Flood Prevention Guayaquil: A feasibility study on local stormwater storage and the effect of sea branch closure to prevent pluvial and coastal flooding

Abstract

The city of Guayaquil suffers from regular floods. During the wet season, typically from late December until late April or early May, multiple floods per week can occur. Mainly the excessive rainfall in combination with high tide penetrating into the city results in a high flood risk, but some flood-prone areas can also flood in case of spring tide only.
The main objective of this research is to investigate the possibility of reducing pluvial and coastal flooding in urban areas by constructing a (semi-permanent) barrier in a sea branch, which retains the incoming tide and creates storage for excessive rainfall. In addition, local storage areas spread over the city are considered to delay stormwater runoff into the sea branches. Based on a system analysis and by numerical modelling, several closure locations and their effects are assessed.
Temporary storage of stormwater behind a barrier in a sea branch is a suitable solution to prevent both coastal and pluvial flooding. Based on the results of this research and possible locations of the barriers, a combination of three selected barriers is most opportune, because all catchment areas adjacent to a sea branch can drain their stormwater in a closed-off part behind one of these barriers. In order for these barriers to be effective, they must be closed during low tide prior to heavy rainfall. All three barriers are able to withhold the stormwater volume from their corresponding catchment areas during a 10-year design rainfall event. Even in the event of the highest possible water level during low tide, being neap tide in combination with the storm surge of El Niño, the storage capacities are sufficiently large. Besides the large-scale and small-scale solutions that are currently considered by the local authorities, they are advised to also consider the intermediate-scale solution presented in this study.
Local stormwater storage in the form of water squares in parks and playgrounds is a small-scale solution to reduce pluvial flooding. The storage capacity of these areas is much smaller than the storage capacity behind a barrier, but it is a solution for low-lying urban areas that are not adjacent to a sea branch or river. When the storage capacity of parks and playgrounds in some catchment areas is not sufficient, underground storage basins can also be considered as local storage areas.
The local authorities are advised to set up regulations on return periods for designing flood risk-reducing structures and to assess the economic losses of floods in urban areas, in order to be able to estimate the acceptable cost of these structures.