Application of satellite imagery to update depth-area-volume relationships in reservoirs in the semiarid region of Northeast Brazil¹

Aplicação de imagem de satélite na atualização de curvas cota-área-volume em reservatórios do Semiárido do Nordeste

HIGHLIGHTS:

The unsupervised ISODATA method successfully estimated the water surface area of the reser-voirs.

The error of the estimated lake volume was comparable to other methods using satellite ima-gery.

Underestimation of the surface area was less than that obtained with a calculation based on spectral indices.

ABSTRACT

Reservoirs are the primary source of water supply in the semiarid region of Pernambuco state, Brazil, because of the constant water scarcity affecting this region. Knowledge of the amount of water available is essential for the effective management of water resources. The volume of water stored in the reservoirs is calculated using the depth-area-volume relationship. However, in most reservoirs in the semiarid region, this relationship is currently out of date. Therefore, the objective of this study was to explore the potential and limitations of the application of the ISODATA unsupervised classification method to calculate the depth-area-volume relationships of reservoirs in the semiarid region of Pernambuco, Brazil. The application of the ISODATA method was evaluated in three reservoirs in the state of Pernambuco, i.e., Poço da Cruz, Barra do Juá, and Jucazinho. The results were compared with the updated curves of reservoirs obtained from bathymetry and recent LiDAR surveys. The ISODATA method presented satisfactory results for the three reservoirs analyzed. The mean absolute error of the volume in Poço da Cruz and Barra do Juá was lower than 1% of the maximum capacity. The use of the ISODATA method meant that the surface area underestimation tendency in the Poço da Cruz reservoir was less than when spectral indices were used.

Key words:
ISODATA; remote sensing; water resources management; water supply