The linear form of the Muskingum model has been widely applied to river flood routing. I iowever, a nonlinear relationship between storage and discharge cxists in most actual river systems, making the use of the linear model irinppropriale. 111 t tiis paper, a nonlinear Muskingum model is solved using the state variable modeling tecliniclue. Various curve fitting techniques are ernployrd for the cdibra[ion of modc4 pranteters, and their performances within the model are compared. thth linear atid nonlincar niodels are applied to an cxaniple with pronounced nonliiwarity between storage and discliarge. The results show that the nonlinear Muskingum modcl is superior to the linear one. I ' s, = K [ x l , + (1x) O f ] .