Job van der Werf
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1
Understanding Live Pole Drains
An open-air laboratory study of the hydrological behaviour of Live Pole Drains
Shallow landslides impact people worldwide and are projected to intensify under future climate conditions, leaving slopes vulnerable to further erosion and recurrent failure. Soil bioengineering, a category of Nature-based Solutions (NbS), offers a promising approach to both stabilising and restoring such slopes, but lacks the empirical evidence needed for widespread implementation. This study focuses on Live Pole Drains (LPD), bundles of willow branches installed in slopes to promote subsurface drainage while sprouting to initiate revegetation. While predominantly documented as a measure against superficial erosion, LPD have also been proposed as a measure against shallow landslides, though empirical evidence remains scarce. The central aim was to develop an evidence-based conceptual model of LPD hydrological behaviour, advancing from qualitative perceptual models through experimental investigation. This was carried out using an Open-Air Laboratory (OAL) approach at Flood Proof Holland in Delft, the Netherlands.
Three experiments were conducted: two in which a controlled flux was applied to isolate specific hydrological processes, and one infiltration experiment assessing the lumped effect of LPD on infiltration. The resulting conceptual model characterises LPD as threshold-dependent lateral drains that simultaneously enhance infiltration capacity through root-driven improvements to soil structure. In the current setup, situated above a permeable sand layer, the drainage threshold was rarely met, indicating that the effectiveness of LPD as a slope drainage measure is conditional on the surrounding soil's hydraulic properties. The sandy base layer facilitated generalisation of the underlying processes but prevented the conditions required for full LPD activation.
Future research in settings with a lower-conductance base layer is needed to demonstrate LPD effectiveness under the conditions in which they are intended to operate, with the determination of the activation threshold as an explicit objective. As an additional contribution, a novel siphonic flow meter was developed for low-cost flow measurement within the OAL framework, though further development is required for reliable use under continuous inflow conditions. ...
Three experiments were conducted: two in which a controlled flux was applied to isolate specific hydrological processes, and one infiltration experiment assessing the lumped effect of LPD on infiltration. The resulting conceptual model characterises LPD as threshold-dependent lateral drains that simultaneously enhance infiltration capacity through root-driven improvements to soil structure. In the current setup, situated above a permeable sand layer, the drainage threshold was rarely met, indicating that the effectiveness of LPD as a slope drainage measure is conditional on the surrounding soil's hydraulic properties. The sandy base layer facilitated generalisation of the underlying processes but prevented the conditions required for full LPD activation.
Future research in settings with a lower-conductance base layer is needed to demonstrate LPD effectiveness under the conditions in which they are intended to operate, with the determination of the activation threshold as an explicit objective. As an additional contribution, a novel siphonic flow meter was developed for low-cost flow measurement within the OAL framework, though further development is required for reliable use under continuous inflow conditions. ...
Shallow landslides impact people worldwide and are projected to intensify under future climate conditions, leaving slopes vulnerable to further erosion and recurrent failure. Soil bioengineering, a category of Nature-based Solutions (NbS), offers a promising approach to both stabilising and restoring such slopes, but lacks the empirical evidence needed for widespread implementation. This study focuses on Live Pole Drains (LPD), bundles of willow branches installed in slopes to promote subsurface drainage while sprouting to initiate revegetation. While predominantly documented as a measure against superficial erosion, LPD have also been proposed as a measure against shallow landslides, though empirical evidence remains scarce. The central aim was to develop an evidence-based conceptual model of LPD hydrological behaviour, advancing from qualitative perceptual models through experimental investigation. This was carried out using an Open-Air Laboratory (OAL) approach at Flood Proof Holland in Delft, the Netherlands.
Three experiments were conducted: two in which a controlled flux was applied to isolate specific hydrological processes, and one infiltration experiment assessing the lumped effect of LPD on infiltration. The resulting conceptual model characterises LPD as threshold-dependent lateral drains that simultaneously enhance infiltration capacity through root-driven improvements to soil structure. In the current setup, situated above a permeable sand layer, the drainage threshold was rarely met, indicating that the effectiveness of LPD as a slope drainage measure is conditional on the surrounding soil's hydraulic properties. The sandy base layer facilitated generalisation of the underlying processes but prevented the conditions required for full LPD activation.
Future research in settings with a lower-conductance base layer is needed to demonstrate LPD effectiveness under the conditions in which they are intended to operate, with the determination of the activation threshold as an explicit objective. As an additional contribution, a novel siphonic flow meter was developed for low-cost flow measurement within the OAL framework, though further development is required for reliable use under continuous inflow conditions.
Three experiments were conducted: two in which a controlled flux was applied to isolate specific hydrological processes, and one infiltration experiment assessing the lumped effect of LPD on infiltration. The resulting conceptual model characterises LPD as threshold-dependent lateral drains that simultaneously enhance infiltration capacity through root-driven improvements to soil structure. In the current setup, situated above a permeable sand layer, the drainage threshold was rarely met, indicating that the effectiveness of LPD as a slope drainage measure is conditional on the surrounding soil's hydraulic properties. The sandy base layer facilitated generalisation of the underlying processes but prevented the conditions required for full LPD activation.
Future research in settings with a lower-conductance base layer is needed to demonstrate LPD effectiveness under the conditions in which they are intended to operate, with the determination of the activation threshold as an explicit objective. As an additional contribution, a novel siphonic flow meter was developed for low-cost flow measurement within the OAL framework, though further development is required for reliable use under continuous inflow conditions.
Africa is the world’s second driest continent, supporting 15% of the global population with only 9% of the global renewable water resource. The 2015 to 2018 drought in the Western Cape of South Africa, where a Day-Zero scenario was narrowly avoided, highlighted the need to start looking at alternative water resources in conjunction with preserving the current water resources.
Globally, the water sector is moving towards a circular water economy - where all water sources, including wastewater, stormwater and rainwater are treated as a resource that can be used, recycled, and replenished into the system. Stormwater harvesting (SWH) has successfully been implemented in countries such as Australia, Israel, Singapore & South Africa.
The success of any SWH scheme depends on effective site selection. Yet, there is little guidance available, and site choices have traditionally relied on the subjective judgment of urban water managers. This demonstrates the need for an objective, data-driven approach that integrates multiple spatial datasets to identify optimal SWH locations.
This research develops such a method: an integrated hydrological and GIS-based screening tool that identifies high yield (hotspot) SWH sites using publicly available datasets in Africa. The collection models showed that high yielding stormwater harvesting sites can be identified with publicly available data, with all 4 weightings consistently pointing out the top 8 stormwater harvesting sites.
The storage and distribution models showed that with a storage facility that has a capacity of 10x the maximum daily demand, high reliability figures can be achieved in excess of 80% in terms of volume and time-based reliability. The storage and distribution models also showed that if the storage capacity can be increased, the reliability and resilience of the facility can also be increased.
The study also has some limitations and intrinsic uncertainties, and the framework should be used as a screening tool.
This study places focus on stormwater harvesting as an integral part of sustainable management of urban water and presents a robust, adaptable and scalable tool that can support urban areas across Africa to address the growing water demand challenges.
...
Globally, the water sector is moving towards a circular water economy - where all water sources, including wastewater, stormwater and rainwater are treated as a resource that can be used, recycled, and replenished into the system. Stormwater harvesting (SWH) has successfully been implemented in countries such as Australia, Israel, Singapore & South Africa.
The success of any SWH scheme depends on effective site selection. Yet, there is little guidance available, and site choices have traditionally relied on the subjective judgment of urban water managers. This demonstrates the need for an objective, data-driven approach that integrates multiple spatial datasets to identify optimal SWH locations.
This research develops such a method: an integrated hydrological and GIS-based screening tool that identifies high yield (hotspot) SWH sites using publicly available datasets in Africa. The collection models showed that high yielding stormwater harvesting sites can be identified with publicly available data, with all 4 weightings consistently pointing out the top 8 stormwater harvesting sites.
The storage and distribution models showed that with a storage facility that has a capacity of 10x the maximum daily demand, high reliability figures can be achieved in excess of 80% in terms of volume and time-based reliability. The storage and distribution models also showed that if the storage capacity can be increased, the reliability and resilience of the facility can also be increased.
The study also has some limitations and intrinsic uncertainties, and the framework should be used as a screening tool.
This study places focus on stormwater harvesting as an integral part of sustainable management of urban water and presents a robust, adaptable and scalable tool that can support urban areas across Africa to address the growing water demand challenges.
...
Africa is the world’s second driest continent, supporting 15% of the global population with only 9% of the global renewable water resource. The 2015 to 2018 drought in the Western Cape of South Africa, where a Day-Zero scenario was narrowly avoided, highlighted the need to start looking at alternative water resources in conjunction with preserving the current water resources.
Globally, the water sector is moving towards a circular water economy - where all water sources, including wastewater, stormwater and rainwater are treated as a resource that can be used, recycled, and replenished into the system. Stormwater harvesting (SWH) has successfully been implemented in countries such as Australia, Israel, Singapore & South Africa.
The success of any SWH scheme depends on effective site selection. Yet, there is little guidance available, and site choices have traditionally relied on the subjective judgment of urban water managers. This demonstrates the need for an objective, data-driven approach that integrates multiple spatial datasets to identify optimal SWH locations.
This research develops such a method: an integrated hydrological and GIS-based screening tool that identifies high yield (hotspot) SWH sites using publicly available datasets in Africa. The collection models showed that high yielding stormwater harvesting sites can be identified with publicly available data, with all 4 weightings consistently pointing out the top 8 stormwater harvesting sites.
The storage and distribution models showed that with a storage facility that has a capacity of 10x the maximum daily demand, high reliability figures can be achieved in excess of 80% in terms of volume and time-based reliability. The storage and distribution models also showed that if the storage capacity can be increased, the reliability and resilience of the facility can also be increased.
The study also has some limitations and intrinsic uncertainties, and the framework should be used as a screening tool.
This study places focus on stormwater harvesting as an integral part of sustainable management of urban water and presents a robust, adaptable and scalable tool that can support urban areas across Africa to address the growing water demand challenges.
Globally, the water sector is moving towards a circular water economy - where all water sources, including wastewater, stormwater and rainwater are treated as a resource that can be used, recycled, and replenished into the system. Stormwater harvesting (SWH) has successfully been implemented in countries such as Australia, Israel, Singapore & South Africa.
The success of any SWH scheme depends on effective site selection. Yet, there is little guidance available, and site choices have traditionally relied on the subjective judgment of urban water managers. This demonstrates the need for an objective, data-driven approach that integrates multiple spatial datasets to identify optimal SWH locations.
This research develops such a method: an integrated hydrological and GIS-based screening tool that identifies high yield (hotspot) SWH sites using publicly available datasets in Africa. The collection models showed that high yielding stormwater harvesting sites can be identified with publicly available data, with all 4 weightings consistently pointing out the top 8 stormwater harvesting sites.
The storage and distribution models showed that with a storage facility that has a capacity of 10x the maximum daily demand, high reliability figures can be achieved in excess of 80% in terms of volume and time-based reliability. The storage and distribution models also showed that if the storage capacity can be increased, the reliability and resilience of the facility can also be increased.
The study also has some limitations and intrinsic uncertainties, and the framework should be used as a screening tool.
This study places focus on stormwater harvesting as an integral part of sustainable management of urban water and presents a robust, adaptable and scalable tool that can support urban areas across Africa to address the growing water demand challenges.
Overcoming challenges for the implementation of swale monitoring
An overview from the current practice to implementation
Extreme weather events such as heat waves and heavy rainfall are becoming more frequent due to climate change, threatening the liveability of urban environments. High building and infrastructure densities and impervious surfaces intensify heat and flood risks. This vulnerability has led to an increase in climate adaptation strategies, which often include the implementation of Nature based Solutions (NbS). In the Netherlands, one of the most widely used NbS is the swale, a green ditch that facilitates drainage, infiltration, and rainwater storage. Swales are seen as cost-effective and no-regret measures that, just as other NbS, can have multiple functions which provide multiple benefits. Despite these potential benefits, practitioners struggle with the design, development and maintenance of swales, partly due to limited local monitoring practices.
The research had two main objectives: (1) to explore current practice in research and in Dutch municipalities to identify performance criteria and monitoring techniques for swales to track the key functions of swales, and (2) to investigate motivators and challenges for municipal swale monitoring and develop a communication tool to address these.
A systematic literature review identified five key swale functions: water quantity, water quality, biodiversity, liveability and wellbeing. Water quantity and water quality functions are relatively well studied, with swales proven to reduce runoff and remove certain pollutants when properly designed and maintained. However, research is still lacking for the functions biodiversity, liveability, and wellbeing. The connections between the different functions were also explored, which showed the importance of recognising the connections and the influences of the different functions on each other. From this review, eight criteria were identified: infiltration rate, soil moisture, in- and outflow of pollutants, soil quality, vegetation development, temperature, resident experience and resident usage. For each criterion, quick-scan and in-depth monitoring techniques were proposed.
A survey among municipal workers who are involved with urban water management (mainly from South Holland) found that swales are seen as multifunctional objects, where water quantity and biodiversity are the most important functions. Monitoring is not part of the current practice, and swales are often only assessed on the functions during the design. However, there is interest in the implementation of monitoring, especially for water quantity and water quality. The main motivators for monitoring are to know the effect of swales on the long term and the ability to identify problems in time. The main challenges are keeping track of data and ensuring sufficient resources, like staff and budget.
To overcome these challenges, a workshop was designed to motivate practitioners to start monitoring the multiple swale functions. The workshop is aimed at municipal staff responsible for the organisation of maintenance for the different functions. By learning about the different functions and monitoring possibilities, the participants can create a monitoring plan that serves as a starting point for the actual implementation of monitoring. Evaluation by experts indicated that this workshop can motivate the target audience, because it increases the audience's awareness of swales, encourages them to consider the different functions and lets them practice with measuring, monitoring and retrieving data. It also provides them with a concrete and practical output that can be used in practice.
This study offers a framework to improve swale monitoring in the Netherlands. An overview of performance criteria with corresponding monitoring techniques is provided together with a communication tool that can bridge the gap between knowledge and practice.
...
The research had two main objectives: (1) to explore current practice in research and in Dutch municipalities to identify performance criteria and monitoring techniques for swales to track the key functions of swales, and (2) to investigate motivators and challenges for municipal swale monitoring and develop a communication tool to address these.
A systematic literature review identified five key swale functions: water quantity, water quality, biodiversity, liveability and wellbeing. Water quantity and water quality functions are relatively well studied, with swales proven to reduce runoff and remove certain pollutants when properly designed and maintained. However, research is still lacking for the functions biodiversity, liveability, and wellbeing. The connections between the different functions were also explored, which showed the importance of recognising the connections and the influences of the different functions on each other. From this review, eight criteria were identified: infiltration rate, soil moisture, in- and outflow of pollutants, soil quality, vegetation development, temperature, resident experience and resident usage. For each criterion, quick-scan and in-depth monitoring techniques were proposed.
A survey among municipal workers who are involved with urban water management (mainly from South Holland) found that swales are seen as multifunctional objects, where water quantity and biodiversity are the most important functions. Monitoring is not part of the current practice, and swales are often only assessed on the functions during the design. However, there is interest in the implementation of monitoring, especially for water quantity and water quality. The main motivators for monitoring are to know the effect of swales on the long term and the ability to identify problems in time. The main challenges are keeping track of data and ensuring sufficient resources, like staff and budget.
To overcome these challenges, a workshop was designed to motivate practitioners to start monitoring the multiple swale functions. The workshop is aimed at municipal staff responsible for the organisation of maintenance for the different functions. By learning about the different functions and monitoring possibilities, the participants can create a monitoring plan that serves as a starting point for the actual implementation of monitoring. Evaluation by experts indicated that this workshop can motivate the target audience, because it increases the audience's awareness of swales, encourages them to consider the different functions and lets them practice with measuring, monitoring and retrieving data. It also provides them with a concrete and practical output that can be used in practice.
This study offers a framework to improve swale monitoring in the Netherlands. An overview of performance criteria with corresponding monitoring techniques is provided together with a communication tool that can bridge the gap between knowledge and practice.
...
Extreme weather events such as heat waves and heavy rainfall are becoming more frequent due to climate change, threatening the liveability of urban environments. High building and infrastructure densities and impervious surfaces intensify heat and flood risks. This vulnerability has led to an increase in climate adaptation strategies, which often include the implementation of Nature based Solutions (NbS). In the Netherlands, one of the most widely used NbS is the swale, a green ditch that facilitates drainage, infiltration, and rainwater storage. Swales are seen as cost-effective and no-regret measures that, just as other NbS, can have multiple functions which provide multiple benefits. Despite these potential benefits, practitioners struggle with the design, development and maintenance of swales, partly due to limited local monitoring practices.
The research had two main objectives: (1) to explore current practice in research and in Dutch municipalities to identify performance criteria and monitoring techniques for swales to track the key functions of swales, and (2) to investigate motivators and challenges for municipal swale monitoring and develop a communication tool to address these.
A systematic literature review identified five key swale functions: water quantity, water quality, biodiversity, liveability and wellbeing. Water quantity and water quality functions are relatively well studied, with swales proven to reduce runoff and remove certain pollutants when properly designed and maintained. However, research is still lacking for the functions biodiversity, liveability, and wellbeing. The connections between the different functions were also explored, which showed the importance of recognising the connections and the influences of the different functions on each other. From this review, eight criteria were identified: infiltration rate, soil moisture, in- and outflow of pollutants, soil quality, vegetation development, temperature, resident experience and resident usage. For each criterion, quick-scan and in-depth monitoring techniques were proposed.
A survey among municipal workers who are involved with urban water management (mainly from South Holland) found that swales are seen as multifunctional objects, where water quantity and biodiversity are the most important functions. Monitoring is not part of the current practice, and swales are often only assessed on the functions during the design. However, there is interest in the implementation of monitoring, especially for water quantity and water quality. The main motivators for monitoring are to know the effect of swales on the long term and the ability to identify problems in time. The main challenges are keeping track of data and ensuring sufficient resources, like staff and budget.
To overcome these challenges, a workshop was designed to motivate practitioners to start monitoring the multiple swale functions. The workshop is aimed at municipal staff responsible for the organisation of maintenance for the different functions. By learning about the different functions and monitoring possibilities, the participants can create a monitoring plan that serves as a starting point for the actual implementation of monitoring. Evaluation by experts indicated that this workshop can motivate the target audience, because it increases the audience's awareness of swales, encourages them to consider the different functions and lets them practice with measuring, monitoring and retrieving data. It also provides them with a concrete and practical output that can be used in practice.
This study offers a framework to improve swale monitoring in the Netherlands. An overview of performance criteria with corresponding monitoring techniques is provided together with a communication tool that can bridge the gap between knowledge and practice.
The research had two main objectives: (1) to explore current practice in research and in Dutch municipalities to identify performance criteria and monitoring techniques for swales to track the key functions of swales, and (2) to investigate motivators and challenges for municipal swale monitoring and develop a communication tool to address these.
A systematic literature review identified five key swale functions: water quantity, water quality, biodiversity, liveability and wellbeing. Water quantity and water quality functions are relatively well studied, with swales proven to reduce runoff and remove certain pollutants when properly designed and maintained. However, research is still lacking for the functions biodiversity, liveability, and wellbeing. The connections between the different functions were also explored, which showed the importance of recognising the connections and the influences of the different functions on each other. From this review, eight criteria were identified: infiltration rate, soil moisture, in- and outflow of pollutants, soil quality, vegetation development, temperature, resident experience and resident usage. For each criterion, quick-scan and in-depth monitoring techniques were proposed.
A survey among municipal workers who are involved with urban water management (mainly from South Holland) found that swales are seen as multifunctional objects, where water quantity and biodiversity are the most important functions. Monitoring is not part of the current practice, and swales are often only assessed on the functions during the design. However, there is interest in the implementation of monitoring, especially for water quantity and water quality. The main motivators for monitoring are to know the effect of swales on the long term and the ability to identify problems in time. The main challenges are keeping track of data and ensuring sufficient resources, like staff and budget.
To overcome these challenges, a workshop was designed to motivate practitioners to start monitoring the multiple swale functions. The workshop is aimed at municipal staff responsible for the organisation of maintenance for the different functions. By learning about the different functions and monitoring possibilities, the participants can create a monitoring plan that serves as a starting point for the actual implementation of monitoring. Evaluation by experts indicated that this workshop can motivate the target audience, because it increases the audience's awareness of swales, encourages them to consider the different functions and lets them practice with measuring, monitoring and retrieving data. It also provides them with a concrete and practical output that can be used in practice.
This study offers a framework to improve swale monitoring in the Netherlands. An overview of performance criteria with corresponding monitoring techniques is provided together with a communication tool that can bridge the gap between knowledge and practice.
Soil Moisture Dynamics in Urban Areas
Identifying the relationship between soil moisture content and drought in urban areas
Master thesis
(2025)
-
M.S.J. van Zon, A.M.J. Coenders, Job van der Werf, J.G. Langeveld, Bor van der Scheer
Climate change poses increasing challenges to urban environments, with rising temperatures, sea-level rise, and altered precipitation patterns contributing to both flooding and drought. While much research has been dedicated to flood mitigation, urban drought has received comparatively less attention, despite its significant impact on vegetation, water availability, and overall ecosystem stability. The Paris Agreement of 2016 aims to limit global temperature increases, yet urban areas continue to experience extreme weather variations, necessitating a deeper understanding of their hydrological implications.
This thesis investigated the influence of urban environmental conditions on soil moisture dynamics, particularly during drought periods. The study aims to identify the relationship between green spaces in urban areas and soil moisture dynamics in relation to drought. It specifically examines how factors such as sun, shadow, vegetation type, and soil texture impact soil moisture retention and depletion. To achieve this research goal, the following three research questions are determined:
\begin{enumerate}[noitemsep]
\item How do urban environmental conditions affect soil moisture content in green spaces?
\item What is the effect of soil texture on soil moisture dynamics?
\item How do initial soil moisture conditions influence soil moisture dynamics during a drought period, as modelled using HYDRUS-1D?
\end{enumerate}
The study employs a combination of field measurements and HYDRUS-1D modelling, to analyse the soil moisture behaviour under different urban environmental conditions. Data collection took place at the campus of Delft University of Technology, where five distinct environmental conditions were selected as measurement points, sun, shadow, grass, trees and paved areas.
Soil moisture data was collected using the Profile Probe PR1 sensor (in combination with the HH2 Moisture Meter) at depths of 100mm, 200mm, 300mm, 600mm and 1000mm. Measurements were conducted manually over 10 weeks, 3 to 4 times a week, during the summer of 2024, with a total of 33 recorded sessions. Soil texture analysis was conducted using soil samples taken from depths of 150mm, 300mm, 500mm and 800mm. These samples were dried at 105$\degree$C for 24 hours and then sieved through six mesh sizes to determine the proportion of sand, silt and clay in each sample. The soil texture provided understanding of changes in soil moisture dynamics and was used for the critical input data for the HYDRUS-1D simulations.
HYDRUS-1D was employed to model the impact of initial soil moisture conditions and urban environmental conditions on the soil moisture dynamics during longer periods of drought. The model setup included defining soil hydraulic properties using the van Genuchten-Mualem equation and incorporating root water uptake parameters based on the Feddes approach. Monte Carlo simulations were conducted to optimize model performance, using 10.000 iterations to determine the best fitting parameters. The model was then applied to simulate soil moisture depletion during the extreme drought of 2018, to determine the effects of extremely wet or dry initial soil moisture conditions.
The measured soil moisture content results demonstrate significant variations in soil moisture retention among different urban environment conditions. Areas covered with vegetation exhibited higher moisture retention compared to paved surfaces. Within vegetated areas, shaded locations retained moisture for longer periods due to reduced evaporation rates. In contrast, measurement points in sunny areas experienced rapid soil moisture depletion, particularly in the upper 300mm of the soil.
Soil moisture at shallower depths, 100mm to 300mm, was highly responsive to precipitation events, while the deeper layers, 600mm and 1000mm, exhibited more stable moisture levels, indicating a stronger influence of soil texture and groundwater interactions. Statistical analysis using Kendall's and Spearman's correlation coefficients showed strong correlations between shaded grass-covered areas and tree-covered sites up to 300mm depth, but significant divergence beyond that, likely due to differences in root water uptake and soil texture.
Additionally, paved areas consistently maintained lower soil moisture levels across all depths due to limited infiltration, with only minor variations observed at the access tube edges where small gaps allowed some water entry. The modeling results confirmed that urban design choices, such as increasing permeable surfaces and optimizing vegetation placement, can significantly enhance urban resilience to drought.
Soil texture played a crucial role in soil moisture availability, with finer-textured soils (such as silt and clay) demonstrating superior retention capabilities compared to sandy soils, which facilitated rapid drainage.
Modeling results from HYDRUS-1D reinforced these findings, showing that initial soil moisture conditions had a notable influence on drought resilience. Wetter initial conditions resulted in prolonged moisture availability, while extremely dry conditions led to rapid soil desiccation. The impact of extreme initial soil moisture states was most pronounced in shaded grass areas and tree-covered locations, where higher retention capacity helped delay drought effects.
The study's findings align with existing literature on urban drought dynamics, confirming that meteorological, agricultural and hydrological drought factors interact to shape soil moisture behaviour. Meteorological drought, characterized by prolonged low precipitation, was found to be a primary driver of soil moisture deficits, with its effects compounded by urban environmental conditions. The research underscores the critical role of green infrastructure in mitigating the adverse effects of drought by preserving soil moisture.
The limitations of the study are acknowledged, including the constraints of the HYDRUS-1D model, which assumes only vertical water flow and does not account for lateral redistribution. Additionally, the generic settings of the Profile Probe PR1 resulted in soil moisture values not specifically related to the soil type. Finally, only one drought event has been evaluated in the model, limiting the generalizability of the findings.
This research provides valuable insight into the interplay between urban environmental conditions and soil moisture dynamics during drought periods. The findings highlight the importance of green spaces in urban resilience to drought, demonstrating that shaded and vegetated areas significantly enhance moisture retention compared to exposed, paved environments. Soil texture and initial moisture conditions were identified as key determinants of drought response, with finer-textured soils and wetter initial states offering greater resilience.
The study emphasizes the necessity of integrating soil moisture considerations into urban planning and climate change adaptation strategies. Enhancing green infrastructure, optimizing soil management practices, and incorporating soil moisture monitoring into urban water management can help mitigate the impacts of future drought events. Future research should focus on expanding the dataset across multiple urban locations and improving model accuracy by integrating groundwater dynamics and lateral water flow processes.
...
This thesis investigated the influence of urban environmental conditions on soil moisture dynamics, particularly during drought periods. The study aims to identify the relationship between green spaces in urban areas and soil moisture dynamics in relation to drought. It specifically examines how factors such as sun, shadow, vegetation type, and soil texture impact soil moisture retention and depletion. To achieve this research goal, the following three research questions are determined:
\begin{enumerate}[noitemsep]
\item How do urban environmental conditions affect soil moisture content in green spaces?
\item What is the effect of soil texture on soil moisture dynamics?
\item How do initial soil moisture conditions influence soil moisture dynamics during a drought period, as modelled using HYDRUS-1D?
\end{enumerate}
The study employs a combination of field measurements and HYDRUS-1D modelling, to analyse the soil moisture behaviour under different urban environmental conditions. Data collection took place at the campus of Delft University of Technology, where five distinct environmental conditions were selected as measurement points, sun, shadow, grass, trees and paved areas.
Soil moisture data was collected using the Profile Probe PR1 sensor (in combination with the HH2 Moisture Meter) at depths of 100mm, 200mm, 300mm, 600mm and 1000mm. Measurements were conducted manually over 10 weeks, 3 to 4 times a week, during the summer of 2024, with a total of 33 recorded sessions. Soil texture analysis was conducted using soil samples taken from depths of 150mm, 300mm, 500mm and 800mm. These samples were dried at 105$\degree$C for 24 hours and then sieved through six mesh sizes to determine the proportion of sand, silt and clay in each sample. The soil texture provided understanding of changes in soil moisture dynamics and was used for the critical input data for the HYDRUS-1D simulations.
HYDRUS-1D was employed to model the impact of initial soil moisture conditions and urban environmental conditions on the soil moisture dynamics during longer periods of drought. The model setup included defining soil hydraulic properties using the van Genuchten-Mualem equation and incorporating root water uptake parameters based on the Feddes approach. Monte Carlo simulations were conducted to optimize model performance, using 10.000 iterations to determine the best fitting parameters. The model was then applied to simulate soil moisture depletion during the extreme drought of 2018, to determine the effects of extremely wet or dry initial soil moisture conditions.
The measured soil moisture content results demonstrate significant variations in soil moisture retention among different urban environment conditions. Areas covered with vegetation exhibited higher moisture retention compared to paved surfaces. Within vegetated areas, shaded locations retained moisture for longer periods due to reduced evaporation rates. In contrast, measurement points in sunny areas experienced rapid soil moisture depletion, particularly in the upper 300mm of the soil.
Soil moisture at shallower depths, 100mm to 300mm, was highly responsive to precipitation events, while the deeper layers, 600mm and 1000mm, exhibited more stable moisture levels, indicating a stronger influence of soil texture and groundwater interactions. Statistical analysis using Kendall's and Spearman's correlation coefficients showed strong correlations between shaded grass-covered areas and tree-covered sites up to 300mm depth, but significant divergence beyond that, likely due to differences in root water uptake and soil texture.
Additionally, paved areas consistently maintained lower soil moisture levels across all depths due to limited infiltration, with only minor variations observed at the access tube edges where small gaps allowed some water entry. The modeling results confirmed that urban design choices, such as increasing permeable surfaces and optimizing vegetation placement, can significantly enhance urban resilience to drought.
Soil texture played a crucial role in soil moisture availability, with finer-textured soils (such as silt and clay) demonstrating superior retention capabilities compared to sandy soils, which facilitated rapid drainage.
Modeling results from HYDRUS-1D reinforced these findings, showing that initial soil moisture conditions had a notable influence on drought resilience. Wetter initial conditions resulted in prolonged moisture availability, while extremely dry conditions led to rapid soil desiccation. The impact of extreme initial soil moisture states was most pronounced in shaded grass areas and tree-covered locations, where higher retention capacity helped delay drought effects.
The study's findings align with existing literature on urban drought dynamics, confirming that meteorological, agricultural and hydrological drought factors interact to shape soil moisture behaviour. Meteorological drought, characterized by prolonged low precipitation, was found to be a primary driver of soil moisture deficits, with its effects compounded by urban environmental conditions. The research underscores the critical role of green infrastructure in mitigating the adverse effects of drought by preserving soil moisture.
The limitations of the study are acknowledged, including the constraints of the HYDRUS-1D model, which assumes only vertical water flow and does not account for lateral redistribution. Additionally, the generic settings of the Profile Probe PR1 resulted in soil moisture values not specifically related to the soil type. Finally, only one drought event has been evaluated in the model, limiting the generalizability of the findings.
This research provides valuable insight into the interplay between urban environmental conditions and soil moisture dynamics during drought periods. The findings highlight the importance of green spaces in urban resilience to drought, demonstrating that shaded and vegetated areas significantly enhance moisture retention compared to exposed, paved environments. Soil texture and initial moisture conditions were identified as key determinants of drought response, with finer-textured soils and wetter initial states offering greater resilience.
The study emphasizes the necessity of integrating soil moisture considerations into urban planning and climate change adaptation strategies. Enhancing green infrastructure, optimizing soil management practices, and incorporating soil moisture monitoring into urban water management can help mitigate the impacts of future drought events. Future research should focus on expanding the dataset across multiple urban locations and improving model accuracy by integrating groundwater dynamics and lateral water flow processes.
...
Climate change poses increasing challenges to urban environments, with rising temperatures, sea-level rise, and altered precipitation patterns contributing to both flooding and drought. While much research has been dedicated to flood mitigation, urban drought has received comparatively less attention, despite its significant impact on vegetation, water availability, and overall ecosystem stability. The Paris Agreement of 2016 aims to limit global temperature increases, yet urban areas continue to experience extreme weather variations, necessitating a deeper understanding of their hydrological implications.
This thesis investigated the influence of urban environmental conditions on soil moisture dynamics, particularly during drought periods. The study aims to identify the relationship between green spaces in urban areas and soil moisture dynamics in relation to drought. It specifically examines how factors such as sun, shadow, vegetation type, and soil texture impact soil moisture retention and depletion. To achieve this research goal, the following three research questions are determined:
\begin{enumerate}[noitemsep]
\item How do urban environmental conditions affect soil moisture content in green spaces?
\item What is the effect of soil texture on soil moisture dynamics?
\item How do initial soil moisture conditions influence soil moisture dynamics during a drought period, as modelled using HYDRUS-1D?
\end{enumerate}
The study employs a combination of field measurements and HYDRUS-1D modelling, to analyse the soil moisture behaviour under different urban environmental conditions. Data collection took place at the campus of Delft University of Technology, where five distinct environmental conditions were selected as measurement points, sun, shadow, grass, trees and paved areas.
Soil moisture data was collected using the Profile Probe PR1 sensor (in combination with the HH2 Moisture Meter) at depths of 100mm, 200mm, 300mm, 600mm and 1000mm. Measurements were conducted manually over 10 weeks, 3 to 4 times a week, during the summer of 2024, with a total of 33 recorded sessions. Soil texture analysis was conducted using soil samples taken from depths of 150mm, 300mm, 500mm and 800mm. These samples were dried at 105$\degree$C for 24 hours and then sieved through six mesh sizes to determine the proportion of sand, silt and clay in each sample. The soil texture provided understanding of changes in soil moisture dynamics and was used for the critical input data for the HYDRUS-1D simulations.
HYDRUS-1D was employed to model the impact of initial soil moisture conditions and urban environmental conditions on the soil moisture dynamics during longer periods of drought. The model setup included defining soil hydraulic properties using the van Genuchten-Mualem equation and incorporating root water uptake parameters based on the Feddes approach. Monte Carlo simulations were conducted to optimize model performance, using 10.000 iterations to determine the best fitting parameters. The model was then applied to simulate soil moisture depletion during the extreme drought of 2018, to determine the effects of extremely wet or dry initial soil moisture conditions.
The measured soil moisture content results demonstrate significant variations in soil moisture retention among different urban environment conditions. Areas covered with vegetation exhibited higher moisture retention compared to paved surfaces. Within vegetated areas, shaded locations retained moisture for longer periods due to reduced evaporation rates. In contrast, measurement points in sunny areas experienced rapid soil moisture depletion, particularly in the upper 300mm of the soil.
Soil moisture at shallower depths, 100mm to 300mm, was highly responsive to precipitation events, while the deeper layers, 600mm and 1000mm, exhibited more stable moisture levels, indicating a stronger influence of soil texture and groundwater interactions. Statistical analysis using Kendall's and Spearman's correlation coefficients showed strong correlations between shaded grass-covered areas and tree-covered sites up to 300mm depth, but significant divergence beyond that, likely due to differences in root water uptake and soil texture.
Additionally, paved areas consistently maintained lower soil moisture levels across all depths due to limited infiltration, with only minor variations observed at the access tube edges where small gaps allowed some water entry. The modeling results confirmed that urban design choices, such as increasing permeable surfaces and optimizing vegetation placement, can significantly enhance urban resilience to drought.
Soil texture played a crucial role in soil moisture availability, with finer-textured soils (such as silt and clay) demonstrating superior retention capabilities compared to sandy soils, which facilitated rapid drainage.
Modeling results from HYDRUS-1D reinforced these findings, showing that initial soil moisture conditions had a notable influence on drought resilience. Wetter initial conditions resulted in prolonged moisture availability, while extremely dry conditions led to rapid soil desiccation. The impact of extreme initial soil moisture states was most pronounced in shaded grass areas and tree-covered locations, where higher retention capacity helped delay drought effects.
The study's findings align with existing literature on urban drought dynamics, confirming that meteorological, agricultural and hydrological drought factors interact to shape soil moisture behaviour. Meteorological drought, characterized by prolonged low precipitation, was found to be a primary driver of soil moisture deficits, with its effects compounded by urban environmental conditions. The research underscores the critical role of green infrastructure in mitigating the adverse effects of drought by preserving soil moisture.
The limitations of the study are acknowledged, including the constraints of the HYDRUS-1D model, which assumes only vertical water flow and does not account for lateral redistribution. Additionally, the generic settings of the Profile Probe PR1 resulted in soil moisture values not specifically related to the soil type. Finally, only one drought event has been evaluated in the model, limiting the generalizability of the findings.
This research provides valuable insight into the interplay between urban environmental conditions and soil moisture dynamics during drought periods. The findings highlight the importance of green spaces in urban resilience to drought, demonstrating that shaded and vegetated areas significantly enhance moisture retention compared to exposed, paved environments. Soil texture and initial moisture conditions were identified as key determinants of drought response, with finer-textured soils and wetter initial states offering greater resilience.
The study emphasizes the necessity of integrating soil moisture considerations into urban planning and climate change adaptation strategies. Enhancing green infrastructure, optimizing soil management practices, and incorporating soil moisture monitoring into urban water management can help mitigate the impacts of future drought events. Future research should focus on expanding the dataset across multiple urban locations and improving model accuracy by integrating groundwater dynamics and lateral water flow processes.
This thesis investigated the influence of urban environmental conditions on soil moisture dynamics, particularly during drought periods. The study aims to identify the relationship between green spaces in urban areas and soil moisture dynamics in relation to drought. It specifically examines how factors such as sun, shadow, vegetation type, and soil texture impact soil moisture retention and depletion. To achieve this research goal, the following three research questions are determined:
\begin{enumerate}[noitemsep]
\item How do urban environmental conditions affect soil moisture content in green spaces?
\item What is the effect of soil texture on soil moisture dynamics?
\item How do initial soil moisture conditions influence soil moisture dynamics during a drought period, as modelled using HYDRUS-1D?
\end{enumerate}
The study employs a combination of field measurements and HYDRUS-1D modelling, to analyse the soil moisture behaviour under different urban environmental conditions. Data collection took place at the campus of Delft University of Technology, where five distinct environmental conditions were selected as measurement points, sun, shadow, grass, trees and paved areas.
Soil moisture data was collected using the Profile Probe PR1 sensor (in combination with the HH2 Moisture Meter) at depths of 100mm, 200mm, 300mm, 600mm and 1000mm. Measurements were conducted manually over 10 weeks, 3 to 4 times a week, during the summer of 2024, with a total of 33 recorded sessions. Soil texture analysis was conducted using soil samples taken from depths of 150mm, 300mm, 500mm and 800mm. These samples were dried at 105$\degree$C for 24 hours and then sieved through six mesh sizes to determine the proportion of sand, silt and clay in each sample. The soil texture provided understanding of changes in soil moisture dynamics and was used for the critical input data for the HYDRUS-1D simulations.
HYDRUS-1D was employed to model the impact of initial soil moisture conditions and urban environmental conditions on the soil moisture dynamics during longer periods of drought. The model setup included defining soil hydraulic properties using the van Genuchten-Mualem equation and incorporating root water uptake parameters based on the Feddes approach. Monte Carlo simulations were conducted to optimize model performance, using 10.000 iterations to determine the best fitting parameters. The model was then applied to simulate soil moisture depletion during the extreme drought of 2018, to determine the effects of extremely wet or dry initial soil moisture conditions.
The measured soil moisture content results demonstrate significant variations in soil moisture retention among different urban environment conditions. Areas covered with vegetation exhibited higher moisture retention compared to paved surfaces. Within vegetated areas, shaded locations retained moisture for longer periods due to reduced evaporation rates. In contrast, measurement points in sunny areas experienced rapid soil moisture depletion, particularly in the upper 300mm of the soil.
Soil moisture at shallower depths, 100mm to 300mm, was highly responsive to precipitation events, while the deeper layers, 600mm and 1000mm, exhibited more stable moisture levels, indicating a stronger influence of soil texture and groundwater interactions. Statistical analysis using Kendall's and Spearman's correlation coefficients showed strong correlations between shaded grass-covered areas and tree-covered sites up to 300mm depth, but significant divergence beyond that, likely due to differences in root water uptake and soil texture.
Additionally, paved areas consistently maintained lower soil moisture levels across all depths due to limited infiltration, with only minor variations observed at the access tube edges where small gaps allowed some water entry. The modeling results confirmed that urban design choices, such as increasing permeable surfaces and optimizing vegetation placement, can significantly enhance urban resilience to drought.
Soil texture played a crucial role in soil moisture availability, with finer-textured soils (such as silt and clay) demonstrating superior retention capabilities compared to sandy soils, which facilitated rapid drainage.
Modeling results from HYDRUS-1D reinforced these findings, showing that initial soil moisture conditions had a notable influence on drought resilience. Wetter initial conditions resulted in prolonged moisture availability, while extremely dry conditions led to rapid soil desiccation. The impact of extreme initial soil moisture states was most pronounced in shaded grass areas and tree-covered locations, where higher retention capacity helped delay drought effects.
The study's findings align with existing literature on urban drought dynamics, confirming that meteorological, agricultural and hydrological drought factors interact to shape soil moisture behaviour. Meteorological drought, characterized by prolonged low precipitation, was found to be a primary driver of soil moisture deficits, with its effects compounded by urban environmental conditions. The research underscores the critical role of green infrastructure in mitigating the adverse effects of drought by preserving soil moisture.
The limitations of the study are acknowledged, including the constraints of the HYDRUS-1D model, which assumes only vertical water flow and does not account for lateral redistribution. Additionally, the generic settings of the Profile Probe PR1 resulted in soil moisture values not specifically related to the soil type. Finally, only one drought event has been evaluated in the model, limiting the generalizability of the findings.
This research provides valuable insight into the interplay between urban environmental conditions and soil moisture dynamics during drought periods. The findings highlight the importance of green spaces in urban resilience to drought, demonstrating that shaded and vegetated areas significantly enhance moisture retention compared to exposed, paved environments. Soil texture and initial moisture conditions were identified as key determinants of drought response, with finer-textured soils and wetter initial states offering greater resilience.
The study emphasizes the necessity of integrating soil moisture considerations into urban planning and climate change adaptation strategies. Enhancing green infrastructure, optimizing soil management practices, and incorporating soil moisture monitoring into urban water management can help mitigate the impacts of future drought events. Future research should focus on expanding the dataset across multiple urban locations and improving model accuracy by integrating groundwater dynamics and lateral water flow processes.
Live Pole Drains (LPDs) are a plant-based drainage system used to drain natural slopes and prevent shallow gully erosion. LPDs are a Nature-based Solution built by placing a live fascine in a shallow ditch or gully along the slope direction, allowing moderate fluxes of surface runoff or seepage to infiltrate and high water fluxes to be conveyed along the fascine without further eroding the slope. Despite their practical implementation, the transient and long-term eco-hydrological behavior of LPDs is not well understood. We aim to better understand the LPD’s water balance, the seasonal and life-span changes in hydrological behavior, as well as the impact of an LPD on surface runoff water quality. To this end, we built and instrumented an artificial slope with full-scale LPDs in an open-air lab (OAL) at TU Delft. The design of the setup and the monitoring plan of the LPDs were developed in collaboration with Glasgow Caledonian University with insights from the construction and monitoring of three LPDs at different growth stages in their OAL on the east coast of Scotland. Herein, the design and possible research experiments that can be performed over the next 5 years are presented, generating a data set to further develop and validate hydrological modeling of LPDs. We expect this long-term demonstrative setup to generate interest and facilitate a more comprehensive understanding of LPD functions, ultimately leading to the incorporation of LPD design and maintenance standards in engineering toolboxes for slope and gully stabilization.
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Live Pole Drains (LPDs) are a plant-based drainage system used to drain natural slopes and prevent shallow gully erosion. LPDs are a Nature-based Solution built by placing a live fascine in a shallow ditch or gully along the slope direction, allowing moderate fluxes of surface runoff or seepage to infiltrate and high water fluxes to be conveyed along the fascine without further eroding the slope. Despite their practical implementation, the transient and long-term eco-hydrological behavior of LPDs is not well understood. We aim to better understand the LPD’s water balance, the seasonal and life-span changes in hydrological behavior, as well as the impact of an LPD on surface runoff water quality. To this end, we built and instrumented an artificial slope with full-scale LPDs in an open-air lab (OAL) at TU Delft. The design of the setup and the monitoring plan of the LPDs were developed in collaboration with Glasgow Caledonian University with insights from the construction and monitoring of three LPDs at different growth stages in their OAL on the east coast of Scotland. Herein, the design and possible research experiments that can be performed over the next 5 years are presented, generating a data set to further develop and validate hydrological modeling of LPDs. We expect this long-term demonstrative setup to generate interest and facilitate a more comprehensive understanding of LPD functions, ultimately leading to the incorporation of LPD design and maintenance standards in engineering toolboxes for slope and gully stabilization.