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(Location: IWMI HQ Call no: IWMI Record No: H047579)
(1 MB)
Springs are the major source of freshwater in many small mountainous watersheds within the Himalayan region. In recent years, their flow rates have diminished, but the reasons for this are not self-evident, and hence this paper reviews the methods to investigate Himalayan springs. The review reveals that chemical and isotope analyses – mostly water dating and stable isotope (e.g., d18O) analyses – could be an appropriate entry point to commence field investigations, because of their potential to map complex spring pathways, including linkages between aquifers. This should be combined with the building of hydrogeological maps with the available data. Output from desktop analyses, field investigations and hydrogeological maps could then contribute to the establishment of a conceptual model, which could form the basis for a numerical model.
(Location: IWMI HQ Call no: e-copy only Record No: H048190)
(4.76 MB)
Recharge assessment is a challenge in snow and glacier dominated Himalayan basins. Quantification of recharge to karst springs in these complex geological environments is important both for hydrologic understanding and for effective water resource management. We used spring hydrographs and environmental tracers (isotopes and solutes) to distinguish and estimate the sources of spring water and to identify the flow paths of the recharging waters in three mountainous basins of the western Himalaya. The karst springs are perennial with high discharge amplitudes. The results indicate that ambient temperature has a strong influence on the hydrological behavior of the springs. Although the spring flow is dominantly controlled by the melting of snow and/or glaciers, rain events produce sharp spikes in spring hydrographs. The facies patterns in springs within the Bringi basin (Ca-HCO3) and the Liddar basin (Ca-HCO3 and Ca-Mg-HCO3) suggest flow dominantly through limestone and dolomite. Higher concentrations of SO4 2 and Na+ in warm springs of the Kuthar basin indicate flow through carbonate, silicate and other rocks. The isotopic composition (d18O, d2 H) of precipitation, snowpacks, glacier melt and karst springs show wide variation both in space and time, and are strongly influenced by the basin relief and meteorology. The tracer-based two- and three-component mixing models suggest that the snowmelt dominantly contributes to the spring flow (55–96%), followed by glacier melt (5–36%) and rain (4–34%). Based on tracer tests with good recovery rates, springs are dominantly recharged through point sources rather than by diffuse infiltration. Changes in the timing, form, and amount of winter precipitation substantially affect the timing and magnitude of spring discharge during the rest of the year.
(Location: IWMI HQ Call no: e-copy only Record No: H049195)
(6.57 MB) (6.57 MB)
Though springs are the primary source of water for communities in the mid-hills of Nepal, an in-depth scientific understanding of spring systems is missing, preventing the design of effective climate-resilient interventions for long-term sustainability of springs. This study marks the first attempt to combine environmental isotopes analysis with hydrometric and hydrogeological measurements to identify dominant recharge zones for springs in two mountainous catchments—Banlek and Shikarpur—in Far-Western Nepal. In total, 422 water samples collected from rainfall, springs and streams between March 2016 and March 2017 were analyzed for their isotopic composition (d18O and dD). Isotopic composition of rainwater shows seasonality, suggesting that different sources of water vapor cause rains in monsoon and in dry season. Rainfall responses of individual springs were used to identify connections to unconfined and deeper groundwater strata. The isotopic composition of springs in the two catchments ranges from -9.55 to -8.06‰ for d18O and -67.58 to -53.51‰ for dD. The isotopic signature of the spring sources falls close to the local meteoric water line for the corresponding season, indicating strong rainfall contribution to springs. Altitudinal isotopic gradients suggest mean recharge elevation of 2,600–2,700 m asl for springs in Shikarpur, which lies beyond the surface-water catchment, and a recharge elevation of 1,000–1,100 m asl for Banlek, which partially extends beyond the surface-water catchment. The demarcated recharge zones will be used by government agencies to implement recharge interventions to increase the resiliency and reliability of springs in Far-Western Nepal.
4 Lapworth, D. J.; Dochartaigh, B. O.; Nair, T.; O'Keeffe, J.; Krishan, G.; MacDonald, A. M.; Khan, M.; Kelkar, N.; Choudhary, S.; Krishnaswamy, J.; Jackson, C. R. 2021. Characterising groundwater-surface water connectivity in the Lower Gandak Catchment, a barrage regulated biodiversity hotspot in the mid-Gangetic Basin. Journal of Hydrology, 594:125923. (Online first) [doi: https://doi.org/10.1016/j.jhydrol.2020.125923]
(Location: IWMI HQ Call no: e-copy only Record No: H050154)
(13.00 MB)
The alluvial aquifer system of the Indo-Gangetic Basin (IGB) is one of the world’s most important freshwater resources, sustaining humans and river ecosystems. Understanding groundwater recharge processes and connections to meteoric and surface water is necessary for effective water resource management for human and wider ecological requirements. Parts of the mid-Gangetic Basin, across eastern Uttar Pradesh and Bihar, are characterised by stable long-term groundwater levels, high annual rainfall, and limited historical groundwater use compared to parts of Northwest India for example. In this paper we use a combination of environmental tracers and hydrograph observations to characterise sources of recharge and groundwater-surface water interaction using a transect approach across the catchment of the River Gandak, a major barrage-regulated tributary of the River Ganga. Stable isotope results show that the dominant source of groundwater recharge, in the shallow (0–40 m bgl) Holocene and underlying Pleistocene aquifer system (>40 m bgl), is local rainfall. The shallow Holocene aquifer is also supplemented by local recharge from river and canal seepage and irrigation return flow in the upper and mid parts of the catchment. These observations are corroborated by evidence from detailed groundwater hydrographs and salinity observations, indicating localised canal, river and lake connectivity to groundwater. In the middle and lower catchment, river discharge is dominated by groundwater baseflow during the peak dry season when barrage gates are closed, which contributes to ecological flows for endangered river dolphins and gharial crocodiles. Groundwater residence time tracers indicate active modern recharge in the shallow alluvial aquifer system across the catchment. In the shallow Holocene aquifer elevated arsenic (As), iron (Fe), and manganese (Mn) exceeded WHO drinking water guidelines in a minority of sites, and uranium (U) and fluoride (F) concentrations approach but do not exceed the WHO guideline values. These observations varied across the catchment with higher As, Fe and Mn in the upper and mid catchments and higher U in the lower catchment. Groundwater salinity was typically between 500 and 1000 µS/cm, and isolated higher salinity was due to recharge from flood-plain wetlands and lakes impacted by evaporation. At present, the Gandak catchment has relatively high rainfall and low abstraction, which maintains stable groundwater levels and thus baseflow to the river in the dry season. Potential future threats to groundwater resources, and therefore river ecology due to the sensitivity to changes in baseflow in the catchment, would likely be driven by reductions in local monsoon rainfall, changes in water management practices and increased groundwater use.
5 Rathod, Roshan; Kumar, Manish; Mukherji, Aditi; Sikka, Alok; Satapathy, K. K.; Mishra, A.; Goel, S.; Khan, M. 2021. Resource book on springshed management in the Indian Himalayan Region: guidelines for policy makers and development practitioners. New Delhi, India: International Water Management Institute (IWMI); New Delhi, India: NITI Aayog, Government of India; New Delhi, India: Swiss Agency for Development and Cooperation (SDC). 40p. [doi: https://doi.org/10.5337/2021.230]
(Location: IWMI HQ Call no: e-copy only Record No: H050807)
(17.8 MB)
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