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| 2. |
- Broekhuizen, Ico, et al.
(författare)
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Calibration event selection for green urban drainage modelling
- 2019
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Annan publikation (populärvet., debatt m.m.)abstract
- Calibration of urban drainage models is typically performed based on a limited number of observed rainfall-runoff events, which may be selected from a longer time-series of measurements in different ways. In this study, 14 single- and two-stage strategies for selecting these events were tested for calibration of a SWMM model of a predominantly green urban area. The event selection was considered in relation to other sources of uncertainty such as measurement uncertainties, objective functions, and catchment discretization. Even though all 14 strategies resulted in successful model calibration, the difference between the best and worst strategies reached 0.2 in Nash–Sutcliffe Efficiency (NSE) and the calibrated parameter values notably varied. Most, but not all, calibration strategies were robust to changes in objective function, perturbations in calibration data and the use of a low spatial resolution model in the calibration phase. The various calibration strategies satisfactorily predicted 7 to 13 out of 19 validation events. The two-stage strategies performed better than the single-stage strategies when measuring performance using the Root Mean Square Error, flow volume error or peak flow error (but not using NSE); when flow data in the calibration period had been perturbed by ±40 %; and when using a lower model resolution. The two calibration strategies that performed best in the validation period were two-stage strategies. The findings in this paper show that different strategies for selecting calibration events may lead in some cases to different results for the validation period, and that calibrating impermeable and green area parameters in two separate steps may improve model performance in the validation period, while also reducing the computational demand in the calibration phase.
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| 3. |
- Broekhuizen, Ico, et al.
(författare)
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Design av biofilter för ökad flödesfördröjning
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Biofilter används idag mest i syfte att förbättra vattenkvalitet, men med tanke på framtida klimatförändringar är det intressant att se om de även kan bidra till minskade översvämningsrisker. Att öka lagringskapaciteten kan göras genom att öka lagringsvolymen på ytan eller att öka dräneringslagrets tjocklek. Denna skrift visar vilka effekter detta har på filtrets hydrologiska prestanda.
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| 4. |
- Broekhuizen, Ico, et al.
(författare)
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Event selection and two-stage approach for calibrating models of green urban drainage systems
- 2020
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Ingår i: Hydrology and Earth System Sciences. - : Nicolaus Copernicus University Press. - 1027-5606 .- 1607-7938. ; 24, s. 869-885
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of urban drainage models is typically performed based on a limited number of observed rainfall–runoff events, which may be selected from a larger dataset in different ways. In this study, 14 single- and two-stage strategies for selecting the calibration events were tested in calibration of a high- and low-resolution Storm Water Management Model (SWMM) of a predominantly green urban area. The two-stage strategies used events with runoff only from impervious areas to calibrate the associated parameters, prior to using larger events to calibrate the parameters relating to green areas. Even though all 14 strategies resulted in successful model calibration (Nash–Sutcliffe efficiency; NSE >0.5), the difference between the best and worst strategies reached 0.2 in the NSE, and the calibrated parameter values notably varied. The various calibration strategies satisfactorily predicted 7 to 13 out of 19 validation events. The two-stage strategies reproduced more validation events poorly (NSE <0) than the single-stage strategies, but they also reproduced more events well (NSE >0.5) and performed better than the single-stage strategies in terms of total runoff volume and peak flow rates, particularly when using a low spatial model resolution. The results show that various strategies for selecting calibration events may lead in some cases to different results in the validation phase and that calibrating impervious and green-area parameters in two separate steps in two-stage strategies may increase the effectiveness of model calibration and validation by reducing the computational demand in the calibration phase and improving model performance in the validation phase.
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| 5. |
- Broekhuizen, Ico, et al.
(författare)
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Flödesstrypning i svackdiken för minskad översvämningsrisk
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Klimatförändring och urbanisering leder till allt större översvämningsrisker i våra städer. Därför finns det ett behov av yteffektiva åtgärder för att hålla riskerna begränsade. En sådan lösning kan vara att strypa utflödet från svackdiken för att tillfälligt lagra mer vatten och öka andelen som kan infiltrera i marken. I denna studie har fältförsök genomförts för att kvantifiera effekten av en sådan lösning för regn med återkomsttider mellan 1 och 50 år. Resultaten visar att såväl flödesvolym som maxflöde kan minskas med upp till 32% för mindre regntillfällen. Effekten av flödesstrypningen blir dock mindre för större regntillfällen, och ytterliggare designalternativ bör utredas.
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| 6. |
- Broekhuizen, Ico
(författare)
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Hydrological modelling of green urban drainage systems : Advancing the understanding and management of uncertainties in data, model structure and objective functions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of green urban drainage systems such as green roofs, swales and pervious areas has in recent years become a popular option to reduce flood risk and water quality problems in a more sustainable way than with traditional pipe-based drainage systems. Computer models are valuable tools for the management of such systems. While uncertainties associated with these models have been investigated for pipe-based systems, their adaptation and application to green areas requires re-examination of these uncertainties, as additional hydrological processes become relevant and new opportunities for model calibration arise. The overall aim of this thesis is to contribute to understanding and reducing of uncertainties in the mathematical modelling of green urban drainage studies. Specific topics adressed are field measurements, data processing, data selection, model structures and objective functions.Weighing-bucket precipitation sensors were confirmed on multiple occasions to be accurate to within ±1% of accumulated precipitation. A new signal processing method was able to convert accumulated precipitation to noise-free 1-minute rainfall rates that reproduced total rainfall volumes with only minor errors.Area-velocity flow sensors were tested and their measurement uncertainties quantified in laboratory experiments for flow rates up to 9 L s-1. Total flow rate uncertainty was ±0.34 L s-1 in optimal conditions (flat pipe), increasing to 0.60 and 0.83 L s-1 for pipe slopes of 2% and 4% respectively. In the presence of an upstream obstacle the uncertainty was 2 to 3 times larger, although in the case of no pipe slope this could be reduced to the same as the optimal conditions by increasing water levels in the pipe.Three different urban drainage models for green areas were compared using long-term simulations of synthetic catchments with different soil types and depth. In all models surface runoff formed a significant component of the annual water balance for some soil profiles, while the models reacted differently to changes in soil type an depth. Inter-model variation was large compared to the variation between different soil profiles.Four different models were tested for the simulation of runoff from two full-scale green roofs. More complex models showed better performance in reproducing observed runoff, while the magnitude and source of model predictive uncertainties varied between the models. It was also found that for all models calibration periods with high inter-event variability in terms of runoff retention provided more information in the calibration process.The use of soil water content observations (SWC) was investigated for the calibration of a detailed model of an urban swale. SWC observations were found to be useful for improving the identifiability of certain model parameters and the model predictions of SWC, and for setting the initial SWC in simulations. Different approaches to combining SWC and outflow observations were compared, revealing that the precision and reliability of model predictions could in some cases be improved by using a different way of determining which parameter sets to use for the generation of uncertain model predictions.The influence of calibration data selection was investigated using a model of a small green urban catchment. Performance of the model when calibrated using different sets of events varied significantly. Two-stage calibration strategies (where first small rainfall events were used to calibrate impervious area parameters, followed by using larger events to calibrate green area parameters) showed good performance especially in terms of runoff volume and peak flow. Finally it was found that the benefits of the two-stage calibration were greater when using a model with a low spatial resolution than with a high spatial resolution.For the same catchment tests were also carried out of an objective function that explicitly allows for timing errors, rather than comparing only simulated and observed values for the same time step. Model predictions generated using this objective function were equally reliable, but more precise and therefore of more practical value.Finally, drawing upon the practical experience from working with different models and drainage systems an overview is provided of the applicability of the modelling techniques used in this thesis for different models and what features may be desirable to add to models to improve this.
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| 7. |
- Broekhuizen, Ico
(författare)
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Hydrologisk modelleringav gröna tak
- 2021
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Gröna tak är en allt vanligare dagvattenåtgärd för att minska avrinningsvolymer vid regn i urbana områden. Utvärdering av gröna tak och deras effekt på dagvattensystemet analyseras ofta med modeller. Det finns dock många olika modeller och det är inte klart hur bra de olika modellerna är. Därför har en jämförelse av fyra olika modeller gjorts med data från två olika gröna tak i olika klimat. Resultaten visar att den allra enklaste modellen har sämre prestanda än mer komplexa modeller. Av de mer komplexa modeller så är olika modeller bättre eller sämre beroende på vilka nyckeltal används för att utvärdera modellens prestanda.
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| 8. |
- Broekhuizen, Ico, et al.
(författare)
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Improving hydrological modelling of urban drainage swales through use of soil water content observations
- 2020
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Ingår i: Journal of Hydrology X. - 2589-9155.
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Tidskriftsartikel (refereegranskat)abstract
- Flow observations alone may not provide sufficient information for calibration of detailed hydrological models of urban drainage swales. Therefore this study investigated the added value of using soil water content (SWC) observations made throughout the swale. This can be done by (1) including SWC in the likelihood function that is used to quantify model performance or (2) by using the SWC observations to set initial conditions in the model. The results show that combining outflow and SWC in the likelihood function is necessary to obtain reliable and precise predictions for both variables, and that this increases the number of parameters that are identifiable from the data. Using SWC observations to set initial model conditions improves model performance and affects the degree to which soil hydraulic parameters are identifiable. Overall, it is concluded that SWC observations may be a valuable complement to outflow observations in the modelling of urbanswales.
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| 9. |
- Broekhuizen, Ico
(författare)
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Jordfuktighetsmätningar för modellering av öppna dagvattenlösningar
- 2021
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Öppna dagvattenlösningar blir alltmer populärt för att minska översvämningsrisken i urbana områden. Matematisk modellering är ett vanligt verktyg för att utvärdera dagvattensystem och eventuella ändringar i gestaltningen. Modellerna kräver oftast kalibrering mot uppmätt data, som i vanliga fall bara består av flödesmätningar. Detta skapar osäkerhet när det gäller modellens funktion för att simulera vad som händer när vattnet har infiltrerat i jorden. Därför har denna studie undersökt mervärdet av att använda mätningar av jordfuktighet vid kalibrering av dagvattenmodeller. Studien visar att mätningar av både flöde och jordfuktighet krävs för att kalibrera en modell på ett pålitligt sätt för både variabler.
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| 10. |
- Broekhuizen, Ico, et al.
(författare)
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Model structure uncertainty in green urban drainage models
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Mathematical storm water models are often used as tools for planning and analysis of urban drainage systems, but the models’ inherent uncertainties need to be understood to make optimal use of them. One source of uncertainty that has received relatively little attention, especially for the increasingly popular green areas as part of urban drainage systems, is the choice of the mathematical model structure. This paper analyses the differences between three different widely-used models (SWMM, MIKE MOUSE and MIKE SHE) when simulating green areas over a 26 year period. A wide range of eleven different soil types and six different soil depths was used to investigate sensitivity of the models to changes in both. Important hydrological factors such as seasonal runoff and evapotranspiration, the number of events that generated runoff, and the initial conditions for rainfall events, varied strongly between the three models. MOUSE generated the highest runoff and was insensitive to changes in soil type and depth, while SHE was sensitive mainly to changes in soil type, and SWMM, which generated the least runoff, was sensitive to changes in both soil type and depth. Explanations for the observed differences were found in the descriptions of the mathematical models. The differences in model outputs could significantly impact the conclusions from design or analysis studies of urban drainage systems. The amount and frequency of runoff from green areas in all three models indicates that green areas cannot be simply ignored in urban drainage modelling studies.
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