SLIDE 1
w w w. t r a n s p o r t a t i o n . o h i o . g o v
1
w w w. t r a n s p o r t a t i o n . o h i o . g o v
2
Extended Detention Basin Design w w w. t r a n s p o r t a t i o n - - PowerPoint PPT Presentation
Extended Detention Basin Design w w w. t r a n s p o r t a t i o n - - PowerPoint PPT Presentation
Extended Detention Basin Design w w w. t r a n s p o r t a t i o n . o h i o . g o v 1 Extended Detention w w w. t r a n s p o r t a t i o n . o h i o . g o v 2 Extended Detention Basin L&D Vol. 2 Section 1117.3 Provides quality and
SLIDE 2
SLIDE 3
w w w. t r a n s p o r t a t i o n . o h i o . g o v
3
Extended Detention Basin
L&D Vol. 2 Section 1117.3 Provides quality and quantity treatment
SLIDE 4
w w w. t r a n s p o r t a t i o n . o h i o . g o v
4
Extended Detention Basin Treatment Processes
SLIDE 5
w w w. t r a n s p o r t a t i o n . o h i o . g o v
5
Design Process
Treatment Goals Preliminary Det. Basin Sizing Siting Analysis
- Det. Basin Shape and Detailed Sizing
Water Quality Outlet Primary Outlet Overflow Weir Other Considerations
SLIDE 6
w w w. t r a n s p o r t a t i o n . o h i o . g o v
6
Siting Analysis - Considerations
Space Enough R/W treatment Tributary area too large? Safety Environmental impacts Floodplain cut/fill R/W acquisition Vehicle access
SLIDE 7
w w w. t r a n s p o r t a t i o n . o h i o . g o v
7
Siting Analysis
It can be difficult to find space. Intersections Interchanges R/W acquisition Underground detention
SLIDE 8
w w w. t r a n s p o r t a t i o n . o h i o . g o v
8
Design Process
Treatment Goals Preliminary Det. Basin Sizing Siting Analysis
- Det. Basin Shape and Detailed Sizing
Water Quality Outlet Primary Outlet Overflow Weir Other Considerations
SLIDE 9
w w w. t r a n s p o r t a t i o n . o h i o . g o v
9
Detention Basin Sizing
Calculate WQV based on tributary area WQV must be between lowest outlet primary outlet (10-yr) 10% WQV additional for forebay
Dead storage
10% WQV additional for micropool
Dead storage
SLIDE 10
w w w. t r a n s p o r t a t i o n . o h i o . g o v
10
Project Example - WQV
SLIDE 11
w w w. t r a n s p o r t a t i o n . o h i o . g o v
11
Stage / Storage Curve
SLIDE 12
w w w. t r a n s p o r t a t i o n . o h i o . g o v
12
Project Example - WQV
SLIDE 13
w w w. t r a n s p o r t a t i o n . o h i o . g o v
13
Project Example - Forebay
SLIDE 14
w w w. t r a n s p o r t a t i o n . o h i o . g o v
14
Project Example - Forebay
SLIDE 15
w w w. t r a n s p o r t a t i o n . o h i o . g o v
15
Project Example - Micropool
SLIDE 16
w w w. t r a n s p o r t a t i o n . o h i o . g o v
16
Project Example - Micropool
SLIDE 17
w w w. t r a n s p o r t a t i o n . o h i o . g o v
17
Design Process
Treatment Goals Preliminary Det. Basin Sizing Siting Analysis
- Det. Basin Shape and Detailed Sizing
Water Quality Outlet Primary Outlet Overflow Weir Other Considerations
SLIDE 18
w w w. t r a n s p o r t a t i o n . o h i o . g o v
18
Water Quality Outlet Design
Drain WQV in 48 hours or more 50% of WQV or less drained in 1/3rd of the drain time
0.422 ac-ft * 50% = 0.211 ac-ft 48 hrs * 1/3 = 16 hrs
Provide time for sedimentation
SLIDE 19
w w w. t r a n s p o r t a t i o n . o h i o . g o v
19
Water Quality Outlet Design
Orifices
SLIDE 20
w w w. t r a n s p o r t a t i o n . o h i o . g o v
20
Water Quality Outlet Design
A Hydrograph drawdown curve is necessary Calculate a stage / discharge curve Or Use Pond Pack or HydroCAD
Pond Pack is part of Bentley Hydraulics Suite
SLIDE 21
w w w. t r a n s p o r t a t i o n . o h i o . g o v
21
Project Example – WQ Outlet
SLIDE 22
w w w. t r a n s p o r t a t i o n . o h i o . g o v
22
Design Process
Treatment Goals Preliminary Det. Basin Sizing Siting Analysis
- Det. Basin Shape and Detailed Sizing
Water Quality Outlet Primary Outlet Overflow Weir Other Considerations
SLIDE 23
w w w. t r a n s p o r t a t i o n . o h i o . g o v
23
Outlet Structure
3 parts of detention basin outlet
Water quality outlet(s)
Slowly draw down the WQV
Primary outlet(s)
Convey the 10-yr design storm (L&D Vol. 2, 1117.3.3
Overflow weir
Convey the 25-yr design storm (L&D Vol. 2, 1104.2.2
SLIDE 24
w w w. t r a n s p o r t a t i o n . o h i o . g o v
24
ODOT SCD WQ-1.1
Orifices Grate Pipe Water Quality Outlets Primary Outlets
SLIDE 25
w w w. t r a n s p o r t a t i o n . o h i o . g o v
25
Project Example – WQ Outlet
No “Cleaning” above 799.00’
SLIDE 26
w w w. t r a n s p o r t a t i o n . o h i o . g o v
26
Primary Outlet Design
Size pipe discharging from catch basin for the 10-yr storm Set the catch basin grate elevation Confirm that the grate has the capacity to pass the 10-yr storm
SLIDE 27
w w w. t r a n s p o r t a t i o n . o h i o . g o v
27
Project Example – WQ Outlet
Discharge Pipe
SLIDE 28
w w w. t r a n s p o r t a t i o n . o h i o . g o v
28
Primary Outlet Design
Size pipe discharging from catch basin for the 10-yr storm Set the catch basin grate elevation Confirm that the grade has the capacity to pass the 10-yr storm
SLIDE 29
w w w. t r a n s p o r t a t i o n . o h i o . g o v
29
Project Example – Grate Elevation
SLIDE 30
w w w. t r a n s p o r t a t i o n . o h i o . g o v
30
Project Example – Grate Elevation
SLIDE 31
w w w. t r a n s p o r t a t i o n . o h i o . g o v
31
14.79 cfs 1.25 ft
SLIDE 32
w w w. t r a n s p o r t a t i o n . o h i o . g o v
32
Overflow Weir Elevation
Grate elevation = 799.0 ft Head needed to pass 14.79 cfs = 1.25 ft Overflow weir elevation:
799.0 ft + 1.25 ft = 800.25 ft
SLIDE 33
w w w. t r a n s p o r t a t i o n . o h i o . g o v
33
Project Example – Overflow Weir
25-yr peak flow = 16.53 cfs Assume top of basin is 0.5 ft higher than overflow weir Weir elevation = 800.25 ft Top of basin = 800.25 ft + 0.5 ft = 800.75 ft
SLIDE 34
w w w. t r a n s p o r t a t i o n . o h i o . g o v
34
Project Example – Overflow Weir
Q = CLH1.5
Q = 16.53 cfs C = 3 (L&D Vol. 2, 1102.3.4) H = 800.75 ft – 800.25 ft = 0.5 ft
16.53 cfs = 3 * L * 0.51.5 L = 15.6 ft
SLIDE 35
w w w. t r a n s p o r t a t i o n . o h i o . g o v
35
Project Example – Overflow Weir
SLIDE 36
w w w. t r a n s p o r t a t i o n . o h i o . g o v
36
Overflow Weir
Flow rates over the 25-yr storm may
- vertop the detention basin
uncontrolled. Consider erosion / scour protection Consider catastrophic failure
SLIDE 37
w w w. t r a n s p o r t a t i o n . o h i o . g o v
37
Design Process
Treatment Goals Preliminary Det. Basin Sizing Siting Analysis
- Det. Basin Shape and Detailed Sizing
Water Quality Outlet Primary Outlet Overflow Weir Other Considerations
SLIDE 38
w w w. t r a n s p o r t a t i o n . o h i o . g o v
38
Consider Catch Basin Invert
Pipe Invert Orifice Invert
SLIDE 39
w w w. t r a n s p o r t a t i o n . o h i o . g o v
39
Call Out Catch Basin Invert
SLIDE 40
w w w. t r a n s p o r t a t i o n . o h i o . g o v
40
Other Det. Basin Considerations
Velocity / Scour Anti-Seep Collars Safety Slope Stability and Item 670 Maintenance Access FEMA Floodplain ODNR Dam Permit?
SLIDE 41
w w w. t r a n s p o r t a t i o n . o h i o . g o v
41
Velocity / Scour
SLIDE 42
w w w. t r a n s p o r t a t i o n . o h i o . g o v
42
Anti-Seep Collars
Reference: Dept. of Interior, 1982
SLIDE 43
w w w. t r a n s p o r t a t i o n . o h i o . g o v
43
Anti-Seep Collars
ODOT Standard Drawing WQ-1.2
SLIDE 44
w w w. t r a n s p o r t a t i o n . o h i o . g o v
44
Project Example – Collar Design
10-yr Elev. 800.25 ft Berm Slope 4:1 Pipe Dia. 24” Pipe Slope 0.005 ft/ft Pipe Inv. 795.0 ft Saturated Zone
SLIDE 45
w w w. t r a n s p o r t a t i o n . o h i o . g o v
45
Project Example – Collar Design
10-yr Elev. 800.25 ft Pipe Inv. 795.0 ft Pipe Dia. 24” Pipe Slope 0.005 ft/ft Ls = 42.86 ft 10 ft Berm Slope 4:1
SLIDE 46
w w w. t r a n s p o r t a t i o n . o h i o . g o v
46
Project Example – Collar Design
SLIDE 47
w w w. t r a n s p o r t a t i o n . o h i o . g o v
47
Safety
Detention basins are safety risks Clear zone: grading and 12” ponding Drowning hazard Local requirements? Fencing, trash rack, aquatic bench Impacts to upstream or downstream flooding
SLIDE 48
w w w. t r a n s p o r t a t i o n . o h i o . g o v
48
Slope Stability
Do not locate on uncompacted fill or steep slopes (2:1 or more). Vegetate sides of basin Item 670, Slope Erosion Protection Don’t plant grass under water
Forebay Micropool
SLIDE 49
w w w. t r a n s p o r t a t i o n . o h i o . g o v
49
Maintenance Access
Regular maintenance necessary Flat bench wide enough for a truck Grass needs to be mowed Woody vegetation cut from berm Regular unclogging of WQ outlet
Every 6 months
SLIDE 50
w w w. t r a n s p o r t a t i o n . o h i o . g o v
50
Maintenance Access
SLIDE 51
w w w. t r a n s p o r t a t i o n . o h i o . g o v
51
FEMA Floodplain
No BMPs in FEMA Floodplain
Floodplains have open space for a reason
No fill in FEMA Floodplain
Unless compensatory cut/fill analysis
Confirm limits of det. basin berms
- utside floodplain
SLIDE 52
w w w. t r a n s p o r t a t i o n . o h i o . g o v
52
ODNR Dam Permit
Only for big detention basins No permit needed if:
<10’ Berm and <50 ac-ft storage; or < 15 ac-ft storage; or < 6’ Berm
SLIDE 53
w w w. t r a n s p o r t a t i o n . o h i o . g o v
53
Re-Run the Numbers!
Many iterations After values are set, re-run the analyses and check
SLIDE 54
w w w. t r a n s p o r t a t i o n . o h i o . g o v
54
BMP Calcs Spreadsheet
SLIDE 55
w w w. t r a n s p o r t a t i o n . o h i o . g o v
55
Sample Plan Note W106
SLIDE 56
w w w. t r a n s p o r t a t i o n . o h i o . g o v
56
Questions ?
Jon Prier, P.E. jonathan.prier@dot.ohio.gov 614-644-1876