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The discussed paper states that the rigid column model is applied for a single air pocket and the nature of the used equations makes it difficult to be employed in case of several air pockets. The discussers do not agree with this assertion.In fact, other authors also use the rigid model approach. Liou and Hunt (1996) proposed a rigid column model of flow start-up in empty pipelines with undulating elevation profiles assuming a vertical interface between the air and water phases. They proposed a velocity-based criterion to justify the application of the rigid-column approach. Zhou et al. (2002) presented an experimental and numerical investigation on the description of the rapid filling of an empty horizontal pipe with limited ventilation. The numerical model was constructed using a lumped inertia approach and assumed a vertical interface separating the advancing waterfront and the air that initially filled the pipe.The discussers have developed a general model for the simultaneous analysis of entrapped air pockets within a pipeline with irregular profile (Fig. 1). Previous papers have paid attention to this problem from both theoretical (Fuertes et al. 1998;Izquierdo et al. 1999;Fuertes 2001) and experimental (Fuertes et al. 2000;Fuertes 2001) approaches. Moreover, and in order to identify the most significant parameters of the

Abstract:The implementation of stormwater Best Management Practices (BMPs) could help re-establish the natural hydrological cycle of watersheds after urbanization, with each BMP presenting a different performance across a range of criteria (flood prevention, pollutant removal, etc.). Additionally, conflicting views from the relevant stakeholders may arise, resulting in a complex selection process. This paper proposes a methodology for BMP selection based on the application of multi-criteria decision aid (MCDA) methods, integrating multiple stakeholder priorities and BMP combinations. First, in the problem definition, the MCDA methods, relevant criteria and design guidelines are selected. Next, information from the preliminary analysis of the watershed is used to obtain a list of relevant BMPs. The third step comprises the watershed modeling and analysis of the BMP alternatives to obtain performance values across purely objective criteria. Afterwards, a stakeholder analysis based on survey applications is carried out to obtain social performance values and criteria priorities. Then, the MCDA methods are applied to obtain the final BMP rankings. The last step considers the sensitivity analysis and rank comparisons in order to draw the final conclusions and recommendations. Future improvements to the methodology could explore inclusion of multiple objective analysis, and alternative means for obtaining social performance values.

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Abstract:The selection of stormwater Best Management Practices (BMPs) for mitigating the effects of urbanization on the hydrological cycle could be a complex process due to conflicting stakeholder views, and varying levels of performance of BMPs across a range of criteria (runoff reduction, erosion control, etc.). Part 1 of this article proposed a methodology based on the application of multi-criteria decision aid (MCDA) methods, which was tested here on a residential stormwater network in the Montreal area. The case study considered green roofs, rain gardens, rain barrels and pervious pavement over a range of economic, social, and water quality and quantity criteria by applying 4 MCDA methods under three different stakeholder views. The results indicated Elimination et Choix Traduisant la Réalité (ELECTRE) III to be the most appropriate method for the methodology, presenting flexibility concerning threshold values, criteria weights, and showing shared top choices across stakeholders (rain gardens, and rain gardens in combination with pervious pavement). The methodology shows potential for more formal applications and research opportunities. Future work may lie in the inclusion of multiple objective optimization, better stakeholder engagement, estimation of economic benefits, water quality modeling, long-term hydrological simulations, and estimating real BMP pollutant removal rates.

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