Lessons for the flooding management in modern cities from traditional planning methods in China

The water management system in traditional Chinese towns consists of multifunctional water bodies such as a moat, canals, rivers, lakes and pools. In the modern era, those water systems of ancient settlements were abandoned and urban drainage systems were constructed alternatively due to the urban development. However, the modern mechanisms are facing challenges over the past decades, especially pluvial flooding events. 

Following explaining the causes of urban waterlogging in Chinese cities, this article proposes a three-tier framework by borrowing the traditional knowledge and methods of water management in ancient cities. Collaborating with different domains of sub plans, this proposed approach aims to establish a local sustainable water system throughout different layers of planning.

1.Background

Waterlogging has been one of the problems in urban management in China today. This issue attracts the attention of the national government, and a policy was issued on 25 March 2013 by the State Council to stress the urgent tasks of water management in cities. It is suggested that studies to cope with urban flooding are imperative to be carried out. 

1.1 The causes of urban waterlogging in Chinese cities

Urban waterlogging is usually caused by multiple reasons, including meteorological circumstances, urban construction, and the design and maintenance of urban infrastructures. 

1.1.1 Meteorological factors

A.Hydrological cycle changes in the context of climate change, and the frequency and magnitude of climatic events show an increasing trend;

B.Microclimate triggers more frequent and violent rainfalls as a result of urbanisation;

C.The rise of sea levels weakens the capacity of drainage systems in coastal cities, which contributes to potential fluvial floods; and

D.The soaring threats of typhoons and storm surges in China are significant. 

1.1.2 Urban construction

A.The impermeable surface of urban ground contributes to soaring flows and velocity of floodwater;

B.Filling natural water bodies for urban construction and the incapacity of drainage systems lead to the potential failure in water management;

C.Low-lying areas in cities could suffer inundations when the levels of water are rising; and

D.The decline of the areas and density of natural water bodies as well as the construction of hard embankments could increase the possibility of urban waterlogging.

1.1.3 The infrastructures 

A.The current standard of drainage systems in China is incapable of violent flooding hazards with the change of meteorological conditions;

B.The construction of drainage systems has been given less attention than buildings above the ground; and

C.A lack of updated drainage facilities and regular maintenance may weaken the effectiveness of flooding management.

1.2 The chief barriers to cope with urban waterlogging

A.Most drainage facilities can only cope with floods with one- to three-year return periods, it is also difficult to improve the standard of the systems in the constructed areas due to the expensive cost to rebuild the drainage pipes beneath the densely populated areas.  

B.Existing water systems in cities greatly rely on hard engineering approaches, and the advantages of natural water bodies in capturing and storing rainwater are underestimated.

C.A lack of interaction between urban drainage systems and flood control systems increases the pressure of management further.

D.Many low-lying areas in cities are created by urban development. To keep these flood-prone areas free from inundations, the inlets of drainage pipes and water pump stations are usually set to clean rainwater. However, lacking a systematical design, these facilities often fail to cope with flooding hazards with surge magnitudes. 

2.The lessons from Chinese ancient cities

Historically, the planning of ancient cities usually facilitated natural water bodies to create and organise artificial water systems, which not only met the demands of water supply for the towns but also performed the functions of flood management, manufacture, transport and landscaping. The most important strategy to resist flooding hazards in traditional towns is to establish a circulatory system that is composed of a moat, canals, rivers, lakes and pools. The arrangements of diverse water bodies in ancient cities contribute to flooding prevention with the functions of water drainage and collection. 

2.1 The layout of water systems in ancient Chinese cities

A moat and different types of water bodies inside city walls constitute the water systems of many ancient cities in China (Figure 1-3). These water systems were connected to the natural rivers out of the cities with water control facilities, such as water gates and culverts. This planning and water engineering method dates back to Pinglangtai (平粮台), an early human settlement, in China in 4300 BC., and this design was inherited by many cities in the following centuries. 

The circulatory water systems played a vital role in flooding controls and water management in ancient towns. The moat surrounding the cities enables the disposal of waste water and run-offs within the city walls. Its circular layout can efficiently absorb water from different directions in the towns, which not only drains off run-offs effectively but also increases the density of waterways and storage capacity of the cities. It creates a balance between the area of cities and the capacity of water channels. Dongjing (东京)，the capital city of North Song Dynasty (960-1127 AD.), as well as Beijing in the Ming and Qing Dynasties (1403 and 1912 AD.) are two typical examples of ancient water management in China. The total perimeter of the three-layer moats of Dongjing is up to 47.4 km, it possesses a water capacity of 17 million square meters which makes up 95 per cent of the collective figure of the city. Having a similar layout of moats, the City of Beijing can store about nine million square meters of water which constitute half capacity of the water system. 

 Figure 1 Plan of Chang’an City in the Tang Dynasty

Figure 2 Plan of Dongjing City in the North Song Dynasty

Figure 3 Plan of Beijing City in the Ming and Qing Dynasties

Also, water channels throughout cities divide the water systems into sub-zones within the city walls, in order to increase the storage capacity of rainwater. Four rivers flowed across the City of Dongjing, and the total length of the waterways was about 30 km and the capacity was nearly 0.9 million square meters. As for Beijing, water channels within and outside the city can contain water about 1.2 million square meters. 

In addition to the moats and water channels, small lakes and pools were positioned in urban districts. These water bodies were embedded in low areas of the towns to absorb flooding water from nearby blocks during hazards. Many examples can be found in ancient cities across China (Figure 4-9). 

2.2 The integration of rainwater drainage and collection

The water management systems in ancient towns mimicked the circulation of natural water systems to drain the waste water and rainwater constantly. Light rains would not cause inundations in cities. When the water level of water bodies outside the cities was lower than that of moats in violent storm events, rainwater would flow through the channels to the moats. In this case, the density of waterways in cities and the water channels’ sections are key criteria of the efficiency of drainage systems. Accordingly, comparing to the design of water management systems in capital cities of different dynasties in China, the Forbidden City in Beijing built between the Ming Dynasty and Qing Dynasty is the most outstanding model. 

The storage capacity of water systems in ancient cities is another key parameter of the effectiveness of flood management. Different components of the systems can collect and store rainwater. When the water level of moats exceeded that of natural rivers, rainwater in cities could be captured and collected temporally by moats, water channels and wet lands in the cities. Thus, the density and sections of them are the criteria to quantify the capacity of the water systems. Comparing the planning of water, the Forbidden City possesses the most effective water management systems midst the main capital cities with regard to its storage capacity of rainwater. 

Figure 4 Plan of Ganzhou City in 1872    

Figure 5 Plan of Heze City in 1960

 Figure 6 Plan of An’yang City in 1933   

  Figure 7 Plan of Jingzhou City in 1880

 Figure 8 Plan of Nanyang City in 1870

Figure 9 Plan of Kaifeng City in 1898

3.How the knowledge of ancient cities informs the planning of modern cities

Urban planning in China was changed due to urbanization and modernisation since the 19th century, and drainage networks beneath the urban ground replaced the traditional water systems in the cities. Impermeable ground surfaces also disrupt the seepage of rainwater, and only a few channels are left for the discharge of floods. These increase the burdens on the drainage systems. However, compared to traditional planning, modern drainage systems are usually incapable of water storage, and their designing standards meet difficulties in update with the rapid expansion of urban areas. Therefore, it is argued that the storage function of flooding systems cannot simply be replaced by the underground drainage, and creating facilities to store rainwater could be a potential solution to cope with flooding risks in Chinese cities. 

When drawing a city plan, water systems and flooding controls need to be integrated with other themes of sub-planning and considered on multi-scale plans. Also, the complementary and mutual functions of drainage and storage should be created to release the pressure of drainage networks. Also, modelling flooding scenarios with information about the drainage capacity, DEM, land use and the magnitude of rainfalls could provide scientific evidence for a more comprehensive urban planning and design. 

Additionally, a sustainable drainage technique-source control aims to maximise ‘the permeability in a site to promote attenuation, treatment and infiltration reducing the need for offsite conveyance^①, which have been promoted by the means of LID (Low Impact Development), GSI (Green Stormwater Infrastructure) and SuDS (Sustainable Drainage Systems), etc. This approach was recommended by national standards of designing in built environments and the Notice (2013) introduced by the State Council. Accordingly, the construction of effective water systems and flooding controls in cities needs to collaborate with different layers of plans and the data obtained in the flooding simulations. 

In the light of the significance of the flooding management system in the master plans and its multiple functions in urban environments, a three-tier framework of water systems is proposed. This framework creates an integrated mechanism of the urban water system, drainage systems and the techniques of source controls on neighbourhood scales, in order to establish sustainable water management throughout the planning of cities. 

Moreover, to reduce flooding hazards in the constructed areas, the improvement of water engineering is a long-term goal that requires the collaboration of different interests and groups. An effective and comprehensive flooding management plan is also necessary to be introduced, including the assessment of flooding risk, the designing of emergency plans, and raising the awareness of potential hazards, etc. 

In sum, modern construction shows its drawbacks in dealing with the increasing urban waterlogging in China. The lessons and knowledge of traditional planning methods in ancient cities inform us of potential solutions to reduce the impacts of floods and create sustainable urban environments in the context of China. An inclusive and holistic planning approach needs to be carried out to consider the management of water and floods in different layers of plans. 

Notes：

^①Source: https://www.susdrain.org/delivering-suds/using-suds/suds-components/source-control/source-control.html

Source: <https://mp.weixin.qq.com/s/XKNdppG5n_2QwwPa5QL6Xg>

Translated and edited by Liang Xiuchun