Stormwater model for quantitative and qualitative analysis: Viinikanoja catchment case study in Tampere

Abstract

Urbanisation and climate change have intensified the risks associated with stormwater, such as flooding, pollution, and the degradation of ecosystems. These issues necessitate the development of effective stormwater management strategies to mitigate adverse effects on urban water bodies and the surrounding environment. Stormwater modelling could be an effective tool to help in the development of stormwater management strategies. This work addressed the critical challenge of stormwater management in the Viinikanoja catchment in Tampere, Finland.

The primary objective of this research was to develop a hydrological-hydraulic-water quality model to analyse both quantitative and qualitative aspects of stormwater in the Viinikanoja catchment. The development involved upgrading a developed hydrological-hydraulic model by adding a water quality component, and calibrating and validating it using numerous sets of data, including continuous monitoring data, laboratory analyses, and spatial data. The simulation software used for model development was Fluidit Storm. The model was applied to examine potential variations in stormwater quantity and quality, particularly Total Phosphorus (TP), under Future Scenarios including climate change RCP6.0 and RCP8.5, as well as urbanisation with medium-density and high-density urban development patterns. The potential impact of these changes on Lake Iidesjärvi was evaluated.

The developed hydrological-hydraulic model, with defined hydrology and hydraulic components, was validated by comparing observed and simulated values for stormwater flow in ditches at monitoring stations. In the water quality model, the Event Mean Concentration (EMC) method was used to model buildup and washoff processes. Literature-based EMC values were used for different land cover types and then adjusted during the calibration process. The spatial data was processed with QGIS software to calculate land use within the catchments in the model. Calibration acceptance Percent Bias (PBIAS) was used for the calibration and validation of both the hydrological-hydraulic and the water quality models. The minimum acceptable level of PBIAS of ±25% for the developed hydrological-hydraulic model and PBIAS of ±35% for the water quality model, as specified in the literature, was achieved. The simulation results of the Future Scenarios showed an increase in stormwater runoff from 7.1% under the climate change scenario (RCP6.0), up to 24% under the combined effects of the climate change scenario (RCP8.5) and high-density urbanisation. Similarly, changes in stormwater quality ranged from 6.1% under RCP6.0 to 26.6% under the combined scenario of RCP8.5 and high-density urbanisation.

The study indicated significant nutrient loading, particularly TP, contributing to the eutrophication of Lake Iidesjärvi. The Future Scenario simulations revealed that climate change and urbanisation are likely to exacerbate stormwater runoff volume and nutrient loading, challenging traditional stormwater management practices. The alterations in stormwater quantity and quality could adversely impact the aquatic environment of Lake Iidesjärvi and the urban environment. To address these challenges, Low Impact Development (LID) techniques were emphasized for urban planning and stormwater management strategies to enhance the resilience of the urban water system in a sustainable manner. The effectiveness of LID practices was also reviewed by looking at other studies that involved actual measurements and stormwater modelling.