The project aims to reduce loading of waterbodies caused by overflows and stormwater from heavy rains by developing methods and develop cities’ readiness to prepare integrated water management plans.

The impact of stormwater on water pollution has been recognized in recent decades and many cities have developed methods for quantitative and qualitative management of stormwater. Although the use of combined sewer systems has been reduced everywhere, stormwater still entering the wastewater sewer system multiplying the amount of wastewaters during heavy rains. These increased amounts cause pollution of local waters through sewer overflows and problems in the wastewater treatment process.

The European Union is proposing, as part of the update of the Urban Wastewater Directive, the preparation of integrated water management plans for cities and urban areas. The plans aim to promote measures to prevent wastewater pollution from rainwater.

The draft directive does not yet have concrete and detailed information on what the plans should be in terms of accuracy and scope. However, it is clear that their implementation will require municipalities to collect and combine new information and to cooperate in a new way between urban stormwater actors and water supply actors.

The project aims to pilot the preparation of an integrated water management plan in accordance with the directive using a pilot area in the Turku city center. The preparation includes the collection and completion of baseline data with measurements and studies, the development of existing stormwater and surface water models, the dynamic cross-checking of the stormwater and wastewater model and the analysis of different scenarios, as well as a site-specific and prioritized list of actions to reduce sewer overflows. A process description of the development of the integrated water management plan is made, which other municipalities can use in developing their own management plans, and which presents, among other things, methods for supplementing typical information gaps, stormwater flow measurements and building cooperation between different actors, as well as an estimate of what kind of modeling analysis can be used to identify the most cost-effective and reliable priority action targets. The functionality of the process description is tested and refined by creating a plan according to it for the development of an integrated water management plan for the city of Kaarina.

The project also tests and develops a cost-effective IoT-based stormwater measurement system for calibrating and validating stormwater models. In addition, the project supports the municipalities in the headwaters of the Turku Region Purification Plant (Turun Seudun Puhdistamo) in promoting overflow management and builds cooperation between the stormwater actors and water utility companies in the Turku area.

The developed process and measurement solutions will be available for other cities to use in preparing their own integrated water management plans.