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

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Systems Analysis of Zaragoza UWS Guillermo Penagos treatment in Zaragoza requires large amounts of chemical reagents implying not jus a high cost of water treatment, but also a risk to public health due to DBPs. Shifting to a different raw water source and thereby reducing treatment cost and improving water quality is a strong need for the city. From 2008 the city will receive water from the Pyrenees, specifically from the Yesa reservoir which regulates the Aragon River and is also used for irrigation and hydropower production. A significant improvement of tap water quality for Zaragoza is expected from this new source. This will be discussed further on in the Scenario Analysis section. 4.2.1.2 Storm water Zaragoza is located in a semiarid region with an average precipitation of 270 mm per year, which is concentrated within 70 to 80 days (see figure 4a, showing 2006 daily based hydrograph as example). Precipitation per day in Zaragoza would rarely exceed 20 mm and dry and wet periods are not quite distinct. However, highest maximums and highest averages are reached in May and in September, but rarely exceeding 50 mm per month. Lowest averages and lowest minimums are usually reached in August and in December (see figure 4b). Daily p recip itation for 2006 ( mm) 50 40 30 20 10 0 Total precipitation = 288 mm Days with precipitation = 86 J F M A M J J A S O N D Month a Month p recip itation (m m) 50 40 30 20 10 0 J F M A M J J A S O N D Month b Figure 4. Annual precipitation hydrographs for Zaragoza. 4a. Daily based hydrograph for 2006 4b. Month averages. Error bars represent standard deviation Source Local Agenda 21 Office of Zaragoza Due to these hydrologic conditions storm water is not considered an issue by the Municipality. Nevertheless eventual overflows of storm water are discharged directly in the Ebro River without any treatment. Therefore Municipality is building two storm 24
Systems Analysis of Zaragoza UWS Guillermo Penagos water tanks to prevent the consequent pollution of the river. They are also considering about using storm water for cleaning public facilities or for landscaping. According to the municipality staff the sewer system has got serous dimensional limitations. Therefore, even under the consideration that Zaragoza is a semiarid region, storm water might saturate the system and overflow to the Ebro River under strong rain events 4.2.1.3 Agriculture irrigation systems The Ebro Valley at Aragon is the driest inland region of Europe. In fact most of the area around Zaragoza is naturally either bare or covered with desert-like vegetation. Water deficits are high due to low precipitation (less than 300 mm) and high evapotranspiration (more than 800 mm). Most of the soils of the region are Aridisols, and show similarities to those of North African deserts. However agriculture is an important activity along the Ebro catchment and the most relevant use of water resources in the catchment is agricultural irrigation. In Zaragoza province, including the surroundings of Zaragoza city, the irrigated area is nearly 177,000 ha (see figure 5). Figure 5. Irrigation in Zaragoza province. This satellite picture shows the desert surroundings of Zaragoza city. All the green areas are irrigated agricultural lands (Source: google maps, http://maps.google.es/maps?oi=eu_map&q=Zaragoza&hl=en) . 25
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