Runoff Flow Research Articles

Rock surface flow accelerates rill erosion of excavated slopes in karst mining areas

Rock surface flow is the secondary distribution of precipitation and inflow on the rock surface, an essential runoff generation mode in karst areas. The effects of rock surface flow on soil erosion in karst regions cannot be ignored. However, its impact on rill erosion in karst slopes remains unclear. The objectives of this study were to investigate the impact of rock surface flow on rill erosion, rill morphological characteristics, rill flow hydraulic characteristics, and hydrodynamic mechanisms. A field runoff plot (3 m long, 1 m wide and 0.3 m deep) with three inflow rates (2, 3, and 4 L/min) was subjected to runoff simulation experiments under two typical rock surface morphologies in karst areas: smooth rock surface (SRS) and karren rock surface (KRS), with bare slope (BS) as the control group. The results revealed that rock surface flow aggravated the soil and water loss of the excavated slope. Compared to BS, the runoff yield for SRS and KRS increased by 81.49 % and 61.91 %, respectively. Meanwhile, the soil loss of SRS and KRS were 2.50 times and 5.56 times greater. The rills below the rock outcrops didn’t develop into a rill network after formation, owing to the rock surface morphology. Rill depth was the best indicator of rill morphology for evaluating rill erosion on slopes below rock outcrops. The Reynolds number and Darcy–Weisbach resistance coefficient were the optimal hydraulic parameters to predict the rill erosion of the SRS and KRS, respectively. At the same time, the runoff power and flow shear stress were the best hydrodynamic parameters to describe the rill erosion mechanism of SRS and KRS. These results provide a scientific basis for further understanding the mechanism of soil erosion on karst slopes and for preventing soil erosion on karst slopes in mining areas.

Evaluation of Drainage Network System (Case Study of Pangkajene Kepulauan State Agricultural Polytechnic Campus Area)

The purpose of this research is to identify the condition of highway drainage channels and evaluate the existing highway drainage network system in accommodating runoff discharge, channel dimensions and flow direction in channels that occur inundation in the Pangkajene Islands State Agricultural Polytechnic Campus area which is expected to help solve flooding problems in the area. The research method used is descriptive quantitative, which is a method of calculation and description of the results of field data processing. Secondary data collection includes; rainfall data for the last 10 years, obtained from the Department of Resources; topographic maps, drainage network maps and situation maps, obtained from the Politani Pangkep Campus planning section. Primary data collection is obtained from direct measurements in the field using a Waterpass measuring instrument to measure elevation and channel length. The results of this study found that the drainage capacity < 2-year and 5-year return period Plan Flood Discharge, so planning is needed to increase drainage capacity

Linking elevated rainfall with sewage discharge volume

Abstract The intricate hydrological processes elucidating the interplay between rainfall and flow manifest through rainwater's traversal along diverse routes, encompassing surface runoff and subsurface flow. While the foundational association between these entities is discernible, the convoluted intricacies characterizing this correlation defy straightforward comprehension. Examining the data between 2019 and 2022, the average daily sewage outflow was 12,518 m3/d, with occasional peaks of up to 50,440 m3/d. The wastewater treatment plant's capacity of 35,000 m3/d was usually not exceeded. Overall, average daily sewage outflows varied between 11,716 m3/d and 13,969 m3/d during the studied period. Comprehending this interrelationship holds pivotal significance for the optimization of water-resource-management strategies. A moderate correlation (r = 0.42) between daily rainfall levels and sewage discharge was found in the dataset covering 2018–2023. When categorizing daily rainfall into groups labelled “A” through “G” and comparing them to sewage flows, a pattern emerged: Rain-free days in group “A” had the lowest average sewage flow (10,996 m3/d), while heavy rain days in group “G”, had the highest average flow (22,112 m3/d). This observation underscores a significant correlation between intensified rainfall and increased volume of sewage discharge. Through a comprehensive analysis of factors such as sewage composition, meteorological dynamics and chronological sequences, we will gain an enhanced ability to prognosticate and govern sewage systems. The significance of this is heightened within the context of evolving climatic dynamics.

Green roof infrastructure outperforms grey technology in flood mitigation in São Paulo’s urbanized region

São Paulo City, Brazil, a densely urbanized area in a tropical climate region, is facing increasing challenges from flooding. However, a promising solution has emerged in the form of Nature-Based Solutions (NBS) infrastructure, surpassing traditional grey technology in flood mitigation. This article examines the effectiveness of green roofs in reducing flood risks and highlights their superiority over conventional approaches. We analyzed the direct impacts of surface permeabilization in public areas (sidewalks, streets, and squares) and private areas (urban lots, subdivisions) on runoff volume and peak flow in the Aricanduva River basin in São Paulo city. We used a thoroughly validated hydrological model to compare the interference in the land use of the watershed between a green infrastructure type called Green Roof (GR) and a gray technology called Permeable Pavement (PP), in terms of hydrological efficiency in mitigating floods. The flow and water level simulations for varying areas with GR or PP covered a wide range, allowing for situations above or below the canal overflow level, which provided a good distinction of the impact of boundary conditions. Overall, we observed a positive hydrological response, with a reduction in peak flow and runoff volume proportional to the increase in permeable area, and consequently, proportional to the increase in GR or PP surface within the contributing area. As the main contribution, the hydrological performance calculated with the variation of GR was remarkably superior to the variation of PP in terms of requiring a smaller coverage area with interference to prevent overflow or achieve equivalent efficiency. It is worth noting that the substitution of approximately 24% of the gray roof area with GR prevented canal overflow, which is notably lower than the required substitution of approximately 40% for PP interference. We reinforce the relevance of green roofs as an option to mitigate intense hydrological effects in urban areas and, more importantly, paves the way for other NBS with the same hydrological principles and environmental co-benefits to work individually or in combination.

Re-Engineering Dew-Harvesting Cactus Macrostructures to Enhance Water Collection as an Adaptive Climate Change Strategy: An Experimental Comparison

The spinal structures found on Copiapoa cinerea var. haseltoniana, an efficient dew-harvesting cactus, were fabricated and evaluated both in a climate chamber and outdoors in dewy conditions. A mix of aluminium and steel was used to fabricate these surfaces, with aluminium being used for everything but the replicated spine features, which were constructed from steel. Each surface was entirely coated with a highly emissive paint containing an alumina–silicate OPUR additive. Three replica versions (stem only, spine only, and stem & spine) were compared to a flat planar reference surface. Experimental results demonstrated that all three biomimetic macro-structured surfaces significantly enhanced dew harvesting compared to the reference surface. It was established that the stem & spine replica, spine replica, and stem replica all demonstrated significantly more dew harvesting, with mean efficiency ratios in respect of the reference surface of 1.08 ± 0.03, 1.08 ± 0.02, and 1.02 ± 0.01, respectively. Furthermore, the method of surface water collection was found to influence the water collection rate. The diagonal run-off flow across a flat planar surface was 34% more efficient than the parallel run-off flow on the same surface. These findings provide valuable insights for the construction and installation of biomimetic-inspired dew-harvesting devices, particularly in regions that are most challenged by decreasing dew yields as a result of climate change.

Drier streams despite a wetter climate in woody-encroached grasslands

Grasslands, covering 40% of ice-free Earth surface, are experiencing woody encroachment globally. The hydrological impacts of woody encroachment are highly uncertain because they are compounded by the concurrent influence of climate change. Here we ask the questions 1) How water balance (evapotranspiration versus streamflow) and streamflow partitioning (into surface runoff and subsurface flows) evolve over time in woody-encroached grasslands? 2) What is the relative influence of climate change and woody encroachment? We used the hydrology model HBV-light and decades of hydrometeorological and streamflow data from two intermittent streams draining catchments with different degrees of woody encroachment at the Konza Prairie, Kansas, US. Results indicate that both streams have become drier and have experienced more hydrological droughts over time, more so in the substantially encroached site, with increasing evapotranspiration despite a wetter climate. In contrast, a modelled hypothetical “Climate Only” scenario without woody encroachment suggests streamflow would have increased under climate change alone. Moreover, results suggest that flow paths have deepened with increasing fractions of deeper groundwater flow in the substantially encroached site. These findings raise questions about mechanisms of these changes and commonality of drier streams in a wetter climate in woody-encroached areas and beyond. Answers to these questions can have far-reaching implications for the occurrence of droughts, water availability, water quality, and ecosystem health.

Can land use/land cover optimization improve the environmental flow guarantee in regulated basins?

Land use/land cover (LULC) change is an important driver of changes in hydrologic processes in watersheds. Many studies have focused on the disruptive effects of human activity-induced urban sprawl and increased impervious surfaces on river runoff and environmental flow (e-flow), and little has been reported on whether LULC changes can improve e-flow security. Therefore, we proposed a hypothesis on whether LULC optimization can improve the e-flow guarantee using the Shayinghe River watershed as an example. To test the hypothesis, we evaluated the runoff response and e-flow security status of seven LULC scenarios (four historical scenarios and three possible optimization scenarios) by constructing the Soil and Water Assessment Tool (SWAT) model to establish the statistical relationship between a single LULC type and the e-flow guarantee rate (EGR) and e-flow deviation rate (EDR) and screened the best land optimization scenario for the Shayinghe River watershed. The results showed that: (1) forest land and grassland have positive effects on EGR, and LULC optimization can counteract the risk of dry season e-flow security caused by urban expansion and increased construction land to a certain extent; (2) construction land was the most active LULC type and inhibited the dry season flow and EGR of rivers, leading to moderate changes in the hydrological process of Shayinghe River; (3) the Grain for Green Project was the best LULC optimization scenario for the Shayinghe River basin, which converts 1342 km2 of cultivated land in the western part of the basin to forest land, resulting in the highest dry season EGR increases of 3.23 % and 2.26 % in Zhoukou and Fuyang, respectively. Our study proposes a relatively simple and easily replicable approach in other watersheds, providing a new reference for rational LULC planning and environmental flow protection in highly regulated watersheds.

Influence of landscape patterns on nitrate and particulate organic nitrogen inputs to urban stormwater runoff

This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3−-N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3−-N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

Hydrological Modeling and Evaluation of the Efficiency of Culverts in Drainage Basins Affecting the North Railway in Wadi Malham

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.

From flood paths to floodways, an efficient method to map, identify and evaluate suitable floodways: A case study from Trondheim, Norway

Due to climate change and rapid urbanisation, many Norwegian cities and urban areas suffer from pluvial flooding caused by intense rainfall exceeding the capacity of the stormwater management system. This results in increased runoff rates, volumes and peak flows in the drainage network. In response to these challenges, the authors explore the potential of utilising the urban surface's ability to transport floodwater as an integral component of the stormwater infrastructure. When the capacity of the stormwater drainage system is exceeded, the overland flow paths transporting floodwater are considered a part of the stormwater management system, as floodways. The study proposes a spatial GIS method to map existing drainage lines and identify existing surface areas that function as floodways, combined with an automated process to identify which drainage lines could be implemented as stormwater management measures. Critical points are introduced to assess the floodways' potential hazards, combined with a classification method to evaluate and sort floodways. A case study from Trondheim, Norway, was used to demonstrate how drainage lines can be identified as floodways using the proposed method. The case study is also used to illustrate how a GIS-based analysis can be extended from identifying to evaluating floodways and whether GIS is sufficient for floodway evaluation. The method enables urban planners and municipalities to identify which areas of the urban surface already function as floodways during extreme events, and to prioritise measures to secure such areas and increase the city's flood resilience. The results highlight the need to assess existing areas that function as floodways, and to implement and design needed areas as floodways. GIS-based methods combined with an evaluation scheme can be an adequate tool to map and evaluate floodways in urban areas. When using GIS-based methods, however, the corresponding hazard potential, and also the uncertainty of the floodway's spatial placement, should be considered.

Multivariate multi-step LSTM model for flood runoff prediction: a case study on the Godavari River Basin in India

Abstract Flood is India's most prevalent natural calamity, devastatingly affecting human lives, infrastructure, and agriculture. Predicting floods can help to mitigate the potential damage and conduct timely evacuation drives. This research proposes a deep-learning regression model to forecast flood runoff. Various climatological, hydrological, land, and vegetation-related data have been collected from multiple sources for 18 years (2002–2019) to create a comprehensive dataset for the Godavari River at the Perur water station in India. The relevant attributes identified through feature selection are river water level, precipitation, temperature, surface pressure, evaporation, soil water content, daily runoff, and average river flow. The selected features were fed into various time series prediction models like AutoRegressive Integrated Moving Average (ARIMA), Prophet, Neural Prophet, and Long Short-Term Memory (LSTM). The LSTM model obtained the best results achieving a Root Mean Squared Error (RMSE) value of 0.05, Mean Absolute Error (MAE) value of 0.007, Willmott's Index (WI) of 0.83, Legates-McCabe's Index (LMI) of 0.58, and R2 of 0.67 for a 1-day prediction with a look-back window of 183 days. The model is also trained to predict the flood runoff value for a week ahead. The proposed model can serve as an essential component in flood warning systems.

Streamflow Response to Climate and Land-Use Changes in a Tropical Island Basin

The effects of climate change and of land use/cover change (LUCC) on streamflow as demonstrated by hydrological models are pressing issues on the frontiers of global environmental change research. The Nandu River Basin (NRB) as the largest of three river basins on the tropical Hainan Island, China, is subjected to an analysis of streamflow response to climate and to land-use change. It is based on the Soil and Water Assessment Tool (SWAT) coupled with climate change signals extracted from the global climate model data in the Coupled Model Intercomparison Project Phase 6 (CMIP6) and with land-use change scenarios modeled by Cellular Automata (CA)—Markov. The results are summarized as follows: (1) Climate change contributed more to streamflow change than land-use change in the NRB, with contributions of 97.57% and 2.43%, respectively. Precipitation and temperature were the most important climate variables, contributing 92.66% and 4.91% to streamflow change. (2) In the tropical island basin from 1990 to 2015, LUCC regulated the hydrological processes in the NRB and affected hydrological processes by increasing evapotranspiration and decreasing surface runoff and subsurface flow, which resulted in decreasing streamflow. (3) Under the climate change and land-use change scenarios of the near-term period (2021–2040), the annual streamflow decreased as during the reference period (1995–2014); particularly, it decreased most (−6.16%) on the SSP126 path. These results present a case study for understanding the hydrological cycle of tropical island basins and to provide a theoretical basis for water resources management and regional sustainable development of tropical islands.

Assessing the Performance and Challenges of Low-Impact Development under Climate Change: A Bibliometric Review

Low-Impact Development (LID) represents a cogent strategy designed to conserve or reestablish antecedent hydrological states through an array of innovative mechanisms and methodologies. Since the dawn of the millennium, LID-centric research has demonstrated a persistent upward trajectory, mainly focusing on its capacity to mitigate climate change repercussions, particularly runoff and peak flows. However, a standardized rubric and toolkit for LID evaluation remain elusive. While numerous studies have documented the hydrological and water quality benefits of LID, the impacts of climate change on its effectiveness remain uncertain due to varying spatial and temporal climate patterns. This comprehensive review examined 1355 peer-reviewed articles in English, comprising both research articles and reviews, indexed in the Web of Science up until 2022. Findings from the bibliometric analysis revealed significant contributions and emergent trends in the field. Notably, there is an increasing emphasis on performance evaluation and efficiency of LID systems, and on understanding their impact on hydrology and water quality. However, this review identified the lack of a standardized LID evaluation framework and the uncertainty in LID effectiveness due to varying climate patterns. Furthermore, this study highlighted the urgent need for optimization of current hydrological models, advancement of LID optimization, modeling, monitoring, and performance, and stakeholder awareness about LID functionality. This review also underscored the potential future research trajectories, including the need to quantify LID’s effectiveness in urban flooding and water quality management and refining LID simulation models. Cumulatively, this review consolidates contemporaneous and prospective research breakthroughs in urban LID, serving as an indispensable compendium for academics and practitioners in the discipline.

Vulnerability Assessment of the Upper-Middle Pleistocene (qp2-3) Aquifer in Ho Chi Minh City, Vietnam Using GIS and Expanded DRASTIC Methods

The groundwater vulnerability assessment model (DRASTIC) for zoning sensitivity based on natural and objective factors of aquifers is currently used and applied widely. In this study, we have expanded the weights in the DRASTIC index through the Entropy weight-based technique and visualized them in association with GIS for assessing the vulnerability of the Upper-Middle Pleistocene aquifer in Ho Chi Minh City, Vietnam. The value of Entropy weights calculated from the collected dataset of 106 monitoring boreholes of the study area. The Entropy-DRASTIC results divided into three categories: 9.45% of the study area was in the high vulnerability zones, low and medium vulnerability zones are 21.5% and 69.05% of the total study area, respectively. The highly vulnerable area, which is shallow aquifer roofs and recharged significantly (directly from rains or runoff from the surface flows exposed to contaminants from runoff flows). Low vulnerability areas with clay cover are weak permeability and medium vulnerability area is a sizable transitional zone surrounding the high and low vulnerability. This result suggests that the DRASTIC index model in association with GIS is a useful tool to assist policymakers in formulating solutions for the use of groundwater resources. Importantly, this finding is useful to the local authorities in shaping regulations on the use and exploitation of groundwater resources in suburban areas, where the public water supply network is inadequate, constrained groundwater resource and exposed to contamination.

Modeling the heat transfer of rainfall runoff in the typical catchment of Beijing

The stormwater runoff formed on the urban impervious surface in summer may carry a large amount of heat, which will have a negative impact on the urban receiving water bodies. In order to simulate the process of runoff generation, confluence, and heat transfer, evaluate the degree of thermal pollution of stormwater runoff, and better quantify the heat of stormwater runoff, a simplified urban stormwater runoff temperature model is developed according to the runoff process of pervious surface and impervious surface and pipe network during rainfall, combined with the heat transfer principle in the process, to calculate the runoff flow and temperature from the small catchment. The heat transfer model mainly considers the heat exchange between runoff and surface, runoff and atmosphere, and runoff and pipe. The proposed model was evaluated by monitoring of typical urban catchment in the summer of 2021–2022, and the calculation formula of Event Mean Temperatures (EMT) in the catchment was proposed based on the model principle. The average root mean square error (RMSE) between the predicted value and the monitoring value of the model is 0.6 ℃. Long duration rainfall and short duration high intensity rainfall could lead to large simulation errors. Runoff temperature is easily affected by air temperature, solar radiation, pre-rain temperature and type of impervious surface. The average error between the EMT calculated by the formula and the actual monitoring EMT is 0.6 ℃, and its significant error rainfall frequency is consistent with the model. The results show that the model and formula can be used to predict the runoff heat in typical catchments, providing a more convenient method for the analysis of runoff heat in small catchments.

Geomorphometric based catchment runoff characterization and assessment of temporal landuse change impact on runoff inflow to an ungauged reservoir under different climatic scenarios using geospatial techniques and SWAT model

Abstract A morphometric analysis was carried out to study runoff characteristics of the Saleran reservoir catchment. Further, the impact of catchment landuse change on runoff generation and inflow to the Saleran reservoir has been assessed using geospatial techniques and SWAT. The geomorphometric analysis shows that the catchment is less elongated in shape, having fourth-order stream network, high stream frequency (9.36 no./km2), drainage density (4.55 km/km2) and high relief (220 m), which indicates that catchment would generate a moderate amount of runoff. The SWAT (ArcSWAT) model was used for the simulation of runoff and the average annual runoff inflow was simulated to be 14.2 mm (1995–1999), 13.2 mm (2000–2009) and 11.8 mm (2010–2019) per 100 mm of rainfall under the landuse 1999, 2009 and 2019, respectively. The results indicated that the temporal change in catchment landuse has significantly increased the runoff generation and its inflow to the reservoir but there is a decrease in the volume of runoff inflow which may be due to the decreasing trend in monsoon rainfall. Hence, an appropriate conservation strategy needs to be developed and adopted in the Shivalik foot-hills for managing the catchment landuse for sustainable water supply through reservoirs.

Using the SWAT+ model to assess the conditions of water inflow to a reservoir in an uncontrolled agricultural catchment. Case Study of the Nanan Reservoir in the Lake Taabo catchment (Côte d'Ivoire)

In this study, the agro-hydrological model Soil and Water Assessment Tool + (SWAT+) is used to simulate runoff in an uncontrolled agricultural catchment with paddy fields irrigated by plots submersion. The objectives are to evaluate the ability of this new, improved version of the SWAT model to reproduce the flows in a complex catchment and to analyse the evolution of these flows over the historical period 1986-2020 (35 years). Sensitivity analysis, calibration and validation were carried out with monthly flow data. The decision tables for irrigation operations and reservoir water release were filled in the SWAT+ Editor to establish the reservoir water balance. The Mann-Kendall trend test with the threshold of the standard normal statistic = 1.96, was applied to the time series of flows to the Nanan Reservoir. The results reveal that SWAT+ is more sensitive to eight parameters, including the new CN3_SWF parameter (-0.04329), which gave the user control of the soil saturation level. Good performances were obtained during calibration and validation, respectively: NSE (0.78; 0.69); R² (0.81; 0.70); PBIAS (-18.58; -23.9) and RSR (0.47; 0.56), with a tendency to slightly overestimate flows. The analysis shows that flows to the Nanan Reservoir are highly variable yearly, with a non-significant upward trend (|Z|=1.3<1.96) from 1986 to 2020. The water balance reveals that the runoff inflow generated will compensate for water withdrawals for irrigation of the Nanan paddy scheme during this period. Furthermore, this study provides a methodological framework for SWAT+ reservoir model calibration in an uncontrolled catchment.

Water Balance Components Estimation using WetSpass Model: A Case study of Mekelle Area, Tigray, Ethiopia

This research was aimed at estimating the spatially distributed Water balance components of the catchments in Mekelle area by using WetSpass hydrological model and verifying the model outputs with ground truth. Long term mean metrological data and physical characteristics of the catchments were used as an input to the model. The input data were manipulated using Arc- GIS tools. Results of this model depicted that about 73.13% and 19.96% of the precipitation in the study area was lost through evapotranspiration and surface runoff respectively. However, 7% of it replenished the groundwater. The annual runoff and groundwater recharge estimated in WetSpass model accumulated using Arc-GIS were verified using the annual runoff gauged records and base flow measurements. Accordingly the accumulated runoff and base flow derived from the WetSpass model using Arc-GIS software results were quite close to the observed runoff and base flow values measured in the gauging points. Therefore, WetSpass model is appropriate model in estimating water balance components in the study area.

Hydrogeological characterization of karst springs of the white (Proteus anguinus anguinus) and black olm (Proteus anguinus parkelj) habitat in Bela krajina (SE Slovenia)

The springs west of Črnomelj, in SE Slovenia, are the habitat of the black (Proteus anguinus parkelj) and the white olm (Proteus anguinus anguinus). Some of these springs are also the only known habitat in the world of endemic species of black olm. A steady decline in olm populations has been observed in this area over the past decades. Owing to the rapid runoff and groundwater flow high-resolution monitoring is essential in providing better insight into the hydrogeological characterization of the catchment area of springs. Specific factors and critical parameters of water behind said olm degradation have not yet been defined. Because the olm’s environment is largely aquatic, one potential critical parameter could be the higher water temperatures (&gt;12 °C) or higher nitrate concentration (&gt;9.2 mg/l). The six-month observation of the springs (July – December 2021) point to water temperature as a potential critical parameter since the water temperature of the springs exceeded 12 °C in months July and August. Nitrate concentrations could also be a second critical parameter in the degradation of the olm’s habitat. Maximum nitrate concentrations above 9.2 mg/l throughout much of the observation period (except for Dobličica spring). Due to less agricultural activity in December in the spring catchment area and a higher dilution rate due to reduced evapotranspiration and increased effective precipitation during this time of the year, the nitrate concentrations are decreased. The results of the measured parameters of groundwater could show the hydrogeological connection between the Otovski and Pački breg springs and between Šotor, Jamnice and Dobličica. The Obršec spring has an independent catchment area. A detailed estimation of the springs catchment area is possible due to a detailed geologic map. It is necessary to determine the origin of the nitrate (nitrate isotope analysis), to quantify the threshold values of the critical parameters, to define precisely all the causes of the olm deterioration, and to make proposals for appropriate measures to limit or even stop the decline of the olm population.

Water–soil interactions: Unravelling the processes and stages involved in the wetting of water repellent soils

The water repellent behaviour of soils is a widely studied phenomenon given its implications for infiltration, runoff, erosion and preferential flow. However, the principles underlying the eventual penetration of water into affected soils remain poorly understood. Theoretical considerations of the energetics and kinetics involved as a water drop makes contact with a water repellent soil surface and eventually penetrates into the soil suggest three distinct stages in the overall process. These stages are 1) adhesional wetting as soil and water first make contact, followed by 2) a kinetic barrier transitional stage in which molecular reorganisation of organics on soil reduces the water-soil contact angle to allow the water drop to sit deeper over soil particles of initial contact such that there is contact with particles in directly underlying soil layers, and finally 3) branching interstitial wetting as water penetrates into the bulk soil. Studies presented here of optical microscopy, mass of soil initially wetted, penetration time through layers of soil of different thicknesses, and time-dependent measurements of contact angle, volume of water penetrated, and mass of soil wetted, all give results consistent with this model. However, only for highly water repellent soils can distinct stages in wetting be clearly resolved experimentally, presumably because only these soils have a high enough kinetic barrier in the transitional stage for good separation between stages. For less water repellent soils, while the general time dependent behaviour remains consistent with the model, the distinction between the three stages is not so easy to resolve experimentally. The roles of contact angle, particle size distribution and drop size in determining the rates of these stages is considered, and the implications of the model for understanding soil water repellency are discussed.