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Land Development Characteristics

(Module 6)

Robert Pitt and Celina Bochis

Department of Civil, Construction and Environmental Engineering The University of Alabama

Tuscaloosa, AL 35487 Example of 1 m monochromatic aerial photograph (USGS photo)

Example of high resolution color satellite image (Google)

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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

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Residential Area Source Areas

1.07Undeveloped area

0.57Streets

3.961.752.21Subtotals

2.681.071.61Landscaped areas

0.100.040.06Sidewalks

0.270.120.15Driveways

0.910.520.39Roofs

Total area

Small lots

Large lots

Area (acres)

Total area: 5.60 acres

Jefferson Co. MS4Monitoring SitesBirmingham, AL

Little Shades CreekJefferson Co, AL

Little Shades Creek Subwatersheds

52182589585951676417Total

120762116419915370All other

824271788Commercial

10958133800School/church

8727013470Multi-family

1229408200Town homes

36111747401676448339Single family

Total All others

4321Area (acres)

Field Data Collection• Delineation of the watersheds and neighborhoods

• Single land use neighborhood surveys: 6 to 12 per study area land use to determine the variability of the development characteristics

• Site Inventory had 2 parts:– Field data collection– Aerial photographic measurements of different land

covers

• Each site had at least two photographs taken: – one as a general view– one as a close-up of the street texture

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Field InventorySheet Prepared for EachNeighborhood

When in the field we look for:

1. Roof types (flat or pitched)

2. Roof connections (connected, disconnected)

3. Pavement conditions and texture (smooth, interm., rough)

4. Storm drainage type(grass swales, curb andgutters, and roof drains)

Village Creek Site (SWMA 002)Birmingham, AL Characteristics of Land Development in Rocky Ridge

100100100100100Total

38.679.47684.8289.19Pervious Areas

1.14096.24.7Impervious areas draining to pervious areas

60.1990.6158.986.11Directly connected imperviousness

Office parks

Strip commercial

High density

Medium density pre 1960

Low density

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Little Shades Creek WatershedAverage Land Cover DistributionHigh Density Residential (6 houses/acre)

TIA = 25%

DCIA = 15%

TR-55 = 52 - 65%

TIA = 20%

DCIA = 15%

TR-55 = 25-52%

TIA = 10%

DCIA = 6.7%

TR-55 = 20-25%

TIA = 61%

DCIA = 60%

TR-55 = 85%

TIA = 67%

DCIA = 64%

TR-55 = 85%

Little Shades Creek WatershedVariation in Land Cover Distribution Little Shades Creek and Jefferson Co.

Drainage Areas: TIA by Land Use

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Little Shades Creek and Jefferson Co.Drainage Areas: DCIA by Land Use

Average Percent Directly Connected Impervious Area

8571COM7250IND

6523APARTMENTS235LDR (< 2 units/ac)

3911MDR (2-6 units/ac)

5221HDR (> 6 units/ac)

TR – 55 (using interpolation)

Local ConditionsLand Use

• TR- 55 assumes all impervious areas to be directly connected to thedrainage system

• Overestimation of impervious cover for local conditions

Curb Length vs Land Use

1 mile = 1.6 km 1 ac = 0.4 ha

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Relationship between basin development, riparian buffer width, and biological integrity in Puget Sound lowland streams. (From May, C.W. Assessment of the Cumulative Effects of Urbanization on Small Streams in the Puget Sound Lowland Ecoregion: Implications for Salmonid Resource Management. Ph.D. dissertation, University of Washington, Seattle. 1996.

PoorFair/GoodGood/ExcellentAquatic Life Biodiversity

Highly UnstableUnstableStableChannel Stability

Damaged26–100%

Imperviousness

Impacted11– 25%

Imperviousness

Sensitive0 – 10%

Imperviousness

Urban Steam Classification

Figure and Table from Center of Watershed Protection

00.10.20.30.40.50.60.70.80.9

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1 10 100Directly Connected Impervious Area (%)

Rv

Sandy Soil Rv Silty Soil Rv Clayey Soil Rv

GoodFair

Poor

Relationship between Directly Connected Impervious Areas, Volumetric Runoff

Coefficient, and Expected Biological Conditions

WinSLAMM v 9.2 Output Summary

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Poor0.291221675120RESLittle

Shades Creek

Poor0.613.46136228COM ALJC 012

Poor0.307.92864133Resid. Med. Dens.

ALJC 010

Poor0.37123454102Resid. High Dens.

ALJC 009

Poor0.517.35340721INDALJC 002

Poor0.672.87225341INDALJC 001

Expected Biological

Conditions of Receiving

Waters

Vol. Runoff Coeff. (Rv)

DisconnectedImperviousAreas (%)

DirectlyConnectedImperviousAreas (%)

PerviousAreas

(%)

Area(ac)

MajorLand Use

WatershedID

Flow-Duration Curves for Different Stormwater Conservation Design Practices

0

20

40

60

80

100

120

140

0.1 1 10 100

% Greater than Discharge Rate

Dis

char

ge (c

fs)

Top Set:No ControlsSwales

Bottom Set:BiorententionSwales and BioretentionPond and Bioretention Pond, Swales and Bioretention

Flow Duration Curves are Ranked in Order of Peak Flows

Middle Set:PondPond and Swales

Cost Effectiveness of Stormwater Control Practices for Runoff Volume Reductions

Swales andBioretention

Pond andBioretention

Bioretention

Pond, Swales and Bioretention

Pond

Pond and Swale

Swale

0

10

20

30

40

50

60

70

80

0 20 40 60 80

Max % Runoff Reduced

$/10

00 c

u. F

t R

educ

ed

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Example of Stormwater Control Implementation

fairpoorpoorpoorpoorExpected biological conditions in receiving waters(based on Rv)

0.030.030.030.07n/aUnit Removal Costs for Runoff Volume ($/ft3)

67%58%10%1.4%n/a% Reduction of Total Runoff Volume Discharges

0.200.260.540.600.61Runoff Coefficient (Rv)

245619744041180Annualized Total Costs ($/year/ac)

Pond, Swales and Bioretention

Bioretention Only

SwalesOnly

PondOnly

No controls

• Site ALJC 012

• Area 228 acres = 92.3 ha

• Bioretention devices give the greatest reduction in runoff volume discharged

• The biological conditions improved from “poor” to “fair” due to stormwater controls

• These graphs illustrate the relationships between the directly connected impervious area percentages and the calculated volumetric runoff coefficients (Rv) for each land use category (using the average land use characteristics), based on 43 years of local rain data.

• Rv is relatively constant until the 10 to 15% directly connected impervious cover values are reached (at Rv values of about 0.07 for sandy soil areas and 0.16 for clayey soil areas), the point where receiving water degradation typically is observed to start.

• The 25 to 30% directly connected impervious levels (where significant degradation is observed), is associated with Rv values of about 0.14 for sandy soil areas and 0.25 for clayey soil areas, and is where the curves start to greatly increase in slope.