Water quality target management in watershed is the fundamental choice of city rivers suffering both serious pollution and severe water shortage. In this study, we performed a case study regarding river pollution control plan based on water quality target management in the North Canal River catchment of Beijing section, in order to obtain effective water quality improvement programs. The ammonia nitrogen (NH 3-N) and chemical oxygen demand (COD) were taken as the main controlling pollutants. Water quality targets and basic water quality improvement scenarios were set up considering different intensities of population regulation scenarios and gradually strengthening emission control measures. The MIKE11 model was adopted to simulate the effects of a range of water quality improvement scenarios. Results indicated that the basic scenarios could dramatically improve the surface water environment. However, additional intensive and combined measure programs should be implemented to ensure that the water quality would basically meet the targets of corresponding water function zones. The results highlight the need to implement water conservation in water shortage urban river basin and show the importance of enhancing drainage communication and conducting ecological water replenishment in such kind basins. It is expected to provide a reference for the water environment management practice of other metropolis in the world facing both crisis of water resource shortage and water environment pollution.
With the continuous growth of population and the rapid development of urbanization, as well as the emergence of megacities and urban agglomerations, a large amount of uncontrolled domestic sewage and industrial wastewater has been discharged into urban rivers, and the quality of large-scale regional water environment and the water ecological status continue to deteriorate, posing new challenges to urban water system and water environment management [
Currently, water quality target management has been introduced in legislation of many developed countries as the basic policy for water environment management, including the Clean Water Act in the United States [
For the water pollution control in China, it has been staying at the total amount control level of setting emission targets for main pollutants, which is not closely connected with water quality targets, and is not enough to support the improvement of water environment quality of river basins. It lacks systematic research on watershed scale and the technical basis of water quality target management is insufficient, which are two important reasons why the deterioration of water quality in China has not been most effectively improved. Although the total capacity control is constraint by the water quality target, the application is limited in the urban watershed with water shortage and high development intensity. In this type of basin, the natural runoff is scarce and the water body has almost no environmental capacity, which results in great difficulties to implement total capacity control. Thus, the total pollutant load control program currently implemented in China will be supplemented by the water quality target-oriented management to form the framework for future medium- and long-term watershed management in China.
Water quality models can be useful tools to simulate and predict chemical pollutants in water environment, and the modeling results from these models under different pollution scenarios can provide a technique support for environmental management agencies to make right decisions. In view of the practice of water environment protection in the European and American developed countries, water environment models have been widely used in the process of documenting and implementing legally effective water pollution prevention and environmental planning as well as total pollutant emission reduction schemes [
The North Canal River is a typical water shortage urban river in North China, which has both crisis of water resource shortage and water environment pollution. It is urgent to find suitable technological method to improve water quality of this kind of river basin. In this thesis, Beijing part of this seriously polluted river basin is selected as the object area to explore the technical solutions for achieving water quality standards, and the base year is 2013. This study aims at easing the contradiction between water resource shortage and water environment pollution in the target basin. It can also provide a reference solution for water pollution control of urban river basin in North China and another similar metropolis in the world.
The North Canal River system originates from the south of the Yanshan Mountains. The upstream of the river is Wenyu River. It is called the North Canal River (NCR) from the Beiguan Sluice of Tongzhou district, and it flows out of Beijing near the Yangwa Sluice of Tongzhou. The total length of the mainstream of the river in Beijing is 94 km and the basin area is 4249 km2. According to the water system pattern of “storage in the west and drainage in the east” in Beijing, the NCR system undertakes the main drainage task of the city. The main tributaries including Qing River, Ba River, Tonghui River and Liangshui River all flow through the central city. The amount of water flowing out of Beijing from the river accounts for 72% to 90% of the total according to the statistical data in recent 10 years. The degree of water resource development and utilization is very high in Beijing city which suffers from a serious water shortage. There is almost no natural runoff in the downstream river which takes the sewage treatment plant water and other types of sewage as the main source of water. Thus, there is basically no self-purification capacity in the water bodies of the river. Among the five major water systems of the city, the level of urbanization of NCR basin is the highest and the water quality is the worst, with an average compliance rate of only 17.6%. The water pollution of the river is mainly dominated by both organic pollution and nutrient pollution. The main pollution indicators are ammonia nitrogen (NH3-N), chemical oxygen demand (COD), and total phosphorus (TP), among which the NH3-N is the most prominent one. According to the results of surface water environmental assessment in Beijing in 2013, the water quality of the main evaluation reaches of NCR is completely below Grade V standard. The water bodies exceeding the water quality standard are mainly distributed in the Grade IV and V water function zones. The average concentration of NH3-N in Grade IV and V water function zones of the river was 6.1 mg/L and 12.1 mg/L in 2013, which was 3.06 and 5.05 times higher than the standard value, respectively. Among the main tributaries, the pollution of Qing River, Ba River, Xiaozhong River and Liangshui River is quite serious, and the concentration of NH3-N exceeded the permissible limit of 4.64-11 times. While the pollution in the Tonghui River was relatively light, the NH3-N concentration exceeded the limit of 2.05 times. The mean value of COD in Grade IV and V water function zones of the NCR was 41.1 mg/L and 56.9 mg/L, which was 37% and 42% over the permissible limit respectively. Based on the measured data in 2017, it was observed that the average concentration of NH3-N of the whole city had reduced by 55.9% since the implement of Beijing’s Action Plan for Prevention and Control of Water Pollution (in abbreviation as the Action Plan) [
The water pollution control of Beijing is still in the stage of total amount control of pollutants. The NH3-N and COD were regarded as the priority-controlled pollutants, and they have always been on the list of mandatory reductions in key pollutants since the “tenth five-year plan” period (10th FYP, 2001-2005) of China for water quality protection. Thus, these two pollutants were selected to characterize the effect of the water quality improvement practice in the NCR basin.
In this paper, the emissions information of water pollution sources includes industrial sources, agricultural sources, life sources and urban runoff pollution, among which the first three are listed in the Beijing’s Environmental Statistics Handbook. Industrial sources include key industrial enterprises under supervision and non-key industrial sources. Agricultural sources include pollution from livestock and poultry breeding, planting and aquaculture. Life source pollution includes recycled water treated by centralized disposal facilities (i.e., effluent water of sewage treatment plant and landfill sites) and sewage of urban and rural areas directly discharged into the river. Compared with China’s 12th FYP emission reduction accounting scope, this study increases pollution loads in rural life emissions and urban runoff, basically covering all the pollution sources. The type and data source of water pollution source in this study are listed in
Based on the environmental statistics of Beijing in 2013, the emission amount of various types of pollution sources in the NCR basin was calculated. The data of Beijing’s Environmental Statistics Handbook in 2013 was directly used for the emissions of point sources such as industrial sources, livestock and poultry breeding, sewage treatment plant and landfill sites. Each type of point source emission can be easily allocated to corresponding sub-basin of the NCR, according to their spatial coordinates and the receiving water body. The pollutant amount from urban domestic sewage without treatment was obtained by deducting the part of sewage treatment plant from the total production of domestic pollutants. The pollutant excretion coefficient method was adopted to calculate the total production of domestic pollutants. The excretion coefficient of NH3-N and COD for the urban population was 9.7 and 79 gram per person per day [
The pollution loads in urban runoff were estimated using the modified Johnes’s export coefficient method [
L = ∑ i = 1 n ∑ j = 1 k C i j × A i × H j × φ × 10 − 3 (1)
where: L represents the output load of urban non-point source pollutants, ton; Cij represents the average mass concentration of a pollutant corresponding to the i-type urban underlying surface under the j-type of rainfall, mg/L; Ai represents
Pollution source type | Sub-type | Data source & processing |
---|---|---|
Industrial sources | Key industrial enterprises and non-key industrial sources | Beijing’s Environmental Statistics Handbook in 2013 |
Agricultural sources | Planting, livestock and poultry breeding and aquaculture | |
Life sources | Sewage treatment plants and landfill sites | |
Domestic sewage without treatment | Beijing Statistics Information Network; pollutant excretion coefficient method | |
Urban runoff pollution | Road, square, parking lot, roof, woodland and grassland | On-site monitoring, Beijing landuse data in 2013; modified Johnes’s export coefficient method |
the area of the i-type city underlying surface, km2; Hj represents the amount of j-type of rainfall, mm; ϕ is an integrated rainfall-runoff coefficient; 10−3 is an unit conversion factor.
The urban underlying surface is divided into six types of road, square, parking lot, roof, woodland and grassland in this study. According to the classification of rain intensity, there are five types of rainfall including light rain, moderate rain, heavy rain, rainstorms and heavy rainstorms. The average mass concentration data of main pollutants were obtained according to the on-site monitoring results of 13 rainfall processes and 29 typical monitoring sites in Haidian, Dongcheng, Daxing, Shunyi and Fengtai districts of Beijing from 2009 to 2012. The integrated rainfall-runoff coefficient was calculated by weighted average calculation of different runoff surface coefficients given by the relevant design standard.
In addition to pollution source data, a lot of hydrological, environmental, and topographic data were used for the MIKE11 model building, parameter calibration and verification. Among them, the river flow data (including dam discharge flow), daily water level data in the upper and lower reaches near dams, as well as rainfall station and evaporation station data for the rainfall-runoff module were provided by Beijing Hydrological Station. The monthly water quality data of main monitoring sections were provided by Beijing Environmental Protection Monitoring Center. The river sewage outlet information including both flow and main pollutants concentration was obtained from Beijing Pollution Source Survey Information Database. The topographic data of 16 river sections were obtained by field measurement. Planning information for simulation scenario settings mainly came from the Action Plan as well as other related planning documents. The discharge standards of water pollutants were controlled according to two local standards (DB 11/890-2012, DB 11/307-2013) for water pollution prevention of Beijing. The data sources for model building and simulation scenario settings are listed in
Based on statistical and computational analysis, the total emissions of NH3-N
Item | Data type | Data source |
---|---|---|
Data for model building, parameter calibration and verification | Flow and water level data | Beijing Hydrological Station |
Rainfall and evaporation data | ||
Water quality data | Beijing Environmental Protection Monitoring Center | |
River sewage outlet information | Beijing Pollution Source Survey Information Database | |
Topographic data | Field measurement | |
Planning information for simulation scenario settings | Basic emission reduction measures, intensive measures for water quality improvement | The Action Plan; other related planning documents |
Discharge standard of water pollutants | Discharge standard of water pollutants for municipal wastewater treatment plants (DB 11/890-2012); Integrated discharge standard of water pollutants (DB 11/307-2013) |
and COD in the NCR basin in 2013 were 12.1 and 123.7 thousand tons, respectively. The composition of NH3-N and COD pollution was presented in
Based on the “Environmental Quality Standards for Surface Water” of China (GB 3838—2002), the surface water environment is divided into five grades, and each grade has its corresponding standard value. The upper reach of Wenyu River (U-WR, from the Shahe Reservoir dam site to the section near Shaziying sluice) belongs to Grade IV water bodies. While the lower Wenyu River (L-WR, from the section near Shaziying sluice to Beiguan sluice section) and the NCR belong to Grade V water bodies. The standard value of NH3-N and COD for Grade IV water bodies is 1.5 mg/L and 30 mg/L, respectively, and that for Grade V is 2 mg/L and 40 mg/L, respectively. According to the water quality data observed in 2013, the average concentration of main water pollutants, especially the NH3-N, is far beyond the standard value (see in
The emission of life source accounts for the largest proportion of all kinds of pollution sources, thus the reasonable prediction of future population change is a key to accurately predict the emission of the major pollutants. The outline of the coordinated development plan for the Beijing-Tianjin-Hebei region proposes that the total resident population must be controlled within 23 million in Beijing by 2020 and the population of central city will decrease by 15%. Because 86% of
River | Water functional zones | NH3-N (mg/L) | COD (mg/L) | ||
---|---|---|---|---|---|
Standard value | Observed value in 2013 | Standard value | Observed value in 2013 | ||
U-WR | IV | <1.5 | 7.64 (0.29~15.6) | <30 | 43 |
L-WR | V | <2 | 14.75 (9.24~21.6) | <40 | 49.5 |
NCR | V | <2 | 16.22 (8.9~23.5) | <40 | 49.4 |
the central city area is distributed in the NCR basin, a total of approximately 1.65 million permanent residents will be reduced in this basin. At the same time, the population will increase in the suburban districts which undertake the function of accepting the population of the central city. In addition, considering the setup of Tongzhou district as the subsidiary administrative center of Beijing, population migration as well as population aggregation caused by regional economic development will also increase the population of Tongzhou district.
Relative to the urban population, the rural population generally distributed in the suburbs of the county, will be less affected by the population control policy. According to the population number in 2013 and the total 23 million population control red line in 2020, the average annual population growth rate cannot exceed 1.2% during the “13th five-year plan” period (13th FYP, 2016-2020) of China and the rural population incremental scale of the NCR basin is about 100 thousand. At the same time, due to the impact of transformation construction of the urban and rural adjacent areas, urban villages and shantytowns, as well as the implementation of the national new urbanization construction, the number of rural populations may also show no significant change or even decreases.
1) Sewage Treatment Plants
The scenario of the capacity and level of sewage treatment was set based on the goals and requirements proposed in the Action Plan, which had been issued by the Beijing municipal government in December 2015. A definite goal on the municipal sewage treatment capacity of Beijing at the end of the 13th FYP of China has been put forward in this plan. In this study, the sewage treatment capacity goals in the basic scenario scheme are consistent with those of the Action Plan. The discharge limits of municipal sewage treatment plants regulated by the DB 11/890-2012, the concentrations of COD and NH3-N of the effluent water of municipal sewage treatment plants were set 30 mg/L and 1.5 mg/L, respectively. Rural sewage treatment facilities are relatively simple, and their effluents were set according to the discharge standard regulated in the DB 11/307-2013.
2) Industrial Sources
Because of the continuous adjustment and optimization of urban function orientation, the emission of industrial sources in Beijing accounts for a small proportion in recent years. The possibility for further emission reduction in industrial source is very small. Thus, the industrial source emissions forecast can be appropriately simplified. According to the Action Plan, the key industrial enterprises should strictly execute the discharge standard of DB 11/307-2013. As an important measure for source control of pollutants, the enterprises which do not meet the municipal industrial policies and seriously contaminate the river, should be eliminated gradually. In addition, the industrial space layout should be further optimized, and industrial enterprises are encouraged to be assembled to industrial parks.
3) Agricultural Sources
Considering that the livestock and poultry pollution accounts for the largest proportion of the total agricultural source pollution, its governance should be the focus of agricultural pollution control. According to related agricultural management planning, it will not be allowed to establish new and enlarge the existing large-scale livestock and poultry farms after 2020. The layout of livestock and poultry breeding should be further adjusted and optimized according to the land carrying capacity and the evaluation of spatial suitability of existing farms. Prohibited breeding area will be designated and all the farms in this district will be closed.
4) Urban Runoff Pollution
It is encouraged to promote the early stormwater collection and utilization under the technology guide for sponge city construction-low impact development stormwater system construction (trial) issued by MOHURD [
Specific measures in terms of water ecological environment protection and assurance of ecological base flow have been put forward in the Action Plan. It is required in this plan to carry out ecological water demand analysis of the river and lake, in order to determine the ecological base flow, and to increase the amount of ecological water use in river and lake. For the watershed management of the NCR basin, it is recommended to take measures of ecological replenishment, collection and purification of the initial stormwater and other measures to ensure water quality stability of the upper reach of Qing River, and improve water quality of the upper reach of Liangshui River, the lower reach of Tonghui and Ba River, and also eliminate the water bodies Grade V below in the lower reach of Qing River and other river reaches.
At present, the first phase of the Middle Route of South-to-North Water Transfer Project of China has been put into service. It is able to supply 1.05 billion m3 water for Beijing every year. The water amount of the second phase of the project will increase to 1.49 billion m3, which will be realized in 2030 according to the national planning. According to the approved planning of the overall configuration of the diversion water in Beijing city, the water allocated to the river and lake is approximately 0.09 billion m3 during the first phase of the project; and that will reach 0.145 billion m3 during the second phase.
In this paper, both the Hydrodynamics Module (HD Module) and the Advection-diffusion Module (AD Module) of MIKE11 were used to establish the water dynamics and quality model of the Beijing NCR basin. The upstream flow and the downstream water level were taken as the external boundary conditions in this model. At the same time, the internal boundary conditions were set considering the effect of the control and regulation of ten sluices as well as the inflow of twelve trenches or tributaries, and that of 53 pollution sources directly into the mainstream of the river and 28 pollution sources into the Qing River, Tonghui River, Liangshui River and the other major tributaries. In addition to the point sources, the urban runoff pollution and agricultural non-point source pollution were also considered in this model. And these two types of pollution were considered as the form of line source into the river with the rainfall-runoff. Limited by the size of the paper, the basic principles and the detailed modeling process of the MIKE11 model were not presented in this work. Here we only briefly introduce the model calibration and verification effects. The detailed information of the model can be referenced from the authors’ another literature [
As there is almost no natural runoff in the target river basin, the major water sources are the urban sewage treatment plant water and other types of sewage. Thus, the flow conditions which affect the hydrodynamic and water quality simulation of the river are actually the different scenarios of drainage conditions, rather than the natural runoff of the different guarantee rates. According to the outbound water quantity change of the river from 2003 to 2014, the main factor influencing the outbound water volume was the change of the precipitation in the basin. Therefore, the river flow data of 2010 (the equivalent of 90% precipitation frequency) which is relatively complete and easily obtained, was taken as the design flow for the model building and water quality simulation of different scenarios in this study.
The Yulinzhuang section in the downstream of the NCR was taken as the typical section for hydrodynamic parameter calibration. This section has long series of water level data and flow data, and is also a national section of China for Beijing’s outbound water quality assessment. The Yulinzhuang section as well as some typical sections in tributaries, including Shaziying in Qing River, Tonghui Bridge in Tonghui River, Xugezhuang in Liangshui River, were selected for the water quality calibration and verification.
The water level simulated by the model is basically consistent with the measured value of the Yulinzhuang section (see in
verification sections was controlled within a reasonable range. Thus, the related simulation analysis of multiple scenarios can be carried out based on the model.
According to the uncertainties in future population changes, different intensities of population regulation scenarios were set up in the prediction of population changes. The results are shown in
The basic scenario program was set mainly based on the requirements and objectives of the Action Plan. 1) All the sewage discharge enterprises should establish sewage treatment facilities to prevent the straight discharge of sewage, and the discharge standard should meet the requirements of DB 11/307-2013. 2) The area within the Sixth Ring Road is set up as the forbidden area of livestock and
Sub-basins | Resident population in 2013 | Week regulation program | Medium regulation program | Strong regulation program | ||||
---|---|---|---|---|---|---|---|---|
Population | Change | Urban | Rural | Change | Population | Change | ||
Ba River | 142.6 | 121.2 | −15% | 116.6 | 0.3 | −18% | 114 | −20% |
NCR | 19.3 | 26 | 35% | 16.2 | 8.8 | 30% | 23.1 | 20% |
Feng River | 79.0 | 94.9 | 20% | 59.2 | 34.1 | 18% | 90.9 | 15% |
Liangshui River | 319.1 | 280.9 | −12% | 255.3 | 16.0 | −15% | 261.7 | −18% |
Lingou River | 13.9 | 16.4 | 18% | 5.3 | 10.7 | 15% | 15.4 | 10% |
Qing River | 264.1 | 227.2 | −14% | 213.6 | 3.0 | −18% | 211.2 | −20% |
Sha River | 134.5 | 158.6 | 18% | 130.0 | 24.7 | 15% | 147.9 | 10% |
Tonghui River | 382.0 | 324.7 | −15% | 312.0 | 0.7 | −18% | 305.6 | −20% |
Wenyu River | 73.3 | 86.6 | 18% | 74.2 | 10.2 | 15% | 80.7 | 10% |
Xiaozhong River | 72.3 | 86.7 | 20% | 71.3 | 14.0 | 18% | 83.2 | 15% |
Total | 1500.1 | 1423.1 | −5% | 1253.5 | 122.4 | −8% | 1333.7 | −11% |
poultry breeding, and all the farms in this area should be closed. The fecal control of large-scale pig and cattle farms should be completed, and the resource utilization would be achieved. The agriculture in central urban area (including the whole basin of Ba River, Qing River and Tonghui River, and about half of the Liangshui River Basin) should not be reserved. 3) According to 13th five-year water development plan of Beijing, the per capita living water consumption should not grow under a resource management scheme known as the Most Stringent Water Resources Management System. The full coverage of sewage treatment facilities should be basically realized in the city’s built-up area and towns, where sewage will be entirely collected and the urban sewage treatment rate will reach 100%. The rural sewage treatment rate should reach 90%, and the effluent water should meet the relatively strict water quality standard of DB 11/307-2013, with a concentration limit of 5 mg/L for NH3-N and 40 mg/L for COD. 4) The volume capture ratio of annual runoff should reach 85%, and the control rate of runoff pollution was set up as 80%. Meanwhile, the utilization ratio of storm water was set to 60%.
Under the medium population regulation program, when the basic emission reduction scenarios are applied, the emission amount of NH3-N and COD in the NCR basin will be reduced by 83% and 69%, respectively based on 2013. The evaluation results are listed in
If the conventional emission reduction measures cannot achieve satisfying results of pollution control, water quality goals should be achieved by strengthening water saving, improving hydrodynamic conditions, increasing water environmental capacity and implementing other comprehensive and strengthening measures.
1) Strengthening Water-Saving
The control of total domestic water consumption would greatly contribute to the reduction of water pollutant emission. According to the National Water Resources Comprehensive Plan (2010-2030) approved by the State Council of China, the national average quota for domestic water use of urban residents in 2030 is forecasted to be 156 liters per person and per day, and that of Beijing city is 143. Then if the drainage coefficient is set to be 0.9, the daily domestic sewage discharge coefficient is approximately 128 liters per capita. In this study, that value of 202 was initially adopted according to the environmental statistics of Beijing in 2013, and the rural sewage discharge coefficient was estimated to be
Item | Medium population regulation program | ||
---|---|---|---|
Emission amount | Reduction amount | Reduction ratio | |
NH3-N | 2073 | 10,011 | −83% |
COD | 38,384 | 85,306 | −69% |
133 based on relevant literature review. In accordance with the above national plan, the urban domestic water saving potential of Beijing can reach a maximum of 36%. Therefore, three intensities of domestic water-saving schemes of low (urban and rural domestic water quota are reduced by 10% and 5%, respectively), medium (urban domestic water quota is reduced by 25%, and rural ones 15%) and high (urban domestic water quota is reduced by 36%, and rural ones 25%) have been set in this study.
The effects of emission reduction for different water-saving schemes are shown in
2) Ecological Base Flow Protection
The ecological base flow of the U-WR is mainly derived from Shahe Reservoir release. This reservoir is a water supply reservoir for agricultural irrigation. In recent years, the reservoir release happens only under the flood control situation. Taking the 90% precipitation frequency year of 2010 as an example, there are totally 184 days without reservoir release. Based on the historical reservoir release in dry season (during December, January and February), a discharge flow of 1.2 m3/s was set for environmental flow need in the lower reaches. As the reservoir has the main function of agricultural water supply with Grade IV functional water bodies, the release water quality is also set according to the same grade standard value.
3) Drainage Communication
In accordance with the requirements of speeding up the construction of drainage communication and regional water circulation projects in Beijing city, the “three-ring water systems” and the regional drainage communication pattern will be gradually established. The degradation rate of water pollutants can be accelerated to a certain extent when the fluidity of river and lake water bodies is enhanced, and the self-purification and pollution capacity of water bodies can be then improved. In this study, we set up three scenarios with an increase of 50%, 100% and 200% in the comprehensive degradation coefficient of the main pollutants, relative to the baseline scenario. These three scenarios correspond to the
Item | Low scheme | Medium scheme | High scheme | |||
---|---|---|---|---|---|---|
Reduction amount | Reduction ratio | Reduction amount | Reduction ratio | Reduction amount | Reduction ratio | |
NH3-N | 152 | −7% | 386 | −19% | 564 | −27% |
COD | 2867 | 7216 | 10456 |
low, medium and high intensities of drainage communication schemes, respectively in the simulation.
4) Ecological Water Replenishing
It is proposed in the Action Plan that ecological water replenishment should be prioritized in the Qing River. The Qing River is an important tributary of the Wenyu River currently with severe black and odorous water bodies. It is estimated that the implementation of various types of comprehensive emission reduction measures is still not enough to eliminate the water bodies inferior Grade V function in the Qing River throughout the year. Bearing in mind that the main purpose of ecological water replenishment here is to eliminate the black and odorous water bodies in the Qing River, thus the magnitude and period of water replenishment is not fixed. For example, when not considering the water-saving schemes, the water replenishment should be executed during the period of January-April, June-July and December, with a total of 41.75 million m3. While if the medium domestic water-saving scheme is further adopted, the water replenishment should only be executed in January, February, April and December, with a total of 16.25 million m3. And if the high water-saving scheme is further adopted, the amount of water replenishment will decrease to 7.7 million m3 which is less than one fifth of that without considering water saving schemes.
5) Reinforcement Scheme in Key Basins
Both the Tonghui River and Liangshui River are the focus and difficulties of water environment management in the NCR basin. According to the results of model calculation, even under the high water-saving scheme in 2030, the annual average concentrations of NH3-N of the Tonghui bridge section in Tonghui River and Xugezhuang section in Liangshui River were 2.61 mg/L and 3.64 mg/L, respectively, which could still fail to meet the water quality targets of Grade V standard water bodies. After the two tributaries converge into the NCR, the water quality of the mainstream in the lower reach will be adversely affected. According to the discharge structure of NH3-N, the sewage treatment plant emission accounts for the largest proportion. However, the effluent water of sewage treatment plant has already met the discharge standard of Grade IV water bodies, and the space for further emission reduction is extremely small. In addition to the sewage treatment plant emission, the urban non-point source is the biggest one of Tonghui River Basin. It ranks first of the 10 sub-basins of NCR, accounting for more than 30% of total emission. While for the Liangshui River Basin, the industrial source emission accounts for a large proportion, and it is also the largest in the 10 sub-basins, accounting for 42% of the total emission. Therefore, the water pollution control of the Tonghui River and Liangshui River can be proceeded from urban non-point source and industrial source, respectively, in order to further tap the potential of emission reduction.
The Action Plan proposed a solution for urban runoff pollution in the Tonghui River Basin which will be taken as a pilot of early rainwater collection and treatment. According to the simulation results, if 45 tons of the urban non-point source pollutants in the Tonghui River Basin are effectively controlled, the average annual concentration of NH3-N in Tonghui Bridge section can be reduced from 2.61 mg/L to 2.18 mg/L. It is also proposed in the Action Plan that the industrial layout should be optimized, and industrial enterprises are encouraged to move to industrial parks. It is estimated that the optimization of the industrial spatial layout can reduce a total of 34 tons of industrial source pollutants in the Liangshui River Basin, and the annual average concentration of NH3-N in Xugezhuang will decrease from 3.64 mg/L to 3.23 mg/L.
6) Combined Enhancement Schemes
When an individual measure cannot achieve satisfactory results, combined schemes should be adopted to achieve the water quality goal. There are two categories and 6 items in the combination schemes as follows: one category is the three combination programs based on the medium domestic water-saving scheme. And the other is the three combination programs based on the high water-saving scheme.
i) Combination programs of the medium water-saving scheme, medium drainage communication scheme and ecological water replenishment scheme.
ii) Combination programs of the medium water-saving scheme, medium drainage communication scheme and key basin reinforcement scheme.
iii) Combination programs of the medium water-saving scheme, medium drainage communication scheme, key basin reinforcement scheme, and ecological water replenishment scheme.
iv) Combination programs of the high water-saving scheme and medium drainage communication scheme.
v) Combination programs of the high water-saving scheme, medium drainage communication scheme, and key basin reinforcement scheme.
vi) Combination programs of the high water-saving scheme, medium drainage communication scheme, key basin reinforcement scheme, and ecological water replenishment scheme.
It can be reflected by the simulated concentration of the characteristic contaminants of typical simulation sites that whether the simulated river reaches have achieved a relevant standard. Because the U-WR and L-WR belong to different water function zones with different standard values, different simulation sites should be selected for that two simulated river reaches. Though the water function of the L-WR is the same as that of the NCR, the determination of simulation sites should consider the influx of tributaries which may evidently affect the simulation results. Finally, four simulation sites were determined. The Tugou bridge section and the Houweigou bridge are located in the U-WR and L-WR, respectively. The NCR 1# section is located in the river reach where is after the Tonghui River flows in and before the Liangshui River flows in, and the NCR 2# section is located in the river reach where is after the Liangshui River converges into the mainstream of the NCR. The locations of the four typical simulation sections are shown in
Firstly, the water quality improvement effect of the basic emission reduction scenarios was simulated. In general, the water quality targets of COD can be relatively easy to achieve. Results show that all the simulated COD concentrations of the four indication sections can meet the requirement standards even under the week population regulation program, and the water quality remains stable throughout the year (see in
Thus, intensive measure programs should be implemented to meet satisfactory targets for water quality improvement. On the basis of the medium population regulation program, the effect of reducing the NH3-N concentration for
Typical simulation sites | Daily average concentration, mg/L | Qualified days, d | Peak concentration, mg/L |
---|---|---|---|
Tugou bridge | 1.46 | 249 | 2.65 |
Houweigou bridge | 2.04 | 200 | 3.44 |
NCR 1# | 2.58 | 97 | 3.75 |
NCR 2# | 3.07 | 11 | 5.65 |
Typical simulation sites | Medium population regulation program (base) | Strengthening water-saving scheme | Ecological base flow protection scheme | Drainage communication scheme | Ecological water replenishing scheme | ||||
---|---|---|---|---|---|---|---|---|---|
low | medium | high | k increases by 50% | k increases by 100% | k increases by 200% | ||||
Tugou bridge | 1.52 | 1.40 | 1.23 | 1.10 | 1.58 | 1.49 | 1.46 | 1.41 | 1.52 |
Houweigou bridge | 2.10 | 1.92 | 1.66 | 1.46 | 2.04 | 2.07 | 2.04 | 1.99 | 1.75 |
NCR 1# | 2.64 | 2.44 | 2.14 | 1.92 | 2.60 | 2.56 | 2.49 | 2.37 | 2.46 |
NCR 2# | 3.15 | 2.92 | 2.57 | 2.30 | 3.11 | 3.08 | 3.02 | 2.92 | 2.97 |
each individual intensive measure scheme was further simulated. The results are presented in
The water quality improvement effect of six combination enhancement schemes was then simulated, and the results are represented in
The improvement of water environment quality is a serious challenge for Beijing’s urban environmental planning and governance. In this paper, we propose a technical plan for the regulation of the main water pollutants in the Beijing North Canal River Basin. It is the first systematic study aiming at the long-term countermeasures for the improvement of water environment in this river basin. The research fully displays the arduous and long-term performance of the water environment quality improvement in the basin. There is no doubt that the
Typical indication sites | Medium population regulation program(base) | Based on the medium water-saving scheme | Based on the high water-saving scheme | ||||
---|---|---|---|---|---|---|---|
Scheme i | Scheme ii | Scheme iii | Scheme iv | Scheme v | Scheme vi | ||
Tugou bridge | 1.52 | 1.16 | 1.16 | 1.16 | 1.03 | 1.03 | 1.03 |
Houweigou bridge | 2.10 | 1.44 | 1.57 | 1.44 | 1.37 | 1.37 | 1.31 |
NCR 1# | 2.64 | 1.91 | 1.87 | 1.81 | 1.74 | 1.64 | 1.62 |
NCR 2# | 3.15 | 2.36 | 2.25 | 2.19 | 2.14 | 1.98 | 1.96 |
Note: The specific measures included in the combined scenarios i-vi presented in
implement of the Action Plan for Prevention and Control of Water Pollution in Beijing is dramatically improving the surface water environment of the city. The concentration of the main water pollutants has been reduced by a large amount and the black and odorous water bodies have been basically eliminated. However, in order to achieve the water quality targets, intensive and combined measure programs should be further implemented.
Based on the evaluation results of water quality improvement effects under different scenarios, the strengthening water-saving scheme is highly recommended. It is especially important for the reduction of domestic water pollutant emission which accounts for the largest proportion of all kinds of pollution sources. Bearing in mind that the main source of water for the North Canal River is the urban sewage treatment plant drainage, the sewage treatment plants carry out the current local standard of DB 11/890-2012 requiring the drainage water to meet the standard value of Grade IV water bodies. As the target river belongs to the same grade or Grade V water function zones, which means there is almost no environmental capacity without considering the river’s self-purification ability. Therefore, both the drainage communication scheme and ecological water replenishing scheme are highlighted to enhance the environmental capacity of river water bodies. When the total control requirements and measures are allocated to each sub-basin and administrative districts, they can be used as the basis for planning decision-making and governance assessment.
This work was supported by the National Natural Science Foundation of China under Grant [number 51809281 and 51509268] and the IWHR Research & Development Support Program under Grant [number JZ0145B022017].
The authors declare no conflicts of interest regarding the publication of this paper.
Wang, G., Yan, D.H., Pan, T., He, X.Y., Qi, J., Ren, M.L., Zhao, L.P., Wang, F., Zhang, Z.B., Jiang, X.M. and Fu, X.D. (2019) Study on Technical Schemes for Major Pollutants Emission Reduction in Beijing North Canal River Basin Based on Watershed Water Quality Target Management. Journal of Water Resource and Protection, 11, 1327-1350. https://doi.org/10.4236/jwarp.2019.1111077