Assessment of spatial–temporal patterns of surface and ground water qualities and factors influencing management strategy of groundwater system in an urban river corridor of Nepal
Introduction
The Bagmati river Corridor is the principal resource base of municipal water in the Kathmandu valley (Fig. 1), providing almost 92% of the wet season and 60% of the dry season water supply (CBS, 1998). However, the increasing demand for water as a result of an increasing population has placed pressure on the water quality. Moreover, both the surface and groundwater levels have been degraded as a result of unplanned urbanization and inadequate sewerage facilities, which have accelerated the discharge of untreated domestic liquid waste into the river corridor (MOPE, 2000).
Domestic sewage and industrial effluent appears to be the major contributors to water pollution in the Kathmandu valley. The polluting industrial activities include the processing of agricultural products, textiles and carpets. The intensive use of fertilizers and pesticides in agriculture around the drainage basin of the river had further aggravated the situation. The average use of chemical fertilizers per hectare, such as nitrogen, phosphorus and potassium, has increased considerably in the country from 7.6 kg in 1975 to 26.6 kg in 1998 (MOPE et al., 2001).
The recharge area for groundwater in the valley is shrinking due to urbanization. The urban areas have increased from 26% in 1978 to 46.2% in 1996. Likewise, the rural built-up areas have increased from 11.2% to 24% during the same interval (Pradhan, 2000). Groundwater is being heavily used for drinking as well as for other activities, which has resulted in a decline in its water level (MOPE et al., 2001). According to a study by Metcalf and Eddy (2000) in 1999, there was a drop in the pumping water level from 9 to 68.5 m over a few years. The total sustainable level of groundwater withdrawal is approximately 26.3 million liters per day (Stanley et al., 1994). According to the Snowy Mountains Engineering Corporation (SMEC, 1992), the maximum limit of groundwater extraction should be approximately 40.1 million liters per day. However, the total groundwater currently extracted per day is approximately 58.6 million liters (Metcalf and Eddy, 2000). The impact of such water withdrawal from the groundwater reservoir is the infiltration of polluted stream water.
In such circumstances, information on the temporal and spatial trends of the water quality should help in the decision-making process, particularly in developing countries, where there is insufficient data (Massoud et al., 2003). Moreover, there is incomplete understanding of the influence of surface water to reinforce the notion that the management of surface water and groundwater should be integrated for sustainable development. Khatiwada et al. (2002) examined the extent and sources of groundwater contamination in the Kathmandu valley. However, there have been no studies examining the spatial and temporal variations in groundwater water pollution along the corridor of the Bagmati River. Therefore, this study assessed the state of groundwater pollutions, the spatial–temporal variations and investigated the influential factors of water quality along the river corridor in order to provide the basis for future management strategies.
Section snippets
Study area
The study area consisted of an approximately 20 km stretch of the Bagmati River Corridor (Fig. 1), which lies in the Kathmandu valley of the country, Nepal. The valley, which is located in the midland of the Himalayas, lies between 27°32′ and 27°49′ North and 85°12′ and 85°32′ East, and is an almost round in shape with a diameter of approximately 30 km E–W and 25 km N–S (Dill et al., 2001). The valley has a central flat part at an elevation of 1300–1400 m above mean sea level (Sharma, 1997). It
Materials and methods
A monitoring network was designed along the Bagmati river corridor (Fig. 1). Nine locations were sampled: three sampling stations, G01, G02, and G09, in rural areas and six stations, G03–G08, in urban areas. Table 1 gives a description of the sampling sites with their locations and types.
The water quality was monitored to determine the chemical and physical parameters: temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN) and
Results and discussion
Table 2, Table 3 summarize the measured variables in the water and sediment samples. Table 4(a) shows the results of the two-tail t-test for the comparison of the water quality between the pre-monsoon and post-monsoon season. Similarly, Table 4(b) gives the result of the t-test for the comparison of the water quality between the rural and the urban areas. Table 5 shows the correlation coefficients for the observed data. Fig. 2, Fig. 3, Fig. 4, Fig. 5 gives the plot of the results of the
Conclusions
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The groundwater locations along the Bagmati river corridor are exceeding the permissible limits with some exceptions. The water quality is less polluted in rural areas than in urban areas. In urban areas, the BOD concentration ranged from 8.41 to 29.74. Similarly, the TN and TP concentrations ranged from 6.7 to 128.96 and 0.06–1.5 mg/L, respectively. In rural areas, the BOD concentrations ranged from 0.78 to 18.25 mg/L. Similarly, the TN and TP ranged from 4.8 to 11.56 and 0.07–0.65 mg/L,
Acknowledgement
This work was supported by the Institute of Science and Technology for Sustainability (ISTS) at the Gwangju Institute of Science and Technology (GIST), South Korea.
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