The groundwater and surface water are two interrelated systems of the water resources and belong to one of the processes of hydrologic cycle. If the interconnectivity between these two systems can be recognized and established for particular rivers, the probable contamination of any one of the systems caused by anthropogenic activities can be indicated and suggested for necessary mitigative measures. Thus, this study was focused on identifying the interconnection of groundwater and river water using hydrogen (δD) and oxygen (δ 18 O) stable isotopes of water. Monthly water samples (June 2010 to March 2011) collected from shallow groundwater and river water were used for this research. The river water samples were collected from the Bagmati River (3 locations), the Bishnumati River (2 locations), the Dhobi Khola (2 locations) and the Manahara River (1 location) whereas some groundwater samples (from 7 locations) were collected from these river corridors (2 samples from 35 to 60 m and 4 samples from 90 to 200 m from the river channel) and three samples were collected far from the river channel. The concentration of chemical parameters, especially Na + and Clfrom the river water, was higher in the dry season (Dec-Jan), which decreased to nearly half in the wet season (July-Sep). The values of δ 18 O and δD show significant temporal variation ranging from -6.4‰ to -9.3‰ and -43.3‰ to -64.5‰, respectively. The concentration of Na + and Clof groundwater varied with the distance from the river channel. Significant temporal variation of stable isotopes and Na + and Clwas observed in that groundwater which was collected from 35 to 60 m from river channel whereas constant values were measured in water samples taken from 90 to 200 m. Similarity in isotopic composition of groundwater and river water in dry season conforms the recharge of the river water from nearby groundwater (GW1, GW3 and GW6). Contrarily, GW2 and GW4 (located within 35-60 m) have higher probability of recharge from the river water. Page 30 (isotope and geochemical), solute tracer methods, methods based on Darcy's Law [2] and geophysical methods [3][4][5]. Among these methods, stable environmental isotopes (hydrogen and oxygen) and hydrochemistry are widely applied for such study [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The interconnection of groundwater and surface water can affect the quantity and quality of both water systems. But in the context of Nepal, such studies has just started in few areas [13]. Earlier studies had only focused on quality of groundwater [20][21][22][23][24][25] as well as of surface water. Previous studies based on quality of groundwater of Kathmandu valley have reported high value of chloride, nitrate and coliform in shallow groundwater. Nitrate level at shallow depth is higher as compared with high depth in urban areas due to anthropogenic sources such as poorly managed septic tanks, sewer pipes and solid waste disposal [26]. Previous researches on river water quality of the Kathmandu valley have reported that the ...

Five representative segments of the river were surveyed in detail for evaluating its dynamics and stability condition. The first (downstream) to the fifth (upstream) segments are classified as 'F4', 'C4', 'C4', 'B4' and 'B4' streams characterised by gravelly substrates. All these streams are competent enough to transport their bed material (d 90 ) as shown by the exceeding dimensionless shear stress over critical dimensionless shear stress of the river segments. The existing depth and slope of the river is far enough to carry d 90 of the substrate grain size. Stream power of segments 1 to 5 are respectively, 622.6, 79.0, 146.6, 354.6 and 15617.0 KN/s. The 'B4' streams show greater stream power, i.e., transport capacity compared to 'F4' followed by 'C4' streams. Therefore, the 'B4 streams (3rd and 4th order streams) are potential to degradation, and the 'C4' and 'F4' (both 5th order) streams are potential to aggradation depending on river morphology and dynamics. Meander geometry of the Manahara River exhibit deviation of variables (meander wavelength vs channel width, and meander belt width vs channel width) from the stability, suggesting existence of instability to some extent in the river.

The Manahara River located in northeast part of the Kathmandu Valley has been disturbed for last one decade by several anthropogenic activities and natural causes thereby deteriorating its recreational functions and stream habitat. To obtain an existing environmental condition and disturbances of the river, the river was surveyed for its habitat, pollution level and surface water quality. Among the five representative segments of the river, the downstream segment (Sano Thimi) was scored into intermediate category showing more pollution and environmental deterioration compared to the upstream segments. Turbidity, electrical conductivity, chemical oxygen demand, biological oxygen demand and ammonia increase, whereas dissolved oxygen decreases from upstream to downstream with exponential functions. Aquatic lives like Garra sp. (Buduna), Schizothorax sp. (Asala), Channa sp. (Hiele) and Heteropneustes sp. (Singe) were observed except in downstream of the Jadibuti Bridge situated downstream from Sano Thimi stretch. Fish species were rare from the Jadibuti area most probably due to reduced dissoved oxygen (5 mg/l). Coliform bacteria ranged from 3000 to 4000 in the Manahara River showing high amount of bacterial contamination. Major disturbances, which affect river habitat and surface water quality of the Manahara River were destruction of riparian buffer zones, excavation excessive amount of sand from the river, encroachment of floodplains and bars, solid waste and sewer effluent, and tendency of landuse change. To retard environmental degradation of the Manahara River from the human-induced activities, local government needs to take immediate action.

Interconnection between river water and groundwater plays an important role in maintaining water quantity and quality in hydrological systems. Furthermore, the exact interconnection is often difficult to observe and measure. This study attempts to explain river and shallow groundwater interconnection in urbanized areas of the Kathmandu Valley, Nepal. Isotopic (δD and δ18O) and chemical analyses were performed on river and groundwater samples, and the results were analyzed using statistical methods to identify areas of interconnection between river water and groundwater. Higher concentrations and positive strong correlations of Na+ with K+, NH4+-N, Cl−, HCO3−, and PO4−-P, and a change of water type from Ca-HCO3 during the wet season to Na-K-HCO3 during the dry season indicate higher contamination in river water during the dry season. Hierarchical cluster analysis was used in grouping water samples into clusters on the basis of isotopic and chemical (Na+ and Cl−) composition. Grouping of river and groundwater samples in one–one clusters from wet and dry seasons shows the presence of interconnection, indicating the contribution of river water in recharging shallow groundwater. These results imply that shallow groundwater found near rivers is chemically contaminated by polluted river water through bank infiltration, in both wet and dry seasons.

The rivers of the Kathmandu Basin are vulnerable to flash floods and disturbances caused by anthropogenic as well as climatic changes. Two southern tributaries of the Bagmati River: the Kodku and the Godavari Rivers, have been considered for their (i) watershed-scale geomorphic parameters such as relative relief, drainage texture and stream order, (ii) stretchscale planform parameters such as sinuosity (K), meander belt width (Wblt), meander wavelength (Lm) and radius of curvature (Rc), and (ii) longitudinal profiles and slopes. Both Kodku and the Godavari Rivers are elongate basins with wide ranges of the watershed-scale parameters. The Godavari River is longer, larger and more sinuous compared to the Kodku River. The development of the patterns of the fifth order main stem stretches of both rivers with respect to the stream slopes, and asymmetric patterns of the meander loops indicate anomalous growth of the river stretches. DOI: http://dx.doi.org/10.3126/bdg.v15i0.7414 Bulletin of the Department of Geology, Vol. 15, 2012, pp. 15-22