Admitting brackish water or expanding the freshwater supply: insights into the cost-effectiveness of measures

Introduction

During dry periods, the freshwater supply in West Netherlands may come under pressure. This project investigates the effects of admitting brackish water on the salinisation of the regional water system and on agricultural damage, as an alternative to expanding the freshwater supply.

Duration: 2019–2020
Client: Rijnland Water Board
Keywords: freshwater supplies, freshwater supply, blending in, freshwater shortage
Models & Tools: Northern Delta Basin Model (NDB), €ureyeopener model (EEO), National Water Model (NWM)

Background

Salinisation

In times of low river discharges, chloride concentrations on the Hollandsche IJssel can rise. Since West Netherlands depends on the Hollandsche IJssel for its freshwater supply, in such situations the Climate-Resilient Water Supply (KWA) can be deployed for the freshwater supply to West Netherlands. Based on the expectation that the capacity of the KWA will not be sufficient in the future, the Freshwater Region West Netherlands has, for the Delta Programme Freshwater (DPZW), had the possibilities investigated for expanding the capacity of the alternative freshwater supply. In this study, increasing the regional supply capacity was weighed against the option of supplementing the freshwater supply with water from the Hollandsche IJssel.

Method

Modelling and scenario analysis

Using models and scenario analyses, HydroLogic provided insight into the consequences of admitting brackish water. Chloride concentrations were determined for various salinisation situations on the Hollandsche IJssel. The model results for the Hollandsche IJssel were linked to analyses of the spread of the admitted water in the regional water system of Rijnland and the occurrence of agricultural damage. Insight into the effects and damage of blending also provides insight into the cost-effectiveness of the possible measures for capacity expansion.

More about our method

The result

Future-proof

This study has quantified the expected salinisation events (frequency and duration of occurrence) in the future under various scenarios, as well as the effects of measures to strengthen the Hollandsche IJssel freshwater buffer. For agriculture, the damage reduction that can be achieved with those freshwater measures has been determined indicatively. In this way, the project supports water managers and policymakers in weighing measures for a robust freshwater supply now and in the future.

What did the project deliver?

Insight into the spread of the brackish water in the boezem and in the polders of Rijnland
Quantification of the order of magnitude of the expected agricultural damage, comparing the admission of brackish water with additional freshwater supply measures
Substantive basis for the discussion on the cost-effectiveness of measures
Contribution to substantiating measures in the Delta Programme Freshwater

“The combined analysis of salt spread and agricultural damage offers interesting starting points for the discussion on the cost-effectiveness of freshwater measures.”

Meike Coonen | Senior advisor