Combination of CFCs and stable isotopes to characterize the mechanism of groundwater–surface water interactions in a headwater basin of the North China Plain

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwater–surface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwater–surface water interactions mechanism, with important catchment management implications.     

Quantification of surface water and groundwater salinity sources in irrigated lowland area of North China Plain

Seasonally variation of water salinity is observed worldwide, the mechanisms of water salinity are not well understood due to natural factors and anthropogenic activities. Quantification water salinity source are challenging since complex influence factors, especially in agricultural regions irrigated with multi-water sources. In the lowland area of North China Plain, transferred water, brackish shallow groundwater and fresh deep groundwater were combinative utilized to relieve prominent contradictions between regional water shortages and grain production. In this study, influence factors of surface water (canal water, pond water) and shallow groundwater salinity were identified and quantified through statistical analysis, deuterium excess, and ionic relationship. Salinity of canal water and pond water increased in dry season and decreased in rainy season, while salinity of shallow groundwater decreased in dry season after water transfer and rainy season, but increased in dry season. Evaporation and mineral dissolution were main factors for surface water salinity in dry season, with mineral dissolution was the more important one. The contribution ratio of evaporation and mineral dissolution for canal salinity were 4.4 and 49.1% in dry season after water transfer, 7.1 and 34.4% in dry season, and that for pond water salinity were 12.4 and 18.3% in dry season, respectively. Precipitation and surface runoff were main factors for surface water salinity in rainy season. The contribution of surface runoff for canal water and pond water salinity were 66.1 and 45.8%, respectively. Salinity of canal water and shallow groundwater was temporary decreased by water transfer. Domestic sewage from rural areas had larger influence than agricultural activities for salinity increase of pond water and shallow groundwater. Mineral dissolution was the main contributor for shallow groundwater salinity, with contribution ratio larger than 60% in different periods. This study demonstrated and quantified salinity source of surface water and shallow groundwater and may deepen our understanding of water management under multi-water resources utilization.     

Impact of water transfer on interaction between surface water and groundwater in the lowland area of North China Plain

The contradiction between the freshwater shortage and the large demand of freshwater by irrigation was the key point in cultivated lowland area of North China Plain. Water transfer project brings fresh water from water resource‐rich area to water shortage area, which can in turn change the hydrological cycle in this region. Major ions and stable isotopes were used to study the temporal variations of interaction between surface water and groundwater in a hydrological year after a water transfer event in November 2014. Irrigation canal received transferred Yellow River, with 2.9% loss by evaporation during water transfer process. The effect of transferred water on shallow groundwater decreased with increasing distance from the irrigation canal. Pit pond without water transfer receives groundwater discharge. During dry season after water transfer event, shallow groundwater near the irrigation canal was recharged by lateral seepage and deep percolation of irrigation, whereas shallow groundwater far from irrigation canal was recharged by deep percolation of deep groundwater irrigation. Canal water lost by evaporation was 2.7–17.4%. Influence of water transfer gradually disappeared until March as the water usage of agricultural irrigation increased. In the dry season, groundwater discharged to irrigation canal and pond; 2.2–31.6% canal water and 11.3–20.0% pond water were lost by evaporation. In the rainy season (June to September), surface water was fed mainly by precipitation and surface run‐off, whereas groundwater was recharged by infiltration of precipitation. The two‐end member mix model showed that the mixing ratio of precipitation in pond and irrigation canal were 73–83.4% (except one pond with 28.1%) and 77.3–99.9%, respectively. Transferred water and precipitation were the important recharge sources for shallow groundwater, which decreased groundwater salinity in cultivated lowland area of North China Plain. With the temporary and spatial limitation of water transfer effects, increased water transfer amounts and frequency may be an effective way of mitigating regional water shortage. In addition, reducing the evaporation of surface water is also an important way to increase the utilization of transfer water.     

Temporal variation of stable isotopes in a precipitation–groundwater system: implications for determining the mechanism of groundwater recharge in high mountain–hills of the Loess Plateau,China

The groundwater in shallow loess aquifers in high mountain–hills in the western Loess Plateau in China is almost the sole water resource for local residents. However, the question about how the loess groundwater naturally circulates in these high mountain–hills, characterized by low precipitation and high potential evaporation, remains unclear. The objectives of this study are to evaluate the application of hydrogen and oxygen isotopes to (1) examine temporal variations of the isotopic composition of precipitation and shallow groundwater and (2) uncover the mechanism of groundwater recharge in high mountain–hills. Results from 2 years of monitoring data show a difference in the stable isotopes for groundwater and local precipitation between the winter and summer periods. Similar to precipitation, stable isotopes in groundwater are observed to be depleted in winter and enriched in summer, particularly in oxygen isotope. A prominent characteristic is that H and O isotopes of groundwater show a very clear response to strong precipitation in the rainy season in 2013. The results highlight that local precipitation is the likely recharge source for groundwater in shallow loess aquifers. Annual recharge from local precipitation maintains the groundwater resource in the shallower loess aquifer. The mechanisms governing shallow loess groundwater recharge in high mountain–hills were evaluated. In addition to possible vertical slow percolation of soil water through the unsaturated zone, rapid groundwater recharge mechanisms have been identified as temporal preferential infiltration through sinkholes, slip surface or landslide surface and through the interface of loess layer and palaeo‐soils. Most groundwater can be recharged after a heavy rainy season. Copyright © 2015 John Wiley & Sons, Ltd.     

The spatial and temporal variability of groundwater recharge in a forested basin in northern Wisconsin

Recharge varies spatially and temporally as it depends on a wide variety of factors (e.g. vegetation, precipitation, climate, topography, geology, and soil type), making it one of the most difficult, complex, and uncertain hydrologic parameters to quantify. Despite its inherent variability, groundwater modellers, planners, and policy makers often ignore recharge variability and assume a single average recharge value for an entire watershed. Relatively few attempts have been made to quantify or incorporate spatial and temporal recharge variability into water resource planning or groundwater modelling efforts. In this study, a simple, daily soil–water balance model was developed and used to estimate the spatial and temporal distribution of groundwater recharge of the Trout Lake basin of northern Wisconsin for 1996–2000 as a means to quantify recharge variability. For the 5 years of study, annual recharge varied spatially by as much as 18 cm across the basin; vegetation was the predominant control on this variability. Recharge also varied temporally with a threefold annual difference over the 5‐year period. Intra‐annually, recharge was limited to a few isolated events each year and exhibited a distinct seasonal pattern. The results suggest that ignoring recharge variability may not only be inappropriate, but also, depending on the application, may invalidate model results and predictions for regional and local water budget calculations, water resource management, nutrient cycling, and contaminant transport studies. Recharge is spatially and temporally variable, and should be modelled as such. Copyright © 2009 John Wiley & Sons, Ltd.     

Methods of groundwater recharge estimation in eastern Mediterranean—a water balance model application in Greece,Cyprus and Jordan

Groundwater recharge studies in semi‐arid areas are fundamental because groundwater is often the only water resource of importance. This paper describes the water balance method of groundwater recharge estimation in three different hydro‐climatic environments in eastern Mediterranean, in northwest Greece (Aliakmonas basin/Koromilia basin), in Cyprus (Kouris basin and Larnaka area) and in Jordan (northern part of Jordan). For the Aliakmonas basin, groundwater recharge was calculated for different sub‐catchments. For the Upper Aliakmonas basin (Koromilia basin), a watershed‐distributed model was developed and recharge maps were generated on a daily basis. The mean annual recharge varied between 50 and 75 mm/year (mean annual rainfall 800 mm/year). In Cyprus, the mean groundwater recharge estimates yielded 70 mm/year in the Kouris basin. In the Larnaka area, groundwater recharge ranged from 30 mm/year (lowland) to 200 mm/year (mountains). In Jordan, the results indicated recharge rates ranging from 80 mm/year for very permeable karstified surfaces in the upper part of the Salt basin, where rainfall reaches 500 mm/year to less than 10 mm/year and to only about 1 mm/year in the southernmost part of the basin. For the north part of Jordan, a watershed‐distributed model was developed and recharge maps were generated. This water balance model was used for groundwater recharge estimations in many regions with different climatic conditions and has provided reliable results. It has turned out to be an important tool for the management of the limited natural water resources, which require a detailed understanding of regional hydro(geo)logical processes. Copyright © 2007 John Wiley & Sons, Ltd.     

The effects of climate change on potential groundwater recharge in Great Britain

The predicted increase in mean global temperature due to climate change is expected to affect water availability and, in turn, cause both environmental and societal impacts. To understand the potential impact of climate change on future sustainable water resources, this paper outlines a methodology to quantify the effects of climate change on potential groundwater recharge (or hydrological excess water) for three locations in the north and south of Great Britain. Using results from a stochastic weather generator, actual evapotranspiration and potential groundwater recharge time‐series for the historic baseline 1961–1990 and for a future ‘high’ greenhouse gas emissions scenario for the 2020s, 2050s and 2080s time periods were simulated for Coltishall in East Anglia, Gatwick in southeast England and Paisley in west Scotland. Under the ‘high’ gas emissions scenario, results showed a decrease of 20% in potential groundwater recharge for Coltishall, 40% for Gatwick and 7% for Paisley by the end of this century. The persistence of dry periods is shown to increase for the three sites during the 2050s and 2080s. Gatwick presents the driest conditions, Coltishall the largest variability of wet and dry periods and Paisley little variability. For Paisley, the main effect of climate change is evident during the dry season (April–September), when the potential amount of hydrological excess water decreases by 88% during the 2080s. Overall, it is concluded that future climate may present a decrease in potential groundwater recharge that will increase stress on local and regional groundwater resources that are already under ecosystem and water supply pressures. Copyright © 2007 John Wiley & Sons, Ltd.     

Tracer hydrology of the data-scarce and heterogeneous Central American Isthmus

Numerous socio-economic activities depend on the seasonal rainfall and groundwater recharge cycle across the Central American Isthmus. Population growth and unregulated land use changes resulted in extensive surface water pollution and a large dependency on groundwater resources. This work combines stable isotope variations in rainfall, surface water, and groundwater of Costa Rica, Nicaragua, El Salvador, and Honduras to develop a regionalized rainfall isoscape, isotopic lapse rates, spatial–temporal isotopic variations, and air mass back trajectories determining potential mean recharge elevations, moisture circulation patterns, and surface water–groundwater interactions. Intra-seasonal rainfall modes resulted in two isotopically depleted incursions (W-shaped isotopic pattern) during the wet season and two enriched pulses during the mid-summer drought and the months of the strongest trade winds. Notable isotopic sub-cloud fractionation and near-surface secondary evaporation were identified as common denominators within the Central American Dry Corridor. Groundwater and surface water isotope ratios depicted the strong orographic separation into the Caribbean and Pacific domains, mainly induced by the governing moisture transport from the Caribbean Sea, complex rainfall producing systems across the N-S mountain range, and the subsequent mixing with local evapotranspiration, and, to a lesser degree, the eastern Pacific Ocean fluxes. Groundwater recharge was characterized by (a) depleted recharge in highland areas (72.3%), (b) rapid recharge via preferential flow paths (13.1%), and enriched recharge due to near-surface secondary fractionation (14.6%). Median recharge elevation ranged from 1,104 to 1,979 m a.s.l. These results are intended to enhance forest conservation practices, inform water protection regulations, and facilitate water security and sustainability planning in the Central American Isthmus.     

A study of interaction between surface water and groundwater using environmental isotope in Huaisha River basin

The surface water and groundwater are important components of water cycle, and the interaction between surface water and groundwater is the important part in water cycle research. As the effective tracers in water cycle research, environmental isotope and hydrochemistry can reveal the interrelationships between surface water and groundwater effectively. The study area is the Huaisha River basin, which is located in Huairou district, Beijing. The field surveying and sampling for spring, river and well water were finished in 2002 and 2003. The hydrogen and oxygen isotopes and water quality were measured at the laboratory. The spatial characteristics in isotope and evolution of water quality along river lines at the different area were analyzed. The altitude effect of oxygen isotope in springs was revealed, and then using this equation, theory foundation for deducing recharge source of spring was estimated. By applying the mass balance method, the annual mean groundwater recharge rate at the catchment was estimated. Based on the groundwater recharge analysis, combining the hydrogeological condition analysis, and comparing the rainfall-runoff coefficients from the 1960s to 1990s in the Huaisha River basin and those in the Chaobai River basin, part of the runoff in the Huaisha River basin is recharged outside of this basin, in other words, this basin is an un-enclosed basin. On the basis of synthetically analyses, combining the compositions of hydrogen and oxygen isotopes and hydrochemistry, geomorphology, geology, and watershed systems characteristics, the relative contributions between surface water and groundwater flow at the different areas at the catchments were evaluated, and the interaction between surface water and groundwater was re- vealed lastly.     

Does hillslope trenching enhance groundwater recharge and baseflow in the Peruvian Andes?

As Andean glaciers rapidly retreat due to climate change, the balance of groundwater and glacial meltwater contributions to stream discharge in tropical, proglacial watersheds will change, potentially increasing vulnerability of water resources. The Shullcas River Watershed, near Huancayo, Peru, is fed only partly by the rapidly receding Huaytapallana glaciers (<20% of dry season flow). To potentially increase recharge and therefore increase groundwater derived baseflow, the government and not‐for‐profit organizations have installed trenches along large swaths of hillslope in the Shullcas Watershed. Our study focuses on a nonglacierized subcatchment of the Shullcas River Watershed and has 2 objectives: (a) create a model of the Shullcas groundwater system and assess the controls on stream discharge and (b) investigate the impact of the infiltration trenches on recharge and baseflow. We first collected hydrologic data from the field including a year‐long hydrograph (2015–2016), meteorological data (2011–2016), and infiltration measurements. We use a recharge model to evaluate the impact of trenched hillslopes on infiltration and runoff processes. Finally, we use a 3‐dimensional groundwater model, calibrated to the measured dry season baseflow, to determine the impact of trenching on the catchment. Simulations show that trenched hillslopes receive approximately 3.5% more recharge, relative to precipitation, compared with unaltered hillslopes. The groundwater model indicates that because the groundwater flow system is fast and shallow, incorporating trenched hillslopes (~2% of study subcatchment area) only slightly increases baseflow in the dry season. Furthermore, the location of trenching is an important consideration: Trenching higher in the catchment (further from the river) and in flatter terrain provides more baseflow during the dry season. The results of this study may have important implications for Andean landscape management and water resources.     

Semi‐Arid Aquifer Responses to Forest Restoration Treatments and Climate Change

The purpose of this study was to develop an interpretive groundwater‐flow model to assess the impacts that planned forest restoration treatments and anticipated climate change will have on large regional, deep (>400 m), semi‐arid aquifers. Simulations were conducted to examine how tree basal area reductions impact groundwater recharge from historic conditions to 2099. Novel spatial analyses were conducted to determine areas and rates of potential increases in groundwater recharge. Changes in recharge were applied to the model by identifying zones of basal area reduction from planned forest restoration treatments and applying recharge‐change factors to these zones. Over a 10‐year period of forest restoration treatment, a 2.8% increase in recharge to one adjacent groundwater basin (the Verde Valley sub‐basin) was estimated, compared to conditions that existed from 2000 to 2005. However, this increase in recharge was assumed to quickly decline after treatment due to regrowth of vegetation and forest underbrush and their associated increased evapotranspiration. Furthermore, simulated increases in groundwater recharge were masked by decreases in water levels, stream baseflow, and groundwater storage resulting from surface water diversions and groundwater pumping. These results indicate that there is an imbalance between water supply and demand in this regional, semi‐arid aquifer. Current water management practices may not be sustainable into the far future and comprehensive action should be taken to minimize this water budget imbalance.     

极端天气下三峡库区土地利用对河流水质的多时空尺度影响

为探究极端天气下流域内水质对土地利用的响应关系,本研究基于不同空间尺度(1000 m河段缓冲区、500 m河岸带缓冲区及子流域)的土地利用指数以及旱季(2019年11月)、雨季-洪水期(2020年7月)和雨季-干旱期(2022年8月)的水质数据,探究流域内土地利用对水质的多时空尺度影响,从而得到保护流域水质和规划流域内土地利用格局的最佳时空尺度和对水质影响最显著的预测因子。研究表明:(1)流域水质受极端天气影响,降雨会增强水体的稀释能力,高温会加快水中微生物反应速率,具体表现为雨季-洪水期的水质较好,雨季-干旱期次之,旱季较差。(2)土地利用对水质指标的影响存在时空尺度效应,土地利用在子流域和旱季尺度下对河流水质影响最显著。(3)不同土地利用指数对流域水质影响存在差异,耕地、林地、斑块密度、最大斑块指数和边缘密度是影响水质指标最显著的解释变量。其中林地与多数水质指标具有负相关关系,建设用地、耕地、斑块密度与较多水质指标存在正相关关系。本研究结果为合理规划土地利用格局以及保护河流水质提供科学依据,对三峡库区环境可持续发展及生态保护具有一定意义。     

Distinguishing Mountain Front and Mountain Block Recharge in an Intermontane Basin of the Himalayan Region

Intermontane basin aquifers worldwide, particularly in the Himalayan region, are recharged largely by the adjoining mountains. Recharge in these basins can occur either by water infiltrating from streams near mountain fronts (MFs) as mountain front recharge (MFR) or by sub-surface mountain block infiltration as mountain block recharge (MBR). MFR and MBR recharge are challenging to distinguish and are least quantified, considering the lack of extensive understanding of the hydrological processes in the mountains. This study used oxygen and hydrogen isotopes (δ¹⁸O and δ²H), electrical conductivity (EC) data, hydraulic head, and groundwater level data to differentiate MFR and MBR. Groundwater level data provide information about the groundwater-surface water interactions and groundwater flow directions, whereas isotopes and EC data are used to distinguish and quantify different recharge sources. The present methodology is tested in an intermontane basin of the Himalayan region. The results suggest that karst springs (KS) and deep groundwater (DGW) recharge are dominated by snowmelt (47% ± 10% and 46% ± 9%) as MBR from adjacent mountains, insignificantly affected by evaporation. The hydraulic head data and isotopes indicate Quaternary shallow groundwater (SGW) aquifer system recharge as MFR of local meteoric water with significant evaporation. The results indicate several flow paths in the aquifer system, a local flow for KS, intermediate flow for SGW, and regional flow for DGW. The findings will significantly impact water resource management in the area and provide vital baseline knowledge for sustainable groundwater management in other Himalayan intermontane basins.     

Estimating groundwater recharge for an arid karst system using a combined approach of time‐lapse camera monitoring and water balance modelling

Groundwater is the principal water resource in semi‐arid and arid environments. Therefore, quantitative estimates of its replenishment rate are important for managing groundwater systems. In dry regions, karst outcrops often show enhanced recharge rates compared with other surface and sub‐surface conditions. Areas with exposed karst features like sinkholes or open shafts allow point recharge, even from single rainfall events. Using the example of the As Sulb plateau in Saudi Arabia, this study introduces a cost‐effective and robust method for recharge monitoring and modelling in karst outcrops. The measurement of discharge of a representative small catchment (4.0 · 10⁴ m²) into a sinkhole, and hence the direct recharge into the aquifer, was carried out with a time‐lapse camera. During the monitoring period of two rainy seasons (autumn 2012 to spring 2014), four recharge events were recorded. Afterwards, recharge data as well as proxy data about the drying of the sediment cover are used to set up a conceptual water balance model. The model was run for 17 years (1971 to 1986 and 2012 to 2014). Simulation results show highly variable seasonal recharge–precipitation ratios between 0 and 0.27. In addition to the amount of seasonal precipitation, this ratio is influenced by the interannual distribution of rainfall events. Overall, an average annual groundwater recharge for the doline (sinkhole) catchment on As Sulb plateau of 5.1 mm has estimated for the simulation period. Copyright © 2015 John Wiley & Sons, Ltd.     

Proglacial groundwater storage dynamics under climate change and glacier retreat

Proglacial aquifers are an important water store in glacierised mountain catchments that supplement meltwater-fed river flows and support freshwater ecosystems. Climate change and glacier retreat will perturb water storage in these aquifers, yet the climate-glacier-groundwater response cascade has rarely been studied and remains poorly understood. This study implements an integrated modelling approach that combines distributed glacio-hydrological and groundwater models with climate change projections to evaluate the evolution of groundwater storage dynamics and surface-groundwater exchanges in a temperate, glacierised catchment in Iceland. Focused infiltration along the meltwater-fed Virkisá River channel is found to be an important source of groundwater recharge and is projected to provide 14%–20% of total groundwater recharge by the 2080s. The simulations highlight a mechanism by which glacier retreat could inhibit river recharge in the future due to the loss of diurnal melt cycling in the runoff hydrograph. However, the evolution of proglacial groundwater level dynamics show considerable resilience to changes in river recharge and, instead, are driven by changes in the magnitude and seasonal timing of diffuse recharge from year-round rainfall. The majority of scenarios simulate an overall reduction in groundwater levels with a maximum 30-day average groundwater level reduction of 1 m. The simulations replicate observational studies of baseflow to the river, where up to 15% of the 30-day average river flow comes from groundwater outside of the melt season. This is forecast to reduce to 3%–8% by the 2080s due to increased contributions from rainfall and meltwater runoff. During the melt season, groundwater will continue to contribute 1%–3% of river flow despite significant reductions in meltwater runoff inputs. Therefore it is concluded that, in the proglacial region, groundwater will continue to provide only limited buffering of river flows as the glacier retreats.     

Importance of river water recharge to the San Joaquin Valley groundwater system

Groundwater is not a sustainable resource, unless abstraction is balanced by recharge. Identifying the sources of recharge in a groundwater basin is critical for sustainable groundwater management. We studied the importance of river water recharge to groundwater in the south‐eastern San Joaquin Valley (24,000 km², population 4 million). We combined dissolved noble gas concentrations, stable isotopes, tritium, and carbon‐14 analyses to analyse the sources, mechanisms, and timescales of groundwater recharge. Area‐representative groundwater sampling and numerical model input data enabled a stable isotope mass balance and quantitative estimates of river and local recharge. River recharge, identified by a lighter stable isotope signature, represents 47 ± 4% of modern groundwater in the San Joaquin Valley (recharged after 1950) but only 26 ± 4% of premodern groundwater (recharged before 1950). This implies that the importance of river water recharge in the San Joaquin valley has nearly doubled and is likely the result of a 40% increase in total recharge, caused by river water irrigation return flows and increased stream depletion and river recharge due to groundwater pumping. Compared with the large and long‐duration capacity for water storage in the subsurface, storage of water in rivers is limited in time and volume, as evidenced by cold river recharge temperatures resulting from fast infiltration and recharge. Groundwater banking of seasonal surface water flows and expansion of managed aquifer recharge practices therefore appear to be a natural and promising method for increasing the resilience of the San Joaquin Valley water supply system.     

Application of environmental isotopes to identify recharge source,age, and renewability of phreatic water in Yinchuan Basin

The accurate understanding of groundwater circulation pattern and its renewable capacity is vital for groundwater resource assessment and the rational exploitation and utilization of groundwater. Estimation of groundwater recharge is difficult in arid or semiarid area due to the low amount and variability of recharge. A combination of isotope investigation with hybrid model allows a direct calculation of renewability of the aquifer. In this paper, the phreatic water circulation pattern and its renewable capacity of phreatic water in Yinchuan Basin, a semiarid area located at the northwest China, are investigated by the application of environmental isotope method, which mainly focusses on the isotope characteristics of different water bodies, phreatic water isotope age, phreatic water circulation pattern, and phreatic water renewal rate. The results demonstrate that the two dominant recharge sources of groundwater in Yinchuan Basin, local atmospheric precipitation and Yellow River, account for 13% and 87%, respectively. The average residence time of phreatic water in Yinchuan Basin is about 48 years, and the average renewal rate is 3.38%/a. The results indicate that the phreatic water has a strong renewable capacity and the regeneration rate distribution is consistent with that indicated by isotope age.     

Distributed Temperature Sensing to Measure Infiltration Rates Across a Groundwater Recharge Basin

Managed aquifer recharge is used to augment groundwater resources and provide resiliency to water supplies threatened by prolonged droughts. It is important that recharge facilities operate at their maximum efficiency to increase the volume of water stored for future use. In this study, we evaluate the use of distributed temperature sensing (DTS) technology as a tool to measure high-resolution infiltration rates at a large-scale recharge facility. Fiber optic cable was laid out inside a spreading basin in a spiral pattern, at two different depths. The cables measured the propagation of diurnal surface water temperature oscillations into the basin depth. The rate of heat propagation is proportional to the velocity of the water, making it possible to estimate the infiltration rate from the temperature measurements. Our results showed that the infiltration rate calculated from DTS, averaged over the entire basin, was within 5% of the infiltration rate calculated using a conventional metering method. The high-resolution data obtained from DTS, both spatially and temporally, revealed heterogeneous infiltration rates throughout the basin; furthermore, tracking the evolution of infiltration rates over time revealed regions with consistently high infiltration rates, regions with consistently low infiltration rates, and regions that evolved from high to low rates, which suggested clogging within that region. Water utilities can take advantage of the high-resolution information obtained from DTS to better manage recharge basins and make decisions about cleaning schedule, frequency, and extent, leading to improved basin management strategies, reduced O&M costs, and increased groundwater recharge.     

Simulated groundwater interaction with rivers and springs in the Heihe river basin

Surface water and groundwater in the Heihe river basin of China are interconnected and the pattern of water resources exploitation has a direct effect on the interaction of groundwater and surface water, especially on a downstream oasis. A three‐dimensional groundwater flow simulation model with eight model layers was established to simulate the regional groundwater flow in the multilayered aquifer system and the interaction among the rivers, springs, and groundwater. The model was calibrated not only with historical water levels but also with the investigated baseflow and spring flux. The simulation results of the numerical model match reasonably well with the observed groundwater levels, baseflow to rivers, and spring flux. The numerical simulation also demonstrates that the hydraulic connection between the river and the aquifers has transferred from the coupling to decoupling at some reaches. It is suggested that there is a vital need to reduce groundwater withdrawal and to rationalize the use of both groundwater and surface water in order to maintain sustainable development in the study area. Copyright © 2007 John Wiley & Sons, Ltd.     

Field data and flow system response in clay (vertisol) shale terrain,north central Texas,USA

The water budget in clay shale terrain is controlled by a complex interaction between the vertisol soil layer, the underlying fractured rock, land use, topography, and seasonal trends in rainfall and evapotranspiration. Rainfall, runoff, lateral flow, soil moisture, and groundwater levels were monitored over an annual recharge cycle. Four phases of soil–aquifer response were noted over the study period: (1) dry‐season cracking of soils; (2) runoff initiation, lateral flow and aquifer recharge; (3) crack closure and down‐slope movement of subsurface water, with surface seepage; (4) a drying phase. Surface flow predominated within the watershed (25% of rainfall), but lateral flow through the soil zone continued for most of the year and contributed 11% of stream flow through surface seepage. Actual flow through the fractured shale makes up a small fraction of the water budget but does appear to influence surface seepage by its effect on valley‐bottom storage. When the valley soil storage is full, lateral flow exits onto the valley‐bottom surface as seasonal seeps. Well response varied with depth and hillslope position. FLOWTUBE model results and regional recharge estimates are consistent with an aquifer recharge of 1·6% of annual precipitation calculated from well heights and specific yield of the shale aquifer. Copyright © 2005 John Wiley & Sons, Ltd.