Land use change and impact on drainage in the satellite city of Daule

Abstract

Context: This study analyzes the impact of land-use change on the drainage system of the Sabanilla Estuary watershed in the Daule Canton, Guayas Province, a rapidly growing area within the greater Guayaquil region. Uncontrolled urban growth and human intervention, resulting in soil impermeability, are identified as key factors exacerbating vulnerability to flooding. Objective: The overall objective was to evaluate the hydrological and hydraulic response of the 115.42 km² watershed under current conditions. Method: The methodology involved a statistical analysis of extreme values ​​from the Guayaquil DAC station's daily maximum precipitation records (1962–2021) to define the Gumbel Type I distribution, Intensity-Duration-Frequency (IDF) curves, and design hyetographs for various return periods (Tr) up to 100 years. A hydrologic model was developed using HEC-HMS with a Curve Number (CN) of 60, characterizing the watershed into three sub-basins. The resulting hydrographs were then used in the HEC-RAS hydraulic model to simulate water surface profiles. Results: The results indicate that the current channel of the Sabanilla stream is unable to efficiently convey runoff, even during periods of lower intensity, primarily due to land-use change and the natural characteristics of the watershed. This deficiency suggests a high risk of flooding for the area. Conclusions: To mitigate this problem, the study proposes several structural interventions, including improving the channel's cross-section (e.g., a composite or trapezoidal section) and dredging it to increase its flow capacity. In addition, lining the channel with concrete is recommended to improve flow velocities and the hydraulic area. A key additional recommendation is to establish a barrier at the confluence with the Daule River to manage the adverse effects of high tide, which obstructs the normal outflow.