1 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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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)
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
1
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.