In Yinchuan, China, a new urban area is planned for 160,000 inhabitants, in the vicinity of the Yellow River and close to a valuable natural landscape. To achieve sustainable development, an approach integrating urban planning, transport, energy, solid waste and water resources management is necessary. In order to achieve this, the SimbioCity approach was applied, where resource use and pollutant loads are reduced by creating cycles in which materials and water are recycled to the largest possible extent. In this context, the stormwater system is an important component. The objectives for the planned stormwater system in Yinchuan New City were to reduce flood risk and introduce stormwater purification, to maintain or improve water quality in the existing water bodies. A Sustainable Urban Drainage System approach was proposed and applied, during configuration and design of the new town's infrastructure. This proved both successful and cost effective.

Objectives

The configuration and design objectives for water and solid waste management in the Yinchuan New Town project were to:

• Determine a general water balance for the project area

• Develop guidelines and a design for the stormwater drainage in the area

• Design a wastewater system integrated with the solid waste system

• Design a wastewater treatment plant including nutrient reduction

• Prepare a proposal for potable water use reduction by separating black and grey waters

The water balance included an estimate of water need for the area, including evaporation from Mingcui Lake, and predicted water use in Yinchuan New Town, as well as estimates of water availability from different sources like water reuse and abstraction from existing irrigation channels.

The objective of this paper is to present the methodology applied in order to achieve SuDS in the project area and the results obtained.

INTRODUCTION AND BACKGROUND

Yinchuan is the capital of Ningxia Hui Autonomous Region, China (People's Republic of China (PRC)). It has a typical, temperate continental monsoon climate, with little rain and high evaporation rates. Given its proximity to the Yellow River and a developed channel system, the area has relatively good surface- and ground-water conditions. The surrounding region, however, is very short of water.

The main driving forces in Yinchuan's new urban area are housing and tourism. When fully developed, the new town is expected to have approximately 160,000 inhabitants. The aim is to develop it on an artistic and cultural profile, as well as sustainability principles. The Mingcui Lake, a valuable natural landscape, together with a large area of fishponds, channels and ditches, makes up the basic texture of the site. A key requirement was to safeguard the hydrologic and water quality conditions of the lake and wetland in the north of the project area (Sweco 2013). The original site is shown in Figure 1. The wetland is the shallow zone around the lake.
Figure 1

Existing texture and structure of the project area.

Figure 1

Existing texture and structure of the project area.

To achieve sustainable urban development, an approach integrating urban planning, transport, energy, and solid waste and water resource management is necessary, with the latter playing a key role. The design of these components was an integral part of the urban planning and design process.

The approach to achieving sustainable urban development was based on the SimbioCity methodology (Ranhagen et al. 2007). The principles of SimbioCity incorporate a multi-disciplinary mode of operation that enables combined problems to be solved successfully, taking into account social, institutional, environmental, technical, economic and spatial aspects (Ranhagen et al. 2012). A basic tool in the methodology is the eco-cycle model, where reduced resource use and pollutant loads are sought by creating cycles where materials and water are recycled to the largest possible extent, or used in energy generation. Resource use is reduced by introducing efficient techniques, and taking advantage of the synergies created by integrating the water, waste and energy cycles. An example of this is the generation of biogas (energy cycle) from organic waste (waste cycle) and wastewater sludge (water cycle). Similar approaches have been proposed by others (Novotny 2011).

The relevant standards for urban drainage in China are GB 50318-2012 Code of Urban Drainage Engineering Planning, GB 50318-2000 Code of Urban Wastewater Engineering Planning, and GB 50014-2006 Code for the Design of Outdoor Wastewater Engineering.

Average precipitation around Yinchuan is 189 mm/year, with average water surface (potential) evaporation of 1,197 mm/year. Precipitation occurs from June to August, inclusive, and the twenty first century has seen some flooding in the existing urban areas, such as that in the central areas of the city in July 2012.

The relevant Chinese water quality standard is GB 3838-2002. Water quality in Mingcui Lake is below grade III, where grade I is the best and grade V the worst. Water quality in the lake is moderate, due to agriculture drainage and the discharge of untreated wastewater from rural villages in the area.

The Chinese standard states that stormwater pipes must be designed for a storm with a return period up to 3 years, based on the characteristics of the catchment, and its topography and climate conditions, and from 3 to 5 years for important roads (GB 50014-2006).

METHOD

With respect to stormwater management and flood prevention, alternatives to a conventional stormwater sewer system were needed because flood events have been relatively frequent, even though the project area has low average annual precipitation, because of the very concentrated rainy period. Moreover, the stormwater management system had to avoid polluting existing water bodies during rainfall events. In order to comply with these demands, a new approach was applied based on stormwater detention and treatment.

The method and solution applied had two objectives:

  • To avoid flooding important roads, as well as residential and commercial areas, for a 100-year return period flood, although the costs for achieving this must be reasonable.

  • To introduce stormwater treatment to maintain or improve water quality in Mingcui Lake.

To achieve these goals, a SuDS approach was applied during configuration and design of Yinchuan New Town's infrastructure.

The approach proposed in the CIRIA SuDS Manual (Woods-Ballard et al. 2007) was used as the design basis. According to CIRIA, stormwater should be managed in small, cost-effective landscape features in small sub-catchments, rather than being conveyed to and managed in large systems at the bottom of drainage areas (end of pipe solutions). In addition, solutions used in Malmö, Sweden (Stahre 2006, 2008) as well as Portland, USA (Liptan 2011) were applied, with some adaptation to local conditions in Yinchuan.

Three stormwater management levels were proposed for Yinchuan (Figure 2): plot level, channels leading to a purification pond, and discharge to the existing wetland or lake.
Figure 2

Basic configuration of the stormwater system in Yinchuan New Town.

Figure 2

Basic configuration of the stormwater system in Yinchuan New Town.

The detention volumes required for a catchment area, at plot and channel level, were calculated using the Equation (1) below: 
formula
1

where:

  • Vdetention: detention volume (m3)

  • tr: rain duration (min)

  • Qin: runoff flow, calculated as 
    formula
    2
  • Δk: Area k within the plot or channel watershed (ha)

  • ik: runoff coefficient for Area k (dimensionless)

  • Qout: given outflow from the channel or detention structure at plot level (l/s)

  • L rainfall intensity (l/s/ha)

The rain intensity equation recommended for Yinchuan by China's Meteorological Agency is 
formula
3

where T is the return period (years). The return period for the plot level detention structures was 10 years, that for the channels 100.

Detention volumes were calculated using formulas (1) to (3) above, for different values of rain duration (tr). The maximum of these detention volumes is thus that required for the catchment.

The pollutant loads and treatment requirements were estimated using the StormTac watershed modelling tool (StormTac version 2015-1, StormTac Storm Water Solutions). The structure of Storm Tac is presented in Figure 3.
Figure 3

Simplified flowchart for the watershed management model StormTac.

Figure 3

Simplified flowchart for the watershed management model StormTac.

Stormwater discharge was identified as one of the major polluting emissions in urban areas in Sweden (Alm et al. 2010). StormTac is used to estimate the mean pollutant concentration based on the specific land use(s) in the catchments. It uses ‘standard concentrations' per land use type, to calculate pollution loads at the catchment discharge point.

In Yinchuan New Town, the treatment facilities considered will comprise the channels or ditches, and the treatment ponds upstream of the discharge point. There is also some treatment at plot level; however, since there will be some stormwater detention facilities at this level, so it is not possible to establish which load reduction is applicable. Because of this, the treatment at plot level was excluded from the load reduction estimates – i.e., no load reduction is considered in the estimates at plot level – yielding a conservative approach.

For wet ponds and constructed wetlands, reduction efficiency is calculated using Equation (3) (Larm 2014) 
formula
4

where:

  • Ap: Pond or constructed wetland area (m2)

  • Ared: Reduced catchment area, calculated as , that is the area multiplied by its runoff coefficient

  • Ak: Area k within the catchment (ha)

  • Ck: runoff coefficient for Area k

  • k1, k2: regression coefficients for the individual pollutant

  • fCin : inlet concentration factor

  • fveg : vegetation factor

  • fbypass : bypass factor

  • fVd : detention volume factor

  • fCirr : irreducible concentration factor

  • ftemp: temperature factor.

  • fshape : shape factor.

The runoff and regression coefficients, and all factors above, are dimensionless.

The minimum outlet concentration, the ‘irreducible concentration’ (Cirr), arises from influent content and internal processes in ponds and wetlands (decomposition of plants, seepage of anaerobic liquors from the bottom, exchange with sediment, sediment disturbance by benthic animals, etc.), which limit the extent to which pollutants can be removed. In StormTac, the reduction efficiency is adjusted so that nothing less than minimum concentrations are obtained at the outlet. The irreducible concentrations were estimated from effluent concentration data from facilities in Europe. Some examples of these are Cirr (Ptot) 20–30 μg/l, Cirr (Cu) 6–7 μg/l, Cirr (Zn) 14–25 μg/l and Cirr (SS) 5–10 mg/l (Larm 2014).

For channels, swales and ditches, the reduction efficiency is calculated using Equation (5) below: 
formula
5

where:

  • Aditch: channel or ditch area (m2)

  • Ared: reduced catchment area (ha)

  • k1, k2: Regression coefficients for the individual pollutants, dimensionless.

The regression coefficients and factors used in the equations above have been obtained from existing ponds, swales and other stormwater detention and treatment facilities, mainly in Europe and North America (Larm 2000; Larm & Hallberg 2008). The annual precipitation at these overseas sites is higher than that at Yinchuan but, as precipitation in Yinchuan occurs mainly between June and August, rainfall intensity is similar to that at the sites used as a base for StormTac. Other factors which may influence removal efficiency, apart from pond size and form, are the vegetation and soil types used in the treatment ponds, which are basically the same or very similar in Yinchuan and the sites where the factors and coefficients were deduced.

The recommended surface area for a channel or ditch to achieve a satisfactory pollutant removal rate is at least 2% of the reduced catchment area (Larm & Banach 2011).

RESULTS

The project area was divided into sub-catchments on the basis of topographic levels, and road and green areas, as well as stormwater infrastructure planned for Yinchuan New Town. The topographic levels, and the proposed infrastructure and landscape, were all based on the site's existing natural characteristics. The main roads usually established the watershed limits, while the green corridors and channels constituted the flooding areas. This required an iterative process involving different professionals – e.g., hydrologists, road engineers, landscape architects and city planners.

The catchment area for Channel B, is shown in Figure 4. The sub-catchment characteristics are presented in Table 1.
Figure 4

Catchment area for Channel B.

Figure 4

Catchment area for Channel B.

Table 1

Main data sub-catchments in Yinchuan New Town

Sub-catchment A + B H + I 
Area (ha) 232 167 249 207 164 
Average runoff coefficient 50% 49% 53% 53% 54% 
Reduced area (ha) 116 82 132 110 89 
Sub-catchment A + B H + I 
Area (ha) 232 167 249 207 164 
Average runoff coefficient 50% 49% 53% 53% 54% 
Reduced area (ha) 116 82 132 110 89 

The required detention volumes at plot level for a 10-year return period and channel level for a 100-year period for the sub-catchments in Yinchuan New Town are presented in Table 2.

Table 2

Required detention volumes

  Required detention volumes (1,000 m3
Sub-catchment plot level channel 
A + B 67 78 
47 51 
81 90 
26 30 
H + I 55 61 
  Required detention volumes (1,000 m3
Sub-catchment plot level channel 
A + B 67 78 
47 51 
81 90 
26 30 
H + I 55 61 

Stormwater detention structures, such as road planters (Figures 5 and 6) and detention ponds, were proposed as means of detaining the plot level volumes reported above.
Figure 5

Type drawing for road planters.

Figure 5

Type drawing for road planters.

Figure 6

Road planters, Yinchuan New Town.

Figure 6

Road planters, Yinchuan New Town.

Multi-functional areas have been used in Yinchuan to obtain the necessary detention volumes at channel level. The landscape channels and adjacent parks have been designed to function as floodwater holding areas during rainfall events. Landscape levels have been designed to secure the necessary volumes, maintaining flood levels below road and building thresholds. As an example, see Figure 7.
Figure 7

Floodwater retention area, Channel B (WL 100 = 100-year return period water level).

Figure 7

Floodwater retention area, Channel B (WL 100 = 100-year return period water level).

The detention pond surface areas and volumes, and calculated pollutant loads before and after treatment in channels and ponds are shown in Tables 3 and 4. One of the detention ponds in Yinchuan New Town is shown in Figure 8.
Table 3

Detention ponds areas and volumes

Sub-catchment A + B H + I 
Pond area (m212,000 28,000 7,000 7,000 34,000 
Pond volume (m371,200 85,500 153,200 150,200 142,700 
Sub-catchment A + B H + I 
Pond area (m212,000 28,000 7,000 7,000 34,000 
Pond volume (m371,200 85,500 153,200 150,200 142,700 
Table 4

Anticipated pollutant concentrations

    Concentrations prior to treatment, calculated using StormTac, μg/l
 
 Grade III limit concentrations, μg/l (Chinese standard GB 3838-2002) A + B H + I 
Tot P 50 197 195 195 185 172 
Tot N 1,000 1,773 1,547 1,775 1,838 1,858 
Tot Pb 50 11 11 11 10 
Tot Cu 1,000 20 19 21 21 21 
Tot Zn 1,000 86 82 85 79 71 
Tot Cd 0.6 0.5 0.5 0.5 0.4 
Tot Cr 50 5.0 4.2 5.1 5.4 5.6 
Tot Hg 0.1 0.0 0.0 0.0 0.0 0.0 
oil index 50 821 627 762 733 628 
COD 20,000 56,437 62,482 54,245 46,057 36,583 
BOD 4,000 6,887 7,960 6,733 5,731 4,780 
    Concentrations prior to treatment, calculated using StormTac, μg/l
 
 Grade III limit concentrations, μg/l (Chinese standard GB 3838-2002) A + B H + I 
Tot P 50 197 195 195 185 172 
Tot N 1,000 1,773 1,547 1,775 1,838 1,858 
Tot Pb 50 11 11 11 10 
Tot Cu 1,000 20 19 21 21 21 
Tot Zn 1,000 86 82 85 79 71 
Tot Cd 0.6 0.5 0.5 0.5 0.4 
Tot Cr 50 5.0 4.2 5.1 5.4 5.6 
Tot Hg 0.1 0.0 0.0 0.0 0.0 0.0 
oil index 50 821 627 762 733 628 
COD 20,000 56,437 62,482 54,245 46,057 36,583 
BOD 4,000 6,887 7,960 6,733 5,731 4,780 
Figure 8

One of the detention/treatment ponds in Yinchuan New Town.

Figure 8

One of the detention/treatment ponds in Yinchuan New Town.

The length to width ratio of a detention pond should be 3:1 or greater, and vegetation in the shallow zones should cover 25 to 45% of the pond's area (Larm & Banach 2011). The anticipated pollutant concentrations in stormwater runoff were calculated on the basis of the proposed land use(s), see Table 4:

As shown in Table 4, the anticipated – i.e., calculated – concentrations of Tot P, Tot N, oil index, Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD), in the untreated run-off waters all exceed the permissible Grade III water quality levels. The values given in Table 4 were used to determine the pollutant load reduction required from the stormwater detention and treatment facilities. The proportional pollutant load reduction given by channel areas of between 2 and 6% of the reduced sub-catchment and pond areas – Table 3 – are shown in Table 5:

Table 5

Proportional pollutant load reduction arising from treatment in channels and ponds

  Proportional pollutant load reduction (%)
 
 A + B H + I 
Tot P 79 79 79 78 76 
Tot N 51 50 52 52 49 
Tot Pb 87 86 86 84 81 
Tot Cu 61 60 61 62 62 
Tot Zn 83 82 82 81 79 
Tot Cd 83 83 84 84 79 
Tot Cr 68 68 69 70 71 
Tot Hg 80 80 82 82 78 
oil index 98 98 98 98 98 
COD 96 96 97 97 94 
BOD 96 96 97 97 95 
  Proportional pollutant load reduction (%)
 
 A + B H + I 
Tot P 79 79 79 78 76 
Tot N 51 50 52 52 49 
Tot Pb 87 86 86 84 81 
Tot Cu 61 60 61 62 62 
Tot Zn 83 82 82 81 79 
Tot Cd 83 83 84 84 79 
Tot Cr 68 68 69 70 71 
Tot Hg 80 80 82 82 78 
oil index 98 98 98 98 98 
COD 96 96 97 97 94 
BOD 96 96 97 97 95 

These pollutant load reductions, from those anticipated in the storm run-off waters, would lead to the post-treatment pollutant concentrations shown in Table 6. All of the latter now meet the Grade III water quality requirements.

Table 6

Proportional pollutant concentrations after treatment, μg/l

    Concentrations after treatment, μg/l
 
 Grade III limit concentrations, μg/l A + B H + I 
Tot P 50 41 41 41 41 41 
Tot N 1,000 875 768 851 881 948 
Tot Pb 50 
Tot Cu 1,000 
Tot Zn 1,000 15 15 15 15 15 
Tot Cd 0.1 0.1 0.1 0.1 0.1 
Tot Cr 50 1.6 1.3 1.6 1.6 1.6 
Tot Hg 0.1 0.0 0.0 0.0 0.0 0.0 
oil index 50 18.5 14.1 17.1 16.5 14.1 
COD 20,000 2,295 2,541 1,646 1,397 2,056 
BOD 4,000 249 288 178 151 244 
    Concentrations after treatment, μg/l
 
 Grade III limit concentrations, μg/l A + B H + I 
Tot P 50 41 41 41 41 41 
Tot N 1,000 875 768 851 881 948 
Tot Pb 50 
Tot Cu 1,000 
Tot Zn 1,000 15 15 15 15 15 
Tot Cd 0.1 0.1 0.1 0.1 0.1 
Tot Cr 50 1.6 1.3 1.6 1.6 1.6 
Tot Hg 0.1 0.0 0.0 0.0 0.0 0.0 
oil index 50 18.5 14.1 17.1 16.5 14.1 
COD 20,000 2,295 2,541 1,646 1,397 2,056 
BOD 4,000 249 288 178 151 244 

CONCLUSIONS

Stormwater detention – i.e., flood control – was achieved for residential and commercial areas, and roads using a combination of detention at plot and building level, and planned green corridors and spaces. Between them, these provide detention volumes sufficient to maintain the water level below building thresholds for a 100-year return period flood event.

Stormwater treatment is achieved initially at plot level, then at channel level and finally at pond level, before discharge to the natural wetland.

An important factor in the introduction of SuDS in Yinchuan New Town has been its cost-effectiveness, due to the use of multifunctional areas. The green structure was used in an effective way to enable both flood management and stormwater run-off treatment.

High levels of cooperation between different professions – e.g., hydrologists, road engineers, landscape architects and city planners – were fundamental to achieving the necessary agreement on subjects such as topographic planning settings and land use. This, among other factors, helped make a successful stormwater detention and treatment strategy and application possible.

It is recommended that monitoring points are set up to obtain real water quality values. Since the pollutant load calculations are based on development and stormwater detention facilities in Europe and North America, measurements of the actual loads and load reductions should be made. They will form the basis of a follow-up strategy, allowing adaptive measures to be taken to ensure a successful outcome, when the new development and proposed stormwater facilities are complete and functioning.

ACKNOWLEDGEMENTS

The authors would like to thank Sweco personnel in Malmö and Beijing, in particular Peter Krigström, Project Manager and Main Planning Designer, as well as personnel from Minsheng Real Estate in Yinchuan.

REFERENCES

REFERENCES
Alm
H.
Banach
A.
Larm
T.
2010
Occurrence and Treatment of Substances of Priority, Metals and some other Substances in Stormwater
.
Swedish Water Development
,
Report 2010-06 (in Swedish).
Larm
T.
2000
Watershed-based design of stormwater treatment facilities: model development and applications
PhD Thesis, Dep Civil & Environmental Engineering, KTH
,
Stockholm, Sweden
.
Larm
H.
Banach
A.
2011
General Design Criteria for wet Ponds and Wetlands for Storm Water Treatment
,
Memorandum StormTac design criteria, Sweco
.
Larm
T.
Hallberg
M.
2008
Design methods for stormwater treatment – site specific parameters
. In:
11th International Conference on Urban Drainage, ICUD
,
Edinburgh
,
Scotland, UK
.
Liptan
T.
2011
Integrating Water and Vegetation to Transform our Cities: Experiences from Portland
,
Water Seminar Series, Nebraska Water Center
,
Oregon
.
Novotny
V.
2011
Holistic approach for distributed water and energy management in the cities of the future
. In:
Proceedings Cities of the Future Conference
,
IWA
,
Xi'an
,
China
.
Ranhagen
U.
Groth
K.
2007
The Sustainable City Approach
,
Swedish International Development Cooperation Agency (SIDA)
,
Stockholm
,
Sweden
.
Ranhagen
U.
Billing
K.
Lundberg
H.
Karlberg
T.
2012
The SymbioCity Approach a Conceptual Framework for Sustainable Urban Development
.
SKL International
,
Stockholm
,
Sweden
.
Stahre
P.
2006
Sustainability in Urban Storm Drainage: Planning and Examples
.
Svenskt Vatten
,
Stockholm
,
Sweden
.
Stahre
P.
2008
Blue-green fingerprints in the city of Malmö
.
VA SYD
,
Malmoe
,
Sweden
.
Sweco
2013
Yinchuan Cultural Tourism Eco-Town, Conceptual Detail Planning
,
Yinchuan
,
PR China
.
Woods-Ballard
B.
Kellagher
R.
Martin
P.
Jefferies
C.
Bray
R.
Shaffer
P.
2007
The SuDS Manual, C697
.
CIRIA
,
London
.