Mechanism of Gully-Head Retreat - A Study at Ganganir Danga, Paschim Medinipur, West Bengal

Twenty three gully heads were randomly selected from a representative gully basin at Ganganir Danga, Paschim Medinipore West Bengal for understanding mechanism of gully head retreat. The study was made during June to September, 2011. Height and slope of gully heads, width at top and base of the gully head were monitored. Geotechnical properties of soil like cohesion and angle of internal frication, bulk density were measured to estimate shear stress and shear strength at gully head. Linear retreat of the gully heads was monitored by pegging technique. Depths of tension cracks were measured at regular interval. The study shows that, gully heads retreated at different rates ranging from 13 cm to 121 cm depending on instability factors. Gully heads are few times steeper than angle of internal friction that introduces instability. Alcove structure and plunge pools, developed at the bottom of gully heads, lead to formation of overhanging slope. Near vertical and overhanging slope of considerable height develop tension cracks leading to mass failure and gully head retreat. Number of instability factors is operating at the gully heads and no linear relation can be established between these factors and gully erosion.Key words: Tension crack, Mass failure, Gully head retreat, Geotechnical properties

Assessment of wetland ecosystem health using the pressure-state-response (PSR) model: A case study of Mursidabad District of West Bengal (India)

© 2020 by the authors. Wetlands are essential for protein production, water sanctification, groundwater recharge, climate purification, nutrient cycling, decreasing floods and biodiversity preservation. The Mursidabad district in West Bengal (India) is situated in the floodplain of the Ganga-Padma and Bhagirathi rivers. The region is characterized by diverse types of wetlands; however, the wetlands are getting depredated day-by-day due to hydro-ecological changes, uncontrolled human activities and rapid urbanization. This study attempted to explore the health status of the wetland ecosystem in 2013 and 2020 at the block level in the Mursidabad district, using the pressure-state-response model. Based on wetland ecosystem health values, we categorized the health conditions and identified the blocks where the health conditions are poor. A total of seven Landsat ETM+ spaceborne satellite images in 2001, 2013 and 2020 were selected as the data sources. The statistical data included the population density and urbanization increase rate, for all administrative units, and were collected from the census data of India for 2001 and 2011. We picked nine ecosystem indicators for the incorporated assessment of wetland ecosystem health. The indicators were selected considering every block in the Mursidabad district and for the computation of the wetland ecosystem health index by using the analytical hierarchy processes method. This study determined that 26.92% of the blocks fell under the sick category in 2013, but increased to 30.77% in 2020, while the percentage of blocks in the very healthy category has decreased markedly from 11.54% to 3.85%. These blocks were affected by higher human pressure, such as population density, urbanization growth rate and road density, which resulted in the degradation of wetland health. The scientific protection and restoration techniques of these wetlands should be emphasized in these areas