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Debris flow is one of the most common types of geological disasters in China. Owing to the influence of topography, geomorphology, geological conditions, human activity, and rainfall debris flow disasters frequently occur in the mountainous areas of Beijing. The research on debris flow in the Beijing area focuses on rainfall and risk evaluation, material sources, and early warning and prevention of debris flow. However, there are few studies on the development characteristics of single-gully debris flow and the prediction of hazardous areas in the Beijing area. Therefore, we chose the debris flow of Bangou Village in Yanqing District of Beijing as the research object. We analyzed the recharge conditions in the ditch domain and predicted the extent of the hazardous area around the gully, providing suggestions for control measures. The dynamic reserves of the loose deposits in the debris flow gully, currently in the development stage, were estimated as 15.48 × 104 m3, representing four supply sources: artificial deposits, alluvium and diluvium, residual slope deposits, and collapse. The peak flow is 24.49 m3/s for a 10-year rainfall event, 27.64 m3/s for a 20-year rainfall event, 31.79 m3/s for a 50-year rainfall event, and 34.93 m3/s for a 100-year rainfall event. The total amounts of solids washed out by a debris flow from the preceding events are 0.70 × 104 m3, 0.79 × 104 m3, 0.91 × 104 m3, and 1.00 × 104 m3, respectively. The size of the debris flow is small, with a maximum hazardous area of 0.2810 km2. We conclude that a small debris flow outbreak in the Bangou Village gully is possible. We expect that the results of this study will provide basic information and help improve debris flow research in Beijing.

Hydrological modeling can be challenging due to significant data requirements and computational complexities. Hydrological models must be sufficiently complex to describe physical processes yet simple enough to use. This paper describes the development of a simplified watershed-scale input–output model to simulate runoff quantity and quality during a storm event. This work builds upon an existing semi-distributed rainfall–runoff model by adding calculations for pollutant concentrations based on simplified mass balance equations. The model was tested against various watershed examples of increasing complexity. The results show the change in peak flow and pollutant concentration in different areas of the watershed, demonstrating the model's ability to account for the dynamics of runoff movement through the watershed. This paper advances watershed management by addressing data scarcity through the development of a simplified hydrological model that effectively incorporates spatial variability within a watershed while requiring minimal data input. [ABSTRACT FROM AUTHOR]

The floods of the Lahdar River cause repeated inundations and damage to road infrastructures, particularly crossing structures in the territorial center of Had Msila. Our study involved the application of various methods to estimate flood flows for different return periods along the Lahdar River. The selected flows were chosen after a comparative analysis of values calculated by the different methods used. These results served as the basis for hydraulic modeling aimed at assessing water levels to establish risk zone mapping. This step is crucial in flood risk assessment. Two main approaches were distinguished: hydrometeorological methods, based on regional parameters derived from rainfall data, and empirical methods, used in the absence or with limited data on flood flows in a given region. Hydraulic modeling was carried out using two software programs: a Geographic Information System (GIS) such as Arc-GIS, and a specific river modeling software like Hec-Ras, allowing for the numerical representation of the natural state of the territory. The results obtained serve as the foundation for all river hydraulic modeling, thereby facilitating flood prediction and hydrological risk management in floodplains. Modeling Lahdar River floods in the studied sections enables the prediction of flood risk and its impacts on constructions and infrastructure in the Had Msila Center. [ABSTRACT FROM AUTHOR]

Suite aux inondations catastrophiques les 2 et 3 octobre 2020 dans le département des Alpes-Maritimes, le Cerema a été chargé de coordonner une expertise hydrologique sur les bassins versants du Var et de la Roya. Elle a été réalisée dans le cadre d’un retour d’expérience (RETEX) technique piloté par la Direction Départementale des Territoires et de la Mer (DDTM 06) pour le compte du Préfet des Alpes-Maritimes. Les principaux résultats, qui ont fait l’objet d’un consensus avec les partenaires, permettent de caractériser l’évènement ALEX pour les vallées de l’Estéron, de la Tinée, de la Vésubie, du Var et de la Roya. Le travail de consensus s’est appuyé sur une comparaison graphique de diverses approches d’estimations provenant des différents organismes impliqués. L’objectif était de faciliter la visualisation des convergences et divergences des multiples estimations de débits de pointe pour aboutir à un consensus. Le résultat final permet la fourniture de graphiques de débit de pointe par vallée avec des estimations basses et hautes. Cela permet un partage commun d’information associé à des incertitudes des débits sur ce type de retour d’expérience, en particulier dans un contexte torrentiel.

BACKGROUND AND OBJECTIVES: Peak flow in watershed is important in designing and controlling soil erosion, as well as assessing the potential water yield. It also serves as a basis for assessing and managing the risk of environmental damage. However, there is no accurate information on peak flow to ensure sustainable management and conservation of Wuno Sub-Watershed in Palu Watershed which serves as a buffer for the capital of Central Sulawesi Province. Therefore, this study aimed to assess and determine the potential runoff and peak flows in watershed using soil conservation service-curve number.METHODS: Soil conservation service-curve number method was calculated to analyze rainfall from runoff as a function of cumulative rainfall, land use, soil type, and humidity. This method was developed by the United States Soil Conservation Service in 1972 and applied in this study with due consideration for several variables, including (a) land use classification and intensity for settlements, rice fields, plantations, rivers, etc., (b) basic physical conditions of the area such as rainfall and hydrology, as well as (c) classes of soil hydrology significantly influencing carbon-nitrogen value.FINDINGS: The result showed that carbón-nitrogen values for all types of land use or cover were in normal conditions from 5 to 25 years. Moreover, carbón-nitrogen range was observed to have significantly large quantitative consequences on direct runoff. The trend showed the need for precision and effectiveness in planning watershed management and conservation. Soil conservation service also had a positive influence on land use, specifically runoff, as observed in carbón-nitrogen values for return periods of 2, 5, 25, and 100 years. However, several other factors were identified to influence land use such as land cover and soil texture.CONCLUSION: Soil Conservation Service presented an analysis of how land use affected runoff, specifically with a focus on carbon-nitrogen values. Land use was not only affected by carbon-nitrogen values but other factors such as land cover and geomorphometric properties. The trend showed the need for a more comprehensive exploration of soil conservation service-curve number method in accurately predicting runoff patterns in sub-watershed areas to ensure effective and sustainable management and conservation practices.

Studies focusing on the degradation of arable land are particularly numerous, given the scale of the threat posed to soil worldwide, particularly in the context of global climate change and socio-economic transformations. This fact has motivated the scientific community to visualize various research projects aimed at improving the application of empirical models to provide new answers to the problem of water erosion. The use of adjustment parameters was of crucial importance in adapting the model terms to local conditions in the study area. To develop a detailed understanding of the performance of empirical models in quantifying soil losses, a test was carried out on the scale of the Wadi Chaâf basin in the Assir region using two empirical models. The choice was made to adopt the Modified Universal Soil Loss Equation (MUSLE), because it uses peak flow as an input parameter. This is in recognition of the fact that the study area has all too often been subject to the concentration of run-off water due to steep slopes and the capricious rainfall. For its part, the EPM formula is applied owing to its formula design, which allows for the consideration of thermal contrasts linked to altitude and the different exposure of the slopes. The specific losses recorded ranged between 38 t ha-1 year-1 and 24 t ha-1 year-1 respectively for the MUSLE and EPM models, with some areas exceeding the tolerance threshold. [ABSTRACT FROM AUTHOR]

Objectives A growing body of research shows that early-life exposure to war has adverse effects on later-life health. Research has emphasized the importance of exposure timing implicating domain-specific developmental processes and associated critical/sensitive periods. This study looks at the impacts of early childhood war exposure and the repercussions for later-life physical and functional health, with a focus on time of exposure as a source of variability. Methods We use residential histories from the Survey of Health Ageing, and Retirement in Europe linked to external data on the location and timing of hostilities to examine the impact of early-life exposure to World War II on later-life physical and functional health. Results Exposure to war increases the risk of objective (grip strength, chair rise, and peak expiratory flow) and self-reported (mobility limitations and activities of daily living) measures of functional health. Effects are especially pronounced for those born during the war and for those with more prolonged exposures. There is little evidence that the impact of war is mediated by war-related hardships, socioeconomic conditions, health behaviors, or adult chronic disease. Discussion Our results suggest early-life exposure to war has a lasting impact on physical functional health. Exposure appears to largely operate via direct effects, indicative of altered initial development of physical capacity in early life. Because exposure was so pervasive among some cohorts of older individuals, understanding the health of present older European populations requires wrestling with the residual consequences of wartime exposure at the start of their lives. [ABSTRACT FROM AUTHOR]

The integration of green‐gray infrastructures with advanced control approaches is revolutionizing the stormwater system retrofitting, emerging as an innovative strategy to mitigate urban flood risks. However, a major challenge lies in balancing the substantial investments of these infrastructure projects with their environmental benefits, such as reduced flooding volume and lower peak flow. Model predictive control (MPC), a dynamic and intelligent control approach, optimizes these environmental benefits but is underutilized in the system design phase for cost‐effectiveness analysis. This study introduces a multi‐scenario model framework that incorporates MPC and other control approaches into stormwater system designs, including the implementation of controlled storage tanks and green infrastructures. This framework provides comprehensive modeling tools for practitioners to evaluate the flood control benefits and costs across various infrastructure designs and control scenarios, ultimately identifying solutions that are both environmentally and economically viable. A case study conducted in a small urban catchment area in Shenzhen City, China, demonstrates the effectiveness of this framework. The results indicate that MPC outperforms other control scenarios, particularly under heavy or extreme rainfall conditions. Notably, MPC not only provides superior environmental benefits but also yields considerable cost savings, ranging from 1,787 to 9,371 USD per hectare compared to static control, equating to a 5% reduction in cost relative to rule‐based control. Such findings suggest that integrating MPC is a cost‐effective alternative to extensive infrastructure expansion for flood management, which significantly enhances the benefit contribution of controlled infrastructures without substantial additional expenses. Plain Language Summary: Implementing advanced control methods for green‐gray infrastructures is a new method to reduce urban flooding. However, constructing and updating these infrastructures can be very expensive, which is a significant challenge for many urban areas. Our research explores how to use a smart control approach, specifically the model predictive control (MPC), to enhance environmental benefits and save money in the system design phase. We present a multi‐scenario model framework that combines MPC and other methods into the design of stormwater systems, which include controlled storage tanks and green infrastructures. This framework can be used to evaluate the flood control benefits and costs across various infrastructure designs and control scenarios, and to identify the solutions that are both environmentally and economically viable. We conducted a case study in Shenzhen City, China, to test our framework. The results show that MPC is effective particularly during heavy or extreme rainfalls, offering higher environmental benefits and cost savings compared to the scenarios without MPC. Integrating MPC is more cost‐effective than expanding infrastructures for flood management as it notably increases the benefit contribution of controlled infrastructures at a modest cost. Key Points: A framework is proposed to assess the environmental and economic impacts of integrating model predictive control (MPC) with stormwater infrastructure designsAssessments are conducted in a small urban catchment involving heavy rainfall eventsThe MPC yields higher environmental benefits and saves economic costs compared to other control approaches [ABSTRACT FROM AUTHOR]

South Fork Quantico Creek (SFQ; 19.8 square kilometre (km2), forested) and Fourmile Run (4MR; 32.4‐km2, urban) are small watersheds in northern Virginia, United States. Precipitation and streamflow data for both watersheds were examined from water year (WY) 1952 through 2022. Temporal changes in hydrologic metrics were identified by calculating trends in annual precipitation, annual peak flow, mean daily flow, minimum daily flow, stream flashiness, and the runoff ratio. The impact of climate and urbanization on watershed hydrology was assessed by computing trends on both raw and precipitation‐adjusted data. Despite increasing precipitation in both watersheds, increasing monotonic trends in most hydrologic metrics were observed only in 4MR. At 4MR, the long‐term trend in annual peak flow was non‐linear, thus trends were calculated on separate periods. Annual peak flow increased from WY 1952 through 1968, coinciding with a period of rapid urbanization. During WY 1969 through 1981, annual peak flows decreased, coinciding with construction of a flood channelization project. Trends for both periods were robust to precipitation adjustment. From WY 1982 through 2022, no change in the precipitation‐adjusted annual peak flows occurred, suggesting annual peak flows increased due to climate factors during this period. Comparison of area‐normalized hydrologic metrics between the two watersheds revealed higher flows in 4MR than SFQ across all flows, not just high flows. Runoff ratio and stream flashiness also were higher in 4MR. Differences in hydrologic metrics between the two watersheds were driven primarily by differences in land use, land cover, and modifications to the water balance related to urbanization. Climate change has altered watershed hydrology at both sites, but extensive urbanization in 4MR has altered the hydrology more than that of SFQ. We conclude that urban watersheds are likely at greater risk of increased flooding than less developed areas as the climate intensifies. [ABSTRACT FROM AUTHOR]

Downstream impacts of large hydropower dams are often neglected or underestimated, especially for areas situated at long distances from a dam. Naturalization of the flow hydrograph is an important step in assessing hydro‐ecological and socio‐economic impacts of regulation. Using reservoir inflows, a recently developed, lagged‐flow naturalization method is applied to the lower portion of the regulated Peace River, which forms the northern boundary of the Peace‐Athabasca Delta (PAD). The PAD is a Ramsar wetland of international importance that depends on overland flooding for recharge of its high‐elevation or "perched" basins. Such flooding can be caused by ice jams during the spring breakup of the ice cover or by exceptionally high runoff during open‐water flow conditions. Herein, the focus is on the latter type of event and the resulting recharge of basins located within the Peace sector of the PAD. For the period 1972–2017, regulation has reduced open‐water flow peaks by ~4100 m3/s on average, while limiting the possibility of overbank flooding from the Peace River during the summer. Consistent with earlier findings on spring breakup flows, naturalized open‐water peaks do not exhibit a temporal trend. Recharge of non‐perched basins can also occur with moderately high flows that cause no overland flooding but generate flow reversals in Peace River tributaries. In turn, this mechanism can deliver river water to various basins either directly or via connecting channels. Our results show that flow‐based variables that index the hydrological sustenance of non‐perched basins have been significantly reduced by regulation. [ABSTRACT FROM AUTHOR]

Introduction:A better understanding of the cerebrospinal fluid (CSF) flow dynamics of Chiari 1 malformation (CM-1) may help to reach more specific parameters for indicating therapy and response to therapy. This study developed a parameter to better characterize CSF flow alterations in the cerebral aqueduct in patients presenting with CM-1.Methods:We retrospectively scanned archives for CM-1 patients who underwent CSF flow analysis between January 2016 and December 2022. Eighty-eight CM-1 patients and 83 control cases were included in the study. The cerebellar tonsillar descensus was measured in all patients. In 11 cases with the syrinx cavity, the largest transverse diameter of the cavity was measured. Phase-contrast magnetic resonance imaging was performed using a 1.5 T scanner. Peak velocity (P-Vel) (cm/s), average velocity (A-Vel) (cm/s), forward flow volume (μL), reverse flow volume (μL), peak flow (P-Fl) (mL/s), and time to peak velocity (TP-Vel) (s) and cerebral aqueduct’s stroke volume (μL) were calculated. Sixteen CM-1 patients underwent decompression surgery, and we examined postoperative CSF flow analyses.Results:A-Vel and P-F1 were statistically significantly higher in CM-1 cases than in controls (p=0.006, p=0.037). There was a significant negative correlation between the diameter of the syrinx cavity and P-Vel and P-Fl, and a positive correlation between TP-Vel. We found no significant difference between the postoperative and preoperative CSF flow parameters of the CM-1 patients.Conclusion:P-Fl differs between the patient and control groups and correlates with the syrinx diameter; therefore, it could be a useful parameter in CSF flow analysis in CM-1 cases. However, higher case numbers can achieve more effective results.

Study region: The Xiying and Heihe River basins, cold and arid mountainous regions of northwestern China. Study focus: In data-limited areas of Northwestern China, satellite- and reanalysis-based precipitation products provide crucial assistance. However, a comprehensive evaluation of their advantages, limitations, and hydrological performance has yet to be ascertained. This knowledge gap impedes a deeper understanding of hydrological processes within the region. This study evaluates the accuracy of ERA5L, IMERG-F, GSMaP-G, and FY4A-QPE from three aspects: time, space, and extreme precipitation. Comprehensive validation was conducted on four products using discharge, flood events, and peak flood simulated by Geomorphology-Ecology-Hydrology Model. New hydrological insights for the region: ERA5L data can be used to build long-term studies on regional meteorological and hydrological trends. IMERG-F is valuable for analyzing extreme precipitation and hydrological events. GSMaP-G is well-suited for identifying precipitation events in the region. It is essential to be cautious of precipitation underestimation when using satellite precipitation products at high elevations and during the winter.This study highlights the differences in accuracy among various precipitation products and provides recommendations for policymakers in selecting data for high-altitude research. It also offers critical information on hydrometeorology and directions for producing high-accuracy precipitation products.

Hydrological extremes can be influenced by climatic inputs (e.g., rainfall), but are controlled by topographical and anthropogenic factors. Note that the combined effect of topography and land use/cover on hydrological extremes is not fully explored and requires further research. This study considered five watersheds in the Baro River basin with varying topographic and land use/cover combinations to investigate the integrated impacts of topography and land use/cover on the hydrological extremes. The selected watersheds were classified as forest-dominated (i.e., Uka, Sor, and Gumero watersheds) and agriculturally dominated (i.e., Meti and Keto watersheds), as well as flat-to-gently sloped watersheds (Uka and Gumero) and moderate-to-sloped watersheds (Sor, Meti, and Keto). Google Earth Engine (GEE) was used to analyze the land-use/land-cover change from 1990 to 2018, and the topographical variables were quantified using the GIS tool. Finally, the elasticity approach was used to estimate the sensitivity of low and peak flow to the individual and combined impacts of land use/cover and topography. Generally, the results revealed that both low and peak flows were more sensitive to sloped watersheds with forest land-cover types, with elasticity's of 0–2.6% for low flow and 0–4.6% for peak flow, respectively. [ABSTRACT FROM AUTHOR]

Background: Air pollution, a global concern with an annual emission of 600 million tons of pollutants, poses a significant health threat, particularly in cities like Peshawar. Our objectives were to study the nature and distribution of particulate matter (PMs) in the air of fourteen sites in Peshawar city and assess its association with respiratory symptoms and peak flow. Materials & Methods: This study selected 14 sites in Peshawar for air sampling. Air quality was assessed for PM 1-10, Cadmium, and lead in milligrams/m3 of the air through a device called High volume Air sampling system (PM 10-4200 AFC, HI-Q Environmental Health Services, San Diego, California USA). By systematic random sampling, one hundred and eighteen individuals were questioned on these 14 sites for their demographic details and respiratory symptoms through a structured questionnaire. The researchers measured the peak flow through a portable Mini-Wright peak flow meter. SPSS version 20 conducted the statistical analysis. The chi-square test and Pearson's correlation test were applied. The criterion standard for the p-value was less than 0.05. Results: In a study involving 118 individuals from diverse professions in Peshawar, evaluated air pollutant levels, particularly PM1-10, lead, and Cadmium, exceeded WHO recommendations. The active cough was the predominant symptom in 55% (n=66) of the study sample. In contrast, 54% exhibited lower-than-predicted peak flow values, clinical symptoms like cough, impaired exercise tolerance, and exposure to pets correlated with reduced peak flow. Positive correlations were found between peak flow and age and inverse correlations with symptom duration. Conclusion: Particulate matter in the air of Peshawar city is higher than the upper limits recommended by the WHO. This bad air quality in Peshawar affects its residents through active coughing and low peak flow readings, amongst many other respiratory problems. [ABSTRACT FROM AUTHOR]

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

Digital elevation models (DEMs) are one of the most important data required in watershed modeling with hydrological models and their spatial resolution has a significant impact on the accuracy of simulating hydrological processes. In the present study, the effect of spatial resolution of five DEMs derived from the topographic map (TOPO) with a scale of 1:25000, ALOS PALSAR, ASTER, SRTM, and GTOPO with a spatial accuracy of 10, 12.5, 30, 90, and 1000 m, respectively, on the estimation of parameters of geomorphological and geomorphoclimatic unit hydrographs models has been evaluated in Amameh watershed. Thirty-four single flood events were used during the years 1970 to 2015. The results showed that in the GUH method, the application of the TOPO and ALOS PALSAR DEMs had the best results with root mean square error (RMSE) of 1.7 and 1.8 m3/s and Nash-Sutcliffe Efficiency (NSE) of 0.4 and 0.3, respectively. While the GTOPO DEM had the least efficiency with RMSE of 2.8 m3/s and NSE of -2. Similarly, the lowest and highest RMSE in the GCUH method belonged to TOPO and GTOPO DEMs with RMSE of 3.8 and 18 m3/s and NSE of 0.2 and -6, respectively. Generally, the GUH method had more favorable results than the GCUH method in all DEMs.

A culvert is an important structure in Road construction to allow the conveyance of Channels crossing the road. Culverts are sized for a road to accommodate the volume of water crossing the road network to avoid flooding. Ghana Highways has a standard manual for culvert sizing at channel crossing. This manual serves as a guide for the proper sizing of culverts, however, lots of culverts have been found to have failed. Among the reasons for the failure of culverts could be under-sizing, urbanization, climate change, lack of maintenance, etc. The Daboya-Mankarigu Road is situated in the Savanah Region of Ghana in the North Gonja District. The section of the road from Chainage 9 + 075 to 10 + 200 has been experiencing flooding from 2020 to 2021 with a flood depth of 3.315 m in 2020 and 2.00 m in 2021. This study seeks to use integrated GIS and hydrological-based methods to propose new culverts to supplement the existing culverts to control flooding at section (9 + 075 to 10 + 200) of Daboya-Mankarigu Road (IR10). Geographic Information system (GIS) model (SWAT), Hydrological and hydraulic models were used to determine the peak flow at the catchment to Propose new culverts to supplement the existing culverts. Using a design period of 25 years for culverts, the modified rational method was used to determine the Peak flow of the catchment. A 25-year peak flow of 367.155 m3/s was determined and used for hydraulic analysis of the existing culverts. From the study, the existing culvert structures at the section had a hydraulic capacity of 78.732 m3/s which could not accommodate the remaining flow of 288.423 m3/s in the catchment. An observation was made that the changes in the rainfall can cause a change in rainfall intensity. An increase in built-up areas in the catchment can also increase the runoff coefficient which can result in higher peak flow in the catchment. Climate change, change in slope, and Land use in the catchment were also determined to have a huge influence on the adequacy of culverts since the peak flow is dependent on these parameters in the catchment as the years go by. A 4No. 4 m × 4 m box culvert, 3No. 3.5 m × 3.5 m box culvert, and 13 No. 1200 mm pipe culverts with 2 each at different chainages were proposed at suitable locations to supplement the existing culverts using the HDS-5 equations in AutoCAD Civil 3D. A recommendation is made to consider the installation of these new culverts at the flood section to control flooding and avoid overtopping of water on the IR10 road section (Daboya-Mankarigu) in the north Gonja District.

The North Railway is one of the longest railway lines in the world, extending for 2750 km from the Riyadh region to Al-Jawf Province through many diverse topographies, including valleys where direct runoff is generated that cross the existing hydraulic protection installations on the railtrack. Direct runoff flows in quantities that exceed the capacity of existing drainage installations and cause several types of damage, owing to the nature of the drainage basins and the impact of changing natural factors and human errors. To ensure the safety of the design of hydraulic drainage installations, this indicates the need for hydrological studies of drainage basins, especially those that include important strategic facilities such as railway lines. In this study, the hydrological modeling of four subdrainage basins (No. 6, 7, 13, and 14) within Wadi Malham was applied and evaluated to determine if the drainage installations can accommodate the direct peak runoff flow. According to the results, the peak flows of 8.9 m3/s for basin No. 7 and 18.2 m3/s for basin No. 13 indicate that they are unable to handle the direct peak runoff flow from the designed storm for a return period of 100 years. The other two basins are able to pass through the peak flow. Based on the findings of this study, we recommend adding an opening for culvert C0400 in basin No. 7 and adding two openings for C0244 in basin No. 13 to accommodate the peak flow. [ABSTRACT FROM AUTHOR]

Boreal catchments are composed of different land covers, such as forests, peatlands and lakes, which differ in their runoff response to rainfall events. Understanding the individual and combined responses to rainfall events of these different land cover types is crucial for predicting potential impacts of future climate conditions on boreal water cycling. A common assumption is that peatlands attenuate peak flows, which is used as a motivation to restore drained boreal wetlands. However, it remains unclear how and to what extent peatlands can affect peak flow response. Only a few previous studies have looked at the hydrologic dynamics of peatlands in response to specific rainfall events across a wide range of nested sub‐catchments with varying peatland cover. In this study, we use nine years of hourly hydrometric data from 14 catchments within the Krycklan Catchment Study in northern Sweden to examine how peatlands contribute to flood attenuation at both local and stream network scales. Our analysis at the local scale demonstrated that during large events with low antecedent wetness conditions, peatland‐dominated catchment exhibited more muted responses compared to the similar‐sized forest‐dominated catchment. However, during events with high antecedent wetness conditions, the peatland‐dominated catchment exhibited flood magnitudes similar to the forest‐dominated catchment, although the elevated flow condition at the peatland‐dominated catchment persisted for longer periods. Finally, our analysis revealed no significant influence of peatlands on the attenuation or amplification of floods at the stream network scale. [ABSTRACT FROM AUTHOR]

A modelling framework for the simulation of stormwater runoff in ground-mounted photovoltaic solar parks is proposed. Elements in the solar park and their mutual interactions during precipitation events are conceptualized in EPA-SWMM. We demonstrate the potential of the framework by exploring how different factors influence runoff formation. Specifically, we carry out simulations for different sizes of the installation, soil types and input hyetographs. We also show the effect of ground cover, by changing the surface roughness. Outflow discharge from the park is compared to that from a reference catchment to evaluate variations of peak flow and runoff volume. Results highlight no practical changes in runoff in the short term after installation. However, in the long term, modifications in soil cover may lead to some potential increase of runoff. For instance, increments of the peak flow from the solar park up to 21% and 35% are obtained for roughness coefficient reductions of 10% and 20%, respectively. The proposed modelling approach can be beneficial for studying hydrological impacts of solar parks and thus for planning measures for their mitigation. [ABSTRACT FROM AUTHOR]

The effect of unsteady currents on scour at piers was investigated. The tests were run for nine pier shapes, three installation positions along a 180° bend, four flood durations, and four ratios of rising limb to flood duration for the 100-minute flood durations. Overall, including seven tests performed in the bend without piers, 196 tests were performed. The flow rapidity ranged from the movement threshold to live bed situations. The results indicated that the deepest scour-hole in front of the piers with different shapes was a function of flood duration and the ratio of ascending branch to descending branch had little effect on the final maximum scour-hole depth around the pier. The scour-hole volume is affected by the nose and the cross-sectional shape of the pier. For the rectangular pier, the scour-hole volume is greater than that of the other piers. The average shape coefficient was calculated. [ABSTRACT FROM AUTHOR]

Introduction: A better understanding of the cerebrospinal fluid (CSF) flow dynamics of Chiari 1 malformation (CM-1) may help to reach more specific parameters for indicating therapy and response to therapy. This study developed a parameter to better characterize CSF flow alterations in the cerebral aqueduct in patients presenting with CM-1. Methods: We retrospectively scanned archives for CM-1 patients who underwent CSF flow analysis between January 2016 and December 2022. Eighty-eight CM-1 patients and 83 control cases were included in the study. The cerebellar tonsillar descensus was measured in all patients. In 11 cases with the syrinx cavity, the largest transverse diameter of the cavity was measured. Phase-contrast magnetic resonance imaging was performed using a 1.5 T scanner. Peak velocity (P-Vel) (cm/s), average velocity (A-Vel) (cm/s), forward flow volume (µL), reverse flow volume (µL), peak flow (P-Fl) (mL/s), and time to peak velocity (TP-Vel) (s) and cerebral aqueduct's stroke volume (µL) were calculated. Sixteen CM-1 patients underwent decompression surgery, and we examined postoperative CSF flow analyses. Results: A-Vel and P-F1 were statistically significantly higher in CM-1 cases than in controls (p=0.006, p=0.037). There was a significant negative correlation between the diameter of the syrinx cavity and P-Vel and P-Fl, and a positive correlation between TP-Vel. We found no significant difference between the postoperative and preoperative CSF flow parameters of the CM-1 patients. Conclusion: P-Fl differs between the patient and control groups and correlates with the syrinx diameter; therefore, it could be a useful parameter in CSF flow analysis in CM-1 cases. However, higher case numbers can achieve more effective results. [ABSTRACT FROM AUTHOR]

Within this work, the impact of mitigation measures and infiltration on flash floods is investigated by using a 2D robust shallow water model including infiltration with the Green-Ampt model. The results show the combined effects of infiltration and mitigation measures as well as the effectiveness of bypass channels in addition to retention basins. Retention basins at appropriate locations could reduce the maximum water depth at critical locations by 23%, while the additional implementation of drainage channels lead to a reduction of 75%, considering also infiltration lead to a further reduction of 97%. If infiltration was considered without mitigation measures, the peak water depth was reduced by 67%. For an exceptional extreme event the measures lead to a reduction of 73% at some locations, while at other locations the overflow from retention basins due to overstraining generated even higher inundations with an increase of 58%.

The development of an integrated theory of subsurface drainage based on hydrology and hydrogeology concepts is presented. The historical context, the main hypothesis derived from the Boussinesq equation and the validation of the model predictions are discussed. Theoretical developments of this equation demonstrate that a single parameter ($\sigma $)—a combination of soil and drainage system properties—is sufficient for predicting the dynamics of subsurface drain flow rates. We also demonstrate that these drain flow rates are a function of the level of water replenishment in the system (classically the water table elevation), of the recharge intensity of the aquifer and of a buffer function related to the swelling or deflation of the water table shape during recharge events. For values of $\sigma >1$, the buffer role of the water table is negligible. In that case approx. 13% of the water table recharge contributes to the flow rate, which is shown to explain the observed disconnection between water table elevations and peak flow rates at the outlet of classic agricultural drainage systems and to predict these peak flow rates accurately. A modelling approach based on this theory and validated experimentally (SIDRA model) allowed us to test the quality of the peak flow prediction. The SIDRA model also includes a surface runoff module and has been coupled to different modelling tools and used to analyse the impacts of subsurface drainage on water quality. The approach contributed towards the development of tools that helped to connect better the drainage systems to the hydrological functioning of watersheds.

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5–7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT: spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [−15% (−46–32)] and expiratory [10% (−32–20)] flows and inspiratory [−6% (−25–18)] and expiratory [5% (−9–20)] times. Agreement for nadir flows was poor [−22% (−87–369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horse. [ABSTRACT FROM AUTHOR]

Changes in peak flow response time governed by rainfall and physical configurations of watersheds have been the topic of many studies, but other factors are also important. We aimed to analyze the dynamics in the lag time (TL) of peak flow for a tropical watershed (Kecha) and its sub‐watersheds (Dokmit, Zenjero Maderia, and Wotit Minch) in Ethiopia, as influenced by land‐use changes from 1982 to 2017 and the implementation of soil and water conservation (SWC) practices since 2011. Layered maps of land use, soil type, and SWC practices were used to determine the curve number, and the Natural Resource Conservation Service hydrologic model was used to estimate TL. We compared the estimated values against measured median values of TL for 30 rainfall–runoff events. The estimated TL of 1982, 2005, and 2017 varied from 9 to 19 min, 8 to 18 min, and 10 to 22 min, respectively, in the Dokmit, Zenjero Maderia, and Wotit Minch sub‐watersheds. The smallest (8 min) and greatest (22 min) values of TL were observed during 2005 and 2017, respectively. These results are likely attributable to the increased amount of cultivated area at the expense of bushland and forest in 2005 as compared to 1982, and the implementation of SWC practices in 2011–2017. Dokmit had the lowest TL values of the three sub‐watersheds, most likely because of its greater coverage of grazing and cultivated lands and degraded Nitic Luvisol. The variation in TL values among the sub‐watersheds was related to changes in both land use and SWC practices but also to the presence of degraded areas inherited from past human activities. Overall, such spatiotemporal flow response time analysis can provide useful information for the proper design of sustainable development strategies for particular niches in tropical regions of Ethiopia and elsewhere. [ABSTRACT FROM AUTHOR]

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5–7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [−15% (−46–32)] and expiratory [10% (−32–20)] flows and inspiratory [−6% (−25–18)] and expiratory [5% (−9–20)] times. Agreement for nadir flows was poor [−22% (−87–369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.

Digital elevation models (DEMs) are one of the most important data required in watershed modeling with hydrological models and their spatial resolution has a significant impact on the accuracy of simulating hydrological processes. In the present study, the effect of spatial resolution of five DEMs derived from the topographic map (TOPO) with a scale of 1:25000, ALOS PALSAR, ASTER, SRTM, and GTOPO with a spatial accuracy of 10, 12.5, 30, 90, and 1000 m, respectively, on the estimation of parameters of geomorphological and geomorphoclimatic unit hydrographs models has been evaluated in Amameh watershed. Thirty-four single flood events were used during the years 1970 to 2015. The results showed that in the GUH method, the application of the TOPO and ALOS PALSAR DEMs had the best results with root mean square error (RMSE) of 1.7 and 1.8 m3 /s and Nash-Sutcliffe Efficiency (NSE) of 0.4 and 0.3, respectively. While the GTOPO DEM had the least efficiency with RMSE of 2.8 m3 /s and NSE of -2. Similarly, the lowest and highest RMSE in the GCUH method belonged to TOPO and GTOPO DEMs with RMSE of 3.8 and 18 m3 /s and NSE of 0.2 and -6, respectively. Generally, the GUH method had more favorable results than the GCUH method in all DEMs. [ABSTRACT FROM AUTHOR]

A bifurcation in an engineered river system (i.e., fixed planform and width) has fewer degrees of freedom in its response to interventions and natural changes than a natural bifurcation system. Our objective is to provide insight into how a bifurcation in an engineered river responds to peak flows and human interventions. To this end, we analyze the change in hydraulics, bed level, and bed surface grain size in the region of two bifurcations in the upper Rhine delta in the Netherlands over the last century. We show that, over the last two decades, the water discharge in one bifurcate (the Waal branch) has steadily increased at the expense of the other. This gradual increase in the water discharge of the first branch is associated with its erosion rate being larger than the other branch. The quick succession of two or three peak flow events (1993, 1995, and 1998) caused rapid sediment deposition over the upstream part of the bifurcate that has gradually lost discharge, which seems to have triggered the slow change in flow partitioning. Plain Language Summary: A river bifurcation is where a river splits into two branches. Water and sediment from the upstream channel are divided between the bifurcation's downstream branches. This division is important for flood risk, freshwater supply, and navigation. Here we investigate the flow division and related changes in bed level and bed surface grain size in the bifurcation region in the upper Rhine delta in the Netherlands over the last century. We find that, over the last two decades, one branch (the Waal branch) has gradually received a larger share of the water discharge at the expense of the other branch. This gradual increase in the water discharge of the first branch seems to be associated with its erosion rate being larger than the other branch. This slow change in the division appears to be triggered by two or three successive peak flows (1993, 1995, and 1998), which caused sediment to deposit at the upstream end of the branch that subsequently started losing discharge gradually. Our analysis shows that peak flows can play a large role in bifurcation development in engineered river systems. Key Points: Water discharge in one branch at a Dutch Rhine bifurcation has slowly increased at the expense of the other bifurcateThis slow change in flow partitioning is associated with one bifurcate eroding faster than the other bifurcateSudden deposition in one bifurcate (due to rapid succession of peak flows and sediment flux coarsening) likely triggered these changes [ABSTRACT FROM AUTHOR]

Spirometry and peak expiratory flow measurement (PEF) are combined during functional respiratory assessments. The new digital peak flow meter (DPM) evaluates the forced expiratory volume in the first second (FEV1) and PEF. To compare lung function measurements using spirometry and DPM. This cross-sectional analytical study assessed FEV1 and PEF in children with and without asthma. Statistical analysis was performed to assess the agreement between the measures using the intraclass correlation coefficient (ICC), Bland–Altman, and survival agreement plot. 125 (3–12 y) and 196 (6–18 y) children without and with asthma, respectively, were studied. In children without asthma, the ICC for FEV1 and PEF were 0.89 and 0.86, respectively, while the corresponding values were 0.87 and 0.79, respectively, in patients with asthma. The Bland–Altman method showed a difference of −0.4 to 0.5 for FEV1 in patients without asthma, with a tendency to increase as the FEV1 increased to a certain extent. In patients with asthma, the pattern was similar for FEV1, and the PEF had a greater dispersion than among those without asthma; however, a good agreement pattern was maintained. In the survival agreement plot, when accepting a tolerance of 0.150 mL for FEV1, there was an agreement of close to 55% in both groups. Likewise, when accepting a tolerance of 0.5 L/s for PEF, an agreement of close to 60% and 50% was observed in patients without and with asthma, respectively. DPM was effective as a measure of lung function in pediatric patients with and without asthma. [ABSTRACT FROM AUTHOR]

The Caribbean has displayed a capacity to fulfill climate change projections associated with tropical cyclone-related rainfall and flooding. This article describes the hydrometeorological characteristics of Hurricane Fiona in Puerto Rico in September 2022 in terms of measured and interpolated rainfall and observed peak flows relative to previous tropical cyclones from 1899 to 2017. Hurricane Fiona ranks third overall in terms of island-wide total rainfall and fourth in terms of daily rainfall. Maximum daily rainfall during Hurricane Fiona exceeded those previously reported (excluding Hurricane María in 2017) in the eastern interior and eastern portions of the island. In terms of peak flows, no value approached the world's or Puerto Rico's flood envelope, although 69% of the observations are considered 'exceptional'. About 26% and 29% of all peak flows were in the 5–10 year and 10–25 year recurrence interval ranges, respectively, yet none matched the 25-year levels. The highest peak flows were concentrated in the central-eastern and southeastern regions. Even though Hurricane María provoked a more extreme hydrometeorological response, some of Hurricane Fiona's hydro-meteorological characteristics were among the highest ever recorded in Puerto Rico, particularly for the south-central and eastern portions of the island, and it displayed the island's current level of vulnerability to extreme rainfall. [ABSTRACT FROM AUTHOR]

Climate change-induced extreme precipitation causes coastal flooding. A streamflow simulation in coastal watersheds, Wolf River Watershed (WRW) and Jourdan River Watershed (JRW), was conducted using the Soil and Water Assessment Tool (SWAT) to compare variation in flow at different climates and to analyze the flood frequency. Baseline models were auto-calibrated with SWAT calibration and uncertainty programs (SWAT-CUP). Kling–Gupta efficiency (KGE), defined as the objective function in SWAT-CUP, ranged from 0.8 to 0.7 in WRW and from 0.55 to 0.68 in JRW during the calibration–validation process. Results indicated reliability of the model performances. Monthly averaged baseline flow was 1% greater than historical and 8.9% lower than future climate in WRW. In JRW, monthly averaged baseline flow was 11% greater than historical and 5.7% lower than future climate. Flood frequency analysis showed the highest 1% exceedance probability in annual maximum series (AMS) of baseline model in WRW, whereas AMS of projected model was estimated the highest in JRW. This study aids in preparing for future flood management. [ABSTRACT FROM AUTHOR]

Floods are incredibly dangerous and disruptive, and flooding is on the rise around the globe due to climate change. For these reasons, flood management will be one of the top challenges for communities around the world for the next half-century and beyond. This study is based on the knowledge of extreme hydrological mechanisms and a strong urban growth. It constitutes a first step towards a better management of the flood risk, in particular by the proposals materialized by documents in the form of cartographic tools as decision support. In this article, we'll provide a sky-high view of the configuration of the flood risk management solution through a new scientific approach by hydroclimate analysis. The study relied on the maximum daily rainfall data over an observation period of 47 years (1970-2017). The statistical treatment of the Maximum daily rainfall and short duration showers highlights the frequency values characterizing the intensity of rainfall representative of the study area. The peak flows were evaluated using the rational method and the Sokolovski flood hydrograph method. The objective of this study is to assess the flood risk in the city of Skikda by comparing the hazard and vulnerability and to propose cartographic tools to assist decision-making. [ABSTRACT FROM AUTHOR]

A paucity of precipitation data often precludes the application of traditional unit hydrograph and synthetic unit hydrograph methods for generating the design flood hydrograph (DFH) at a catchment outlet. However, flow data, either recorded or derived by deterministic approaches, are readily obtained for many catchments. In this paper, analytical methods for generating a DFH having its peak matching the peak flow of a specified return period, or a flood hydrograph beneath a known peak flow at a site, are presented. Only flow data in the case of a gauged site, and flow data together with data of physical descriptors of catchments at gauged sites in the vicinity in the case of an ungauged site, are used to develop a parametric semi-dimensionless characteristic flood hydrograph (CFH); finally, the CFH, which also enables volume estimation, is scaled up for fleshing out a DFH beneath a specified peak flow at that site. [ABSTRACT FROM AUTHOR]

A cluster of recent floods in the UK has prompted significant interest in the question of whether floods are becoming more frequent or severe over time. Many trend assessments have addressed this in recent decades, typically concluding that there is evidence for positive trends in flood magnitude at the national scale. However, trend testing is a contentious area, and the resilience of such conclusions must be tested rigorously. Here, we provide a comprehensive assessment of flood magnitude trends using the UK national flood dataset (NRFA Peak Flows). Importantly, we assess trends using this full dataset as well as a subset of near-natural catchments with high-quality flood data. While headline conclusions are useful for advancing national flood-risk policy, for on-the-ground flood-risk estimation it is important to unpack these local changes to determine how climate-driven trends compare with those from the wider dataset that are subject to a wide range of human disturbances and data limitations. We also examine the sensitivity of reported trends to changes in study time window using a ‘multitemporal’ analysis. We find that the headline claim of increased flooding generally holds up regionally to nationally, although we show a much more complicated picture of spatio-temporal variability. While some reported trends, such as increased flooding in northern and western Britain, appear to be robust, trends in other regions are more mixed spatially and temporally – for example, trends in recent decades are not necessarily representative of longer-term change, and within regions (e.g. in southeast England) increasing and decreasing trends can be found in close proximity. While headline conclusions are useful for advancing national flood-risk policy, for flood-risk estimation it is important to unpack these local changes, and the results and methodological toolkit provided here could provide such supporting information to practitioners. HIGHLIGHTS Up-to-date national assessment of trends in flood magnitude for the UK.; We examine long-term trends in a multitemporal context (sensitivity to time period).; We compare sites at near-natural catchments with the wider network of disturbed sites.; Results generally confirm the robustness of previously highlighted increases in flooding.; However, we provide significantly greater spatial and temporal detail.;

This study explores the impact of urban densification on peak flow response in an urban catchment. The catchment runoff potential grew up to 33% for the case of the runoff coefficient and 12% for the curve number due to the increase of effective impervious areas (EIA) of up to 93%, which caused the peak flow to double (101%) in some cases. Results also indicated that in highly disturbed catchments: (a) the catchment response is very sensitive even among low-return-period storms; (b) the lack of urban planning exacerbates the impact of imperviousness on peak flow increase as it promotes, among others, the presence of large EIA; (c) the values of percentage of imperviousness causing peak flow increase both vary with rainfall intensity and show a non-linear behavior; and (d) an increase in EIA of 9% seems to be the starting point of peak flow growth. The findings of this study not only outline the importance of more studies in areas with urban sprawl for the understanding of the interaction between catchment imperviousness and peak flow increase at a local level but also serve as an input for the improvement of integrated urban planning, considering the effects of urbanization in stormwater management. [ABSTRACT FROM AUTHOR]

The local scour around the bridge piers is the main cause of their destruction. Based on this, extensive studies have been done to understand this phenomenon. Most of these studies have been done under steady flow conditions. This is while the flow in the river is unsteady. Therefore, the experiments of this research were carried out under unsteady flow conditions. The purpose of this research is to investigate the scour around the dual bridge piers at different distances of the piers from each other in a uniform flow as well as unsteady flow using symmetric hydrographs. The hydrographs used in the experiments are stepped hydrographs in 5 steps. The experiments were conducted under clear water conditions and U/UC=0.95. In all experiments, the diameter of the bridge pier (D) was constant and equal to 2.5 cm. The center-to-center distance between the dual bridge piers (S) was selected as 2D, 3D, 4D and 5D. In the unsteady flow, with increasing relative distance between the dual bridge piers, the maximum dimensionless scour depth of the first and second piers was increased and its maximum was measured at a relative distance of S/D=5 (in the range of relative distances studied in the research). But in the uniform flow, the maximum dimensionless scour depth of the first and second pier was observed at S/D=3 and S/D=4, respectively. Also, at a constant distance between the piers, increasing the peak and base flow of the hydrographs step-by-step, increased the maximum dimensionless scour depth of the first pier of dual bridge piers with an increasing rate. However, increasing the peak and base flow of the hydrographs step-by-step, increased the maximum dimensionless scour depth of the second pier with a decreasing and increasing rate, respectively.

Study region: Six small agricultural watersheds in three tropical climatic regions of Ethiopia. Three regions of contrasting climate: highland, midland, and lowland regions with respectively high, middle, and low elevations and rainfalls. Study focus: Lag time (TL) and time of concentration (TC) are two measures of how quickly a stream responds to runoff-producing rainfall. These parameters are the main inputs used to estimate peak flow under flood conditions in ungauged watersheds. Many empirical methods have been proposed to estimate TL and TC, but the validity of none of them has been tested. This study compared 10 commonly used methods by using measured TL and TC. New hydrological insights: Measured median values of TL and TC for 176 rainfall–runoff events were used to evaluate the performance of empirical methods. For individual watersheds, the estimates of TL and TC differed by up to 2.6 h and 4.4 h, respectively. Most of the empirical methods tended to substantially underestimate TL and TC, which would lead to overestimation of runoff volume. TL and TC computed by two methods that consider both overland and channel flow were closest to the measured values of TL and TC, because such mixed flow is typical of tropical climate regions. Our results show the need for caution when empirical methods developed in regions with a particular climatic and geomorphological conditions are applied elsewhere.