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