1. Res. Engr., National Institute for Water (INA), National Univ. of Cordoba, Ambrosio Olmos 1142 (5000) Cordoba, Argentina. E-mail: flopez@com.uncor.edu
2. Prof., Ven Te Chow Hydrosystems Laboratory, Dept. of Civ. and Envir. Engrg., Univ. of Illinois at Urbana-Champaign, Urbana, Ill. 61801. E-mail: mhgarcia@uiuc.edu