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erodible channel calculation was performed for the grass lined channel. The grouted section did <br />not need an erodible channel calculation due to the nature of its structure. However, flow <br />calculations were performed. Due to the high velocity discharge at the bottom of the slope, three <br />to four D50 = 5' boulders and rip-rap will be used as an energy dissipater before allowing the <br />water to discharge into the natural drainage. Since some of the channels have already been built <br />and they are designed to handle more flow than needed, the channel designs will remain the <br />same in the 2009 amendment as they were in the 2003 amendment. <br />Time of Concentration (TR-55 Method) <br />Time of Concentration (Tc) of Travel Time (Tt) 8/20/2008 14:43 <br />Project: Cugnini By: Ryan Ellis Date: 08/20/08 <br />Location: Grass Channel #1 Checked: Greg Lewicki <br />Sheet Flow (Applicable to Tc only) <br />2. Manning's Roughness Coeff. (n): 0.2400 <br />3. Flow Length, L (total L <= 300 ft): 257.83 ft <br />4. Two-yr 24-hr Rainfall, P: 3.20 in <br />5. Land Slope, s: 6.00 % <br />6. Tt: 0.327 hr (19.6 min) <br />Shallow Concentrated Flow <br />7. Surface Description: Unpaved <br />8. Flow Length, L: 2300.00 ft <br />9. Watercourse Slope, s: 3.50 % <br />10. Average Velocity, V: 2.95 ft/s <br />11. Tt: 0.217 hr (13.0 min) <br />Channel Flow <br />12. Cross Sectional Flow Area, a: 0.00 SgFt <br />13. Wetted Perimeter, Pw: 0.00 ft <br />14. Hydraulic Radius, r: 0.00 ft <br />15. Channel Slope, s: 0.00 % <br />16. Manning's Roughness Coef£ (n): 0.00 <br />17. Velocity, V: 0.00 ft/s <br />18. Flow Length, L: 0.00 ft <br />19. Tt: 0.000 hr (0.0 min) <br />20. Watershed or Subarea Tc or Tt: 0.544 hr (32.6 min) <br />Cugnini Pit, November 2009 D-9