Extracted images: Low Impact Development Techniques

Printed revision: February 2004.

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PDF page 16, image 1

Mistral ID: img-0.jpeg. Extraction bundle(s): 2026_BMP_2_Low_Impact_Development_Techniques. Original page | Image file

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Figure 2-1: Schematic of Lot with Connected Impervious Areas

## Reduction of Runoff Volumes Due to Reduced Impervious Surfaces

Note: The computations were done by evaluating the runoff from the pervious and the impervious areas separately, and summing the volumes.

## Example A

Given: A 32670 sf lot with 27470 sf lawn, HSG "B", CN = 61, 5200 sf impervious surface, CN = 98.
No impervious cover is disc

PDF page 17, image 1

Mistral ID: img-1.jpeg. Extraction bundle(s): 2026_BMP_2_Low_Impact_Development_Techniques. Original page | Image file

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Figure 2-2: Schematic of Lot with Connected and Unconnected Impervious Areas

# Changes in Runoff Volumes Due to Disconnection of Impervious Surfaces

# Example C

Given: A 32670 sf lot with 29870 sf lawn, HSG "B", CN = 61, 2800 sf impervious surface of total impervious area, CN = 98.

2000 sf of impervious area discharges to 8900 sf of lawn, and 800 sf impervious area is directly connected

$\mathrm{P}

PDF page 18, image 1

Mistral ID: img-2.jpeg. Extraction bundle(s): 2026_BMP_2_Low_Impact_Development_Techniques. Original page | Image file

Tables on the same PDF page: Table 1

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Figure 2-3: Schematic of Existing Lot and Standard Development Lot

# Comparison of Changes in Runoff Due to Low Impact Development Techniques

# Predeveloped Condition

0.75 acre lot

20,650 sf woods, HSG "B"

12,020 sf woods, HSG "C"

$\mathrm{P}_2 = 3.3$  inches,  $\mathrm{P}_{10} = 5.2$  inches, and  $\mathrm{P}_{100} = 7.5$  inch

$\mathrm{Tc} = 0.52$  hours

125 If sheet flow,  $1.3\%$  slope,  $\

PDF page 19, image 1

Mistral ID: img-3.jpeg. Extraction bundle(s): 2026_BMP_2_Low_Impact_Development_Techniques. Original page | Image file

Tables on the same PDF page: Table 2 | Table 3

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Figure 2-4: Schematic of Lot With LID Techniques

# Postdeveloped Condition (With LID Techniques)

0.75 acre lot, 2800 sf of total impervious area

800 sf of impervious area, directly connected,  $\mathrm{Tc} = 0.1$  hours

2000 sf of impervious area, unconnected, discharging to 8906 sf of lawn

$\mathrm{P}_2 = 3.3$  inches,  $\mathrm{P}_{10} = 5.2$  inches, and  $\mathrm{P}_{100} = 7.5$  inch

Nonstruc