25 October 2004
Figure 10-8. Map of Proposed Conditions (LID Design)
Table 10-5. Composite CN Calculation for Proposed Condition Using LID
Product of CN
Lawn (good condition)
Sum of Products
Time Of Concentration For Existing And Proposed Conditions. The time
of concentration (Tc) was calculated for the pre-development and conventional post-
development conditions using the procedures in TR-55. A summary of these
calculations is included in Appendix C. The conventionally developed condition causes
Tc to decrease from 0.24 hours to 0.22 hours, or a 1.2 minute difference. The LID site
design results in a Tc that matches the existing condition; in this case, 0.24 hours.
Additional calculations for flow through the bioretention cells or rougher vegetated areas
were not included in the analysis, but would be expected to further increase post-
development LID Tc.