While a policy of more decentralized stormwater management is increasingly being pursued in areas containing new housing developments, the question arises as to how stormwater management is handled in existing settlements, where restructuring the drainage system is a much more complex affair and often requires the active involvement of property owners. Recognizing that the multidimensional objectives of stormwater management in settlements call for a range of local strategies, this article examines the interaction and strategic contribution of two key municipal institutions for regulating stormwater management, namely, compulsory connection and usage and stormwater charges, in order to examine how they meet these objectives when property owners are involved. The following questions are addressed: How do these two key institutions link the varied objectives of stormwater management with practical options for decentralization? Which institutional designs are capable of integrating property owners into a municipal stormwater strategy in a coherent manner? What is current local government practice? This article begins by analyzing the interactions between different objectives of stormwater management, the interplay of the two key institutions, and options for stormwater management on private properties. On this basis, we then present an empirical study of current practice in 44 medium to large cities in Germany. This shows that while local governments devise very different—and often inconsistent—institutional designs, decentralization is quite commonly pursued in existing settlements.

Cities worldwide are facing problems to mitigate the impact of urban stormwater runoff caused by the increasing occurrence of heavy rainfall events and urban re-densification. This study presents a new approach for estimating the potential of the Management of Urban STormwater at Block-level (MUST-B) by decentralized blue-green infrastructures here called low-impact developments (LIDs) for already existing urban environments. The MUST-B method was applied to a study area in the northern part of the City of Leipzig, Germany. The Study areas was divided into blocks smallest functional units and considering two different soil permeability and three different rainfall events, seven scenarios have been developed: current situation, surface infiltration, swale infiltration, trench infiltration, trough-trench infiltration, and three different combinations of extensive roof greening, trough-trench infiltration, and shaft infiltration. The LIDs have been simulated and their maximum retention/infiltration potential and the required area have been estimated together with a cost calculation. The results showed that even stormwater of a 100 year rainfall event can be fully retained and infiltrated within the blocks on a soil with low permeability (kf = 10−6 m/s). The cost and the required area for the LIDs differed depending on the scenario and responded to the soil permeability and rainfall events. It is shown that the MUST-B method allows a simple down- and up-scaling process for different urban settings and facilitates decision making for implementing decentralized blue-green-infrastructure that retain, store, and infiltrate stormwater at block level.

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The European Water Framework Directive (WFD) has set the objective of good ecological and chemical status for all European waters by 2027 at the latest. However, exemptions from good status are allowed in cases where economic/social costs outweigh the benefits of water improvement (disproportionality). Eco-efficiency analysis (EEA) is usually applied to evaluate products and processes. The paper argues that EEA can also be used as a methodical approach to evaluate disproportionality of WFD measures. The approach is applied to a potash and magnesium mine discharging effluents into a German river basin (Werra/Weser). Here, the EEA relates water quality improvement to the economic costs of the measures ranking them according to their eco-efficiency. In doing so, EEA structures information on effectiveness and cost-effectiveness of WFD measures, and provides inputs to evaluate affordability and disproportionality of them.

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