Espol researcher: Dredging does not solve by itself the problem of flooding in Guayaquil and Durán

Dr. Mercy Borbor, professor at the Faculty of Maritime Engineering and Marine Sciences at Espol and member of the Pacific International Center for Disaster Risk Reduction, agrees with the authorities of Guayaquil and Durán that the sewage systems are saturated completely when the tide levels are high and the rain is intense, but he does not agree in blaming the floods on the lack of dredging of the El Palmar islet, in the Guayas River.

With or without dredging, the problem is that resilience ecosystems such as mangroves and wetlands that helped absorb excess water and sediment from floods have been eliminated, says the academic, who focuses on the floods in Durán, because A study of vulnerable areas and the Climate Resilience project have been carried out there for four years.

Why are areas like El Recreo flooded, where there is a sewage system?

The sewage system does not have the capacity to evacuate the volumes of intense rain (greater than 40 mm for three hours), since they were not designed for it, the population growth of single-family homes passed to three-story buildings. The sewage system is completely saturated when the tide levels are high, this happens twice a day and on Friday it reached 3.87m at 02:30, with high levels of rain reaching up to 110mm of water. Therefore, there is no way that they can evacuate the water to the estuary at high tide. It is necessary to evacuate the water to the drainage channels or flood basins established for it.

What else happens there?

The impermeability of the sector means that all the rain does not infiltrate, but instead runs off through the streets, sidewalks, curbs, increasing the level of flooding. In addition, it increases the sediment in the sewage systems and in the drainage areas towards the channels. The plugging of natural and artificial drainage channels must be managed with the concept of nature-based solutions to favor water capture, infiltration and drainage.

Does the lack of dredging of the Guayas River affect the flood or not?

Dredging does not solve the problem of flooding by itself in Guayaquil and Durán, comprehensive solutions are required that come mainly in the planning of the territory considering the tidal conditions, extreme precipitation events, type of soil and natural ecosystems such as mangroves, wetlands and dry forest. Comprehensive solutions must consider urban hydrology and design sustainable drainage systems, considering nature-based solutions.

What would be the solutions?

Our group has reviewed the options to reduce the impact of flooding in Durán, and we establish three types of solutions:

1. Favor the drainage of housing areas towards open channels and areas destined for water to accumulate, for example, create linear parks around the channels, but which serve as flood basins. The park is flooded, but not my house, until the water can subside. Also develop areas for mangrove ecosystems or vegetation that help capture water on the banks of outlet channels.
2. Build rain gardens throughout the city where possible, avenues, flower beds, pedestrians, to capture water during the rains and infiltrate it there. Each rain garden can store between 7,000 and 10,000 gallons of water, depending on the design. They are cost-effective and highly effective in reducing runoff water in urban systems, but require proper technical design and low maintenance.
3. Rainwater capture solutions in homes, which, while reducing the amount of water that runs off through the streets and sewers, allow residents, especially in areas where there is no piped water service, to have access to rainwater for washing and use in bathrooms and gardens.

Would it help Duran to have parks like Samanes in Guayaquil?

Metropolitan-type urban parks with forests and areas of native vegetation, wetlands, dry forest, hills should be incorporated into urban land planning, because they definitely help flood management, in addition to generating other benefits such as reducing islands of urban heat, generate public spaces for physical activity and walking and recreation.

The linear urban parks around the canals in Durán such as La Matanza, San Enrique and San Camilo and hills such as Los Almendros and even Las Cabras, must be adapted as protected forest areas in sectors where the dry forest can be reforested or conserved. This is also part of nature-based solutions and helps improve public spaces for the city.

Many citadels end up paving their pedestrian walkways. Should it be understood that not leaving land or gardens in the middle of the sidewalks is harmful?

It is important to prepare guidelines for the community and neighborhood organizations to build rain gardens, they have some important technical issues, but accompanied by Espol as an academy, demonstration projects can be carried out with the collaboration of the Municipality, private companies and the community. It would be a very positive initiative for Durán and other cities. But certainly any garden helps, especially if it has native trees.

Does the Municipality of Durán know all this?

Of course, in Durán we have been working since 2018, with financing from the GAD and Espol, and I think we are on the right track.

We already have risk maps on an adequate scale for floods, heat islands and, lately, COVID-19; we know which are the vulnerable sites; We have designed an early warning system for COVID-19 and floods, which will be implemented this year by the GAD. And we have the proposals for nature-based solutions for rain gardens, urban wetlands and recovery of canals and surrounding areas, which we propose to develop to generate evidence of their effectiveness in flood management.

Our work in Durán demonstrates that the Ecuadorian academy, in this case Espol, has all the capabilities and human talent to design solutions to GAD problems in disaster risk reduction issues, building resilience. And it also shows how a GAD can work in co-production with academia to improve the quality of life of its inhabitants and how its inhabitants, through environmental monitoring and the formation of community risk management brigades, contribute. (I)