Sensitivity of peak flow response to imperviousness increase in a tropical Caribbean urban catchment

This study explores the impact of urban densification on peak flow response in a catchment in Cartagena, Colombia. For this, hydrological modeling was performed via both the Personal Computer Storm Water Management Model (PCSWMM) and the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), using remotely sensed catchment’s land cover for years 1990, 2000, 2010, and 2020. The catchment runoff potential (expressed as the runoff coefficient and curve number) grew, in some areas, up to 33% for the case of the runoff coefficient and 12% for the curve number as a result of total impervious area increase. Furthermore, the volumetric runoff coefficient (gross to net rainfalls ratio) indicated high runoff potential with values close to 1.0. Three well-fitted linear correlations (R2 ≥ 0.92) were obtained between the percentages of increase of catchment impervious area and peak flow values. The plots showed that, in highly developed areas, the catchment response is very sensitive to storm frequency to the point that, even among low return period storms, there exist significant differences: the peak flow rate of increase from a 1-year storm almost double and quadruple that of a 2- and 3-year storms, respectively. The peak flow started to increase at different rates after a nine-percent imperviousness, which was assumed to be the trigger point. The findings of this study contribute to the understanding of the interaction between storm frequency with catchment imperviousness, and serves as an input for the improvement of integrated urban planning, considering the effects of urbanization in stormwater management.

Keywords: stormwater management, imperviousness, peak flow, low return period storms, urban sprawl, flooding