A Nonlinear Reservoir Model to Simulate Blue-Green Stormwater Systems – An Application to Augustenborg Catchment in Malmö, Sweden

Abstract: The increasingly rapid urbanization has led to vast impervious surface areas in the urban environment. This situation of impervious surfaces has increased the surface temperature and interrupted the natural water circle, which has negatively impacted the urban environment. Human activities' continuous greenhouse gas emission has contributed to global climate change, which has caused some atmospheric abnormalities like increased precipitation, leading to environmental hazards like pluvial flooding and combined sewer overflow (CSO). Several different stormwater control measures have been practiced and implemented to control the excess rainfall-runoff and help avoid overloading the drainage systems. Research has proven blue-green infrastructures to be efficient for managing stormwater runoff. However, the techniques for modeling blue-green stormwater systems have also been identified to be very complex and complicated due to the large number of parameters involved. This characteristic has made it challenging to develop simple simulation models to relate the area's physical characteristics where the systems are being implemented. Hence, this study aimed to develop a simple model with few parameters (corresponding to physical characteristics of the systems) for fast and reliable simulation of blue-green systems. The methodology used in this study was to couple "nonlinear reservoir model" to "hydraulic representation". This quantification and calibration were done in a simple nonlinear reservoir simulation model developed in this study using Excel software. Augustenborg is an area located in Malmö, Sweden, consisting of two main sustainable drainage systems (SuDS) implemented in the North and South of the neighbourhood. This thesis focused on the blue-green stormwater systems in Northern SuDS in Auguestenborg. The Northern SuDS consists of seven stormwater control measures (SCMs), including swales, wet ponds, and a rectangular channel connected to a sewer pipe network. Each system has a connecting catchment, and the governing equations used in developing the nonlinear reservoir model are the continuity equation and flow equations. The flow equations used in this study are Manning's equation (for swales and rectangular channel) and a discharge equation through an orifice (for wet ponds). The nonlinear routing parameters were calibrated for each catchment connecting to a system after relating the physical characteristics of the catchments using Manning's equation. After developing the model and obtaining the calibrated parameter values, the model was tested and validated with measured data. The discharge flows from the model were compared to the measured discharge flows. The model showed a good response time to the discharge flow when validated with measured data. This study developed an easy-to-use physical-based model and was able to quantify nonlinear reservoir routing parameters based on the physical characteristics of the blue-green stormwater systems implemented in the case study.