Groundwater constitutes the Earth’s largest reservoir of fresh water and accounts for a significant portion of total water use worldwide. Due to population growth, increasing demand and the impact of climate change, groundwater use is expected to dramatically increase. Because of the growing importance of groundwater resources, it is important to improve tools and methods used for quantification of groundwater recharge rates, particularly at the basin scale, where groundwater is most effectively managed. Despite its importance, the recharge rates are often difficult to quantify at the basin scale, hampering effective and sustainable use of groundwater resources.
Environmental isotope tracers are valuable and powerful tools that can offer significant insight into identifying recharge mechanisms and providing good estimates of recharge rates, often with fewer infrastructure requirements and at a lower cost than traditional methods. In addition, many environmental isotope techniques yield information on long-term recharge rates, while other methods can only be used to determine recharge rates. However, because environmental isotope methods typically yield point- or local-scale recharge estimates, a method for upscaling is included for estimating basin scale recharge.
Upscaling of isotope based recharge estimates to basin level is needed because recharge rates can vary significantly within basins. For example, recharge rates can vary greatly between focused recharge pathways (e.g., from a canal or drainage channel) and diffuse recharge pathways (i.e., broadly distributed recharge across the landscape). These can also vary substantially between the surrounding highlands and lower elevation areas in the mid- or lower basin. Upscaling of recharge values is best performed via a geographic information system (GIS), where basin-wide data on pertinent characteristics can be analysed and visualized rapidly. GIS would allow upscaling of point measurements over broader areas of similar geographical and physical characteristics.
The eight case studies conducted in this CRP represented a broad range of climatic, geological, hydrological, topographic and vegetation conditions. As a result, the conceptual models of recharge sources, distribution, timing, and rates varied greatly between study areas. Approaches to assess groundwater recharge fall into three broad categories: 1) Mountain block/mountain front recharge (Mexico, Morocco, Pakistan, Slovakia, Syria and Turkey), 2) focused recharge in topographic depressions, including stream infiltration (Kuwait and parts of Mexico, Pakistan, Slovakia, Syria and Vietnam), and 3) diffuse recharge (particularly in study areas with more humid settings such as Pakistan, Slovakia, Vietnam and Turkey). In most cases, direct precipitation is the predominant source of recharge. However, infiltration of irrigation water is also important in some study areas (for example, in Pakistan). In Turkey, precipitation that recharges in the mountains recharges aquifers at lower elevations by deep circulation and upward movement into those aquifers.
The CRP showed that useful groundwater recharge vulnerability to pollution maps at basin scale can be developed for water resources assessment, but only in the case of experimented counterparts in the combined use of hydrogeological, geochemical and GIS tools.
Researchers from Kuwait, Mexico, Morocco, Pakistan, Slovakia, Syria, Turkey, the United States and Viet Nam participated in this CRP.
For more information, please see the CRP description:
http://www.dgdingfa.net/projects/crp/f33017
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