A hybrid approach associating flow network modeling with AHP-Entropy for simulating and ranking water-demand management alternatives

Araújo, Matheus Duarte de; Oliveira, Rui de

doi:10.4136/ambi-agua.2627

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ARTICLES • Rev. Ambient. Água 16 (2) • 2021 • https://doi.org/10.4136/ambi-agua.2627 copy

A hybrid approach associating flow network modeling with AHP-Entropy for simulating and ranking water-demand management alternatives

Uma abordagem híbrida associando modelagem de rede de fluxo a AHP-Entropia para simulação e hierarquização de alternativas de gerenciamento da demanda de água

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

In view of the water crises historically experienced by Brazil’s semi-arid region, it is necessary to search for methodological tools that allow us to propose efficient alternatives for managing water demand. In this regard, the present study developed and applied a hybrid approach of flow network modeling and the Analytic Hierarchy Process (AHP) combined with Shannon’s entropy for simulating and prioritizing water demand management alternatives in the Epitácio Pessoa Reservoir in the Brazilian semiarid region. The approach initially performed simulations of the hydro system flow network to explore rational alternatives that evaluated the following criteria: meet the demands of human supply, meet the demands for irrigation, maintain the reservoir above the target volume, and reduce consumption. Subsequently, Shannon's entropy was used to assess the importance of the criteria and the multicriteria analysis of ranking of alternatives was built. Finally, a sensitivity analysis of the model was performed regarding the dependence on respective weights of the criteria. The results made enabled evaluation of the hydro system’s water security, highlighting insufficient supply by the single measure of water management transposition of the São Francisco River, and based on the hierarchy of alternatives, suggesting actions to improve the sustainability of water use, such as reuse of water, reduction of losses in supply systems and increasing irrigation efficiency. The proposed hybrid approach permitted the synthesis of the simulation’s results, which may simplify and support the decision-making process in water-demand management.

Keywords:
AHP-Entropy; consumption reduction; flow network; water demand management

Scenario		Ranking
Scenario		1	2	3	4	5	6	7	8	9	10	11	12	13
Sc₁	Equal weight	A12	A8	A6	A9	A5	A4	A11	A10	A1	A3	A2	A7	A0
Sc₂	Human supply	A12	A8	A6	A9	A5	A4	A11	A10	A1	A3	A2	A7	A0
Sc₃	Irrigation	A12	A8	A6	A9	A5	A4	A11	A10	A1	A3	A2	A7	A0
Sc₄	Maintenance of Reservoir	A12	A8	A6	A9	A5	A4	A11	A10	A1	A3	A2	A7	A0
Sc₅	Reduction of consumption	A12	A8	A9	A5	A4	A11	A10	A1	A3	A6	A2	A7	A0

Instituto de Pesquisas Ambientais em Bacias Hidrográficas Instituto de Pesquisas Ambientais em Bacias Hidrográficas (IPABHi), Estrada Mun. Dr. José Luis Cembranelli, 5000, Taubaté, SP, Brasil, CEP 12081-010 - Taubaté - SP - Brazil
E-mail: ambi.agua@gmail.com

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[1] ^*Corresponding author: Matheus Duarte de Araújo, e-mail: matheusduarte887@gmail.com

		Alternative description
A0	Reference Scenario	The reference scenario does not allow management measures. Therefore, it considers the water consumption in homes by hydraulic devices without sparing devices, without sustainable projects for reuse, and simulated from the inflow through precipitation.
A1	Saving equipment	Replacement of common equipment by saving equipment, which are: showers with flow restrictors, sanitary basins with double activation, sink faucets with aerators, and lavatory faucets with aerators.
A2	Rainwater harvesting	Implementation of a rainwater catchment system composed of gutter, pipe, first water diversion device, lower reservoir, pumping, upper reservoir, and home distribution.
A3	Residential reuse	Use of a graywater reuse system with treatment for recirculating wastewater from showers and washing machines to the sanitary basin.
A4	Equipment + Rainwater harvesting	This alternative combines the alternatives (A1) and (A2).
A5	Equipment + reuse	This alternative combines the alternatives (A1) and (A3).
A6	Water transpositionevery month	This alternative considers a water supply of 1.52 m³ s^-1(ANA, 2017)ANA (Brasil). Pré-operação do eixo leste PISF: Sistema Hídrico Rio Paraíba-Açude Boqueirão. 03 out. 2017. Available at: Available at: https://www2.camara.leg.br/atividade-legislativa/comissoes/comissoes-permanentes/cindra/arquivos/sr-rodrigo-ana Access: 01 Apr. 2020. https://www2.camara.leg.br/atividade-leg... to the reservoir every month, coming from the East Axis of the São Francisco River Transposition Program. It should be noted that the frequent context of scarcity in the São Francisco River Basin would have to be considered for the transfer of water to basins in the semiarid (Rêgoet al., 2017).
A7	Water transposition in the period of lesser influx	Considering the rainy season from February to May (Andradeet al., 2019ANDRADE, A. R.; LIMA, P. R. C.; OLIVEIRA, J. V. P.; LUCENA, D. B. Análise da relação entre precipitação e volume nas sub-bacias contribuintes para o açude Epitácio Pessoa. Revista Brasileira de Climatologia, v. 25, 2019. http://dx.doi.org/10.5380/abclima.v25i0.62973 http://dx.doi.org/10.5380/abclima.v25i0.... ); the minimum average rainfall of 20mm in January, June, and July; water scarcity in the São Francisco River Basin; and the high costs of operating the system, the alternative considers the water supply of 1.52 m³ s^-1in the months of August to December, as those of lowest inflow to the reservoir.
A8	Equipment + residential reuse + water transposition in the lesser influx	This alternative combines the alternatives that use saving equipment (A1), a residential reuse system (A3), and the alternatives that use the water supply of the transposition of the São Francisco River in the months of less affluence (A7).
A9	Equipment + ETA reuse	This alternative combines the alternatives that use saving equipment (A1) with the use of 20% of the treated effluent (filter washing water + sludge) from the ETAs of the Epitácio Pessoa Reservoir for irrigation.
A10	Equipment + Loss reduction	This alternative combines the alternatives that use saving equipment (A1) with a 20% reduction in losses in the distribution system by the water and sewage company.
A11	Equipment + Irrigation efficiency	According to CEMIG, the incorrect management of water in irrigation causes a waste of 20% of water and 25% of electricity. This alternative combines the alternatives that use saving equipment (A1) with efficient management measures that increase water-use efficiency from 75% to 90%.
A12	Water transposition in the lesser influx + irrigation efficiency + equipment + reuse + loss reduction	This alternative combines the main water demand management alternatives in the study. The alternatives that use saving equipment (A1), graywater reuse (A3) to transfer water to the lowest inflow months (A7), reducing losses in the supply system (A10) and increasing water supply irrigation efficiency (A11).

Criteria		Scenario 1: Equal weight	Scenario 2: Human supply	Scenario 3: Irrigation	Scenario 4: Maintenance of Reservoir	Scenario 5: Reduction of consumption
C₁	Meeting the human supply demand	0.25	0.5	0.167	0.167	0.167
C₂	Meeting the irrigation demand	0.25	0.167	0.5	0.167	0.167
C₃	Reservoir volume above the target volume	0.25	0.167	0.167	0.5	0.167
C₄	Reduced consumption	0.25	0.167	0.167	0.167	0.5

Management alternatives of demand	Demand reduction percentages (%)	Total consumption reduction (m³ s^-1)	External water supply (m³ s^-1)	Frequency below target volume (%)	Failure to meet demand
Management alternatives of demand	Demand reduction percentages (%)	Total consumption reduction (m³ s^-1)	External water supply (m³ s^-1)	Frequency below target volume (%)	Human (%)	Irrigation (%)
A0	-	-	-	88.1	36.3	88.1
A1	20.7	0.45	-	74.3	30.9	86.9
A2	11.2	0.24	-	76.5	33.9	88.1
A3	19.7	0.43	-	74.8	30.9	86.9
A4	31.9	0.71	-	69.8	28.6	85.1
A5	32.6	0.72	-	69.7	28.0	85.1
A6	-	-	1.52	47.8	5.4	72.0
A7	-	-	1.52¹	64.6	30.9	80.3
A8	32.6	0.71	1.52¹	50.7	7.7	76.8
A9	32.8	0.71	0.0033²	69.8	28,0	85.1
A10	29.2	0.64	-	73.8	29.2	85.7
A11	35.6	0.67	-	72.7	29.2	85.7
A12	42.7	0.88	1.52¹	46.8	3.6	73.2

	Criteria	Objective Weight	Ranking
C₁	Meeting the human supply demand	0.273	1
C₂	Meeting the irrigation demand	0.260	3
C₃	Reservoir volume above the target volume	0.270	2
C₄	Reduced consumption	0.201	4