Extreme rainfall is causing actual, sudden urban flooding disasters. The dangers are not hiding in the distant future but what might threaten us tomorrow. Unlike the flooding caused by rising sea and river levels, urban local flooding is more frequent and destructive, which is caused by sudden heavy short-duration storms and overland flow.
Based on high-resolution urban flood modelling, an alternative drainage system, which is composed of urban overland flow paths and a multi-functional stormwater park, was built in a depressed urban area in Guyuan City, China. Within two years, the system not only protected the area from 50-year storms’ threats but also provided sound recreational and ecological benefits.
Project Background
The project is located in Guyuan City, northwest China, an arid area with an average annual precipitation of less than 450 mm. However, climate change brings more intense rainfall, overloading existing urban drainage system and resulting in flooding issues. During heavy rain, the surface runoff overflows from nearly half of the city area would flow to one depression area, causing a 1-kilometer-long ponding in the road corridor with water depths over 30 cm. Worse, subsequent hazards such as road subsidence and building damage may occur due to collapsible loess.
Build an Alternative Drainage System
Upgrading the existing drainage system to cope with 5- to 50-year storms could reduce the urban flooding risk. However, it is not considered as a preferred option due to the low-cost benefit ratio and long construction period. Facing the upcoming threats, the city needed a fast-implementable but efficient solution. Considering the existing urban terrain system as a part of overland flow path design element, landscape architects cooperated with drainage engineers to build an alternative drainage system against extreme storms using existing facilities such as roads, green spaces, culverts, etc. This approach is considered to be safe, sheltered, and multifunctional as well.
The Lidar-based high-resolution (0.5 m×0.5 m) flood risk modelling is a decisive factor for designing, presenting the flood consequences of 5 to 50 year ARI. The simulation scenario shows, during heavy rain, urban roads have become the main drainage channel for overland flow. And there will be a significant flooding because of overland flow path disconnection between the depressed urban area and the Qingshui River, the major river of the city, caused by the elevated riverbank.
Therefore, Landscape architects creatively integrated different landscape features into an emergency surface drainage system and reconnected the overland flow path to the Qingshui River with a multi-functional park. The park was envisioned to have the function of both1- to 5-year storms detention and 5- to 50-year storms overland flow conveyance while enriching public recreational spaces.
Under the close cooperation of all parties, an 8.3-hm² sponge park was constructed before the following year’s wet season and equipped with the capability to handle 50-year storms.
Create a Resilient “Artificial Stream”
The park trail system and waterfronts were elaborately organized into the main channel after an overall assessment of overland flow velocity and erosion, implementation and maintenance difficulties, and users’ recreational demands. The recycled rainwater is used to supply the base flow of the main channel during dry season, forming an “artificial stream”. The stream is composed of torrents, tranquil flows, cascades, and shallows just like natural rivers. It not only provides a playground for children but also attracts adults to reconnect with nature. The sound of running water from the stream and the singing of frogs and birds in the Willow Pond Wetland offer a joyful background for people’s recreational activities.
Enhance Ecological Benefits and Biodiversity
The preserved Willow Pond Wetland provides a high-quality habitat for the birds living around the Qingshui River. The weeds and willows in and along the main channel can shelter them from predators. The gravel bed of the stream is not only a safe footrest for birds, but also an ideal habitat for insects and small mammals.
Location:
The intersection of Dongguan North Street and Liupanshan East Road, Yuanzhou District, Guyuan, Ningxia Hui Autonomous Region
Design year:
2020
Year Completed:
2021
