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I I II i I I I I I I II I I I I I I I I I 4.1.2 Network Development The network incorporated into the UDSWM2-PC runoff block is a model of the basin's drainage network, representing each of the drainage subbasins and facilities along the major drainageway, The first step in forming the network is to conceptualize and develop a schematic linking the drainage subbasins to the drainage facilities within the major drainageway. Identification of each drainage facility is based on the information compiled from the field reconnaissance and surveying efforts, Facilities incorporated into the modeling network are referred to by UDSWM2-PC as: conveyance elements (conduits and open channels), subcatchments( or subbasins), storage units (detention ponds), flow dividers (diversions), and manholes (nodes or design points). The subbasin delineation was accomplished through the use of mapping and survey data generated during the project. Drainage network schematics were developed for the Godding Hollow and Tri- Town Basins for the three scenarios previously discussed: (a) existing condition with existing facilities; (b) future development condition with existing facilities; and (c) future development conditions with on-site detention and proposed improvements. The network schematic diagrams are provided in the project notebook that accompanies this report. In general, the numbering scheme integrated into the modeling network was developed to allow easy identification of each type of facility, The numbering convention is presented below. 1 - 99 100 - 199 200 - 299 300 - 399 400 - 499 700 - 799 Subbasin hydro graph inputs (from CUHP) Conveyance elements (i.e" storm sewers and open channels) N odes (design points and diversions) Existing and future regional detention facilities Simulated detention facilities (approved and future development) Nodes (combination design points) 4.2 Rainfall Design Storms The rainfall design storms used in the hydrologic analysis of the Godding Hollow and Tri- Town Basins were based on information presented in the Precipitation Frequency Atlas of the Western United States, NOAA Atlas 2, Volume III, Colorado (1973). The one-hour rainfall values obtained for the Tri-Town area from the NOAA Atlas were used to develop a three-hour design storm, The three-hour storms developed for each remrn period are presented in the project notebook which accompanies this document. Further documentation and details regarding the development of the design storms can also be found in the Urban Storm Drainage Criteria Manual. T,.IOPEMCaweldO/lcoweldO/ pi rpt. wpd 4.2 September 8, 1999