Impacts of soil conservation on groundwater recharge in the semi-arid Loess Plateau, China

Soil conservation measures undertaken to address land degradation can alter the hydrologic cycle by changing partitioning of water fluxes at the land surface. While effects on runoff are well documented, impacts of soil conservation activities on fluxes to groundwater are poorly understood. The goal of this study was to examine fluxes to groundwater in a semi-arid area of China’s Loess Plateau that has been subject to extensive soil conservation activities. Unsaturated zone pore-water pressures and concentrations of chloride show that impacts on deep drainage differ between ecological and structural soil conservation approaches. High matric potentials and low chloride beneath cultivated terrace and gulley sites are consistent with deep drainage occurring at these sites. Estimated recharge rates for dryland cultivated upland sites were approximately 55??0?mm/year (11??8% of mean annual rainfall) based upon chloride mass balance. In contrast, results suggest that mature tree and shrub plantations prevent deep drainage. Stable isotope signatures of unsaturated-zone moisture and groundwater indicate that focused infiltration through gullies and other topographic lows is likely to be the primary recharge mechanism. The results of this study highlight the potential for inadvertent effects of some soil conservation approaches on regional water resources.     

Application of environmental isotopes to groundwater recharge studies in a semi-arid fractured crystalline basement area of Dodoma, Tanzania

The distribution of ¹⁸O and ²H in various water sources indicates that groundwater recharge is due to local rainfall occurring within the basins. Groundwater recharge takes place under a bypass flow mechanism and matrix diffuse flow and is 3% and 2% of the long-term mean annual rainfall of 550 mm for the Makutapora and Hombolo basins, respectively. Chloride mass balance indicates that 60% and 40% of the total groundwater recharge takes place through macropores and matrix flow, respectively. Sporadic variations in ¹⁸O, ²H and chloride among adjacent boreholes suggest existence of a discrete fractured aquifer and/or dominance of local recharge. The relationship between δ²H and chloride indicates that groundwater salinization is due to the leaching of surficial and soil salts during high intensity rainfall, which causes high surface runoff and flash floods. It has been concluded that the isotopic and chemical character of groundwater in fractured semi-arid areas may provide the most effective complementary means of groundwater recharge assessment and therefore is very useful in the management of the water resources.     

Artificial groundwater recharge to a semi-arid basin: case study of Mujib aquifer,Jordan

Mujib watershed is an important groundwater basin which is considered a major source for drinking and irrigation water in Jordan. Increased dependence on groundwater needs improved aquifer management with respect to understanding deeply recharge and discharge issues, planning rates withdrawal, and facing water quality problems arising from industrial and agricultural contamination. The efficient management of this source depends on reliable estimates of the recharge to groundwater and is needed in order to protect Mujib basin from depletion. Artificial groundwater recharge was investigated in this study as one of the important options to face water scarcity and to improve groundwater storage in the aquifer. A groundwater model based on the MODFLOW program, calibrated under both steady- and unsteady-state conditions, was used to investigate different groundwater management scenarios that aim at protecting the Mujib basin. The scenarios include variations of abstraction levels combined with different artificial groundwater recharge quantities. The possibilities of artificial groundwater recharge from existing and proposed dams as well as reclaimed municipal wastewater were investigated. Artificial recharge options considered in this study are mainly through injecting water directly to the aquifer and through infiltration from reservoir. Three scenarios were performed to predict the aquifer system response under different artificial recharge options (low, moderate, and high) which then compared with no action (recharge) scenario. The best scenario that provides a good recovery for the groundwater table and that can be feasible is founded to be by reducing current abstraction rates by 20% and implementing the moderate artificial recharge rates of 26 million(M)m³/year. The model constructed in this study helps decision makers and planners in selecting optimum management schemes suitable for such arid and semi-arid regions.     

Relationship between the effective diffusion coefficient of soil radon and groundwater recharge in semi-arid areas

Herein, the relationship between soil radon behavior and groundwater recharge in the town of Hosha, a semi-arid area of Jordan is explored. The annual rainfall average in this area is between 60–100 mm year⁻¹. Soil radon concentration levels, using CR-39 detectors, have been measured at several depths. Nine sampling sites on a hill slope, in the summer and winter 2006 were chosen. Other soil parameters such as moisture, soil type and porosity were also measured. Correlation between the latter and the calculated effective diffusion coefficients, based on a linear approximation, was done in order to explore water movement. A weak correlation between the soil radon concentration and water recharge in this particular semi-arid area is observed. The results show that water recharge takes place vertically, i.e., water moves downward and in one of the nine sampling sites this movement seems to be more rapid compared to the other sites.     

Hydrochemical study of groundwater in recharge area,Wadi Fatimah basin,Saudi Arabia

The present study deals with the hydrochemical characteristics of groundwater in the upper catchment of Wadi Fatimah basin. The analysis of data indicated strongly that the chloride and sulfate in the groundwater are mainly of marine origin, concentrated by high evaporation processes. Flushing is the most important factor that modifies the ionic concentrations and almost stands for the short-term variation in groundwater chemistry. Weathering reactions of the rock-forming minerals take place under relatively high P_CO2 condition in water and soil zone; it can be an important long-term neutralization process. It is accounted as a contributor for Ca and Mg ions in the groundwater. Using the chloride method the recharge rate has been estimated at 72 mm yr^–1.     

The investigation of fault-controlled groundwater recharge within a suburban area of Damascus,Syria

Al-Mazraa is a heavily populated suburb of Damascus (Syria) with agricultural activity. It is adjacent to the Cretaceous Qassioun Mountain Range, from which it is structurally separated by the Damascus fault. Al-Mazraa waterworks abstracts from a shallow Quaternary aquifer, whose recharge processes are unidentified. The functions of Qassioun Mountain, the Damascus fault, the agricultural activities, the ascending deeper groundwater, and the through-flowing Tora River are not well understood and they are, hence, subject to study. The application of hydrochemical parameters and ratios in combination with signatures of δD and δ¹⁸O revealed that recharge predominantly occurs in the outcropping Cretaceous rocks through subsurface passages rather than through influent conditions of the Tora River or through direct rainfall. Interestingly, high Na/Cl ratios indicate contact with volcanic rocks which exist within the Cretaceous anticline and also in the subsurface of the studied Quaternary aquifer. Evidence for deeper circulating groundwater is given, since replenishing waters are up to 4 °C warmer and have much lower nitrate concentrations than the groundwater in the study area. From these points, it is indicated that the Damascus fault is conductive in respect to groundwater, rather than being impermeable, as it is elsewhere.     

The groundwater geochemistry in a semi-arid, fractured crystalline basement area of Dodoma, Tanzania

The chemical character of groundwater is generated through processes including the leaching of surficial and near-surface soil salts, cation exchange and mineral dissolution of, in this case, mainly amphiboles and sodic plagioclase. Molar ratios thermodynamic analysis using a NETPATH geochemical model and standard Piper trilinear and Gibbs diagrams have been used to establish these geochemical processes. Though the groundwater is dominantly of NaCl type, it is apparently suitable for general irrigation purposes.     

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.     

GIS for the assessment of the groundwater recharge potential zone

Water resources in Taiwan are unevenly distributed in spatial and temporal domains. Effectively utilizing the water resources is an imperative task due to climate change. At present, groundwater contributes 34% of the total annual water supply and is an important fresh water resource. However, over-exploitation has decreased groundwater availability and has led to land subsidence. Assessing the potential zone of groundwater recharge is extremely important for the protection of water quality and the management of groundwater systems. The Chih-Pen Creek basin in eastern Taiwan is examined in this study to assess its groundwater resources potential. Remote sensing and the geographical information system (GIS) are used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The weights of factors contributing to the groundwater recharge are derived using aerial photos, geology maps, a land use database, and field verification. The resultant map of the groundwater potential zone demonstrates that the highest recharge potential area is located towards the downstream regions in the basin because of the high infiltration rates caused by gravelly sand and agricultural land use in these regions. In contrast, the least effective recharge potential area is in upstream regions due to the low infiltration of limestone.     

Determining the groundwater potential recharge zone and karst springs catchment area: Saldoran region,western Iran

Assessing the groundwater recharge potential zone and differentiation of the spring catchment area are extremely important to effective management of groundwater systems and protection of water quality. The study area is located in the Saldoran karstic region, western Iran. It is characterized by a high rate of precipitation and recharge via highly permeable fractured karstic formations. Pire-Ghar, Sarabe-Babaheydar and Baghe-rostam are three major karstic springs which drain the Saldoran anticline. The mean discharge rate and electrical conductivity values for these springs were 3, 1.9 and 0.98 m³/s, and 475, 438 and 347 μS/cm, respectively. Geology, hydrogeology and geographical information system (GIS) methods were used to define the catchment areas of the major karstic springs and to map recharge zones in the Saldoran anticline. Seven major influencing factors on groundwater recharge rates (lithology, slope value and aspect, drainage, precipitation, fracture density and karstic domains) were integrated using GIS. Geology maps and field verification were used to determine the weights of factors. The final map was produced to reveal major zones of recharge potential. More than 80 % of the study area is terrain that has a recharge rate of 55–70 % (average 63 %). Evaluating the water budget of Saldoran Mountain showed that the total volume of karst water emerging from the Saldoran karst springs is equal to the total annual recharge on the anticline. Therefore, based on the geological and hydrogeological investigations, the catchment area of the mentioned karst springs includes the whole Saldoran anticline.     

Choosing appropriate techniques for quantifying groundwater recharge

Various techniques are available to quantify recharge; however, choosing appropriate techniques is often difficult. Important considerations in choosing a technique include space/time scales, range, and reliability of recharge estimates based on different techniques; other factors may limit the application of particular techniques. The goal of the recharge study is important because it may dictate the required space/time scales of the recharge estimates. Typical study goals include water-resource evaluation, which requires information on recharge over large spatial scales and on decadal time scales; and evaluation of aquifer vulnerability to contamination, which requires detailed information on spatial variability and preferential flow. The range of recharge rates that can be estimated using different approaches should be matched to expected recharge rates at a site. The reliability of recharge estimates using different techniques is variable. Techniques based on surface-water and unsaturated-zone data provide estimates of potential recharge, whereas those based on groundwater data generally provide estimates of actual recharge. Uncertainties in each approach to estimating recharge underscore the need for application of multiple techniques to increase reliability of recharge estimates. Electronic Publication     

Characterisation of groundwater recharge conditions and flow mechanisms in bedrock aquifers of the Johannesburg area,South Africa

Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ¹⁸O and δ²H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m³ from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO₂ as a dominant source of carbon (δ¹³C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.     

Estimation of groundwater recharge using water balance coupled with base-flow-record estimation and stable-base-flow analysis

In this paper, the long-term mean annual groundwater recharge of Taiwan is estimated with the help of a water-balance approach coupled with the base-flow-record estimation and stable-base-flow analysis. Long-term mean annual groundwater recharge was derived by determining the product of estimated long-term mean annual runoff (the difference between precipitation and evapotranspiration) and the base-flow index (BFI). The BFI was calculated from daily streamflow data obtained from streamflow gauging stations in Taiwan. Mapping was achieved by using geographic information systems (GIS) and geostatistics. The presented approach does not require complex hydrogeologic modeling or detailed knowledge of soil characteristics, vegetation cover, or land-use practices. Contours of the resulting long-term mean annual P, BFI, runoff, groundwater recharge, and recharge rates fields are well matched with the topographical distribution of Taiwan, which extends from mountain range toward the alluvial plains of the island. The total groundwater recharge of Taiwan obtained by the employed method is about 18 billion tons per year.An erratum to this article can be found at     

The effect of the variation of river water levels on the estimation of groundwater recharge in the Hsinhuwei River,Taiwan

Land subsidence is a serious problem in Taiwan’s Yunlin area due to groundwater overpumping. There are safety risks in the high-speed railway structures in the areas of Siluo, Huwei, Tuku, and Yuanchang towns that run from north to south in the Yunlin area. Therefore, it is important to increase the groundwater recharge and to remedy the land subsidence in this area. The purpose of this study is to use the stream-flow estimation model (SF) and the groundwater flow numerical software MODFLOW (MF) to estimate the stream infiltration with consideration to the variation of the river water level in the Hsinhuwei River. The Ferris analytical model (FA) and MF are used to estimate the increased stream infiltration after the water level of the river rises. The hydraulic parameters required for each model are obtained from field observations and laboratory experiments. The results indicate that the assessment of the stream infiltration obtained through the SF and MF models are 264.2 × 10⁴ and 170.9 × 10⁴ m³/year, respectively. When the river water level increases by about 2.5 m, the annual stream infiltration obtained through the FA and MF models significantly increases by 31.6 × 10⁴ and 26.4 × 10⁴ m³/year, respectively. Taken together, the stream storages estimated using these two models indicate that an increasing efficiency of groundwater recharge is within the range of 10.0–18.5%.     

Quantification of groundwater recharge in the city of Nottingham, UK

 Groundwater is an important and valuable resource for water supply to cities. In order to make full and wise use of the asset value, a clear understanding of the quantities and sources of urban groundwater recharge is needed. The water supply and disposal network is often an important source of recharge to urban groundwater through leakage from water mains and sewers. An approach to establishing the spatial and temporal amounts of the three urban recharge sources (precipitation, mains and sewers) is developed and illustrated using the Nottingham (UK) urban aquifer. A calibrated groundwater flow model is supplemented by calibrated solute balances for three conservative species (Cl, SO₄ and total N), thus providing four lines of evidence to use in the recharge estimation. Nottingham is located on a Triassic sandstone aquifer with average precipitation of 700 mm/year. Using the models, current urban recharge is estimated to be 211 mm/year, of which 138 mm/year (±40%) is from mains leakage and 10 mm/year (±100%) is from sewer leakage. The wide confidence intervals result from the scarcity of historical field data and the long turnover time in this high volume aquifer, and should be significantly lower for many other aquifer systems. Received: 1 December 1997 · Accepted: 14 September 1998     

Redemarcation of recharge area of stressed confined aquifers of Neyveli groundwater basin, India, through tritium tracer studies

Natural recharge due to rainfall (annual average 1,200 mm) over an area of 1,500 km² of the Neyveli groundwater basin was carried out for two consecutive hydrological years, using the tritium injection technique. The lignite seams, occurring within the Upper Miocene formation in the basin have been mined for the last 40 years. The confined aquifer underlying the lignite seams has been pumped continuously since 1961, for depressurization and safety around the mine. The recharge zone is identified as an elongated zone, oriented in a NE–SW direction within the basin. Natural recharge measurements were made at several sites (single and duplicate injections), covering the entire basin. They indicate a recharge rate of 333–556 mm/year (24–40% of rainfall) in the north and northeastern parts, covering the previously defined recharge areas as well as some adjoining areas. Soil moisture movement at several duplicate sites in these areas showed significant downward migration of tracer during the non-monsoon period, probably caused by pumping in the mine area. Isotopic data of ground water samples in the northern and northeastern part of the basin indicates modern ages. Concurrent field observations like deep water table with high annual fluctuations and exposure of pebble beds, enabled the redemarcation of the aggregate recharge area as 650 km². The redefined recharge area includes the areas identified by earlier workers as well as the new area on the northeastern side of the lignite mine.     

Hydrology models approach to estimation of the groundwater recharge: case study in the Bulgarian Danube watershed

The groundwater (GW) makes an important part of a region runoff. GW bodies playing the role of accumulating reservoirs regulate the GW discharge enabling the river flow to have more uniform long-term distribution. Along with other important advantages, the GW offers the users stable water abstraction rate independent from the recharge rate. The GW recharge quantification belongs to the uneasy tasks in the water resource management. Applying the conventional methods needs multiyear observation records of the variation of the groundwater body (GWB) characteristics. The employment of hydrology models avoids that necessity but requires great amount of data related to the soil hydraulic properties, the land topography and cover of the GWB watershed and long-term records of the climatic effects. The paper presents an introduction of the mathematical model CLM3 into the GW recharge estimation problem. It is a complex and advanced model with adequate interpretation of the water-related processes in the soil and on the land surface under atmospheric effects. The input is available from NCEP/NCAR reanalysis atmosphere data and the International Geosphere-Biosphere Program (IGBP) data base. The model is applied to GW recharge assessment of the Bulgarian Danube district for the year 2013. The obtained monthly and yearly total district values and the areal distribution of the infiltration intensity are matched to the existing field observation-based estimates. The study shows that the CLM3 model approach leads to encouraging results. The method comes very useful with GWB lacking regime observation data as well as for GW recharge prognostic assessments under climatic scenarios.