What are the keys to urban river management?
1. Basic water conservancy elements of urban river management
From a traditional water conservancy perspective, the river management process should focus on three factors: water level, flow velocity and rainwater inlet elevation. These three factors These factors directly affect the success or failure of river management. The design water level of the river must be determined based on the urban flood control plan and the city's overall plan. At the same time, the inner top of the river mouth where rainwater enters must be higher than the design water level. The flow speed of urban rivers is an important parameter in river channel design. Generally, the flow speed of urban rivers should not be too fast or too slow. The water level and flow rate of the river can be controlled through gates and dams along the way.
2. Selection of urban river sections
Different river sections have different river functions, and there are many river sections to choose from, such as rectangular sections, trapezoidal sections, duplex sections, etc. Due to the shortage of urban land, the spatial layout of river channels is subject to multiple restrictions. The use of rectangular and trapezoidal cross-section designs can improve land utilization in waterfront areas, but the water level fluctuates greatly between wet and dry seasons, and the rigid protection blocks the material and energy exchange between the river water body and the river bank, resulting in poor landscape and ecological effects. . Section selection in the process of urban river regulation is a process of regional landscape structure selection. The number, type, size, shape and appearance characteristics of the elements that make up the landscape have a direct or indirect impact on the movement characteristics of ecological objects, which in turn affects the overall function of the system.
The river section design focuses on examining the scope of influence of standard floods, reserving as wide a river width as possible according to land conditions, and then designing the distribution ratio of river channels, troughs and beaches based on the basic water volume and water level relationship of the river. This not only ensures It meets the space requirements of urban river landscape design, and can play a buffering role under extreme weather conditions and improve the flood discharge capacity of urban rivers.
3. Urban river landscape design
Urban river is a linear system. Appropriate design scale must be selected based on the characteristics of linear engineering and the principle of economic feasibility. The core of its landscape design is Guide the healthy operation of urban rivers and surrounding ecosystems based on ecological principles, and maximize the use of natural forces to promote the regeneration of the system's organic renewal capabilities. In terms of design strategy, it is necessary to meet the landscape needs of multiple scales and objectives as much as possible, and understand the regional residents and office workers. , the differences in needs of travelers in different periods (such as different seasons, different weather, different time points, etc.). At the same time, designers must think about the changes and development processes of the natural system itself from a development perspective, and use appropriate artificial intervention to guide the natural system to develop in a favorable direction. For example, the aquatic community and amphibious community produced by the river in its natural state will gradually evolve into a complex "aquatic, amphibious, and terrestrial" ecosystem. Taking into account the landscape changes brought about by the development of the system, the design should Make scientific and reasonable solutions at every stage.
The planning and design of river waterfront space is an important part of current urban landscape planning. Different from single water management, waterfront space planning is guided by ecological theory and will affect the river and riverside ecology. All issues (such as flood control, embankments, tidal flats, vegetation, aquatic life, etc.) should be considered and a comprehensive plan should be formulated to achieve the purpose of restoring the ecological stability of the waters.
4. Urban river ecological environment and landscape benefits
River ecological restoration means the restoration of ecological functions of rivers and waterfront areas, which can support the normal operation and derivation of river ecosystems. Generally speaking, the ecological functions of river corridors mainly include habitat function, channel function, filtering and barrier function, source-sink function, etc. In the process of river management, the banks formed by hard lining can be considered as artificial corridors. According to The distance-benefit analysis of artificial corridors shows that as the distance increases, the economic benefits gradually decrease, while the environmental benefits of natural corridors gradually increase as the distance increases. Among them, there is a balance point. Under this length condition, the economic benefits of artificial corridors are roughly equivalent to the environmental benefits of natural corridors. This reflects that urban rivers can maximize their strengths and avoid weaknesses through moderate artificial intervention. It can also be explained that moderate local lining can improve flood control benefits and play a positive role in regional public safety and property safety.
When designing urban river ecological restoration, artificial measures need to be reinforced in important parts of the river, which has a positive effect on ensuring economic benefits and exerting comprehensive environmental benefits. Landscape ecological design needs to understand the connectivity between landscape elements, avoid reducing landscape diversity and biodiversity, and consider retaining habitats and corridors in key areas that affect biological communities. When designing the ecosystem, local plants should be used as the mainstay as much as possible to reduce the damaging effects of invasion of alien species on the ecosystem. The riverbed slope design should avoid large water drops and fully consider fish migration and the two-way material and energy connection between the upstream and downstream.
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