Contribution of offshore islands in the prediction of water levels due to tide�Csurge interaction for the coastal region of Bangladesh

In this study, a doubly nested tide?Csurge interaction model was established for the coastal region of Bangladesh. A fine grid model, capable of incorporating all major offshore islands, was nested into a coarse grid model extending up to 15°N latitude of the Bay of Bengal. To take into account the thickly populated small and big islands between Barisal and Chittagong and the extreme bending of the coastline accurately, a very fine grid model for this region was again nested into the fine grid model. Along the northeast corner of this very fine grid model, the Meghna River discharge was taken into account. The boundaries of the coast and islands were approximated through proper stair step, and the model equations were solved by semi?Cimplicit finite difference technique using staggered grid. Appropriate tidal regime over the model domain was generated by forcing the sea level to be oscillatory with the constituent M2 along the southern open boundary of the coarse grid model omitting wind stress. This previously generated tidal regime was introduced as the initial state of the sea for nonlinear tide?Csurge interaction phenomenon. The model was applied to estimate water levels along the coastal region of Bangladesh due to the interaction of tide and surge associated with the storm April 1991, and the results were found to be in a reasonable agreement with those observed. The model was used to investigate the influence of offshore islands on water levels and water levels were found to be significantly influenced by offshore islands.     

Clay mineralogy of the pleistocene soil horizon in Barind Tract, Bangladesh

Pleistocene red soil horizons were exposed in different areas of the Barind Tract in north-west Bangladesh. X-ray diffractions of twenty seven samples from different depths of these soil horizons revealed that the soil horizons consisted of kaolinite, illite and chrysotile with significant amount of opal-CT. Samples from Maddhapara, Bogra, and Nachole contain kaolinite, illite, quartz and opal-CT, and the samples from Kantabari contain chrysotile instead of kaolinite. Clay mineral compositions of different soil horizons indicated two different types of clay assemblages, viz. (a) illitekaolinite and (b) illite-chrysotile. In the village of Kantabari, illite-chrysotile clay mineral assemblage indicate that soil horizons were formed under low temperatures with alkaline and reducing conditions. However, other soil horizons of illite-kaolinite clay mineral assemblage indicate that soils were possibly formed under humid, temperate and welldrained conditions. These two soil horizons were formed under different geochemical, geomorphological and climatic conditions from different parent materials. Scanning Electron Microscopy photographs showing the presence of glass shards and no opal-A were found using XRD, suggesting that the opal-A might not be a precursor to opal-CT in the red soil horizon of the study area. This opal-CT along with the general lack of fossils and presence of glass shards was indicative of a volcanogenic rather than biogenic origin for the Opal-CT in the study area, and X-ray fluorescence data reveals higher percentages of silica which is comparable to the Toba Ash of Toba Caldera, Indonesia of about 75,000 B.P.     

Geoelectrical resistivity survey for the evaluation of hydrogeological condition of Bagerhat Sadar and the adjacent areas, Bangladesh

This study has been conducted to find out the aquifer characteristics of Bagerhat Sadar and adjacent areas in Bangladesh using geoelectrical resistivity method and borehole logs. The interpretation of resistivity soundings (14 nos.) shows that the sub-surface lithological sequence can be divided into four geoelectric units. The deepest geoelectric unit (with resistivity from 8 Ohm-m to 18 Ohm-m) represents the deep aquifer with usually fresh water. Resistivity values of 12 ?m or more for this unit may indicate formation water as acceptable for coastal people. In the study area, the shallow aquifer inferred is not suitable for groundwater development.     

Groundwater arsenic contamination in Ganga–Meghna–Brahmaputra plain, its health effects and an approach for mitigation

The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km²; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources.     

Societal application of geophysics as an aid to a rescue operation at Jaipur

Geophysical techniques are normally employed to explore the subsurface and determine the anomalies but they are always much larger in dimension. However, a very precise measurement was needed to pin point a misaligned horizontal tunnel made at 47 m depth to intercept an old bore well and rescue a four year child fallen accidently on 9^th November at Jagatpura village in Jaipur, India. Due to the greater depth and presence of iron casing, electric power, etc., no equipment could work to determine the orientation of the tunnel that has lost its direction. The dimension of the site and many other constrains didn’t allow conventional geophysical methods to be used. An innovative method was then designed and successfully applied, which determined 1.92 m deviation of the tunnel end point to the east from the old bore well. The digging was redirected accordingly and the bore well was intercepted. This paper describes the theoretical background, forward simulations and the field experiment of the newly designed geophysical method.     

Assessing the resilience of Delhi to climate-related disasters: a comprehensive approach

The study addresses disaster risks in Delhi through a resilience approach. It utilizes the Climate Disaster Resilience Index (CDRI) tool, which assesses disaster resilience from five dimensions: physical, social, economic, institutional, and natural. Each dimension comprises 5 parameters, and each parameter consists of 5 variables. The study is carried out in the nine revenue districts of Delhi and reveals that East Delhi is least resilient and New Delhi is most resilient. The CDRI analysis in East Delhi points out the urgent need to focus on key parameters such as housing and land use, population, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. On the other hand, New Delhi is the most resilient due to all five dimensions, where most significant parameters responsible for its high resilience are housing and land use, population, income, employment, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. In addition, the overall results of all nine districts show an inverse relationship between resilience score and population density. For example, districts with higher population density show low resilience and vice versa. Moreover, districts located on hazard-prone areas show low resilience. For example, East Delhi and North East Delhi scored low resilience because they both are situated on the Yamuna flood catchment areas. The study further develops key suggestions that are required to address disaster risk in all nine districts of Delhi and discusses future implications of CDRI to address city??s vulnerability. The approach??s distinctness is reflected through its consideration of micro-level diversities and presents some implications to resilience.     

Hydrological behaviour of a drained agricultural peat catchment in the tropics. 1: Rainfall,runoff and water table relationships

Abstract

Hydrological data of a drained tropical peat catchment have been analysed through conventional quantitative hydrological approaches to characterize its hydrological behaviours and changes due to continuous drainage for a long period. The results show that the hydrology of the catchment is extremely dynamic and the catchment is flashy in nature. A decreasing trend in peak flow amount and an increasing trend in baseflow amount was observed in the catchment, indicating that continuous drainage has reduced the risk of both flooding and water scarcity in the catchment. Correlation analysis among rainfall, runoff and groundwater table reveals that saturation excess-near surface flow is the dominant mechanism responsible for rapid runoff generation in the catchment. Therefore, any physical alterations or disturbances to the upper part of the peat profile would definitely affect the overall hydrological behaviour of the peat catchment.

Editor Z.W. Kundzewicz; Associate editor D. Hughes

Citation Katimon, A., Shahid, S., Abd Wahab, A.K., and Ali, M.H., 2013. Hydrological behaviour of a drained agricultural peat catchment in the tropics. Part 1: Rainfall, runoff and water table relationships. Hydrological Sciences Journal, 58 (6), 1297–1309.     

Seasonal flooding in Bangladesh – variability and predictability

At present, Bangladesh has a flood forecasting lead time of only 3 days or so. There is demand for a forecasting lead time of a month to a season. The primary objectives of this paper are to study the variability and predictability of seasonal flooding in Bangladesh, as revealed by large‐scale predictors of the climate across the watersheds. To explore the source of predictability, accessible Bangladesh hydrological indicators are related to large‐scale oceanic variability and to large‐scale atmospheric circulation patterns predicted by general circulation models (GCMs). Correlation analyses between the flood‐affected area (FAA) for July–September and tropical sea‐surface temperature (SST) indicate connections to tropical Pacific and Indian Ocean SSTs, at a short lead time of a month or so. These are related to El Niño–southern oscillation (ENSO). Correlations between the SSTs of the preceding October–December and the July–September FAA are weaker but notable. Forecasts of the FAA using the leading principal components (PCs) of SST were made, which provided good skill with a lead time of a month or so. The streamflows and rainfall observed in Bangladesh have been added to these prediction models. Finally, the SST PCs were replaced with PCs of GCM prediction fields (precipitation). The prediction models at short lead time that were constructed for FAA were of generally similar levels of skill to that for SST. This is encouraging, as it suggests that linkages with SST can be successfully recovered in a physical model of the climate system in Bangladesh. This study concludes that seasonal flood prediction in Bangladesh is possible from the unusually warm or cold SST in parts of the tropics. This predictability can be enhanced with the information achievable from monitoring the downstream streamflows (which are generated mainly from upstream rainfall conditions) in advance of the flooding season. Finally, this study recommends formalizing a regional cooperation among the countries in the principal co‐basin areas of the Ganges–Brahmaputra–Meghna to achieve this goal. Copyright © 2006 John Wiley & Sons, Ltd.