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Mineral Joe Mine — Drainage Design Plan 9 <br />All riprap will be installed with a granular (Type 1) bedding or filter fabric below Type II bedding to protect <br />underlying soils per Urban Drainage and Flood Control District specification for gradation and thickness <br />( UDFCD, 2011) as shown in Attachment 1. For drop structures, the UDFCD (2011) specifications allow a <br />combination of filter fabric and Type It bedding as an acceptable alternative to a 2 -layer filter (bedding). <br />Riprap sizing for the SWRP spillway was conducted using the design curves in the USBR (1998) design <br />procedure to predict stable stone size. The calculated flow over the spillway (Section 5.4) was used with <br />the following USBR design curves for sizing riprap protection on embankments of various slopes, then the <br />calculated D50 was multiplied by 3.0 for an appropriate factor of safety. The resulting spillway design is <br />discussed in Section 4.5.2. <br />Ut? 01 <br />ry <br />0 <br />0 oat <br />0 021 <br />0 001 001 01 <br />Unit discharge q (MA31s /m) <br />4148B.131029 Whetstone Associates <br />�S Q <br />S�U.4 <br />—5 <br />0 001 001 01 <br />Unit discharge q (MA31s /m) <br />4148B.131029 Whetstone Associates <br />