Systems Analysis of Zaragoza Urban Water - SWITCH - Managing ...

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Systems Analysis of Zaragoza UWS Guillermo Penagos 4.4.3.5 Setting priorities for pollution loads This report provides insights about the environmental impacts of Zaragoza UWS operation on a year basis. However such impacts are not constant all over the year and might vary seasonally. In fact, even if pollution loads remained constant all over the year, there will be a seasonal variation of the receiving environment. This is more evident for the water bodies and is remarkable for the Ebro River which exhibits an important variation of its discharge along the year. The current hydrograph for the Ebro river on a month average basis is provided in figure 25. This figure also shows the worst climate change scenario expected for water availability in this basin for the year 2020 and the year 2060. 500 Current 2020 2060 Average discharge (m 3 s -1 ) 400 300 200 100 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month Figure 25. Regimes for Ebro River at Zaragoza under current conditions and projected conditions under Sc3 Scenario. Error bars represent standard deviations on a month basis (Source for current regime: CHE, 2007) In current conditions maximum discharges of nearly 400 m 3 s -1 are expected between December and April. Minimum discharges are expected during summer time, especially in August, where they can be as low as 30 m 3 s -1 . This also means that the impact of Zaragoza UWS upon the Ebro River is not constant all over the year and it reaches a maximum in August. Figure 26 provides an example of the seasonality of this impact taking total phosphorus as an example. 54
Systems Analysis of Zaragoza UWS Guillermo Penagos TP concentration (ug l -1 ) 1000 800 600 400 200 Concentration upstream Zaragoza Current impact 2020 2060 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month Figure 26. Impact of Zaragoza UWS upon TP concentrations at the Ebro River. Only upstream concentrations have been actually measured (CHE, 2007). Error bars represents standard deviation on a month basis. The other three concentrations are the ones that can be predicted from Zaragoza TP loads to the river at current conditions and at worst climate change scenario (Sc3?...worst climate change conditions, population growing at same rate as in the last ten years, no changes on WWT technology, no changes on people consumption patterns) TP concentrations in the Ebro River, upstream from Zaragoza, range between 100 to 200 µg l -1 . Under current conditions the city does not have a significant impact on the river from October to May, but from June onwards the impact becomes more important and it may raise the TP concentrations up to 400 µg l -1 . In August when –as previously described– river discharge may drop down to 30 m 3 s -1 . For the 2020 scenario the pattern is quite similar, but for the 2060 scenario August TP concentration goes up to 900 µg l -1 , which is more than three times the present upstream concentration. 55
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