diversion level can be pre-regulated according to the existing diversion capacity of each floodplain. If this allowance is not exceeded, a regular diversion cost can apply; however, if it is exceeded, this will then means a surplus for diversion associated with economic penalties and/or expansion costs. Penalties can be expressed in terms of raised operation costs for flood diversion and/or destruction of land-based infrastructure. Expansions of floodplains can help increase the allowable flood diversion levels and thus reduce penalties. Thus the total diverted flow is the sum of primal allowance, incremental quota, and probabilistic excess flows.
In the study system, the flood flows vary among different levels. The system costs also vary temporally and spatially. Table 1 presents the existing normal and maximum capacities of the three flood regions, as well as the regular and penalty costs for diverting allowable and surplus flood streams. Table 2 shows the safety coefficient for flood diversion (h±) under different a-cut levels. Table 3 provides different flood flow levels associated with varied proba-