Shallow Groundwater Table Research Articles

Detection and evaluation of changes induced by the diversion of River Danube in the territorial appearance of latent effects governing shallow-groundwater fluctuations

The paper assesses the impact on the fluctuation of the shallow-groundwater table of the diversion of the Danube upstream from the Gabčikovo/Bős hydroelectric power plant in a hydraulically connected, geologically identical, and structurally not decomposable geological area in North-West Hungary. On the basis of shallow-groundwater level monitoring data the impact was traced back to the effect of the Danube’s changed flow course, and quantized for the whole study area. To this end the influence of the river had to be separated from the effect of precipitation. The means chosen was the application of dynamic factor analysis to the registered hydrograph time series. We conclude that the originally homogeneous and dominant effect of the Danube has split and now consists of a diverted and a returning component (downstream from the power plant), and that this is a likely cause of ram-effect and river bed clogging. Furthermore the effect of precipitation ceased to be suppressed, and came to the fore.

Comparative advantages of conservation agriculture based rice–wheat rotation systems under water and salt dynamics typical for the irrigated arid drylands in Central Asia

In Central Asia, the increasing water shortage and labor scarcity, high cost of production, increasing secondary soil salinization, and land abandonment are compelling farmers to change to water saving irrigation and conservation agriculture (CA) technologies. Such CA practices aim at maximizing profits while making a better use of soil and water resources lowering labor demands, farm power and production costs. The CA experiments with rice–wheat systems combined two establishment methods (beds and flats) with three residue levels (all zero tillage) and with alternate wet and dry (AWD) irrigation followed by surface seeded wheat (SSW); and conventional tillage (dry tillage) and continuously flooded rice (water seeded rice, WSR) followed by SSW. These were evaluated for 2 years (2008–2010) by using several financial indicators such as gross margins (GMs) estimates and benefit/cost ratio (BCR) while accounting for the soil water balance and soil salinity dynamics. The GM and BCR were higher under WSR–SSW than under treatments of dry seeded rice (DSR)–SSW. Both were higher under residue removal compared to residue retainments in DSR-SSW. Surface seeded wheat, which involved minor production costs, yielded >6tha−1 in both years in all treatments. Furthermore, >80% of the total irrigation water was applied to rice. Yet, >90% from WSR–SSW and ∼67% from DSR–SSW were lost through seepage and percolation. Dry seeded rice in bed (DSRB)–SSW saved 15% more irrigation water compared to dry seeded rice in flat (DSRF)–SSW and 67% compared to WSR–SSW. Soil salinity decreased with rice cultivation. After 2 years, WSR–SSW had the lowest while residue-removed DSRB–SSW had the highest salinity level at all soil depths. Groundwater salinity under deep groundwater tables was higher under treatments of DSR–SSW than under WSR–SSW. However, under shallow groundwater tables, groundwater salinity was higher under WSR–SSW than under DSR–SSW. Under the conditions that irrigation water is subsidized or even free of charge, conventional WSR–SSW into the standing rice field (20 days before rice harvest) is the most profitable option. However, under water scarce conditions, the CA based rice–wheat system could be a suitable alternative to cope with water scarcity and secondary soil salinization. Before this crop production system can be advocated and promoted, it needs to be flanked by adequate water pricing policies.

A MODFLOW Infiltration Device Package for Simulating Storm Water Infiltration.

This article describes a MODFLOW Infiltration Device (INFD) Package that can simulate infiltration devices and their two-way interaction with groundwater. The INFD Package relies on a water balance including inflow of storm water, leakage-like seepage through the device faces, overflow, and change in storage. The water balance for the device can be simulated in multiple INFD time steps within a single MODFLOW time step, and infiltration from the device can be routed through the unsaturated zone to the groundwater table. A benchmark test shows that the INFD Package's analytical solution for stage computes exact results for transient behavior. To achieve similar accuracy by the numerical solution of the MODFLOW Surface-Water Routing (SWR1) Process requires many small time steps. Furthermore, the INFD Package includes an improved representation of flow through the INFD sides that results in lower infiltration rates than simulated by SWR1. The INFD Package is also demonstrated in a transient simulation of a hypothetical catchment where two devices interact differently with groundwater. This simulation demonstrates that device and groundwater interaction depends on the thickness of the unsaturated zone because a shallow groundwater table (a likely result from storm water infiltration itself) may occupy retention volume, whereas a thick unsaturated zone may cause a phase shift and a change of amplitude in groundwater table response to a change of infiltration. We thus find that the INFD Package accommodates the simulation of infiltration devices and groundwater in an integrated manner on small as well as large spatial and temporal scales.

Topographic migration of 2D and 3D ground‐penetrating radar data considering variable velocities

ABSTRACTWe present a 2D/3D topographic migration scheme for ground‐penetrating radar (GPR) data which is able to account for variable velocities by using the root mean square (rms) velocity approximation. We test our migration scheme using a synthetic 2D example and compare our migrated image to the results obtained using common GPR migration approaches. Furthermore, we apply it to 2D and 3D field data. These examples are recorded across common subsurface settings including surface topography and variations in the GPR subsurface velocity field caused by a shallow ground water table. In such field settings, our migration strategy provides well focused images of common‐offset GPR data without the need for a detailed interval velocity model. The synthetic and field examples demonstrate that our topographic migration scheme allows for accurate GPR imaging in the presence of variations in surface topography and subsurface velocity.

Identifying the Transport Pathways of Dissolved Organic Carbon in Contrasting Catchments

Dissolved organic C (DOC) plays an important role in the cycling and distribution of energy and nutrients. However, factors controlling the transport of DOC both within and between ecosystems are not clear. The aim of this work was to identify the contributing pathways for transport of DOC to surface water in catchments contrasting in land use and hydrogeology and during different flow regimes. Stream water was sampled to observe temporal variation of DOC concentrations and quality both seasonally and at the time scale of a rain event. Major cation and silica concentrations in stream water, groundwater, soil pore water, precipitation/throughfall, and riparian zone water samples were combined in an end‐member mixing analysis to determine the contributing end‐members for DOC delivery at the catchment outlet. Results show that the change in DOC concentrations and quality observed in the stream water during a rain event can be explained by a change in contribution of the different end‐members. In the forested catchments with deep groundwater tables, the main pathway for DOC transport from the soil to the surface water during base flow was via the groundwater. Rising stream DOC concentrations during rainfall events were attributed to additional throughfall and riparian zone transport pathways. In the grassland catchments with shallow groundwater tables, DOC in the stream mainly originated from seeps. During rain events, contributions from a surficial transport pathway and riparian zone water gained importance. The importance of contributing pathways changed seasonally and highly depended on the degree of saturation of the vadose zone.

Status of Groundwater Table Depth Under Long-Term Irrigation in Wonji Plain: Concerns for Sustainability of Wonji-Shoa Sugar Estate, Upper Awash Valley, Ethiopia

<p>The present study attempted to highlight the concerns of shallow groundwater table depth (GWTD) to the sustainability of Wonji-Shoa Sugar Estate (WSSE), Upper Awash Valley of Ethiopia. The recent magnitude and fluctuation of GWTD is mapped in ArcView GIS (using universal kriging technique) from the monthly GWTD monitoring data (2007-2009) using piezometer tubes. The study result clearly showed that the GWTD at WSSE was extremely shallow, showed great spatio-seasonal variability and rising trend; thus, threatening the sustainability of WSSE significantly. About 90% of the plantation fields have GWTD above the critical depth of 1.5 m below the soil surface and, hence, critically waterlogged. As a result, the estate is recently achieving only 55% of the production potential realized in the 1960s. Past trends indicate that the GW has the potential to inundate Wonji plain and is anticipated to devastate production during the next 10-15 years. Therefore, in order to sustain production system in the region, there is an urgent need to identify the possible causes of waterlogging and investigate the feasible remedial measures to combat its problems. The spatial mapping of GWTD with identified problematic areas, indicated in the current study, is believed to provide a tool for water management and, hence, crucial for the decision making and actions taking processes.</p>

Assessing the efficiency of switchgrass different cultural practices for pellet production

Switchgrass is a perennial crop producing high amounts of biomass for good quality pellet production. The objective of this study is to examine the efficiency of different cultural practices of switchgrass for pellet production under field conditions for four different N-fertilization (0, 80, 160 and 240kgha−1) and two different irrigation levels (0 and 250mm), in two soils in central Greece with rather different moisture status over the period 2009–2012. Moreover, comparison between three harvest methods (two different types of bales and silage) was made. The results derived from this study revealed that the bale at 22kg is the harvesting practice with the highest costs while there was reduction of efficiency scores when nitrogen levels increased. At both environments the efficiency scores followed the same trend, confirming that low levels of nitrogen fertilization enhance the economic competitiveness of switchgrass production. Palamas site is the area where switchgrass for pellet production had positive income ranging from 400 to 1600€ha−1, while Velestino site had always negative. Therefore, places like Velestino with non-aquic soil should be avoided for switchgrass. These data suggest that growing switchgrass for solid biofuel production as energy crop is a worthwhile decision only in areas with a moderately shallow groundwater table (aquic soil) or maybe in high precipitation regions.

Multi-objective Assessment of Groundwater Quality in Madinah City, Saudi Arabia

In this research, a comprehensive assessment of groundwater quality in the city of Madinah, Saudi Arabia was carried out. The main objective was to evaluate whether the groundwater in the city is contaminated by leakage from different sources which will, in turn, give insight into the sources contributing to the shallow groundwater table rise (SWTR) that is observed in many locations in the city. In addition, the assessed groundwater quality helps in determining the most appropriate reuse of the excess water. Out of the 23 wells that were drilled in the study area for the purposes of this study, 20 wells were sampled for water quality analyses. Results showed that the groundwater in the study area is not contaminated by waste water or organic and inorganic compounds or by pesticides and herbicides from excess irrigation of agricultural areas. This suggests that the recent accelerated urban development in the city did not negatively impact the quality of groundwater and did not significantly contribute to SWTR in the city. Lithological description based on soil samples collected from drilled wells revealed the presence of impervious aquitard that extends over the aquifer in the city. This impervious aquitard has most likely played a role in protecting groundwater quality in the study area. Piper and Schoeller diagrams showed that the water type in the study area is a sodium-chloride type with a significant presence of sulfate. Results of this research give useful information about groundwater quality in Madinah city and will help authorities in planning the most appropriate reuse of excess water that may be pumped out to control SWTR.

Towards hydrological and geochemical understanding of an ephemeral palustrine perched water table “wetland” (Lanseria Gneiss, Midrand, South Africa)

Wetland delineation is commonly based on terrain unit, soil form, soil wetness and vegetation indicators which along with the shallow groundwater or proximate surface water are often absent in many ephemeral inland South African areas due to, for instance, prolonged dry periods (seasons to years) which mask these indicators, as well as disruption of surface materials due to construction, agricultural activities and field fires. Furthermore, many “wetlands” in South Africa comply with the four indicators, but the notable absent requirement for wetlands is missing, namely the shallow groundwater table, as many of these systems form in hillslope seeps, catenas or from perched water tables. A 200-m-long excavation through one such a system is being studied in Midrand (Gauteng, South Africa). The site is underlain by Lanseria Gneiss and is waterlogged after long and intense periods of intense rainfall. Frequent downslope soil profiling, horizon-specific laboratory analyses for grading and Atterberg Limits, X-Ray Diffraction and X-Ray Fluorescence Spectroscopy data are interpreted together with soil percolation tests to generate a conceptual model of the system. The results are discussed in terms of the need to consider these temporary systems that do not have a shallow groundwater table and that are not in direct contact with surface drainage features as a possible special type of wetlands, notably in arid regions where they play a very important role in biodiversity and should, therefore, be protected.

Water sources of Medicago sativa grown in different slope positions in Yanchi County of Ningxia

Aims Alfalfa (Medicago sativa) is considered as an elite forage with high economic and ecological values. In semi-arid areas of Northwest China, the low rainfall is far from satisfying water demand of alfalfa. The northern part of Yanchi County is adjacent to Mu Us desert and has a shallow groundwater table. In this area, groundwater could be the potential water sources for growing alfalfa. Our objective was to investigate the growth performance and potential water sources of alfalfa grown in four slope positions with different altitudes in the bottomland of northern Yanchi County. Method Stable O and D isotope compositions (δO and δD) of different water sources and xylem water were analyzed in April, June, July and August 2013. IsoSource was used to calculate the probable contribution of different water sources to the total plant water uptake. Stomatal conductance, carbon isotope discrimination (ΔC) of whole plant, soil volumetric water content in the 0–300 cm soil profile were also determined. Important findings Slope position had a significant effect on water content in the 0–300 cm soil profile. Highest soil water content was found in the slope position of lowest altitude. The δO-δD coordinates of soil water and plant stem xylem water were distributed on the right of Northwest China local meteoric water line (LMWL), indicating that oxygen and hydrogen isotopic compositions in the water sources of alfalfa were subjected to enrichment due to evaporation. The δO values of soil water in the 0–450 cm profile increased with altitude. Soil water δO values decreased with the depth of soil profile for a given slope position. Soil water δO values in deep profile were similar to those in groundwater, implying that groundwater would move to the upper soil layer via soil capillary. Seasonal fluctuation was observed in soil water δO in the 0–40 cm profile, while soil water δO in 朱林等: 宁夏盐池不同坡位旱地紫苜蓿水分来源 1227 doi: 10.3724/SP.J.1258.2014.00118 profile below 270 cm was stable seasonally. Plant stem xylem water δO value was significantly lower (p < 0.001) in the slope position 1 than in other three slope positions in April, July and August. Highest water utilization rate from deep soil profile (below 270 cm) was recorded for alfalfa grown in the slope position 1 in April, June and July. In August, alfalfa grown in the slope positions 1, 3 and 4 mainly used soil water in the 150–270 cm and 270–450 cm profiles and groundwater; highest dependence on soil water in the shallow profile (0–20 cm) was found in alfalfa grown in the slope position 2. Higher yield, whole plant ΔC value and stomatal conductance were observed in alfalfa grown in the slope position 1 than in other three slope positions. These results suggest that bottomland with lower altitude and shallow groundwater table should be adopted when planting alfalfa without irrigation in the semi-arid areas of Northwest China where average annual rainfall is around 280 mm. Thus, groundwater could contribute to better growth performance of alfalfa, leading to higher ecological and economic returns.

Surface water hydrology and geomorphic characterization of a playa lake system: Implications for monitoring the effects of climate change

Playa lakes are sensitive recorders of subtle climatic perturbations because these ephemeral water bodies respond to the flux of diffuse and channelized flow from their watersheds as well as from direct precipitation. The Black Rock Playa in northwestern Nevada is one of the largest playas in North America and is noted for its extreme flatness, varying less than one meter across a surface area of 310 km2. Geo-referenced Landsat imagery was used to map surface-area fluctuations of ephemeral lakes on the playa from 1972 to 2013 to provide baseline data on surface water hydrology of this system to compare to future hydrologic conditions caused by climate change. The area measurements were transformed into depth and volumetric estimates using results of detailed topographic global positioning system (GPS) surveys and correlated with available surface hydrological and meteorological monitoring data. Playa lakes reach their maximum size (<350 km2) in spring, fed by melting snows from high mountains on the periphery of the drainage basin, and usually desiccate by early- to mid-summer. The combination of a shallow groundwater table, sediment deposition, and hydro-aeolian planation probably are largely responsible for the flatness of the playa. When lakes do not form for a period of several years, the clay- and silt-rich playa surface transforms from one that is hard and durable into one that is soft and puffy, probably from upward capillary movement of water and resultant evaporation. Subsequent flooding restores the hard and durable surface. The near-global availability of Landsat imagery for the last 41 years should allow the documentation of baseline surface hydrologic characteristics for a large number of widely-distributed playa lake systems that can be used to assess the hydrologic effects of future climate changes.

Long-term variability in the water budget and its controls in an oak-dominated temperate forest

Water availability is one of the key environmental factors that control ecosystem functions in temperate forests. Changing climate is likely to alter the ecohydrology and other ecosystem processes, which affect forest structures and functions. We constructed a multi-year water budget (2004–2010) and quantified environmental controls on an evapotranspiration (ET) in a 70-year-old mixed-oak woodland forest in northwest Ohio, USA. ET was measured using the eddy-covariance technique along with precipitation (P), soil volumetric water content (VWC), and shallow groundwater table fluctuation. Three biophysical models were constructed and validated to calculate potential ET (PET) for developing predictive monthly ET models. We found that the annual variability in ET was relatively stable and ranged from 578 mm in 2009 to 670 mm in 2010. In contrast, ET/P was more variable and ranged from 0.60 in 2006 to 0.96 in 2010. Mean annual ET/PET_FAO was 0.64, whereas the mean annual PET_FAO/P was 1.15. Annual ET/PET_FAO was relatively stable and ranged from 0.60 in 2005 to 0.72 in 2004. Soil water storage and shallow groundwater recharge during the non-growing season were essential in supplying ET during the growing season when ET exceeded P. Spring leaf area index (LAI), summer photosynthetically active radiation, and autumn and winter air temperatures (Ta) were the most significant controls of monthly ET. Moreover, LAI regulated ET during the whole growing season and higher temperatures increased ET even during dry periods. Our empirical modelling showed that the interaction of LAI and PET explained >90% of the variability in measured ET. Altogether, we found that increases in Ta and shifts in P distribution are likely to impact forest hydrology by altering shallow groundwater fluctuations, soil water storage, and ET and, consequently, alter the ecosystem functions of temperate forests. Copyright © 2013 John Wiley & Sons, Ltd.

Economic Efficiency of Different Agricultural Practices of “Panicum virgatum L. (switchgrass)” for Fodder Production

Switchgrass is a multipurpose perennial crop characterized by high yield (for fodder or raw material for pellet production) under low inputs conditions. This study sought to analyse the economic efficiency of different cultivating practices of switchgrass for hay or silage production. To assess the economic efficiency, three-year field experiments were established in two contrasting environments in central Greece (Palamas and Velestino) and contained two experimental factors: quantity of irrigation water (two levels: 0 and 250 mm) and applied nitrogen fertilization (four levels: 0, 80, 160 and 240 kg N ha-1). Moreover, the costs of four different harvest methods (three different types of straw-bales for hay production and silage) were taken into account. The results demonstrated that production cost is largely depended on the harvesting practice. In addition, an attractive income of 1,745 €/ha (the higher one at Palamas site) for fodder production was found. The efficiency scores follow the same tendency at both sites, verifying that there is no necessity of high levels of nitrogen fertilization in order to improve switchgrass production efficiency. These data suggest that switchgrass is attractive as a fodder crop in regions with high precipitation or in areas with a moderately shallow groundwater table and should be seriously taken into consideration for future land use systems in Greece and more generally in the Mediterranean basin.

Shallow groundwater uptake and irrigation water redistribution within the potato root zone

Knowing the crop water uptake pattern and soil water movement within the root zone is important for the optimum design of irrigation and drainage systems. The objective of this study was to monitor the soil water redistribution within the potato root zone after irrigation and to quantify shallow groundwater contribution to water use by potatoes. The water uptake pattern in a vertical plane was monitored by TDR miniprobes installed at five different depths and at three different radial distances from the base of the potato plants. Three such planes of TDR miniprobes were used as replicates. The soil within the root zone was brought to field capacity by surface application of water. The water content measurements were carried out prior to this irrigation event and at periodic intervals thereafter over a four-day period, three times/day. The groundwater level was measured at 3h intervals. Soil core samples were taken at each TDR probe location to determine the root density. The soil water content and upward flux from the groundwater was simulated using HYDRUS-1D model and the results were compared with the upward flux estimated from the change in groundwater levels. The maximum root density was found to be 14.5 and 252g/m−3 at two and three months after planting. Soil layers at shallower depths showed signs of drying while the deeper layers remained wet. Model simulations closely matched the measured soil water contents and upward flux. In a fine sandy loam, up to 92% of the crop water demand was met by capillary rise from the shallow groundwater table. Knowing the shallow water table contribution can decrease the net depth of irrigation water applied and save water and energy needed for pumping.

Simulating soil water regime in lowland paddy fields under different water managements using HYDRUS-1D

The widely adopted alternate wetting and drying (AWD) irrigation for rice production in lowland paddy fields with shallow groundwater table is increasingly needed to quantify the soil water regime for irrigation schedule design. Field experiments were conducted to compare the soil water flow between paddy fields under AWD and continuously flooded irrigation (CFI), during the rice growing season in 2010–2011. Model simulations using HYDRUS-1D were also conducted based on the measured pressure head distribution of soil profiles. Modeling results show that the pressure head derived from forward simulation using the point estimated soil hydraulic parameters did not agree well with the measured pressure head. However, from inverse modeling of saturated hydraulic conductivities of plow pan (mean of 0.68cmd−1 in AWD plots and 0.54cmd−1 in CFI plots), the HYDRUS-1D model can properly simulate the water flow in multi-layer paddy soil flow, where the plow pan plays an important role in determining the vertical pressure head distribution. The measured pressure head and simulated pressure head derived from inverse modeling agreed well (NSE of 0.93–0.98) during the whole rice growing season. Measurement and simulation results indicated that the practice of AWD decreased the percolation 38.2–40.3% in 2010 and 23.3–27.2% in 2011, compared to that of CFI. It is also found that groundwater capillary rise amounted to 26.1–27.4% in AWD plots, and 10.2–18.1% in CFI plots of respective water input (irrigation and rainfall).

Geostatistical monitoring of soil salinity in Uzbekistan by repeated EMI surveys

Soil salinization in the lower reaches of Amudarya is a constant threat. High seepage losses in irrigation water delivery network and deteriorated drainage network result in rising groundwater tables. The shallow groundwater table contributes to salinization of the rooting zone which is tackled by leaching at the end or beginning of the vegetation season. However, there is growing concern that the efficiency of the leaching with application of high amounts of water is low, and besides that the leaching effects are not long-lasting. To monitor local soil salinity an efficient strategy is developed, using electromagnetic induction (EMI) meter measurements. The monitoring strategy is applied and evaluated in a case study in Uzbekistan. The study area of 80ha was surveyed in 2008–2011, at the end of the vegetation season (October–November), with the EMI in vertical dipole mode. In addition, at 142 calibration locations (including 28 revisited) both EMI was recorded and the soil was sampled to determine electrical conductivity (ECe) in laboratory. Log-transformed values of EMI and ECe were used to fit a simple linear regression model. Maps of ECe at the four time points were obtained by simulating multiple maps of log(EMI) using the ordinary kriging model. Besides, multiple vectors of regression coefficients were simulated, which were used to transform the simulated log(EMI) maps. Finally, simulated maps of regression residuals were added to the transformed log(EMI) fields, and backtransformed. Besides maps with predicted ECe the simulations were used to derive maps of the probability that ECe exceeds the critical threshold of 8dSm−1, and a map of the predicted linear temporal trend in ECe. The results show that in 2008–2011 most of the area was not saline, with only several spots reaching a predicted ECe of 6dSm−1. The probabilities that ECe exceeds the critical threshold of 8dSm−1 were small, and the predicted percentage of the area where ECe exceeds this threshold was very small. At most places a slight positive linear trend in ECe was predicted, but this predicted local trend was not significant at most places. Two areas of concern could be distinguished. First, spots occur displaying pronounced fluctuations in salinity from year to year with peaks close to the critical threshold, suggesting that these areas might be prone to soil salinization over short periods of time. Second, in the central part of the area a gradual build-up of soil salinity was seen, which calls for interventions to halt or reverse the build-up.

Assessment of Groundwater Pollution Potential Using GIS and Modified Drastic Model in Selangor, Malaysia

This study covered the assessment of groundwater pollution potential using modified DRASTIC model and GIS based on hydro-geological environmental parameters Selangor State in Malaysia. The modification of ranges and ratings index in DRASTIC was done using GIS to accommodate hydro-geological settings to implement and adopt data according to Selangor hydro geological environmental parameters. The groundwater pollution potential map showed that the high risk groundwater pollution potential covered 17% of study area in west side of Selangor however, 27% of the east side of Selangor exposed to low risk groundwater pollution potential. Most of the affected area was considered in low land area along the coastal in shallow groundwater table alluvial aquifer. The results significantly show that groundwater pollution potential map was successfully developed using hydro-geological parameters for Selangor area.

A simplified model of soakaway infiltration interaction with a shallow groundwater table

This paper presents a new and simplified modeling concept for soakaway infiltration in the presence of a shallow groundwater table, including representation of the local groundwater mound and its effects on the infiltration rate. The soil moisture retention curve is used to represent the influence of the mound on infiltration rates. The model is intended to be used in situations when distributed urban drainage models with soakaways or similar infiltration devices are coupled to distributed groundwater flow models. With this new modeling concept, the local mounding from small-scale infiltration systems, and its effects on the infiltration rate, can be represented even if the spatial resolution of the groundwater flow model is coarser than the extent of the mound. The new model has been run for a number of scenarios and soil parameters, and the results compared to the output from a two-dimensional unsaturated/saturated flow model based on Richard’s equation. The comparison shows that soakaway emptying times calculated by the new model are on average 13% higher than the emptying times of the two-dimensional model. The deviation is smaller for scenarios including a shallow groundwater table, only around 5% on average. Groundwater mounding depths are underestimated close to the soakaway and overestimated far from the soakaway. At 5 m distance from the soakaway center, the average deviation is 18% for the shallow groundwater scenarios. Mass balance errors were checked and found to be below 1% for all scenarios at all times during the simulation period. The extra uncertainty introduced by this new model is compensated for by the reduction in runtime; it is on average 600 times faster than the two-dimensional model. Furthermore, the new model is based on the same input parameters as the two-dimensional model and thus requires no extra calibration. The new modeling concept is therefore a useful tool for simulating small-scale stormwater infiltration in the presence of a shallow groundwater table with distributed models on larger scales.

Appraising options to reduce shallow groundwater tables and enhance flow conditions over regional scales in an irrigated alluvial aquifer system

Some of the world’s key agricultural production systems face big challenges to both water quantity and quality due to shallow groundwater that results from long-term intensive irrigation, namely waterlogging and salinity, water losses, and environmental problems. This paper focuses on water quantity issues, presenting finite-difference groundwater models developed to describe shallow water table levels, non-beneficial groundwater consumptive use, and return flows to streams across two regions within an irrigated alluvial river valley in southeastern Colorado, USA. The models are calibrated and applied to simulate current baseline conditions in the alluvial aquifer system and to examine actions for potentially improving these conditions. The models provide a detailed description of regional-scale subsurface unsaturated and saturated flow processes, thereby enabling detailed spatiotemporal description of groundwater levels, recharge to infiltration ratios, partitioning of ET originating from the unsaturated and saturated zones, and groundwater flows, among other variables. Hybrid automated and manual calibration of the models is achieved using extensive observations of groundwater hydraulic head, groundwater return flow to streams, aquifer stratigraphy, canal seepage, total evapotranspiration, the portion of evapotranspiration supplied by upflux from the shallow water table, and irrigation flows. Baseline results from the two regional-scale models are compared to model predictions under variations of four alternative management schemes: (1) reduced seepage from earthen canals, (2) reduced irrigation applications, (3) rotational lease fallowing (irrigation water leased to municipalities, resulting in temporary dry-up of fields), and (4) combinations of these. The potential for increasing the average water table depth by up to 1.1 and 0.7 m in the two respective modeled regions, thereby reducing the threat of waterlogging and lowering non-beneficial consumptive use from adjacent fallow and naturally-vegetated lands, is demonstrated for the alternative management intervention scenarios considered. Net annual average savings of up to about 9.9 million m3 (8000 ac ft) and 2.3 million m3 (1900 ac ft) of non-beneficial groundwater consumptive use is demonstrated for the study periods in each of the two respective study regions. Alternative water management interventions achieve varying degrees of benefits in each of the two regions, suggesting a need to adopt region-specific interventions and avoid a ‘one-size-fits-all’ approach. Impacts of the considered interventions on return flows to the river were predicted to be significant, highlighting the need for flow augmentation to comply with an interstate river compact and portending beneficial impacts on solute loading.

Evaluation of the soil water balance in an alluvial flood plain with a shallow groundwater table

Many of the hydrological and ecological functions of alluvial flood plains within watersheds depend on the water flow exchanges between the vadoze soil zone and the shallow groundwater. The water balance of the soil in the flood plain is investigated, in order to evaluate the main hydrological processes that underlie the temporal dynamics of soil moisture and groundwater levels. The soil moisture and the groundwater level in the flood plain were monitored continuously for a three-year period. These data were integrated with the results derived from applying a physically-based numerical model which simulated the variably-saturated vertical water flow in the soil. The analysis indicated that the simultaneous processes of lateral groundwater flow and the vertical recharge from the unsaturated zone caused the observed water table fluctuations. The importance of these flows in determining the rises in the water table varied, depending on soil moisture and groundwater depth before precipitation. The monitoring period included two hydrological years (September 2009–September 2011). About 13% of the precipitation vertically recharged the groundwater in the first year and about 50% in the second. The difference in the two recharge coefficients was in part due to the lower groundwater levels in the recharge season of the first hydrological year, compared to those observed in the second. In the latter year, the shallow groundwater increased the soil moisture in the unsaturated zone due to capillary rise, and so the mean hydraulic conductivity of the unsaturated soil was high. This moisture state of soil favoured a more efficient conversion of infiltrated precipitation into vertical groundwater recharge. The results show that groundwater dynamics in the flood plain are an important source of temporal variability in soil moisture and vertical recharge processes, and this variability must be properly taken into account when the water balance is investigated in shallow groundwater environments. Citation Pirastru, M. and Niedda, M., 2013. Evaluation of the soil water balance in an alluvial flood plain with a shallow groundwater table. Hydrological Sciences Journal, 58 (4), 898–911.