open channel design and case studies barry baker june 1, 2012

Open Channel Design Open Channel Design and Case Studiesand Case Studies

Barry BakerBarry Baker

June 1, 2012June 1, 2012

My BackgroundMy BackgroundBA – Ambassador CollegeBA – Ambassador CollegeBS – Civil Engineering – University of WashingtonBS – Civil Engineering – University of WashingtonProfessional Engineer (Civil) – WAProfessional Engineer (Civil) – WA

My Job:My Job:Consulting Engineering Firm – Gray & Osborne, Inc.Consulting Engineering Firm – Gray & Osborne, Inc.Head of GIS Group/Stormwater GroupHead of GIS Group/Stormwater GroupSurface Water Engineering for Small to Medium Surface Water Engineering for Small to Medium CitiesCities

Planning & Design to meet Stormwater RegulationsPlanning & Design to meet Stormwater Regulations Stream/River Bank Restoration and StabilizationStream/River Bank Restoration and Stabilization Sediment Transport/ManagementSediment Transport/Management Levee Construction and Setback Levee/Stream RestorationLevee Construction and Setback Levee/Stream Restoration Associated permitting related to storm and surface watersAssociated permitting related to storm and surface waters

Lecture Take-awaysLecture Take-aways

Water runs downhillWater runs downhill(and the resultant consequences) (and the resultant consequences)

The equations are the easy The equations are the easy partpart(but you need to learn how they are (but you need to learn how they are determined and what each element determined and what each element represents) represents)

OverviewOverview

Open Channel Flow: Open Channel Flow: Fluid passageway that allows part of the Fluid passageway that allows part of the fluid to be exposed to the atmosphere.fluid to be exposed to the atmosphere.

Pipes (not pressurized system)Pipes (not pressurized system)ChannelsChannelsControlControl

WeirsWeirsOrificesOrifices

Real World ExamplesReal World Examples

Open Channel – Primary Open Channel – Primary EquationsEquations

Mannings Mannings Equation(s):Equation(s):

Orifice DischargeOrifice Discharge

Weir DischargeWeir Discharge

sHnV R 3

249.1 sHA

nQ R 3

249.1

ghCAQ 2

HgCbQ 23

232

Mannings EquationMannings Equation

sHAn

Q R 3249.1

Q = flow (cfs)Q = flow (cfs)n = friction valuen = friction valueA = cross sectional area (sf)A = cross sectional area (sf)R = hydraulic radius (A/P)R = hydraulic radius (A/P)s = slope (ft/ft)s = slope (ft/ft)


sHAn

Q R 3249.1

Q = flow (cfs)Q = flow (cfs)n = friction valuen = friction valueA = cross sectional area (sf)A = cross sectional area (sf)R = hydraulic radius (A/P)R = hydraulic radius (A/P)s = slope (ft/ft)s = slope (ft/ft)

3

2

2

3

i

iic P

nPn

Mannings EquationMannings EquationHDPE pipe (smooth wall)HDPE pipe (smooth wall) 0.009 0.009 Brass or glassBrass or glass 0.009-0.013 0.009-0.013 Clean cast ironClean cast iron 0.012-0.0150.012-0.015Dirty tuberculated cast ironDirty tuberculated cast iron0.015-0.0350.015-0.035Wood stave Wood stave 0.011-0.0130.011-0.013Concrete Concrete 0.011-0.0170.011-0.017Smooth earthSmooth earth 0.0180.018Firm gravelFirm gravel 0.0230.023Corrugated metal pipeCorrugated metal pipe 0.0220.022Natural channels (good condition)Natural channels (good condition)0.0250.025Natural channels (stones/weeds)Natural channels (stones/weeds)0.0350.035Natural channels (very poor)Natural channels (very poor) 0.0600.060Cobbles/bouldersCobbles/boulders 0.0750.075

Estimate based on substrateEstimate based on substrate

sHAn

Q R 3249.1

Challenge is in Challenge is in finding n, A, and finding n, A, and rr

Mannings n Mannings n valuesvalues

6

1

75CDn

Mannings EquationMannings EquationMannings n values make a big difference in flow. Assuming a Mannings n values make a big difference in flow. Assuming a trapezoidal channel, 20 ft wide at the bottom, 1H:1V side trapezoidal channel, 20 ft wide at the bottom, 1H:1V side slopes, 1 ft depth of flow, and channel slope of 0.002 ft/ft, the slopes, 1 ft depth of flow, and channel slope of 0.002 ft/ft, the table below represents only a change in the n valuetable below represents only a change in the n value

n Q % of Flow

0.009 180 100%

0.013 125 69%

0.017 95 53%

0.022 74 41%

0.035 46 26%

0.075 22 12%


sARn

Q49.1

Also difficult to find the factors of area Also difficult to find the factors of area and hydraulic radius, such as depth of and hydraulic radius, such as depth of flow, bottom width, and side slopes, flow, bottom width, and side slopes,

when you have the flow ratewhen you have the flow rate

Open Channel – Open Channel – NomographsNomographs

Sanitary Sewer AnalysisBasin Flows

New density of development proposed for existing sewered basin.

Calculate the capacity of existing pipe Estimate flows from new development

density Does the existing pipe have capacity or

not If not, how much will it cost to upgrade

Pipe Capacity

L

IEIEs du

22

4drA

drP 2

Downstream Rim

Upstream Rim

Downstream Invert

Upstream Invert

Length

P

ARH

sHAn

Q R 3249.1

Pipe Capacity

0008.0370

3.236.23

s

068.734

22 rA

425.932 rP

31.5 30.3

23.323.6

370 ft

75.0425.9

068.7

P

ARH

mgdcfsQ 224.1292.180008.075.0*068.7013.0

49.13

2


Mannings Mannings Equation(s):Equation(s):Mannings Equation for partially full gravity pipe flow

Q= 26.2180 1.5 radius of pipen= 0.0130 3.1415927 arccos(r-d)/r)s= 0.0008 7.0685835 Area of flowd= 3.0000 9.424778 Wetted perimeterD= 3.0000 0.75 Hydraulic radius

Unknown Quantity (calculated from input above)Q V n s d/D

18.91593 2.6760574 0.0093793 0.001537 1.00008474.339 gpm 12203048 mgd

Data input

Formula does not calculate d or D directly but can be found through iteration of other variables.

Flow Estimate

Calculate existing flow Calculate proposed flow Compare to existing capacity = 12.2

mgd

Map of Puyallup Study area

Flow Estimate

Number of houses, apartments, businesses

Number of people per dwelling Water use per person Peaking factor Infiltration & Inflow

Existing Flow Estimate

Houses/connections Provided by City Planning or Public Works

1.8 to 2.9 people per dwelling 65 gallons per person per day Peaking factor ranges 2.0 to 4.5 Infiltration & Inflow 1,100 gallons per acre per

day

10,700 * 2.9 * 65 * 2.5 + 1,100 * 4,500 = 10 mdg

Future Flow Estimate



day

17,100 * 2.9 * 65 * 2.5 + 1,100 * 4,500 = 13 mdg

Proposed Flow Estimate



day

25,000 * 2.9 * 65 * 2.5 + 1,100 * 4,500 = 17 mdg

Sanitary Sewer AnalysisLand Use

Study Area Sanitary Sewer Comp Plan

No

Action Alternative 1 Alternative 2 Existing 2030 Buildout

Residential Dwellings

419 817 1,137 382 793 1,522

Population 930 1,814 2,524 925 1,722 3,135

Commercial Square Feet

446,526 871,541 1,136,114

Commercial Acres

83.6 83.6 83.6 79.0 83.6 91.8

Infiltration & Inflow Acres

50.7 50.7 50.7 40.3 50.7 69.2

Residential Average Flow

61,008 118,998 165,574 60,666 112,960 205,646

Commercial Average Flow

133,816 261,186 340,473 126,406 133,816 146,950

I&I Flow (gpd) 55,785 55,785 55,785 44,337 55,785 76,077


Study Alternative

Flow Scenario

Total Flow (gpd) Change from Comp Plan

North South North South

No Action

1 (N) 376,105 406,257 167,603 -

2 (S) 208,503 376,105 - (30,152)

3 (N&S)* 197,023 197,023 (11,480) (209,234)

1

1 (N) 649,935 406,257 441,432 -

2 (S) 208,503 649,935 - 243,677

3 (N&S)* 340,981 340,981 132,479 (65,276)

2

1 (N) 839,706 406,257 631,203 -

2 (S) 208,503 839,706 - 433,448

3 (N&S)* 441,181 441,181 232,678 34,924

20-Year Comp Plan 208,503 406,257*Changes in peaking factor based on tributary population accounts for greater total peak flow using the two smaller basins than all additional flow in one basin.

Existing Scenario Buildout Buildout with CIP

Upstream Node

Downstream Node

Pipe Dia. (in.) Slope

Length (ft)

Design Capacity (mgd)

Flow (mgd)

Excess Capacity

(mgd)

Flow (mgd

)

Surcharge

(ft)

Excess Capacity (mgd)

Flow (mgd)

New Pipe Dia. (in.)

Excess

Capacity

(mgd)CIP Project

ID

South Basin Flows

80-046 80-078 36 0.08% 370 12.27 20.61 -8.3426.2

2 2.0 -13.94 14.48 42 4.03 NW-5

80-056 80-046 36 0.16% 370 17.36 20.61 -3.2526.2

2 2.8 -8.86 14.48 2.88

80-060 80-056 36 0.24% 210 21.03 20.61 0.4226.2

2 3.0 -5.18 14.48 6.55

80-063 80-060 36 0.15% 20 16.69 20.61 -3.9226.2

2 3.1 -9.52 14.48 2.21

80-071 80-063 36 0.18% 150 18.29 20.52 -2.2326.1

9 3.4 -7.90 14.45 3.84

113-007 80-071 36 0.23% 350 20.61 20.52 0.0926.1

9 3.9 -5.58 14.45 6.16

113-017 113-007 36 0.26% 380 22.11 20.45 1.6626.1

4 4.2 -4.02 14.40 7.72

113-021 113-017 36 0.15% 325 16.91 20.16 -3.2625.2

0 4.7 -8.29 13.39 3.51

113-028 113-021 36 0.08% 265 11.84 20.08 -8.2325.1

7 4.0 -13.33 0.00 11.84 NW-4


Nine pipes exceed capacity for the planned flow Project NW-4 Estimated Cost $202,00 Project NW-5 Estimated Cost $480,000 Project VT-1 Estimated Cost $3,929,000

Open Channel – Bioswale Open Channel – Bioswale DesignDesign

Stormwater NPDES Permit requires Stormwater NPDES Permit requires treatment of average annual storm treatment of average annual storm AND provide capacity for 100-year AND provide capacity for 100-year stormstorm

Bioswale (grass lined ditch) is a Bioswale (grass lined ditch) is a prescriptive method of water quality prescriptive method of water quality treatment allowed by the Washington treatment allowed by the Washington State Department of Ecology State Department of Ecology Stormwater Management Manual for Stormwater Management Manual for Western Washington.Western Washington.


Develop Hydrologic Flows Develop Hydrologic Flows Runoff from precipitation events (WWHM)Runoff from precipitation events (WWHM)

Model Input to determine flowsModel Input to determine flows

10 acres10 acres6.5 Dwelling units/acre6.5 Dwelling units/acreModerate slopesModerate slopesC SoilsC Soils

Model Input

Typical Lot Coverage

Percent of Gross Area 10

Lot Size 5000 75% 7.46

Street Frontage 1200 18% 1.79

Sidewalk Width 500 7% 0.75

Vehicle Parking Area (#) 400 6% 0.60

House Coverage - 35% 1750 26% 2.61

Patios, decks, hardscapes 800 12% 1.19

Total Impervious Areas 4650 69% 6.94

Total Lot + Frontage 6700 100%

Total Pervious Areas (Lawn) 2050 31% 3.06

Percent Impervious 69%


Develop Hydrologic Flows = Run the Develop Hydrologic Flows = Run the modelmodel

Flow Frequency - Flow(CFS) Flow Frequency - Flow(CFS) WQ On-line BMP = 1.4276WQ On-line BMP = 1.42762 Year = 3.0153 2 Year = 3.0153 5 Year = 4.0518 5 Year = 4.0518 10 Year = 4.7903 10 Year = 4.7903 25 Year = 5.7848 25 Year = 5.7848 50 Year = 6.5714 50 Year = 6.5714 100 Year = 7.3980100 Year = 7.3980

Treatment Storm Runoff = 1.43 cfsTreatment Storm Runoff = 1.43 cfs100-year Storm Runoff = 7.40 cfs100-year Storm Runoff = 7.40 cfs

Solve for b with simplifying assumptions (see DOE Manual)

sd

Qnb

2/549.1

Top of swale >>y

Z^2 >>1

R~y (hydraulic radius ~ depth)


Calculate bottom width based on: Calculate bottom width based on:

Mannings “n” = 0.2 for WQ eventMannings “n” = 0.2 for WQ eventDesign depth of flow = 2” (typical mower Design depth of flow = 2” (typical mower height)height)Longitudinal slope = 0.02 ft/ftLongitudinal slope = 0.02 ft/ft

b= 26 ft Manual allows no greater than 10 b= 26 ft Manual allows no greater than 10 ftft

Increase depth of flow to 4” Increase depth of flow to 4”

b= 8.12 ft Okayb= 8.12 ft Okay


Calculate flow velocity and residence Calculate flow velocity and residence timetime

Calculate area of flow (trapezoid) = 3.162 Calculate area of flow (trapezoid) = 3.162 sfsfCalculate velocity = 0.4515 ft/sCalculate velocity = 0.4515 ft/s

Velocity must be < 1 ft/s OkayVelocity must be < 1 ft/s Okay

Requires 9 minutes residence timeRequires 9 minutes residence time

Length = 540 s * 0.4515 ft/s = 244 ftLength = 540 s * 0.4515 ft/s = 244 ft

Do you have that much space? Do you have that much space?


Check 100 year flow velocity Check 100 year flow velocity

Mannings Equation again to find depth of Mannings Equation again to find depth of flow flow (n value will change)(n value will change)

Calculate area of flow (trapezoid) = 2.944 Calculate area of flow (trapezoid) = 2.944 sfsfCalculate velocity = 2.5128 ft/sCalculate velocity = 2.5128 ft/s

Velocity must be < 3 ft/s OkayVelocity must be < 3 ft/s Okay

5

3

49.1

sb

Qnd


Spreadsheet greatly simplifies the Spreadsheet greatly simplifies the math.math.

But 4” of grass and length of bioswale But 4” of grass and length of bioswale may not be acceptable to the client. may not be acceptable to the client.

Alternative treatment method may be Alternative treatment method may be needed, even if the capital cost is much needed, even if the capital cost is much higher. higher.

Flow Splitter DesignFlow Splitter Design

Filtration treatment requires much less Filtration treatment requires much less real estate but has a much higher real estate but has a much higher capital cost. capital cost.

Biowswale cost ~$2,000Biowswale cost ~$2,000Filtration Unit ~$75,000Filtration Unit ~$75,000

Flow Splitter DesignFlow Splitter Design

Filtration system has limited Filtration system has limited overflow/bypass capacity. Too much overflow/bypass capacity. Too much high flow will lead to re-suspension of high flow will lead to re-suspension of solids and cause turbidity downstream. solids and cause turbidity downstream. Solution is to split WQ treatment flow to Solution is to split WQ treatment flow to the filtration system and by pass higher the filtration system and by pass higher flows.flows.

Flow Splitter Design PlanFlow Splitter Design Plan

Incoming flow

High flow Bypass

Water Quality flow

Treated Stormwater Outfal

l

Flow Splitter Design SectionFlow Splitter Design Section

WQ Discharge

Orifice


Orifice DischargeOrifice Discharge

Stage

Total Discharge (cfs)

Orifice 1 Discharge

Orifice 2 Discharge 0.62 Orifice Height (ft) Elevation

Diameter (inches) Area (sf)

0.0 0 1 0 0.0 7 0.26730.2 0.594666 0.594666 0 2 1 0.8 12 0.78540.4 0.840985 0.840985 0 3 0 0 0 0.00000.6 1.029992 1.029992 00.8 1.189332 1.189332 01.0 1.329714 1.329714 01.2 3.204218 1.456628 1.747591.4 4.044803 1.573338 2.4714651.6 4.708884 1.681969 3.0269141.8 5.279178 1.783998 3.495182.0 5.788229 1.880499 3.907732.2 6.252987 1.972284 4.2807032.4 6.683671 2.059983 4.6236882.6 7.087029 2.144099 4.942932.8 7.467806 2.225036 5.2427693.0 7.829496 2.303131 5.526364

ghCAQ 2

Flow Splitter As-built SectionFlow Splitter As-built Section

WQ Discharge

Orifice

Flow Splitter As-built PlanFlow Splitter As-built Plan

WQ Discharge

Orifice

Flow Splitter Retrofit PlanFlow Splitter Retrofit Plan

WQ Discharge

Orifice

Flow Splitter Retrofit SectionFlow Splitter Retrofit Section

WQ Discharge

Orifice

Sharp crested

weir


Weir DischargeWeir DischargeSharp Rectangular Weir, free outfall

H = 0.2 ftY = 4 ft

b_actual = 4 ftContracted? y

N= 2b_eff = 3.96 ft

C1= 0.622Q = 1.178642885 cfsQ= 528.9749266 gpm

Submurged CorrectionH_upstream = 0.2

H_downstream = 0.083333333Q_submurged = 1.044720757

At 0.2 ft, the overflow will nearly match the orifice flow to the WQ filtration system.

At 0.6 ft of head, the overflow will convey all the overflow up to the 100-year event

Sediment Trap DesignSediment Trap Design

Steep tributary basins contribute Steep tributary basins contribute significant sediment load that settles significant sediment load that settles out at the outlet of a large diameter out at the outlet of a large diameter culvert under I-90 in North Bend. culvert under I-90 in North Bend. Aggregation of the stream bed causes Aggregation of the stream bed causes flooding of the commercial outlet mall. flooding of the commercial outlet mall.


Weir DischargeWeir DischargeC= 3.367

Stage Incriment 0.33

Weir Height (ft) ElevationBottom Width (ft)

1 0 442.8 42 1 443.84 53 1.5 444.34 3

StageDepth of Flow (ft)

Velocity (ft/s)

Total Discharge

Weir 1 Discharge

Area Weir 1 (sf)

Weir 2 Discharge

Area Weir 2 (sf)

442.8 0.0 0.00443.2 0.3 2.9 3.93 2.59 1.33 0.00 0.00443.5 0.7 3.7 10.00 7.33 2.67 0.00 0.00443.8 1.0 4.4 17.47 13.47 4.00 0.00 0.00444.2 1.3 4.4 30.98 20.74 5.33 3.24 1.67444.5 1.6 4.7 48.83 28.98 6.67 9.16 3.33444.8 2.0 4.9 71.50 38.09 8.00 16.83 5.00445.2 2.3 5.3 97.61 48.00 9.33 25.92 6.67445.5 2.6 5.6 126.60 58.65 10.67 36.22 8.33445.8 3.0 6.0 158.16 69.98 12.00 47.62 10.00446.1 3.3 6.3 192.04 81.96 13.33 60.00 11.67446.5 3.6 6.6 228.09 94.56 14.67 73.31 13.33

HgCbQ 23

232

Sediment Control Vault

Questions?Questions?

open channel design and case studies barry baker june 1, 2012

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