Areas close to the Scheldt are high-risk zones for flooding. In 1976 the dyke of Ruisbroek broke resulting in the flooding of one third of the Province of Antwerp. Following these events, a new plan arose to protect the basin of the Zeeschelde against flooding: the Sigmaplan. In the plan the same safety measurements are taken into account as those on the Western Scheldt (Deltaplan), which essentially means a chance of storm tide in 1/100 year, a water level of 9.05m TAW in Antwerp.
After a new storm in 1994, causing the highest water levels ever measured on the Zeeschelde, a disaster and emergency program was accepted. Its implementation had to fit within a full vision on the management of watercourses. This led to an environmental impact study (AMIS – Algemene Milieu Impact Studie) for the Sigmaplan and was followed by Research on the environmental effects of the Sigmaplan (OMES – Onderzoek Milieu – Effecten Sigmaplan).

The OMES project aims to actualize the biogeochemical knowledge of the Zeeschelde and to extend it where possible. In continuation of these studies a large monitoring program was set up: Research on the impact of the Sigma plan, dredging activities and harbor expansion in the Zeeschelde on the environment (named OMES). An estuary is a very complex system, influenced by different (human) factors. In the new vision, in which safety, accessability an naturality is handled together, extensive knowledge of the estuarine ecosystem is necessary.
OMES has become an important instrument for scientific research in the estuary. Monitoring can only be really valuable when measurements are systematic, and taken over long periods, in order for long term effects to be distinguishable from short term effects. This also meant the dataset could not contain any gaps. OMES has had a consistent dataset since december 1995, for which monthly samples were taken on fixed stations and by a fixed schedule. Some (station) adaptations were made, but no interruptions were made in the measurement pattern.

Early 2008, MONEOS was presented: a program for integrated monitoring of the Scheldt Estuary in The Netherlands and Flanders. The program defines the the desirable monitoring to describe the evolutions in the Scheldt and to identify causal relationships. This is essential to manage the estuary in a scientific manner. The monitoring contains several aspects of the ecosystem: hydro- and morphodynamics, diversity of habitats, physico-chemistry, ecological functioning and diversity of species. OMES monitors several of the physico-chemical and ecological monitoring of the Zeeschelde. In 2009, OMES and MONEOS were matched.

Since then, monitoring campaigns of OMES have 3 sampling days (on Monday, Tuesday and Wednesday).

In the first 3 phases of OMES an attempt to understand and model the role of the intertidal zone on the functioning of the ecosystem was undertaken. Modelling and data gathering were the main activities and a detailed dataset on chemical, biological and ecological data of the Scheldt is since then available. With this multidisciplinary knowledge of the Scheldt estuary, it would be possible to visualize possible alternatives of the Sigma dykes that are still under construction and to develop a suitable water management protocol. The 4th phase of OMES started in 2006 and continued the monitoring of the third fase. This phase specifically focused on the possible role of controlled flooding areas to secure the land of flooding and protect the functioning of the estuarine environment.

A 5th phase continues the monitoring of the Scheldt. The project is integrated in the new monitoringprogram MONEOS from O&M, a collaboration between the Dutch and Flemish government aimed at a coördinated and integrated monitoring of the Scheldt. More information about OMES is in MONEOS.

The different phases within OMES: