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Two Rivers Gravel Pit Mine <br /> Riverside Berm Failure Analysis <br /> and Flood Control Mitigation Plan <br /> 7ech"olooicess January 22,2020 <br /> NORTHWEST FIELD <br /> 4690.0 FILL TIME VS HEADCUT <br /> H adcutting i itiates HeadcuttinE stops <br /> 4685.097 <br /> Pit Crest discharge ex eeded 106% of <br /> allowable at 0.25 hours. <br /> 4680.0 <br /> 4675.0 <br /> Headcutting stops <br /> 4670.0 Length 30 ft <br /> C <br /> O <br /> +r 4665.0 <br /> H adcutting stops Weakest <br /> W 4660.0 Length = 13C ft Best <br /> Strongest <br /> a —Fill Time <br /> Pit Toe 4655.0 <br /> 4650.0 <br /> 0 0.5 1 1.5 2 2.5 3 3.5 <br /> Time (hr) <br /> Figure 7.Northwest Pit <br /> Pit fill time and water surface elevation vs. head cut elevation for a typical riverside <br /> berm. <br /> The main differences in degree of head cutting/erosion between Central Pit(South Platte River <br /> side) and Northwest and Northeast Pits (Big Thompson Side) are, (1)pit fill times due to volume <br /> differences, and (2)inflow flood differences. <br /> pg. 20 <br />