Environmental Issues in the la Plata Basin. Carlos E. M. Tucci and Robin T. Clarke. Institute of Hydraulic Research

Transcription

1 Environmental Issues in the la Plata Basin Carlos E. M. Tucci and Robin T. Clarke Institute of Hydraulic Research Federal University of Rio Grande do Sul Porto Alegre Brazil Erro! A origem da referência não foi encontrada. ABSTRACT: The la Plata River basin is one of the largest in the world, with an area of about 3 million km 2. It includes parts of five countries (Paraguay, Argentina, Bolivia, Brazil, Paraguay and Uruguay) and the water resources of the La Plata basin are essential for their economic development.. The main tributaries are the rivers Parana, Paraguay and Uruguay. Some of the main developments having environmental impacts that influence the basin have been the following: (i) developments of many hydro-power reservoirs in the Upper Parana River, in Brazil, from ; (ii) deforestation in the Parana, Uruguay and Paraguay basins from ; (iii) introduction of intensive agricultural practice after 1970; (iv) urban developments with change to flood regimes; (v) navigation and conservation of Upper Paraguay River. Since 1970, flow increases have been observed which may have been caused by changes in vegetation cover, or by climate variation. The changes raised important issues both for water resource development and environmental conservation. This paper discusses the water management and environmental issues, taking account of climate patterns and the development of the five countries sharing the basin.

2 INTRODUCTION The la Plata River flows through five countries in South America: Argentina, Bolivia, Brazil, Paraguay and Uruguay. Throughout almost its entire course, it is known as the River Paraná, and only becomes the la Plata River below its junction with the River Uruguay. This basin of the la Plata is one of the largest in the world and the region has the highest level of development in South America. Economical developments have had important consequences for the environment, the main issues being the following: (i) deforestation and intensive agriculture in the Paraguay, Paraná and Uruguay basins: the agriculture expansion since the 60 s, mainly in Brazil, has left some areas with only 5% of natural cover; (ii) developments of many hydropower in the Paraná River: most of the hydropower of Brazil, and indeed of South America, comes from this basin. Dams have modified rivers behaviour and environmental conditions both upstream and downstream; (iii) climate variations: the hydrological records show increases in both rainfall and runoff after The increases have had important impacts in areas such as the Pantanal, in the basin of the River Paraguay, and in the basin of the River Paraná; (iv) environmental degradation in main cities: the population in the region is highly concentrated in urban areas. The Brazilian State of São Paulo with 36 million people, has 92% of its population in cities. Urban development has had severe environmental impacts; (v) proposed improvements to navigation in the Upper Paraguay will 2

3 have grave consequences for the Pantanal wetland; (vi) flood hazard in the main rivers: floods of the main rivers have resulted in extensive damage, particulary since the 80 s. This paper presents some of the main characteristics of La Plata River Basin and discusses some of the main issues related to development and environment conservation. THE LA PLATA RIVER Main characteristics In terms of area, the drainage basin of La Plata river is second only to that of the Amazon in South America, and it is the fifth largest in the world. As shown in Figure 1, its area of 3.1 million km 2 is shared among five countries (Argentina, Bolivia, Brazil, Paraguay and Uruguay), through the principal subbasins of the Rivers Paraná, Paraguay and Uruguay. The la Plata basin is important in different ways for the economy of each; about 70% of the total GNP of the five countries combined is produced within the basin, which is also inhabited by about 50% of their combined population. Table 1, giving the distribution of drainage basin area by country and by subbasin, shows that almost half the total basin area is drained by the River Paraná, and of this area 59% lies within Brazil and 37.5% in Argentina. The River Paraguay is the next largest sub-basin, making up a little over 35% of the La Plata basin as a whole; of the area drained by the River Paraguay, about a third lies within each of Paraguay and Brazil (32% and 34% respectively), 15% lying in Argentina and 19% in Bolivia. The much smaller sub-basin of the River Uruguay makes up about 12% of the total, of which about 43% lies in Brazil, 3

4 41% in Uruguay, and 16% in Argentina. In the years , the five countries Argentina, Bolivia, Brazil, Paraguay and Uruguay set up an Intergovernmental Committee which led to the signing of a development agreement for the La Plata basin. Its aim was the rational development of the basin in all its aspects. However, between the years there were many diplomatic conflicts, mainly between Brazil and Argentina, because upstream dam construction caused detrimental effects downstream. Early in the decade of the seventies, Paraguay, Brazil and Argentina signed an agreement concerning the operation of the hydropower plant at Itaipú, and this was followed by various bi-national agreements such as those concerning Salto Hydropower in the Uruguay Basin (agreement between Argentina and Uruguay); Yacereta Hydropower on the River Parana (between Argentina and Paraguay) and the planned Garabi Project (between Argentina and Brazil). With the growth of Mercosul, which began as an agreement on commercial trade among some South America countries and has now has been extended to others areas, there are many projects in progress. Some hydrologic aspects The hydrological behaviour of the main rivers draining the la Plata basin is the product of basin topography - itself a product of geology and climate - and human activities within its boundaries. Natural conditions vary greatly from North to South (the general direction of drainage) and from West to East. In the eastern half of the basin, the basin boundary is clearly defined with mean altitude of 1000 m; however the water divide can reach 1500 m in the extreme eastern part, but falls to as low as 200 m in the South. On the western boundary, the Andean cordillera 4

5 reaches altitudes between 1000 and 4000 m, although there are stretches of this western basin boundary, notably in the North-West and South-West, where altitudes reach only to about 500 m and 300 m respectively. Mean annual rainfall decreases both from north to south, and from east to west; rainfall in the maritime uplands along the Brazilian coast reaches about 1800 mm, but falls to 200 mm along the western boundary of the basin. Rainfall is greatest 5

6 in the upper parts of both the Paraguay and Parana River basins (Figure 2). Table 2 presents mean annual flows at selected points within the three subbasins, together with the lengths of upstream sections and the areas drained. A point of interest concerns the relative contributions to the La Plata flows of the Rivers Paraná and Paraguay; where it joins the River Paraná, the Paraguay has a mean annual discharge of m 3 s - 1, for a total drained area of million km 2. At the outfall of the Paraná, on the other hand, annual mean discharge is m 3 s - 1, over six times that of the Paraguay, for a drained area of million km 2. Thus the specific yield of the Paraguay is 2.47 m 3 per 1000 km 2, compared with m 3 per 1000 km 2 for the Paraná. The difference (by a factor of 4.75) can partly be explained by high evaporation losses in the wetlands lying in the upper reaches of the Paraguay, particularly the Pantanal wetland described below. Channel slope is very shallow for much of the River Paraguay. From Cáceres to the sea is a distance of over km, whilst the difference in altitude between Cáceres and mean sea level is a few tens of metres. The poor natural drainage of the region has created the Pantanal, one of the world's largest wetlands with area approximately 140,000 km 2 (Figure 1). Between the Pantanal and Corrientes in Argentina, where the Paraguay joins the Paraná, the mean slope is about 0.04 m km - 1, falling to 0.01 m km - 1 in some parts. The slope of the Pantanal itself is 0.25 m km - 1 in the east-west direction but only 0.01 m km - 1 in the North-South direction. The time difference in the flood peak to the North and South of the Pantanal is about four months, and the flow regime in the Paraguay as a whole is strongly influenced by the Pantanal storage, one consequence being that annual peak water levels in the Upper Paraguay are correlated between one 6

7 year and the next, regardless of rainfall conditions. We return to the hydrology of the Pantanal later in this paper. As is to be expected in such a large area, the principal matters of hydrological concern vary considerably from sub-basin to sub-basin and from upper reaches to lower reaches. In the Upper Paraná River, above the confluence with the River Iguaçu, the principal matter of hydrological concern is the change in land use from natural forest to arable cropping systems based on soybean production. In the lower courses of the Rivers Paraguay and Paraná, principal matters of hydrological concern are navigation, and flood control; in the recent past, floods have caused significant loss of life and damage to property. Sub- Table 1 Distribution of area between sub-basins and countries (OEA, 1969) Area % of Argentina % of Bolívia % of Brazil % of Paraguay % of Uruguay % basin 10 3 km 2 Prata 10 3 km 2 each 10 3 km 2 each 10 3 km 2 each 10 3 km 2 each 10 3 km 2 each Basin basin basin basin basin basin 7

8 Paraná Paragua y Uruguay Prata Table 2 Some characteristics of the three principal sub-basins (Internave, 1990) Main River Paraná River Junction of Paranaiba and Grande Distance from upstream km 2 Basin area 10 3 km 2 Mean anual flow m 3 s (Paranaiba) and (Grande Junction with Paraguay Mouth Paraguay River At Cáceres Final section Uruguay WATER RESOURCE DEVELOPMENTS AND IMPACTS The river basin is the region where water is available for planning water resources use, yet demands usually occur according to a different geographic division, since, in the past, rivers provided clearly defined boundaries. Thus, part of the basin is managed by one state or country, and part by another which involve organizations from different states or countries with different water use policies. The la Plata basin is an example of this situation. Basin planning involves definition and projection of water use in the basin. Often, water resources planning is seen as the study of different alternatives for a specific project, with one or more purposes, or for a water course reach. Planning for the whole basin involves the integration of efforts to identify needs and define water use priorities 8

9 for multiple purposes. Water use in the river basin has been dictated by national goals such as energy production and water supply. The reservoirs have been designed according to specific objectives which reflect economically tangible benefits. Consequently, areas around headwaters reservoirs, which store water for irrigation, flood control or navigation regulation reserve, do not enjoy the benefits or may makes things worse. Planning is required to harmonize the multiple water uses and obtain tangible economics benefits, as well benefits such as avoiding loss of human life and environmental conservation. We now consider aspects of the main factors influencing the water resources of the la Plata basin. Hydropower Hydropower power plants are usually sited in large basins and require significant investment with eight years of planning. Their performance depends on two main factors: hydraulic head and flow. Since these developments regulate large flows, large volumes of storage are required, so that extensive areas must be flooded. Development design in a large river usually makes use of regulating reservoirs and several others with small volume and high hydraulic head. Due to the environment impact of large flooding it becomes increasingly difficult to obtain approval for regulating reservoirs which flood large areas. As a result, a cascade of small regulation reservoirs with high heads becomes likely, with important consequences for the downstream environment. Throughout the la Plata basin, the total capacity identified is about MW; 53% of this total has been utilised or works are are in progress to exploit it. The number of plants planned is significant, both at the domestic level of countries such as 9

10 Brazil, and as international projects. The main areas with hydropower potential are on the upper Paraná River and on the River Uruguay. Brazil's energy is largely supplied by hydropower (93%), and during 1965 to 1985 many dams were built for hydropower production (Figure 2) in the Paraná River, which yields more than 50% of all Brazil's energy production. Today, some hydropower plants are planned for in the Iguazu and other tributaries of the Paraná (Piquirí and Ivaí). In the international reach, Corpus (downstream, of Itaipú) is the dam which remains to be built but some difficulties await resolution, since although the dam is to be built by Argentina and Paraguay, part of Brazilian territory will be flooded. The Uruguay River basin presents a large hydropower potential with a yield of 40,5 KW km - 2. The total energy available from the basin is MW, while the total energy so far developed is 6680 MW. Existing hydropower developments in the Uruguay River basin are on the Passo Fundo River, also a tributary of the left bank in the international reach, and the Salto Power Plant in the international reach between Argentina and Uruguay. The greatest hydropower potential of the basin is found in the upper part, where several projects have been planned. Navigation In the last century and in the beginning of the twentieth, the navigable waterway of the la Plata tributaries provided the main channel for human settlement and development. Today the principal navigable stretches (Figure 2) are: 10

11 (i) On the Paraná-Paraguay: from the coast up to Cáceres in the Brazilian Mato Grosso, a distance of 3,600 km. There is a major proposal to improve this waterway to increase river depth, thus allowing more permanent traffic through the countries having territory within the basin. This project will have an important impact on the environment, to be discussed later in this paper; (ii) Tietê Paraná: The Tietê river is one of the Paraná's main tributaries, flowing through the highly developed region of the State of São Paulo which yields about 36% of GNP of Brazil and has 36 million inhabitants. This waterway has dams for navigation purposes, allowing transport by water from near the city of São Paulo downstream to the River Paraná. (iii) River Uruguay: According to OEA (1985) the River Uruguay is navigable in its lower reaches which form the border between Argentina and Uruguay up to the dam of Salto Grande. Upstream from Salto Grande, the river is navigable up to São Borja. Agriculture and land use impacts Until 1970 most of the agriculture in the State of Paraná and in a large part of São Paulo State was devoted to coffee production under permanent cover, but after a series of cold years, in the end of the 60s, coffee plantations were destroyed by burning over a large area, with important economical losses. Subsequently, coffee was substituted by annual crops such as corn and soya. This land use practice increases the soil erosion in rural areas. At the end of the 70s, some soil conservation programmes were initiated, mainly in the Planalto towards the headwaters of the River Paraguay, and in the upper reaches of the rivers Paraná and Uruguay (see Figure 1). Soil erosion from the upper Paraguay is 4 t. yr -1.ha -1 (Borges et al, 1996). In Rio 11

12 Grande do Sul the estimated erosion is from 16 to 32 t yr -1.ha -1 (Benetti et al 1989). Another important area of erosion and river bed mobility is in the Bermejo River which flows to the Paraguay River near Assuncion. Natural conditions of high bed river slope, rainfall and soil have magnified the changes caused by human activities, and cities had suffered from severe flooding. Very little of the water in the upper Paraná is used for irrigation. In the Uruguay there are some private developments for rice production. This irrigation occurs mainly along the Ibicuí River, a tributary of the Uruguay. In this area there is some conflict between the requirements for water supply and for irrigation during dry months. The present demand is about 13 % of the mean flow. Floods Flooding is of major concern in the la Plata river basin. Most of the rivers have long and wide flood plains which have been occupied by settlement or used for crop production. The River Paraguay has a wide flood plain from its upstream reach in the Pantanal down to its junction with the Paraná. Flood plains of the River Parana in Brazil and its tributaries such as the Iguaçu, contained many settlements which experienced damage after Two major conurbations - São Paulo, with 16 million inhabitants, and Curitiba with 2.5 million occupy large areas of the flood plains of the Rivers Tietê and Iguaçu, respectively. In the international reaches and in Argentina, the River Paraná commonly extends over large areas during the flood season. These areas are used for some agriculture and contain some important cities such as Santa Fé, Corrientes and Rosário. Over a considerable period ( ), the annual floods were not extensive, and this gave rise to the belief that settlements could be built on areas which 12

13 were subsequently shown to be at severe risk from flooding. The largest flood of the century occurred along the rivers la Plata and Paraná in 1983, when for a year and a half, the Paraná flood level was above street-level in parts of Santa Fé, Argentina, although the city is protected by dikes. In União da Vitória on the River Iguaçu, the cost of the flood amounted to US$ 78 million. In the State of Santa Catarina the damages represented 8% of that State's Gross product for the year. The steep gradient of the upper reach of the River Uruguay produces floods with large and rapid changes in water level, whereas downstream in the international reaches the plains can be under deep floods for long periods. Table 3 shows the number of cities and population affected by the floods in some years. Water Supply Demands for water supply and irrigation can usually be met by small basins, in which developments for water supply tend to be sited near to areas of demand. However, water supply and irrigation may compete for available water, especially during low flow periods, when demands increases. Tabel 3 Population affected in Uruguay river basin during floods Year Loss of life Population affected Number of cities affected , , , , , , , Source: Civil Defence: State of Rio Grande do Sul Despite the fact that demand is not high relative to the available resource in the basin, uneven temporal and spatial distribution of flow in the headwaters and water quality degradation are of major concern in the la Plata basin, particularly in and 13

14 around the metropolitan areas of São Paulo and Curitiba. The city of São Paulo requires about 60 m 3 s - 1 of which 33 m 3 s - 1 is imported from basins other than that of the Tietê, which lacks water of a sufficiently high quality. Curitiba uses 7 m 3 s - 1 for water supply from the River Iguaçu but has some restrictions during floods because of the contamination of the water and because water catchment areas need to be protected from urban development.. THE MAIN ENVIRONMENTAL ISSUES The main basin developments and environmental impacts are the issues discussed here. Due to the size of the basin, the choice of environmental issues discussed is somewhat selective. Climate variation, deforestation and agriculture practices. Climate variation and its impacts have been a major issue for the la Plata basin since the 70s, when the mean annual flow increased markedly in some river sections. Table 4 shows flow increases from 19 to 46 %. Figure 3 shows the flood level variation of the River Paraguay at Ladário and mean rainfall in the basin, both standardised so as to be dimensionless. It can be seen that, after 1970 there is a large increase in the level and a smaller increase in the rainfall. Table 5 Mean annual discharges em m 3 s - 1. River Section Before Increase % Parana River at Jupiá 5,852 (+) 6,969 19,1 R. Paranapanema at Rosana 1,057 (+) 1,545 46,2 R. Paraná at São José 6,900 (+) 8,520 23,3 R. Paraná at Guaira 8,620 (+) 11,560 34,1 R. Paraná r at Posadas 11,600 (*) 14,255 22,9 R. Paraná at Corrientes 15,265 19,510 27,8 + series from ; * series from

15 2 1, 1, 1, 1, 1 Rainfall llevel 0,8 0,6 Nondimensional P, H 0,4 0, Year Figure 3 Variation in annual water level at Ladário, (Upper Paraguay) and rainfall (three year moving average) at Cuiabá, River Paraguay. The main effects of increased flow and rainfall in the basin are the following: (i) soil erosion and sediment deposition in river channels, decreasing the depth of soil available for agriculture; (ii) increase in river level and flood frequency; (iii) change in the river bed and the riparian environment ; (iv) (v) (vi) decrease of reservoir volume capacity with sediments deposition; increased production of energy from hydropower; changes in water quality due to resuspension of bed material during flood conditions. These increases in flow and rivers water level may be due to one or both of the following causes: 15

16 (i) rainfall increase after 1970:Anderson et al (1993) using data from the River Paraná at Corrientes (both rainfall and runoff) concluded that the unusual heavy precipitation of 1980s and early 1900s was the most important factor accounting for the flooding of these years. In addition, they also concluded that there is no consistent evidence, statistical or otherwise, that changes in rainfall-runoff dynamics associated with land use changes played an important role in recent flooding in the Basin. The same paper says There is, however, some evidence that when precipitation is not extremely high, some change has taken place that causes streamflow to be greater than otherwise would have been expected. The mean annual rainfall from 1901 to 1970 in the Paraná basin at Corrientes was 1364 mm and for the period 1971 to 1991, 1438 mm, 5.4 % greater. This increase was very similar to that observed in the part of the Paraná basin lying within the Brazilian State of Paraná. In theory, if all the additional rainfall were to generate runoff, an increase of 6% in rainfall over a river basin with runoff coefficient of 17% (the value for the Paraná), the increase in runoff would be 35%. However this is, of course, an upper limit to the increase in runoff.. Barros et al (1995) analysed rainfall trends in Southern South America to the East of the Andes, citing many other authors who had concluded that rainfall has increased in some parts of the la Plata basin. In particular, Castaned and Barros (1994) found an increase from 850 mm during the 1920s to 1150mm in the 1980s in the mean rainfall for humid Pampa. They found strong positive trends since the 1960s over the subtropical region to the East of the Andes. (ii) deforestarion and soil use: Bosch and Hewlett (1982), Bruijnzeel (1995) and Sahin and al (1996) reported many experiments in small basin showing the following: 16

17 (i) deforestation increases the mean flow; (ii) deforestation followed by annual crops which uses machinery for soil preparation are those practices which shows higher increase in the mean flow. The development of agriculture and settlement resulted in much deforestation in the upper Paraná, Paraguay and Uruguay basins in Brazil. Table 5 shows the changes in original cover in the States of Paraná and São Paulo, both of which lie in the basin of the River Paraná. In the State of Rio Grande do Sul, Southern Brazil, which hasone third of its area is in the Uruguay basin, the forest cover at the beginning of this century was about 40% of the total area of the State; today, it is estimated at just 2.6%. It can be seen that although deforestation started before 1970, most of the increase in flow occurred after 1970; but an important change in agriculture practice from coffee to soya production occurred in Brazil after 1970 as described above. Soya is a high value crop and its cultivation spread over large areas. Figure 4 shows an example of the change in vegetation cover from one area of the Paraná basin. Soya is also an annual crop which requires machinery for soil preparation (Figure 5 shows the increase in machinery sold in the region after 1970). Such changes commonly increase mean flow as reported above; but the area is large and the extent of the impact of such changes at the basin-wide scale is not yet clear. Tabel 3 Deforestation evolution in the States of São Paulo and Paraná in Brazil and Year Original cover of São Paulo State % Year eastern Paraguay Original Cover of Parana State % Year Original cover(*) % < ,8 < , , ,

18 , , , , , , , , , , ,2 (*) eastern Paraguay ( Anderson Jr. et al,1993) (i) As can be seen, there are more questions than answers, and much more research is required in order to solve them. The main conclusion are (i) that flow has increased in the Upper Paraguay, Paraná and Uruguay basins; (ii) rainfall and land-use changes have both contributed to cause the flow increase, although there is not yet a clear answer as to the relative magnitudes of the two contributory causes. In the context of water resource development and environment protection, the main question is: how permanent is the increase in flow? In terms of energy production, a permanent increase in flow represents greater firm energy yield, but possibly a shorter reservoir life due to sedimentation; in terms of navigation, water depth is increased and the period during which the rivers is navigable may be lengthened; in terms of the flood regime, flood damage may be greater. The question is difficult, requiring more research before quantitative answers can be given. 18

19 Figure 4 Soil use change in a sampled area in North of Paraná (Kroner, 1990) Pantanal: climate variation, soil erosion and effects of channel works The River Paraguay and its tributaries flow from an upstream area called the Planalto, with altitude greater than 200 m, into the large wetland of the Pantanal, with altitude less than 100 m. The Pantanal is one of the world s largest wetlands, with area about km 2. The ecosystem of the Pantanal is very distinctive and its preservation is important for Brazil. Nevertheless, current human activities and proposed developments constitute a considerable threat to its existence. Although cattle production in the Pantanal is widespread, there is increasing mineral development, whilst intensive soya production in the Planalto has increased soil erosion and sediment deposition in the Pantanal. Most important of all is the proposal to extend the navigable length of the Paraguay in order to open up central South America to trade and for the export of the region s agricultural production. 19

20 Figure 5 Number of equipments sold in Paraná ( Parchen and Bragagnolo, 1991) The consequences of this development must be carefully studied if the Pantanal is to avoid total destruction. In addition, to establish how development will influence the region it is first necessary to understand its hydrology. Flow in the Paraguay and its tributaries is drastically reduced where they enter the Pantanal, since the abrupt decrease in the gradient leads to deposition of sediment on the river bed. The reduced erosive power of the river thus causes a reduction in the cross-section relative to that farther upstream. In periods of flood, downstream sections of the Pantanal rivers have smaller conveyance than those upstream, resulting in extensive overbank spillage to a broader channel, and the greater the flood the more extensive is the overbank spillage. However the plain of the Pantanal contains a large number of depressions which are filled during floods, forming a landscape of small lakes which merge together as the water level rises and which retain water as the level falls again in the main channel. A large part of the inflow from upstream is therefore retained as storage in depressions having no direct link with the main channels of rivers flowing across the Pantanal. The flow and sediment which are the basis of the ecosystem are reduced by about half.. 20

21 Climate: changes over time have been marked. The mean annual flood level at Ladário on the River Paraguay fluctuated around 4 m from 1900 to During 1960 to 1973 the annual flood level varied around 2 m. This reduction of flow energy and consequent siltation diminished the channel cross-section relative to that of the preceding period. The inhabitants of the region - especially cattle ranchers - began to utilise areas which previously had been flooded for long periods. After 1973, however, the mean annual flood level increased again to around 5 m. Areas which had been free of flooding for several months of the year became almost permanently flooded. During the 1960s, the flooded areas of the Pantanal extended to about km 2, but after 1973 the flooded area exceeded km 2, reaching a maximum of about km 2 in 1988 (Hamilton et al., 1995). Soil erosion: In the Planalto, there has been a dramatic increase since the 1970s in areas planted to annual crops, principally soya, which has resulted in significantly increased soil erosion and sediment transport to the Pantanal. At the same time, the short-term increases of annual rainfall in the upper part of the basin have caused soil loss in the Planalto with deposition in some reaches and, in the Pantanal, greater deposition of sediment and reduced channel conveyance. Within the Pantanal itself, land-use changes have been largely restricted by the hydrological regime, although some dykes have been constructed to control flooding. However during floods, rivers may change course by cutting across meanders, and where this results in a land-owner losing part of his property, he may seal off the new course, so that the river will revert to its old one; where this occurs, there is a consequent high mortality of fish and other aquatic life in the cut-off section. Paraná- Paraguay waterway: This is a km long waterway, from Nueva Palmital, near the coast, to a point upstream of Cáceres in Brazil (Figure 6). To 21

22 improve transport, works are planned that will improve the river channel through the entire waterway. The first project were presented by Intervave and the last one by Hidroservice-Louis Berger-EIH. This last project presented the following alternative: Figure 6 Paraná-Paraguay waterway (i) from Santa Fé (Argentina) until Assunción (Paraguay) a channel 100 m wide and with 3m deep; (ii) from Assunción to Corumbá (Brazil), a channel 90 m wide and 2.6 m deep; (iii) from Corumbá to Cáceres, many works are proposed that will result in at least 1.5 to 1.8 m of water depth. A major concern is the environmental impact on of these works on the Pantanal wetland. The works will improve the river conveyance which may decrease the flood area. The decrease in over-bank flow and flood-plain sedimentation will tend to change the Pantanal from wetland to savannah, since the difference between 22

23 rainfall and potential evapotranspiration is negative. In a sequence of drought years, the effect would be even more critical. The main question relating to this issue are: (i) Will the proposed works in the waterway modify flow conditions so as to reduce flow volume to the flood plain, and if so, by how much will it be reduced? (ii) What would be the effect on the flood-plain environment of a sequence of drought years? More research based in field data is required before these questions can be satisfactorily answered. CONCLUSION The basin of the la Plata is one of the world's largest, and its 100 million people are responsible for a major part of the economy of South America. Countries sharing the basin are receiving high investment and have a high index of economic growth, with consequent pressures on the environment. This paper lists the main environmental issues related to water resources and discussed the following issues: Climate variation, agriculture practices and flow increase. Increased runoff after the 1970s may be due to rainfall and agriculture practices, or both. If rainfall has been the principal cause of the increased runoff, the increase may not be permanent and river behaviour may revert to conditions of the 1960s; but if changes in land-use and agricultural practices have contribued to the increased runoff, it is possible that higher flows are more 23

24 permanent. If they are, this has important economic and environmental consequences for strategies for sustainable development, which will need to take into account: (i) increases in water depth, and in duration of navigable conditions, in the watercourses; (ii) increased energy production; (iii) possible decrease of reservoir capacity from sedimentation; (iii) more extreme flood conditions. It will become more necessary than ever to: (i) improve agriculture practices for water and soil conservation; (ii) develop nonstructural measures for flood control in critical areas, such as: flood zoning, real time flood forecasting and insurance. Pantanal wetlands conservation: The Pantanal is a major wetland environment of South America which has been greatly influence in the last thirty years by climate variation and changes in land-use and agriculture practices. In addition, a waterway has been proposed for the la Plata basin countries which could greatly affect the wetland system. In broad terms, increasing the channel transport capacity by dredging, as planned by the waterway improvements, would reduce the volume of water retained in the Pantanal wetland, possibly changing it from wetland to savannah, but sound quantitative evaluation is necessary to establish how and where the changes would occur before any decision of investment is taken. Sustainable development of this region must be achieved without damaging its natural behaviour and an important conservation planning programme is required to reconcile the conflicting requirements of conservation and economic development. 24

25 References ANDERSON, R. J. ; RIBEIRO, N. F.; DIAZ, H.F An analysis of Flooding in the Parana/Parguay River Basin. The World Bank Latin America Technical Department. BOSCH, J.M.; HEWLETT, J.D., A review of catchment experiments to determine the effect of vegetation changes on water yield and evapotranspiration. Journal of Hydrology 55: 2-23 BRUIJNZEEL, L. A, Hydrology of Moist Tropical Forests and Effects of Conversion: A State of Knowledge review. IHP. IAHS. UNESCO. 224 p. BARROS, V.; CASTANEDA, M. E.; DOYLE, M Recent precipitation Trends in Southern South America to the East of the Andes: and indication of a mode of climatic variability. Proceendings of Latin America Workshop on Greenhouse gas emission of Energy sector and their Impacts COPPE/ UFRJ, Rio de Janeiro. HAMILTON, S.K.; SIPPEL, S.J.; MELACK, J.M Innundations Patterns in the Pantanal wetland of South America determined from passive macrowave Remote Sensing. Hydrobiologie, January KRONER, 1990 A erosão do dolo de 1952 a 1985 e seu controle no Paraná. Londrina IAPAR Boletim técnico n º OEA, Bacia do Prata. Estudo para sua Planificação e Desenvolvimento. Organização dos Estados Americanos. PARCHEN, C. A. P. ; BRAGAGNOLO, N., Erosão e Conservação de Solos no Paraná. Emater PR. SAHIN, M. J.; HALL, M.J., 1996 The effects of afforestation and deforestation on water yields Journal of Hydrology 1178 p

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