Chambel, A.

Geophysics Centre of Evora, Department of Geosciences, University of Evora, Apartado 94, 7002-554 Evora, Portugal, achambel@uevora.pt

 

Agriculture is clearly the main user of water resources in Portugal (87 % of the total), against 8 % of the urban supply water and 5 % of the industry, but, in terms of costs, the urban supply water represents much more financial effort them any other activity, due to water and wastewater treatment necessary for that purpose.

The total costs of water inefficiency represented, in 2001, a calculated value of 39 % of the total yearly estimated water value. This is the water fraction that must be under better management in order to try to avoid so much economic losses.

Key words: surface-and groundwater uses, Portugal

1 Introduction

Groundwater uses in rural and urban areas of South Portugal has changed in the last decades. Till the eighties, the water supply systems were mostly based on groundwater. But, with most part of the territory based on hard rocks, the increasing water demands and the climatic conditions, political and technical decisions led to the increasing use of surface water, permitted by the construction of a net of dams, the biggest one with a total capacity of 4,150 hm³ and a water surface of 25,000 hectares, built on the turn of the 20 to 21 century, the Alqueva dam, that will permit the urban supply to a large net of villages in one of the most dry regions in South Portugal. It will also permit the irrigation of 110,000 hectares of land. Partially this will substitute areas that previously had irrigation based on groundwater, but mainly it will permit to irrigate new areas.

The first effect of this politics was the substitution of the groundwater supply to the bigger cities (between 20,000 and 50,000 inhabitants) for surface waters and, in the last years, with the privatisation of the water supply systems, more and more villages are using surface waters.

2 General Characterization of the Portuguese Territory

The Portuguese continental territory represents 89,300 km² e has a form roughly rectangular, with a dimension between approximately 560 by 220 km (INAG 2005). It is situated on the western part of the Iberian Peninsula, western part of Europe, between the meridians 6º W and 10º W and between the parallels 37º N and 42º N. Its border is with the Atlantic Ocean at West and South and with Spain at North and East (figure 1).

Portugal has about 11,400,000 inhabitants. About 50 % of the population is concentrated in the urban coastal municipalities and the inner part of the territory has been depleted of people in the last years. The tertiary sector represents 70 % of the economic activity, 27 % the secondary sector and the primary sector is only represented by 3 % of the population.

The climate in Portugal puts together the atlantic and Mediterranean influence, the first one responsible by high precipitation levels in the winter, essentially on the NW part of the country, and the second one responsible by high temperatures and low precipitation levels in the summer (INAG 2005).

The average total precipitation value in Portugal is about 89,000 hm³, equivalent to an average year precipitation of a 1,000 mm (INAG 2005).

Figure 1. Position of Portugal in Europe.

The spatial distribution of the precipitation shows that the more rainy regions are present on the NW part of the territory, where the precipitation can reach average mean values higher than 2,800 mm. On the other northern parts of the territory the precipitation values are between 1,200 and 1,400 mm on the high lands and are less than 500 mm on the low lands (figure 2).

On the central part of the country, two areas of high relief are present, where the precipitation can reach 2,400 mm in an average year. On the south the average precipitation can vary between 800 and 1,200 mm in mountain areas and can reach a minimum of 400 mm on the south coast (INAG 2005).

The precipitation is concentrated in the period between October and March. The highest values correspond to the months of December and January and the lower values occur in July and August. Big variations can also occur from one year to the other, putting sometimes all the country in a situation of severe dryness and, other times, flood problems or torrential rains can occur.

The Portuguese territory is formed by 3 geologic unities: igneous and metamorphic rocks of the Hercynian Massif, the sedimentary rocks of the Meso-Cenozoic western and south basins and the Tertiary rocks of the Tejo-Sado basin (figure 3).

The first unit represents about 1/3 of all the country and is formed by pre-Mesozoic terrains (metamorphized and deformed pre-Cambrian and Palaeozoic rocks), partially covered by more recent formations (Teixeira & Gonçalves 1980). The main litologies are igneous rocks (granites to gabbros, andesites, etc.), metamorphic rocks (schists, shales, greywackes, quartzites, gneisses, etc.) and sedimentaries (cover deposits) and meta-sedimentaries (meta-conglomerates) rocks.

The main direction of the structural hercynian features is NW-SE and, more recently, the Alpine Orogeny created some NNE-SSE direction fault structures, some with high interest on the hydrogeologic prospecting, namely on the specific area of the mineral waters.

Figure 2 – Distribution of the precipitation in continental Portugal (adapted from SNIRH-INAG 2005).

The Meso-Cenozoic basins are composed by sedimentary rocks like limestones, dolomites, marles, clay, arenites, conglomerates, etc., intersected in many places by eruptive intrusions and volcanic rocks.

The more recent cover rocks (terraces, alluviums, ancient beaches) are formed by sand, clay, gravel that fulfil the ancient fluvial valleys, forming big deposits, as the tertiary and quaternary basin of Tejo-Sado.

 

 

Figure 3. The main geologic features of the Portuguese territory (the Hercynian Massif is an igneous and metamorphic Palaeozoic massif; all the other unities are represented by sedimentary rocks).

3 Hydrogeology

On the Hercynian Massif (figure 4) the aquifers are highly dependent on the fracturation, kind and deep of the weathering layer. The most ancient and basic rocks are the most productive ones, specially when affected by late orogenic movements, like the Hercynian and Alpine orogenies. Between them, the most productive ones are metamorphic limestones that occur on the south half of the country (they present median yields of about 0.8 to 5 L/s and the transmissivity can go to 4,000 m²/day) and some of the quartzite ridges that occur on the central part of Portugal. Also important are some aquifers formed by gabbros, migmatites, gneisses, some tonalitic and quartzdioritic rocks and some meta-volcanic acid and basic rocks. Between the less productive rocks, the schists, shales and greywackes are normally more productive than the granites, which constitute the less productive litologies. In these ones, some of the drillings are completely dry and the average exploration values are under 0.4 L/s.

Considering all the less productive rocks, the median of the yields can vary between 0.5 to 1.8 L/s, representing the value of 1 L/s the considered average yield for this kind of hard rocks, at least on the south of the country (ERHSA 2001). The transmissivity values can reach a maximum near 200 m²/day.

On the Western basin (figure 4), 28 aquifers were identified, on variable geologic environments: tertiary and quaternary detritic unities, cretacic sandstones and limstones and jurassic limstones, reflected in the high heterogeinity of the aquifer systems and its hydrogeologic parameters. The median of the yields are between 0.8 and 22 L/s and the transmissivities between 20 and 1,500 m²/day, with no significant differences between the karstic and sandy aquifers.

On this basin, also some less productive areas occur, associated in generally to clay or volcanic rocks.

The South basin has 17 identified aquifer systems (figure 4), mainly karstic, with some of them mixed, karstic and porous and only two exclusively porous. Limestones, dolomitic limestones, sand and gravel form the mixed ones.

These aquifers have generally less area than the ones on the western basin, once the South basin is less extended. The median of the productivities are between 2.8 and 15.5 L/s and the medians of the transmissivity are between 5 and 1,000 m²/day, with the few registered storativity coefficient values between 10^-2 and 10^-4 (Almeida et al. 2000; SNIRH-INAG 2005).

Also some less productive areas occur in this area related with less permeable formations.

The Tejo-Sado basin is formed essentially by tertiary and quaternary detritic formations (figure 4), but there are also some carbonate formations. It is the most important hydrogeologic unity of the Portuguese territory and are divided in 4 aquifer systems, formed by sandstones, sand, conglomerates, gravel and some limestones and marbles.

The productivities are high, with medians between the 5 and 35 L/s and median transmissivity values between the 100 and 1500 m²/day. The storage coefficient are in scale of 10^-3 (Almeida et al. 2000; SNIRH-INAG 2005).

Figure 4. Aquifers of the main hydrogeologic unities in Portugal.

4 Water Uses and Economic Consequences

The water necessities in Portugal were estimated around 7,500 hm³/year, in 2001 (PNUEA 2001).

By sectors, based on the National Water Plan (PNA 2003), the agriculture is clearly the main water user in Portugal, with a total volume of about 6,550 hm³/year (87 % of the total), against 570 hm³/year of the urban water supply to populations (8 % of the total) and 385 hm³/year of the industry (5 % of the total).

About the effective water use costs, the urban supply systems represent the most relevant sector (46 % of the total costs), against 28 % of the agriculture and 26 % of the industry (PNUEA 2001).

But, in terms of desegregation of the uses, the biggest part correspond to agriculture, essentially on the individual use and irrigation by gravity, followed by the domestic urban use (shower, bathroom, wc discharges) and finally the transformer industry.

On the economic side, most part of the expenses with water is related with the domestic urban uses, followed by the agriculture individual irrigation and by the uses on the transformer industry (PNUEA 2001).

By other side, the losses in the diverse uses must be added to the costs of water treatment after use. In the case of urban water uses, the affluence coefficient is considered 0.9 and the losses 40 %. This implied, in 2001, a total cost of about 1.5 € by m³. For agriculture the cost was calculated in 0.08 € and for industry 1.25 € by m³ (PNUEA 2001).

Considering the relative importance of the water uses, the main total one year costs are:

- 855 m€ for urban supply

- 524 m€ for the agriculture

- 481 m€ for the industry

In the case of agriculture, the resulting costs don’t consider the contaminated water losses that return to the environment and the respective economic consequences for the environment or respective treatment, by impossibility on the calculation of the quantities of water that return to the hydrogeological cycle. For the industrial water the costs considered the uses of the public supply water (16 % of the consumption) private water (84 %) and the drainage and treatment of the waste water, considering an affluence coefficient of 0.8 % (PNUEA 2001).

5 Water Management Problems

Explained the problematic of:

-the groundwater potential and spatial distribution on Portugal;

- the asymmetric spatial and timing distribution of the precipitation on the territory (North/South);

- the asymmetric spatial concentration of the population (coastal/inner areas);

and considering that:

- Portugal is a country with a high touristic affluence, concentrated on the weather good conditions (hot season) and beach facilities;

- some of the coastal areas can, in summer, have 5 to 10 times more population than in the winter season;

- almost all the industries are located near the coastal areas;

the asymmetric surface- and groundwater distribution is a big problem and an issue that must be managed carefully.

So, the biggest cities (on the western/central-north coast) are now almost completely dependent on surface water supply, with the big artificial lakes over the Hercynian Massif and tens of kilometres of tubes transporting the water.

The south province (Algarve), mainly a touristic area, roughly coincident with the south Meso-Cenozoic basin, was on the past totally dependent on groundwater, but has been, on the last years, focus of attention, and new dams were built north of the area. They will supply in the future part of Algarve water, using probably both surface- and groundwater origins.

The main fractured aquifers (crystalline limestones, gabbros, gneisses, etc.) will continue to supply water to some villages (till 10,000 inhabitants), and the more isolated villages will also continue to use water from other less productive fractured aquifers, once they need low water volumes.

In 2004 about 45 % of the public supply water in Portugal was groundwater and 55 % result from artificial lakes (Ribeiro 2004). But, in the case of the Hercynian Massif, this percentage is much higher than 50 %. The spatial distribution of the groundwater uses, in percentage, by municipality, is represented in figure 5.

On what concerns the use for industry, the surface origins represent about 55 % of the total volume, on a total of 206 hm³ and the groundwater origins represent about 179 hm³.

The agriculture is the higher consumer of water in Portugal and 65 % of the volume is groundwater, representing 4,215 hm³, against 2,340 hm³ of surface origins (artificial lakes or rivers).

The management between surface and groundwater is not done in Portugal, at least in the way this must be done. Due to the asymmetric month distribution of the precipitation between summer and winter (low precipitation rates in summer and high in winter) and due to the same asymmetry related with the temperatures, very hot in summer and cold in winter, the recommendation is to use the surface water in the winter, when there are more available water in the lakes and the water temperature is lower, and to use the groundwater in summer, when the water of the lakes began to have quality problems, due to the presence of red algae and the lower water levels.

The actual politics is to implement the surface water uses for urban consumption in all the big places and near the tubes linking the lakes and these defined places. Places with less than 2 or 3,000 inhabitants, if far way from the tubes, are object of studies trying to show if it is sustainable to guarantee the supply systems based on groundwater or if it is necessary to invest on new distribution nets.

In terms of opportunities to save water on the different sectors, the agriculture is responsible by 88 % of all the losses (2,750 hm³/year), against 240 hm³/year of the urban supply systems (8 %) and 112 hm³/year of the industry (4 % of the total). But, in terms of economic losses, it is the urban sector that is the most important one, with 369 m€/year (51 % of the total), followed by the agriculture, with 219 m€/year (30 %) and industry, with 140 m€/year, 19 % of the total. So, the total costs of the inefficiency were, in 2001, 728 m€/year, representing 39 % of the total yearly estimated water value.

Figure 5. Percentage of groundwater use in the urban supply water to Portuguese municipalities (based on data from APDA 2004).

6 Legislation and Groundwater Quality

The Portuguese law n. 236/1998, of the Ministry of the Environment, established the criteria and objectives of quality to protect the aquatic environment and increment the quality of the water for its main uses, namely the maintenance of the necessary quality of groundwater that support the human supply production.

The law 243/2001 introduced changes on some parameters, according the new scientific knowledge, which has caused recently some problems, like the legal change on the permitted arsenium concentration, which passed from 50 to 10 g/L, causing an increment on the number of groundwater points that are out of the law new limit. Also the new rules for the radiation contents are causing problems on many points that were previously inside the legal limits.

One of the ways why the costs of the water will go up in the future in European Union is these changes on the water laws, which reflect the recent and evolutionary knowledge about the physical-chemical characteristics of the water. Being the limits every time more restrictive, the tendency is now to increase the treatment processes, increasing the costs of the final water supply. The alternative is always also expensive, being it to drill new wells and create new infrastructures, or create new dams or new distribution systems from previous artificial lakes.

7 Final Remarks

The water problem in countries like Portugal, with asymmetric regional and temporal distribution of precipitation (North/South) and asymmetric distribution of population (coastal urban areas/inner areas) is of no easy management. From a past based on groundwater, the water politics in Portugal have changed in the last years, with each time more and more surface origins supplying water to urban agglomerates. Even so, space for groundwater is yet available, once it is practically impossible, on the economic point of view, to extend the surface supply systems to all the places where people leave. Today, every time that the investment in surface water is high, the groundwater has a possibility to maintain its use.

The uses on agriculture and industry are many times dependent of the access to surface water or not and, in the last case, groundwater is an important alternative. Industries and agriculture use private water in high percentages, being it groundwater or surface water.

The activity of agriculture is the main water consumer and where there are more possibilities to increment measures in order to save higher percentages of water, but it is in home that most part of the cost saves will reflect, once the urban supply uses the most expensive water, due both to water and wastewater treatment.

The total costs of water inefficiency represented, in 2001, a calculated value of 39 % of the total yearly estimated water value.