Urban stormwater drainage network assessment using an expert geographical information system

The assessment of urban stormwater drainage network using rational method was fully automated within Arc/Info geographic information system. The methodology was implemented for a subset of stormwater drainage system of City of Asheville, North Carolina. Capacity of each pipe and inlet in the drainage system is compared with design discharges of 10 and 25 year return period. Based on that comparison a capacity index was assigned to each drainage structure that indicates whether the structure is capable of conveying the design discharges or not. Implementation of rational method for design discharge computations is accomplished using the intrinsic Arc/Info functions. Local time of concentration can be obtained from triangulated irregular network terrain representation, while local C-coefficient can be obtained by overlaying individual inlet drainage areas with land use types. The individual inlet drainage areas are defined manually due to the complexity of the urban terrain and lack of precise terrain information. Cumulative parameters for rational method are obtained from local parameters and Arc/Info's Network routine that provides automated determination of upstream contributing drainage areas. An overview of the Network routine for other water routing applications is given. A general method for relating and using for analysis the information attached to point, line, and polygon features of Arc/Info is developed. A prototype interface between Arc/Info and Nexpert Object on command level is developed. This is the first interface developed between any commercially available GIS and expert system software. The interface was used to develop "intelligent network builder", an expert system application that performs logical integrity checking of the pipe network with respect to drainage analysis. A connectivity checking is performed on pipe coverage in order to establish a hydrologically connected network that can be used for discharge computations. Also, an example of intelligent mapping is presented using logic developed in Nexpert Object, and mapping features of Arc/Info.