Estimation Of Groundwater Recharge Rate Research Articles

Estimation of groundwater recharge rates using soil-water isotope profiles: a case study of two contrasting dune types on Langeoog Island, Germany

The creation of artificial dunes for coastal protection may have important consequences for freshwater lenses in coastal aquifers. The objective of this study was to compare the recharge processes below such a young dune with scant vegetation to an older dune covered by grass and herbaceous vegetation. To this aim, soil and water samples were collected from the unsaturated zone at two sites on Langeoog Island in northern Germany, and the soil water was analysed for stable water isotopes and chloride. Recharge rates were calculated by using a new version of HYDRUS-1D, which was modified to simulate isotope fractionation during evaporation. Both the model outcomes and the data highlight the importance of fractionation, which is slightly more pronounced at the older, more vegetated dune. At the newly constructed dune, vegetation dieback seemingly reduces the importance of transpiration during summer. Recharge occurs year-round, albeit predominantly during the winter months. Calculated recharge rates are consistent with lysimeter measurements, but are significantly higher than previously reported rates based on groundwater age data, which is primarily attributed to the absence of dune shrub at the sites investigated here. More data are needed to establish the importance of soil-water repellency and overland flow. Based on the results, it is proposed that repeated isotope sampling can yield important insights into the dynamics of recharge processes, including their response to climate change.

Numerical Analysis of Recharge Rates and Contaminant Travel Time in Layered Unsaturated Soils

This study focused on the estimation of groundwater recharge rates and travel time of conservative contaminants between ground surface and aquifer. Numerical simulations of transient water flow and solute transport were performed using the SWAP computer program for 10 layered soil profiles, composed of materials ranging from gravel to clay. In particular, sensitivity of the results to the thickness and position of weakly permeable soil layers was carried out. Daily weather data set from Gdańsk (northern Poland) was used as the boundary condition. Two types of cover were considered, bare soil and grass, simulated with dynamic growth model. The results obtained with unsteady flow and transport model were compared with simpler methods for travel time estimation, based on the assumptions of steady flow and purely advective transport. The simplified methods were in reasonably good agreement with the transient modelling approach for coarse textured soils but tended to overestimate the travel time if a layer of fine textured soil was present near the surface. Thus, care should be taken when using the simplified methods to estimate vadose zone travel time and vulnerability of the underlying aquifers.

Advantages and challenges of using soil water isotopes to assess groundwater recharge dominated by snowmelt at a field study located in Canada

ABSTRACTSeasonal signals of stable isotopes in precipitation, combined with measurements of isotope ratios in soil water, can be used for quantitative estimation of groundwater recharge rates. This study investigates the applicability of using the piston flow principle and the peak shift displacement method to estimate actual groundwater recharge rates in a humid Nordic region located in the province of Quebec, Canada. Two different sites with and without vegetation (C1 and C2) in an unconfined aquifer were tested by measuring soil water isotope ratios (18O/16O and 2H/1H) and volumetric pore water content. Core samples were obtained along the vadose zone down to the groundwater table at the two sites (2.45 m for Site C1 and 4.15 m for Site C2). The peak shift method to estimate groundwater recharge rates was shown to be accurate only in certain specific conditions inherent to the soil properties and the topographical situation of the investigated sites. Indeed, at Site C2, recharge from the snowmelt could not be estimated because of heterogeneity in the lower part of the vadose zone. At this same site the later recharge after the snowmelt (in the period from late spring to early autumn) could be estimated accurately because the upper part of the vadose zone was homogeneous. Furthermore, at site C1, runoff/runon phenomena hampered calculations of actual infiltration and thus produced inaccurate results for recharge. These two different site effects (heterogeneity in the first site and runoff/runon in the other site) were identified as being limiting factors in the accurate assessment of actual recharge. This study therefore recommends the use of the peak shift method for (1) humid Nordic regions, (2) homogeneous and thick vadose zones, and (3) areas with few or limited site effects (runoff/runon).

Comparison of groundwater recharge estimation techniques in an alluvial aquifer system with an intermittent/ephemeral stream (Queensland, Australia)

This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred.

Estimating groundwater recharge in the humid and semi-arid African regions: review

Reliable estimation of groundwater recharge rate is crucial for the assessment of groundwater resource potential in Africa. In this study, we reviewed existing studies on groundwater recharge, especially in the semi-arid and humid regions of Africa. After the assessment of the main advantages and disadvantages of each method, we strongly agree that among the distinct existing methods, Water-Table Fluctuations (WTF), Recession-Curve Displacement, and Chloride Methods can be used with a better certainty of improved estimation of groundwater recharge in these regions. In addition, the features of existing studies on groundwater recharge are outlined. The major challenge of these regions on recharge study is the lack of basic data. Therefore, this paper suggests methods for dealing with this limitation and also the future outlook using recently developed technologies such as Remote Sensing (RS) and Geographical Information System (GIS). Watershed hydrologic modeling, which is a robust method for recharge estimation that is widely applied around the world, should also be applied for future perspective by solving the problems of its use and data requirements to find a better result. Strictly speaking, the key to the successful estimation of groundwater recharge lies in the utilization of a variety of independent methods. Therefore, by bringing together the advantages, limitations, and cost of each method, the study of the recharge estimation in different climatic environments of African regions can enter a new era.

Review on soil water isotope-based groundwater recharge estimations

Groundwater recharge estimations are necessary for sustainable management of groundwater resources. Among various hydraulic, hydrogeological and hydrological approaches, tracer methods are proposed to improve groundwater recharge estimations. Soil water isotope-based estimates of groundwater recharge rates were developed in the 1960s and have been applied in more than 40 studies reviewed within this manuscript. This comprehensive review research distinguishes three fundamental research approaches: (1) labelling method with tritium or deuterium, which can be used to trace unsaturated zone water movement, (2) tracing soil water movement using a seasonal signal of stable isotopes in precipitation, mainly applied in humid zones, and (3) interpretation of an evaporation signal that impacts soil water stable isotope composition, mainly applicable in arid and semiarid regions. More recently, advances in soil water extraction and analytical methods allow a higher sampling resolution and in situ measurements of soil water stable isotopes. Analytical advances may strengthen and improve the applicability of stable isotope methods for quantitative recharge. We present, compare and discuss studies of unsaturated zone isotope profiles with an emphasis on necessary prerequisites, such as a substantial thick porous sedimentary layer, or negative influences through high clay and silt contents or dry soil conditions. Copyright © 2015 John Wiley & Sons, Ltd.

Estimation of groundwater recharge via deuterium labelling in the semi-arid Cuvelai-Etosha Basin, Namibia

The stable water isotope deuterium (2H) was applied as an artificial tracer (2H2O) in order to estimate groundwater recharge through the unsaturated zone and describe soil water movement in a semi-arid region of northern central Namibia. A particular focus of this study was to assess the spatiotemporal persistence of the tracer when applied in the field on a small scale under extreme climatic conditions and to propose a method to obtain estimates of recharge in data-scarce regions. At two natural sites that differ in vegetation cover, soil and geology, 500 ml of a 70 % 2H2O solution was irrigated onto water saturated plots. The displacement of the 2H peak was analyzed 1 and 10 days after an artificial rain event of 20 mm as well as after the rainy season. Results show that it is possible to apply the peak displacement method for the estimation of groundwater recharge rates in semi-arid environments via deuterium labelling. Potential recharge for the rainy season 2013/2014 was calculated as 45 mm a−1 at 5.6 m depth and 40 mm a−1 at 0.9 m depth at the two studied sites, respectively. Under saturated conditions, the artificial rain events moved 2.1 and 0.5 m downwards, respectively. The tracer at the deep sand site (site 1) was found after the rainy season at 5.6 m depth, corresponding to a displacement of 3.2 m. This equals in an average travel velocity of 2.8 cm d−1 during the rainy season at the first site. At the second location, the tracer peak was discovered at 0.9 m depth; displacement was found to be only 0.4 m equalling an average movement of 0.2 cm d−1 through the unsaturated zone due to an underlying calcrete formation. Tracer recovery after one rainy season was found to be as low as 3.6 % at site 1 and 1.9 % at site 2. With an in situ measuring technique, a three-dimensional distribution of 2H after the rainy season could be measured and visualized. This study comprises the first application of the peak displacement method using a deuterium labelling technique for the estimation of groundwater recharge in semi-arid regions. Deuterium proved to be a suitable tracer for studies within the soil–vegetation–atmosphere interface. The results of this study are relevant for the design of labelling experiments in the unsaturated zone of dry areas using 2H2O as a tracer and obtaining estimations of groundwater recharge on a local scale. The presented methodology is particularly beneficial in data-scarce environments, where recharge pathways and mechanisms are poorly understood.

Vadose zone transport in dry forests of central Argentina: Role of land use

Most sedimentary plains occupied by semiarid woody ecosystems have low groundwater recharge rates and high vadose zone salt accumulation. Their cultivation has often led to drainage of water below root zone, displacement of solutes, and rising water tables, affecting, in most extreme cases, long‐term viability of agriculture. To explore this possibility in semiarid plains of South America, we characterized vadose flow using chloride data in dry forests of central Argentina, in an area that has been subject to intense deforestation and agricultural expansion during the last century. We selected five paired stands under natural dry forests and dryland agriculture (sites deforested ≥30 years ago) and sampled sediments (n = 3 boreholes) down to 6 m depth. Profiles were consistently dry and salty in forest stands with chloride inventories (0–6 m) of 150 g/m2 to 9 × 103 g/m2. Under cultivation 78% to 99% of the chloride stock was leached, and total water storage was ≥30% higher than in the dry forest, with soil water content close to field capacity. Estimates of groundwater recharge rates based on residual moisture flux approach (cumulative chloride versus cumulative water curves) suggested maximum values of 0.33 to 128.4 mm/yr for dry forest and agriculture, respectively. At agricultural stands recharge was also estimated using chloride front displacement, yielding minimum values ≥5.3 mm/yr. While the long‐term impact of cultivation on regional groundwater hydrology is still unclear in the region, our findings suggest that land salinization processes are possible and need careful monitoring in areas with high agricultural expansion.

광릉 원두부 소유역에서의 우기 중 지하수 함양률 평가

Groundwater recharge rates were estimated and compared in a headwater catchment at the Gwangneung Supersite using three different methods: water-table fluctuation (WTF), mass balance, and hydrograph separation techniques. Data were obtained during the rainy season from June to September 2005. Two different WTF methods estimated the groundwater recharge rate as 25.9% and 23.6%. The mass balance calculation of chloride ions indicated recharge rates of 13.4% on average. Baseflow separation using chloride ion as a tracer from six storm hydrographs produced a 14.0% net baseflow rate on average. Because of the implicit assumption of a long-term steady state without storage change, recharge rates calculated by mass balance and hydrograph separation were smaller than those done with WTF methods, which include the amount of increased storage due to the water-level rise. Subsequently, the WTF method is superior to others in the estimation of groundwater recharge rate to comprehend the dynamic characteristics of the hydrologic cycle.

NRCS-CN방법과 기저유출 분리법을 이용한 지하수함양률 산정

Groundwater recharge from precipitation is affected by the infiltration from ground surface and the movement of soil water. Groundwater recharge is directly related to the groundwater amount and flow in aquifers, and baseflow to rivers. Determining groundwater recharge rate for a given watershed is a prerequisite to estimate sustainable groundwater resources. The estimation of groundwater recharge rate were carried out for three subwatersheds in the Wicheon watershed and two subwatersheds in the Pyungchang River basin and for the period 1990-2000, using the NRCS-CN method and the baseflow separation method. The recharge rate estimates were compared to each other. The result of estimation by the NRCS-CN method shows the average annual recharge rate 15.4-17.0% in the Wicheon watershed and 26.4-26.8% in the Pyungchang River basin. The average annual recharge rates calculated by the baseflow separation method ranged 15.1-21.1% in the W icheon watershed, and 25.2-33.4% in the Pyungchang River basin. The average annual recharge rates calculated by the NRCS-CN method is less variable than the baseflow separation method. However, the average annual recharge rates obtained from the two methods are not very different, except NO. 6 subwatershed in Pyungchang River basin.