“…One is the so-called Saint Venant equations (Chow, 1959). From Saint Venant equations, a class of models are derived (discretized in Balogun, Hubbard, & De Vries, 1988;Garcia, Hubbard, & De Vries, 1992;Georges, 1994, and linearized in Baume & Sau, 1997;Chentouf, Xu, & Boulbrachene, 2001;Duviella, Charbonnaud, Chiron, & Carrillo, 2005;Litrico, 2001;Litrico & Georges, 1997, 1999a, 1999bLitrico, Georges, & Trouvat, 1998). The other principle is the water volume or mass balance principle (Corriga, Patta, Sanna, & Usai, 1979;Corriga, Sanna, & Usai, 1983;Schuurmans, Bosgra, & Brouwer, 1995;Schuurmans, Hof, Dijkstra, Bosgra, & Brouwer, 1999), with which some volume (mass) balance models are presented.…”