关键词: 大江大河水环境治理, 项目群, 支付方式, 鲁棒性阈值, 费用现值, 多利益主体

Abstract: Firstly, we define the research question and analyze the mechanism and principle of the impact of uncertainty on the present value of employer costs under different payment methods. Secondly, we analyze the connotation and characteristics of program robustness, and propose the concept of program robustness threshold. Thirdly, we construct a balance model between the present value of employer’s expenses and the robustness threshold under different payment methods, and analyze the impact of different parameters and levels on the present value of employer’s expenses. Fourthly, we study the robustness thresholds, buffer settings, robustness constraints, and robustness constraints of contract items under different payment methods. Finally, based on the Yangtze River Protection Water Environment Governance Program Z, a case study is conducted to propose management insights. The research results indicate that there is a trade-off between the present value of costs based on different degrees of delay and the robustness threshold under different payment methods. The sensitivity of the discount rate is the strongest, followed by the buffer cost coefficient, robustness threshold, claim rate, and contract project duration compression rate. The sensitivity of the five factors to the present value of delay costs is greater than that to the present value of costs, with the former being 30 to 40 times higher than the latter. The research results of this article provide a basis for employers to develop a robust program benchmark schedule and effectively control the present value of costs.
(1)Programs are the fundamental units for the implementation of large-scale projects. Compared with single interest parties, delays in contracted projects under multi-interest parties have a more significant adverse impact on programs, namely a more significant cascading effect. Under a single stakeholder system, when activities are delayed, contractors can take remedial measures to achieve the goal of expediting work without affecting other contractors. The subordinate linkage effect of multiple stakeholders is very limited. In contrast, delays in contracted projects under multiple stakeholders will cause significant cascading effects on other contractors. It can be seen that in the implementation process of programs, different payment methods have different impacts on the distribution of cost flow and present value of cost for program owners in uncertain environments. Therefore, it is necessary and complex to achieve the minimization of present value of cost for owners under different payment methods and the robustness of program schedule by adding time buffers and setting robustness thresholds.
(2)According to the current rules on compensation and claims for delay damages (such as FIDIC), losses (including costs and/or construction period) caused to other contractors due to project delays in the contract are borne by the owner, and different payment methods (one-time payment, monthly payment, milestone payment, etc.) have an impact on the present value of program owner costs. In this situation, the owner hopes to accurately assess their own risks and reduce the losses caused by contracted project delays by setting the robustness threshold of the contracted project. At the same time, in order to meet the preferences of homeowners for decision-making, it is necessary to clarify the trade-off between the present value of homeowner costs and the robustness threshold.
Part 1: Defining the robustness and robustness threshold of water environment governance programs and large river water environment governance programs. One is the water environment governance program, which refers to a group of interrelated and centrally managed water environment governance contracted projects in a contractual environment. The second is the robustness of the large river water environment governance program, which refers to the ability to truly reflect the anti-interference ability of the governance program, and also reflects its adaptability to complex and changing environments. The third is the robustness threshold for water environment management of large rivers, which refers to a reasonable value set in an uncertain environment to reduce the adverse effects between different stakeholders, avoid frequent adjustments to program plans due to uncertainty factors, and ensure the robust execution of program plans. The program plans need to have a certain degree of robustness, and therefore, are set accordingly.
Part 2: Analyzing the impact mechanism of three payment methods, including one-time, monthly, and milestone payments, on the present value of program owner costs. The impact of a one-time payment method on the present value of costs depends on the completion time of each contracted project. As long as the completion time remains unchanged, the impact of a one-time payment method on the present value of costs will not change. The second is that the impact of milestone payment methods on the present value of costs is not only related to the program schedule and its implementation status, but also closely related to the milestone schedule and its implementation status in the contracted project. Thirdly, in the monthly payment method, the payment for the current month shall be calculated based on the actual amount of work completed by the contractor in the current month and in compliance with the measurement rules, and the owner shall pay the corresponding amount to the contractor.
Part 3: In response to delays in the implementation process of the program contracted project, with the goal of minimizing the present value of owner costs, research is conducted on the relationship between the present value of program costs and robustness thresholds under one-time and monthly payment methods. Firstly, a trade-off model is constructed between the present value of program costs and the robustness threshold under both one-time and monthly payment methods. The second is to analyze the sensitivity of relevant parameters under different payment methods to the optimization results of the present value of owner costs.
The calculation results indicate that there is a trade-off between the present value of costs and the robustness threshold under different payment methods. The second is that the discount rate is the most sensitive, followed by the buffer cost coefficient, robustness threshold, claim rate, and contracted project duration compression rate. The sensitivity of five factors to the present value of delay costs is greater than that to the present value of costs, with the former being 30 to 40 times higher than the latter.
Next research direction: research on cost present value optimization model based on robustness threshold under mixed pricing methods.

Key words: water environment treatment of big rivers, program, payment method, robustness threshold, present value of expenses, multi-stakeholder