From the perspective of traditional water conservancy, the process of river regulation should pay attention to three factors: water level, flow rate and the elevation of rainwater entering the estuary, which directly affect the success or failure of river regulation. The design water level of the river should be determined according to the urban flood control planning and the overall urban planning, and the top of the estuary where rainwater enters should be higher than the design water level. The velocity of urban rivers is an important parameter in river design, and generally it should not be too fast or too slow. Dams along the way can control the water level and velocity of the river.
2, the choice of urban river section
Different river sections have different functions, and there are many available river sections, such as rectangular section, trapezoidal section and composite section. Due to the shortage of urban land, the spatial layout of rivers is subject to multiple restrictions. Adopting rectangular and trapezoidal cross-section design can improve the land utilization rate in waterfront area, but the water level fluctuates greatly in high water season and low water season, and rigid masonry cuts off the exchange of material and energy between river water body and bank, resulting in poor landscape and ecological effects. The selection of section in the process of urban river regulation is the process of regional landscape structure selection. The quantity, type, size, shape and appearance of landscape elements have a direct or indirect impact on the movement characteristics of ecological objects, and then affect the overall function of the system.
The design of river section focuses on the influence range of standard flood, reserving a wider river width as far as possible according to the land conditions, and then designing the distribution ratio of river and beach according to the basic water level relationship of the river, which can not only meet the space requirements of urban river landscape design, but also play a buffering role in extreme weather conditions and improve the flood discharge capacity of urban rivers.
3. Landscape design of urban rivers
Urban river is a linear system, so it is necessary to choose the appropriate design scale according to the characteristics of linear engineering and the principle of economic feasibility. The core of its landscape design is to guide the benign operation of urban rivers and surrounding ecosystems based on ecological principles, and to maximize the use of natural forces to promote the regeneration of the system's organic renewal ability. In the design strategy, we should not only meet the multi-scale and multi-objective landscape needs as much as possible, but also understand the residents, office workers and travelers in different periods (such as different seasons, different weather and different time points). At the same time, designers should think about the changing and developing process of natural system from the perspective of development, and guide the natural system to develop in a favorable direction by using appropriate manual intervention. For example, the aquatic community and amphibian community produced by rivers in natural state will gradually evolve into a complex "aquatic-amphibious-terrestrial" ecosystem. Considering the landscape changes brought by system development, scientific and reasonable solutions should be made in the design stage.
The planning and design of river waterfront space is an important content of current urban landscape planning. Different from single water area management, waterfront space planning takes ecological theory as the guiding ideology and considers all issues (such as flood control, river banks, beaches, vegetation, aquatic organisms, etc.). ) affect the river and riverside ecology, formulate comprehensive planning, and restore the ecological stability of water areas.
4. Ecological environment and landscape benefits of urban rivers.
Ecological restoration of rivers refers to 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, filter barrier function, source and sink function and so on. In the process of river regulation, dikes formed by hard lining can be regarded as artificial corridors. According to the distance benefit analysis of artificial corridor, its economic benefit will gradually decrease with the extension of distance, while the environmental benefit of natural corridor will gradually increase with the extension of distance. Among them, there is a balance. Under the condition of this length, the economic benefit of artificial corridor is roughly equivalent to the environmental benefit of natural corridor. This reflects that urban rivers can make full use of their strengths and avoid their weaknesses through moderate human intervention, and also shows that moderate local lining can improve flood control benefits and play a positive role in regional public safety and property safety.
In the design of urban river ecological restoration, it is necessary to strengthen the important parts of the river by artificial measures, 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 preserving habitats and corridors in key areas that affect biological communities. In the design of ecosystem, we should give priority to local plants as much as possible to reduce the damage of alien species to the ecosystem. The design of river bed gradient should avoid large drop scheme and fully consider the material and energy relationship between fish migration and upstream and downstream.
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