25 October 2004
Figure 10-5. Map of Existing Conditions
Post Development Curve Number Calculations. The conventional method
for assigning a curve number to a residential development is to choose a single curve
number for the entire site from a source such as Table 2-2a of TR-55.41 Figure 10-6 is a
picture of the proposed housing type, which can be classified as "Townhouse
Residential District". For this land use, the CN from Table 2-2a of TR-55 is 85.
The LID method allows for the calculation of a "customized" CN that reflects
the actual field conditions rather than a broad estimation. For this example, the
amounts of impervious cover and other land covers were calculated directly from Figure
10-7. Table 10-3 is a summary of the proposed condition's "customized" CN using the
LID calculation method.
Table 10-3. Composite Curve Number Calculation for Proposed Condition
Product of CN
Lawn (fair condition)
Sum of Products