Evaluation of the hydrological performance of grassed swales usually needs long-term monitoring data. At present, suitable techniques for simulating the hydrological performance using limited monitoring data are not available. Therefore, current study aims to investigate the relationship between saturated hydraulic conductivity (Ks) fitting results and rainfall characteristics of various events series length. Data from a full-scale grassed swale (Enschede, the Netherlands) were utilized as long-term rainfall event series length (95 rainfall events) on the fitting outcomes. Short-term rainfall event series were extracted from these long-term series and used as input in fitting into a multivariate nonlinear model between Ks and its influencing rainfall indicators (antecedent dry days, temperature, rainfall, rainfall duration, total rainfall, and seasonal factor (spring, summer, autumn, and winter, herein refer as 1, 2, 3, and 4). Comparison of short-term and long-term rainfall event series fitting results allowed to obtain a representative short-term series that leads to similar results with those using long-term series. A cluster analysis was conducted based on the fitting results of the representative rainfall event series with their rainfall event characteristics using average values of influencing rainfall indicators. The seasonal index (average value of seasonal factors) was found to be the most representative short rainfall event series indicator. Furthermore, a Bayesian network was proposed in the current study to predict if a given short-term rainfall event series is representative. It was validated by a data series (58 rainfall events) from another full-scale grassed swale located in Utrecht, the Netherlands. Results revealed that it is quite promising and useful to evaluate the representativeness of short-term rainfall event series used for long-term hydrological performance evaluation of grassed swales.
DOCUMENT
The stability of upstream deposited tailings dams is dependent on maintaining a drawn down phreatic surface and unsaturated profile in its outer edge. However, it has been speculated that intense rainfall events could induce unexpected translation of pore air and water pressures into the tailings profile and thus compromise the effective stress in the unsaturated zone or result in a sudden rise in the phreatic surface. This phenomenon, known as the Lisse effect, has been observed and studied in hydrological sciences to explain the rapid delivery of antecedent hillslope groundwater during storm events. However, the phenomenon has not been comprehensively applied to evaluating tailings dam slope stability. In this paper, the outcomes of controlled observations of the phenomenon in column and analytical experiments, are assembled and evaluated in terms of the surface water application volumes and rate, the properties of the porous media and the resultant nature of pore pressure and phreatic surface responses. In addition, application of applied theories to evaluate the rapid transmission of pore pressures through a profile in response to an advancing wetting front, leads to the development of a methodology that could be applied to tailings materials of a range of hydraulic conductivities and water retention characteristics. The theory is applied to a series of profiles of different tailings porous media, using varied water application rates. Resultant perturbations in phreatic surface elevation and changes to pore pressures in the unsaturated zone are used to evaluate changes in effective stress distribution in the unsaturated outer wedge and subsequent stability criteria. A possible evaluation algorithm for assessing stability criteria is suggested.
MULTIFILE
Natural disasters are a growing concern around the globe. In the Netherlands, water has always played an important role as both friend and enemy. To quickly analyze and visualise possible disaster outcomes has been really difficult. In collaboration with engineering company Tauw we improved this modellingwith an interdisciplinary team of GIS experts, High performance computing and real time visualisation. In a pilot for the city center of Groningen we developed a 3D version of flooding landscape maps (RUG, 2014) after modelling extreme rainfall. With a flooding landscape map you can see at a glance where water isgoing and where problem areas arise in case of extreme rainfall. Any municipality or county can thus quickly determine which measures are to be taken to prevent for example disruption to traffic or flooding damage tobuildings.
DOCUMENT
Due to climate change the frequency of extreme precipitation increases. To reduce the risk of damage by flooding, municipalities will need to retrofit urban areas in a climate-resilient way. To justify this investment, they need insight in possibilities and costs of climate-resilient urban street designs. This chapter focused on how to retrofit characteristic (Dutch) typologies of urban residential areas. For ten cases alternative street layouts were designed with a determination of the life cycle costs and benefits. All designs are resilient to extreme rain events. The results show that most flat urban typologies can easily be retrofitted in a climate-resilient way without additional costs compared to the standard way of retrofitting. Climate proofing sloping areas are highly dependent on the situation downstream. When there is no space downstream to divert the water into waterways or parks, costs to provide storage easily rise above traditional levels for retrofitting. In addition to reducing flood risk, for each case one variant includes resilience to extreme heat events making use of green. The life cycle costs and benefits of the green variants showed that especially green designs in high-density urban areas result in a better value for money.
MULTIFILE
Swales are widely used Sustainable Urban Drainage Systems (SuDS) that can reduce peak flow, collect and retain water and improve groundwater recharge. Most previous research has focused on the unsaturated infiltration rates of swales without considering the variation in infiltration rates under extreme climate events, such as multiple stormwater events after a long drought period. Therefore, fieldwork was carried out to collect hydraulic data of three swales under drought conditions followed by high precipitation. For this simulation, a new full-scale infiltration method was used to simulate five rainfall events filling up the total storage volume of the swales under drought conditions. The results were then compared to earlier research under regular circumstances. The results of this study show that three swales situated in the same street show a variation in initial infiltration capacity of 1.6 to 11.9 m/d and show higher infiltration rates under drought conditions. The saturated infiltration rate is up to a factor 4 lower than the initial unsaturated rate with a minimal rate of 0.5 m/d, close to the minimum required infiltration rate. Significant spatial and time variable infiltration rates are also found at similar research locations with multiple green infrastructures in close range. If the unsaturated infiltration capacity is used as the design input for computer models, the infiltration capacity may be significantly overestimated. The innovative method and the results of this study should help stormwater managers to test, model, plan and schedule maintenance requirements with more confidence, so that they will continue to perform satisfactorily over their intended design lifespan.
DOCUMENT
In today’s city environments, extreme weather conditions are a fact oflife. Amsterdam, Mumbai, Nairobi or Sydney… climate change issuesneed to be tackled all around the world.In the last couple of decades, Amsterdam has dealt with largeramounts of rainwater, severe heat stress and a decreased biodiversity.In order to strengthen urban resilience to climate change, blue-green(BG) roofs are increasingly being introduced. BG roofs placean additional water layer underneath the green layer. The idea is thatthese roofs reduce runoff after rainfall by retaining precipitation andmitigate heat stress, caused by increased evapotranspiration (the sumof evaporation from the land surface and transpiration from plants)and a higher albedo effect (the ability of surfaces to reflect sunlight).
MULTIFILE
The Northern Netherlands is like many delta’s prone to a wide range of climate change effects. Given the region its long history with floods and adaptation, there are numerous initiatives to be found that tried to battle these effects. As part of the Climate Adaptation Week Groningen, an inventory was made of these initiatives. The most inspiring ones were coined ‘best practices’, and analysed in order to learn lessons. A distinction was made between 4 regional landscape types. The first consists of the coastline itself, where the effects of the rising sea level begin to show. The second covers the farmlands near the coastlines, where challenges such as salinisation and the loss of biodiversity prevail. A third landscape covers the historically compact cities, which have to deal with rising temperatures and heavy rainfall in increasingly limited spaces. The fourth and final landscape comprises the wetlands surrounding the cities, where the natural capacity to retain and store rainwater is undermined by its agriculture usage. Most of these challenges form a risk for maintaining a liveable region. The best practices that were collected show a diverse set of innovations and experiments, both on small and large scales. Three main characteristics could be distinguished that illustrate trends in climate adaptation practices. First, many best practices were aimed at restoring and embracing the natural capacity of the different landscapes, giving more and more room for the building with nature concept as part of building resilience. Second, climate adaptation is seldomly focussed on as the sole function of a spatial intervention, and is almost always part of integrated plans in which biodiversity, agriculture, recreation or other themes are prolonged with it. A third and last characteristic shows that many projects embed a strong focus on the historical context of places as a source of inspiration and cultural identity. The best practices show how different ways of adapting are emerging and can inspire planners across the world.
DOCUMENT
Bergen city centre is prone to both subsidence and flooding. With a predicted increase in precipitation due to climate change, a higher proportion of rainfall becomes surface runoff, which results in increased peak flood discharges. In addition, it has been predicted that sea-level rise and increasing storm surges will result in coastal flooding. In this study, the dual hazards of flooding and subsidence are analysed to exemplify possible risk assessment maps for areas most prone to the combination of both. Risk assessment maps are a support tool to identify areas where mitigation of subsidence and adaptation for surface water management will be most efficient and measures can be implemented. The results show that dual hazard assessment, like that described in this paper, can be a useful tool for decision-makers when prioritizing areas to implement measures such as Sustainable Urban Drainage Systems.
MULTIFILE
The changing climate has an effect on the quality of life in our cities: heavier rainfall (resulting infloodings), longer periods of drought, reduced air and water quality and increasing temperatures incities (heat stress). Awareness about these changes among various stakeholders is of greatimportance. Every Dutch region is required to perform a stresstest indicating the effects of climatechange (o.a. flooding and heatstress) before 2020. The level of execution, area size and level ofparticipation of stakeholders, has intentionally been made flexible.To provide more insight into the approaches and best management practices to climate resilience,this article provides 3 examples of stresstests performed on several levels: single object real estatelevel, city level and national district level. The method ‘stresstestíng’, involves flood and heatstressmodeling, defines the current status of climate adaptation characteristics of an object, city or district.The stresstest form the base line and starting point for the national 3 step approach adaptationstrategy ‘analyse, ambition and action’.The 3 pilots have been evaluated as ‘successful’ by stakeholders and yielded a significant amount ofvaluable information, further improvement is recommended as increasing the participation of theprivate sector, in a ‘quadruple helix approach’. The learning points from these 3 examples ofstresstests will subsequently be implemented in the form of improved stresstesting in the nearfuture in (inter)national cities around the world.
DOCUMENT
Permanent grassland soils can act as a sink for carbon and may therefore positively contribute to climate change mitigation and adaptation. We compared young (5–15 years since latest grassland renewal) with old (>20 years since latest grassland renewal) permanent grassland soils in terms of carbon stock, carbon sequestration, drought tolerance and flood resistance. The research was carried out on marine clay soil at 10 dairy farms with young and old permanent grassland. As hypothesized, the carbon stock was larger in old grassland (62 Mg C ha−1) topsoil (0–10 cm) than in young grassland topsoil (51 Mg C ha−1). The carbon sequestration rate was greater in young (on average 3.0 Mg C ha−1 year−1) compared with old grassland (1.6 Mg C ha−1 year−1) and determined by initial carbon stock. Regarding potential drought tolerance, we found larger soil moisture and soil organic matter (SOM) contents in old compared with young grassland topsoils. As hypothesized, the old grassland soils were more resistant to heavy rainfall as measured by water infiltration rate and macroporosity (at 20 cm depth) in comparison with the young grassland soils. In contrast to our hypothesis we did not find a difference in rooting between young and old permanent grassland, probably due to large variability in root biomass and root tip density. We conclude that old grasslands at dairy farms on clay soil can contribute more to the ecosystem services climate change mitigation and climate change adaptation than young grasslands. This study shows that under real farm conditions on a clay topsoil, carbon stock increases with grassland age and even after 30 years carbon saturation has not been reached. Further study is warranted to determine by how much extending grassland age can contribute to climate change mitigation and adaptation.
DOCUMENT
