Lateral Subsurface Flow Research Articles

The impact of the geologic setting on the Quaternary aquifer, El-Tur area, Southwest Sinai, Egypt

The groundwater extracted from the unconfined Quaternary aquifer is the main source of water supply in El-Tur area. The area is bounded from the east by the elevated basement complex of Southern Sinai and from the west by El-Qabaliyat Ridge. The wadis dissecting these highlands form effective watersheds of the Quaternary aquifer. These wadis form areas of focused recharge. Recharge also occurs directly via the Quaternary sediments covering El-Qaa Plain. Subsurface lateral groundwater flow from the fractured basement contributes significant recharge to the aquifer as well. The aquifer sediment facies affect the type and quality of groundwater. In the eastern part where the aquifer is composed mainly of gravel and coarse sand with fragments of weathered basement, the Na-Cl-SO4 water dominates. In the west where the facies change is rapid and complex, many water types arise. The base exchange index (BEX) is positive in this part reflecting the role of clay minerals in changing the water types via cation exchange. In the east where clays are insignificant in the aquifer, the BEX is negative. In the western part next to El-Qabaliyat Ridge, the wells discharging from the calcareous sand zone have low groundwater salinities compared to the wells discharging from the alluvium. In general, the groundwater salinity increases in the direction of groundwater flow from the northeast to the southwest which reflects the dissolution of aquifer sediments. The concentration relationships between the major ions on one hand and chloride on the other reflect the dissolution of calcium carbonates, precipitation of K- and Mg-bearing minerals, and cation exchange of Ca for Na on clay minerals. The hydrochemical models support these reactions. In addition, they show that the effect of evaporation on the recharge water in the western catchment is about four times its effect on the eastern recharge water which reflects the rapid recharge through the wadis draining the fractured basement. Moreover, the contribution from the eastern catchment in sample No. 23 is more than four-folds the contribution from the western recharge area. The stable isotopes (2H and 18O) show that the Quaternary aquifer is recharging from recent rainfall. However, upward leakage of Paleogene groundwater (depleted in 18O) also occurs. The groundwater level map shows strong overpumping impact especially in the areas close to El-Tur city.

Numerical Analysis of Groundwater Ridging Processes Considering Water-Air Flow in a Hillslope.

In this study, a water-air two-phase flow model was employed to investigate the formation, extension, and dissipation of groundwater ridging induced by recharge events in a hypothetical hillslope-riparian zone, considering interactions between the liquid and gas phases in soil voids. The simulation results show that, after a rain begins, the groundwater table near the stream is elevated instantaneously and significantly, thereby generating a pressure gradient driving water toward both the stream (the discharge of groundwater to the stream) and upslope (the extension of groundwater ridging into upslope). Meanwhile, the airflow upslope triggered by the advancing wetting front moves downward gradually. Therefore, the extension of groundwater ridging into upslope and the downward airflow interact within a certain region. After the rain stops, groundwater ridging near the stream declines quickly while the airflow in the lower part of upslope is still moving into the hillslope. Thus, the airflow upslope mitigates the dissipation of groundwater ridging. Additionally, the development of groundwater ridging under different conditions, including rain intensity, intrinsic permeability, capillary fringe height, and initial groundwater table, was analyzed. Changes in intrinsic permeability affect the magnitude of groundwater ridging near the stream, as well as the downward speed of airflow, thereby generating highly complex responses. The capillary fringe is not a controlling factor but an influence factor on the formation of groundwater ridging, which is mainly related to the antecedent moisture. It was demonstrated that groundwater ridging also occurs where an unsaturated zone occurs above the capillary fringe with a subsurface lateral flow.

Identification of runoff formation with two dyes in a mid-latitude mountain headwater

Abstract. Subsurface flow in peat bog areas and its role in the hydrologic cycle has garnered increased attention as water scarcity and floods have increased due to a changing climate. In order to further probe the mechanisms in peat bog areas and contextualize them at the catchment scale, this experimental study identifies runoff formation at two opposite hillslopes in a peaty mountain headwater; a slope with organic peat soils and a shallow phreatic zone (0.5 m below surface), and a slope with mineral Podzol soils and no detectable groundwater (> 2 m below surface). Similarities and differences in infiltration, percolation and preferential flow paths between both hillslopes could be identified by sprinkling experiments with Brilliant Blue and Fluorescein sodium. To our knowledge, this is the first time these two dyes have been compared in their ability to stain preferential flow paths in soils. Dye-stained soil profiles within and downstream of the sprinkling areas were excavated parallel (lateral profiles) and perpendicular (frontal profiles) to the slopes' gradients. That way preferential flow patterns in the soil could be clearly identified. The results show that biomat flow, shallow subsurface flow in the organic topsoil layer, occurred at both hillslopes; however, at the peat bog hillslope it was significantly more prominent. The dye solutions infiltrated into the soil and continued either as lateral subsurface pipe flow in the case of the peat bog, or percolated vertically towards the bedrock in the case of the Podzol. This study provides evidence that subsurface pipe flow, lateral preferential flow along decomposed tree roots or logs in the unsaturated zone, is a major runoff formation process at the peat bog hillslope and in the adjacent riparian zone.

Identification of runoff type and an assessment of water balance for the megadune area of the Badain Jaran Desert

The Badain Jaran Desert contains numerous megadunes that are characterised by the largest height difference in the world. Various rare landforms are also found on the slopes of the Badain Jaran megadunes, including spring streams, surface infiltration-excess runoff, erosion rills caused by surface runoff, slow-seepage runoff, as well as physical and chemical sediment resulting from subsurface lateral flow outflows. A variety of analyses were performed using electron microscope observation, X-ray diffraction, particle size analysis and field survey, investigating properties such as the mineral composition of the chemical sediment, the particle size composition of the physical sediment and aeolian sand, runoff type, the recharge conditions of precipitation to groundwater and lake water, and the water balance of the megadune area. The formation of the different types of runoff demonstrates that although precipitation in this area is low, effective heavy precipitation processes characterised by single events of more than 15 mm are present that likely act as a source for groundwater. Seven indicators, including the formation of spring water at the bottom of megadunes, multiple runoff types, as well as both physical and chemical sediments, clearly show that precipitation in the area reaches the bottom of megadunes via infiltration, which constitutes an effective supply of lake water and groundwater. The water-resisting property of the fine sand layer is likely the reason why the region is characterised by an outflow of subsurface runoff, with the latter and its sediment further confirming that the area also possesses a positive water balance. This positive water balance is the result of four unique characteristics: the presence of effective heavy precipitation, low transpiration due to scarce vegetation, the high infiltration rate of the sand layer and the small depth of the sand layer affected by evaporation. This in turn means that atmospheric precipitation is sufficient to supply groundwater, leading to the development of the numerous lakes found in the desert area. Water balance calculations revealed that, after accounting for evaporation, transpiration and other sources of consumption of atmospheric precipitation, around 134,648.4–135,976.9 m3 of water per square kilometre per year is still supplied to the groundwater and lake water.

Simulation of Hydrology and Nutrient Transport in the Hetao Irrigation District, Inner Mongolia, China

Intensive agricultural activities in the Hetao irrigation district have severely degraded local aquatic ecosystems and water quality, and Ulansuhai Lake is now the most rapidly degrading eutrophic lake in China. A better understanding of the hydro-agronomic and pollutant transport processes in the area is thus urgently needed. This study simulated monthly streamflow, total nitrogen (TN) and total phosphorus (TP) for the Hetao irrigation district using the Soil and Water Assessment Tool (SWAT) to evaluate the nutrient load, source areas, and hydrological pathways. The Nash-Sutcliffe efficiency (NSE) values obtained for the streamflow simulations were 0.75 and 0.78 for the calibration and evaluation periods, respectively. The SWAT model captured the temporal variation in streamflow (R2 > 0.8) for two periods; the NSE values for the TN and TP loads were 0.63 and 0.64 for the calibration period and 0.48 and 0.42 for the evaluation period, respectively. The predicted monthly TN load was correlated with irrigation (r = 0.61) and the monthly TP load with precipitation (r = 0.89), indicating that nitrogen transport is primarily associated with soil leaching and groundwater flow, and phosphorus is primarily transported by sediments caused by rainfall erosion. A case study of split nitrogen fertilizer applications demonstrated reduced annual TN load by as much as 13% in one year. Fertilization timing also affects the load in different pathways especially in lateral subsurface flow and shallow groundwater. Better agricultural management could thus reduce nitrogen losses, and buffer strips could minimize phosphorus transport.

Modeling Streamflow in a Snow-Dominated Forest Watershed Using the Water Erosion Prediction Project (WEPP) Model

Abstract. The Water Erosion Prediction Project (WEPP) model was originally developed for hillslope and small watershed applications. Recent improvements to WEPP have led to enhanced computations for deep percolation, subsurface lateral flow, and frozen soil. In addition, the incorporation of channel routing has made the WEPP model well suited for large watersheds with perennial flows. However, WEPP is still limited in modeling forested watersheds where groundwater baseflow is substantial. The objectives of this study were to (1) incorporate nonlinear algorithms into WEPP (v2012.8) for estimating groundwater baseflow, (2) auto-calibrate the current and modified WEPP model using a model-independent parameter estimation tool, and (3) evaluate and compare the performance of the current version of WEPP without baseflow (WEPP-Cur) and the modified WEPP model with baseflow (WEPP-Mod) in simulating the hydrology of a snow-dominated watershed in the U.S. Pacific Northwest. A subwatershed of the Upper Cedar River Watershed in western Washington State was chosen for WEPP application and assessment. Simulations were conducted for two periods: 1997-2003 to calibrate the model and 2004-2011 to assess the model performance. The WEPP-Cur simulations resulted in Nash-Sutcliffe efficiency (NSE) and deviation of runoff volume (Dv) values of 0.55 and 24%, respectively, for the calibration period, and 0.60 and 21%, respectively, for the assessment period. The WEPP-Mod simulated streamflow showed improved agreement with observed streamflow, with NSE and Dv values of 0.76 and 6%, respectively, for the calibration period, and 0.74 and 2%, respectively, for the assessment period. The WEPP-Mod model reproduced hydrograph recessions during the low-flow periods and the general trend of the hydrographs, demonstrating its applicability to a watershed where groundwater baseflow was significant. The incorporation of a baseflow component into WEPP will help forest managers to assess the alterations in hydrological processes and water yield for their forest management practices. Keywords: Baseflow, Forest watershed, Hydrological modeling, Streamflow, U.S. Pacific Northwest, WEPP.

Wrap a Wreck! In Situ Conservation of a Ship on Land Suffering from Fungal Decay

Many sixteenth- to eighteenth-century shipwrecks have been found after land reclamation in parts of the former Zuiderzee, one of the busiest waterways in Dutch history. After the land fell dry, some shipwrecks were excavated, destroyed, reburied, or covered with sand or clay. In the late 1970s a method was developed to mitigate degradation processes of some of the wrecks remaining in good condition by wrapping them in plastic foil. The idea was that the plastic would prevent evaporation and lateral subsurface flow. Wet conditions prevent decomposing of wood by especially soft rot fungi. Oxygen will be rapidly depleted by decomposition of organic matter.Recent monitoring of wrapped shipwrecks has shown that this method of preventing rot worked exceptionally well. We adapted wrapping using new technology nowadays applied for sealing tunnels and landfills. We will present the implementation requirements, materials and new adapted method for wrapping shipwrecks.

Field and Laboratory Dissipation of the Herbicide Fomesafen in the Southern Atlantic Coastal Plain (USA).

To control weeds with evolved resistance to glyphosate, Southeastern (USA) cotton farmers have increased fomesafen (5-(2-chloro-α,α,α-trifluoro-p-tolyloxy)-N-mesyl-2-nitrobenzamide) use. To refine fomesafen risk assessments, data are needed that describe its dissipation following application to farm fields. In our study, relatively low runoff rates and transport by lateral subsurface flow, <1.0 and 0.15% of applied respectively, were observed. The low runoff rate was linked to postapplication irrigation incorporation and implementation of a common conservation tillage practice. Moderate soil persistence (t1/2 = 100 days) was indicated in laboratory incubations with surface soil, however, analysis of soil cores from treated plots showed that ≈3% of fomesafen applied persisted in subsoil >3 years after application. Findings suggest low potential for fomesafen movement from treated fields, however, the fate of fomesafen that accumulated in subsoil and the identity of degradates are uncertain. Soil and water samples were screened for degradates, but, none were detected.

Vertical and lateral subsurface preferential flow along an agricultural catena

Despite all efforts, agricultural contaminants remain at alarming concentrations in Quebec surface waters. Preferential flow (PF) of soluble contaminants has been suggested as a contributing factor but has not been specifically studied in the humid climate of eastern Canadian soils. Three tracers were surface applied on plots along a catena on a loamy sand under intensive agricultural production in Beauce, Quebec. Tracer distribution in soil profiles was monitored three times over a 12-month period. At the summit, finger flow rapidly transported tracers into the subsurface. The subsurface preferential lateral flow rapidly brought the tracers downslope. Narrow points of preferential seepage and discharge and underground lateral PF were observed at the footslope. The summit and the backslope of the catena showed strong vertical and lateral subsurface PF, which made their contribution to subsurface tracer movement toward surface water equal to or greater than that of the footslope, in part because of the hydrological connectivity between summit, backslope, and surface water. PF and matrix flow were both significant in all parts of the catena. Therefore, all parts of a catena, even those far from surface water, should be considered when evaluating potential belowground contaminant transport toward surface water.

Influence of lateral subsurface flow and connectivity on soil water storage in land surface modeling

AbstractLateral surface/subsurface flow and their connectivity play a significant role in redistributing soil water, which has a direct effect on biological, chemical, and geomorphological processes in the root zone (~1 m). However, most of the land surface models neglect the horizontal exchanges of water at the grid or subgrid scales, focusing only on the vertical exchanges of water as one‐dimensional process. To develop better hydrologic understanding and modeling capability in complex landscapes, in this study we added connectivity‐based lateral subsurface flow algorithms in the Community Land Model. To demonstrate the impact of lateral flow and connectivity on soil water storage we designed three cases including the following: (1) with complex surface topography only, (2) with complex surface topography in upper soil layers and soil hydraulic properties with uniform anisotropy. and (3) with complex surface topography and soil hydraulic properties with spatially varying anisotropy. The connectivity was considered as an indicator for the variation of anisotropy in the case 3, which was created by wetness conditions or geophysical controls (e.g., soil type, normalized difference vegetation index, and topographic index). These cases were tested in two study sites (ER 5 field and ER‐sub watershed in Oklahoma) comparing to the field (gravimetric and remote sensing) soil moisture observations. Through the analysis of spatial patterns and temporal dynamics of soil moisture predictions from the study cases, surface topography was found to be a crucial control in demonstrating the variation of near surface soil moisture, but not significantly affected the subsurface flow in deeper soil layers. In addition, we observed the best performance in case 3 representing that the lateral connectivity can contribute effectively to quantify the anisotropy and redistributing soil water in the root zone. Hence, the approach with connectivity‐based lateral subsurface flow was able to better characterize the spatially distributed patterns of subsurface flow and improve the simulation of the hydrologic cycle.

Dissolved Nitrogen, Chloride, and Potassium Loss from Fields in Conventional and Conservation Tillage

Losses of soluble nutrients from cropland and their transport to surface and groundwater are a continuing water quality concern. In this study, we evaluated tillage impacts on dissolved losses of ammonium (NH4-N), nitrate nitrogen (NO3-N), chloride (Cl), and potassium (K) during rotational cotton and peanut production. Tillage treatments were strip tillage (ST), in which crops were planted into 15 cm strips tilled into cover crop residue mulch, and conventional tillage (CT), in which all crop residues were turned into the soil prior to planting. Winter cover crops were used in both tillage systems. Tillage and irrigation treatments were uniformly applied within two 0.6 ha fields located on a moderately sloping hillslope in the southern Atlantic Coastal Plain region of south-central Georgia. Tile drains were installed at the base of the slope of each field to capture and measure lateral subsurface flow. Each field was subdivided into three 0.2 ha plots, with the three plots making up a single tillage block. H-flumes were used for flow measurement and sample collection. During the five-year study, annual precipitation ranged from 910 to 1488 mm, with an annual average of 1201 mm. Annual surface runoff averaged 17% of annual rainfall from the CT field and 11% from the ST field. Because of relatively low variability in concentrations, surface runoff loads closely tracked surface runoff volumes. Annual surface runoff loadings of NH4-N, NO3-N, and Cl from the ST treatment were found to be significantly less than those from the CT treatment. The total five-year load of N (NH4-N and NO3-N) in surface runoff from CT was 8.3 kg ha-1, while it was 5.6 kg ha-1 from ST, equivalent to 1.5% of the total N applied to CT and 1.0% of that applied to ST. Annual subsurface flow averaged 12% of annual precipitation for CT and 21% for ST. Annual average subsurface flow loadings of NH4-N, NO3-N, and K from ST were significantly greater than from CT. The total five-year load of N (NH4-N and NO3-N) in subsurface flow was 45 kg ha-1 from CT and 99 kg ha-1 from ST, equivalent to 8.3% and 18.4% of the total N applied to CT and ST, respectively. Data showed that subsurface flow was the primary hydrologic pathway for dissolved N and Cl loss in both tillage systems. Overall, ST was found to be an effective method for reducing surface runoff and associated soluble losses, but increased infiltration with this practice significantly increased subsurface losses. This introduces a challenge to nitrogen management in reduced tillage systems such as ST in the region.

Genesis of soils with an abrupt textural contrast in the United States

Identified from the USDA Natural Resources Conservation Service databases, soils with an abrupt textural change (ATC)occur in four orders (Alfisols > Mollisols, Ultisols > Aridisols), 14 suborders and 31 great groups and represent nearly 1000 series in the USA. More than three-quarters (79%) of the soils have an argillic horizon and 21% have a natric horizon. An albic horizon is present in 40% of the soils. More than half (58%) of the soils with an ATC occur in Pale- great groups, suggesting older materials. Soil series with an ATC occur primarily in fine (56%) and clayey (14%) particle-size classes; smectitic (49%) and mixed (40%) mineral classes; mesic (39%) and thermic (33%) soil-temperature classes; and ustic (31%), xeric (27%), and aridic (21%) soil-moisture classes. On average, the texture of the eluvial and illuvial horizons varies by two classes on the soil-textural triangle. Of the several theories accounting for the origin of soils with an ATC, clay illuviation from the eluvial to the illuvial horizon must be considered a major process. More than halfof the soils are derived from alluvium and other stratified materials; residual soils may also contain sedimentary layering, which is important in the development of an ATC. Elevenpercent of the soils have a lithologic discontinuity at the eluvial-illuvial junction, which may influence the development of an ATC. The ATC in soils with an aquic soil-moisture regime (13%), such as the Argialbolls, may reflect plugging of the argillic horizon with fine clays which causes lateral subsurface flow that removes clay from the albic horizon.Climate may be important in the development of ATC in the USA, in that many of the soils are subject to extended dry periods, followed by intense thunderstorms. A third (34%) of the soils with an ATC occur in Texas. There are about 271,000 km2 of soils with an ATC in the USA, which accounts for 3.2% of the total land area.

A trench study to assess transfer of pesticides in subsurface lateral flow for a soil with contrasting texture on a sloping vineyard in Beaujolais.

Subsurface lateral flow in both texture-contrast soils and catchments with shallow bedrock is suspected to be a non-point source of contamination of watercourses by pesticides used in agriculture. As a case study, the north of the Beaujolais region (eastern France) provides a favorable environment for such contamination due to its agro-pedo-climatic conditions. Environments seen in the Beaujolais region include intense viticulture, permeable and shallow soils, steep hillslopes, and storms that occur during the periods of pesticide application. Watercourse contamination by pesticides has been widely observed in this region, and offsite pesticide transport by subsurface lateral flow is suspected to be involved in diffuse and chronic presence of pesticides in surface water. In order to confirm and quantify the potential role of such processes in pesticide transfer, an automated trench system has been designed. The trench was set up on a steep farmed hillslope in a texture-contrast soil. It was equipped with a tipping bucket flow meter and an automatic sampler to monitor pesticide concentrations in lateral flow at fine resolution, by means of a flow-dependent sampling strategy. Four pesticides currently used in vine growing were studied to provide a range of mobility properties: one insecticide (chlorpyrifos-methyl) and three fungicides (spiroxamine, tebuconazole, and dimethomorph). With this system, it was possible to study pesticide concentration dynamics in the subsurface lateral flow, generated by substantial rainfall events following pesticide applications. The experimental design ascertained to be a suitable method in which to monitor subsurface lateral flow and related transfer of pesticides.

Inorganic nitrogen losses from irrigated maize fields with narrow buffer strips

Vegetated buffer strips (BS) can help prevent nitrogen (N) losses from fields by subsurface lateral flow, thus protecting water resources. The purpose of this study was to determine if narrow BS would effectively remove dissolved inorganic N from subsurface lateral flow. Nitrate–N (NO3–N) and ammonia–N (NH3–N) concentrations in subsurface lateral flow were measured at 1 m depth in a BS system consisting of five treatments: G: strip of grass (Fescue arundinacea); GS: strip of grass and line of native shrubs (Fuchsia magellanica); GST1: strip of grass, line of shrubs and line of native trees 1 (Luma chequen); GST2: strip of grass, line of shrubs and line of native trees 2 (Drimys winteri); and C: bare soil as control. Water samples for the NO3–N and NH3–N measurements were collected between June 2012 and August 2014 in observation wells located at the inlet (input) and outlet (output) of each treatment. The analyses showed that vegetated BS had NO3–N removal efficiency ranging from 33 to 67 % (mean 52 %), with the G treatment showing the best performance in reducing NO3–N concentrations in subsurface lateral flow. The BS treatments were not effective in reducing NH3–N concentrations. The results suggested that N uptake by grass is the main process associated with the NO3–N retention capacity of vegetated BS.

Tillage impact on herbicide loss by surface runoff and lateral subsurface flow

There is worldwide interest in conservation tillage practices because they can reduce surface runoff, and agrichemical and sediment losses from farm fields. Since these practices typically increase infiltration, their use may increase subsurface transport of water-soluble contaminants. Thus, to assess long-term environmental benefits of conservation tillage data may be needed that quantify both surface and subsurface contaminant fluxes. This study focused on the herbicide fluometuron (N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl]-urea) and its soil degradate DMF (N-methyl-N′-[3-(trifluoromethyl) phenyl]-urea). Both compounds are classed as “leachable”. They were measured for 10years in surface runoff and lateral subsurface flow from paired fields located on a hill slope in the Atlantic Coastal Plain region of the southeastern USA. One group of fields was conventionally tilled incorporating all crop residues into soil prior to planting. The second was strip tilled, a common conservation tillage practice. Seven fluometuron applications were made to cotton (Gossypium hirsutum) produced in rotation with peanut (Arachis hypogea). Combined fluometuron and DMF surface and subsurface losses from the conventionally tilled fields were equivalent to 1.2% and 0.13% of fluometuron applied and 0.31% and 0.32% from the strip tilled fields. Annual surface runoff losses were significantly greater from the conventionally tilled fields while the strip tilled fields had significantly greater annual subsurface losses. Results demonstrated that shifting from conventional to conservation tillage management of farm fields in this landscape will reduce surface runoff losses of herbicides like fluometuron but subsurface losses will likely increase. The same trends can be expected in landscapes with similar soil and hydrologic properties. This should be considered when planning implementation of programs that promote conservation tillage use.

Preferential flow mechanisms identified from staining experiments in forested hillslopes

AbstractField staining experiments in five different plots at two sites in Japan (Okaya in Nagano Prefecture and Konohara in Mie Prefecture) were undertaken to improve understanding of subsurface stormflow runoff within organic layers of natural forested hillslopes. This type of shallow lateral subsurface flow, specifically referred to as biomat flow, was observed only at the Okaya site based on staining experiments conducted under controlled water application rates. When the same irrigation rate (50–100 mm h−1) was applied to the Konohara site, overland flow without a significant shallow subsurface component was the dominant flow mechanism. Even in gently sloping (15–20°) forest soils at the Okaya site, biomat flow was responsible for lateral dye transport over much longer distances than subsurface flow in the matrix of mineral soil layers. Based on analysis of staining pattern images observed in the Okaya site, we conclude that (i) the organic biomat layer could be divided into two sub‐layers of different structure, (ii) biomat flow transported the dye tracer longer distances than subsurface flow in the matrix and (iii) the biomat layer topography affected biomat flow by generating preferential flowpaths and subsequent percolation into the deeper soil. Based on field experimental results and pore‐scale consideration of water infiltration into pores of soils with varying wettability properties, we hypothesized and developed a conceptual model for two key biomat flow mechanisms. The first mechanism considers lateral subsurface flow because of a permeability contrast between the much more porous and hence permeable biomat layer and the underlying mineral soil. The second mechanism involves a hydrophobic soil layer between the biomat and the underlying mineral soil. Flow across the hydrophobic layer is believed to occur when a threshold pore pressure is exceeded, i.e. as a result of a perched water table within the biomat layer. Lower pore pressures are needed to initiate flow when preferential flow paths exist, which are less hydrophobic than the surrounding organic layers. Numerical models of catchment hydrology should include lateral biomat flow when such layers are present in hillslope soils, in addition to typical subsurface flow within the soil matrix. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Field observations of soil water content and nitrogen distribution on two hillslopes of different shape

Summary The features of water regimes and nitrogen distribution in hillslope soil could provide information on the design suitability of hillslope shapes near water bodies and knowledge about the interception of nutrients before entering water bodies. Hillslope shape effects on overland flow and subsurface flow have been demonstrated by many previous studies, particularly in arid and semiarid regions. We present results from a 1-year monitoring study of two naturally formed hillslopes (convex and concave) with average gradients of 41% in a humid area (eastern China) to better understand the soil water content (SWC) variations and nitrogen concentration distributions. The SWC at the upper position of the convex hillslope (CVS) varied widely with relatively high coefficients of variance, while those at the lower position of the concave hillslope (CCS) maintained continuous, relatively high values during the study period. Comparatively, the low segment soil profile (top 80 cm) of the CCS maintained the highest soil water storage, followed by the up segment (top 80 cm) of the CCS and the low segment of the CVS, and finally the up segment of the CVS. Lateral subsurface flow discharged out from the 30–80 cm soil layer at the mid positions of the two hillslopes and the lower position of CVS; while the lateral subsurface flow from the upper hillslope recharged into the 30–80 cm soil layer at the upper and lower positions of the CCS and the upper position of CVS. Most of the soil nitrogen infiltrated the hillslope with water. Nitrogen concentrations at 30 cm depth on both the CVS and CCS varied temporally, responding strongly with rainfall events, while nitrogen concentrations at 80 cm depth changed slightly throughout the study period and maintained relatively low values. Nitrogen concentrations remained relatively low at the upper position on the CCS compared with those at the mid and lower positions. Inversely, on the CVS, the upper position had relatively higher or proximate nitrogen concentrations compared to its mid and lower positions. Nitrogen storage in the low segment soil profile of the CCS was higher than its up segment, but they were similar on the CVS. The nitrogen redistributions on the hillslopes were dominantly from water regimes, in particular, from the lateral subsurface flow. Due to the diversity of water regimes in different shaped hillslopes, the interception of lateral subsurface flow and its nitrogen pollution should receive more attention in a humid region.

Soil hydrology: Recent methodological advances, challenges, and perspectives

AbstractTechnological and methodological progress is essential to improve our understanding of fundamental processes in natural and engineering sciences. In this paper, we will address the potential of new technological and methodological advancements in soil hydrology to move forward our understanding of soil water related processes across a broad range of scales. We will focus on advancements made in quantifying root water uptake processes, subsurface lateral flow, and deep drainage at the field and catchment scale, respectively. We will elaborate on the value of establishing a science‐driven network of hydrological observatories to test fundamental hypotheses, to study organizational principles of soil hydrologic processes at catchment scale, and to provide data for the development and validation of models. Finally, we discuss recent developments in data assimilation methods, which provide new opportunities to better integrate observations and models and to improve predictions of the short‐term evolution of hydrological processes.

청미천 유역 내 산림사면에서 단면선에 따른 토양수분특성의 공간적 계절적 변동

사면스케일에서 토양수분의 시공간적 분포를 이해하기 위해서는 사면의 단면선(Transect line)에 따른 토양수분 분포 및 변동에 대해 기본적인 해석과 이해가 선행되어야 한다. 이에 단면선에 따라 설계된 여러 토양수분 측정지점으로부터 토양수분 자료에 대해 토양수분 특성인자를 고려하여 토양수분의 특성변동에 대해 이해하고자 하였다. 또한 사면의 위치 및 지형 그리고 토성의 공간적 분포의 토양수분 특성에 대한 영향도 분석하였다. 연구 사면에서 깊은 토양 층에서 평균적 토양수분의 공간적 분포는 지표 층에서의 공간적 분포 경향과는 많이 달랐으며, 사면의 지형 및 위치 그리고 토성의 공간적 분포는 토양수분의 시공간적 분포특징에 큰 영향을 주는 것으로 나타났다. 특히 상부흐름의 기여가 상당한 측정지점에서는 토양수분 변동의 안정화가 진행이 되는 것으로 나타나, 수문학적 경계(hydrologic Threshold)에 대한 추가 연구가 진행되어야 할 것으로 보인다. 또한 토양수분의 불균질한 공간적 경향은 우선적 흐름의 영향과 관련이 있다고 보여진다. Soil moisture is critical for understanding the spatial-temporal variability of hydrologic processes. The distributions of soil moisture have been explored along transect line in hillslope hydrology. In this study, we measured several soil moistures along transect lines during ten-month period at a hillslope located the Cheong-mi catchment. The soil moisture properties were expressed by simple statistical methods (average, standard deviation, and recession slope) and analyzed in terms of soil depths and transects from the seasonal context. Supplementary studies were also performed about the effect of location, topography and soil texture to the soil moisture responses. The spatial distributions of average soil moisture at deep soil layer were distinguished from those at near surface due to the possibility of expected factors such as subsurface lateral flow from upslope, preferential flow and existence of bedrock. The soil moistures in combined line affected from significant contribution of upper transect line were relatively higher(wetter), low variability compared to those in other transect lines and seemed to be under stabilization process. There are confirmed heterogeneity of soil moisture variation related with preferential flow and significant influence of soil texture for soil moisture properties in upslope.

Estimation of Lateral Subsurface Flow in Lateritic Formations Using Well Hydrograph Analysis

The lateritic formations in west coast of India face a unique problem. In spite of good recharge in unconfined aquifer during monsoon every year, these aquifers drain very quickly in summer season. This is mainly due to the high porosity and permeability of these formations. Proper estimation of lateral subsurface flow from these formations is necessary for sustainable water management. This component is estimated by considering groundwater balance equation. Well hydrograph analysis has been carried out to obtain the gross and net recharge components. 42 open wells of varying diameters and depths spread over the entire microwatershed have been identified for the purpose. A recession equation is developed to predict the water level below ground level in the well at any particular time period of the dry season. Recession curve corresponding to dry periods is considered in obtaining specific yield (Sy)of the formation. The recession flow analysis carried out for the wells show an average value of recession constant for the shallow wells as 0.003 and for deep wells as 0.001. The specific yield determined from recession curves vary from 0.013 to 0.036. The average subsurface flow (SSF) from the microwatershed is found to be 0.09 m /year which is equal to 2.78% of the total annual rainfall. The lateral subsurface flow is estimated as a residue of groundwater balance equation.