6101 23RD DR W NORPRO 2025-07-29

1 B. Pre Developed Hydrology drolo P Y gY ' The existing land coverage is entirely pervious and made up of second growth conifer and deciduous trees with moderate ground cover. Narbeck Creek: ' As discussed in Section III, Minimum Requirement#7 of this report, flow control for Narbeck Creek will be designed with SBUH methodology. Table 2 ' Existing Conditions—Narbeck Creek Basin Basin Area(AC) Description CN 0.31 Wood/forest land (young 2nd growth/brush) 81 Powdermill Gulch Creek: ' Since the Powdermill Gulch Creek portion of the property drains to an existing regional detention pond, no onsite flow control is required. Since runoff treatment is required, developed site hydrology is discussed in the next section; however pre-developed hydrology analysis is not applicable. c� n C. Developed Hydrology U Narbeck Creek: 43,5—&° z/e9G All runoff draining to Narb Creek in the developed condition will be roof runoff as described in Table 3A below: ' Table 3A Proposed Conditions-Narbeck Creek Are Description CN ' C 0.23 Rooftop 98 �3`08 Landscape 86 0.31 Total Basin Area 95 ' Since all runoff draining the Narbeck Creek basin is from non-pollution generating surfaces, no water quality is required. Powdermill Gulch Creek: Since only runoff that requires water quality treatment needs to be routed through the runoff treatment structures, the portion of the basin that will bypass the runoff treatment structures (separate roof leaders, perimeter landscaping) is presented in a separate table from the area that will be routed to the runoff treatment structures. All runoff draining to the Powdermill Gulch Creek basin that can be feasibly collected onsite and requires runoff treatment is described in Table 3B below: 1 6/16/2011 Stormwater Site Plan Page 23