Localized Ks assessment for bioretention in Thailand : improving SWMM accuracy

Authors

• Chulalux Wanitchayapaisit
• Damrongsak Rinchumphu
• Prattakorn Sittisom
• Thidarat Kridakorn Na Ayutthaya
• Chana Sinsabvarodom
• Oleg Gorbunov
• Sitthikorn Sitthikankun

Publication Date

2026

Abstract

Urbanization in Thailand has significantly reduced natural infiltration surfaces, intensified stormwater runoff, and increased the demand for effective urban drainage solutions. Bioretention systems, guided by water-sensitive urban design (WSUD) principles, offer a promising approach for enhancing infiltration and mitigating urban flooding. However, the effectiveness of bioretention depends critically on the accurate estimation of saturated hydraulic conductivity (Ks), a key input parameter in hydrological models such as the Storm Water Management Model (SWMM). Despite international guidelines, local Ks values for tropical soils and vegetation remain scarce, limiting model reliability. This study aims to determine its suitability as a filter media layer in bioretention systems developed specifically for the Thai context. Two surface conditions, vegetated and unvegetated, were tested using coarse construction sand as filter media. The results showed a significantly higher Ks (an 18.55% increase, p<0.001) in the vegetated system (306.57 ± 4.58 mm h-1) compared to the unvegetated system (258.61 ± 4.98 mm h-1), confirming a significant influence of vegetation on infiltration capacity. The localized Ks data produced in this study fall within international bioretention design standards and offer a practical alternative to SWMM’s default parameters. A sensitivity analysis using SWMM and actual Chiang Mai rainfall data demonstrated the critical impact of these localized Ks values, showing that integrating them can reduce simulated runoff volumes by up to 30% for high-frequency storms, thereby enhancing the predictive accuracy of urban stormwater models. This research contributes to bridging the gap between hydrological modeling and site-specific environmental conditions in Southeast Asia.

DOI

10.54028/NJ202625603

First Page

1

Last Page

22

Recommended Citation

Wanitchayapaisit, Chulalux; Rinchumphu, Damrongsak; Sittisom, Prattakorn; Kridakorn Na Ayutthaya, Thidarat; Sinsabvarodom, Chana; Gorbunov, Oleg; and Sitthikankun, Sitthikorn (2026) "Localized Ks assessment for bioretention in Thailand : improving SWMM accuracy," NAKHARA (Journal of Environmental Design and Planning): Vol. 25: No. 1, Article 3.
DOI: 10.54028/NJ202625603
Available at: https://digital.car.chula.ac.th/nakhara/vol25/iss1/3