WATER SURFACE AREA CALCULATION IN THE LOWER COURSE OF THE TIBAGI RIVER, THROUGH ARITHMETIC OPERATIONS OF BANDS: SUBSIDY FOR THE UNDERSTANDING OF FLOODING CAUSES OCCURRING IN THE CITY OF JATAIZINHO, PARANA STATE, BRAZIL

The aim of this paper was to calculate the area of the water surface, in the lower course of the Tibagi river, Parana state, Brazil, in different periods, encompassing atypical years with bigger- than- the- average discharges, and years with a nearly normal, average discharge. The area of the water surface was 47.5mi(2) (123.1Km(2)) in 20/02/2005 and 39.4 mi(2) (102Km(2)) in 09/10/2007. It was calculated through arithmetic operations of bands, specifically through the technique called dark- pixel subtraction. The area variation was 8.1m(2) (21,1Km(2)), considered a small one due to the fact that the Paranapanema river's discharge in its medium course, which is a borderline between Parana and Sao Paulo states, Brazil, is regularized by the Capivara hydroelectric. It is important to point out that the building of Capivara hydroelectric changed the discharge at Tibagi river's mouth, transforming this local in a backwater area. The analysis of the orbital images did not show the occurrence of backwater in Jataizinho town.