Surface Water Flow Research Articles

An empirical test of groundwater pumping effects on river flow and temperature: Chemainus River case study

Groundwater abstraction from pumping wells can reduce the flows and water levels of hydraulically connected surface waters, which can affect aquatic communities and water rights of other users. Four pump tests were implemented in the 2016 summer low-flow period to measure groundwater pumping effects to Chemainus River surface water flow and temperature. The effect of pumping on surface flow was estimated using four metrics based on differences between measured and predicted flow at a hydrometric gauge located 340 m from the groundwater wells. Differences were estimated as residuals from a regression model relating flow at this gauge to flow at a gauge 1.3 km upstream of the wells. The effect of pumping on surface water temperature was assessed using daily maximum and daily average water temperature at gauges located 340 m and 1.4 km downstream of the wells. An effect of pumping on river flow was measurable when the pumps were turned on and shut off. The consistency of measured effects across all tests and the absence of discernable trends within and across tests indicate that the average effect of pumping across a broader period is equivalent to the average of all before and after comparisons, which was estimated as 9.9 L/s ± 12.1 L/s, or 5.5% of river discharge at the time of the tests. Groundwater pumping did not result in a detectable shift in water temperature. The results indicate that changes in water temperature in relation to the pump tests were smaller in magnitude or spatial scale than the detection limits of the implemented experimental design. This case study provides an example of quantification of pumping effects on stream flow and temperature, as required by the Water Sustainability Act for licensing of groundwater abstraction. We suggest this approach could be used elsewhere to quantify effects of groundwater abstraction.

Influence of Micro-Furrow Depth and Bottom Width on Surface Water Flow and Irrigation Performance in the North China Plain

Improving traditional surface irrigation technology and vigorously promoting water-saving surface irrigation are important ways to improve the efficiency of water resource utilization. In our study, we propose a new technology of surface irrigation, micro-furrow irrigation, which combines the advantages of furrow irrigation and border irrigation. The objective of this experiment was to evaluate the effects of micro-furrow depth and bottom width on surface water flow and irrigation performance. Field experiments were conducted from 2019 to 2020 in Zhengzhou City, northern China. This work designed three bottom widths, BW1 (18 cm), BW2 (12 cm), and BW3 (6 cm), respectively, and three depths, D1 (15 cm), D2 (10 cm), and D3 (5 cm), respectively. Moreover, border irrigation was set as control treatment (CK). Additionally, field experiments were validated and simulated using the WinSRFR 5.1 model (Arid-Land Agricultural Research Center, USA). The results showed a significant negative correlation between depth and advance time and between depth and recession time. However, no significant correlation was found between bottom width and advance time, nor between bottom width and recession time. The advance times of micro-furrow irrigation were 1.23–4.77 min less than those of border irrigation. Concerning irrigation performance, compared to that of border irrigation, the application efficiency and distribution uniformity increased by 8–30% and −5–18%, respectively. However, the requirement efficiency decreased by 0–40%. Compared to that of border irrigation, the irrigation quota increased 21.61% under BW3D3 but decreased by 10.46–57.94% under other treatments. Therefore, micro-furrow irrigation can meet irrigation requirements despite low irrigation quota. Comprehensively considering the advance time, recession time, irrigation performance, and irrigation quota, we recommend a micro-furrow shape with a depth of 10 cm or 15 cm and bottom width of 6 cm.

A Comprehensive Approach to Develop a Hydrological Model for the Simulation of All the Important Hydrological Components: The Case of the Three-River Headwater Region, China

The objective of the study was to configure the Hydrological Modeling System (HEC-HMS) in such a way that it could simulate all-important hydrological components (e.g., streamflow, soil moisture, snowmelt water, terrestrial water storage, baseflow, surface flow, and evapotranspiration) in the Three-River Headwater Region. However, the problem we faced was unsatisfactory simulations of these hydrological components, except streamflow. The main reason we found was the auto-calibration method of HEC-HMS because it generated irrational parameters, especially with the inclusion of Temperature Index Method and Soil Moisture Accounting (an advanced and complex loss method). Similar problems have been reported by different previous studies. To overcome these problems, we designed a comprehensive approach to estimate initial parameters and to calibrate the model manually in such a way that the model could simulate all the important hydrological components satisfactorily.

Comparing alternative conceptual models for tile drains and soil heterogeneity for the simulation of tile drainage in agricultural catchments

• The seepage node concept was used to simulate tile drainage at the catchment scale. • Tile drainage was simulated without the specific location of tile drains. • Similar drainage discharge volumes were simulated with different conceptual models. • Drainage discharge was sensitive to soil heterogeneity. • Observed stream discharge and depth to water table were well simulated. Tile drains are important water flow paths in agricultural catchments and must be included in hydrological models. However, their locations are rarely known and the explicit incorporation of tile drains in hydrological models requires refined meshes around the drains, which can significantly increase computational times. Although seepage nodes have been used to represent tile drains with satisfactory performance, they have never been applied to represent all tile drainage systems in a catchment. The goal of this study is to compare different conceptual models for tile drains and soil heterogeneity for the numerical simulation of tile drainage in an agricultural catchment in Denmark. The first conceptual model for tile drains uses seepage nodes to represent only the main collector drains in the catchment and the second model uses seepage nodes distributed over all the agricultural areas, without considering the specific locations of tile drains. A third conceptual model, labelled the Benchmark Model, represent all tile drains at their known locations with seepage nodes and a fourth conceptual model implicitly represents tile drains as a high-permeability layer. The four models performed satisfactorily to simulate the observed outlet stream discharge and could be recommended almost interchangeably. The simulation of the water table depth was very satisfactory compared to modeling studies with similar mesh resolution (∼50 m). Results indicated that the three models using seepage nodes i) simulated similar monthly discharges and cumulative discharge volumes for most of the studied tile-drained areas, and ii) simulated surface water flow in tile-drained fields without runoff or ponding water. The shorter simulation times (around 35% faster) of the model representing the main drains and the distributed seepage node model suggest that they are suitable for model calibration, compared to the Benchmark Model. Whenever the location of tile drains is unavailable, using seepage node to represent drains in agricultural areas may satisfactorily simulate catchment-scale stream and drainage discharges. Four alternative soil models were developed to evaluate the effect of soil heterogeneity on the simulations. Our results suggest that at smaller scales (drainage area) soil heterogeneity is more relevant than the drainage conceptualization to improve model results. However, at the subcatchment scale, the opposite was observed and, at the catchment scale, both criteria had a comparable effect.

Determination of ice production in a natural river: a case study in the Inner Mongolia Reach of the Yellow River

Abstract In the present study, ice production in a natural river reach has been studied by means of the thermodynamic theory regarding the heat flux between ice, air, riverbed, and water. The heat transfer coefficient and equivalent total heat flux were determined for different periods during winter. The characteristics of variation and distribution of ice production in the Inner Mongolia Reach of the Yellow River (IMRYR) were studied in combination with the change of heat flux. A model for describing the temporal–spatial variation of ice production for the IMRYR has been developed. The ice production process of the IMRYR from 2017 to 2021 was simulated using the proposed model, and the simulation results were in good agreement with those of the measurements. Results of the analysis showed that when the total ice production in the Bayangaole gauging station reaches 3.18 × 107 m3, a freeze-up process in this river reach is likely to occur. The influence degree of each variable on the ice production was in the following descending order: water surface area, air temperature, radiation, and flow. Particularly, a change of 20% of the water surface area will lead to a 11.48% change in the final calculated result of ice production.

Flood hazard and susceptibility assessment in a semi-arid environment: A case study of Seyad basin, south of Morocco

Flood, is a constant phenomenon, especially in semi-arid and flood plain regions are one of the most destructive natural hazards endangering a people's life, property, and physical and economic well-being. This paper focuses on hydraulic modelling using the HEC-RAS model in combination with the Watershed Modeling System (WMS) tools and compares the results to the Flood Hazard Index (FHI) method using GIS in the Seyad Basin situated in the southwestern region of Morocco with an area of 1512.85 km2. The goal of the study is to evaluate flood hazards in the Seyad Basin in which the cities of Taghjijt, Aday, Amtoudi, and Tagriante are located. The HEC-RAS approach combines the hydraulic surface water flow model and the digital terrain model data. This combination allows the mapping of the flood zones by using the WMS tools. This approach predicts flood occurrence probability for different times and determines the intensity of the flood (depth and velocity of floodwater) using the existing hydrological data.On the other hand, the Flood Hazard Index method (FHI) presents a multi-criteria index to assess areas prone to flood hazards, using six physical parameters: permeability, slope, distance from rivers, land use, drainage density, and flow accumulation. A weight is calculated from the analytic hierarchy process method and applied to each parameter. HEC-RAS method allows the mapping of a flood with a flood water surface profile that shows the flood depth for Annual Exceedance Probability (AEP). At the same time, FHI permits establishing flood hazard levels without showing the water depth. In both approaches, six simulations were performed with the return periods of 10, 20, 50, 100, 200, and 500 years. The simulation revealed that the most susceptible areas to flooding are the areas along the Wadi Seyad.

Geophysical studies of permafrost conditions of the Kangalassky coal mine dam

Problem statement. Geophysical studies of the ground dam body and base at the Kangalassky coal mine were carried out as part of monitoring related to the dam’s destruction, propagation of flank release fractures parallel to the ledge, and water seepage into the open pit. The main function of the ground dam is to protect the mining site from the inflow of surface water and preserve frozen rocks of the geological base. The mine workings of the coal mine are watered due to precipitation in the summer, snow melting and frozen rock thawing in the spring. Research objective is to assess the permafrost-ground conditions of the site according to geophysical methods and establish the boundaries of seepage flows that seep through the body and base of the ground dam. Methods of research. Electrical sounding at the dam site were performed by the electrical resistivity tomography method. The research was carried out with the Omega-48 equipment. Ground Penetrating Radar (GPR) study was carried out with a georadar of the OKO-2 series (AB-250M, central frequency 250 MHz). Georeferencing for comparative analysis of GPR parameters and positioning was carried out by the Geobox Fora Smart high-precision (geodetic) GNSS receiver. The cryogenic condition of rock was determined from the drilling data and FLIR SC660 thermal imaging camera data (device by the Shared core facilities of the Federal Research Center “Yakutsk Science Center SB RAS”, grant no. 13.TsKP.21.0016). Results. The results of GPR studies by the method of multi-season measurements in spring and autumn made it possible to objectively assess open pit permafrost conditions that reflect rock mass condition features (frozen or thawed rocks) and the position of the weakness zones (seepage areas and the presence of waterlogged soils). The analysis of geoelectric sections has identified anomalous areas with reduced electrical resistivity interpreted as zones of suprapermafrost surface water penetration into the embankment body with further dam base soil erosion. Possible surface waters migration routes and frozen rock degradation areas have also been identified. Scope of results. The described technique can be used at the enterprises of the mining complex in the North of Russia for engineering-geological and geocryological monitoring of mining and engineering structures.

Evolution of agricultural development and land-water-food nexus in Central Asia

Agricultural water use in heavily irrigated regions can reduce surface water flow. The most remarkable hydrological change in recent times in Central Asia is the rapid dry-up of the Aral Sea. In this paper, the evolution of agricultural development was traced back to the 1910s, Land-Water-Food (LWF) nexus in Central Asia was evaluated, and the relationship between agricultural development and Aral Sea dry-up was built. It was noted that for the 1910–2010s, the harvested land area in the region expanded nearly two folds — from 7.2 to 21.6 million ha. Production of cereal crops increased over eight folds — from 4.0 to 37.6 million tonnes. Cotton production reached 5.5 million tonnes, a seven-fold increase. The high increase in productivity was driven by increasing agricultural irrigation since the 1950s. Irrigation water requirement for the five main crops (wheat, cotton, maize, barley and rice) increased by about 50%; from 64.3 km3 in the 1950s to 95.9 km3 in the 2010s. Cotton and wheat were the top two crops, with respective total irrigation water use of 66.9% and 16.4%. For the study area, LWF nexus was quantified in terms of production efficiency using the data envelopment analysis method, and it was shown that excess water and land resources made agricultural production inefficient. Analysis of the irrigated area and the Aral Sea water surface area suggested that for every 1.0 km2 increase in irrigated land area, water surface area in the Aral Sea declined by 1.2 km2. The analysis of LWF tradeoff was key not only for sustainable land, water and ecological management, but also for food production in degraded arid lands around the globe.

Hydraulic characteristics of the Parshall flume entrance wingwall: Numerical simulation and test

AbstractThe Parshall flume is a common open channel water‐measuring facility that is widely used in hydrological monitoring, agricultural irrigation and municipal water supply. In engineering applications, there is no clear requirement for the form of the wingwalls connecting the channel and Parshall flume. Therefore, it has different effects on flow measurement accuracy, flow velocity distribution and hydraulic characteristics. To standardize its construction requirements, a wingwall form with high flow measurement accuracy is evaluated. Computational fluid dynamics (CFD) numerical simulations and hydraulic experiments have shown the influence of different wingwalls on hydraulic characteristics. The governing test parameters include wingwall forms, incoming flow and degree of submergence. By measuring water surface fluctuation, streamline distribution and flow measurement error, the effects of different wingwall forms on flow measurement accuracy and hydraulic characteristics were evaluated. The results showed that the fluctuation of the water surface is affected by the boundary conditions. Layout I has the highest flow measurement accuracy and has an arc‐shaped wingwall with a radius of 1.5 m. By comparing the results of the tests and simulations, the average error is 3%. The results showed that the hydrodynamic model of the Parshall flume can provide a theoretical basis for the design and development of the measurement structure in the future.

A multi-criteria approach of assessing groundwater potential, recharge and flow in the transboundary Tuli Karoo Basin

Abstract Quantitative estimates of amount of groundwater resources are required in the transboundary Tuli Karoo Basin to better manage and promote sustainable conjunctive use of the aquifer. Unfortunately, such important data and information are lacking. The aim of this study was to map groundwater potential zones and model groundwater recharge as well as groundwater flow in the Tuli Karoo Basin (12,164 km2) using geospatial techniques. To delineate groundwater potential zones, nine thematic maps of groundwater conditioning factors were computed and weighted using Saaty's Analytical Hierarchy Process (AHP). To validate the groundwater potential map, a Kruskal–Wallis test was performed. Groundwater recharge and groundwater flow direction were estimated in a coupled Geographic Information System (GIS) and modelling environment using the soil–water–balance model (SWB) and British Geological Survey (BGS) groundwater tool, respectively. Results for groundwater potential mapping showed that the area is dominated by high ground water potential which covers about 57.8% (6,915.1 km2) of the basin. The Kruskal–Wallis test showed that the median values of the borehole yields vary significantly between the different groundwater potential zone classes (P-value <0.0001). Estimated groundwater recharge using SWB model showed that the maximum annual potential recharge for the Tuli Karoo Basin was 13.2 mm/year for the 10-year period from 2010 to 2020. Results from the BGS tool for groundwater flow show that the dominant groundwater flow direction is southeast. The results showed that there is no link between groundwater flow direction and surface water flow direction. This study is relevant in water development policy, water-related development aid, community planning and technical decision making for hydrogeologists, catchment managers, water planners and non-specialists alike.

Azerbaijan effects on Agrochemical Indications and Effect of Erosion Process on Plant Productivity

Taking all these into account, it is important to increase the fertility of the soil from the erosion process in Ismayilli and to prevent the washing of fodder crops from perennial herbs. The cultivation of these plants in the mountainous regions protects the slopes from the terrible erosion process and provides the animals with a strong fodder. It is proved by the results of the research that restoration of fertility and ecological balance of erosion lands and the implementation of soil-agro-technical measures to increase productivity are of great importance. Due to the application of these measures, I, as a result of improving the water and physical properties of the affected land, prevent surface water flows. In addition, the results of the study have been proven by the fact that, for certain reason, erosion and erosion hazards are most likely to be taken over by the sowing of perennial herbs. Thus, perennial herbs, in particular, accumulate the nitrogen atmosphere of the legumes, enriches the soil with organic matter, accelerates the formation of water-resistant granular - topical structure and improves its water-physical properties, which in turn facilitates the rapid digestion of foodstuffs.

Analisis Karakteristik Hujan Ekstrim Menggunakan Model Iklim di Wilayah Gunung Merapi

Extreme rainfall is one of the trigger factors for debris floods in stratovolcanos. It caused by volcanic materials will be easily eroded in large quantity with surface water flow as the result of extreme rainfall. Extreme rainfall is avnatural phenomenon which is often related with climate change. In the future, changes in extreme rainfall characteristics may occur. Therefore, it’s necessary to conduct extreme rainfall analysis for historical and future periods. In this study, the characteristics of rainfall analyzed were the variability of extreme rain as shown by trend analysis of extreme rain indices namely RTOT. Hourly rainfall data at eight rain stations used as input. Future rainfall data was projected using the global climate model CanESM2 (RCP4.5 and RCP8.5 and downscaling process using Statistical Downscaling Model (SDSM). Comparison of the projection rainfall with historical rainfall shows a different trend at each station. Increasing trend occurred at four stations including Plosokerep, Pucanganom, Sopalan, and Talun stations, with the highest increasing trend occurring at Sopalan stations. In addition, there was also a decreasing trend that occurred at Ngandong station for both scenarios and at Sorasan station in the RCP8.5 scenario. The Jrakah and Randugunting stations show a steady trend.

Effects of morphology and sediment permeability on coastal lagoons’ hydrological patterns

Mediterranean coastal lagoons are influenced from a wide variety of external factors such as surface and groundwater flows and climate dynamics. They are also vulnerable to human activities, which have caused a significant loss of these types of habitats. As a result, the EU habitat management have now prioritized restoration of natural wetlands. However, there is a lack of systemic studies on the mechanisms of coastal wetland degradation and ecohydrological processes that determine restored ecological functioning as an end goal, as well as a lack of reference sites to make comparisons. Furthermore, while lagoon morphometry and underlying sediment permeability have been studied extensively, combining these disciplines to evaluate lagoon hydrology and salinity dynamics is yet to be fully explored. The aim of this study was to analyze the hydrological dynamics of 4 newly constructed lagoons and compare them with 2 natural lagoons in the La Pletera salt marshes and evaluate the restoration and conservation efforts. We use the General Lake Model (GLM) to assess water volume fluctuations, salinity variability and lagoon water circulation (groundwater and surface water inflows, outflows and evaporation). We also combine data of the underlying lithological characteristics and lagoon morphometry, to compare and better understand the interplay of these parameters on the hydrological behavior of each lagoon. Results indicated that the older and natural lagoons exhibited more consistent patterns of confinement; with deeper morphologies, lower evaporation effect, lower water circulation, and more annual patterns of salinity fluctuation. The presence of low-permeability layers also resulted in less fluctuation of higher salinity levels. Conversely, three of the four new lagoons had similar, shallower morphologies and higher evaporation fluxes, but exhibited different water circulation patterns due to the presence or absence of low permeability layers. Also, their salinity fluctuations were more influenced by seasonal mixing than by evaporation, indicating more susceptibility to climatic influence in their annual hydrological pattern than in the natural lagoons. This could prove important when constructing and restoring lagoons according to predetermined morphology and underlying sediment patterns, as it could ultimately limit or enhance the success of set objectives and overall ecological functioning in a flooding – confinement driven lagoon ecosystem conditioned by irregular and unpredictable climatic events.

The extent and magnitude of edge effects on woody vegetation in road‐bisected treed peatlands in boreal Alberta, Canada

AbstractTreed peatlands can exhibit dramatic shifts in woody plant cover when they are bisected by roads, a product of change in the flow of surface and subsurface water; however, the edge effects that roads have on overstory cover remain poorly understood. We examined how road and environmental conditions influence woody cover in treed fens in northeastern Alberta, Canada. We used generalized linear mixed models to explain variation in cover as measured using airborne laser scanning (ALS) data obtained for 48 road‐bisected fens. Over half of the study fens had >10% differences in canopy cover between the upstream and downstream sides. Variation in cover was best explained by a complex interaction between road side, distance, and type, as well as distance to upland forest and open water, in both rich and poor treed fens. Substrate texture (fine vs. coarse) further explained cover in rich fens. Gravel roads appeared to have the most dramatic effect on cover adjacent to roads (0–20 m) in both fen types, with differences persisting beyond 100 m. In fens bisected by gravel and paved roads, differences in cover between road sides tended to be ameliorated within 200 m, except for unimproved roads where changes were more linear. This study demonstrates the complexity of landscape conditions under which roads built through peatlands can cause structural changes in woody cover and the usefulness of ALS data for studying this phenomenon.

Photochemical behavior of constructed wetlands-derived dissolved organic matter and its effects on Bisphenol A photodegradation in secondary treated wastewater

Free water surface flow (FWS) constructed wetlands (CWs) have been broadly applied for polishing secondary treated effluents. Dissolved organic matter derived from FWS CWs (WDOM) plays key roles in contaminants transformations. Conversely, photodegradation could shape the quantity and quality of WDOM, thereby affecting its roles in the photolysis of organic micropollutants (OMPs). Nevertheless, whether and how solar irradiation-induced photodegradation modify the properties of WDOM, and the effects of WDOM on the photodegradation of OMPs remain unclear. This study elucidates the photochemical behavior of two WDOM isolated from field-scale FWS CWs for effluent polishing under simulated sunlight irradiation using spectroscopic tools and high-resolution mass spectra. Furthermore, the roles of WDOM in the photodegradation of Bisphenol A (BPA), as a representative endocrine-disrupting compound (EDC), were comprehensively investigated. Solar irradiation was demonstrated to lower the molecular weight and aromaticity of WDOM, as well as weaken its light absorption. Ultrahigh-resolution mass spectra further confirmed that aromatic and unsaturated structures were susceptible to solar irradiation-induced photodegradation reactions. Subsequently, less aromatic and more saturated structures eventually formed under sunlight irradiation, consistent with the result from spectroscopic characterization. The reactive species produced from WDOM significantly enhanced the photodegradation of BPA with the kobs noticeably increasing 4-fold compared with the kobs for direct photolysis. Additionally, 3WDOM* was identified as the dominant reactive species leading to the photolysis of BPA in the presence of WDOM. These findings improve understanding of the phototransformation behavior of WDOM under sunlight irradiation and the roles that WDOM plays in the photochemical fate of coexisting OMPs in CWs treatment systems.

Revisiting subglacial hydrology as an origin for Mars' valley networks

Although the nature of the early Martian climate is a matter of considerable debate, the presence of valley networks (VN) provides unambiguous evidence for the presence of liquid water on Mars' surface. A subaerial fluvial origin of VN is at odds with the expected phase instability of near-surface water in the cold, dry Late Noachian climate. Furthermore, many geomorphic properties of VN (e.g., deep U-shaped valleys with constant widths; longitudinal profile reversals) are inconsistent with surface water flow. Conversely, subglacial channels exhibit many of these characteristics and could have persisted beneath ice sheets even in a cold climate. Here we model basal melting beneath a Late Noachian Icy Highlands ice sheet and map subglacial hydrological flow paths to investigate the distribution and geomorphometry of subglacial channels. We show that subglacial processes produce enough melt water to carve Mars' VN; that predicted channel distribution is consistent with observations; and corroborate reversed channel gradient measurements of VN consistent with subglacial formation mechanisms. We suggest that, given a sufficient historical global water inventory and Late Noachian geothermal heat flux, subglacial hydrology may have played a significant role in the surface modification of Mars.Plain language summary. Thousands of valley networks on Mars appear to have been carved by flowing water, and exhibit branching characteristics akin to river networks on Earth. Their origins, however, remain enigmatic for two primary reasons. First, ancient Mars was potentially cold, dry, and unable to support liquid water on its surface. Second, many physical characteristics of the valleys are inconsistent with features formed by precipitation and runoff. On Earth, water flowing beneath ice sheets produces channels with similar characteristics to Mars' valley networks. Here we model the deposition and evolution of Martian ice sheets and show that melting at the ice sheet base is likely even under cold and dry surface conditions. The volume, regional distribution, and flow patterns of melt are consistent with the volume and dynamics needed to carve the observed valley networks. A subglacial origin for Mars' valley networks accounts for their formation in a cold, dry climate and produces valley characteristics that match observations.

Investigation of the detachment of oil droplets driven by water shear field on solid surfaces with different wettabilities

The movement and detachment of tiny oil droplets in water on a substrate is the key technology to strengthen oil–water separation by using corrugated plate oil–water separation technology. Here, the detachment behaviors of oil droplets adhered to substrates with different wettabilities in a laminar flow field are studied experimentally and theoretically. The morphologic changes of mother and daughter oil droplets are obtained when the adhered oil droplets are continuously separated. The shedding mechanism of oil droplets is analyzed in detail, and the critical condition for the effective detachment of oil droplets is obtained, which can be used to guide the design of the surface wettability and water flow velocity in the actual production of oil–water separation.

A New Clustering Method to Generate Training Samples for Supervised Monitoring of Long-Term Water Surface Dynamics Using Landsat Data through Google Earth Engine

Water resources are vital to the survival of living organisms and contribute substantially to the development of various sectors. Climatic diversity, topographic conditions, and uneven distribution of surface water flows have made reservoirs one of the primary water supply resources in Iran. This study used Landsat 5, 7, and 8 data in Google Earth Engine (GEE) for supervised monitoring of surface water dynamics in the reservoir of eight Iranian dams (Karkheh, Karun-1, Karun-3, Karun-4, Dez, UpperGotvand, Zayanderud, and Golpayegan). A novel automated method was proposed for providing training samples based on an iterative K-means refinement procedure. The proposed method used the Function of the Mask (Fmask) initial water map to generate final training samples. Then, Support Vector Machines (SVM) and Random Forest (RF) models were trained with the generated samples and used for water mapping. Results demonstrated the satisfactory performance of the trained RF model with the samples of the proposed refinement procedure (with overall accuracies of 95.13%) in comparison to the trained RF with direct samples of Fmask initial water map (with overall accuracies of 78.91%), indicating the proposed approach’s success in producing training samples. The performance of three feature sets was also evaluated. Tasseled-Cap (TC) achieved higher overall accuracies than Spectral Indices (SI) and Principal Component Transformation of Image Bands (PCA). However, simultaneous use of all features (TC, SI, and PCA) boosted classification overall accuracy. Moreover, long-term surface water changes showed a downward trend in five study sites. Comparing the latest year’s water surface area (2021) with the maximum long-term extent showed that all study sites experienced a significant reduction (16–62%). Analysis of climate factors’ impacts also revealed that precipitation (0.51 ≤ R2 ≤ 0.79) was more correlated than the temperature (0.22 ≤ R2 ≤ 0.39) with water surface area changes.

Spatial Patterns of Infiltration on a Bench Terraced Hillslope in Kigezi Highlands, South-Western Uganda

The spatial patterns of infiltration on bench terraced hillslopes are not fully understood. Moreover, these patterns are pivotal for assessing hydrological processes affecting water distribution, surface flow and soil erosion, and groundwater recharge. Our objective was to determine the spatial patterns of steady-state infiltration rates on a bench terraced hillslope; and assess the influence of soil properties on the infiltration process. We employed Geo-Information Science (GIS) to stratify the terraced bench hillslope into three slope position sequences, namely, Upslope, Middle slope, and Downslope. Besides, in each slope position segment, a bench terrace was randomly selected; and later stratified into three plot segments, namely, Upper (A), Middle (B), and Bottom (C), for purposes of conducting infiltration experiments. At each plot segment, three infiltration experiments were replicated to ascertain the intra-bench and inter-bench terrace steady-state infiltration rates. The experimental field design consisted of three slope position sequences, three plot segments, and three replicates, hence, leading to a total of twenty-seven (27) experiments. The infiltration measurements were conducted using a standard double-ring infiltrometer. We sampled soil for two different depths, namely; 0-15 cm and 15-30 cm, at each infiltration experiment to establish its relationship to the infiltration process. Using a Spatial Autocorrelation tool embedded in ArcGIS 10.2, we analysed the spatial patterns of infiltration along the hillslope. Furthermore, a Two-Way analysis of variance (ANOVA) was used to determine differences between the means of the infiltration rates across the hillslope sequences. Descriptive Statistics were used to investigate the Degree of Variability in infiltration rates. Results showed that beyond 15 m, infiltration rates vary significantly (P<0.018) from 5 cm hr-1 to 40 cm hr-1 between the bench terraced hillslope sequences, with a mean rate of 21 cm hr-1. Intra-bench steady-state infiltration rates varied higher in the Bottom (C) compared to Upper (A) and Middle (B) segments, especially in the Upslope sequence, where rates varied from 6 cm hr-1 to 20 cm hr-1 with a coefficient of variation (CV) of 45%. The clay content in the soil had a significant influence (P<0.003) on infiltration in the study sites of the hillslope with a correlation coefficient (R, r2 = -0.5). We concluded that the spatial patterns of infiltration on a bench-terraced hillslope are influenced by slope position. Infiltration is higher at the Downslope and Middleslope bench terraces as compared to the Upslope bench terrace. Soil texture and the structural condition of the bench terraces themselves play a cardinal role in the variations in infiltration. Within the bench terraced land parcels, infiltration is higher on the downslope and lower in the upslope positions. Since percent clay content increased with slope, it was noted as a fundamental soil characteristic affecting infiltration within the bench terraces. Our recommendation was that in bench terraces where steady-state infiltration was high such as in downslope and middle slope positions, the terrace bunds should be strengthened with grass and stone embarkments to consolidate them coherently. This strategy may reduce terrace bund breakages and consequently counter surface flow on the bench terraced hillslope. Besides, in areas where low steady-state infiltration rates were recognised, such as the upslope position, agronomic practices should be enhanced.

Alternative stable states and hydrological regime shifts in a large intermittent river

Non-perennial rivers and streams make up over half the global river network and are becoming more widespread. Transitions from perennial to non-perennial flow are a threshold-type change that can lead to alternative stable states in aquatic ecosystems, but it is unknown whether streamflow itself is stable in either wet (flowing) or dry (no-flow) conditions. Here, we investigated drivers and feedbacks associated with regime shifts between wet and dry conditions in an intermittent reach of the Arkansas River (USA) over the past 23 years. Multiple lines of evidence suggested that these regimes represent alternative stable states, including (a) significant jumps in discharge time series that were not accompanied by jumps in flow drivers such as precipitation and groundwater pumping; (b) a multi-modal state distribution with 92% of months experiencing no-flow conditions for <10% or >90% of days, despite unimodal distributions of precipitation and pumping; and (c) a hysteretic relationship between climate and flow state. Groundwater levels appear to be the primary control over the hydrological regime, as groundwater levels in the alluvial aquifer were higher than the stream stage during wet regimes and lower than the streambed during dry regimes. Groundwater level variation, in turn, was driven by processes occurring at both the regional scale (surface water inflows from upstream, groundwater pumping) and the reach scale (stream–aquifer exchange, diffuse recharge through the soil column). Historical regime shifts were associated with diverse pressures including network disconnection caused by upstream water use, increased flow stability potentially associated with reservoir operations, and anomalous wet and dry climate conditions. In sum, stabilizing feedbacks among upstream inflows, stream–aquifer interactions, climate, vegetation, and pumping appear to create alternative wet and dry stable states at this site. These stabilizing feedbacks suggest that widespread observed shifts from perennial to non-perennial flow will be difficult to reverse.