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Gringa Club

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Araguaya River VERIFIED

Along its course, the river forms the border between the states of Goiás, Mato Grosso, Tocantins and Pará. Roughly in the middle of its course the Araguaia splits into two forks (with the western one retaining the name Araguaia and the eastern one being called the Javaés River). These later reunite, forming the Ilha do Bananal, the world's largest river island.[3] The vein of the Javaés forms a broad inland where it pours back into the main Araguaia, a 100,000 hectare expanse of igapós or flooded forest, blackwater river channels, and oxbow lakes called Cantão, protected by the Cantão State Park. It is one of the biologically richest areas of the eastern Amazon, with over 700 species of birds, nearly 300 species of fish, large populations of species such as the giant otter, the black caiman, the pirarucú, one of the world's largest freshwater fish, and the Araguaian river dolphin (or Araguaian boto), all occurring within a large area.

araguaya river

Several parts of the river's course are protected by national parks and other reserves like the Emas National Park and the Araguaia National Park. The Araguaia has "beaches" - bright sandy banks that seam the stream from May to October.

Deforestation and expansion of cattle ranching and agriculture in the Araguaia basin has been extreme during the last four decades.[7][non-primary source needed] As a consequence, strong linear erosion has produced thousand of gullies just in the upper Araguaia basin, and the river mainstem suffered strong sedimentation and fluvial metamorphism (changes in its channel pattern).[8][non-primary source needed]

The Tocantins-Araguaia Basin is one of the largest river systems in South America, located entirely within Brazilian territory. In the last decades, capital-concentrating activities such as agribusiness, mining, and hydropower promoted extensive changes in land cover, hydrology, and environmental conditions. These changes are jeopardizing the basin's biodiversity and ecosystem services. Threats are escalating as poor environmental policies continue to be formulated, such as environmentally unsustainable hydropower plants, large-scale agriculture for commodity production, and aquaculture with non-native fish. If the current model persists, it will deepen the environmental crisis in the basin, compromising broad conservation goals and social development in the long term. Better policies will require thought and planning to minimize growing threats and ensure the basin's sustainability for future generations.

The Araguaia River floodplain is a large wetland in the tropical savanna belt (cerrado) in the southern Amazon basin. Studies using multitemporal satellite Landsat 5 TM images with a spatial resolution of 30 m indicate a surface area at maximum flood level of 88,119 km2. During the low-water period, only 3.3 % of the area is covered by water. Flooding is the result of the annual rise in the water level of the Araguaia River and of local rainfall and insufficient drainage during the rainy season. Sedimentology studies have distinguished between an active recent and sub-recent floodplain, which covers 20 % of the area, and a paleo-floodplain probably several hundreds of thousand years in age. Paleo-floodplain sediments are strongly weathered and marked by the clay mineral association of kaolinite, gibbsite, goethite, and Al-chlorite, predominantly formed from feldspars and micas. The active paleo-floodplain participates in the hydrological cycle but does not receive recent sediments from the river. Higher-lying, not flooded areas (inactive paleo-floodplain) are probably the remnants of paleo-levees, now in an advanced stage of erosion. A hypothesis to explain the genesis of the floodplain is proposed herein.

This study examined the hydrological behavior of the Araguaia River through reference flow, analyzing the capacity of granting the river segments in three different fluviometric stations. The study exposed the comparison of monthly and annual reference flow, considering a hydrological series of 33 years. Consequently, it was proposed seasonal flow comparing to the methodology of annual reference flow for water grants in national rivers. The adoption of the annual reference flow restricts the grants of water use in most of the time, because the proposal of monthly and seasonal Q 95% in the rainy period for grants processes showed much higher values. The proposal of monthly and seasonal reference flows to grant the multiple right of use of water may be the most adequate for power generation, because it presents the inherent characteristics of the flows of each month and per period, respectively. However, the use of seasonality for grants must be analyzed along with the environmental aspect of the river basin concerning to the damage of aquatic life of the Araguaia River.

To obtain more concrete results to meet all usage demands, it is necessary to know the fluvial behavior of watershed, using the reference flow methodology. According to Silva et al. (2006), the reference flow is the establishment of a flow rate that becomes the maximum limit of water use in stream. Therefore, there are different standards for adoption of reference flows in Brazil, and the variability of these standards is related to the individual characteristics of each river basin.

The Araguaia River forms the natural landmark initially between the states of Mato Grosso (MT) and Goiás (GO), and then between Mato Grosso and Tocantins (TO) and finally between Pará (PA) and Tocantins. According to the Agência Nacional de Águas (ANA), the river is therefore classified as a national river, which divides or passes through two or more states or even crosses the border between Brazil and another country. Therefore, it is incumbent upon ANA to issue the right to use of water resource in the Araguaia River for several types of uses, thus defining the maximum flow rate to be granted.

Therefore, the aim of the study is to evaluate the hydrological behavior of the Araguaia River through temporal variability, analyzing the concession capacity of the river segments, divided into upper, medium and lower Araguaia. Different standards were defined to calculate reference flows through monthly, seasonal and annual analyses.

According to Oliveira (2008), the low flows are naturally linked to the critical periods of the river; so it is essential to know the flow rate for studies of water availability. The low flow Q 7,10 method analyses drought flow which occurs for a period of seven consecutive days at a period in 10 years. Therefore, it is examined 365 daily average flows by the database of daily flows, calculating the moving average of seven consecutive days (Q 7), in which it is calculated for seven terms that are moving (average from the 1st to the 7th day, from the 2nd to 8th day, from the 3rd to 9th day), and so on.

The permanence flows are obtained by permanence curves that relate the flow with the percentage of the time in which it is equalized or exceeded; Q 90 and Q 95 are frequently applied by the Brazilian legislation (Mendes 2007). The Q 90 is the flow with 90% permanence in time and Q 95 with 95%, with an extrapolation in the rainy periods in which there is a great increase of the river flow.

The determined criterion for granting rivers in the domain of the Federal Government by ANA is that the granting flow must be up to 70% of Q 95% and may vary according to the peculiarities of each region (ANA 2011). Therefore, the value of k will be 0.70 for this situation. Following the methodology of Cruz (2001), it was possible to evaluate the maximum flow rate, by performing seasonal and annual analysis.

The flow behavior is directly related to the rainfall regime, as well as the use and occupation of the soil and physical properties of the river basin. Discharge changes over time are represented by a hydrograph of each station analyzed and provide an idea of the temporal variability of annual periodicities of dry and rainy seasons, as shown in Fig. 2.

According to Castro et al. (2004), when the water demand is high in the watershed, the practice of applying a more restrictive limit may make it impossible to grant an adequate concession for surface water catchment for the existing demands in the region, leading to conflictive situations. The flow rate Q 7,10 is required when verifying the self-purification capacity of a river to get effluents under more unfavorable conditions.

In fact, the criterion of the seasonality for granting favors the right of use for power generation. However, this criterion must be analyzed concomitantly with the environmental aspects of the river basin, since the indiscriminate use of the water resource can lead to water stress and damage to aquatic life. Thus, the greater amount of granted flow induces a greater exploration of the aquatic environment.

The hydrological characterization through reference flows is utilized for the process of analysis of the river regime of the Araguaia River, which allows obtaining data of significant importance for the planning of water resources, applying them to the granting of environmental licenses articulately. This articulation allows to evaluate the enterprises in all its phases regarding its environmental aspect and the water availability.

It was observed that the adoption of the annual reference flow restricted the grants of water use most of the time, since the proposal of monthly and seasonal Q 95% in the rainy period for the granting processes presented values much higher. This significant restriction can influence the regional economy. It was also verified that the river has a greater capacity of granting, mainly from February to April for Araguatins and Conceição do Araguaia stations, and from January to March for the Aruanã station.

Therefore, the ways of analyzing the reference flows influence the grants: between a state and another one, and from these to the Federal Government. The proposal of monthly and seasonal reference flows to grant the multiple right of water use may be the most adequate for power generation, since it presents the inherent characteristics of the flows of each month and per period, respectively. However, the use of seasonality for grants should be analyzed along with the environmental aspects of the river basin as well as the impact on aquatic life. 041b061a72


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