| The growing gap between supply and demand of water resources has forced many cities to seek multi-source water supply pattern,which results in a significant increase in the complexity of urban water supply systems.How to realize and promote the efficient use of water resources under the multi-source water supply pattern has become a severe challenge for urban water resources management.This paper focuses on three key issues in urban water resources management:joint optimal allocation of multiple water sources,determining the utilization scale of unconventional water source and stimulating water-saving and reallocation of water resources.Tianjin's water supply system after the Mid-route of South-to-North Water Diversion Project(SNWDP)begins to divert water is taken as a case study to carry out systematic research.The main research contents and results are as follows:1)Firstly,the basic situation of Tianjin is introduced from the aspects of geographical location,social economy,and water resources condition.Then,the multi-source water supply pattern in Tianjin is analyzed.Based on the above,the water demand of partition users and water availability of multiple water sources are analyzed in detail.And then,the supporting water supply projects connecting the water sources,water plants and partition users are introduced to provide a data foundation for the follow-up research.2)A multi-water source refinement allocation model for complex urban water supply system is constructed.The model is based on the three-layer water supply network topology of"Water Source-Water Plant-Partition User",which carefully considers the water supply engineering capability from water source to water plant and then to partition user,as well as multi-water source utilization priority,dual water supply rules,etc.The objectives of this model include maximizing social benefit and minimizing total water supply cost.The case study shows that this model can achieve the refinement and effective distribution of various water sources,deeply explore the causes of water shortage in the city,and solve the problem that the previous macro water resource allocation plan is difficult to guide the actual water resources management.At the same time,it can also reflect the weak links within the complex urban water supply system.Above all,this model is feasible to a certain extent and provides technical support for ensuring urban water-supply security.3)A cost-benefit analysis method combining the scale economy analysis with the unified allocation of multiple water sources is proposed to determine the utilization scale of desalinated seawater in Tianjin.Firstly,the variation characteristics of desalinated seawater cost under the influence of scale,output yield and desalination plant layout are analyzed based on the principle of scale economy.Then.concentrating on the joint allocation of desalinated seawater and two major inter-basin transferred water sources in Tianjin,the multi-water source refinement allocation model is used to achieve the Pareto frontier of water shortage index and inter-basin water supply cost under different desalination seawater utilization scenarios,through replacing the previous fixed cost price with the variable cost price of desalinated seawater.Finally,under the water shortage index that meets the needs of decision makers,the total water supply cost of the inter-basin transferred water and desalination seawater corresponding to the water shortage index under each desalination seawater utilization scenario are calculated.The results show that the variable cost of desalinated seawater has an impact on the tradeoff between the water shortage index and the total water supply cost,resulting in a curve of the total water supply cost with the increase of desalination yield,and an optimal desalination yield can be determined at the curve's turning point.This method is proven to be effective in identifying the best conjunctive use of inter-basin water and desalinated seawater,which can contribute to relieve urban water shortage.4)In view of the "engineering water shortage" caused by the uneven water diversion process of SNWDP,a measure to increase the scale of the reservoir at the diversion inlet to Tianjin is proposed.To determine the reasonable reservoir scale,an optimization method based on multi-objective competition and synergy analysis is constructed.Firstly,a reservoir operation module is added to the multi-water source refinement allocation model.Then,the original two-objective model is changed to a new multi-objective model involving cost(adding reservoir construction cost to the original cost),reliability,vulnerability(average shortage and maximum shortage)and resilience(average damage duration and maximum damage duration).And then,the weights of the objectives are identified using a weight design method based on improved crowding distance to transform this multi-objective problem into a single-objective problem.Finally,the competition and synergy relationships between each two of the six objectives are analyzed,through which the decisive indicators affecting the choice of reservoir size are identified and the non-essential indicators are eliminated.This method simplifies the complex decision-making process under the influence of multiple factors,and can help decision makers to optimize the scale according to their own preferences.5)Based on price elasticity theory of water demand and the marginal benefit analysis of water resources,a temporary raising strategy of residential water price is proposed to deal with the problem that residents are wasting water while industries are lack of water in drought years.Firstly,considering the water demand limit and residents' acceptability of raising water price,an optimization model with the objective of maximizing the increased net benefit of the water supply for resident and industry after water price increase is established,to determin the price raising coefficient of each step in the context of residential progressive water pricing scheme.Then,urban water shortages are concentrated in industrial users due to the lower priority of industrial water,and thus the water shortage of industrial users is used to reflect the scarcity of water resources in the case of complex multi-source water supply system.A curve of the water price raising coefficient with the increase of industrial water shortage is formed to identify the starting and ending conditions and the range of the price increase.The strategy can facilitate more residential water to be saved and transferred to industry,thereby reducing industrial losses and improving urban water use efficiency. |
PDF Full Text Request