The Yangtze River Delta is a flat and low-lying place of the highest density of the river network in China with poor mobility of rivers within the network, prone to the disasters of typhoons, storm surges and floods, while it is China's most economically developed area with dense population and high urbanization rate. However, with the fast development of industrialization and urbanization, the water environment of the Yangtze River Delta is far beyond its carrying capacity, making the water environment problems increasingly prominent, such as squeezed urban rivers, segmented river network, poor connection of river systems, serious siltation of urban river courses, low qualified rate of water function zones, poor feeling of urban water bodies resulting from low degree of urban sewage treatment, etc.
Water environment deterioration is attracting more and more attention. Explicit requirements on qualification of water function zones in the Yangtze River Delta have been raised by the nation. It is stated in Action Plan for Prevention and Control of Water Pollution issued by the State Council that water quality of at least 70% of water bodies in the Yangtze River Basin shall reach to or be better than Class Ⅲ, and the percentage of black and odorous water bodies in urban built-up areas of or above prefecture level shall be controlled within 10% by 2020. The State Council also issued the most stringent water resources management system, which requires that the qualified rate of water quality in water function zones of major rivers and lakes shall be improved to more than 80%. Besides, the Ministry of Water Resources called for accelerating water ecological progress as well. Meanwhile, various cities in the Yangtze River Delta (such as Shanghai, Suzhou, Changshu, etc.) also worked out the action plans for urban water ecological progress. On the occasion of G20 Summit Meeting held in Hangzhou in 2016, necessary emergency protection of water environment of the core area of Hangzhou G20 Summit Meeting should be made.
Therefore, there was an urgent need to improve the urban water environment of plain river network areas. Under the premise of safeguarding flood control safety, optimal regulation of water resources and improvement of water ecological environment of rivers and lakes can guarantee the social and economic development in the Yangtze River Delta area.
1. Major Innovative Achievements
1.1 A series of basic theories and methods, including the assessment methods of water environment carrying capacity improvement effects, hydrodynamic-water quality response relationship, prediction method of river clarity, impacts of water diversion and rivers and lakes connection on algae, and water system pattern and water allocation response relationship, have been studied for urban water environmental improvement.
1.2 A set of techniques has been formed for water quality improvement by smooth flow of running water in urban river network. The efficient utilization and virtuous circulation of water resources have been realized by the fine control of flow velocity, water table and volume, suitable to local conditions, to improve river network flowability and water quality with the control targets of sensory indices and hydrodynamic indices, taking into account the regional flood control and water quality improvement, based on detailed surveying and mapping data and real-time monitoring data of hydrology and water quality. The techniques include the refined simulation of hydrology-hydrodynamic force-water quality, spatio-temporal allocation of water source, optimization of water system pattern, fine deployment of optimal water volume-water level, engineering regulation of moveable overflow weirs, in-situ purification of water source quality, and hydrodynamic-water quality joint regulation of engineering cluster of sluice gates, pumps and weirs.
1.3 A series of water environment improvement devices have been developed. RD-DMBR series of integrated deep water treatment equipment were developed with the core techniques of decentralized sewage interception and treatment, and successfully applied in the core area of G20 Summit Meeting in Hangzhou. Soft isolation facilities were invented for clean water and sewage in the connecting water zone of rivers and lakes, which were successfully applied in the Baodaiqiao Scenic Spot, Dantai Lake, Suzhou and the core area of G20 Summit Meeting in Hangzhou. A temporary fast-moving water level control device was developed and successfully applied in the ancient district of Changshu. A new technique of connection and treatment of breaking creeks was developed with the help of in-situ isolation and connection technique, composite connection technique of in-situ isolation, pumps and sluice gates, connection technique of graded control and circulation, and reconstruction technique of shallow tunnels.
2. Academic Outputs and Third-Party Evaluation
After the implementation of flowing water in the river courses in the ancient districts of Suzhou, all-year-round connection of big and small rivers has been fundamentally realized with remarkable increase of water volume in the urban area, enhanced mobility of river network, and obvious improvement of urban drainage capacity. Suzhou Municipal Environmental Protection Bureau conducted continuous water quality monitoring of the main parameters of COD, ammonia nitrogen and total phosphorus, and found out that the water quality had been upgraded to Class IV or III. The flowing water project in Suzhou was evaluated as one of the Ten Morale Projects in 2013.
Under the circumstances of short implementation period and heavy tasks, NHRI smoothly accomplished the major phased water quality protection task for G20 Summit Meeting in Hangzhou with a series of abundant achievements and overfulfillment of the project target. CMA water quality tests conducted by a third party Zhejiang Surveying Institute of Estuary and Coast indicated the main water quality parameters of total phosphorus, ammonia nitrogen, permanganate had reached to those of Class II water, and transparency more than 1m with monitoring points at each rivers within the region. More than 30 central, provincial or municipal mainstream media, such as People’s Daily, CCTV, Xinhua News Agency, CNR, etc., made field reports of the project. LU Guihua, Vice Minister of Water Resources and HUANG Xuming, Vice Governor of Zhejiang Province respectively headed delegations for field investigation and gave full affirmation of the project effects. Congratulations were expressed via the websites of the Ministry of Water Resources, China, Pearl River Water Resources Commission and local water authorities after the successful completion of water quality assurance task of G20 Summit Meeting by NHRI.
In 2015, the project of smooth flow of running water was implemented in the ancient urban area of Changshu. The scheme of smooth flow of running water designed by NHRI was realized with 2 overflow weirs, through which clean water runs into the ancient urban area and flow volume and velocity are greatly improved so as to obviously improve the water quality. The planned big encirclement project can be used not only for urban flood control but also for running water course. For the in-depth study on water quality improvement of water function zone in Dianbei Region, Shanghai, tidal force has been fully utilized in the scheme of “Storage in upstream and discharge in downstream” to increase the water environmental capacity. In this way, flow velocity of river courses is remarkably improved and so is hydrodynamic force. The water function zone is expected to meet the standard.
3. Application, Promotion and Comprehensive Benefits
After the implementation of smooth flow of running water in cities of plain river network, the technical indexes of each project are consistent with the design expectations, which fully verify the reliability of research findings. The joint regulation technique of water quality-hydrodynamic force for the smooth flow of running water utilizes the model as core, and scientific arrangement of water level difference and flow ratio can effectively improve the water environment of river courses. Compared with other water environment treatment methods, this technology possesses greater advantages in the aspects of technical advancement, safety reliability and economical rationality with wide application perspective.
3.1 Environment benefits. The smooth flow of running water in cities of plain river network has improved the hydrodynamics of river network, environmental carrying capacity and water environment of river courses.
3.2 Social benefits. Regional flood control is safeguarded, and orderly flow of urban river water promoted so as to eliminate the black and odorous water bodies in cities and beautify urban landscapes. The smooth flow of running water has realized the optimal regulation of water resources, improved the aquatic environment of rivers and lakes, and increased the utilization rate and reliability of water resources. Overflow weirs and sluice gates have been used in varying water level so as to produce the smooth flow of running water, replacing pumps with electricity consumption and mechanical wear, and resulting in great reduction of investment and operation cost.
3.3 Ecology benefits. The water body mobility of urban river network has been increased, and people’s living environment and water ecological progress improved. The guarantee rate of water supply in dry season has been improved, which effectively mitigates ecological water shortage. The aquatic carrying capacity of urban river network and lakes has been improved so as to provide support to water ecological and environmental security with remarkable ecological benefits.
