Modeling blue-green stormwater measures using nonlinear reservoirs

Blue-green stormwater measures are being more commonly utilized and implemented in cities to address the need for more sustainable and livable urban spaces. The large potential of blue-green measures in stormwater management at the local scale supports their citywide implementation. To be able to investigate and study the effects of blue-green stormwater measures in different scenarios, easy-to-use and efficient models are required. There are different modeling tools available that consider a detailed physical description of blue-green stormwater measures. Such descriptions are found to be demanding regarding parameter estimation and their variations in time and space, especially for infiltration medium and evapotranspiration processes. In order to overcome the difficulties of a detailed physically based description, a fast and robust schematic model was developed to simulate blue-green measures (Haghighatafshar et al., 2019). The developed model focused initially on properly representing the runoff volume followed by a heuristic approach to describe the smoothing (equalizing) effect of the measures on the outflow through a nonlinear reservoir at the downstream end of the system.

A natural next step in the model development is to individually describe each blue-green measure, both with regard to its volume retention (i.e., volume reduction; the runoff is not being released to the downstream system, but retained locally) and volume detention (i.e., flow equalization; the volume is not reduced, but the flow magnitude is, leading to a longer runoff event). Such a description can still be based on the nonlinear reservoir concept; however, using this concept in a behavior-oriented manner will lead to many coefficients with values that need to be estimated through calibration for each individual measure. Thus, the hypothesis is that if the reservoir model for a blue-green measure can be given a physical interpretation, the number of coefficient values needed to be estimated can be reduced, yielding a more reliable and easier-to-use model.

Thus, this thesis proposal aims to describe several different blue-green measures as nonlinear reservoirs, yielding physically based expressions for the reservoir routing coefficients. Although these coefficients may still require calibration for accurate predictions, approximate estimates of the coefficient values are available based on the theory, which is a considerable advantage compared to a purely behavior-oriented model.

The thesis work includes developing descriptions of a variety of blue-green measures using the concept of a nonlinear reservoir and formulating a model that can connect an arbitrary number of blue-green measures to simulate their effects on the runoff during rainfall events. Such a model will be of great value for consultants, municipalities, and government organizations. The model will be tested with unique data from Augustenborg in Malmö and it is expected that the students will interact with different stakeholders during the work.

Who should apply?
Students with a background in Environmental Engineering or Civil Engineering with knowledge of rainfall-runoff processes, urban hydrology, and hydrodynamic modelling/hydraulics are encouraged to apply. Skills in Python programming and coding is highly relevant and recommended for this thesis project. This thesis is believed to be suitable for two students, considering the estimated workload.

How to apply?
Send an e-mail with a few words about yourself, your educational background, and why you are interested in this Master´s thesis project to Salar.Haghighatafshar@chemeng.lth.se and/or Magnus.Larson@tvrl.lth.se.

When?
Flexible, Autumn 2020 – Spring 2021

References

Haghighatafshar, S., Yamanee-Nolin, M., Larson, M., 2019. A physically based model for mesoscale SuDS – an alternative to large-scale urban drainage simulations. Journal of Environmental Management 240, 527–536.

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