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SECTION 3 Flood Control Euaination hydrologic data gaps, specifically related to the subbasin delineations and locations of runoff nodes in the model (a runoff node is a point where runoff from a subbasin area enters the modeled system). Since the original Study was prepared, data gaps have been addressed by the City of Eugene and Lane County. Specifically, survey data collected by Lane County between October and December 2005 allowed for refinement of the original subbasin delineations and node locations in the model (described in more detail in Subsection 3.1.2 and in Appendix G). These refinements have been applied to the original model, and the following discussion summarizes the overall hydrologic input data in the refined model. Hydrologic Data Based on the Piped and Surface Water Drainage System The River Road Santa Clara basin was subdivided into five major subbasins. The major subbasin boundaries are presented in Figure 3 -1. The five major subbasins were further divided into 75 subbasins for modeling purposes. The subbasin boundaries presented on Figures 3 -2 through 3 -8 were delineated based on both topography and the piped and open channel drainage system layout. The subbasin boundaries were digitized into the City's /County's GIS so that hydrologic data could be compiled for each subbasin. Seven - character names were assigned to each subbasin. The first two characters represent a two - letter abbreviation for the major basin; in this case RS for River Road Santa Clara. The second two characters represent a two - letter abbreviation for the major subbasin. The 5 major subbasins in the River Road Santa Clara basin are as follows: Al = A -1 Channel Drainage System FC = Flat Creek Drainage System SC = Spring Creek Drainage System WO = Willamette Overflow Drainage System (also referred to as the East Santa Clara Waterway) 99 = Highway 99 The last three characters of the subbasin name consist of numbers, starting with 010 and increasing in increments of 10 for each additional subbasin. For example, the first two subbasins in the Willamette Overflow major subbasin of the River Road Santa Clara basin are RSWO010 and RSWO020. In addition, each subbasin has an associated inlet node number. The hydrologic component (i.e., RUNOFF block) of XP -SWMM was used to generate a stormwater runoff hydrograph for each subbasin. This hydrograph was routed by the hydraulic component (i.e., the EXTRAN block) of XP -SWMM to model the storm drainage system. The subbasin inlet node is the point where the subbasin hydrograph enters the storm drainage system for routing. The following parameters were required for each subbasin in the hydrology component of XP- SWMM: 1. Subbasin name or number. 2. Channel or pipe inlet node number into the storm drainage system. 3. Subbasin area (acres). 4. Hydraulically connected impervious percentage for both existing and future land use scenarios (percent). 0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 3-2