1. A method for evaluating the effect of proposed developments or system modifications upon a flood control system, the steps of which comprise: (a) establishing a system watershed data base including data representing a plurality of watersheds and associated parameters, said parameters including data relating to hydrological and hydraulic characteristics of primary and secondary water channels, location and surface acreage of existing developments, expected rainfall levels, and terrain data associated with said watersheds; (b) identifying the watershed within which the proposed development or system modification is located; (c) developing data representative of the boundaries of the proposed development or modification; (d) calculating the hydrological parameters associated with the proposed land development or system modification within the selected watershed; (e) reviewing a data file including data representative of the status of previously approved developments or modifications within the selected watershed to determine whether such previously approved developments or modifications are current; (f) determining the hydrological parameters associated with the portion of the flood control system comprising the existing, currently approved and proposed land developments or modifications within the selected watershed; (g) modifying the watershed data base to include data representative of the hydrological parameters of the proposed and previously approved and current new developments; (h) determining modified hydrological flow rates for main and secondary channels within the selected watershed utilizing the modified watershed data base; (i) determining modified flows for a plurality of stations or locations located along the main water channels within the selected watershed; (j) establishing a modified hydraulic analysis input data base including data representative of the hydrological and hydraulic parameters of the portion of the flood control system comprising the existing watershed, the approved developments and the proposed development or modifications; (k) determining the effects of the proposed development or modification upon the selected watershed and associated flood control system utilizing the data within the modified hydraulic analysis input data file, including a determination of the water surface profile for stations or locations along the primary water channel within the selected watershed; (l) comparing the effects of the proposed development or modification with prescribed minimum or maximum parameters to determine if the effects of the proposed development or modification cause the watershed parameters to satisfy the prescribed minimums or maximums.