Runoff Flow Research Articles

Main water pathways in cultivated clayey calcisols in molassic hills in southwestern France: Toward spatialization of soil waterlogging

AbstractLocal waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot.

Agricultural land management alters the biogeochemical cycling capacity of aquatic and sediment environments

Nutrient loading from agricultural landscapes continues to pose a threat to downstream aquatic systems, contributing to degraded water quality and eutrophication. Nutrient loading to adjacent aquatic environments is influenced by the type of applied fertilizer (chemical and manure), field management, and seasonal weather patterns. The risk these nutrients pose to downstream systems may be mitigated by the capacity of the microbial community in receiving water catchments to process those nutrients. This study evaluated the interactive effects of agricultural practices and seasonal weather patterns on nutrient cycling communities in catchment ponds within a long-term Agriculture and Agri-Food Canada research trial, located in the Lake Erie watershed in Ontario, Canada. Microbial nitrogen (N) and P (phosphorus)-cycling functions in water and sediment environments, receiving direct tile drainage and surface runoff flow, were quantified with respect to nutrient loads from liquid cow manure, solid cow manure, inorganic phosphorus, and a control fertilizer treatment, over a full year. High bacterial nitrification potential in the water column coincided with nitrogen loading, which was driven by manure/fertilizer application, tillage practices, and precipitation. The highest overall phosphorus concentrations occurred in the liquid cow manure treatment, but the availability of phosphorus in all treatments was strongly associated with microbial phosphorus mobilization capacity in both aquatic and sediment environments. Seasonality also influenced the aquatic environment, where N and P- cycling potential significantly increased during the winter months. Microbial functional potential in the water column was strongly influenced by the external environment, including season and precipitation, while the functional potential in the sediment was more resistant to environmental fluctuations, and was primarily influenced by long-term management fertilizer/manure practices. Overall, this study provides evidence that agricultural management alters the capacity of the microbial communities in adjacent aquatic environments to process nutrients.

ТОБЫЛ ӨЗЕНІ АҒЫНЫНЫҢ ЖЫЛ ІШІНДЕГІ ТАРАЛУЫНА АНТРОПОГЕНДІК ӘСЕРДІ БАҒАЛАУ

The article considers the use of the Tobol River water resources in Kazakh part of the river basin for the needs of economic complex for the period from 2000 to 2021. The impact of economic activity on the annual runoff and intra-annual flow distribution of the Tobol River near the city of Kostanay for the period from 1965 to 2021 was assessed according to the data of the observation station near the village Grishchenko after the construction of Karatomarsky and Verkhne-Tobolsk water reservoirs. It has been found that during the period of consideration, the average annual water resources of the Tobol River, as well as its spring runoff decreased, and the river runoff in summer and autumn increased compared to the natural period.

Are high-severity burns in Alpine beech forests related to eruptive fire behavior?

Abstract In the complex Alpine topography, canyon-like terrain morphology combined with steep slopes may cause sudden changes in fire behavior, for instance, turning fast-spreading surface fires into eruptive fires. This phenomenon was observed during the vegetation dormancy in mountain beech (Fagus sylvatica L.) stands, a forest type usually spared from wildfires. The aim of this study is to understand the impact of eruptive fire behavior on the post-fire trajectories of beech trees. To this end, over the course of 3 years, we monitored the post-fire dynamics of 100 beech trees subjected to different fire intensities in February 2020, including a small-scale eruptive fire behavior associated with a steep slope (~41.4° on average) and canyon-like terrain features. Dendrometric and sylvicultural parameters and fire-related damages such as the presence of bark blackening, scars, foliage loss, crashes of branches or whole trees, and parasitic attacks were assessed. The observed medium to high fire severity was highly dependent on the position of the tree within the eruptive fire sector, whereas the relationship with dendrometric and sylvicultural tree characteristics, such as the crown position or the stem diameter, was less clear. Due to the lethal temperatures generated by the heat convection within the eruptive fire sector, the exposed bud and cambium tissues of the beech trees partially or totally failed to develop in the first post-fire season. Beech crown and stem tissue killed by exposure to convective heat fluxes rapidly dries out, loses its elasticity, and becomes brittle. Starting from the second post-fire season, this greatly increases the risk of the crashing of these crown parts and/or entire trees. A detailed understanding of the factors leading to an eruptive fire behavior would highly benefit the fire risk assessment and the detailed planning of the firefighting tactics in mountain areas, eventually increasing the safety of firefighters and preventing post-fire natural hazards, such as rockfall, erosion, surface runoff, and debris flow.

Blue-Green Infrastructure for Jakarta’s Sustainable Planning and Resilience

The concept of a sustainable city that has been described in the Sustainable Development Goals (SDGs) requires all cities in the world to implement it to solve climate problems that if not handled are increasing every year. The impact of climate change, which is a global problem, can affect lives, such as hydrometeorological disasters especially floods. Flood problems can be overcome with the Blue Green Infrastructure (BGI) development approach, one of which is green open space with a retention pond as an effort to achieve the SDGs in the Sustainable City component. Based on this statement, this study will identify in determining the location of BGI development in this case green open space with retention ponds to support the concept of sustainable planning and resilience in one of the metropolitan cities in Indonesia, Jakarta, which is the most populous city that has high rainfall and has minimal open space. The construction of the BGI is carried out as an effort to reduce the impact of climate change in the form of flooding by structural mitigation in the conservation of water balance in urban development, improving water quality, and reducing rainwater runoff and peak flows. This research was carried out in stages in the form of identification of urban land cover changes with image crawling as justification for the massive addition of built-up land, identification of vegetation density and temperature with Land Surface Temperature (LST) and flood hazard, with identification of retention pond needs. Eventually, recommendations for BGI development locations were given based on changes in urban land, temperature, vegetation, and flood hazard as well as the fulfilment of supporting infrastructure needs.

Influence of Non-Woven Geotextile Over Chemically Stabilized Soil in Controlling Erosion

Abstract: Soil erosion is the most significant hazard in sloping terrain. It affects the hilly regions by the loss of top layer of the soil. Soil erosion is mainly induced by rainfall. As the surface runoff flows with high velocity, the detachment of soil particles takes place and it moves down slope. It causes instability and leads to slope failure. The soil erosion depends on erodibility, rainfall erosivity and spatial variability. Non-woven geotextile has the interlocking fibers which retain the fine soil particles and allow water to pass through the fabric. In this study, non-woven geotextile is used over chemically stabilized soil to control the erosion. The stabilizers used are Guar gum powder and Magnesium Stearate powder. Erosion tests are conducted in the slope model for maximum hourly rainfall intensities of 60mm/hr and 70mm/hr on an inclined slope having inclination of 20°. The erosion rates for the slope wherein geotextile is used as reinforcement on soil treated with Guar gum powder in the slope model for rainfall intensities 60mm/hr and 70mm/hr are 2112g/m²/hr and 2798g/m²/hr respectively. Similarly, the same soil slope model in which the stabilizer used as Magnesium Stearate and reinforced with geotextile sheet and for the same rainfall of 60mm/hr and 70mm/hr intensities produced reduction in erosion rate of 1950g/m²/hr and 2312g/m²/hr respectively. The results show, that the erosion rate decreased with the use of geotextile on chemically stabilized soil with Magnesium Stearate when compared to the other method

The impacts of climate change on hydrological processes of Gilgel Gibe catchment, southwest Ethiopia.

Climate change is a significant driver of water resource availability, affecting the magnitude of surface runoff, aquifer recharge, and river flows. This study investigated the impact of climate change on hydrological processes within the Gilgel Gibe catchment and aimed to determine the level of exposure of water resources to these changes, which is essential for future adaptability planning. To achieve this objective, an ensemble mean of six regional climate models (RCMs) from the coordinated regional climate downscaling experiment (CORDEX)-Africa was used to simulate future climatic scenarios. The RCMs outputs were then bias corrected using distribution mapping to match observed precipitation and temperature. The Soil and Water Assessment Tool (SWAT) model was used to assess the hydrological impacts of climate change on the catchment. The results indicated that the ensemble mean of the six RCMs projects a decline in precipitation and an increase in temperature under both the RCP4.5 and RCP8.5 representative concentration pathways. Moreover, the increases in both maximum and minimum temperatures are higher for higher emission scenarios, indicating that RCP8.5 is warmer than RCP4.5. The projected climate change shows a decrease in surface runoff, groundwater, and water yield, resulting in an overall decline of annual flow. This decline is mainly due to the reduction in seasonal flows driven by climate change scenarios. The changes in precipitation range from -11.2% to -14.3% under RCP4.5 and from -9.2% to -10.0% under RCP8.5, while the changes in temperature range from 1.7°C to 2.5°C under RCP4.5 and from 1.8°C to 3.6°C under RCP8.5. These changes could lead to reduced water availability for crop production, which could be a chronic issue for subsistence agriculture. Additionally, the reduction of surface water and groundwater could further exacerbate water stress in the downstream areas, affecting the availability of water resources in the catchment. Furthermore, the increasing demands for water, driven by population growth and socioeconomic progress, along with the variability in temperature and evaporation demands, will amplify prolonged water scarcity. Therefore, robust climate-resilient water management policies are indispensable to manage these risks. In conclusion, this study highlights the importance of considering the impact of climate change on hydrological processes and the need for proactive adaptation measures to mitigate the impacts of climate change on water resources.

The current ecological and ichthyotoxicological state of the shlis-selburg bay lake Ladoga

The article presents the materials of biological and chemical-analytical studies of the Shlisselburg Bay of Ladoga lake, that plays an important fishery and sanitary-hygienic role as a source of water supply of St. Petersburg. The dominant role of ichthyo-fauna in the assay of the ecological and toxicological state of the studied water area is shown. The purpose of the conducted research is to assess the ecological and ichthyo - toxicological state of the Shlisselburg Bay of Ladoga lake, as one of the main fishery water areal and the only source of water supply of St. Petersburg (the source of the Neva River). Biological and chemical analytical studies of the water area of the Shlisselburg Bay in laboratory conditions were carried out in the summer-autumn period in 2022 in three water areas. A feature of the Shlisselburg Bay is the presence of a runoff flow, that initiates the removal of pollutants and the nature of bottom sediments, which makes the Bay less vulnerable to anthropogenic impact. Currently, the methods used to assess water quality for the fisheries perspective are biological – bioindication and biotesting, as well as the results of chemical analysis in comparison with the standards for the content of harmful substances in water, sediments, precipitation and fish. Preference is given to “express’ methods: biotesting and bioindication of fish research results. Analysis of materials from previous studies have given reason to consider a gradual decrease in anthropogenic load (exposure to pollutants) on fish, as generally recognized indicators of water quality, given from fisheries positions. The results of the research showed that the ecological and toxicological condition of the Shlisselburg Bay has now improved, but cannot be considered satisfactory. Taking into acount the state of the ichthyo fauna and the level of its pollution, it can be characterized as weakly expressed sublethal with a possible transition to medium-expressed, conditionally sublethal in the spring period.

Flow patterns and pathways of legacy and contemporary pesticides in surface waters in tropical volcanic catchments

Severe water pollution issues due to legacy and contemporary pesticides exist in tropical regions and are linked to cash crops requiring intensive plant protection practices. This study aims to improve knowledge about contamination routes and patterns in tropical volcanic settings to identify mitigation measures and analyse risk. To this aim, this paper analyses four years of monitoring data from 2016 to 2019 of flow discharge and weekly pesticide concentrations in the rivers of two catchments grown predominantly with banana and sugar cane in the French West Indies. The banned insecticide chlordecone, applied in banana fields from 1972 to 1993, was still the major source of river contamination, while the currently used herbicide glyphosate, its metabolite aminomethylphosphonic acid (AMPA), and postharvest fungicides also exhibited high contamination levels. A value of 0.5 of the Gustafson Ubiquity Score (GUS) was shown to separate contaminant and noncontaminant pesticides, indicating a high vulnerability to pollution by pesticides in this tropical volcanic context. The patterns and routes of river exposure to pesticides differed markedly between the pesticides in accordance with the hydrological behaviour of volcanic islands and the history and nature of pesticide uses. Concerning chlordecone and its metabolites, observations confirmed previous findings of a main subsurface origin of river contamination by this compound but also showed large erratic short-term variations, suggesting the influence of fast surface transport processes such as erosion for legacy pesticides with large sorption capacity. Concerning herbicides and postharvest fungicides, observations have suggested that surface runoff and fast lateral flow in the vadose zone control river contamination. Accordingly, mitigation options need to be considered differently for each type of pesticide. Finally, this study points out the need for developing specific exposure scenarios for tropical agricultural contexts in the European regulation procedures for pesticide risk assessment.

Using Dye and Bromide Tracers to Identify Preferential Water Flow in Agricultural Hillslope Soil under Controlled Conditions

Processes in hillslope soils present a particular challenge for agricultural production and soil management due to their hydropedological specifics and high soil erosion risk. Soil heterogeneities can cause preferential and/or lateral flow on the entire hillslope resulting in the off-site movement of water, fertilizers and chemicals used in crop production. A study was conducted under controlled conditions in a laboratory with undisturbed soil cores (250 cm3), which were used to estimate the soil hydraulic properties (SHP) using HYPROP and WP4C devices, while undisturbed soil columns (diameter = 16 cm, length = 25 cm) were used for the evaluation of preferential flow pathways using potassium bromide and Brilliant Blue. Samples were excavated in triplicate from the hilltop, backslope and footslope regions within the inter-rows of a vineyard from a critical zone observatory, SUPREHILL, in Croatia in Dystric Luvic Stagnosol. The aim of this study was to determine if the erosion-affected hillslope position affected the physical, chemical and hydraulic properties of soil and to identify water flow and possible preferential flow using dye and bromide tracers. The results of the sensor measurements and estimated SHPs were in agreement, showing a faster leaching of the irrigated rainwater in the footslope column. The tracer experiments showed variability even in the columns taken from the same position on the hillslope, which can be linked to plant roots and soil fauna activity. Altogether, the results showed a deeper loose layer at the footslope as a consequence of the soil erosion, which then resulted in higher hydraulic conductivity and the leached mass of the bromide due to better soil structure and pore connectivity. Thus, due to significant differences in the leached mass of bromide, this research should be later expanded in field experiments to reveal the impact of surface runoff, subsurface preferential and lateral flow on a larger scale.

Study of groundwater recharge using combined unsaturated‐and saturated‐zone chloride mass balance methods

AbstractUnderstanding groundwater recharge mechanisms is essential for reliable groundwater recharge estimation for sustainable groundwater resource assessment and management, especially in arid and semiarid areas. In this study, chloride, together with stable isotopes (18O and 2H), in 1‐year rainfall, soil water from representative profiles, and groundwater samples, collected in the Ordos Plateau, northern China were analysed. Groundwater recharge was estimated using unsaturated‐ and saturated‐zone chloride mass balance (CMB). An equation that describes the relationship between chloride concentrations in saturated zone water (Csz) and soil water residence time (τ) was derived. With the help of the relationship, chloride concentrations in unsaturated zone water (Cuz) and in groundwater (Csz) can be used to uncover water flow and chloride transport in the unsaturated zone. The relationship between Csz and Cuz indicates that, the groundwater was recharged mainly by intense rainfall events. Small rainfall events did not lead to groundwater recharge but contributed to the flux of chloride to soil surface. Stable isotopic compositions of 18O and 2H provided corroborative evidence of the recharge processes. The relationship between Csz and τ indicates further that there is no source of chloride in the groundwater other than that from precipitation. Thus, Csz can give more reliable recharge estimates. Cuz was influenced by heavy rainfall‐induced runoff, run‐on and bypass flow events and cannot give reliable recharge estimates. However, if used jointly with Csz, Cuz can help to gain insights into recharge processes and yield groundwater recharge estimates with higher certainty. The outcomes of this study can assist for groundwater recharge investigation and assessment in regions where the assumptions and boundary conditions necessary for the correct application of the CMB method may not be met.

Environmental Flow Assessment (EFA) of Tawi River Discharge at the Jammu Location Using the Global Environmental Flow Calculator (GEFC)

The water, food, and energy demands are the basic requirements of society. These demands are increasing daily due to an increase in population or lifestyle changes. To fulfill these ever-increasing demands, several water resource projects have come up which require the storage or diversion of river water. These interventions have caused widespread degradation of aquatic ecosystems. Due to the degradation of the aquatic ecosystem, several programs all around the globe began. In this series, Brisbane Declaration (2007) provided a more holistic definition of Environmental Flows (EFs) as the quantity, timing, duration, frequency, and quality of flows required to sustain freshwater, estuarine and near-shore ecosystems and the human livelihoods and well-being that depend on them. The present study was envisaged to assess for environmental flows of the Tawi river with a major objective of assessing the environmental flows of the Tawi river using the Global Environmental Flow Calculator developed by IWMI. The method provides E-Flows for different Environmental Management Classes. For the western Himalayan region, the river stretches in Environmental Management Class ‘B’ and ‘C’. The assessment provides E-Flows in two ways: (i) the percentage of Mean Annual Runoff and (ii) average monthly environmental flows. E-Flows were estimated as 42.34% to 56.96% of Mean Annual Runoff and varied from 5.73 cumecs during November to 68.23 during August.

Hydrologic Modeling System HEC-HMS Application for Direct Runoff Determination

The process of identifying the peak discharge using the rational method was introduced in the 1880s. This method is a simple procedure for determining the peak discharge derived from surface runoff flow. Therefore, this research modified a simple hydrological formulation (rational method) based on fieldwork and compared a numerical rainfall model to the relationship model by using the simulation parameters, namely rainfall, infiltration, land use, and stream for hydrological conditions. The novelty of this research is a modification of the theoretical formula (rational method) through the use of fieldwork factors to modify the run-off coefficient. The first scene-up was overlay mapping between land and land use shape files, while the scene-up sampling point was upstream and downstream. This was continued with the estimation curve number until a specific composite curve number was initiated. The rate of infiltration was determined using the Horton method to distinguish the soil type, while the Water Stage Data Logger Starter Kit 13" HOBO KIT-S-U20-04 was used to measure the water level, HEC HMS, and rating curve analysis. The relationships between the fieldwork data using hydrology analysis and modeling were then compared. The results showed that the maximum rainfall calculated and analyzed from the box-and-whisker plot was 140 mm in the year 2019. In addition, the infiltration rate at the upstream and downstream areas was 90 mm/hour and 26.4 mm/hour, or 30% out of the upstream area value. Finally, the estimations of the runoff coefficient were 0.60, 0.45, and 0.0133, while the discharges for the maximum rainfall intensity were observed at 405.7 m3/s, 304.3 m3/s, and 25 m3/s. The simulation using Hydrological Modelling HEC HMS 4.11 computed results of 0.1 m3/s and observed flow of 0.3 m3/s. Doi: 10.28991/HEF-2023-04-02-02 Full Text: PDF

Effects of Climate Change on Surface Runoff and Soil Moisture in the Source Region of the Yellow River

The impact of climate change on surface runoff and soil moisture in the source region of the Yellow River is analyzed, which will provide a scientific basis for the rational use and protection of water resources in the source area. In this paper, the SWAT hydrological model was coupled with the Coupled Model Intercomparison Project (CMIP) to predict future changes in surface runoff and soil moisture in the source region of the Yellow River. The prediction of surface runoff and soil moisture in the Yellow River Basin was analyzed by a linear regression model. The SWAT model rate had a calibration period R2 of 0.876 and a validation period R2 of 0.972. The trend of surface runoff and annual mean temperature in the source region of the Yellow River from 2011 to 2022 showed an overall increasing trend, and soil moisture showed a general decreasing trend. 2011–2022 trends between surface runoff and annual mean temperature in the source region of the Yellow River showed a highly significant difference, indicating that surface runoff flow was significantly influenced by temperature. The difference between the trends in soil moisture and the annual mean temperature was highly significant. The surface runoff fluctuated greatly in different years, and the surface runoff changed greatly in different scenarios of CMIP5 (RCP2.6, RCP4.5, and RCP8.5). For all three climate change scenarios, the surface runoff displayed a downward trend. The surface runoff showed a similar uneven distribution for all scenarios on a yearly cycle. Under the three climate scenarios, the runoff was highest between May and August, with a slowly increasing trend from January to April and a slightly decreasing trend from September to December. The interannual and interannual distribution of soil water was basically consistent with the distribution of surface runoff, and there was an overall trend in the length of all soil water reduction scenarios. Surface runoff and soil moisture are and will be greatly affected by climate change (mainly temperature and precipitation). Under the three climate scenarios, the precipitation increases to some extent, but the surface runoff and soil moisture will both decrease, which may be attributed to the greater evaporation than the precipitation.

Integrated SUSTAIN-SWMM-MCDM Approach for Optimal Selection of LID Practices in Urban Stormwater Systems

Rapid urbanization has increased impervious areas, leading to a higher flood hazard across cities worldwide. Low Impact Development (LID) practices have shown efficacy in reducing urban runoff; nevertheless, choosing the best combinations in terms of implementation cost and performance is of great importance. The present study introduces a framework based on green infrastructure, multi-objective optimization, and decision support tools to determine the most cost-effective LID solutions. The Storm Water Management Model (SWMM) was employed for rainfall-runoff and hydraulic modeling in Region 1, District 11 of Tehran, Iran. Six scenarios of different combinations of LID practices were developed. The system for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) was used to optimize and evaluate each scenario. The selected solutions were imported to the SWMM to evaluate the stormwater system performance. Then, two multi criteria decision making (MCDM) models, including TOPSIS and COPRAS, were employed to rank the scenarios based on four technical and economic criteria. Results showed that scenario 4, consisting of rain barrels, porous pavements, and vegetated swales, had the best performance under TOPSIS with a 7.68 million USD and reduced the runoff volume and peak flow by 20.77% and 19.2%, respectively. However, Under the COPRAS method, Scenario 2 with a combination of rain barrels, bio-retention cells, and vegetated swales showed higher performance than the other scenarios with 3.25 million USD and led to a 15% reduction in the runoff volume and 4.30% in the peak flow. The COPRAS method was more sensitive to cost weights and chose the most economical scenario as the ideal. However, Scenario 4 concluded to be more feasible due to spatial limitations in the study area. The proposed SWMM—SUSTAIN—MCDM framework could be helpful to decision-makers in the design, performance evaluation, cost estimation, and selection of optimal scenarios.

Prediction of climate change impacts on availability of surface water resources in the semi-arid Tugwi Mukosi catchment of Zimbabwe

Climate change impact drivers includes increased rainfall variability, increased extreme events, and changes in the mean behaviour of hydro-meteorological variables such as air temperature, rainfall, and runoff. As such, this study assessed the potential impacts of climate change on surface water resources in a semi-arid Tugwi Mukosi catchment of Zimbabwe. The Mann-Kendall trend analysis, climate change downscaling and streamflow modelling were used as the primary methodology. The analysis of historical hydro-climatic data trends were performed using the Mann-Kendall trend test and Sen's slope method. Equally, observed daily rainfall was extended using bias-corrected CHIRPS satellite rainfall. Thus, a total of 9 Global Climate Models including (CCCma-CanESM2, Miroc Miroc 5, MOHCHadGEM2, MPI-M-MPI-ESM-LR, and NCCNorESM1-M) on the Sveriges Meteorologiska och Hydrologiska Institut (SMHI) Rosby Centre Atmosphere model version 4 (RCA4) RCM under the Representative Concentrated Pathways 4.5 and 8.5 were extracted and analysed for the 2030s (2021–2050) and 2060s (2051–2080) period. The results show significant (p<0.05) decreasing rainfall trends at the analysed stations, as well as significant decrease in rainfall for the 2030s and the 2060s under GCMs CCCma-CanESM 2 model. The Hydrologic Engineering Centre-Hydrological modeling System (HECHMS) (1997–1999) was calibrated and validated for the period 1981–2016. Calibration results on gauged catchment runoff and peak flows are satisfactory (Ngezi observed peak discharge and simulated peak discharge at 42.4 m3/s and 34.8 m3/s respectively, NSE 62.8%, Upper Muzhwi 30 m3/s and 19.5 m3/s, NSE 53.55%, Musogwezi 18.7 m3/,s and 16.5 m3/s, NSE 58.4%). The GCM-CanESM RCP 4.5 model showed a decrease in the runoff predicted of above 17% in both the 2030s and a significant decrease in the 2060s of 28.41% and 5% respectively. The combination of climate downscaling and water resources modelling is paramount to the management of water resources in a semi-arid area. Hydrological modelling and climate downscaling techniques gives important insights for water resources planning and development to support the water sector adaptation to climate change. The methodology applies to other data-scarce and semi-arid areas whose climate change impacts require further investigation.

Assessing Potential Effects of Nature-Based Solutions (NBS) on Water Ecosystem Service in the Interurban Micro-Watershed Río Torres, Costa Rica

The implementation of green infrastructure (GI) as Nature-Based Solutions (NBS) generates positive effects on the water ecosystem service in an urban context. Practices such as bioretention cells, green roofs, rain gardens, permeable pavements, and infiltration trenches contribute to treating large volumes of runoff and providing safe spaces for populations living in highly urbanized areas. With the aim to simulate these effects, a hydrological modeling was carried out using the i-Tree Hydro Plus model, which quantified the runoff generated from precipitation events and effective transformations (NBS) to cope with runoff. Eight scenarios were developed: a baseline scenario, five future scenarios with green infrastructure, a scenario with increased tree coverage, and a scenario with increased urbanization. Our hypothesis is that NBS would reduce runoff and increase permeable flow. The analysis of the feasibility of implementing the modeled green infrastructures was carried out through consultation with local stakeholders in the micro-watershed. We found that bioretention cells decrease runoff by 5%, green roofs by 4%, rain gardens by 4%, permeable pavements by 4.5%, and infiltration trenches by 7.5% compared to the baseline scenario where runoff accounts for 32% of water balance flows. The scenario of increased tree coverage had a similar behavior to the baseline scenario, indicating that efforts in this alternative would generate a limited impact on the reduction of runoff. With increased urbanization, impermeable flow increases up to 78%, which would generate floods. Implementing NBS would be feasible since this type of initiative is included in the agenda of many regulatory instruments of urban planning in Costa Rica.

A contemporary approach on water sensitive urban design for sustainable urban development

There are a number of irreversible environmental impacts associated with urbanization, such as soil degradation, a reduction in biodiversity, and temperature rises. Run-off flows are rising as a result, and sanitary networks are having issues, which leads to spills and floods. They are a collection of water management methods and infrastructural elements, as opposed to the traditional practise of letting water drain into rivers. By planning our streets and public areas, we can improve both the environment and the quality of life in our communities. Sustainable Urban Drainage Systems (SUDS) have frequently been put into place with the primary goal of mitigating drainage issues brought on by poor landscaping. For better integrating water cycles, urban planning, and landscaping in urban areas, a set of criteria for WSUD (Water Sensitive Urban Design) is recommended.

A novel Eulerian SPH shallow water model for 2D overland flow simulations

A 2D Eulerian meshless shallow water model based on smoothed particle hydrodynamics (SPH) is proposed to study overland flow. Rain on a dry bed to generate a runoff flow is one common hydraulic phenomenon. However, it is difficult for existing Lagrangian SPH shallow water models to present the flow because no computational particle exists on a dry bed. To overcome this difficulty, the Eulerian form of the 2D shallow water equations is used to describe flow behavior in the proposed model. An HLLC approximate Riemann solver is applied to calculate fluxes between two neighboring particles to smear out the instabilities caused by the discretization of the nonlinear convective term and the discontinuity of wet-dry beds. Additionally, we use a surface reconstruction method (SRM) to ensure that the proposed model has well-balanced and positivity-preserving properties. Bed friction and infiltration effects are also analytically considered. Eight case studies involving various overland flows with wet-dry transitions, rainfall, infiltration, bed friction and complex topography are adopted to test the proposed model capacity. The first-order convergence rate is obtained in the convergence analysis. Against the exact and measured results, in the analytical case studies, the relative root-mean-square errors of depth and velocity are approximately 0.02% to 0.3% and 1.3% to 1.7%, respectively. In the experimental case studies, the relative root-mean-square errors of depth and discharge (velocity) are approximately 3.8% and 1.2% to 6.1%, respectively. The good agreement demonstrates between the results shows the reliability of the proposed 2D Eulerian SPH shallow water model for real-world overland flows.

Long-term effects of land-use change on water resources in urbanizing watersheds

The changes in energy balance resulting from land-use change may significantly affect the amount and timing of water loss to the atmosphere as evapotranspiration (ET). Also, these will impact water fluxes in the watershed system, influencing runoff rate, flow volume, intensity, and frequency of floods. During the past century, land-use change in the SuAsCo (Sudbury-Assabet and Concord) watershed has altered basin hydrology, sediment, and nutrient load that is detrimental to water resources in SuAsCo. This study uses an integrated physically-based model Hydrological Simulation Program-FORTRAN (HSPF), along with Land Transformation Model (LTM), to assess predicted temporal and spatial changes in water, nutrient, and sediment yields for future land-use scenarios of 2035, 2065, and 2100. Results showed that a 75% increase in effective impervious area and a 50% decrease in forest area in 2100 (from 2005 baseline levels) are projected to cause a 3% increase in annual streamflow and a 69% increase in total yearly mean surface runoff. The average annual total suspended solid (TSS) yield at the watershed outlet is estimated to increase by 54% in 2100. An increase of 12% and 13% concentrations of average annual total phosphorus (TP) and total nitrogen (TN) are predicted by 2100 due to urban expansion and increased runoff volume. This integrated modeling approach will inform watershed managers and landowners about critical areas of the SuAsCo watershed to apply best management practices (BMPs) to mitigate the effects of land-use land cover (LULC) change.