A watershed-simulation and hybrid optimization modeling approach for water-quality trading in soil erosion control

Sediment load from agricultural watersheds is a threat to the quality of downstream waters in many countries. Water-quality trading thus is employed to lower the cost of controlling soil erosion. However, a trading program is not always successful since uncertainties pertaining to erosion control are often not well acknowledged. Such uncertainties can be caused by both physical characteristics of a watershed and agricultural activities. This study presents a modeling approach to investigate water-quality trading in soil erosion control, based on watershed-simulation and optimization models in which various uncertainties are reflected. The simulation–optimization approach is bridged through an assumed linear relationship between simulation outcomes and decision variables in optimization models. The developed modeling approach is demonstrated within the Swift Current Creek watershed, Canada. Results show that the uncertainties play a major role in the successful of lunching a water-quality trading program, and trading costs is also critical for the trading system.