Water2014, 6(8), 2501-2518; doi:10.3390/w6082501 - published 15 August 2014 Show/Hide Abstract
Abstract: The variation of river flow within a natural range plays an important role in promoting the social-ecological sustainability of a river basin. In order to determine the extent of the natural range of variation, this study assesses hydrologic flow thresholds for the Lower Ganges River Basin. The flow threshold was calculated using twenty-two “Range of Variability (RVA)” parameters. The impact of Farakka Dam on the Lower Ganges River flow was calculated by comparing threshold parameters for the pre-Farakka period (from 1934 to 1974) and the post-Farakka period (1975–2005). The results demonstrate that due to water diversion by the Farakka Dam, various threshold parameters, including the monthly mean of the dry season (December–May) and yearly minimum flows, have been altered significantly. The ecological consequences of such hydrologic alterations include the destruction of the breeding and raising grounds for a number of Gangetic species, the increase of salinity in the southwest coastal region of Bangladesh and a reduction of fish and agricultural diversity. The major findings in this paper have a number of policy-level implications to aid water sharing mechanisms and agreements between the government of Bangladesh and India. The methodological approach presented in this study is applicable to other river basins.
Water2014, 6(8), 2482-2500; doi:10.3390/w6082482 - published 15 August 2014 Show/Hide Abstract
Abstract: Lakes and wetlands provide valuable water resources. Wetland evapotranspiration (ET) is a key hydrologic component; however, the effects of lake fluctuation on wetland ET remain unclear. The Poyang Lake is the largest freshwater lake in China and experiences a dramatic fluctuation in water level and inundated area. This study used remote sensing data to estimate the wetland ET for Poyang Lake and to illustrate the distribution of wetland ET and its response to lake fluctuations. Our results showed that wetland ET was related to lake fluctuation both spatially and temporally. Within the same year, the difference between annual water evaporation (Ewater) and wetland ET (ETwetland) was primarily attributed to lake fluctuation through its effects on inundated area and exposure days. A 1% increase in inundated area would result in a 7.87 ± 1.13 mm a−1 reduction in annual Ewater-to-ETwetland differences, and a 10-day elongation of exposure could lead to an 11.1 ± 1.6 mm a−1 increase in annual Ewater-to-ETwetland differences, on average. Inter-annually, the Ewater-to-ETwetland differences were attributed to the combined effects of atmospheric and environmental variables and lake fluctuation. The lake fluctuation contributed 73% to the inter-annual ET difference, followed by relative humidity (19%), net radiation (5%), and wind speed (4%). Overall, lake fluctuation effectively regulates wetland ET, and its effect should receive careful consideration in hydrological and water resources studies under the current changing climate.
Water2014, 6(8), 2467-2481; doi:10.3390/w6082467 - published 15 August 2014 Show/Hide Abstract
Abstract: The mean annual recharge of Al-Khazir Gomal Basin was estimated as a basis for decision makers regarding the renewability and sustainability of groundwater. For this purpose, two approaches were used: hydrograph analysis and water table fluctuation (WTF). The long-term mean daily stream-flow records of Al-Khazir River (1969–1981) were used to estimate groundwater discharge by base-flow hydrograph separation and displacement recession curve methods. Four base-flow separation methods were used; one is the graphical separation method, and three are automated separation methods included in the web-based Hydrograph Analysis Tool. The annual recharge estimated by WTF was 111.6 mm/y, and the average annual recharge estimated by the four base-flow separation methods was 125.8 mm/y. Estimating recharge by the water table fluctuation method does not incorporate spatial variability contained in the whole watershed, because the specific yield did not represent the entire basin. However, the hydrograph analysis method can give a comprehensive estimation of the net integrated recharge for the entire watershed, which includes different recharge mechanisms. The displacement recession curve method deviates a lot (>30 mm/y) from the other methods, which indicates that this method may not be suitable to apply in such large watersheds.
Water2014, 6(8), 2449-2466; doi:10.3390/w6082449 - published 14 August 2014 Show/Hide Abstract
Abstract: Due to the special hydrographic and physiographic conditions in Taiwan, flooding is likely to occur in the middle and lower reaches of a plain whenever serious rainstorm events occurred. Note worthily, the loss of lives and property caused by flooding are always most considerable in a metropolitan area, and the densely distributed buildings would, not only increase the impervious area, but also decrease the water storage area. Furthermore, a large number of intensive buildings have changed the original land flow conditions, resulting in a beam shrinking flow and the additional form drag phenomenon, which makes the flooding phenomenon more serious. The main purpose of this research is to find the correlation between building coverage and the Manning’s coefficient n through a water flume model experiment. To probe into this issue, the Manning’s roughness adjustment is further divided into a part caused by the surface impedance and a part caused by the building impedance. Thus, building coverage can be added to the general computing grid to reflect the flooding situation with buildings. The two-dimensional inundation model, based on this research, was applied to Taichung City for an actual case simulation. The simulation result of Typhoon Kalmaegi showed that the presented model can obtain a more accurate flooding situation in urban area by considering the blockage effects of buildings and adjusting the surface roughness.
Water2014, 6(8), 2436-2448; doi:10.3390/w6082436 - published 13 August 2014 Show/Hide Abstract
Abstract: This study presents the potential of combining anaerobic grey water sludge treatment with black water in an up-flow anaerobic sludge blanket (UASB) reactor to improve energy recovery within source-separated sanitation concepts. Black water and the mixture of black water and grey water sludge were compared in terms of biochemical methane potential (BMP), UASB reactor performance, chemical oxygen demand (COD) mass balance and methanization. Grey water sludge treatment with black water increased the energy recovery by 23% in the UASB reactor compared to black water treatment. The increase in the energy recovery can cover the increased heat demand of the UASB reactor and the electricity demand of the grey water bioflocculation system with a surplus of 0.7 kWh/cap/y electricity and 14 MJ/cap/y heat. However, grey water sludge introduced more heavy metals in the excess sludge of the UASB reactor and might therefore hinder its soil application.
Water2014, 6(8), 2412-2435; doi:10.3390/w6082412 - published 12 August 2014 Show/Hide Abstract
Abstract: Predicting sediment yield is necessary for good land and water management in any river basin. However, sometimes, the sediment data is either not available or is sparse, which renders estimating sediment yield a daunting task. The present study investigates the factors influencing suspended sediment yield using the principal component analysis (PCA). Additionally, the regression relationships for estimating suspended sediment yield, based on the selected key factors from the PCA, are developed. The PCA shows six components of key factors that can explain at least up to 86.7% of the variation of all variables. The regression models show that basin size, channel network characteristics, land use, basin steepness and rainfall distribution are the key factors affecting sediment yield. The validation of regression relationships for estimating suspended sediment yield shows the error of estimation ranging from −55% to +315% and −59% to +259% for suspended sediment yield and for area-specific suspended sediment yield, respectively. The proposed relationships may be considered useful for predicting suspended sediment yield in ungauged basins of Northern Thailand that have geologic, climatic and hydrologic conditions similar to the study area.