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Solution for Secondary Water Supply in Urban Areas

2024-05-28
In urbanization construction, most of the pipeline networks of the water supply and drainage systems in municipal road projects are buried underground. If problems arise, they may affect the normal operation of production equipment, or even cause safety accidents or explosions. Moreover, detecting and resolving such issues can take a long time. Therefore, strengthening the quality control of municipal water supply and drainage engineering has become particularly crucial. This article identifies the current challenges faced by China's urban water supply and drainage pipeline systems, summarizes problem-solving measures, and discusses approaches to optimize urban water supply and drainage design.

Keywords: Urban water supply and drainage; Problem-solving measures; Design methods       Solution for Secondary Water Supply in Urban Areas

       

I. Current Challenges Faced by China's Urban Water Supply and Drainage Pipeline Systems

1. Prominent Contradictions Between Urban Water Supply and Demand

With the continuous acceleration of China's economic development, the contradiction between urban water supply and demand has become increasingly prominent. This stems from several factors:

  • First, the continuous growth of the population. Currently, China's urban population is increasing at an annual rate of 0.2%, leading to a significant surge in urban water consumption.

  • Second, increased water consumption per capita. Due to industrial development and improved living standards, urban per capita water consumption in China has nearly doubled compared to the past.

  • Third, rising industrial water demand.

  • Fourth, water resource shortages caused by pollution. Statistics show that nearly half of China's 670+ cities face water shortages, with 60–70% of these shortages attributed to water pollution. This exacerbates the pressure on China's already scarce water resources.

2. Conflict Between Deteriorating Water Supply Quality and Standardized Water Quality Requirements

As people's lifestyles accelerate and change, the demand for domestic water continues to rise. However, increasingly severe water pollution, coupled with outdated water treatment technologies, has led to a relative decline in drinking water quality. Consequently, the safety of water supply has become a focal point of public concern. China has not yet established a system for upgrading water quality monitoring standards, making it difficult to accurately grasp the current status and future trends of urban drinking water quality. Additionally, it has failed to fully and effectively apply the latest global research on the health impacts of drinking water quality, resulting in outdated national drinking water quality monitoring standards.

3. Tension Between the Urgency of Water Pollution Control and Inadequate Drainage Systems

Urban water pollution is a widespread issue in China, damaging water ecosystems, expanding water-scarce areas, and exacerbating water resource imbalances. This problem has threatened residents' daily lives, health, and urban modernization.
China's urban drainage infrastructure struggles to meet the urgent needs of wastewater treatment, manifested in:

  • (1) Low construction standards. Most urban drainage systems in China still use combined sewer systems, even in newly built areas. The planning and construction of drainage channels are unsystematic and disjointed, with leaks or groundwater infiltration in sewer pipes preventing effective collection of wastewater for treatment plants. This undermines the designed capacity of sewage treatment facilities.

  • (2) Poor coordination among design, construction, maintenance, and management of urban drainage systems. Accumulating debts from drainage infrastructure projects have constrained the development of urban road projects.

  • (3) Mismatch between urban drainage infrastructure and urban development speed or land planning. During urbanization, the pursuit of immediate industrial interests and growth has caused rapid urban expansion. While new roads and technologies are adopted above ground, underground facilities—particularly drainage systems—fail to keep pace. This results in repeated road excavations after completion, causing significant waste and damage.

II. Measures to Address the Above Challenges

1. Prioritize Scientific Research and Leverage Modern Technology to Support Water Supply and Drainage Projects

Enhance scientific research on urban water supply and drainage projects, and apply mature global research achievements and case studies—especially cutting-edge modern technologies—to provide robust support for China's urban water projects. Ensure solid foundations and standardization in project construction. Increase investment in research resources and budgets, and promptly translate research results into practical applications to provide reliable technical guarantees for water projects.

2. Expand Funding Channels and Use Market Economy Principles to Secure Project Financing

Shift from a "closed operation" model to a "government-led, market-promoted" approach. While ensuring government investment and fiscal financing, create a favorable policy environment for investment, diversify funding sources, break monopolies, and establish an investment benefit and risk constraint mechanism based on the principle of "who invests, benefits, and assumes responsibility." This ensures the efficient development of financing systems and promotes comprehensive progress in urban water supply and drainage.

3. Improve Laws and Regulations to Ensure Implementation of Construction and Management Requirements Through Accountability

Establish internationally applicable standards, improve legal frameworks through administrative legislation, clarify the responsibility system for water supply and drainage project construction and management, define authority boundaries, and form a clear division of rights, responsibilities, and supervision among planning, construction, maintenance, and regulatory agencies.

III. Optimizing Urban Water Supply and Drainage Design Methods

1. Pipeline Construction Planning

In practice, for pipelines with minimal mutual interference, the spacing can be appropriately reduced. For example, standards specify a horizontal distance of 1.5m between heating pipes and sewage pipes, but with improved pipe quality, this distance can be adjusted based on specific conditions without affecting normal operation. Designers should enhance labeling and documentation of pipeline foundations, embedded parts, diameters, elevations, etc., and use as many standard or detailed drawings as possible to avoid unnecessary errors. During general layout design, follow these principles: ensure pipes are not crushed under load; in cold regions or winters, prevent pipe contents from freezing; meet longitudinal planning requirements; and maintain reasonable vertical spacing between pipes as per standards. The minimum backfill depth should be determined based on the selected pipe material and its pressure-bearing capacity.

2. Pipeline Network Optimization

Optimizing the structural design of water supply and drainage pipeline networks involves finding optimal combinations of pipe diameters and pump parameters within a given layout. In existing pipelines, rationalize flow distribution using algorithms like ant colony optimization to optimize pipe diameters. Based on urban topography, partition water supply areas with different pressure zones to minimize overall system operating costs. Common algorithms for water supply and drainage optimization include linear programming, nonlinear programming, dynamic programming, and genetic algorithms. For small-to-medium pipeline optimization, genetic algorithms are often suitable for finding optimal designs. Integrate direct pipeline superimposed pressure water supply technology with non-negative pressure pipeline booster and pressure-stabilizing equipment. When municipal water supply networks have sufficient flow and stable pressure, use non-negative pressure booster equipment. In areas with concentrated water demand or sudden high flow, employ direct pipeline superimposed pressure systems to reduce peak flow impacts on the network and ensure equipment operates normally.

3. Rainwater Drainage Design

When predicting rainfall, determine the design return period for stormwater pipes based on catchment area characteristics, topography, and climate. Traditional methods struggle to promptly update parameters in storm intensity formulas, but genetic algorithms’ global search capabilities and direct manipulation of objective functions can avoid complex calculations involving higher-order derivatives or equations, improving formula accuracy. For main roads, critical areas, or locations where short-term waterlogging could cause severe damage (especially low-lying intersections), appropriately increase the design return period. In urban areas or industrial zones with high building density and heavy traffic, use buried pipes for rainwater drainage. In flat terrain, adopt covered slab systems for efficient drainage, easy maintenance, and management. In suburban areas or low-density zones, consider open channels to reduce project investment and pipeline costs. Surface rainwater can be drained via ground ditches, with the starting end of main pipes using ground ditches to reduce buried pipe length by approximately 100–150m.

4. Sewage Drainage Design

Sewage mains under streets are often laid before detailed community planning is finalized, leaving drainage points uncertain. To facilitate connections between sewer pipes and risers, design connecting pipes at regular intervals along the main pipe, extending beyond building red lines and into sidewalks. This avoids road damage during future riser connections, reducing construction volume and costs. The spacing of connecting pipes should be balanced to avoid waste while enabling nearby buildings to drain efficiently. Avoid conflicts with other underground pipelines using measures such as drop manholes for elevation adjustment, partial cross-sectional expansion to maintain flow capacity, or inverted siphons in special cases. During urban water supply and drainage design, analyze the uniqueness and specifics of each project to promote more economical solutions under the premise of reliability and rationality. This is particularly important in new urban development, old old town renovation, and road construction, where pipeline network planning and optimization are increasingly critical. Address design flaws, adapt to urban development needs, and optimize structural designs based on real-world conditions.

As China implements the strategy of sustainable development, water sustainability holds a pivotal position, as water has become a major constraint on economic and social development. Therefore, creating a new landscape for urban water supply and drainage systems has become a historical responsibility for relevant engineers.


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