Water quality based impact assessment of urban drainage impact in Europe

Title:	Water quality based impact assessment of urban drainage impact in Europe
Category:	Miscellaneous
Detail:	SWW Seminar
Date:	17. Mar. 2011, 15:30 - 16:30
Venue:	Eawag Dübendorf
	Forum Chriesbach D 24
Speaker:	Philipp Staufer, Eawag
Leader:	Jörg Rieckermann, Eawag
Download:	as calendar event

Ambient water quality impact assessments provide for a procedure to evaluate urban discharges with respect to the state of the aquatic environment. They are used to identify critical discharge points and they give a framework for the re-development of urban drainage infrastructure. This development has become necessary because the EU Water Framework directive promotes achieving good water quality (chemically and biologically) as well as good water quantity. 
Discontinuous wet-weather discharges are known to have various detrimental impacts on receiving waters. Due to their high variability and their number they are difficult to monitor. Therefore, mathematical models are commonly used to specify the hydraulic impact and pollutant concentration in the recipient. These numerical results are then interpreted with respect to the (probable) abundance of aquatic species.

For the last decade guidelines have been available addressing engineers who want to optimize the urban water management system without endangering water quality goals. The urban water and the natural systems vary greatly in size and complexity. Therefore, the models have to be chosen accordingly with the background that more complex models require more basic data and extended skills. In the end choosing and parameterizing the model often becomes decisive whether a wet-weather discharge is considered detrimental or not. In practice, economic constraints and misused models lead to contradicting results expressing a subjective impact assessment. Therefore, currently available ambient water quality assessment guidelines were reviewed to (i) identify a structure ensuring objectivity, (ii) determine properties supporting the decision making, and (iii) pin-point knowledge gaps that hinder an efficient transition towards water quality based urban water management.

To these aims seven European guidelines were structurally analyzed and published cases studies were critically reviewed. Furthermore, the algorithms behind the three most comprehensive guidelines were compared against a generic decision support algorithm used in river rehabilitation. Because simplified models are an important part within the assessment, three models were applied to a didactical example.