Spatial variability of groundwater recharge - I. Is it really variable?

The spatial variability of recharge is an important consideration in estimating recharge especially as all methods of estimating it are 'point' estimates and in most places recharge varies in space. This paper along with the accompanying paper attempts to find a suitable answer to the question of taking this variability into account in estimating groundwater recharge. This paper attempts to determine if recharge is actually varying in space and that this is 'true' variability and that it is not an artefact of the method used for estimating recharge. It also pulls together information on spatial variability of recharge reported by various workers in the literature, in order to determine if recharge is truly variable in space

Spatial variability of groundwater recharge - II. Factors affecting variability and taking account of it in estimating recharge

The accompanying paper provided evidence to suggest that spatial variability of groundwater recharge is ‘true’ variability. This paper attempts to determine the major causes of such variability even at small distances, if there appear to be a frequency distribution to this spatial variability and lastly if it is possible take this variability into account in estimating recharge in an area. The clay content of the top soil appear to have a significant effect on recharge. The spatial variability of recharge appear to be log normally distributed and a way is shown where simple statistics can be used to take account of the spatial variability in estimating recharge

Cost Effectiveness of Rainwater Harvesting for Groundwater Recharge in Micro-Watersheds of Kolar District of India: The Case Study of Thotli Micro-Watershed

This study has estimated the supply augmentation of groundwater recharge due to creation of water harvesting structures and has assessed the cost-effectiveness of rainwater harvesting for groundwater recharge on watershed basis in one of the sub-watersheds of the Kolar district, Peninsular India — a typically hard-rock area. The study is based on the primary data for the year 2008-09 collected from a sample of 90 farmers having irrigation bore-wells in the selected watershed named Thotli. The study has indicated that the annual draft of irrigation water exceeds the annual recharge, causing a negative balance. On an average, the returns per rupee investment have been found to be ` 1.80 on farm pond, ` 1.78 on recharge pit and ` 1.39 on field bund. The cost incurred to impound a metre cube of water has been found as ` 3.01 in the case of field bund, where estimated recharge benefit is 5.6 m3, ` 1.67 /m3 in the case of recharge pit (with an estimated recharge benefit of 720 m3), and ` 1.33 /m3 in the case of farm pond (recharge benefit of 1350 m3). The discounted cost-benefit analysis of the investment on water harvesting structures has indicated that the investment on water harvesting structures is cost-effective and financially-viable.Rainwater harvesting, Economic feasibility, Groundwater recharge, Watershed, Agricultural and Food Policy, Q15, Q25,

The effect of using different time steps in a soil water balance model to estimate groundwater recharge in the dry zone of Sri Lanka

Importance of groundwater as a natural, renewable resource is well documented. The rate of replenishment of water table (or rate of groundwater recharge) is a key issue central to sustainable development of this valuable resource. Although many workers have used a soil water balance to estimate groundwater recharge, not many workers have investigated the effect of using different time steps (i.e. a day, 7 days etc.) in the water balance on the estimates of recharge. This study looks at the effect of using weekly, 10 daily and monthly time steps in a soil water balance to estimate recharge in the dry zone of Sri Lanka. The findings suggest that the larger the time step, the lower the recharge estimate as found in a different study in Grimsby in UK (Howard and Lloyd, 1979). Combining the results of documented studies and the current study, it is shown that wherever possible, a daily time step needs to be used in a soil water balance and if daily evapotranspiration data is not available, the available data may be evenly distributed (e.g. say weekly data divided by 7) and used as daily data in order to arrive at reasonable estimates of recharge together with actual daily rainfall data, which are likely to be available in most parts of the world

Global-scale estimation of diffuse groundwater recharge : model tuning to local data for semi-arid and arid regions and assessment of climate change impact

Groundwater recharge is the major limiting factor for the sustainable use of groundwater. To support water management in a globalized world, it is necessary to estimate, in a spatially resolved way, global-scale groundwater recharge. In this report, improved model estimates of diffuse groundwater recharge at the global-scale, with a spatial resolution of 0.5° by 0.5°, are presented. They are based on calculations of the global hydrological model WGHM (WaterGAP Global Hydrology Model) which, for semi-arid and arid areas of the globe, was tuned against independent point estimates of diffuse groundwater recharge. This has led to a decrease of estimated groundwater recharge under semi-arid and arid conditions as compared to the model results before tuning, and the new estimates are more similar to country level data on groundwater recharge. Using the improved model, the impact of climate change on groundwater recharge was simulated, applying two greenhouse gas emissions scenarios as interpreted by two different climate models.Die Höhe der Grundwasserneubildung ist oft limitierend für die nachhaltige Nutzung von Grundwasserressourcen. Um das Wassermanagement in der globalisierten Welt zu unterstützen ist es notwendig, die Grundwasserneubildung räumlich differenziert abzuschätzen. In diesem Forschungsbericht werden Modellierungsergebnisse der Grundwasserneubildung in einer räumlichen Auflösung von 0.5° x 0.5° auf globaler Skala vorgestellt. Die Ergebnisse basieren auf Berechnungen des globalen hydrologischen Modells WGHM (WaterGAP Global Hydrology Model), dessen Ergebnisse für semi-aride und aride Gebiete durch Anpassung an unabhängige Punktmessungen verbessert wurden. Diese Anpassung führte zu einer Verringerung der Grundwasserneubildung. Die Unterschiede der Modellergebnisse zu Schätzungen der Grundwasserneubildung auf dem Länderniveau haben sich durch diesen Ansatz verringert. Mittels des verbesserten Modells wurde der Einfluss des Klimawandels auf die Grundwasserneubildung bei Verwendung von zwei unterschiedlichen Treibhausgasszenarien und zwei unterschiedlichen Klimaszenarien quantifiziert

Regional assessment of groundwater recharge in the lower Mekong Basin

Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations

Battery simulation program

Computer program calculates spacecraft battery energy at specific times dictated by input sequence of recharge, discharge, and no activity phases. Recharge phases are assumed during times not specified, unless batteries are fully charged. Warnings are printed when energy falls below specified level. Program assumes two identical batteries

Microbial community changes induced by Managed Aquifer Recharge activities: linking hydrogeological and biological processes

Managed Aquifer Recharge (MAR) is a technique used worldwide to increase the availability of water resources. We study how MAR modifies microbial ecosystems and its implications for enhancing biodegradation processes to eventually improve groundwater quality. We compare soil and groundwater samples taken from a MAR facility located in NE Spain during recharge (with the facility operating continuously for several months) and after 4 months of no recharge. The study demonstrates a strong correlation between soil and water microbial prints with respect to sampling location along the mapped infiltration path. In particular, managed recharge practices disrupt groundwater ecosystems by modifying diversity indices and the composition of microbial communities, indicating that infiltration favors the growth of certain populations. Analysis of the genetic profiles showed the presence of nine different bacterial phyla in the facility, revealing high biological diversity at the highest taxonomic range. In fact, the microbial population patterns under recharge conditions agree with the intermediate disturbance hypothesis (IDH). Moreover, DNA sequence analysis of excised denaturing gradient gel electrophoresis (DGGE) band patterns revealed the existence of indicator species linked to MAR, most notably Dehalogenimonas sp., Nitrospira sp. and Vogesella sp.. Our real facility multidisciplinary study (hydrological, geochemical and microbial), involving soil and groundwater samples, indicates that MAR is a naturally based, passive and efficient technique with broad implications for the biodegradation of pollutants dissolved in water.Peer ReviewedPostprint (published version