Adhikari et al. (2026) Design of stormwater bioretention systems for improved volume and peak runoff reduction

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-03-06
• Authors: Utsav Adhikari, Ico Broekhuizen, Godecke-Tobias Blecken, Maria Viklander
• DOI: 10.1016/j.jhydrol.2026.135248

Research Groups

Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water, Luleå University of Technology, Sweden

Short Summary

This study investigated 54 bioretention system design combinations using a calibrated SWMM model to optimize hydrologic performance for both common and intense rainfall events. It found that a storage connection consistently improved performance, while higher filter media fractions enhanced volume reduction during common events, and lower fractions were more beneficial for reducing overflows during high-intensity rainfall.

Objective

• To investigate alternative design options for stormwater bioretention systems to improve their hydrologic performance during storm events of various intensities.
• To analyze the synergistic effects of multiple design parameters (filter media fraction, hydraulic conductivity, ponding depth, and storage connection) on volume reduction during common rain events, peak flow reduction during extreme events, and the number of annual overflow events.

Study Configuration

• Spatial Scale: Field-scale bioretention system (total depth 1 meter) in V¨axj¨o, Sweden, modeled using SWMM.
• Temporal Scale:
  • Peak flow reduction: Simulated 10-year return interval Chicago design rain event (30 mm total rainfall, 180 mm/h maximum intensity, 1 hour duration).
  • Volume reduction: Simulated a representative storm event (event #10) from monitoring period (56 mm total rainfall, 144 mm/h maximum intensity, 84 hours duration).
  • Number of overflow events: Continuous simulation over a one-year rain series (June 2021 – June 2022, 699 mm total rainfall).
  • Model calibration and validation: Two-year period (one year for calibration, one year for validation).

Methodology and Data

• Models used: Storm Water Management Model (SWMM) version 5.1 (US EPA), PyDREAM (for Bayesian calibration), PySWMM module (for dynamic control of drainage flow).
• Data sources: Drainage flow data collected from four field-scale bioretention systems (S1, S2, SB1, SB2) in V¨axj¨o, Sweden, over a two-year period for model calibration and validation.

Main Results

• Storage Connection: Consistently improved hydrologic performance across all design options, enhancing volume reduction by an average of 10% (up to 32% in some cases) and reducing the number of overflow events (up to 11 fewer events out of 29 annually).
• Filter Media Fraction: Higher fractions (85%) improved volume reduction during common rain events by approximately 50%. Conversely, lower fractions (15%) were more beneficial for reducing overflow events (in about 17 out of 29 events annually).
• Ponding Depth: Increasing ponding depth from 100 mm to 300 mm improved peak flow reduction by 21% and volume reduction by approximately 7%. The combination of higher ponding depth and a storage connection was particularly effective in reducing annual overflows.
• Hydraulic Conductivity: Higher hydraulic conductivity (400 mm/h) improved peak flow reduction during high-intensity events. It had a minimal effect on volume reduction during extended events and on the number of annual overflow events.
• Interactions: A significant negative interaction was found between a high filter media fraction (0.85) and the presence of a storage connection, leading to a 25.27% decrease in peak flow reduction compared to non-interacting scenarios.

Contributions

• Addressed a knowledge gap by investigating the synergistic effects of multiple design parameters on bioretention system hydrologic performance under varying storm intensities using a calibrated field-scale model.
• Demonstrated that strategic design modifications, including the combination of factors, can substantially improve bioretention system performance, achieving over 90% peak flow reduction even for intense rain events.
• Provided insights into the trade-offs between optimizing for volume reduction during common events (e.g., higher filter media fraction) and reducing overflows during high-intensity events (e.g., lower filter media fraction, storage connection).
• Highlighted the importance of factorial design in revealing interaction effects between design factors that single-factor analyses would miss, offering a more comprehensive understanding for climate resilience.

Funding

• VINNOVA competence center DRIZZLE (Vinnova grant 2022-03092)
• Research cluster Dag&N¨at (Stormwater&Sewer, funded by the Swedish Association for Water and Wastewater Svenskt Vatten, grant number 25-104)

Citation

@article{Adhikari2026Design,
  author = {Adhikari, Utsav and Broekhuizen, Ico and Blecken, Godecke-Tobias and Viklander, Maria},
  title = {Design of stormwater bioretention systems for improved volume and peak runoff reduction},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135248},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135248}
}