Decision support systems for rainwater harvesting and runoff control in watersheds

• Autor(a) principal: Terêncio, Daniela Patrícia Salgado
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10348/10214
• topic: Rainwater harvesting; GeograpRainwater harvesting; Geographic Information Systemhic Information System

Pressure on water resources have been increasing over time, due to external forces such as population growth, irregular distribution, water waste, aquifer contamination and also climate change. Global climate change is expected to intensify current and future tensions over water resources and will increase the frequency and intensity of droughts and floods. Thus, in addition to extreme events such as floods and droughts, water quality and forest fire problems are also a concern. Therefore, some methodologies have been tested to improve, mitigate or help better management and planning of water and thus combat these water-related problems. In Chapter 1, a brief introduction is made about pressures on the water resources and their consequences for the environment and society, while some solutions are suggested. An improved framework model to allocate optimal rainwater harvesting sites in small watersheds for agro-forestry uses is presented in Chapter 2. The developed model aims to select optimal RWH sites based on a multi-criteria analysis involving physical, socioeconomic and ecologic parameters. The choice of specific socio-economic parameters allowed the selection of optimal places away from urban centres or large farming areas, which prevent the use of stream water with excessive anthropogenic nutrients in irrigation that may cause accumulation of nitrosamines in the food chain with severe consequences to human health. Chapter 3 discusses rainwater harvesting in catchments for agro-forestry uses: A study focused on the balance between sustainability values and storage capacity. This model follows the line of the previous chapter, but was significantly improved. In this case, attention was paid to the balance between sustainability values and storage capacity of RWH systems. The study aimed at ranking 384 rainfall collection sub-catchments as regards installation of RWH sites for crop irrigation and forest fire combat. The practice of RWH at the catchment scale is frequently concerned with ecological sustainability values, namely through the aesthetic landscape enhancement. To naturally cope with these values, RWH infrastructure (dam wall) heights must not exceed ≈3 m. The results showed that more engineered dams may not always ensure all sustainability values but warrant much better storage. The limiting parameter was the dam wall height, because 217 sub-catchments were found to drain enough water for irrigation and capable to store it if proper dam wall heights were used. Chapter 4 argue about flood risk attenuation in critical zones of continental Portugal using sustainable detention basins. Within the framework of Directive 60/2007/EC (Floods Directive), Flood Risk Management Plans were developed for 23 critical flood risk zones identified in Portugal, capable to eliminate the high and very high flood risk areas instead of attempting to ensure full control of the flood in all potentially threatened areas. The results showed that the number of sustainable detention basins is reduced by about 30% when the full flood control model is used. Although the results indicate the possibility of installing more unsustainable than sustainable detention basins, in all critical areas, only three do not provide sustainable solutions. Therefore, in these critical areasthe construction of highly designed structures would be mandatory. “Can Land Cover Changes Mitigate Large Floods? A Reflection Based on Partial Least Squares-Path Modeling” was a question we tried to answer in Chapter 5. The aim was to verify, using a Partial least Squares-Path Model (PLS-PM), if changes in specific catchment variables, such as forest occupation or imperviousness of urban areas, would result in lower dam heights. In some realistic scenarios, the forecasted changes comprised 30% increase in forest areas or 30% decrease in impervious urban areas. Other purely academic scenarios were also tested, comprehending, for example, the duplication of forest areas or the reduction of catchment slope. In all cases, however, the dam wall heights did not fall significantly and remained very high. Therefore, the answer to the initial question is that non-structural measures may not always be an efficient way to reduce stream flows in a manner that flood detention can be achieved through construction of sustainable dam structures. Finally, in Chapter 6, the general conclusions and future perspectives were presented.