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) 1
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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 4
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Roofs Residential Area Source Areas Area (acres) Large lots.39 Small lots.52 Total area.91 Driveways.15.12.27 Sidewalks.6.4.1 Landscaped areas 1.61 1.7 2.68 Subtotals Streets 2.21 1.75 3.96.57 Little Shades Creek Jefferson Co, AL Undeveloped area Total area: 5.6 acres 1.7 Jefferson Co. MS4 Monitoring Sites Birmingham, AL Little Shades Creek Subwatersheds Field Data Collection Area (acres) Single family Town homes 1 339 2 448 2 3 676 8 4 41 All others 1747 94 Total 3611 122 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 Multi-family School/ church Commercial 8 47 8 13 38 17 13 7 27 58 42 87 19 82 Site Inventory had 2 parts: Field data collection Aerial photographic measurements of different land covers All other Total 7 417 153 676 199 951 164 585 621 2589 127 5218 Each site had at least two photographs taken: one as a general view one as a close-up of the street texture 6
Field Inventory Sheet Prepared for Each Neighborhood 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 and gutters, and roof drains) Village Creek Site (SWMA 2) Birmingham, AL Characteristics of Land Development in Rocky Ridge Low density Medium density pre 196 High density Strip commercial Office parks Directly connected imperviousness 6.11 8.98 15 9.6 6.19 Impervious areas draining to pervious areas 4.7 6.2 9 1.14 Pervious Areas 89.19 84.82 76 9.4 38.67 Total 1 1 1 1 1 7
Little Shades Creek Watershed Average Land Cover Distribution High Density Residential (6 houses/acre) TIA = 2% DCIA = 15% TR-55 = 25-52% TIA = 61% DCIA = 6% TR-55 = 85% TIA = 1% DCIA = 6.7% TR-55 = 2-25% TIA = 67% DCIA = 64% TR-55 = 85% TIA = 25% DCIA = 15% TR-55 = 52-65% Little Shades Creek Watershed Variation in Land Cover Distribution Little Shades Creek and Jefferson Co. Drainage Areas: TIA by Land Use 8
Little Shades Creek and Jefferson Co. Drainage Areas: DCIA by Land Use Average Percent Directly Connected Impervious Area APARTMENTS COM IND Land Use HDR (> 6 units/ac) MDR (2-6 units/ac) LDR (< 2 units/ac) Local Conditions 21 11 5 23 71 5 TR 55 (using interpolation) 52 39 23 65 85 72 TR- 55 assumes all impervious areas to be directly connected to the drainage system Overestimation of impervious cover for local conditions Curb Length vs Land Use 1 mile = 1.6 km 1 ac =.4 ha 9
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Figure and Table from Center of Watershed Protection 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. Urban Steam Classification Channel Stability Aquatic Life Biodiversity Sensitive 1% Imperviousness Stable Good/Excellent Impacted 11 25% Imperviousness Unstable Fair/Good Damaged 26 1% Imperviousness Highly Unstable Relationship between Directly Connected Impervious Areas, Volumetric Runoff Coefficient, and Expected Biological Conditions WinSLAMM v 9.2 Output Summary Rv 1.9.8.7.6 Fair Good.5.4.3.2.1 1 1 1 Directly Connected Impervious Area (%) Sandy Soil Rv Silty Soil Rv Clayey Soil Rv 11
Watershed ID Major Land Use Area (ac) Pervious Areas (%) Directly Connected Impervious Areas (%) Disconnected Impervious Areas (%) Vol. Runoff Coeff. (Rv) Expected Biological Conditions of Receiving Waters ALJC 1 IND 341 25 72 2.8.67 ALJC 2 IND 721 4 53 7.3.51 ALJC 9 Resid. High Dens. 12 54 34 12.37 ALJC 1 Resid. Med. Dens. 133 64 28 7.9.3 ALJC 12 COM 228 36 61 3.4.61 Little Shades Creek RES 512 67 21 12.29 Flow-Duration Curves for Different Stormwater Conservation Design Practices 14 Flow Duration Curves are Ranked in Order of Peak Flows Cost Effectiveness of Stormwater Control Practices for Runoff Volume Reductions 8 12 1 Top Set: No Controls Swales 7 6 Pond Discharge (cfs) 8 6 4 2 Bottom Set: Biorentention Swales and Bioretention Pond and Bioretention Pond, Swales and Bioretention Middle Set: Pond Pond and Swales $/1 cu. Ft Reduced 5 4 3 2 1 Pond and Swale Swale Pond and Bioretention Bioretention Pond, Swales and Bioretention Swales and Bioretention.1 1 1 1 % Greater than Discharge Rate 2 4 6 8 Max % Runoff Reduced 12
Example of Stormwater Control Implementation Annualized Total Costs ($/year/ac) Runoff Coefficient (Rv) % Reduction of Total Runoff Volume Discharges Unit Removal Costs for Runoff Volume ($/ft 3 ) Expected biological conditions in receiving waters (based on Rv) No controls.61 n/a n/a poor Pond Only 118.6 1.4%.7 poor Swales Only 44.54 1%.3 poor Bioretention Only 1974.26 58%.3 poor Pond, Swales and Bioretention 2456.2 67%.3 Site ALJC 12 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 fair 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 1 to 15% directly connected impervious cover values are reached (at Rv values of about.7 for sandy soil areas and.16 for clayey soil areas), the point where receiving water degradation typically is observed to start. The 25 to 3% directly connected impervious levels (where significant degradation is observed), is associated with Rv values of about.14 for sandy soil areas and.25 for clayey soil areas, and is where the curves start to greatly increase in slope. 13