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Abstract: The topography, hydroperiod, water table, and selected edaphic characteristics are described for Piermont Marsh, an irregularly flooded tidal marsh in the Hudson River Estuary, New York, USA. Despite variations in microtopography, overall the marsh is flat, and although the observations were conducted at a high point in the Estuary''s 18.6 year metonic cycle, its surface was only inundated 10–12 times a month. Observations of spatial differences in the saturated hydraulic conductivity and surface infiltration rates are also discussed. ‘Edge’ portions of the marsh are characterized by a slightly higher, more uniform, more structured, less organic, and less hydrologically conductive substrate than found in the marsh interior. Preferential flow is facilitated by macropores in the creekbank wall. The water table is close to the marsh surface for a lesser percentage of the lunar month in the marsh ‘edge’ when compared to the interior, where it is almost always within 10cm of the surface. The extent to which the spatial variability of these hydrologic characteristics determines the marsh''s ability to provide various ecosystem services is also discussed and the implications of these observations on tidal marsh restoration efforts briefly presented. [Copyright &y& Elsevier]

The movement of water and potential pollutants in the vadose zone of fluvial deposits is often difficult to predict because fine-over-coarse layers may behave as capillary barriers, funneling water and dissolved solutes into concentrated preferential flow paths. Capillary barriers have been studied in laboratory experiments and by mathematical analysis with well-defined boundaries but little is known about water and solute movement in naturally layered soils. This paper demonstrates how naturally occurring capillary barriers affect water and solute movement. Experiments were carried-out in a river valley near Amherst, MA and on a prehistoric beach near Cornell University in Ithaca, NY. Dye tracer and chloride were initially applied near the soil surface, followed by intermittent rainfall over several weeks. After 2–6 weeks the blue dye, soil water content, and chloride concentration distributions in the soil profile were examined by excavating a trench and photographing and sampling the exposed soil face. At both sites, the infiltrating water was diverted and flowed laterally over a relatively coarse layer. At the Cornell site, flow broke through the fine–coarse interface into the coarse layer at a few points along the barrier. The primary breakthrough at the Cornell site occurred at a horizontal section of the interface, 2 m down-slope from the point of dye application. The capillary diversions generally agreed with current theory, however, the flow patterns were difficult to predict accurately without more detailed information about the soil layering characteristics. [Copyright &y& Elsevier]

Insufficient sub-surface hydraulic data from watersheds often hinders design of water resources structures. This is particularly true in developing countries and in watersheds with low population densities because well-drilling to obtain the hydraulic data is expensive. The objective of this study was to evaluate the applicability of ‘Brutsaert’ recession flow analysis to steeper and more arid watersheds than those that were previously used. Using daily streamflow data (1962–1992), a modified version of the analysis was used to estimate the subsurface hydraulic parameters of four semi-arid, mountainous watersheds (204–764 km2) near Oaxaca, Mexico. In this analysis, a dimensionless recession curve (DRC) was translated to best-fit observed recession flow (Q) data. The basin-wide hydraulic parameters were directly related to the magnitude of the translation used to fit the DRC to the data. One unique aspect of this study was too few high flow data to confidently fit the DRC to the data via previously published protocols. We, thus, proposed using three different approaches for translating the DRC in order to establish a range for the hydraulic parameters. Our analyses predicted a narrow range of basin-wide hydraulic parameters that were near regionally measured values and consistent within commonly published values for similar geology, suggesting that the Brutsaert method is applicable to arid, mountainous basins like those used here. This method potentially provides a cost-effective alternative to traditional geohydrological field methods for determining groundwater parameters. [Copyright &y& Elsevier]

Soil and water conservation practices are increasingly being considered for curbing non-point source pollution from agricultural land. Several studies have demonstrated that stream power is a simple and good predictor of soil detachment and transport and can be used to predict the effect of soil and water conservation practices on soil loss. Our objective was, therefore, to develop a simple water erosion simulation model that is physically based on stream power, handles vegetation in terms of contact cover, and considers the settling velocity characteristics of the eroding sediment. The model assumes that rill flow can occur on hillslope segments with net erosion, but on segments with net deposition sheet flow is assumed. Input parameters include the depositability of the soil, rill shape, rill density, net precipitation, and an empirical power function describing the decrease of sediment concentration with vegetative cover increase. The model was evaluated by comparison of predicted and observed relationships between sediment concentration, slope, and vegetative residue cover in two experimental studies using simulated rainfall: one that involved erosion plots with various uniform slopes and levels of vegetative cover, and another that involved the observation of soil movement on mechanically shaped concave, uniform, and convex slopes with negligible vegetation. Without calibration, the model appeared to represent soil erosion relationships observed in these studies and is simple enough to be included in grid-based variable source hydrology models. [Copyright &y& Elsevier]

Soil and water conservation structures, promoted by local and international development organizations throughout rural landscapes, aim to increase recharge and prevent degradation of soil surface characteristics. This study investigates this unexamined relationship between recharge, water table depths, and soil surface characteristics (nutrients) in a small sub-watershed in the northwestern Ethiopian highlands. These highland watersheds have high infiltration rates (mean 70 mm hr −1 , median 33 mm hr −1 ), recharging the shallow unconfined hillslope aquifer with water transport occurring via subsurface pathways down the slope. The perched water tables reflect the subsurface flux and are deep where this flux is rapid in the upland areas (138 cm below surface). Soil saturation and overland flow occur when the subsurface flux exceeds the transport capacity of the soil in the lower downslope areas near the ephemeral stream (19 cm below surface). Land use is directly related to the water table depth, corresponding to grazing and fallowed (saturated) land in the downslope areas and cultivated (unsaturated) land in the middle and upper parts where the water table is deeper. Kjeldahl Total Nitrogen (TN), Bray II available phosphorus (AP), and exchangeable potassium (K + ) averages exhibit different behaviors across slope, land use transects, or saturation conditions. TN was moderate to low (0.07% ± 0.04) in various land uses and slope regions. Bray II AP had very low concentrations (0.25 mg kg −1  ± 0.26) among the different slope regions with no significant differences throughout (p > .05). The exchangeable cation (K + , Ca 2+ , Mg 2+ ) concentrations and pH, however, were greater in non-cultivated (seasonally saturated) lands and in a downslope direction (p < .001, p < .005, p < .05, and p < .005, respectively). These results show that the perched groundwater plays an important role in influencing land use, the amount of water seasonally available for crop growth, and exchangeable cations, but have no clear effect on the concentration of the two primarily applied nutrients in fertilizers (N, P). [ABSTRACT FROM AUTHOR]

Summary In response to anthropogenic disturbances, alluvial rivers adjust their geometry. The alluvial river channels in the upper Blue Nile basin have been disturbed by human-induced factors since a longtime. This paper examines channel adjustment along a 38-km stretch of the Gumara River which drains towards Lake Tana and then to the Blue Nile. Over a 50 years period, agriculture developed rapidly in the catchment and flooding of the alluvial plain has become more frequent in recent times. The objectives of this study were to document the changes in channel planform and cross-section of the Gumara River and to investigate whether the changes could have contributed to the frequent flooding or vice versa. Two sets of aerial photographs (1957 and 1980) were scanned, and then orthorectified. Recent channel planform information was extracted from SPOT images of 2006 and Google Earth. Channel planform and bed morphology (vertical changes) were determined for these nearly 50 years period. The vertical changes were determined based on aggradation along a permanent structure, historic information on river cross-sections at a hydrological gauging station, and field observations. The results indicate that the lower reach of Gumara near its mouth has undergone major planform changes. A delta with approx. 1.12 km 2 of emerged land was created between 1957 and 1980 and an additional 1 km 2 of land has been added between 1980 and 2006. The sinuosity of the river changed only slightly: negatively (−1.1% i.e. meandering decreased) for the period from 1957 to 1980 and positively (+3.0%) for the period 1980–2006. Comparison of cross-sections at the hydrological gauging station showed that the deepest point in the river bed aggraded by 2.91 m for the period 1963–2009. The importance of sediment deposition in the stream and on its banks is related to land degradation in the upper catchment, and to artificial rising of Lake Tana level that creates a backwater effect and sediment deposition in Gumara River. Direct anthropogenic impacts (irrigation activities and building of dykes along the river banks) have contributed to the huge deposition in the river bed. Where the abstraction of water for irrigation is intensive, seepage water through the banks has contributed to river bank failure. In general, this study showed that changes to the planform at the mouth of the river and to the riverbed level are substantial. Moreover, the study indicated that the flood carrying capacity of the Gumara River channel has diminished in recent times. [ABSTRACT FROM AUTHOR]

Summary: Recently, the interactions between soil structure and microbes have been associated with water transport, retention and preferential or column flow development. Of particular significance is the potential impact of microbial extracellular polymeric substances (EPS) on soil porosity (i.e., hydraulic conductivity reduction or bioclogging) and of exudates from biota, including bacteria, fungi, roots and earthworms on the degree of soil water repellency. These structural and surface property changes create points of wetting instability, which under certain infiltrating conditions can often result in the formation of persistent preferential flow paths. Moreover, distinct differences in physical and chemical properties between regions of water flow (preferential flow paths) and no-flow (soil matrix) provide a unique set of environmental living conditions for adaptable microorganisms to exist. In this review, special consideration is given to: (1) the functional significance of microbial activity in the host porous medium in terms of feedback mechanisms instigated by irregular water availability and (2) the related physical and chemical conditions that force the organization and formation of unique microbial habitats in unsaturated soils that prompt and potentially perpetuate the formation of preferential flow paths in the vadose zone. [ABSTRACT FROM AUTHOR]

Summary: Current urban water quality models rely on empirical, catchment-scale functions of particulate wash-off that do not clearly represent the governing physical erosion and transport processes. We proposed a saltation-type wash-off model in which particles are repeatedly ejected from an impervious surface by raindrop impacts and are transported laterally by overland flow while settling back to the surface. The rate that particles are ejected is proportional to rain intensity and the spatial density of particles on the surface. We found that for low particle spatial densities, ejection is proportional to spatial density, but for high spatial densities, the ejection rate is independent of spatial density. We tested our model against data from small (10.5×80cm) flume experiments in which rain intensity and upslope overland flow could be independently controlled. We used a rough flume surface (∼1mm roughness element height) and sand particles (diameter=500–590μm). Rainfall rates, upslope overland flow rates, and initial particle amounts were varied among experiments with ranges of, 4.2–7.8cmh−1, 300–565mL min−1, and 0.01–0.07gcm−2, respectively. The model predictions agreed well with the experiments (R 2 >0.85). This work provides a basis for developing new, uniquely mechanistic models for predicting “wash-off” from urban surfaces. [Copyright &y& Elsevier]

Although both raindrop driven processes and diffusion play important roles in the transfer of chemicals from soil to surface runoff, current transport models either do not consider the two processes together, or use ‘effective’ parameters with uncertain physical definitions. We developed a physically based, solute transport model that couples both mechanisms and tested it with laboratory experiments. One unique aspect of this study is that all the parameters were either directly measured or previously published, that is, there was no model ‘calibration’ or ‘fitting.’ Our model assumes that chemicals near the surface of the soil are ejected into runoff by raindrop impact and chemicals deeper in the soil diffuse into a surface layer, or ‘exchange layer,’ via diffusion. The exchange layer depth and transfer processes are derived from the ‘shield’ concept in the Rose soil erosion model (e.g. ). The model''s governing equations were solved numerically and the results agreed well with experimental data (R2>0.90). The model''s sensitivity to various physical and chemical parameters illuminated the importance of both raindrop controlled processes and diffusion on chemical transport from soil to surface runoff. [Copyright &y& Elsevier]

• Forested and revegetated regions show greater levels of hydraulic flux and nutrients. • Greater K s and lower ρ b throughout the upper parts of this Andean watershed. • For common pedotransfer functions, these soils' Ks are significantly underestimated. • Conservation initiatives are coinciding with improved soil surface characteristics. Understanding catchment sediment or solute transport frequently relies on understanding of soil nutrient conditions and physical properties. This study investigates hydropedological patterns in a tropical catchment by understanding soil nutrient and soil surface changes. Soil nutrient concentrations and hydraulic properties were measured from the La Vega micro watershed in the southwestern Colombian Andes at 16 distributed locations in four elevation ranges (between 1450 and 1700 m a.s.l.). The site is a part of a conservation partnerships which implements programs and monitor impacts. Soil samples were analyzed for total nitrogen (TN), Bray II-available phosphorus, exchangeable cations, pH, organic matter, and texture. Soil hydraulic conductivities at two depths (0–5 cm and 5–10 cm) were determined in conservation implementation areas (enclosures and natural regrowth). In the upper elevation range, regrowth of natural vegetation was found on deep soils (∼3 m) with moderate infiltration (26 cm hr−1), the lowest bulk density (0.92 g cm−3), and the highest TN (0.4%). The lowest elevation (mixed land use of grazing and riparian forests with deep profiles) had the lowest infiltration (4 cm hr−1), highest bulk density (1.02 g cm−3), and the lowest TN (0.26%). In the middle elevation ranges, conserved tropical forest vegetation were located on shallow soil depths with high organic matter (∼6%) and high infiltration (86 cm hr−1). The lowest infiltration rate average (2.3 cm hr−1) exceeded the estimated erosive regional precipitation intensity (∼2.5 cm hr−1) about 60% of the time, while the median infiltration rate (10 cm hr−1) exceeded rainfall intensities 94% of the time, indicating that infiltration excess and saturation excess runoff mechanisms are both present. Coupling data with sediment concentration and solute concentration patterns can help discern correlations between scales and will help to monitor effectiveness of conservation programs aimed at sustaining ecosystem services. [ABSTRACT FROM AUTHOR]

• SWAT-C predicts dissolved organic carbon (DOC) export from variable source areas. • Remotely sensed data reduced uncertainty in model predictions. • DOC predictions are sensitive to soil properties. • DOC flux is more sensitive to increases in precipitation than air temperature. Dissolved organic carbon (DOC) in surface water influences the global carbon cycle, ecosystem productivity, and water quality in potable water supply systems. Few physically based watershed models can simulate carbon cycling and predict DOC in surface waters under the influence of natural and anthropogenic drivers. In this work we transform the SWAT-Carbon (C) model to simulate DOC from variable source runoff areas in a humid forested watershed in the northeastern United States. Remotely sensed data were used to parameterize and simulate forest growth and evapotranspiration. The calibrated model accurately simulated streamflow and DOC flux at six sites across the watershed compared to measured data. The DOC predictions across sites showed model sensitivity to soil properties, particularly soil depth and available water capacity. The spatial distribution of DOC export across the watershed followed the pattern of surface runoff from variable source areas. Model sensitivity of DOC flux showed greater sensitivity to changes in precipitation than temperature. The overall good performance of the model makes it a valuable tool for watershed-scale modeling of DOC to understand the influence of climate and watershed management towards developing mitigation strategies. The methods presented in this study can be used in forested watersheds in regions where runoff from variable source areas is important for water quality predictions. [ABSTRACT FROM AUTHOR]

In many developing countries and remote areas of important ecosystems, good quality precipitation data are neither available nor readily accessible. Satellite observations and processing algorithms are being extensively used to produce satellite rainfall products (SREs). Nevertheless, these products are prone to systematic errors and need extensive validation before to be usable for streamflow simulations. In this study, we investigated and corrected the bias of Multi-Sensor Precipitation Estimate–Geostationary (MPEG) data. The corrected MPEG dataset was used as input to a semi-distributed hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) for simulation of discharge of the Gilgel Abay and Gumara watersheds in the Upper Blue Nile basin, Ethiopia. The result indicated that the MPEG satellite rainfall captured 81% and 78% of the gauged rainfall variability with a consistent bias of underestimating the gauged rainfall by 60%. A linear bias correction applied significantly reduced the bias while maintaining the coefficient of correlation. The simulated flow using bias corrected MPEG SRE resulted in a simulated flow comparable to the gauge rainfall for both watersheds. The study indicated the potential of MPEG SRE in water budget studies after applying a linear bias correction. [ABSTRACT FROM AUTHOR]

Water shortage is the major bottleneck that limits sustainable yield of agriculture in the North China Plain. Due to the over-exploitation of groundwater for irrigating the winter wheat–summer maize double cropping systems, a groundwater crisis is becoming increasingly serious. To help identify more efficient and sustainable utilization of the limited water resources, the water consumption and water use efficiency of five irrigated cropping systems were calculated and the effect of cropping systems on groundwater table changes was estimated based on a long term field experiment from 2003 to 2013 in the North China Plain interpreted using a soil–water-balance model. The five cropping systems included sweet potato → cotton → sweet potato → winter wheat–summer maize (SpCSpWS, 4-year cycle), ryegrass–cotton → peanuts → winter wheat–summer maize (RCPWS, 3-year cycle), peanuts → winter wheat–summer maize (PWS, 2-year cycle), winter wheat–summer maize (WS, 1-year cycle), and continuous cotton (Cont C). The five cropping systems had a wide range of annual average actual evapotranspiration ( ET a ): Cont C (533 mm/year) < SpCSpWS (556 mm/year) < PWS (615 mm/year) < RCPWS (650 mm/year) < WS rotation (734 mm/year). The sequence of the simulated annual average groundwater decline due to the five cropping systems was WS (1.1 m/year) > RCPWS (0.7 m/year) > PWS (0.6 m/year) > SPCSPWS and Cont C (0.4 m/year). The annual average economic output water use efficiency ( WUE e ) increased in the order SpCSpWS (11.6 yuan ¥ m −3 ) > RCPWS (9.0 ¥ m −3 ) > PWS (7.3 ¥ m −3 ) > WS (6.8 ¥ m −3 ) > Cont C (5.6 ¥ m −3 ) from 2003 to 2013. Results strongly suggest that diversifying crop rotations could play a critically important role in mitigating the over-exploitation of the groundwater, while ensuring the food security or boosting the income of farmers in the North China Plain. [ABSTRACT FROM AUTHOR]

Summary: This study uses an instrumented (trenched) 0.5ha hillslope in the southern tier of New York State, USA, to provide new data and insights on how variable source areas and associated flow pathways form and combine to connect rainfall with downstream water flows across a hillslope. Measurements of water fluxes in the trench, upslope water table dynamics, surface and bedrock topography, and isotopic and geochemical tracers have been combined for a four-dimensional (space–time) characterization of subsurface storm flow responses. During events with dry antecedent conditions infiltrating rainwater was found to percolate through a prevailing fragipan layer to deeper soil layers, with much (33–71%) of the total discharge of the hillslope originating from deeper water flow below the fragipan. During storm events with wet antecedent conditions and large rainfall amounts, shallow lateral flow of event and pre-event water above the fragipan occurred and was one magnitude greater than the deeper water flow contribution. Spatial surface and subsurface water quality observations indicate that water from a distance of up to 56m contributed runoff from the hillslope during storm events. In addition, mobilization of total dissolved phosphorus (TDP) with subsurface flow played a greater role than with overland or near-surface flow. During all events TDP loads were highest in the total discharge during peak flows (8–11.5kgha−1 d−1), except during the largest storm event, when TDP concentrations were highly diluted. These results have implications for strategies to protect streams and other downstream water recipients from waterborne nutrient and pollutant loading. [ABSTRACT FROM AUTHOR]

Summary: Many water quality models use some form of the Natural Resources Conservation Services (formerly Soil Conservation Service) curve number (CN) equation to predict storm runoff in ways that implicitly assume an infiltration-excess response to rainfall. Because of this, these models may fail to predict variable source areas (VSAs) correctly, i.e. where runoff is typically generated in rural, humid regions. In this study, the Soil and Water Assessment Tool (SWAT) model was re-conceptualized to distribute overland flow in ways consistent with VSA hydrology by modifying how the CN and available water content were defined; the new modeling approach is called SWAT-VSA. Both SWAT and SWAT-VSA were applied to a sub-watershed in the Cannonsville basin in upstate New York to compare model predictions of integrated and distributed responses, including surface runoff, shallowly perched water table depth, and stream phosphorus loads against direct measures. Event runoff was predicted similarly well for SWAT-VSA and SWAT. However, the distribution of shallowly perched water table depth was predicted better by SWAT-VSA and it is this shallow groundwater that governs VSAs. Event based dissolved phosphorus export from the watershed was also predicted better by SWAT-VSA, presumably because the distribution of runoff source areas was better predicted particularly from areas where manure was applied. This has important consequences for using models to evaluate and guide watershed management because correctly predicting where runoff is generated is critical to locating best management practices to control non-point source pollution. [Copyright &y& Elsevier]

Because water shortages limit development in many parts of the world, a systematic approach is needed to use water more productively. To address this need, Molden and Sakthivadivel [Water Resour. Dev. 15 (1999) 55-71] developed a water-accounting procedure for analyzing water use patterns and tradeoffs between users. Their procedure treats groundwater and surface water as a single domain. We adapted this procedure to account for groundwater and surface water components separately, and applied the adapted procedure to the Singkarak–Ombilin River basin, Indonesia, where groundwater is a significant part of the overall water balance. Since 1998, a substantial proportion of water has been withdrawn from Singkarak Lake and diverted out of the basin, resulting in significant impacts on downstream water users and the lake ecosystem. Based on 15–20 years (1980–1999) of hydrometeorological, land use, soil, and other relevant data, a simple groundwater balance model was developed to generate the hydrogeologic information needed for the water-accounting procedure. The water-accounting procedure was then used to evaluate present and potential future water use performance in the basin. By considering groundwater and surface water components separately, a more realistic estimate of water availability was calculated than could be obtained by lumping these components together. Results show that the diversion of 37 m3/s from Singkarak Lake increases the amount of water that is not available for other uses, such as for irrigation, from 57–81 to 81–95% of total water available in the basin. The new water accounting procedure also demonstrates the viability of increasing downstream water supply and water use performance during the dry months (June–September). For example, by increasing irrigation during the wet months (January–April) or tapping water from a shallow, unconfined aquifer during the dry months, while keep maintaining sustainable groundwater levels. [Copyright &y& Elsevier]

Differences in the simulation of hydrologic processes by watershed models directly affect the accuracy of results. Surface runoff generation can be simulated as either: (1) infiltration-excess (or Hortonian) overland flow, or (2) saturation-excess overland flow. This study compared the Hydrological Simulation Program—FORTRAN (HSPF) and the Soil Moisture Routing (SMR) models, each representing one of these mechanisms. These two models were applied to a 102 km2 watershed in the upper part of the Irondequoit Creek basin in central New York State over a seven-year simulation period. The models differed in both the complexity of simulating snowmelt and baseflow processes as well as the detail in which the geographic information was preserved by each model.Despite their differences in structure and representation of hydrologic processes, the two models simulated streamflow with almost equal accuracy. Since streamflow is an integral response and depends mainly on the watershed water balance, this was not unexpected. Model efficiency values for the seven-year simulation period were 0.67 and 0.65 for SMR and HSPF, respectively. HSPF simulated winter streamflow slightly better than SMR as a result of its complex snowmelt routine, whereas SMR simulated summer flows better than HSPF as a result of its runoff and baseflow processes.An important difference between model results was the ability to predict the spatial distribution of soil moisture content. HSPF aggregates soil moisture content, which is generally related to a specific pervious land unit across the entire watershed, whereas SMR predictions of moisture content distribution are geographically specific and matched field observations reasonably well. Important is that the saturated area was predicted well by SMR and confirmed the validity of using saturation-excess mechanisms for this hillslope dominated watershed. [Copyright &y& Elsevier]