The Governance and Optimization of Urban Flooding in Dense Urban Areas Utilizing Deep Tunnel Drainage Systems: A Case Study of Guangzhou, China
Abstract
:1. Introduction
- (1)
- Partial coverage of separate systems leads to a chaotic overall drainage system: scattered separate areas within a predominantly intercepted combined system face significant difficulties in connecting with the old combined system, especially when separate areas are between two combined areas. The effectiveness of separate systems is very limited;
- (2)
- It is difficult to achieve true separate drainage in separate areas: due to the lack of separate discharge systems among drainage users and their non-standard discharge methods, separate pipelines built along municipal roads cannot achieve true separation. New rainwater pipelines often discharge into sewage pipelines due to environmental pressure, turning new separate systems back into combined drainage systems;
- (3)
- Investment in separate systems is large, making promotion difficult: separate areas are often densely populated, involving house demolition, protection, road restoration, pipeline relocation, and traffic relief issues, requiring significant construction costs. The end of the pipeline network involves renovating drainage systems for users, significantly impacting residents’ daily lives. Difficulty in fully understanding all built drainage systems at the drainage terminals can lead to connection errors, causing drainage congestion and flooding issues, further complicating project construction and making promotion difficult;
- (4)
- The initial rainwater pollution problem is not addressed: research shows that the pollution concentration of initial rainwater is even higher than that of typical domestic sewage. Separate systems, without considering initial rainwater collection, face pollution issues during the rainy season, especially in rain-prone areas like Guangzhou.
2. Methods
2.1. Deep Tunnel Planning Objectives
- (1)
- Strictly implement national and local laws, regulations, standards, and specifications;
- (2)
- The deep tunnel drainage system must be combined with local shallow renovation to fully play its role in flood control, drainage, and overflow pollution control, supplementing and enhancing the existing shallow drainage system;
- (3)
- Co-ordinate closely with urban underground space utilization planning, vertical planning, environmental protection planning, and disaster prevention planning, resolving conflicts with subways and other underground facilities to achieve comprehensive utilization of underground space;
- (4)
- Comprehensive planning and reasonable layout benefit water environment protection and water quality improvement. The planning should consider the principles of “combining upstream and downstream, deep and shallow layers”;
- (5)
- The planning of deep tunnel drainage systems should be co-ordinated with the long-term relocation of major sewage treatment plants within the planning scope;
- (6)
- Construction of deep tunnel drainage systems should leverage different conditions through dispatching operations to relieve urban flooding, and control initial rain and combined sewage overflow pollution;
- (7)
- Under the premise of meeting the construction goals and functions, investment should be saved, and operating costs minimized as much as possible.
2.2. Planning Principles of Guangzhou Deep Tunnel Drainage System
- (1)
- The protection of receiving water bodies and public health in the drainage planning of the catchment area during the rainy season is crucial;
- (2)
- The actual water flow conditions during the rainy season, the collection system, and the operating capacity of sewage treatment plants vary greatly with weather conditions. It is necessary to continuously measure, model, monitor, and evaluate under full weather conditions;
- (3)
- Clarify local rainfall patterns, topography, groundwater conditions, initial soil moisture status, and extreme changes in flood control facilities;
- (4)
- Combine infrastructure operating conditions, and infiltration and inflow increment to comprehensively predict future flow changes;
- (5)
- The operation and maintenance of collection systems and treatment facilities should include strict management of all pollution sources in the basin, effective control of initial rain pollution, and measures to maximize the reduction of dry season overflow pollution;
- (6)
- Under the prerequisite of meeting engineering goals and functions, reduce investment and operating costs as much as possible;
- (7)
- Emphasis on sustainable development: maintain and continue the basic principles of planning and design through information systems, avoid structural and functional defects, minimize environmental impact, and ensure long-term effective operation.
2.3. Overall Planning Method for Guangzhou Deep Tunnel Drainage System
2.4. Data Collection and Current Status Assessment
2.5. Development of Drainage Facility Improvement Plans for Each Tributary Basin
2.6. The Calculation Method for the Intercepting Ratio of Combined Piping Network and CSO Retention Rate
3. Results
3.1. Development of Overall Urban Tunnel System and Facilities Planning
- (1)
- Reducing Overflow Pollution: During the rainy season, the tunnel serves as a storage conduit for combined sewage and initial rainwater from the Donghao Creek basin. Post-rainfall, sewage is lifted by the terminal sewage pump station to the shallow drainage system and then sent to the sewage treatment plant. This significantly increases the interception multiple of the entire basin’s interception system, greatly reducing the number of times sluice gates are opened for various tributaries (or culvert boxes) in the Donghao Creek basin. It aims to cut over 70% of the combined overflow pollution (measured by COD) during the rainy season.
- (2)
- Assisting Flood Control and Mitigating Shallow Water Flooding: Under heavy rainfall conditions, the tunnel acts as a flood drainage channel, performing flood discharge functions. After being lifted by the terminal flood pumping station, the floodwater is discharged into the Pearl River, thereby lowering the water level at the culvert box outlet. This works in conjunction with the shallow system renovation to elevate the shallow drainage standard to a P = 5-year return period (95.55 mm), enhancing the drainage standard of the combined main channels in the basin to a P = 10-year return period (109.71 mm), and ensuring the open section of the Donghao Creek meets a 50-year flood control standard.
3.2. Economic Comparison Analysis
- (1)
- Land Space Advantage: It conserves land resources by utilizing underground space, which is crucial in urban areas where surface area is limited;
- (2)
- Increased Detention Ratio: It enhances the existing drainage network’s ability to handle stormwater and sewage loads by increasing the detention ratio, which is the capacity to store and release water during heavy rainfall;
- (3)
- Operational Flexibility of Wastewater Treatment Plants: The system allows for more flexible operation of wastewater treatment plants, accommodating fluctuations in inflow and improving the overall efficiency of the drainage system;
- (4)
- Provides conditions for the treatment of initial rainwater and control of the pollution caused by the first flush of rain.
- (1)
- The initial investment is relatively large;
- (2)
- The operating cost is high. Due to its location in deep underground spaces, the power consumption of the pumping stations during operation is relatively large;
- (3)
- The cost of cleaning and maintenance is relatively high. After each use, cleaning and maintenance are required.
3.3. Analysis of the Effects after Deep Tunnel Implementation
- (1)
- Flood Season—Operation Phase
- (2)
- Non-Flood Season—Maintenance Phase
3.3.1. CSO Reduction Efficiency Analysis
3.3.2. Drainage Standard Analysis of the Basin
- (1)
- Combined Sewer Boxes and River Creeks
- (2)
- Shallow Drainage System
3.3.3. Urban Waterlogging Risk Control Effect
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Duration | Design Storm Value (mm) | |||
---|---|---|---|---|
P = 100 Year | P = 50 Year | P = 20 Year | P = 5 Year | |
1 h | 138.6 | 124.8 | 106.5 | 76.8 |
6 h | 252.0 | 225.0 | 188.0 | 131.0 |
24 h | 340.2 | 303.8 | 253.8 | 176.9 |
72 h | 448.6 | 400.5 | 334.6 | 233.2 |
Cross-Section Name | Catchment Area (km2) | River Length (m) | Slope Gradient (‰) | Urban Hydrological Method Flow Rate (m3/s) | |
---|---|---|---|---|---|
5% | 10% | ||||
Donghao Creek-Luhu basin | 9.42 | 6.81 | 2.84 | 106 | 91 |
Donghao Creek-Yudaihao and Xinhepu basin | 11.10 | 6.81 | 2.84 | 119 | 105 |
Plan | Conventional Scheme (Shallow Drainage Renovation) | Separate Rain and Sewage Scheme | Deep Tunnel Scheme |
---|---|---|---|
Scheme Description | Donghao Creek Whole Basin Waterlogging Transformation: Shallow Network Expansion, etc. | Separate rain and sewage in the entire Donghao basin | Donghao Creek whole watershed waterlogging control and initial rainwater collection |
Project Cost (billion yuan) | 0.47 | 0.98 | 0.59 |
Total Investment (billion yuan) | 1.02 (including 0.37 for land acquisition and pipeline relocation) | 2.87 (including 1.82 for land acquisition and pipeline relocation) | 0.77 (including 0.1 for land acquisition and pipeline relocation) |
Implementation Effect |
|
|
|
No | Outfall Locations | Water Level before (m) | Water Level after (m) |
---|---|---|---|
1 | Mayugang Channel Box | 7.958 | 7.322 |
2 | Zhongshan 3rd | 7.451 | 6.794 |
3 | Haoxian Road | 7.845 | 7.194 |
4 | Yudaihao | 6.891 | 6.299 |
5 | Junction of Xinhepu and Donghao Creek | 6.55 | 5.862 |
6 | Dongchuan Road Channel Box | 6.571 | 5.910 |
7 | Baizichong Channel Box | 6.588 | 5.925 |
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Sun, J.; Wu, X.; Wang, G.; He, J.; Li, W. The Governance and Optimization of Urban Flooding in Dense Urban Areas Utilizing Deep Tunnel Drainage Systems: A Case Study of Guangzhou, China. Water 2024, 16, 2429. https://doi.org/10.3390/w16172429
Sun J, Wu X, Wang G, He J, Li W. The Governance and Optimization of Urban Flooding in Dense Urban Areas Utilizing Deep Tunnel Drainage Systems: A Case Study of Guangzhou, China. Water. 2024; 16(17):2429. https://doi.org/10.3390/w16172429
Chicago/Turabian StyleSun, Jingyi, Xuewei Wu, Guanghua Wang, Junguo He, and Wentao Li. 2024. "The Governance and Optimization of Urban Flooding in Dense Urban Areas Utilizing Deep Tunnel Drainage Systems: A Case Study of Guangzhou, China" Water 16, no. 17: 2429. https://doi.org/10.3390/w16172429