Urban River Interventions in São Paulo Municipality (Brazil): The Challenge of Ensuring Justice in Sociotechnical Transitions

The paper aims to discuss the sociotechnical transitions regarding urban rivers policy in São Paulo Municipality by focusing on programs and projects conducted since 2000. Accordingly, we use a theoretical reflection on sociotechnical transitions and just transitions in interventions related to water and cities. Our work is based on a documental analysis of programs and projects for urban rivers in the municipality conducted via theoretical discussion. The primary focus is on the current sociotechnical regime, the channeling of streams and construction of road systems on its banks, and disputes and pressures brought by the technological landscape and niches, which lead to the construction of linear parks and leisure areas along with the bodies of water. It also shows how the issue of justice has been losing ground in this transition, which although is “in the making,” already presents many factors of injustice. This is due to the low presence of the theme of precarious settlements, in innovative speeches and practices, and the different treatment given by the programs and projects for rivers in the consolidated middle- and upper-class regions and for those located on the peripheries.

Canalized urban rivers

The Biriguizinho Stream, like so many other urban rivers, has undergone changes over the years, with the correction of its banks, channeling and suppression of its source. These measures were seen as the most adequate to enable the urban growth of Birigui-SP. However, with the passage of time and expansion without predetermined guidelines, episodes of flooding occur in the region of the aforementioned stream, overloaded with the runoff of rainwater from a large part of the city. The purpose of this article is to analyze the factors that contribute to flooding on the banks of the Biriguizinho stream, in the city of Birigui/SP, with the aim of proposing green infrastructure solutions that mitigate or definitively affect floods, avoiding risky situations. The methodological procedures adopted include readings on the themes of urban rivers, landscape, perception, risks, and green infrastructure, in addition to observation of the study area.

Immobilization of microorganisms in activated zeolite beads and alkaline pretreated straws for ammonium-nitrogen removal from urban river water

The non-treated wastewater from residential areas contains high concentration of ammonium-nitrogen (NH4+-N). When discharged into the drainage water system, it deteriorates the water quality in urban rivers. This study used two types of materials to form eco-bags, using activated zeolite bead (AZB) and alkaline pretreated straw (APS), in geotextile bags for easy recovery and reuse. The AZB and APS provided the breeding habitat for the microorganisms that promoted biofilm formation on their surface. The immobilization of engineered denitrification microorganisms facilitated the removal of NH4+-N from the urban river water. The NH4+-N removal in the AZB and APS bags were in the range of 64–73%, and 56–61%, respectively, while the chemical oxygen demand (COD) removal in the AZB and APS bags ranged from 33–36%, and 30–31%, respectively. Besides, as evident from DNA and microbial community analysis, the microorganisms demonstrated a greater proclivity to grow and proliferate on the surface of AZB and APS and improved the water quality of urban rivers.

Informing Environmental Flow Planning through Landscape Evolution Modeling in Heavily Modified Urban Rivers in China

Worldwide, urban rivers suffer various degrees of ecological degradation. Rehabilitating heavily modified urban rivers requires holistic approaches, including environmental flow management. We examine the case of Lower Yongding River, Beijing’s mother river, which had dried up since the 1980s and is undergoing a flow replenishment experiment, receiving 342 million m3 of water during 2019–2020 for ecosystem enhancement. Considering the massive cost of replenishment, we address the urgent need to evaluate its outcomes and inform future management through an interdisciplinary modeling approach under the circumstance of severe data shortage. We simulated the study reach’s landscape evolution under five flow scenarios and assessed their ecological effects using the CAESAR-Lisflood model and habitat suitability index method. Despite overall minor morphological differences across scenarios, individual reaches presented pronounced physical changes. Higher-flow scenarios shaped a distinct channel in certain reaches, but historic channel modifications by mining and farming caused minimal responses in others. Additionally, higher-flow scenarios generally created larger and more evenly distributed habitat areas but showed a low payback given the higher flow volumes needed. Targeted channel-floodplain geomorphological restoration is essential for flows to generate desired ecological outcomes. The demonstrated modeling framework offers great promise, informing future rehabilitation actions for heavily modified urban streams.