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Exh. 7-ET-3 Revision Date: 11/8/21 <br /> Revision No.: TR-151 <br />Modeling a constant inflow using SEDCADTM is somewhat complex. The methodology <br />suggested by SEDCADTM primary author, Pam Schwab, was used to model the impact of <br />a constant inflow. In the current version of SEDCADTM, a fixed flow can only be input <br />by inserting a "dummy" upstream reservoir with a watershed large enough to produce a <br />"tank" flow, and then setting the output of the dummy reservoir as a constant "User <br />Defined" outflow curve, independent of pool elevation in the dummy reservoir. A flow of <br />0.56 cfs (250 gpm) was conservatively utilized to represent the flow from the East Taylor <br />Seep, which in reality is lower based on the seasonable availability of water. The <br />watershed, time of concentration, and curve number utilized for this simulated flow are <br />theoretical in natures. The synthesized 250 gpm flow was then dropped into directly into <br />East Taylor Pond. <br /> <br />For the reclamation case at the East Taylor Pond, the 10 year 24 hour storm produces 3.4 <br />acre feet of runoff, and the entire storm event is contained below the principal spillway <br />elevation. The 25 year 24 hour storm event peaks at the 6,953.47 elevation which is <br />below the emergency spill way elevation of 6,954.0’. <br /> <br />East Taylor Permanent Post Mine Channels <br /> <br />The East Taylor watershed is comprised of three post-mining channels. One channel, the <br />Taylor Ditch, conveys all the post mining surface water flows to the East Taylor Pond, <br />while the East Taylor Ditch and Taylor Trib Ditch are tributaries to the Taylor Ditch. <br />The locations of all three channels are presented on Map 12 and Figure Exh. 7-14ET-2. <br />The channel profiles are presented on Map 33. <br /> <br />Taylor Ditch <br /> <br />The area contributory to the Taylor Ditch in some locations is less than one square mile. <br />However, portions of this channel pass over a permanent fill, and the lower portion below <br />the confluence with the East Taylor Ditch is larger than one square mile so the modeled <br />storm event required by rule is the 100 year 24 hour event. The entire length of the <br />Taylor Ditch will be riprap lined. Two stock ponds TD-1 and TD-2 have been <br />constructed inline in the channel to reduce peak flows from larger storm events, and <br />provide a water source to support the post mine land use. <br /> <br />A SEDCADTM model (100 Year 24 Hour Channel Demonstration model) has been <br />included which evaluates the peak flow and total runoff volume for each of the channel <br />segments for the 100 year, 24-hour storm event. The channel configurations for the 100 <br />year, 24 hour storm for the Taylor Ditch summarized below.