VIAS-Hydro: Impact and vulnerability assessment in the drought impacted basins of the Cantareire System

Hazeleger, J.C. (2015) VIAS-Hydro: Impact and vulnerability assessment in the drought impacted basins of the Cantareire System.

Abstract:A recent drought in the Cantareira System – a major water supplier of the metropolitan region of São Paulo – has caused reservoirs to run dry and has forced water agencies to pump water from the reservoir’s dead volume. Water supply has been decreased drastically, albeit too late according to several experts, and the drought has already resulted in economic losses of billions of euro in the water-energy-and-food sector. There is still a need for more risk-based adaptive measures to prevent consequences of future droughts. An assessment of impacts and evaluation of the vulnerability to droughts is hereby highly desirable. The report’s goal is to determine the vulnerability of and impacts on the water supply from the Cantareira system to droughts to allow planners to apply feasible risk-based approaches to future droughts. Research questions focus on the identification of hazards, potential impacts and vulnerability. To achieve this goal, research first focused on a literature study on the functions and the pros and cons of several low flow indicators and drought indices (chapter 2). After a study on the region (chapter 3) – three parallel watersheds with reservoirs which are interconnected through the usage of tunnels – the most applicable indicators have been chosen for the identification of hazards, impacts and vulnerability (chapter 4): the Standardized Runoff Index (SRI) – both for 1 month and for 6 consecutive months – the Flow Duration Curve (FDC), the Base Flow Index (BFI) and the Deficiency Volumes (DV) of the reservoirs. The study on the hazards and (potential) impacts focused on both single watersheds and the whole system. Vulnerability, contrary to hazards and potential impacts taking into account the adaptive capacity of a system, is evaluated for the system as a whole. Results show that annual and seasonal variability in flows cause hazards during dry seasons. Furthermore, SRI and exceedance probabilities in the FDCs reached very critical values during the 2013-2015 drought, imposing big hazards on the metropolitan region of São Paulo. Spatial analysis between the SRI-values of the watersheds (Jaguari-Jacarei, Cachoeira and Atibainha) show more extremes for the relatively smaller watersheds Cachoeira and Atibainha, thus imposing more severe hazards, which are accompanied with lower values for annual base flow index. Assessment of impacts has shown potentially high impacts for low flows due to both annual and seasonal variability; demand exceeds supply for many months throughout a year. The recent drought has, as a result of the severity of the hazard, shown even higher potential impacts with average runoff between May 2013 and May 2015 not even reaching half of the demand for the primary usage of water – the sum of the demand for human and animal consumption and the water necessary to reach 70% of the efficiency of irrigation. The function of the reservoirs as adaptive capacity – they even out both spatial and temporal variability – has a high positive influence on the vulnerability of the water supply to drought hazards. The region is in essence not vulnerable to low flows occurring due to normal seasonal or annual variability. However, consecutive years of mild drought accompanied by continuous outflow matching the total water demand of 36 m³/s, might cause problems on the long term, leaving the water supply system of MRSP slightly vulnerable to mild, consecutive droughts. Calculations have furthermore shown that the region is highly vulnerable to the severe drought which was faced during the past few years. Deficiency volumes exceeded the useful volume of the reservoir to great extent. Interesting to note is however that consequences would have been far less if the outflow of water had been restrained to the outflow for the primary demand of water since 2006.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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