Inventory of Reservoirs in Brazil

INVENTORY OF RESERVOIRS IN BRAZIL[1]

Rogério de Abreu Menescal[2]

Daniel Sosti Perini[3]

Morris Scherer-Warren2

Margareth Sílvia Benício de Souza Carvalho[4]

Eduardo Sávio Passos Rodrigues Martins4

Ana Maria Lebre Soares4

Luiz Carlos Guerreiro Chaves4

Francisco de Assis Jorge de Oliveira4

1introduction

Most fatalities related to dam failures involve those with a height of less than30 meters, so this type of dam represents the greatest risk in the near future [1]. Still, while the breaking of large dams is generally more spectacular and receives much more attention than that of smaller dams, the rupture of small dams built on private farms occurs much more frequently. Therefore, in many cases, the total annual cost of the breakage of small dams is greater than the more infrequentrupture of large dams. [2]

In addition, the breakingof relatively small dams has caused disastrous consequences. For example, in China, the dams of Shimantan and Banquia broke in 1975 as a result of the cumulative rupture of more than 60 small dams upstream, all of which resulted in the death of 230 thousand people. In Italy, the Stava dam located near Trent broke in 1985 and although it launched only 180,000m3 of tailings, killed 268 people and caused serious environmental damage. In the U.S., the dam of KellyBarnesLake, which was only8meters high, broke in 1977, killing a total of 39 people. The LakeLawndam in Colorado, which also was8meters high and had a capacity of only 830,000 m3,broke in 1982, drowning three people and causing US$ 31 million loss despite warnings and evacuation. These past events suggest that without the proper design, construction and maintenance, poorly managed small dams can cause significant damage to persons, property and the environment.

Small dams can pose a real danger for the population. Usually, the number of small dams in a country is an impressive number. Often this number is unknown. Thus, for economic reasons it is impossibleto give attention to a very large number of dams. As a result, the need to focus is recognized by several authors. Therefore, the choice of dams to be included in the dam safety regulations is very important. [3]

Major accidents and incidents in Brazil, with emphasis on records after 2001, are listed in [4]. According to these records, just in 2004 the occurrence of more than 400 incidents and accidents in dams of various sizes and types are estimated, throughout the country. Many of them were due to the inability to support the hydrological events which occurred. For this reason, monitoring the behavior of dams is essential to control and mitigate the effect of floods.

Among highly dangerous civil structures, dams are among those the performance of which is predicted with the highest levels of uncertainty. [5] Some reasons are due to the fact that:

a) each dam is unique. To find useful references to other dams of the type and size is difficult for a reliable diagnosis of symptoms of unusual behavior;

b) dams are complex structures. The artificial barrier is not the predominant part of the system when we consider the uncertainty of behavior. It is the foundation which is less controllable, and which often results in a weaker correspondenceto predict performance. The intricate interaction between these two components increases the level of uncertainty;

c) dams are more exposed to the vicissitudes of nature than other civil structures (e.g. geology, floods, earthquakes, climate changes etc.).

Preliminary estimates indicate the existence of about 300,000 dams throughout the country, some built more than 100 years ago. In this number are included dams of various sizes and types and for different uses, including human supply, irrigation, power generation, mining, farming, industrial waste disposal etc. In the state of Ceará alone, this number may reach 30,000. [6]

Considering the accidents recorded in recent years, in 2004 the Ministry of National Integration (MI) initiated a series of actions in an attempt to minimize risks associated with dams and thus reduce the occurrence of accidents involving these structures throughout the country. This set of actions constitutes the Dam Safety Project. One of the biggest obstacles encountered was the total ignorance of the different government levels about the number, location, physical condition and those responsible for dams in Brazil. [7]

One of the actions to reverse this scenario was to create the National Register of Dams (CNB) in partnership with the National Water Agency (ANA). Initially one tried to perform the registration by means of self-registration, or stimulation to complete the registration sheet from the responsible supervisory agency or institutions in the states and municipalities. Due to the low return of information obtained, a pre-identification of dams extending throughout the Brazilian territory was necessary. This will permit a second stage of filling in more directly targeted information, avoiding the excuse of ignorance on the part of the institutions.The use of satellite imagery was the solution adopted to make the reservoirs and dams survey throughout the Brazilian territory.

2Methodology

For this work, an agreement was signed between the MI and the Cearense Foundation of Meteorology and Water Resources (FUNCEME), organs that have accumulated extensive experience in this area. Thus, the proposed methodology was the result of intense discussion between the MI, ANA and FUNCEME, resulting in the Operational Guidelines for Preparation of the Reservoirs Survey in Brazil. [8]

Since launching the first satellite for earth resources, the LANDSAT in 1972, much has been done with regard to research in the area of environment and natural resources through the use of satellite images. Currently, images from remote sensing are increasingly becoming part of our daily life. The weather forecast is shown in newspapers and on television by satellite weather images; regions and international conflicts are shown in the media through images from space and,in the same way, satellite images are increasingly employed in illustrating books, catalogs, calendars, posters and many other forms of visual communication.

The use of techniques of remote sensing for managing natural resources is a consolidated fact in the world of geo. The orbital images have proven especially useful in mapping large areas and in thetime needed for analysis, allowing the monitoring of changes in environmental scenarios over a given period. [9]

In a country of continental dimensions like Brazil, with a great lack of adequate information for making decisions about urban, rural and environmental problems, geoprocessing offers enormous potential, especially when based on relatively low-cost technologies if the knowledge is acquired locally [10].

Within this perspective the work presented aimed to complete the cartographic mapping of the water surfaces, over 200,000m2 (20ha)[5], covering the Brazilian territory, through pictures CBERS-2, to generate subsidies for the planning of water resources management.

The work which served as orientation for the mapping of the mirrors of 20ha in Brazil, was conducted by the National Water Agency (ANA) in 2004, which was the survey of reservoirs with a capacity greater than 10 million m3 in the Northeast Region through pictures CBERS-2. [12]

For the purpose of the actual survey work, the Satellite Sino-Brazilian Earth Resources (CBERS) was used as a primary source of information, pictures of which (CCD/CBERS-2) are provided free by the National Institute for Space Research - INPE. These images have nominal spatial resolution of 20m and were taken into account in order to make the scale of the work required compatible with the generation of the digital cartographic base of the reservoirs. We used 922 images CCD/CBERS-2 with dates ranging from 2004 to 2007, giving preference to those with more recent dates. In the absence of use of recent images, due to either the presence of clouds or unwillingness to demonstrate the achievements of INPE, images from other dates available were used. All scenes CBERS-2 went through a process of restoration using the algorithm developed by INPE (Restau.exe). Then, using Erdas Imagine 9.0, CBERS images were georeferenced based on the product images of LANDSAT 7 GeoCover [13]. Figures 1a and 1b show the restored scene CBERS 150/102 in color (342) and monochrome (band 4) combination.

The georeferencing of the images was made by picking up points of control (Ground Control Points) in the LANDSAT and the corresponding mark on CBERS-2. These control points were identified at fixed locations (e.g. intersections of roads, corners of streets, buildings, monuments etc.), and never on rivers or bodies of water.

After preparing the pictures, CBERS passed on to the process of vectoring surfaces of water. The vectoring features of the reservoir were performed manually (heads-up), or were made by an operator who followed each raster feature with the cursor, selecting the geometric primitives that best model the structure vector. As the parameter used by the scanner to define the water surfaces was the image CBERS-2 followed the spectral response of the feature, one resorted to the band 4 of the image, sothe resulting monochrome water surfaces appeared in better definition.

The vectoring of surfaces was done using the software Arcgis 9.1. The polygons on the surfaces were designed with closed polylines on a scale of 1:250,000 and 1:50,000 and contour was made to monitor in detail the same enclosure of the water visible on the CBERS-2. Previously, the layer files were created for each type of vectorization that would arise, such as water surfaces, islands, shorelines and estuaries, clouds (to identify the surfaces that had some clouds on them) and water surfaces continuity (if the reservoir covers more than one scene). If the image CBERS-2 did not offer good conditions for viewing the enclosure of the water, either by the presence of clouds or even by a poor spectral response of the water, the vectoring was made by LANDSAT image GeoCover, representing thus the condition the reservoir in 2000. At each vectoring the work done was evaluated by a team of FUNCEME that made the adjustments and corrections of polygons vectorized. Once the polygons had been digitized, a database (dbf) was created with the following fields: perimeter (m), area (m2), owner, type of reservoir (natural or artificial), dam type, location (state, city and county), name of the reservoir, capacity (m3), id scene (CBERS image in which the surface was vectorized) and code. Among these topics, the perimeter, area, type of dam, location and id scene were already met by the program, and the other fields were created for subsequent use of the institutions. In some areas, such as the Northeast region, surfaces from 5hawere mapped using the same methodology, but on the work scale of 1:100,000.

3results

A mosaic covering the whole of Brazil (Fig. 2) was created as a product of georeferenced images of CBERS-2. The formation of this mosaic was undertaken also by Erdas Imagine 9.0 with MosaicPro function. But beforehand it was necessary to improve the visual quality of images by making changes in their contrast scene by scene, aiming to reduce the variability from radiometric sensor and thus achieving greater uniformity between the scenes. Then the images were grouped by state and a mosaic was made according to the limits set by the Brazilian Institute of Geography and Statistics - IBGE.

Altogether, 23,036 water surfaces distributed throughout the Brazilian territory were mapped. About the area of the surfaces, it is important to note that, as a safety margin,surfaces from 19ha up were considered. Thus, the areas of surfaces scanned ranged from 19ha to 1,033,660.65ha, of which the first is located in Ceará, in the municipality of Crateús and the other is the PatosLake, inRio Grande do Sul (RS). Fig. 3 shows the spatial distribution of reservoirs in Brazil.

Regarding the territorial distribution of the water surfaces inBrazil, Amazonas is the State with the highest concentration (5,976), equivalent to 25.94% in contrast to the Federal District with only 10 surfaces, corresponding to 0, 04% of the total (Table 1).

Aboutthe distribution of the types of surfaces by region (Fig. 4), the largest natural reservoirs occurred in the North (8,303) due, probably, the inundated areas that formsignificant large ponds near rivers. Already artificial reservoirs are predominant in the Northeast and South, showing thus the impact of the dam building policy.

The small dams policy presupposes the importance of the stock distributed in the basin, rather than a more efficient option for the storage of available water of the basin. To reach better efficiency, we should give priority to the medium and large reservoirs, since the results already achieved show that the impact of small dams in the middle and high reservoirs can be significant. [14]

Fig. 5 showsexamples of an artificial (Fig. 5a) and a natural (Fig. 5b) reservoir vectorized on the CBERS-2 images.

The analysis of theerror reports summary shows that all the 922 images are in accordance with pre-established standards of quality, i.e., mean square error never greater than 1 pixel, and on average, eight to ten control points per scene. The statistical abstract of the whole process of georeferencing is listed in Table 2.

As regards water surfacesover5ha, the Northeast region presented a total of 17,083, showing an increase of 242.41%, a fact which highlights the impact of small reservoirs in the region.

4conclusion

Among the results of this work is the first mosaic of Brazil made from images of the CCD sensor of the CBERS-2 satellite. The georeferencing of 922 images demonstrates the excellent quality of the images of the geometric sensor CCD/CBERS 2, and the careful work of selecting the control points, resulting in a mosaic with excellent geometric covering all the national territory.

The mapping of the water surfaces of Brazil provided identification of all reservoirs, dams, ponds and lakes of Brazil with a surface area above 20ha. In some areas, such as the Northeast region, the basin of the Paraíba do Sul and the State of Minas Gerais, this threshold has been reduced to 5ha. It is emphasized that not all states have registration of existing dams in their territory. In this context, this product will be available for the entire society, providing valuable resources not only for the Union, but for states and municipalities. [15]

It was concluded that the technique of remote sensing images using CCD/CBERS-2 is suitable for mapping of reservoirs, allowing even for the distinction between natural and artificial water surfaces. In this work 23,036 reservoirs were mapped in Brazil with area from 20ha, 16,108 being natural and 6,928 artificial.

The results showed that the largest number of natural reservoirs occurs in the northern region, while the artificial reservoirs are focused in the Northeast and South region (RS State), highlighting the policy which aims to build dams to store water to supply the months of drought.

The accumulated experience and practice in this work, mainly regarding the applicability of CBERS-2 images, prove its effectiveness in even more detailed maps and can easily identify reservoirs with an area of as little as 5ha.

The mappingwork identified the reservoirs that were not registered by the MI, updated a bank of information on the status of dams for evaluation of potential risks, and provided subsidies for the political-administrative decisions related to management of water resources in Brazil. With the database, the MI and ANA will have information about the spatial distribution of the reservoirs in a unified database, allowing for the monitoring and evaluation of integrated programs for national development.

Now all information collected is being incorporated into the National System of Information of Water Resources - SNIRH, under the legal responsibility of the ANA, and the new version of the Dam National Register System (CNB-WEB). (Fig. 6)

The information obtained through satellite images should now move a step forward in consistency, through a program of inspection of works in the field. Therefore, the creation of a primary database is expected which will be supplemented over the years with the information provided to the National Dam Safety Information System - SNISB, the administration of which, according to the proposal of the Law Project 1181/2003, should also be under the responsibility of the ANA.

ACKNOWLEDGEMENTS

The authors wish to acknowledge the help provided by the National Water Agency, the Ministry of National Integration and the Meteorologicaland Water Resources Foundation of the State of Ceará.

REFERENCES

[1]ICOLD. Dams less than thirty meters high – Costs savings and safety improvements. International Committee on Large Dams, Paris, Bulletin 109. 1998.

[2]MCKAY, J.; PISANIELLO, J. The need for private dam safety assurance: a follow-up ‘model’ policy from Tasmania. The Australian Journal of Emergency Management, v. 21, n. 2, may. 2006.

[3]VISEU, T. M. R. Safety risks of small dams. In: INTERNATIONAL SYMPOSIUM ON NEW TRENDS AND GUIDLINES ON DAM SAFETY, 1998, Barcelona. Proceedings… Barcelona: by L. Berga, v.1, jun. 1998. Rotterdam u.a.: Balkema, ISBN 90-5410-974-2.

[4]MENESCAL, R. A. Gestão da segurança de barragens no Brasil - Proposta de um sistema integrado, descentralizado, transparente e participativo. 2009. 727p. Tese (Doutorado em Recursos Hídricos) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2009.