Water Availability and Use

The Tocantins River rises in the Goiás Planalto (tableland), at about 1000m altitude, and is formed by the Almas and Maranhão rivers. Amongst its main tributaries, up to the confluence with the Araguaia river, are the Bagagem, Tocantinzinho, Paraná, dos Sonos, Manoel Alves Grande and Farinha rivers, on the right bank, and the Santa Teresa River on the left bank. Its main tributary is the Araguaia (2,600 km in length), in which lies the island of Bananal, the largest river island in the world (350 km in length and 80 km wide). After the confluence with the Araguaia River, the Itacaúnas River, on the left bank, is the main river. The total length of the Tocantins River is 1,960 km, with its mouth being located at the Baía de Marajó bay, into which the Pará and Guamá rivers also flow.

The Tocantins Hydrographic Region is divided into four sub-basins (Figure 1):

• Tocantins: total area of 391,078 km² (41.5% of the hydrographic region). This corresponds to the section of the Tocantins River, from its headwaters to the confluence with the Araguaia River.
• Araguaia: total area of 358,125 km² (38% of the hydrographic region). This corresponds to the total basin of the Araguaia River, from the headwaters to its firth on the Tocantins River.
• Pará River: total area of 89,394 km² (9.5% of the hydrographic region).
• Guamá River: total area of 104.408 km² (11% of the hydrographic region).

The Tocantins River records a mean discharge rate of 13,598 m³/s (9% of the national total) and a specific discharge rate of 14.4 l/s/km². The sub-basins have the following specific discharge rates: Tocantins (11l/s/km²), Araguaia (16 l/s/km²), Pará (17l/s/km²) and Guamá (21l/s/km²).

Groundwater is important in the northeast region of Goiás (valley of the Paraná River, São Francisco Province), where the volcanic rock forms a poor standard of river capillarity, favoring a relative abundance of groundwater resources, with hard water prevailing. In the southwest region of Goiás, the use of groundwater from the Paraná province has risen gradually, both for the incipient industrial activity and for crop and pasture lands.

The current situation of the Tocantins Hydrographic Region in terms of availability and demand is laid out in Table 3, in which it can be seen that the sub-basins of the Tocantins and Araguaia rivers present the highest total demands, mainly for irrigation purposes.

In average and annual terms, the total demand for water in the hydrographic region does not exceed 1% of the average availability, indicating that in general the conflicts on water use that exist do not refer to quantitative issues, thanks to the plentiful abundance of surface waters.

Human demand is 12.06 m³/s (10% of total demand), and around half of it is concentrated in the sub-basin of Guamá, which possesses the most populous city of the hydrographic region, Belém, with 1.28 million inhabitants.

Industrial Demand is not significant, as most of the factories are small-scale operations, in the areas of metallurgy, food, timber processing, furniture, leather, dairy products, ceramics and others. There are also some factories that produce cellulose and its derivates, in addition to beef and pork processing facilities. Industrial demand is estimated at 2.0 m³/s, which corresponds to 2% of the hydrographic region's total.

Irrigation Demand is 93.49 m³/s (81% of total demand) and is concentrated in the sub-basins of Tocantins and Araguaia, going to flood rice croplands. The potentially irrigable area (by flooding or otherwise) is estimated at more than 2.5 million hectares. The livestock demand is 7.79 m³/s (7% of total demand).

 

To evaluate and implement steps that will minimize the impact of mining on the quality of the resources To define and implement a program for controlling the erosion and suitable management of the soil, thereby minimizing the contamination brought about by widespread sources, particularly in the springs To implement and/or improve the treatment systems of waste water originating from abattoirs and chilling centers and evaluate their impact To implement the Tocantins-Araguaia waterway in harmony with environmental conservation	To optimize the usage of water in irrigation and define economically feasible areas in the hydrographic region To improve the efficiency of the distribution systems, thereby minimizing the losses in the water supply systems and implement domestic sewage treatment systems To develop the hydroelectrical energy potential through new projects, making environmental preservation compatible with multiple usage and integrating local and regional development

Figure 2 illustrates the distribution of the water demand in the Tocantins Hydrographic Region.

Figure 3 shows the demand distribution by sub-basin, where it can be seen that the highest demand is concentrated in the sub-basins of the Tocantins and Araguaia rivers, which present the highest demand for irrigation and livestock watering.

Figure 3 Demand distribution by sub-basin

The region boasts more than 300 species of fish and has enjoyed a significant increase in fishing tourism, particularly on the Araguaia River, which could lead to sustainable economic development for the region. The deployment of basic infrastructure, with the construction of waterway stations and seafront urbanization, may develop the sector. The multiple use of the lakes of the Tucuruí and Serra da Mesa hydroelectric power stations for tourist purposes. Fishing is also an important activity for the riverside and indigenous populations, and supplements subsistence farming, extractivist and hunting activities. Protecting the water resources and the ecological equilibrium of the rivers is essential to these activities.

One of the main hydroelectric projects is the Tucuruí power plant, which has a final potential of 7,745mW, and is located in the Tocantins lowlands, and the Serra da Mesa highlands power plant, with a nominal potential of 1,200mW, located in the upper Tocantins region. The Tucuruí power plant alone supplies 96% of the electricity used in the state of Pará and 99% of that in Maranhão.

Waterway travel has potential, principally on the Araguaia River, which enables the transportation of 3 million tons of soybeans from the Central-West region. If locks, dredgers and other projects are built, the waterway will be able to boast a navigable main channel of 2,000 km and a further 1,600 km along the tributaries. The environmental impact of this enterprise is currently under discussion.

As for the domestic pollution, the urban organic burden potential is 307 ton of BOD₅/day (4% of the national total) and is mainly concentrated in the vicinities of the Greater Belém Area. Pollution caused by mining mainly results from the actions of mining and sand extractions in small springs.

Events that are considered critical to the water resource are floods, which are a natural characteristic of the hydrographic region. 60% of the vulnerable areas in the River Araguaia basin are situated in the state of Mato Grosso, with the Island of Bananal stretch comprising the largest extension of floodplains. However this area has a low population density. The basin of the River Tocantins possesses almost half the floodable areas situated in the stretch which separates the states of Maranhão and Pará.