists for its restoration as well as management planning.

Impact of human intervention on assessing downstream channel behaviour of Ichamati River on the lower Gangetic Plain of West Bengal, India

River banks are multifaceted earth-forms where different geomorphic processes act together in a complex manner. River bank erosion is an episodic event by which an unstable bank tries to reach into a stable one. This is very common in deltaic meandering river systems. The River Ichamati, located in the eastern part of the Ganga delta region, is susceptible to severe bank erosion. This is because of its diurnal and seasonal fluctuation in the tide-dominated discharge, which is favoured by its channel geometry and local land use. The present paper is based on filed level observations and measurements followed by analysis with reference to theoretical perspectives of channel morphometry as provided by renowned scholars in the field. A set of relevant morphodynamic variables like rainfall, discharge, groundwater, geology and soil, and also human factors have been considered for understanding the nature of river bank erosion. Published by IJSS Indian Journal of Spatial Science EISSN: 2249 – 4316 ISSN: 2249 – 3921 journal homepage: www.indiansss.org Indian Journal of Spatial Science Vol 3.0 No. 2 Winter Issue 2012 pp35 43

West Bengal

Papers

Morphodynamic Setting and Nature of Bank Erosion of the Ichamati River in Swarupnagar and Baduria Blocks, 24 Parganasz(N), West Bengal