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JD -7 Mine — Drainage Design Plan 42 <br />E <br />3 <br />0 <br />LL <br />Hydrog -ph <br />0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 <br />Time (hours) <br />Figure 20. Hydrograph for Catchment 0018 -A South <br />4. S. 3 Upstream Storage Ponds (USPs) <br />■ Inflow <br />Is Primary <br />"Upstream storage" refers to the storage of storm runoff close to the points of rainfall occurrence, including <br />road embankments, borrow pits, parking lots, property line swales, parks, and on -site basins and ponds <br />(UDFCD DP -17, 2001). The ephemeral pool that occurs seasonally in the JD -7 pit provides upstream <br />storage to retain stormwater runoff and thus dampen peak flows. Additional upstream storage occurs above <br />the CV -1 culvert (Figure 12) and in small ponds or pools on site. Although this upstream storage is <br />beneficial to reducing stormwater runon to the site, the runoff modeling conservatively does not take credit <br />for this storage. <br />Although the Drainage Criteria Manual published by the Urban Drainage and Flood Control District <br />(UDFCD, 2001, 2008) is not directly applicable to the JD -7 site, the manual identifies the benefits of <br />upstream storage and the difficulty in quantifying those benefits: <br />The difficulty in quantifying the cumulative effects of very large numbers of small (i.e., <br />on -site) detention/retention facilities (Malcomb, 1982; Urbonas and Glidden, 1983) and the <br />virtual impossibility of assurance of their continued long -term performance or existence <br />(Debo, 1982; Prommersberger, 1984) requires the District to recognize in its floodplain <br />management only regional, publicly owned facilities. Nevertheless, upstream storage is <br />encouraged, such as with the 'Blue- Green" concept first described in Civil Engineering <br />magazine (Jones, 1967). <br />The runoff modeling performed for the JD -7 Mine using WinTR -55 conservatively does not take credit for <br />upstream storage throughout most of the modeled area. One exception is the existing upstream storage at <br />the eastern toe of the OPWRP, which is modeled explicitly in HydroCAD in the planned condition, as <br />described in Section 6.2. <br />4149A.140207 Whetstone Associates <br />