1. Retired, Research Hydraulic Engineer, Bureau of Reclamation, Denver, CO 80225 (corresponding author).
2. ATB Riva Calzoni SpA, 25030 Roncadelle, BS, Italy; formerly, Research Assistant, Technical Univ. of Bari, 70126 Bari, Italy.
3. Dept. of Civil Engineering, Architecture, and Georesources, IST, Technical Univ. of Lisbon, 1049-001 Lisbon, Portugal.