Area Measurements from Site Plans and Introduction to

WinSLAMM Analyses

Robert PittDept. of Civil and Environmental Engineering

University of AlabamaTuscaloosa, AL 35487

Little Shades Creek Subwatersheds

Area (acres) 1 2 3 4 All others

Total

Single family

339 448 676 401 1747 3611

Town homes

0 20 8 0 94 122

Multi-family 0 47 13 0 27 87

School/

church

0 0 38 13 58 109

Commercial 8 8 17 7 42 82

All other 70 153 199 164 621 1207

Total 417 676 951 585 2589 5218

Characteristics of Land Development in Rocky Ridge Low density

Medium density pre 1960

High density

Strip commercial

Office parks

Directly connected imperviousness

6.11 8.98 15 90.6 60.19

Impervious areas draining to pervious areas

4.7 6.2 9 0 1.14

Pervious Areas 89.19 84.82 76 9.4 38.67

Total 100 100 100 100 100

Summary of Measured Areas

• Totally connected impervious areas: 25.9 acres– parking 15.3 acres– roofs (flat) 8.2 acres– streets (1.2 curb-miles and 33 ft wide) 2.4 acres

• Landscaped/open space 15.4 acres

• Total Area 41.3 acres

Stormwater Controls• Biofiltration areas

– 52 units of 40 ft by 8 ft– Surface area: 320 ft2

– Bottom area: 300 ft2

– Depth: 1 ft – Vertical stand pipe: 0.5 ft. dia. 0.75 ft high– Broad-crested weir overflow: 8 ft long, 0.25 ft wide

and 0.9 ft high– Amended soil: sandy loam

Stormwater Controls (cont.)

• Wet detention pond– Surface area at pond surface:

• 3% of 25.9 paved acres = 0.78 acres• 0.5% of 15.4 unpaved acres = 0.077 acres• Total area: 0.95 acres

– Pond areas different depth:• 0 ft 0 acres 4 ft 0.95 acres• 1 ft 0.1 acres 5 ft 1.15 acres• 2 ft 0.3 acres 6 ft 1.25 acres• 3 ft 0.5 acres 7 ft 1.31 acres

Runoff Volume ChangesBase conditions

With biofiltration

With pond With biofilt. and pond

Runoff volume (106 ft3/yr)

2.85 1.67 2.85 1.67

Average Rv 0.59 0.35 0.59 0.35

Average CN 98 96 98 96

% reduction in volume

n/a 41% 0% 41%

Particulate Solids ChangesBase conditions

With biofiltration

With pond With biofilt. and pond

Particulate solids (lbs/yr)

30,250 27,650 3,660 3,320

Part. size controlled (flw-wgt meters)

n/a n/a 3.2 3.7

% reduc. in discharges

n/a 9% 88% 89%

Residential Area Source AreasArea (acres) Large

lotsSmall lots

Total area

Roofs 0.39 0.52 0.91

Driveways 0.15 0.12 0.27

Sidewalks 0.06 0.04 0.10

Landscaped areas

1.61 1.07 2.68

Subtotals 2.21 1.75 3.96

Streets 0.57

Undeveloped area

1.07

Total area: 5.60 acres

Example Area Calculations for Workshop Problem

Roofs Concrete around buildings

Street areas (widths)

Sidewalks Parking islands

Large landscaped areas

Parking

0.49 (35)

0.3 (20)

0.29 (40)

3.57 acres

2.88 acres

1.08 acres

0.07 acres 1.03 acres

3.98 acres 8.07 acres

17.3% 13.9% 5.2% 0.3% 5.0% 19.3% 39.0%