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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
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.