Environmental Changes in Savannah's Area. Occupation and Use of Soil On the Relief Causes and Effects Analysis. The case of Araguari River - MG Hydrographic Basin

 

 

RODRIGUES, S.C.

Laboratory of Geomorphology and Erosion of Soils

Institute of Geography- Universidade Federal de Uberlândia

silgel@ufu.br

 

ABSTRACT

 

This paper presents our reflections over the main geomorphologic characteristics of the Araguari River Basin and offers an analysis about the changes done by man over the landscapes. This region naturally occupied by savannas and in the last 40 years has been strongly altered by human activities. Summarized basic information provided by geomorphological analysis especially done after geomorphological mapping correlated with geology and soil maps and supported by fieldwork. The report divided into two main parts. The first part presents the natural arrangement of the landscapes that occurs into the hydrographic basin, showing the relationships between structural and geomorphic units. The first refers to the attributes of regional landscape presenting information on the inter relationship between structures and geo morphological units, as well as the superficial material and processes. The second part presents the reflections due to man activities in the basin such the types of erosion, channels changes and urban problems. These activities were divided in those that occur in the farms and in the cities, showing the differences between actions over this sensitive system. In this part we showed the main research guidelines in course in this basin.

 

Key words: geomorphological analysis, environmental management, soil erosion, and urban gullies

 

 

INTRODUCTION

 

Nowadays, most of the studies accomplished in Savannah's Biome area have been done in landscapes highly altered in the last 150 years, especially by the agricultural activities. For us to understand what are the existent controls on the environmental characteristics and the landscapes behavior is necessary to understand what are the limiting conditions that these landscapes have been suffering. For instance, in most cases in that gullies have been documented, it has happened extensive alterations in the vegetable covering, modifying the attenuation capacity of infiltration proportionate for the previous natural conditions.

 

The Savannah's area have been target of agricultural occupation intense expansion starting from the beginning of 70's, when the Brazilian Government encouraged the occupation through establishment projects, like PADAP (Alto Paranaiba Direct Establishment Program), POLOCENTRO (Savannah's Development Program), PRODECER (Savannah's Development Project -co-sponsored by JICA-Japan International Cooperation Development). These projects most important objective was to the vast tabulate surfaces with low steepness occupation, typical of the Savannah Biome's area. These areas intensive occupation implicated in significant changes in superficial morphodinamic increasing the speed and magnitude of the same ones, allowing the emergence of geomorphological processes that would have low propensity of natural occurrence in this system.

 

The geomorphologic charging and the processes analysis due to use of soil alterations, as the laminate erosion and gullies in rural and urban areas are examples of superficial processes that has been mostly approached in the works developed by the Geomorphology and Erosion of Soils laboratory from the Universidade Federal of Uberlândia.

 

Several materials have been used to the Araguari River Basin environmental characteristics analyze elaboration, among them stand out a vast bibliographical revision understanding related to specific aspects like geology, geomorphology, pedology and hydrography, as well as integrated works, where the landscape and the processes are the principal focus. Specific works, as the geomorphologic units delimitating have been made through satellite images in the 1:100.000 scale and aerial pictures in several scales. Field works were accomplished along highways, local highways, mining areas and bottoms of valley. Some gullies have been studied in full detail in their dynamics and predominant processes. Integrated profiles of relief have been built using topographical cards and field control. Accomplished experimental studies on the area laminate erosion were also consulted.

 

REGIONAL CHARACTERISTICS

 

Araguari River Basin is located in the Southwest area of Minas Gerais State, being flowed by Paranaiba River, one of Paraná River creators. This area has been occupied starting from middles of XIX century, but it had its true initiate occupational process in the second half of XX century, with the agricultural occupation intensification and urban centers growth.

 

The Araguari River basin has a 21.856 Km2 area, having as principal flowing the Quebra Anzol and Claro rivers. It has the discharges located in Canastra Mountain plane surfaces approximately 1.400 altitude meters, flowing direction east, following the area's main structural directions. The regional geology has as base schist and quartzite of Medium Precambrian in its high course, covered in its medium course for Mesozoic sediments from the Paraná Basin. In the Araguari river bass course it cuts sandstone collations and basalt from the Serra Geral Formation, arriving, in the bottom of valley to erode gneisses and granites of inferior Precambrian. Cenozoic Sediments can be found at the tabulate plateaus and in residual relief, as well as covering again structural terraces.

 

Hydrographic basin certain parts great economical dynamism and the hydrides resources multiple uses has been drastically transforming this basin waters amount and quality as, for instance: hydroelectric plants constructions with consequent artificial lakes creation, able to agriculture large irrigated area and urban consumption in medium cities like Uberlândia, Araguari and Araxá.

 

The Araguari river channel has rocky blooming in almost its all extension, with a profile marked by rapids and waterfalls. Small alveolar fluvial plains happen to up stream of throats, getting to structural traps areas. In its high course Araguari river presents a low flowing out, however when crossing the Canastra Mountain scarps, it presents a series of waterfalls, some with more than 100 meters unevenness. In its medium course, it receives its principal flowing, the Quebra Anzol River, that flows through a strong dissection and high drainage density area. After receiving its tributary, the Araguari river valley becomes very narrow and steep, with a several short and deep landings profile, resembling each other to a canyon.

 

GEOLOGICAL EVOLUTION

 

The rocks belonging to the South American Platform surface in the central part of the Brazil central area, acting as a big stable area from the tectonic point of view, being composed by metamorphic and igneous rocks with great thickness dated of Precambrian Inferior and Medium. This big stable area has not been suffering great tectonic movement from approximately 600 million years.

 

In Brazilian territory, this platform is basically divided in shields, and in the margins of these shields there are Strips of Folding Double Proterozoic (with ages among 1 billion and 600 million of years). These strips conform sutures among the different shields. The Palaeozoic Era was relatively calm from the tectonic point of view, with regional static upping and regional erosive surface formation that created extensive leveled areas. On this era, it feels the beginning of the main sedimentary basins deposition, with sea and continental apprenticeships. In the Mesozoic era these basins were affected for continental basaltic volcanism, in the same moment that alkaline intrusions affected the borders of sedimentary basin, creating domes and similar features. Finally, in the era Cenozoic, upping have been slow and frequent, they are the predominant forms, being constantly retouched by cycles of humid climates. (Tomazzoli, 1990; Nishiyama, 1989; Barcelos, 1993).

 

The Araguari river Hydrographic Basin drains mainly areas with metamorphic rocky base associated the strips of dated Folding Double of Medium Proterozoic and reactivated in Proterozoic Superior (areas of high and medium course) and also Sedimentary Basin of Paraná areas in its low course. Rocks arquean are just found in the bottom of the Araguari river Valley, already in the proximities of its mouth. Illustration 1.

 

Cenozoic deposits located in the tabulate surfaces present superior thickness to 10 meters, being consisted predominantly of sands, silts and lenses of conglomerate, partially consolidated. Ferruginous films, composing in a lot of areas ferruginous crusts, cover these sediments, especially the conglomerate.

 

GEOMORPHOLOGIC UNITS

 

The regional relief presents, inside of Araguari river basin, four geomorphologic units (Rodrigues et alli, 2001): The Canastra Mountain, the Strip of Double Folding, the Volcano-sedimentary Plateau and Rio Araguari's Canyon.

 Illustration 2.

 

 

1. Canastra Mountain: This area is formed by failed and raised blocks in relation to the regional relief, associated Double Folding Brasília's Strip being sculpted on quartzite and schist of the Canastra Formation. It understands a surface tacked by scarps with more than 300 meters of unevenness, being aligned NW/SE approximately. In the base of these scarps, dendrite talus sign the contact with the surface elaborated on rocks of the Strip of Folding Double. A series of rapids and waterfalls have created an area of indescribable beauty and an original ecosystem that is protected because of the National Park of the Mountain of Canastra creation starting from 1972. The altitudes of the Mountain of the Canastra vary between 1.450 and 1.200 meters and the relief general inclination is to the west sense. This unit is covered again by a fine hillside soil come from the top layer and in the tops of the hills and mounts happen fields of lumps.

 

The hydrological system of this unit is marked by a fast superficial drainage that quickly increases the fluvial channels discharge. The humidity almost stays a little time in the soil, due to the small depth of this and for its sand-crushed rock characteristics. The topographical conditions propitiate low temperatures, that associated to the low permanence of water in surface does not allow an intense intemperism of rocks. This fact, explains the great occurrence of rocky blooming, flag and visible lumps in the slopes. Little deep Hillside soil come from the top and composed by pebbles, gravel and sands associated to the organic matter are the main superficial formations.

 

2. Strips of Double Folding: In this unit the relief forms are controlled strongly by the structural directions associated to the Double Folding events and failing of regional width. The main litologies are schist, filit and deformed quartzite for alkaline intrusions of the Superior Cretaceous. The structural control of these forms associated with the sculpturing of the relief in erosive events ends for masking each other, being difficult to distinguish, in the landscape, where the tectonic agents' current effects prevail and when the erosive forces prevail.

 

During and after the Cretaceous this area was affected by regional upping and erosion levels lowered the regional relief independently of the rocky kinds. After the Cretaceous they happened extensive planning processes with the pediplans formation. After Plio-Pleistocene, this area has been affected by a tropical climate, with collations among humid and semi-arid moments. These last events propitiated the erosion of the rocks more suffer intemperism, as filit and schist and the preservation of the quartzite, that occupy the highest positions today, usually conforming residual relief or divisors of hydrological basins.

 

The principal forms are aligned hills and also small isolated mountains, with complex slopes convex-straight, covered by mantles hillside soil come from the top and lumps, highly dissected by the drainage net. Old erosive surfaces are preserved in the tops of some mountains, usually in superior altitude to 1250 meters, while the valleys possess a superior deepening to 100 meters. The soils are little deep and rich in primary minerals, usually in crushed rock way, being classified like Cambissoil or Neosoil Litolic.

 

In function of the events geotectonic and thermal happened in this area, some transformations in mineral are distributed in the area. Niobium deposits and phosphate are explored close the cities of Araxá and Tapira, in dome areas. In some points the mineral enrichment of thermal sources and of the soil for sulfates and alkaline minerals has been used as mineral water and medicinal mud in tourist stations.

 

 

Illustration 1-Geo-structural Units of Araguari River Hydrographical Basin

 

 

 

Fig. 2- Geomorphologic units of Rio Araguari's Hydrographical Basin.

3.

Volcano-sedimentary plateau: This system is developed on the sedimentary rocks and spill basaltic of the Sedimentary Basin of Paraná. The main morphologic features of this system are regional surfaces of planning. These planning surfaces were developed for the retreat of scarps followed by fast and big upping pos-Cretaceous that affected the continental blocks of Brazil southeast. This process associated with the climatic changes in Plio-Pleistocene allowed the extensive erosive surfaces formation, possible pediments, in the base of the regional scarps. Following this interpretation; these surfaces would be formed by the pediments adhesion. Landings were formed in areas with rocky collations through differential erosion of more and less resistant extracts, as the sandy areas and blooming of basalt. This differential erosion created in some areas relic features, as hills testimonies or little mounts located in the top of hill systems. In Araguari River Hydrographical Basin two regional surfaces of planning are observed, a more preserved conforming tabulate relief (plated) and another conforming levels dissected in form of hills.

 

Wide interfluves conform the top of the Plateau to Tabulate, being in sub-horizon way and possessing small depressions denominated locally of  "in hollow form", where the waters of the rains are stored in the rainy station creating small lakes. In the interior and around these depressions they take place small little mounts formed starting from remounts of the soil for termites. These small little mounts are known as "murunduns". These depressions a lot of times are connected to small channels, conforming areas hydromorphic of nascent fluvial or paths. In this kind of valley is not possible to differ a main channel, and after some hundreds of meters and with the progressive deepening of the valley and steepness increase really begins the fluvial channel.

 

These depressions origin is still not totally understood. In the borders S and SW of the tabulate plateaus come about immature sandstones with carbonate cement, limestone lenses and clay. In consequence of this, it can be speculated regarding the action pseudo-carstic as one of the makers of this pattern of forms, because the dissolution of the limestone or of the calcareous cement of the sandstones it could propitiate the subsidence of surface. The termites role in these forms genesis is also questioned, but certainty they are responsible for the emergence of the "murunduns" and transfer of sub-superficial material to surface.

These hydrodynamic forms are strongly correlated to the rainwater. Measurements done in Hollow of Fortaleza (SCHENEIDER, 1993) revealed that in the period between October and March (the rainy station begins in the spring and it lasts until the end of the summer), corresponds to the water sheet larger elevation period and temporary ponds formation. After the first rains, in September or October, the ponds are filled out immediately, however little variation is noticed in the water sheet level in the in the same period. This fact is predominantly due to the composition loamy of the soil (caulinit and gibbsite).

 

This fragile area has been highly altered by farmers that drain hollow forms and this way they modify the hydrological conditions, drying nascent and small channels after some years of agricultural exploration.

 

A second erosion level is located between 100 and 150 meters below the tabulate plateaus, being drained by a net of channels with dendrite pattern. Rocky sills happen where the channels reach the hemorrhages of basaltic rocks. The profile of the slopes is predominantly convex-rectilinear, but relief ruptures happen in the averages slopes and they are associated to exhibitions of ferruginous crusts.

 

4. Canyon of Araguari River: This system is present in the bass course of Araguari River, where after surpassing all the sedimentary and basaltic packages, it reaches the base crystalline Precambrian, composed predominantly by gneisses and mica-schist, in the bottom of the valley. This canyon possesses an unevenness of 500 meters, and higher margins reach from 950 to 1050 meters, while the bottom of the valley varies between 450 and 550 meters. The hillsides of the valley were altered by the climate humid Holocene, and talus deposits are masked for mantles colluviums, that propitiate the decrease of the inclination of the slopes. Complex slope profiles mark this area, with presence of concave ruptures, convex segments, rocky big walls and fluvial terraces. Small fluvial courses begin in the big mouths that tack the canyon and a lot of rapids and waterfalls mark the landscape.

 

Showing strong chiseling valley, the slopes strongly carved and the drainage density very high. The erosive processes, especially ravines, are very common in this system. The use of land in the valley is mainly to pasture and small terraces intensely cultivated, substituting the natural vegetation of Savannah and Mesofitic vegetation. The Araguari River crosses this area with an intense flow and a lot of times swirl, possessing a high hydro-energy potential. Taking advantage of this fact, two hydroelectric plants were built and two another are in final phase of planning, and to the end of these last ones construction, the bass and medium course of the river will be totally transformed at artificial lakes, with consequent alteration of riverine ecosystems. The Table 1 presents a summary of the environmental characteristics of River Araguari's Hydrographical Basin.

 

Geomorphologic Unity

 

Morphology

Morphometry

Rocks and Superficial Materials

Superficial Geodynamic

Canastra Mountain

* Elevated structural block leveled by erosive surface

* Associated limits to scarps.

* 1400 a 1000 m;

* 100 m local width of valley

* Inclination < 10%

* Quartzite e filit;

* Sandy Hillside soil not consolidate,

* Exposed quartzite blocks

* Rocky Exposition and superficial materials removal

* Ravines because of the concentrate pluvial flowing

* Blocks fall in cliffs.

Double Folding Strip

* Aligned Mountain and hills.

* Plane surface kept on tops and divisors.

* 1200 to 900 m;

* 40 to 150 m local unleveled;

* Inclination between 10 and 30%.

 

* Gneisses, filit and schist;

* Hillside soil detritic.

* Rock exposition and intemperism material removed

* Ravines because of the concentrate pluvial flowing

Volcano -

Sedimentary Plateau

* Horizontal Surface weak dissected;

* Small Basins closed in the plane divisors (hollow).

* 1000 to 700 m;

* 40 to 100 m of local unleveled

* Medium Incline < 10%

* Arenit, siltit, conglomerate and basalts;

* Laterite in stone form

* Moved by biological activity material

* latosoil

* Gullies

* Ravines,

* Laminar Erosion,

* Fluvial Channels erosion.

Canyon of Araguari

* Steep Valley and strongly dissected.

* Erosive landing and structural

* Cliffs and deposition of talus and colluviums slope base.

* 1000 to 550 m;

* 200 m of local unleveled,

* Medium Inclination between 10% e 45%

* Basalts, arenit e siltit;

* Talus e colluviums not consolidated

* Ravines,

* Blocks fall

* Laminate erosion

 

Table 1- Araguari River Hydrographical Basin Principal Natural Characteristic.

 

MAN ACTIONS AND ITS REFLEX ON SUPERFICIAL MORPHODYNAMIC

 

Araguari's River Hydrographical Basin has three main kinds of actions that altered significantly the environment causing reflexes on the geomorphologic superficial processes: the agricultural activities that altered the vegetable covering strongly, the urban areas that modified the hydrological dynamics and the barrages construction that altered the characteristics of the main channel strongly and of its immediate spill.

 

* Agricultural activities.

 

The natural vegetation that covered again River Araguari's Hydrographical Basin use to include species of Savannah and Mesofitic forest. This vegetation is adapted to the soil and climatic conditions of the central area of Brazil, where a succession of hot and rainy summers prevails, with dry and soft winters. In the last four decades this vegetation has been substituted quickly by agricultural cultivations, as soy, coffee, corn, citric and cotton, especially in the wide interfluves, little tilted and with latosoils. The agricultural companies that substitute the small rural properties have adopted intense mechanization.

 

Changes in superficial drainage and in infiltration have happened after the changes in the vegetable covering. The superficial drainage increased considerably, especially in the beginning of the rainy station, when the surface is without the vegetable covering protection and the soil is exposed to the rain propitiating ideal conditions for the laminate erosion occurrence in discharge rates. Ravines and gullies, that are common features in Central Brazil increase in intensity and magnitude and they become serious problems in some hydrological basins, where they can reach some square kilometers of arable area.

 

 

 

 

* Ravines and Gullies

 

These types of erosive processes happen expressly in the hills and mounts of the Strip of Folding Double and the Tabulate Plateaus, where the natural vegetation was substituted by pasture and agricultural activities. The lineal erosions are one of the most impressive features of the area relief. Changes in superficial drainage, in infiltration and in water sheet level accelerate the natural erosive processes in the area, creating great scars, especially in the area with sedimentary base.

 

In slopes elaborated on metamorphic rocks with fine layer intemperism and where the superficial organic horizons have been removed, the rainwater generates intense superficial drainage and soon after concentrated creating incisions in the slopes. These incisions become ravines and small gullies, affecting mainly the drainage headboards. An inventory done by CEMIG (1995) when the Nova Ponte Dam construction found 325 gullies in the influence area (approximately 500 km2) with 134 gullies inside the affected area for the lake and 191 in the area immediately around.

 

Studies accomplished by Baccaro (1994), in Uberlândia municipal district, indicate an association between the gullies occurrence and the slopes with steepness between 5 and 10%, usually associated the presence of slope ruptures in blooming of lateritic crusts. Table 2 presents a rising of the gullies in Uberlândia municipal district, in area with middling dissected hills.

 

Basin

Active Gullies Number

Stopped Gullies

Córrego Macumbé

2

 

Córrego Babilônia

20

1

Córrego Macacos

30

1

Ribeirão Douradinho

36

 

Córrego Jataí

5

 

Água Vermelha

8

 

Córrego Água Limpa

10

6

Ribeirão Panga

17

5

Ribeirão Estiva

35

 

Rio Tijuco

11

 

Total

173

13

 

Table 2-Inventory of Gullies in the Hydrological Basins that drain Uberlândia municipal district. (Source: Baccaro, 1994).

 

Illustration 3-National Park of the Canastra Mountain. Area preserved from more intense man action, and the principal problems come from the burned ones accomplished in the neighborhoods and accidents aggravated by tourists. Picture Sílvio C. Rodrigues (1999)

 

 

Illustration 4 - Degraded area close the Perdizes city. In this area the gullies have been used as point of garbage spilling and dump. Picture Sílvio C. Rodrigues (2001)

*

 Determination Studies of Laminate Erosion

 

The laminate erosion is defined as a uniform removal of fine superficial layers of the soil. This is not logically possible, because in reality the soil loss only happens for the superficial layers removal from the rainwater. In the attempt for understanding how these processes reach the different surfaces and slopes of the basin, some experiments and measurements on the laminate erosion to have been made, reaching different relief compartments as well as kinds of soil use.

 

This way, experimental stations have been built with the intention of measuring erosion. These stations consist of twin plots. One of the stations is cultivated with the same procedures of the roughly area and other plot is maintained without any kind of vegetable covering, being exposed to erosive agents. This procedure allows the behavior comparison of the erosion in a same relief situation, however with two different kinds of soil use.

 

To understand which changes happened in the erosion process eroded sediment is collected as the as the volume of drained water inside of the station. That is possible through collector gutters in the terminal portion of the station. Weekly granulemetric and sedimentmetric analyzes are performed with the eroded material, for both the dragged part and the material in suspension. The results of two years in two different stations are offered in the Illustrations 3 and 4.

 

The agricultural practices have changed in the last years and the direct planting has been adopted in most of farms, reducing the laminate erosion sensibly. This technique that consists in maintenance of the straw, leaves, and branches on the surface, protecting the soil, makes it ready to the new crop. Another adopted practice in areas prone to the laminate erosion is the construction of terraces following the land level curves, impeding the laminate erosion propagation slope below.

 

* Water Table Variation

 

The irrigation and the urban consumption are the principal kinds of use of water of Araguari River basin, each one bringing different environmental impacts on water resources. In the urban areas the most important problems are the lease and distribution of the wells, and a lot of times there is a concentration of wells in small areas. The pumped water is used for human consumption or industrial activities. In the urban area of Araguari the water table depression has been monitored in 111 wells between September 1998 and October 1999. The results show that in the dry season the level of the water decreases due to the pumping. There are no long term data regarding this phenomenon, but with the growth of demand and consequent increase of new wells perforation, the situation tends to get worse in a close future.

 

In the tabulate surfaces covered by latosoil, irrigation is extensively used to increase the production and every year more sources of water are necessary. In a lot of farms the solution used for the water supply is the perforation of wells and pumping the water for the irrigation. The mostly used irrigation system is the central pivot with aspersion of water on the cultures. This system when throwing the spray of water on the plants allows a strong evaporation, and consequently a portion of the underground pumped water is lost to the atmosphere. The solution used to avoid this problem is the substitution of system for irrigation by leak, that is a system that works with low pressure, where the losses of water are minimum. In a lot of areas the location of wells is not controlled and they end up interfering mutually to each other, causing the local water table level deepening and in many cases the loss of the wells.

 

* Changes in Fluvial Channel

 

The increase of irrigated areas created a super-exploration of water resources in the whole hydrographic basin. One of the largest problems is the excessive pumping of water from the fluvial channels starting from small barrages built in the farms. These small barrages form lakes from where the water is captured and pumped for the cultivation areas. These operations end for reducing the flow of water to the side the water flow goes and it also causes alterations in the humidity of close soil to the lakes and to irrigated areas. In the largest rivers of the basin, like Araguari and Quebra Anzol, the effects of this practice cannot be felt, however in the tributaries and smaller ones at the end of the dry season they totally disappear. To the small obstruction side the water flow goes. The spring of small channels tend to disappear.

 

Environmental alterations in Urban Area.

 

The urban areas located in the Araguari river hydrographic basin had a fast growth after the 60's, supported by governmental plans of development and occupation of savannah. After the demographic explosion, which happened throughout Brazil, the urban environment also had an accentuated growth. The principal impacts that affect the urban areas are associated to the deficient planning of the pluvial waters drainage and fluvial channels alterations.

 

In the urban areas the two most important environmental impacts are the floods and the gullies appearance. The floods happen because the fluvial channels cannot support the discharges flow out propitiated by the intense impermeability of the urban soil and consequent generation of fast flows from the tops and slopes to the bottom of valley. The occupation of the bottoms of valley and plains for streets and avenues and consequent construction of underground galleries ends for impeding the dispersing of the rains water to the areas where it previously would happen in natural conditions. On the other hand, the fluvial channels that still are in natural conditions, also suffer a bottom deepening process and erosion of the margins because of the flow out intensity increase in the floods. The margins of channels erosion with Holocene deposits and marginal Pleistocene exhibition. The solutions of simpler engineering, as the construction of galleries and support punches, do not solve the problems, because they just attack the effects and not their causes. A geomorphologic approach is necessary for understanding the atmosphere and its dynamics fragility, trying to solve the problems because of their causes.

 

Studies have indicated that starting from rains of 40mm/h the increase of drainage is extremely strong and the extra flows drainage of the galleries for streets and avenues, that start to work as drainage channel in direction to the bottoms of valley. These floods end for generating problems to the residents, as the break of punches and destruction of the asphalted paving, as well as damages to vehicles.

 

Urban Gullies have been generated starting from the drainage headboards where drained pluvial waters of waterproof areas are allocated. The evolution is also conditioned to changes in the water table level, fact due to the deepening of the channels and local base level changes. Associated to this, in some areas, as in the case of the Córrego Lagoinha located in Uberlândia City, it is observed that cuts and excavations end for contributing for the ravines and gullies formation. (Reis Alves, 2001).

 

* Environmental alterations Because of the Barrages Construction

 

The Araguari River valley has a very favorable morphology to the barrages construction. It is deep and narrow, with longitudinal profile presenting several slope ruptures, conforming rapids and waterfalls. Taking advantage of this situation Nova Ponte and Miranda Hydroelectric Plants have been built, and two other ones have been in study phase, being their construction foreseen for this decade.

 

Nova Ponte was built between 1987 and 1993. The barrage possesses 141 meters of height and it has created a lake with 443 km2 and that accumulates a volume of 12,8 billion m3. (CEMIG, 1995) The social and biological impacts, which happened at that time, still generate effects at present. The Nova Ponte city population had to be transferred, therefore the urban area has been below the flood level. A new city has been built approximately 3km of distance and more than 4500 people had to be removed. A lot of waterfalls and rapids were flooded, the lake substituted tourist and leisure areas and new attractive areas were created. The river aquatic fauna was totally modified with species adapted to the lentil environment. With the big lake level of water variation, arriving in the dry stations the a depletion to more than 20 meters, a located strip in the flotation area is subject to the erosion, generating a lot of ravines. Miranda was built between 1994 and 1996 and filled in 1997. It possesses 79 meters of height and created a lake of 51,25 km2 and volume of water of 1,12 billion m3. This plant created the same impacts of Nova Ponte, except for the urban removal. It also presents the creation of leisure division into lots around it.

 

With the construction of two new plants, Capim Branco I and II, the bottom of Valley of Araguari River will be totally transformed into artificial lakes for more than 150 km, with total transformation of the flow of water, alterations in the water table level, punctual climatic characteristics, and aquatic fauna.

 

Other impacts due to the barrages construction are the seismic disturbances because of the accommodation of rocky layers because of the mass pressure of accumulated water in surface. In the Miranda proximities were measured disturbances of 3,0 points in the Scale Richter, causing damages to constructions and pavements. With the reservoir level of water variation some problems could be observed in the rural area, especially in relation to the lowering of water table, with consequent drying of fountains and wells. The action of waves cause damages to constructions, as piers and punches built in the lake proximity. Table 2 presents the correlations between the environmental units and the major reflexes of the human activities on the relief.

 

 

 

 

 

Illustration 5- Area located in Uberlândia municipal district periphery where the real estate speculation causes the destruction of wide savannah areas, failing to protect the soil and making possible the beginning of erosive processes. Adutor Roberto R. Alves (2001)

 

 

 

 

 

 

 

Illustration 6 - Bottom of Valley of the Lagoinha stream where we can observe the results of location inadequate planning of a system of sewers transmission, that was destroyed by the fluvial channel after intense pluvial events. Picture Ricardo R. Alves (2001)

 

 

 

Geomorphologic Unit

Most Important Human Activities

Most Important environment problems sources

Most Important Problems

Relief changes due to man activities

Canastra Mountain

* National Park (tourism and leisure)

* Neighborhood farmers

* Visiting (tourist and neighbor people)

* Fire

* Animal extinction

* Water Flow changes

* Less laminate erosion

* Superficial soil kept or renewed

Double Folding Strips

* Pasture

* Agriculture

* Little Urban Nuclei

* Minering

* Routes fences,

* Livestock ways

* Soil e sub-soil exposed

* Soil erosion and superficial ravine formation;

* Gullies Dump with garbage;

* Crater opened by minering activity and left behind;

* Ravines;

* Dimension of water flows and channels

* Artificial Lakes

* Obstruction by sediments of the channels

* Gullies Dump with garbage

Plateau Volcano-

Sedimentary

* Agriculture

* Cities and Villages

* Pasture

* Exposed Soil

* Pluvial Water flows

* Routes

* Soil Erosion and Superficial ravines;

* Non permeability areas

* Piping de urban streamlets

* Scars of erosion on the watersheds

* Gullies Dump with garbage Obstruction by sediments of the channels

* Water table down,

* Little flows flowing out Diminution

* Soil drying and compacting

Araguari Canyon

* Pasture

* Barrage

* Little Conservation Unit.

* Forests Removal;

* Routes

* Pluvial water flow

* Barrage

* Minering (including fluvial flows)

* Artificial Lake

* Water level reservoir diminution

* Water table change.

 

 

Table 3- Araguari's River Hydrographic Basin Geomorphologic Units and the Processes related to that.

 

 

 

DISCUSSION

 

What are the limits for the human intervention on the environment? What will be the answers from the nature to our attack? Will the hydrographic basin continue to be a unit of useful study to understand the human impacts on the nature? How can the geomorphology contribute to the urban and rural environment under impact study? The answers to the these questions are at the present time master lines of our concerns.

 

If our behavior and consumption pattern in relation to the natural resources continue growing, some natural resources will end or they will become scarce in a close future. In Araguari River hydrographic basin water is already considered a scarce resource and the rural and urban consumption continues growing quickly. New investments in irrigation, production of energy, tourism and human and animal consumption begin every day and the volume of available water continues the same. Alternative sources, as the underground water possess limits to exploration, be technical or financial, and this resource also has limits.

 

The farmers and industrial men continue thinking and treating the water as an infinite resource and acting in a environment in a wrong way, and only after the government performance to prohibit or to draw up a written charge, that measure of environmental compensation will be taken. The accelerated and disordered growth of the cities does not respect the environmental characteristics and even the legislation is defrauded. The government actions grew in the last decades, but they are still insufficient to reduce the wild progress of the economical might on the resources. Although discussions and action plans have been made in some areas of Brazil, including on Araguari River Basin, the future supply of water is in danger.

 

Final considerations

 

Araguari River hydrographic basin is facing a moment in that its landscape suffers the effects of a unsustainable occupation model, initiated to few decades ago. This model of land occupation has impacts that are felt on the relief, especially with the erosive processes growth. The hydrological conditions were strongly altered, including changes in the water table level erosions in the drainage headboards increase, changes in the flow and flowing out of the principal rivers, transformed in a sequence of lakes. These problems also happen in the cities, especially in those in that the explosive population growth happened in the last 30 years, suffering now, years of negligence with the environmental subject.

 

Geomorphologic studies indicate that if the pattern of the use of land does not get alteration for a environmental controlled situation, we will have a chaotic situation in a close future, especially on the supply of drinking water in the cities and also for irrigation. This situation makes the public administration plan new lines to bring water, looking farther and farther away, in another hydrological basin the solution for the lack of water in urban place, however this procedure will cause, certainly, lack of water in other places. In Araguari River basin this fact is already reality for the Uberlândia City.

 

The laminate erosive processes are more or less controlled after the direct planting adoption, however the ravine and gullies processes have become very intense and they grow quickly in the plane surface borders. The pumped water of the water tables will become a great problem in the future, because the increase of this exploration process will reduce the discharges of fluvial channels. Some in hollow form of the top of the tabulate plateaus became dry due to farmers' action and reforestation, and many other will still suffer the same process.

 

In the urban areas the environmental impacts have been increasing mainly in two directions: the recurrence of smaller intervals of floods associated to smaller pluvial events and on the other hand the urban gullies that reach the borders of the cities, destroying slopes. In these gullies another procedure will generate serious consequences in the future, the completion of eroded areas with the dump of urban garbage.

 

Future perspectives

 

In a close future the focus of our environmental analyses, with special emphasis in the geomorphology will be driven for the following items:

 

* Accomplishment of geomorphologic map, because this basin, as the whole national territory, lacks in systematic base mapping, in detail and semi-detail scales.

* Increase of the researches on the human action influences on processes as the laminate erosion, ravines, gullies and modifications of the fluvial channels, trying to understand which are the natural and man mechanisms actuating in these processes.

* Researches in degraded areas, trying to intermediate solutions environmentally thought together with public administrators and opinion makers, in the sense of aligning the urban development associated to a balanced environment. The recovery of degraded areas in borders and inside the urban stains, as well as research in critical areas, as gullies filled out with dump and garbage, will probably be our first work instance.

 

Bibliographical references

 

BACCARO, C. A. D., Estudos Geomorphologics in the municipal district of Uberlândia. Uberlândia. Magazine Society and Nature, Year 1, n° 1-Jun/1989, p. 49 - 51.

 

BACCARO, C. A. D., Unity Geomorphologic of the Mining Triangle-I Study Preliminary. Uberlândia. Magazine Society and Nature, Year 3-n° 5 and 6-Jan. / Ten, 1991 p. 37 - 42.

 

BACCARO, C. A. D., applied Experimental Studies in the Evaluation of the Processos Geomorphologics of Pluvial Drainage in Areas of Savannah. Uberlândia. Magazine Society and Nature. Year 5 n°9 and 10-Jan. / Ten, 1993-p. 55 - 63.

 

BACCARO, C. A. D., The units geomorphologic and the Erosion in the Plains of the Municipal district of Uberlândia. Uberlândia. Magazine Society and Nature. Year 6 n°11 and 120-Jan. / Ten, 1994-p. 19 - 33.

 

BACCARO, C. A. D.; NISHIYAMA, L., Use of the Mineral Resources in the Areas of the Mining Triangle and High Paranaíba-An Aggression to the environment. Uberlândia. Magazine Society and Nature, Year 1, n° 1-Jun/1989, p. 49 - 51.

 

BARCELOS, J. H. Regional geology and Estratigráfica of the Mining Triangle Uberlândia. Magazine Society and Nature. Year 5 n°9 and 10-Jan. / Ten, 1993-p. 09 - 22.

 

CEMIG-Energy Company of Minas Gerais-Hydroelectric Plant of New Ponte. Executive project. Studies Ambientais.Belo Horizonte MG. 1995.89p.

 

DIAS, J. B & AUGUSTIN, C. H. R. R., and BiogeoMorphologie: Termites and Ants, Bioagentes in Reciclagem and Formation of the Soils and in Processos Formadores of the Landscape in Gouveia, Minas Gerais. In: Annals-Brazilian Symposium of Applied physical geography. Belo Horizonte-1999. p. 141 - 142.

 

FERREIRA, I.L.; ROCK, M.R.; BACCARO, C. A. D.; RODRIGUES, S. C. Mapeamento Geomorphologic of the Mining Triangle. Annals of III National Symposium of Geomorphology, Campinas, - 2000, p.195

 

FERREIRA, I. L. Mapeamento Geomorphologic of the Mining Triangle and High Paranaíba. Federal university of Uberlândia, Institute of Geography. Uberlândia, 2001. (Final report - Scientific Initiation - FAPEMIG / UFU).

 

FERREIRA, L. M. & BIRTH, M. A. of the, Latossolos of the Mining Triangle. In: Annals, VIII Brazilian Symposium of Applied physical geography. Belo Horizonte-1999 p. 168 - 169.

 

NISHIYAMA, L, Geology of the Municipal district of Uberlândia and adjacent areas. Uberlândia-Reviewed Society and nature-Year 1-n° 1 June of 1989 p, 09-16.

 

RODRIGUES, S. C.; BACCARO, C. A. D.; MEDEIROS, S. FERREIRA, I.L.; SAINTS, L.S. - the Geomorphology of River Araguari's Basin Hidrográfica and of High Paranaiba. 9o. Brazilian symposium of applied physical geography. Recife. 2001 (in the press)

 

SCHNEIDER, M. O., WHISTLES, D. B., Structures Pedologic and Dinâmica Hídrica of the "Hollow" of the Stream of Fortaleza, Uberlândia. Magazine Society and Nature, Year 3-n° 5 and 6-Jan. / Ten, 1991 p. 75 - 89.

 

TOMAZZOLI, E. R., the geological evolution of the Brazil-central, Uberlândia. Magazine Society and Nature, Year 2, n° 3-June 1990, p. 11 - 26.

 

 

 

 

1