Polder Flushing: Model Predictive Control of Flushing Operations to Effective and Real Time Control of Salinity in Polders

More than 35% of the world’s population live within 100 km of the coast. Groundwater resources in these areas are the main source for domestic, industrial and agricultural use. Worldwide, deltaic areas are under stress due to climate change, sea level increase and decrease in fresh water availability. In addition, in deltaic coastal areas around mean sea level, the saline groundwater will move toward the ground surface and exflitrate to surface water. This saline surface water will not be appropriate for drinking water production, agricultural and industrial use, and therefore, freshwater diverted from rivers is used for flushing the canals and ditches in coastal areas. Due to decreasing fresh water availability and increasing surface water salinization, current saline-fresh water management strategies have to be reviewed, and new sustainable strategies must be developed. Using real time measurements to see the effect of disturbances to the system and updating the control actions in real time will decrease the use of fresh water for flushing operations. Real time control of salinity in polders will result in more effective water management. Control of surface water salinization in a polder is a multi-objective problem such that water quality and quantity have to be considered. Moreover, the constraints of the system and uncertainties must be taken into account. Model Predictive Control (MPC) is a state-of-the-art control technique showing the best performance for these kind of problems. In this study, a MPC configuration for combined water quantity and quality control is discussed on a polder flushing case study for a hypothetical test water course/canal. The exfiltration of saline groundwater to the surface water is also considered and the predictions of saline groundwater exfiltration are used to achieve better control of the local water system.