In the marine ecological system, the prime role of water management and durability of an ecosystem is being played by the vegetation patches. The vegetation patches in open channels can significantly affect the flow velocity, discharge capacity and hinder energy fluxes, which ultimately helps in controlling catastrophic floods. In this study, the numerical simulation for turbulent flow properties, i.e. velocity distribution, Reynolds stresses and Turbulent Intensities (TI) near the circular vegetation patches with progressively increasing density, were performed using the computational fluid dynamics (CFD) code ANSYS FLUENT. For examination of the turbulent flow features in the presence of circular patches with variable densities, Reynolds averaged Navier-Stokes equations, and Reynolds stress model (RSM) were employed. The numerical investigation was performed in the presence of in-line emergent and submerged patches having variable vegetation density in the downstream direction. Two of the cases were investigated with three circular patches having a clear gap to patch diameter ratio of La/D = 1 (where La is the clear spacing between the vegetation patches and D is the diameter of the circular patch), and the other two cases were analyzed with two patches having a clear gap ratio of La/D = 3. The case with a clear gap ratio (La/D = 3) showed 10.6% and 153% inflation in the magnitude of longitudinal velocity at the downstream of the sparse patch (aD = 0.8) and upstream of the dense patch (aD = 3.54), respectively (where aD is the flow blockage, in which “a” represents the patch frontal area and “D” represents the patch diameter). The velocity was reduced to 94% for emergent and 99% for submerged vegetation due to successive increase in vegetation density made by introducing a middle patch which reduced the clear gap ratio (La/D = 1). For La/D = 1, the longitudinal velocities at depth z = 15cm were increased by 319% than at depth z = 6cm at the downstream of the dense patch (aD = 3.54). Whereas it was observed to 365% higher in the case of La/D = 3. The magnitude of turbulent characteristics was observed 36% higher for submerged vegetation cases having a clear gap ratio of La/D = 1. The successive increase in the patch density reduced the Reynolds stresses, turbulent kinetic energy and turbulent intensities significantly within the gap region. The major reduction in the flow velocities and turbulent properties in the gaps provides a stable environment for aquatic ecosystems nourishment and fosters sediment deposition, and supports further vegetation growth.
Variable rate technology (VRT) in nutrient management has been developed in order to apply crop inputs according to the required amount of fertilizers. Meteorological conditions rarely differ within one field; however, differences in soil conditions responding to precipitation or evaporation results within field variations. These variations in soil properties such as moisture content, evapotranspiration ability, etc. requires site-specific treatments for the produced crops. There is an ongoing debate among experts on how to define management zones as well as how to define the required amount of fertilizers for phosphorus and nitrogen replenishment for winter wheat (Triticum aestivum L.) production. For management zone delineation, vegetation based or soil based data collection is applied, where various sensor technology or remote sensing is in help for the farmers. and The objective of the study reported in this paper was to investigate the effect of soil moisture data derived from Sentinel-2 satellite images moisture index and variable rate phosphorus and nitrogen fertilizer by means of variable rate application (VRA) in winter wheat in Mezőföld, Hungary. Satellite based moisture index variance at the time of sowing has been derived, calculated and later used for data comparison. Data for selected points showed strong correlation (R2 = 0.8056; n = 6) between moisture index and yield, however generally for the whole field correlation does not appear. Vegetation monitoring has been carried out by means of NDVI data calculation. On the field level, as indicated earlier neither moisture index values at sowing nor vegetation index data was sufficient to determine yield. Winter wheat production based on VRA treatment resulted significant increase in harvested crop: 5.07 t/h in 2013 compared to 8.9 t/ha in 2018. Uniformly managed (control) areas provided similar yield as VRA treated areas (8.82 and 8.9 t/ha, respectively); however, the input fertilizer was reduced by 108 kg/ha N and increased by 37 kg/ha P.
The paper describes a mathematical and physical modelling of flow of complex slurries in pipelines, i.e. a flow of slurries composed of solids covering a very broad range of particle sizes that overlaps more than one flow patterns – non-Newtonian, pseudohomogeneous, heterogeneous and fully-stratified. A typical examples are residual products (“tailings”) from mining industry with normal average particle sizes of 20 to 100 μm or more. Experimental results of flows of complex slurries composing of non-Newtonian carrier fluid and three fractions of glass particles in 50 mm pipe are presented. Depending on the particle size, particles show different flow patterns and therefore considerable differences in pressure drops. Fine particles tend behave as a homogeneous matter, while coarser particles exhibit heterogeneous behaviour and even coarser particles form a sliding bed. A mathematical 3-component predictive model for turbulent flow of complex slurries is presented based on well-established semi-empirical formulae developed originally for flows with Newtonian carrier. The predicted values of pressure drops show very reasonable agreement with experimental results and indicate suitability of the model for engineering practice.
The two-dimensional particle image velocimetry (PIV) data are inevitably contaminated by noise due to various imperfections in instrumentation or algorithm, based on which the well-established vortex identification methods often yield noise or incomplete vortex structure with a jagged boundary. To make up this deficiency, a novel method was proposed in this paper and the efficiency of the new method was demonstrated by its applications in extracting the twodimensional spanwise vortex structures from 2D PIV data in open-channel flows. The new method takes up a single vortex structure by combining model matching and vorticity filtering, and successfully locates the vortex core and draws a streamlined vortex boundary. The new method shows promise as being more effective than commonly used schemes in open-channel flow applications.
Backward erosion piping is driven by seepage forces acting on the soil grains at the downstream end of the seepage path. A new device for the laboratory testing of backward erosion progression was developed and tested. The device consists of a plexiglass prism at which the seepage path has been predefined. The prism was equipped with an inflow consisting of gravel separated from tested sand by a strainer. The hydraulic gradient along the seepage pipe was observed by a set of piezometers and pressure cells, and the seepage discharge was measured volumetrically. The transported sediment was trapped in a vertical cone located downstream from the device. The progression of the seepage path, the piezometric heads and the trapped material was observed by two synchronous cameras. 15 trial tests have been carried out to date, and from these, the interim results are presented.
Fishway design not only takes into account the swimming abilities of target fishes, but also considers the hydrodynamic characteristics within the fishway. In this study, the flow fields of one vertical-slot fishway (i.e. VSF), five T-shape fishways (i.e. TSF-1~TSF-5) and two H-shape fishways (i.e. HSF-1 and HSF-2) are numerically simulated by solving the three-dimensional Reynolds-averaged Navier-Stokes equations and the K-Omega-SST turbulence model. The numerical results clearly indicate that the hydrodynamic properties of HSF-2 are overall superior to the remaining seven cases, in terms of the time-averaged flow pattern, the time-averaged velocity magnitude, the depth-mean timeaveraged velocity magnitude along the vertical-slot section, the volume percentages of the time-averaged velocity magnitude less than some critical values, and the distribution of the time-averaged turbulent kinetic energy. Therefore, HSF-2 is more friendly for fishes with relatively smaller sizes and weaker swimming capacities to transfer upstream. The novel HSF-2 is firstly proposed in this paper, and it is naturally designed during the process of improving the flow regime. Furthermore, the generalizability of the superiority of HSF-2 over VSF and the original T-shape fishway (i.e. TSF-1) has been exhibited with the aid of the numerical results of four operating conditions (i.e. Q = 400 L/s, 600 L/s, 800 L/s and 1000 L/s).
Accurate estimation of precipitation in mountain catchments is challenging due to its high spatial variability and lack of measured ground data. Weather radar can help to provide precipitation estimates in such conditions. This study investigates the differences between measured and radar-estimated daily precipitation in the mountain catchment of the Jalovecký Creek (area 22 km2, 6 rain gauges at altitudes 815–1900 m a.s.l.) in years 2017–2020. Despite good correlations between measured and radar-based precipitation at individual sites (correlation coefficients 0.68–0.90), the radar-estimated precipitation was mostly substantially smaller than measured precipitation. The underestimation was smaller at lower altitude (on average by –4% to –17% at 815 m a.s.l.) than at higher altitudes (–35% to –59% at 1400–1900 m a.s.l.). Unlike measured data, the radar-estimated precipitation did not show the differences in precipitation amounts at lower and higher altitudes (altitudinal differences). The differences between the measured and radar-estimated precipitation were not related to synoptic weather situations. The obtained results can be useful in preparation of more accurate precipitation estimates for the small mountain catchments.
The design and evaluation of algorithms for adaptive stochastic control of the reservoir function of a water reservoir using an artificial intelligence method (learned fuzzy model) are described in this article. This procedure was tested on the Vranov reservoir (Czech Republic). Stochastic model results were compared with the results of deterministic management obtained using the method of classical optimisation (differential evolution). The models used for controlling of reservoir outflow used single quantile from flow duration curve values or combinations of quantile values from flow duration curve for determination of controlled outflow. Both methods were also tested on forecast data from real series (100% forecast). Finally, the results of the dispatcher graph, adaptive deterministic control and adaptive stochastic control were compared. Achieved results of adaptive stochastic management were better than results provided by dispatcher graph and provide inspiration for continuing research in the field.
We analyse water balance, hydrological response, runoff and snow cover characteristics in the Jalovecký Creek catchment (area 22 km2, mean elevation 1500 m a.s.l.), Slovakia, in hydrological years 1989–2018 to search for changes in hydrological cycle of a mountain catchment representing hydrology of the highest part of the Western Carpathians. Daily air temperature data from two meteorological stations located in the studied mountain range (the Tatra Mountains) at higher elevations show that the study period is 0.1°C to 2.4°C warmer than the climatic standard period 1951–1980. Precipitation and snow depth data from the same stations do not allow to conclude if the study period is wetter/drier or has a decreasing snow cover. Clear trends or abrupt changes in the analysed multivariate hydrometric data time series are not obvious and the oscillations found in catchment runoff are not coherent to those found in catchment precipitation and air temperature. Several time series (flashiness index, number of flow reversals, annual and seasonal discharge maxima, runoff coefficients) indicate that hydrological cycle is more dynamic in the last years of the study period and more precipitation runs off since 2014. The snow cover characteristics and climatic conditions during the snow accumulation and melting period do not indicate pronounced changes (except the number of days with snowfall at the Kasprowy Wierch station since 2011). However, some data series (e.g. flow characteristics in March and June, annual versus summer runoff coefficients since 2014) suggest the changes in the cold period of the year.
δ18O in precipitation at station Liptovský Mikuláš (about 8.5 km south from the outlet of the Jalovecký Creek catchment) remains constantly higher since 2014 that might be related to greater evaporation in the region of origin of the air masses bringing precipitation to the studied part of central Europe. Increased δ18O values are reflected also in the Jalovecký Creek catchment runoff. Seasonality of δ18O in the Jalovecký Creek became less pronounced since 2014. The most significant trends found in annual hydrological data series from the catchment in the study period 1989–2018 have the correlation coefficients 0.4 to 0.7. These trends are found in the number of flow reversals (change from increasing to decreasing discharge and vice versa), June low flow, number of simple runoff events in summer months (June to September) and the flashiness index. The attribution analysis suggests that drivers responsible for the changes in these data series include the number of periods with precipitation six and more days long, total precipitation amount in February to June, number of days with precipitation in June to September and total precipitation in May on days with daily totals 10 mm and more, respectively. The coefficients of determination show that linear regressions between the drivers and supposedly changed data series explain only about 31% to 36% of the variability. Most of the change points detected in the time series by the Wild Binary Segmentation method occur in the second and third decades of the study period. Both hydrometric and isotopic data indicate that hydrological cycle in the catchment after 2014 became different than before.
Study about the mechanical energy balance and the energy loss of 3-D turbulent flows in open-channels has its own complexities. The governing equation of the mechanical energy in turbulent flows has been previously known and includes turbulence parameters that their calculations or measurements are not easy. In this study, a form of the total mechanical energy equation that leads to a number of significant physical insights is analytically investigated, from which analytical relationships for the energy loss estimation in 3-D turbulent flows are defined. The effect of different turbulence parameters is reflected on the new relationships and analyzed by equalizations replacing unknown correlations with closure approximations using the numerical turbulence simulation. In order to investigate the application of the analytical relationships, numerical simulations are performed by using OpenFOAM software to solve the Navier-Stokes equations with the RSM turbulence model in open-channels with different geometries. Then, the contribution of the turbulence parameters to the total mechanical energy balance is evaluated in uniform and nonuniform turbulent flows and their difference is analyzed, that leads to identify the parameters affecting the friction and local losses. The results demonstrate that the magnitudes of the turbulent diffusion, the work done by the viscous stresses pertaining to the mean motion and the viscous diffusion of the turbulence energy are substantially smaller than the other terms of the total energy equation for turbulent flows in open-channels with different geometries, while the effect of the variations of the turbulence kinetic energy and the work done by the turbulence stresses, that has not been considered in the previous mechanical energy equations, is more important in complex flows. From a practical viewpoint, in order to study the details of the total mechanical energy balance and the energy loss in 3-D turbulent flows with the presence of the secondary currents, the proposed method can be useful.
Authors propose a beneficial methodology for hydrological planning in their study. Prospective evaluations of the basins' net capacity can be done using the technique presented. The HEC-HMS (Hydrologic Modelling System) software can be used to estimate in a basin, the sediment emitted. For a certain precipitation, this methodology allows estimating, within a certain range, the gradual blockage of a reservoir, and even a projected date for total blockage. This has some applications to adopt corrective measures that prevent or delay the planned blockage deadlines. The model is of the semi-distributed type, estimating the generation and emission of sediments by sub-basins. The integration of different return periods in HEC-HMS with a semi-distributed model by sub-basins and the application of a mathematical model are the differentiating element of this research. The novelty of this work is to allow prognosing the reservoir sedimentation rate of basins in a local and regional scale with a medium and large temporary framework. The developed methodology allows public institutions to take decisions concerning hydrological planning. It has been applied to the case of "Charco Redondo" reservoir, in Cádiz, Andalusia, in southern Spain. Applying the methodology to this case, an average soil degradation of the reservoir basin has been estimated. Therefore, it is verified that in 50 years the reservoir is expected to lose 8.4% of its capacity.
Vapor condensation, whether due to dew or fog, may add a stable and important source of water to deserts. This was also extensively assessed in the Negev, regarded as a dew desert. Dew deserts necessitate a large reservoir of vapor, and are therefore confined to near oceans or seas. Yet, examples of such deserts are scarce. Here we try to assess whether the Tabernas Desert in SE Spain can be regarded as a dew desert, and may therefore facilitate the growth of certain organisms that otherwise would not survive the dry season. We analyze some of the abiotic conditions of four relatively dry months (June, July, August, September) in the Tabernas and Negev deserts (with the Negev taken as an example of a dew desert) during 2003–2012. The analysis showed substantially lower values of relative humidity (by 10–13%) in the Tabernas in comparison to the Negev, with RH ≥95% being on average only 0.9–1.1 days a month in the Tabernas in comparison to 9.7–13.9 days in the Negev. Our findings imply that the Tabernas Desert cannot be regarded as a dew desert, suggesting that rain will be the main factor responsible for the food web chain in the Tabernas.
The presence of biocrusts changes water infiltration in the Mu Us Desert. Knowledge of the hydraulic properties of biocrusts and parameterization of soil hydraulic properties are important to improve simulation of infiltration and soil water dynamics in vegetation-soil-water models. In this study, four treatments, including bare land with sporadic cyanobacterial biocrusts (BL), lichen-dominated biocrusts (LB), early-successional moss biocrusts (EMB), and latesuccessional moss biocrusts (LMB), were established to evaluate the effects of biocrust development on soil water infiltration in the Mu Us Desert, northwest of China. Moreover, a combined Wooding inverse approach was used for the estimation of soil hydraulic parameters. The results showed that infiltration rate followed the pattern BL > LB > EMB > LMB. Moreover, the LB, EMB, and LMB treatments had significantly lower infiltration rates than the BL treatment. The saturated soil moisture (θs) and shape parameter (αVG) for the EMB and LMB treatments were higher than that for the BL and LB treatments, although the difference among four treatments was insignificant. Water retention increased with biocrust development at high-pressure heads, whereas the opposite was observed at low-pressure heads. The development of biocrusts influences van Genuchten parameters, subsequently affects the water retention curve, and thereby alters available water in the biocrust layer. The findings regarding the parameterization of soil hydraulic properties have important implications for the simulation of eco-hydrological processes in dryland ecosystems.
Agriculture faces several challenges to use the available resources in a more environmentally sustainable manner. One of the most significant is to develop sustainable water management. The modern Internet of Things (IoT) techniques with real-time data collection and visualisation can play an important role in monitoring the readily available moisture in the soil. An automated Arduino-based low-cost capacitive soil moisture sensor has been calibrated and developed for data acquisition. A sensor- and soil-specific calibration was performed for the soil moisture sensors (SKU:SEN0193 - DFROBOT, Shanghai, China). A Repeatability and Reproducibility study was conducted by range of mean methods on clay loam, sandy loam and silt loam soil textures. The calibration process was based on the data provided by the capacitive sensors and the continuously and parallelly measured soil moisture content by the thermo-gravimetric method. It can be stated that the response of the sensors to changes in soil moisture differs from each other, which was also greatly influenced by different soil textures. Therefore, the calibration according to soil texture was required to ensure adequate measurement accuracy. After the calibration, it was found that a polynomial calibration function (R2 ≥ 0.89) was the most appropriate way for modelling the behaviour of the sensors at different soil textures.
The objectives of the study were to: (1) assess the strength of associations of direct CO2 and N2O emissions with the seasonal variations in the relevant soil properties under both tillage systems; 2) evaluate how CT and RT affect magnitudes of seasonal CO2 and N2O fluxes from soil. Field studies were carried out on plots for conventional tillage (up to 0.22–0.25 m) and reduced tillage (up to 0.10–0.12 m) during the growing season and post-harvest period of red clover. The results showed that daily CO2 emissions significantly correlated only with soil temperature during the growing season under conventional and reduced tillage. Soil temperature demonstrated its highest influence on daily N2O emissions only at the beginning of the growing season in both tillage systems. There were no significant inter-system differences in daily CO2 and N2O emissions from soil during the entire period of observations. Over the duration of post-harvest period, water-filled pore space was a better predictor of daily CO2 emissions from soils under CT and RT. The conventional and reduced tillage did not cause significant differences in cumulative N2O and CO2 fluxes from soil.
In an open channel with a mobile bed, intense transport of bed load is associated with high-concentrated sediment-laden flow over a plane surface of the eroded bed due to high bed shear. Typically, the flow exhibits a layered internal structure in which virtually all sediment grains are transported through a collisional layer above the bed. Our investigation focuses on steady uniform turbulent open-channel flow with a developed collisional transport layer and combines modelling and experiment to relate integral quantities, as the discharge of solids, discharge of mixture, and flow depth with the longitudinal slope of the bed and the internal structure of the flow above the bed. A transport model is presented which considers flow with the internal structure described by linear vertical distributions of granular velocity and concentration across the collisional layer. The model employs constitutive relations based on the classical kinetic theory of granular flows selected by our previous experimental testing as appropriate for the flow and transport conditions under consideration. For given slope and depth of the flow, the model predicts the total discharge and the discharge of sediment. The model also predicts the layered structure of the flow, giving the thickness of the dense layer, collisional layer, and water layer. Model predictions are compared with results of intense bed-load experiment carried out for lightweight sediment in our laboratory tilting flume.
Sand-water slurry was investigated on an experimental pipe loop of inner diameter D = 100 mm with the horizontal, inclined, and vertical smooth pipe sections. A narrow particle size distribution silica sand of mean diameter 0.87 mm was used. The experimental investigation focused on the effects of pipe inclination, overall slurry concentration, and mean velocity on concentration distribution and deposition limit velocity. The measured concentration profiles showed different degrees of stratification for the positive and negative pipe inclinations. The degree of stratification depended on the pipe inclination and on overall slurry concentration and velocity. The ascending flow was less stratified than the corresponding descending flow, the difference increasing from horizontal flow up to an inclination angle of about +30°. The deposition limit velocity was sensitive to the pipe inclination, reaching higher values in the ascending than in the horizontal pipe. The maximum deposition limit value was reached for an inclination angle of about +25°, and the limit remained practically constant in value, about 1.25 times higher than that in the horizontal pipe. Conversely, in the descending pipe, the deposition limit decreased significantly with the negative slopes and tended to be zero for an inclination angle of about −30°, where no stationary bed was observed.
The event runoff coefficient (Rc) and the recession coefficient (tc) are of theoretical importance for understanding catchment response and of practical importance in hydrological design. We analyse 57 event periods in the period 2013 to 2015 in the 66 ha Austrian Hydrological Open Air Laboratory (HOAL), where the seven subcatchments are stratified by runoff generation types into wetlands, tile drainage and natural drainage. Three machine learning algorithms (Random forest (RF), Gradient Boost Decision Tree (GBDT) and Support vector machine (SVM)) are used to estimate Rc and tc from 22 event based explanatory variables representing precipitation, soil moisture, groundwater level and season. The model performance of the SVM algorithm in estimating Rc and tc is generally higher than that of the other two methods, measured by the coefficient of determination R2, and the performance for Rc is higher than that for tc. The relative importance of the explanatory variables for the predictions, assessed by a heatmap, suggests that Rc of the tile drainage systems is more strongly controlled by the weather conditions than by the catchment state, while the opposite is true for natural drainage systems. Overall, model performance strongly depends on the runoff generation type.
The occurrence of river floods is strongly related to specific climatic conditions that favor extreme precipitation events leading to catchment saturation. Although the impact of precipitation and temperature patterns on river flows is a well discussed topic in hydrology, few studies have focused on the relationship between peak discharges and standard Climate Change Indices (ETCCDI) of precipitation and temperature, widely used in climate research. It is of interest to evaluate whether these indices are relevant for characterizing and predicting floods in the Alpine area. In this study, a correlation analysis of the ETCCDI indices annual time series and annual maximum flows is presented for the Piedmont Region, in North-Western Italy. Spearman’s rank correlation is used to determine which ETCCDI indices are temporally correlated with maximum discharges, allowing to hypothesize which climate drivers better explain the interannual variability of floods. Moreover, the influence of climate (decadal) variability on the tendency of annual maximum discharges is examined by spatially correlating temporal trends of climate indices with temporal trends of the discharge series in the last twenty years, calculated using the Theil-Sen slope estimator. Results highlight that, while extreme precipitation indices are highly correlated with extreme discharges at the annual timescale, with different indices that are consistent with catchment size, the decadal tendencies of extreme discharges may be better explained by the decadal tendencies of the total annual precipitation over the study area. This suggests that future projections of the annual precipitation available from climate models simulations, whose reliability is higher compared to precipitation extremes, may be used as covariates for non-stationary flood frequency analysis.
Analyses based on precipitation data may be limited by the quality of the data, the size of the available historical series and the efficiency of the adopted methodologies; these factors are especially limiting when conducting analyses at the daily scale. Thus, methodologies are sought to overcome these barriers. The objective of this work is to develop a hybrid model through the maximum overlap discrete wavelet transform (MODWT) to estimate daily rainfall in homogeneous regions of the Tocantins-Araguaia Hydrographic Region (TAHR) in the Amazon (Brazil). Data series from the Climate Prediction Center morphing (CMORPH) satellite products and rainfall data from the National Water Agency (ANA) were divided into seasonal periods (dry and rainy), which were adopted to train the model and for model forecasting. The results show that the hybrid model had a good performance when forecasting daily rainfall using both databases, indicated by the Nash–Sutcliffe efficiency coefficients (0.81–0.95), thus, the hybrid model is considered to be potentially useful for modelling daily rainfall.
The runoff coefficient (RC) is widely used despite requiring to know the effective contributing area, which cannot be known a priori. In a previous work, we defined runoff length (RL), which is difficult to measure. This work aimed to define the minimum RL (mRL), a quantitative and easy proxy of RL, for use in a pilot study on biocrusts in the Tabernas Desert, Spain. We show that RC decreases according to a hyperbola when the contributing area increases, the independent variable being the length of the effective contributing area and its coefficient involving the effects of rainfall and surface features and antecedent conditions. We defined the mRL as the length of the effective contributing area making RC = 1, which is calculated regardless of the area. We studied mRL from three biocrust types and 1411 events clustered in seven categories. The mRL increased with rain volume and intensity, catchment area and slope, whereas plant cover and biocrust succession (with one exception) had a negative effect. Depending on the plot, mRL reached up 3.3–4.0 m on cyanobacterial biocrust, 2.2–7.5 m on the most widespread lichens, and 1.0–1.5 m on late-successional lichens. We discuss the relationships of mRL with other runoff-related parameters.
The paper deals with the determination of the discharge coefficient, effective head and newly the limit head in the Kindsvater-Shen formula for the determination of a relatively small discharge of clear water using a thin-plate weir with a triangular notch. The determination of the discharge coefficient, effective head and limit head is based on extensive experimental research and is verified by previous measurements by other authors. The experimental research was characterised by a large range of notch angles (from 5.25° to 91.17°), weir heights (from 0.00 m to 0.20 m), and water temperatures (from 15 °C to 45 °C), as well as a focus on relatively small heads (from 0.02 m to 0.18 m), which is where the strengths of the Kindsvater-Shen formula stand out. The experimental research supplemented existing knowledge about the overflow occurring with small heads and small weir notch angles. The newly determined dependencies in the Kindsvater-Shen formula extended its applicability to weirs with small notch angles and newly enabled the determination of the limit head, which restricts its applicability in the determination of small discharges.
Recently water resources reanalysis (WRR) global streamflow products are emerging from high- resolution global models as a means to provide long and consistent global streamflow products for assessment of global challenge such as climate change. Like any other products, the newly developed global streamflow products have limitations accurately represent the dynamics of local streamflow hydrographs. There is a need to locally evaluate and apply correction factors for better representation and make use of the data. This research focuses on the evaluation and correction of the bias embedded in the global streamflow product (WRR, 0.25°) developed by WaterGAP3 hydrological model in the upper Blue Nile basin part of Ethiopia. Three spatiotemporal dynamical bias correction schemes (temporalspatial variable, temporal-spatial constant and spatial variable) tested in twelve watersheds of the basin. The temporalspatial variable dynamical bias correction scheme significantly improves the streamflow estimation. The Nash-Sutcliffe coefficient (NSCE) improves by 30% and bias decreases by 19% for the twelve streamflow gauging stations applying leave one out cross-validation approach in turn. Therefore, the temporal-spatial variable scheme is applicable and can use as one method for the bias correction to use the global data for local applications in the upper Blue Nile basin.
Lake Śniardwy is the largest among more than 7000 Polish lakes. So far, it has not been a subject of detailed investigations concerning long-term changes in water temperature or ice regime. A considerable change in thermal and ice conditions has been observed in the period 1972–2019. Mean annual water temperature increased by 0.44°C dec–1 on average, and was higher than an increase in air temperature (0.33°C dec–1). In the monthly cycle, the most dynamic changes occurred in April (0.77°C dec–1). In the case of ice cover, it appeared increasingly later (5.3 days dec–1), and disappeared earlier (3.0 days dec–1). The thickness of ice cover also decreased (2.4 cm dec–1). Statistical analysis by means of a Pettitt test showed that the critical moment for the transformations of the thermal and ice regime was the end of the 1980’s. In addition to the obvious relations with air temperature for both characteristics, it was evidenced that the occurrence of ice cover depended on wind speed and snow cover. The recorded changes in the case of Lake Śniardwy are considered unfavourable, and their consequences will affect the course of physical, chemical, and biological processes in the largest lake in Poland.
Large debris transported by flood affects scour features at bridge piers and increases the risks of structural failure. Geometric characteristics of the debris and the relative position of the pier with respect to the river bank are important parameters for the scour process. The interaction between the water flow and debris accumulation increases the shear stress, turbulence and consequently enhances the scour depth at the pier. This paper aims at analyzing such effects on scour evolution at bridge piers. To this end, two series of tests were carried out under clear water condition with different debris geometries and percentage blockage ratios. Experimental evidences showed that the pier position only influences scour evolution and equilibrium morphology for low water depths. Conversely, its effect becomes negligible for scour at bridge piers with debris accumulation and higher water depths. Useful practical relationships have been derived, with satisfactory prediction capability of the scour evolution for all the tested configurations.
The presence of gravel in soils modifies the porosity, pore connectivity and pore size distribution in the soil matrix as well as the soil matrix-gravel interfaces. The aim of the present study is to investigate the effect of relative volume of gravel in samples with gravel mass fractions of 5,10, 20 wt% and varying bulk densities (1.3, 1.45, 1.55, 1.60, 1.65 g cm–3) on (i) total porosity, field capacity, plant available water holding capacity, (ii) pore size distribution and (iii) thermal capacity of repacked sandy and silty soils. The focus of the study was to determine if laboratory measured soil water retention curves considering (i), (ii), and (iii) can be predicted by a gravel-based weighting factor, Rv, considering comprehensive significance tests. The sand-gravel mixtures show a decrease in the volume fractions of macropores and wide cores pores with an increase in the gravel contents, while the silt-gravel mixtures show an opposite trend. The root mean square errors (RMSE) between measured and fitted volumetric water contents, θ, between 0.006 and 0.0352 and between 0.002 and 0.004 for Rv-weighted volumetric water contents indicate that the van Genuchten-based Peters-Durner- Iden (PDI) model is appropriate for fitting. The soil water retention curves with mass gravel contents of up to 10 wt% for silt and 20 wt% for sand can be well predicted by weighting factors (relative volume of rock fragments) in the range between 0.045 and 0.058 for silt, and between 0.112 and 0.119 for sand. The results also indicate a decrease in the Rv-weighted saturated, cvsat, and dry, cvdry, thermal capacity with an increase in the gravel contents for both soils. Further investigations are needed to examine if and whether measured sand- and silt-gravel mixtures with mass gravel contents below 10 % or rather 20 % can be predicted with a weighting factor.
The interception process in subalpine Norway spruce stands plays an important role in the distribution of throughfall. The natural mountain spruce forest where our measurements of throughfall and gross precipitation were carried out, is located on the tree line at an elevation of 1,420 m a.s.l. in the Western Tatra Mountains (Slovakia, Central Europe). This paper presents an evaluation of the interception process in a natural mature spruce stand during the growing season from May to October in 2018–2020. We also analyzed the daily precipitation events within each growing season and assigned to them individual synoptic types. The amount and distribution of precipitation during the growing season plays an important role in the precipitation-interception process, which confirming the evaluation of individual synoptic situations. During the monitored growing seasons, precipitation was normal (2018), sub-normal (2019) and above-normal (2020) in comparison with long-term precipitation (1988–2017). We recorded the highest precipitation in the normal and above-normal precipitation years during the north-eastern cyclonic synoptic situation (NEc). During these two periods, interception showed the lowest values in the dripping zone at the crown periphery, while in the precipitation sub-normal period (2019), the lowest interception was reached by the canopy gap. In the central crown zone near the stem, interception reached the highest value in each growing season. In the evaluated vegetation periods, interception reached values in the range of 19.6–24.1% of gross precipitation total in the canopy gap, 8.3–22.2% in the dripping zone at the crown periphery and 45.7–51.6% in the central crown zone near the stem. These regimes are expected to change in the Western Tatra Mts., as they have been affected by windstorms and insect outbreaks in recent decades. Under disturbance regimes, changes in interception as well as vegetation, at least for some period of time, are unavoidable.
Microplastics (particles of plastics <5 mm) affect the physical, biological and hydrological properties of agricultural soil, as well as crop growth. We investigated the effect of the addition of three microplastics (high-density polyethylene (HDPE), polyvinyl chloride (PVC), and polystyrene (PS)) at a concentration of 5% (w/w) to a silty loam soil on selected soil properties and growth of radish (Raphanus sativus L. var. sativus). Changes in the soil properties and radish growth in three microplastic treatments were compared with the control. Soil properties (bulk density, hydraulic conductivity, sorptivity, water repellency) were estimated for each treatment at the beginning and at the end of the radish growing period (GP). The bulk density was significantly lower in the HDPE and PVC treatments compared to the control within the measurement at the beginning of the GP and in all microplastic treatments compared to the control at the end of the GP. The values of hydraulic conductivity and water sorptivity did not show significant differences between any treatments within the measurement at the beginning of GP, but they were significantly higher in the HDPE treatment compared to the control at the end of the GP. The growth of radish was characterized by the plant biomass and effective quantum yield of Photosystem II (Y (II)). We did not find a statistically significant difference in the total biomass of radish between any of the experimental treatments, maybe due to used concentration of microplastics. The mean value of Y (II) was significantly higher in all microplastic treatments compared to control only within the last measurement at the end of the GP. A statistically significant change of Y(II) in all microplastic treatments may indicate functional shift in soil properties; however, the measured values of the soil characteristics have not shown the significant changes (except for the bulk density values in all microplastic treatments and hydraulic conductivity together with sorptivity in HDPE treatment within the measurement at the end of GP).
Sand burial is a ubiquitous disturbance that influences the ecological and hydrological properties of moss crusts in many sandy desert areas. There is little available information regarding the effect of sand burial on the water repellency (WR) of moss crusts in desert areas. Therefore, this study evaluated the effects of sand burial (sand depths of 0 (control), 0.5, 1, 2, 4 and 10 mm) followed by three simulated precipitation regimes (through applying 4 and 6 mm, 2 and 3 mm, and 1 and 1.5 mm of distilled water at 8-day intervals in spring and autumn, respectively) on the WR of a widespread moss crust dominated by Bryum argenteum Hedw. in a revegetated area of the Tengger Desert, China. The results showed moss crust WR remained subcritical during the whole experiment, and that it considerably decreased immediately after sand burial, even though the values of WR were significantly higher in autumn than those in spring under the same treatment (p < 0.05). Furthermore, the depth threshold (TD) values for sand burials that reduced WR to zero were 1 and 2 mm in spring and autumn, respectively. After a recovery period of nearly one-season (72 days), the WR of the moss crust significantly increased (p < 0.05). In addition, sand burial had two separate effects on moss crust WR. Specifically, shallower sand burial (burial depth less than 0.5 mm) increased moss crust WR, whereas deeper sand burial (burial depth exceeds 0.5 mm) decreased it. The TD values also significantly increased to 2 and 4 mm in spring and autumn, respectively. These findings about the effects of sand burial on moss crust WR provide additional information that can be used to better understand the influence of sand burial on moss crust colonization and maintenance in arid sandburial- stressed ecosystems, and to help explain why there are some contrasting viewpoints on biocrust WR.
Hillslope hydrology in agricultural landscapes is complex due to a variety of hydropedological processes and field management possibilities. The aim was to test if there are any differences in soil properties and water regime along the hillslope and to compare vineyard rows (vine) with inter-rows (grass) area for those properties. The study determined that there are significant differences in the contents of soil particle fractions, pH, and humus content along the slope (P < 0.0001), with lower confidence level in bulk density (P < 0.05). Differences between row and inter-row space were significant for the pH, humus, and silt content, but for sand and clay content, and bulk density differences were not determined. The study determined differences in soil water content among five slope positions (P < 0.0001), and between row and inter-row vineyard space (all with P < 0.05). Where in the upper slope positions (e. g., P1) soil water content was higher than on lower slope positions. Higher soil water content was observed at higher slope positions, associated with clay content. However, it can be concluded that the retention of moisture on the slope is more influenced by local-scale soil properties (primarily soil texture) and variability of the crop (row/inter-row) than the position on the slope.
An open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study's primary objective is to compare variations of the mean flow pattern along a 180-degree bend with a variety of T-shaped spur dike lengths. In order to do so, parameters such as streamlines, the maximum velocity distribution, and the secondary flow strength under the influence of three T-shaped spur dike lengths will be analyzed and then compared with the case where no spur dikes are implemented. The results show that with the spur dike placed at the bend apex, the mean secondary flow strength at that range increases by approximately 2.5 times. In addition, a 67% increase in the length of the wing and web of the spur dike leads to a 27% growth in the mean secondary flow strength along the bend.
The aim of the study was to assess the possibility of using the empirical formulas to determine the roughness coefficient in gravel-bed streams, the bed slopes of which range from 0.006 to 0.047. Another aim was to determine the impact of taking into account the conditions of non-uniform flow on the application of these formulas and to develop the correlation relationships between the roughness coefficient and water surface slope and also between the roughness coefficient and friction slope in order to estimate the roughness coefficient n in gravel-bed streams. The studies were conducted in eight measuring sections of streams located in the Kraków-Częstochowa Upland, southern Poland. The roughness coefficient n0 for these sections was calculated from the transformed Bernoulli equation based on the results of surveys and hydrometric measurements. The values of n0 were compared with the calculation results obtained from fourteen empirical formulas presenting the roughness coefficient as a function of slope. The Lacey, Riggs, Bray and Sauer formulas were found to provide an approximate estimate of the n value, while the best roughness coefficient estimation results were obtained using the Riggs formula. It was also found that taking into account the non-uniform flow and using the friction slope in the formulas instead of the bed slope or water surface slope did not improve the estimated values of the roughness coefficient using the tested formulas. It was shown that the lack of differences in the RMSE and MAE error values calculated for the developed correlation equations between the roughness coefficient and the friction slope or with the water surface slope also indicate no influence of the assumed friction slope or water surface slope on the value of the estimated roughness coefficient.
This study presents the results of 32 laboratory experiments on local scour at a single pile and a 1 × 4 pile group for both uniform and non-uniform sediments under clear water conditions. The present study aims to evaluate the effects of different sediment beds made up of mixtures of sand and gravel (four-bed configurations) in d50 (1–3.5 mm) and gradation (1.4–3) ranges on scour depth for different flow discharges and flow depths. Further, the findings of the experiments are deployed to describe the effects of pile spacing and flow conditions on the local pier scour for both uniform and non-uniform bed granulometries. In addition, this study addresses the performance of some existing scourdepth predictors. Also, the corresponding results are suitable for validating the numerical models in local pier scour prediction importantly with non-uniform sediments. In summary, the results show that effects of sediment gradation dampen with increasing flow shallowness. Furthermore, the maximum scour depth at pile groups generally increases as pile spacing decreases for uniform sediments, whereas the mentioned trend was not observed for non-uniform sediments for the same flow and sediment conditions. Moreover, the experimental results revealed that bed sediment gradation is a controlling factor in the pile’s scour. Thus, the existing scour depth predictions could be highly improved by considering sediment gradation in the predictions. Finally, the conclusions drawn from this study provide crucial evidence for the protection of bridge foundations not only at the front pile but also at rear piles.
CO2 injection is a well-known Enhanced Oil Recovery (EOR) technique that has been used for years to improve oil extraction from carbonate rock and other oil reservoirs. Optimal functioning of CO2 injection requires a thorough understanding of how this method affects the petrophysical properties of the rocks. We evaluated pore-scale changes in these properties, notably porosity and absolute permeability, following injection of CO2-saturated water in two coquina outcrop samples from the Morro do Chaves Formation in Brazil. The coquinas are close analogues of Presalt oil reservoirs off the coast of southern Brazil. The effects of carbonated water injection were evaluated using a series of experimental and numerical steps before and after coreflooding: cleaning, basic petrophysics, microtomography (microCT) imaging, nuclear magnetic resonance (NMR) analyses, and pore network modeling (PNM). Our study was motivated by an earlier experiment which did not show the development of a wormhole in the center of the sample, with a concomitant increase in permeability of the coquina as often noted in the literature. We instead observed a substantial decrease in the absolute permeability (between 71 and 77%), but with little effect on the porosity and no wormhole formation. While all tests were carried out on both samples, here we present a comprehensive analysis for one of the samples to illustrate changes at the pore network level. Different techniques were used for the pore-scale analyses, including pore network modeling using PoreStudio, and software developed by the authors to enable a statistical analysis of the pore network. Results provided much insight in how injected carbonated water affects the pore network of carbonate rocks.
Trapped or residual air (or gas) is known to affect the multiphase hydraulic properties of both soils and rocks. Trapped air is known to impact many vadose zone hydrologic applications such as infiltration and flow in the capillary fringe, but is also a major issue affecting recoverable oil reserves. Although many studies have focused on the relationship between porosity and trapped gas saturation (Sgt) in sandstones, far fewer studies have been carried out for carbonate rocks. This work aims to analyze the influence of porous media properties on trapped gas saturation in carbonate rocks. For this we used thirteen Indiana Limestone and Silurian dolomite rock samples from the USA, and several coquinas from the Morro do Chaves formation in Brazil. Pore size distributions were obtained for all samples using Nuclear Magnetic Resonance (NMR), and Mercury Injection Capillary Pressure (MICP) data from three of the samples to determine their pore throat size distributions. Additionally, 3D microtomography (microCT) images were used to quantify macropore profiles and pore connectivities. Results indicate a lower capacity of gas trapping in carbonate rocks in which micro- and mesopores predominate. Results also indicate that in carbonate rocks, pore size exerts a greater influence on the ability of gas trapping compared to pore connectivity, so that rocks with a predominance of macropores have greater capacity for gas trapping, even when the macropores are well interconnected. These findings show that pore characteristics very much affect the processes governing gas trapping in carbonate rocks, and indirectly the multiphase hydraulic properties and recoverable oil reserves of carbonate rock reservoirs.
Biochars, depending on the types of feedstocks and technological conditions of pyrolysis, can vary significantly in their properties and, therefore, it is difficult to predict biochar-induced effects on nitrous oxide (N2O) emissions from various soils, their physical properties and water availability. The objectives of this study were (1) to quantify effects of slow pyrolysis biochar (BC) and fast pyrolysis biochar (PYRO) on physical and hydro-physical properties of sandy soil (Haplic Arenosol) and clayey loam soil (Gleyic Fluvisol), and (2) to assess corresponding N2O emissions from these two soils. The study included a 63-day long laboratory investigation. Two doses of BC or PYRO (15 t ha–1 and 30 t ha–1) were applied to the soils in combination or without nitrogen fertilizer (NH4NO3, 90 kg N ha–1). The obtained results have shown a significant decrease in the bulk density of sandy soil after it was amended with either rate of BC or PYRO. Water retention capacity of the soils in all the treatments with BC or PYRO increased considerably although no changes was found in the soil water-filled pore space (WFPS) which was higher than 60%. BC was increasing N2O emission rates from the sandy soil treated with N fertilizer, and reducing N2O emission rates from the clayey loam soil treated with N fertilizer. PYRO was more efficient and was reducing N2O emissions from both fertilized soils, but for the sandy soil the reduction was statistically significant only at higher dose (30 t ha–1) of the biochar.
The Three Gorges Reservoir region suffers from severe soil erosion that leads to serious soil degradation and eutrophication. Interrill erosion models are commonly used in developing soil erosion control measures. Laboratory simulation experiments were conducted to investigate the relationship between interrill erosion rate and three commonly hydraulic parameters (flow velocity V, shear stress τ and stream power W). The slope gradients ranged from 17.6% to 36.4%, and the rainfall intensities varied from 0.6 to 2.54 mm·min–1. The results showed that surface runoff volume and soil loss rates varied greatly with the change of slope and rainfall intensity. Surface runoff accounted for 67.2–85.4% of the precipitation on average. Soil loss rates increased with increases of rainfall intensity and slope gradient, Regression analysis showed that interrill erosion rate could be calculated by a linear function of V and W. Predictions based on V (R2 = 0.843, ME = 0.843) and W (R2 = 0.862, ME = 0.862) were powerful. τ (R2 = 0.721, ME = 0.721) did not seem to be a good predictor for interrill erosion rates. Five ordinarily interrill erosion models were analyzed, the accuracy of the models in predicting soil loss rate was: Model 3 (ME = 0.977) > Model 4 (ME = 0.966) > Model 5 (ME = 0.963) > Model 2 (ME = 0.923) > Model 1 (ME = 0.852). The interrill erodibility used in the model 3 (WEPP) was calculated as 0.332×106 kg·s·m–4. The results can improve the precision of interrill erosion estimation on purple soil slopes in the Three Gorges Reservoir area.
Beerkan infiltration runs could provide an incomplete description of infiltration with reference to either the near steady-state or the transient stages. In particular, the process could still be in the transient stage at the end of the run or some transient infiltration data might be loss. The Wu1 method and the BEST-steady algorithm can be applied to derive soil hydrodynamic parameters even under these circumstances. Therefore, a soil dataset could be developed using two different data analysis methods. The hypothesis that the Wu1 method and BEST-steady yield similar predictions of the soil parameters when they are applied to the same infiltration curve was tested in this investigation. For a sandy-loam soil, BEST-steady yielded higher saturated soil hydraulic conductivity, Ks, microscopic pore radius, λm, and depth of the wetting front at the end of the run, dwf, and lower macroscopic capillary length, λc, as compared with the Wu1 method. Two corresponding means differed by 1.2–1.4 times, depending on the variable, and the differences appeared overall from moderate to relatively appreciable, that is neither too high nor negligible in any circumstance, according to some literature suggestions. Two estimates of Ks were similar (difference by < 25%) when the gravity-driven vertical flow and the lateral capillary components represented the 71–89% of total infiltration. In conclusion, the two methods of data analysis do not generally yield the same predictions of soil hydrodynamic parameters when they are applied to the same infiltration curve. However, it seems possible to establish what are the conditions making the two methods similar.
Many soils and other porous media exhibit dual- or multi-porosity type features. In a previous study (Seki et al., 2022) we presented multimodal water retention and closed-form hydraulic conductivity equations for such media. The objective of this study is to show that the proposed equations are practically useful. Specifically, dual-BC (Brooks and Corey)-CH (common head) (DBC), dual-VG (van Genuchten)-CH (DVC), and KO (Kosugi)1BC2-CH (KBC) models were evaluated for a broad range of soil types. The three models showed good agreement with measured water retention and hydraulic conductivity data over a wide range of pressure heads. Results were obtained by first optimizing water retention parameters and then optimizing the saturated hydraulic conductivity (Ks) and two parameters (p, q) or (p, r) in the general hydraulic conductivity equation. Although conventionally the tortuosity factor p is optimized and (q, r) fixed, sensitivity analyses showed that optimization of two parameters (p + r, qr) is required for the multimodal models. For 20 soils from the UNSODA database, the average R2 for log (hydraulic conductivity) was highest (0.985) for the KBC model with r = 1 and optimization of (Ks, p, q). This result was almost equivalent (0.973) to the DVC model with q = 1 and optimization of (Ks, p, r); both were higher than R2 for the widely used Peters model (0.956) when optimizing (Ks, p, a, ω). The proposed equations are useful for practical applications while mathematically being simple and consistent.
A large-scale piano key weir laboratory study was conducted to investigate the evolution of the scour process occurring in the downstream basin for two non-cohesive granular bed materials, including the analysis of scour-hole geometry and patterns at equilibrium. It was observed that hydraulic conditions, particularly tailwater level, significantly affect the scour mechanisms and equilibrium morphology, eventually resulting in scour depths that exceeded the weir height. Unprecedented insights on the scour dynamics are also provided, along with tools to estimate the time evolution and maximum scour depth, its location in the streamwise direction, and the maximum scour length.
In recent years, due to the occurrence of water shortage and drought problems, particularly in arid and semiarid regions of the world, new methods to reduce evaporation from the surface of dam reservoirs, lakes, and other waterfree surfaces are investigated. This study aimed to use hydrophobic bentonite to reduce water evaporation from water surfaces, on a laboratory scale, and field conditions for the first time. Bentonite initially became hydrophobic by stearic acid (SA). Under such conditions, hydrophobic bentonite floats on the surface of water and forms a thin coating layer. The produced hydrophobic bentonite had a contact angle of 150°, indicating its superhydrophobicity. Evaporation reduction was measured under laboratory and field conditions and it was compared to hexadecanol as the reference material. The results demonstrated that the hydrophobic bentonite efficiency under laboratory conditions was similar to that of hexadecanol and prevented water evaporation by 36%. However, under field conditions, hydrophobic bentonite and hexadecanol efficiencies were 40% and 23% to reduce evaporation for 30 days, respectively. In terms of stability, hexadecanol needed to be re-injected after three days, while hydrophobic bentonite was stable and remained on the surface for more than 100 days under laboratory conditions and for more than 15 days under field conditions without needing reinjection. This coverage with method can be used to reduce evaporation from lakes, tanks, and reservoirs of small dams.
Dams have an important role in the industrial development of countries. Irrespective of the reason for dam break, the flood can cause devastating disasters with loss of life and property especially in densely populated areas. In this study, the effects of the vegetation on the flood wave propagation in case of dam break were investigated experimentally by using the distorted physical model of Ürkmez Dam. The horizontal and vertical scales of the distorted physical model are 1/150 and 1/30, respectively. The dam break scenarios were achieved by means of a gate of rectangular and triangular shape. The results obtained from experiments performed with vegetation were compared and interpreted with those obtained from experiments at which the vegetation configuration was absent. The analysis of the experimental data showed that the presence of vegetation causes a significant decrease in water depths as the flood wave propagates to the downstream and greatly reduces its impact on the settlements. It is also revealed that dam break shape plays an important role in temporal variation of flood wave.
Field tests were carried out to estimate effective unsaturated soil hydraulic properties of layered residual soils in Rio de Janeiro, southeastern Brazil. Data of this type are important for understanding the initiation of rainstorm-induced soil landslides, which often occur in the state of Rio de Janeiro as well as other areas having similar geologic settings and climate conditions. Tests were carried out using a simplified field approach, referred to as the Monitored Infiltration Test, which requires only a tensiometer to measure pressure heads below the wetting front, triggered by flow from a Mariotte bottle which maintains a constant pressure at the top edge of the soil profile. The data can then be analyzed by numerical inversion using the HYDRUS-2D software package. The test is relatively fast since no steady-state flow conditions are needed, and versatile since the test can be carried out quickly on steep slopes with the help of a manual auger. Soil water retention and the unsaturated hydraulic conductivity functions were obtained for a range of young, mature and saprolitic residual soils. The effective hydraulic properties of the distinct residual soil layers can be quite large, reflecting a need to provide a careful analysis of field-scale hydraulic heterogeneity in geotechnical analyses.
An application of different mulch materials may lead to changes in soil properties. Our previous study, focused on the impact of various mulches during the 4-year period, showed that the change in some properties can be very rapid (e.g., soil pH), but in other cases such as hydraulic properties, the changes can be gradual. To find out, whether the extension of the mulching period will further affect the studied soil properties, the experiment continued for another 2 years. Differences between values of organic carbon content (Cox), soil physical quality (Sinf), gravitational water (GW) and readily available water (RAW) of soils not covered by any mulch and under various mulches (bark chips; wood chips; wheat straw; Agrotex EKO+ decomposable matting; polypropylene fabric covered bark chips; crushed stone) were much larger than those observed in our previous study. On the other hand, the opposite trend was observed for the water stable aggregates (WSA) index or soil pH. Differences between additionally measured hydraulic conductivities at the pressure head of −2 cm and repellency index (RI) were mostly insignificant. Results indicated that organic mulches can either positively (e.g., increase WSA index and Cox, and decrease GW) or negatively (e.g., decrease Sinf and RAW, and increase RI) affect soil properties.
The paper introduces the Special Section on the Hydrology of the Carpathians in this issue. It is the result of an initiative of the Department of Land and Water Resources Management of the Slovak University of Technology in Bratislava, the Institute of Hydraulic Engineering and Water Resources Management of the TU Vienna and the Institute of Geomatics and Civil Engineering of the University of Sopron to allow young hydrologists in the Carpathian Basin (and from outside) to present their research and re-network on the emerging topics of the hydrology of the Carpathians at the HydroCarpath Conferences since 2012.
Soil water repellency (SWR) reduces the rates of wetting in dry soils and is known to interfere with water movement into as well as within the soils. The objective of this study was to investigate the hydrophysical characteristics of three water-repellent tropical exotic plantation forest soils in wet and dry seasons. The study sites were Eucalyptus grandis (EG), Pinus caribaea (PC), and Casuarina equisetifolia (CE) plantation forest soils located in the up-country intermediate zone (EG and PC), and low-country dry zone (CE). Field experiments were conducted to measure the infiltration rate, unsaturated hydraulic conductivity (k), water sorptivity (SW). Laboratory experiments were conducted to measure the potential SWR and water entry value (hwe). All three soils showed higher SWR in the dry season, where CE soils showed the highest. The EG soils showed the highest SWR in the wet season. Although SWR in all soils decreased with increasing depth in the wet season, only CE soils showed a significant decrease in SWR with soil depth in the dry season. Compared with the wet season, the k (–1 cm) was lower and hwe was higher in the dry season. However, SW did not show a significant difference between wet and dry seasons. Initial infiltration rate and k (–1 cm) showed a negative correlation with contact angle in all three soils. Soils showed positive linear correlations between k (–1 cm) and SW, and negative linear correlations between SW and hwe showing that surface water absorption is related to both subsurface unsaturated water flow and surface water entry pressure. It was clear that the water entry into soils and the subsurface water flow were hindered by the SWR. High water entry values in the dry season predict high potentials for intensified surface runoff and topsoil erosion. Future research will be required on the interactions between soil biology and soil properties such as pore structure that would influence water flow into and within soils.
This paper explores the impacts of reconfiguration and leaf morphology on the flow downstream of a flexible foliated plant. 3D acoustic Doppler velocimetry and particle image velocimetry were used to experimentally investigate the hydrodynamic interaction between a foliated plant and the flow, testing two plants with different leaves morphology under different bulk flow velocities. The model vegetation was representative of riparian vegetation species in terms of plants hydrodynamic behavior and leaf to stem area ratio. To explore the effects of the seasonal variability of vegetation on the flow structure, leafless conditions were tested. Reconfiguration resulted in a decrease of the frontal projected area of the plants up to the 80% relative to the undeformed value. Such changes in plant frontal area markedly affected the spatial distributions of mean velocity and turbulence intensities, altering the local exchanges of momentum. At increasing reconfiguration, the different plant morphology influenced the mean and turbulent wake width. The leafless stem exhibited a rigid behavior, with the flow in the wake being comparable to that downstream of a rigid cylinder. The study revealed that the flexibility-induced reconfiguration of plants can markedly affect the local distribution of flow properties in the wake, potentially affecting transport processes at the scale of the plant and its subparts.