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REDUCING POLLUTION IN URBAN RIVERS Lessons learnt from China

Welcome to the April edition of the Best Practices Monthly Features. In this edition, we present practical solutions for urban river rehabilitation contained in a recently launched joint publication of UN-Habitat and Tongji University: Making Cities more Sustainable through Rehabilitating Polluted Urban Rivers - Lessons from China and Developing Countries. The recommendations and key messages in this publication offer measures and pathways to pursue the rehabilitation of heavily polluted urban rivers in developing countries.

It is estimated that more than half of the world’s five hundred biggest rivers are seriously polluted. The United Nations World Water Development Report for 2017 reports figures to show that, on average, high-income countries treat about 70 percent of the municipal and industrial wastewater they generate. That ratio drops to 38% in upper middle-income countries and to 28% in lower middle-income countries. In low-income countries, only 8% undergoes treatment of any kind.

In the New Urban Agenda, adopted at the third United Nations Conference on Housing and Sustainable Urban Development (Habitat III) in Quito, Ecuador in 2016, Member States committed to promote the conservation and sustainable use of water by rehabilitating water resources within the urban, peri-urban, and rural areas and reducing and treating wastewater. The Agenda 2030 for Sustainable Development and the New Urban Agenda reaffirm the commitment of world leaders to find sustainable solutions to restore the health of rivers and other water bodies. Increasing wastewater collection and treatment to restore the health of heavily polluted urban rivers is, therefore, an urgent global priority.

CASE STUDY - SUZHOU CREEK, CHINA

The rehabilitation project of the Suzhou Creek has proved that better management of drainage systems is key to controlling pollution discharged into rivers, both in dry and wet weather. These examples also illustrate how UN-Habitat is actively engaged in supporting governments and diverse stakeholders to improve wastewater management and public open spaces in the urban environment.

The mainstream of Suzhou River is 53.1 km in Shanghai, covering an area of 855 km squared, with more than 20,000 rivers, and thousands of pollutant sources. The complex system of pollution migration and transformation from the diverse river networks, huge pipeline network, numerous pollution sources and controlling gate groups all discharge into the outer rivers and seas. Among the international urban river management cases, the Suzhou Creek system counts as one of the most complexes.

The approach adopted included collecting pollution discharged directly to Suzhou creek in dry and wet weather, improving water fluidity to increase the self-purification capacity of the water body and advanced tools for supporting a water environment management decision system. Most of the issues regarding where the pollution comes from and how to control the discharge are also faced by other countries or urban areas, and the rehabilitation of Suzhou Creek provides lessons to other developing countries.

FIVE PRACTICAL WAYS FOR REHABILITATING URBAN RIVERS

1. Urban planning and wastewater management

The main factor that ensures urban river water quality is a well-constructed and functional drainage system. Continuous improvement of construction techniques and management of drainage systems is paramount especially during different stages of development. Highly urbanized areas are characterized by heavy traffic and high population densities.

Apart from emphasizing on proper design and construction of drainage systems, it is equally important to assess, evaluate and repair the existing drainage systems in order to address the cross-connection challenges, including groundwater leakage into the networks and sewage cross-connections. The impact of rain outflows on water quality is significant because of overflow in the municipal drainage systems. These outflows carry pollutants from the ground and flush the sediments into water bodies

This can be addressed by improving the planning, construction, and management of drainage systems in a comprehensive manner to contribute effectively to the pollution control of the urban water environment.

2. Wastewater collection and interception

The lack of systematic urban planning under rapid urbanization in developing countries results in fragmented and incomplete construction of environmental infrastructure. Many governments entities plan and design the urban sewage systems but often neglect the construction of household pipelines. Urbanizing nations need to ensure they avoid such occurrences and consider the location, quantity, and nature of pollution sources in the construction of sewage systems.

Today, the rapid advancement in information technology has made available geographic information software, software data models and database systems that clearly demonstrate the scope of the sewage networks required, and their transport capacity and mode, before constructing the sewage networks.

The identification of pollution sources and magnitude, the establishment of their database and the development of suitable sewage system models, have become an indispensable first step before the construction begins. Drainage information systems include spatial and physical attributes of pipelines, nodes, outlets and pollution sources.

3. Pipeline Repairs

Pipeline corrosion can result in water leakage from the pipeline and groundwater seepage into the pipeline. This, in turn, reduces sewage treatment efficiency due to direct pollution to the environment while reducing the concentration of sewage discharged into the wastewater treatment plant. In addition, pipeline corrosion also causes the sinking of the pavement above the pipelines, thus disrupting the flow of traffic and pedestrians.

The urban drainage pipes need to be comprehensively assessed and necessary repairs are undertaken. Traditional excavation technology and trenchless technology make up some of the pipeline repair methods. However, traditional excavation methods inevitably affect social life and other human activities hence trenchless construction is advised. The use of Trenchless Pipeline Repair (TPR) technology is a type of subsurface construction work that requires few trenches or no continuous trenches.

4. Correction of sewage cross-connections

Cities like Shanghai and Nanjing are proactively correcting faulty stormwater systems. These may be caused by river water inflow or groundwater seepage, residential communities, commercial or administrative units, shops facing streets and industrial enterprises. Identified connection problems mainly arise from a range of circumstances. Firstly, there are separate pipes for sewers and stormwater drains under the municipal roads, but not in old urban communities. The old combined sewer pipes remain connected to the municipal stormwater drains to prevent flooding in case of rainfall. Secondly, there are cases where the laundry water is connected to downspouts due to the installation of washing machines on balconies. Thirdly, road wash or car wash wastewater is connected to stormwater pipes through inlets on the curb in some places.

Current actions about correcting sewage cross-connections include rebuilding the drainage system in old residential communities as a separate system with parallel sewer and stormwater pipes or improper use of separate stormwater pipes in newly built residential communities, a correction technique should be performed by designating balcony downspouts as sewer pipe and rebuilding additional downspouts.

5. Pollution control of wet-weather discharges

Unlike the pollution of first flush discharged from stormwater drains in the separate drainage system in developed countries, cross-connection is common in China, and the flow velocity of sewage in stormwater drains is lower.

This allows pollutants to deposit and accumulate more easily, resulting in a higher concentration of pollutants, more serious organic pollution, and greater contribution of sediment pollution load from the first flush discharge during wet weather. Therefore, it is necessary to take appropriate measures to control or reduce the deposit of pollutants in the drainage network and the deposition pollution load of overflow.

Key Recommendations

Proper design, construction, and maintenance of drainage networks, sewage collection, and an interception, followed by proper treatment, and the pollution load reduction in wet weather, are indispensable to reduce pollutants discharged from drainage systems in developing countries.

  • Good planning and construction of urban drainage systems are important.
  • Complete collection pipe networks should be extended properly to connect to sources of pollution based on investigations.
  • Trenchless Pipeline Repair technology is recommended for pipeline restoration in densely built urban areas.
  • Scientifically simple and low-cost tracing technology is a useful approach to solve sewage cross-connections.
  • Application of patched Low Impact Development (LID), storage tanks, in-site sediment flush gates, and hydrodynamic separators can achieve significant results in reducing pollution loads of overflow discharge in wet weather.

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