Urban stormwater as a water resource opportunity, A nexus approach to decision making

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Farhad Yazdandoost, Fariba Hoseini

Wednesday 1 july 2015

11:00 - 11:15h at Central America (level 0)

Themes: (T) Water resources and hydro informatics (WRHI), (ST) The water-food-energy nexus

Parallel session: 9K. Water resources - Water - food - energy nexus

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With increasing demands on water resources the notion of reusing urban stormwater has earned significant attention. Development of a toolkit for analysis and assessment of stormwater reuse has been addressed here. The proposed toolkit has 3 main steps comprising assessment of harvesting potentials, water management scenarios verification and a nexus approach to decision making. The harvesting potentials are determined through SWMM rainfall-runoff model while a sensitivity analysis is performed to identify the parameters whose values would have influential impacts on acquired runoff volumes. The potential of reuse of the “excess” water is then examined within an integrated allocation model verifying the unmet demand under different projected scenarios. Water Evaluation and Planning System (WEAP) is used to evaluate the current and the future water management scenarios with and without the effect of the proposed reuse, as a new supply source, whilst upholding socio-economical and environmental characteristics of the study area. Although the sequence of investigations may appear adequate for decision making at preliminary planning stages where stakeholders’ preferences in a subjective manner are important, the decision making process is further enhanced using Multi Criteria Decision Making (MCDM) approaches. A comprehensive MCDM tool, “Definite Software”, is used to consider sustainability criteria to rank and prioritise different interactive stormwater and water supply-demand management scenarios. This in turn would imply a nexus approach to decision maker preferences alongside quantitative targets. The proposed toolkit has been utilised in a section of the 22nd municipal district of Tehran. The results indicate that, at least, 14% recompense in the unmet demand may be expected under the most severe demand condition. A combination of the criteria comprising the society’s acceptance of the target qualities, the treatment costs, reduction of the unmet demands and the environmental considerations achieves the highest rank in decision making. The most sensitive parameter in produced runoff volumes were identified as the percentage of impervious area.