Open Channel Design and Case Studies Barry Baker

Open Channel Design and Case Studies Barry Baker June 1, 2012

My Background BA – Ambassador College BS – Civil Engineering – University of Washington Professional Engineer (Civil) – WA My Job: n. Consulting Engineering Firm – Gray & Osborne, Inc. n. Head of GIS Group/Stormwater Group n. Surface Water Engineering for Small to Medium Cities n. Planning & Design to meet Stormwater Regulations n. Stream/River Bank Restoration and Stabilization n. Sediment Transport/Management n. Levee Construction and Setback Levee/Stream Restoration n. Associated permitting related to storm and surface waters

Lecture Take-aways Water runs downhill (and the resultant consequences) The equations are the easy part (but you need to learn how they are determined and what each element represents)

Overview Open Channel Flow: Fluid passageway that allows part of the fluid to be exposed to the atmosphere. Pipes (not pressurized system) Channels Control Weirs Orifices Real World Examples

Open Channel – Primary Equations Mannings Equation(s): Orifice Discharge Weir Discharge

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

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

Mannings Equation Challenge is in finding n, A, and r Mannings n values Estimate based on substrate HDPE pipe (smooth wall) 0. 009 Brass or glass 0. 009 -0. 013 Clean cast iron 0. 012 -0. 015 Dirty tuberculated cast iron 0. 015 -0. 035 Wood stave 0. 011 -0. 013 Concrete 0. 011 -0. 017 Smooth earth 0. 018 Firm gravel 0. 023 Corrugated metal pipe 0. 022 Natural channels (good condition) 0. 025 Natural channels (stones/weeds) 0. 035 Natural channels (very poor) 0. 060 Cobbles/boulders 0. 075

Mannings Equation Mannings n values make a big difference in flow. Assuming a trapezoidal channel, 20 ft wide at the bottom, 1 H: 1 V side slopes, 1 ft depth of flow, and channel slope of 0. 002 ft/ft, the table below represents only a change in the n value n 0. 009 0. 013 0. 017 0. 022 0. 035 0. 075 Q 180 125 95 74 46 22 % of Flow 100% 69% 53% 41% 26% 12%

Mannings Equation Also difficult to find the factors of area and hydraulic radius, such as depth of flow, bottom width, and side slopes, when you have the flow rate

Open Channel – Nomographs

Sanitary Sewer Analysis Basin Flows n n n 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 Downstream Rim Upstream Rim Length Downstream Invert Upstream Invert

Pipe Capacity 31. 5 30. 3 370 ft 23. 3 23. 6

Open Channel – Primary Equations Mannings Equation(s):

Flow Estimate n n n Calculate existing flow Calculate proposed flow Compare to existing capacity = 12. 2 mgd

n Map of Puyallup Study area

Flow Estimate n n n Number of houses, apartments, businesses Number of people per dwelling Water use person Peaking factor Infiltration & Inflow

Existing Flow Estimate n n n Houses/connections Provided by City Planning or Public Works 1. 8 to 2. 9 people per dwelling 65 gallons 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 n n n Houses/connections Provided by City Planning or Public Works 1. 8 to 2. 9 people per dwelling 65 gallons person per day Peaking factor ranges 2. 0 to 4. 5 Infiltration & Inflow 1, 100 gallons per acre per day 17, 100 * 2. 9 * 65 * 2. 5 + 1, 100 * 4, 500 = 13 mdg

Proposed Flow Estimate n n n Houses/connections Provided by City Planning or Public Works 1. 8 to 2. 9 people per dwelling 65 gallons person per day Peaking factor ranges 2. 0 to 4. 5 Infiltration & Inflow 1, 100 gallons per acre per day 25, 000 * 2. 9 * 65 * 2. 5 + 1, 100 * 4, 500 = 17 mdg

Sanitary Sewer Analysis Land 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 79. 0 83. 6 91. 8 Infiltration & Inflow Acres 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 44, 337 55, 785 76, 077

Sanitary Sewer Analysis Basin Flows Study Alternative No Action 1 2 Total Flow (gpd) Change from Comp Plan Flow Scenario North South 1 (N) 376, 105 406, 257 167, 603 - 2 (S) 208, 503 376, 105 - (30, 152) 3 (N&S)* 197, 023 (11, 480) (209, 234) 1 (N) 649, 935 406, 257 441, 432 - 2 (S) 208, 503 649, 935 - 243, 677 3 (N&S)* 340, 981 132, 479 (65, 276) 1 (N) 839, 706 406, 257 631, 203 - 2 (S) 208, 503 839, 706 - 433, 448 3 (N&S)* 441, 181 232, 678 34, 924 208, 503 406, 257 20 -Year Comp Plan *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 Upstream Node Downstre am Node Pipe Dia. (in. ) Buildout Slope Length (ft) Design Capacit y (mgd) Flow (mgd) Excess Capacity (mgd) Flow (mgd ) Sur ch arg e (ft) Excess Capacit y (mgd) Buildout with CIP Flow (mgd) New Pipe Dia. (in. ) Exces s Capac ity (mgd) CIP Project ID 42 4. 03 NW-5 South Basin Flows 80 -046 80 -078 36 0. 08% 370 12. 27 20. 61 -8. 34 26. 22 2. 0 -13. 94 14. 48 80 -056 80 -046 36 0. 16% 370 17. 36 20. 61 -3. 25 26. 22 2. 8 -8. 86 14. 48 2. 88 80 -060 80 -056 36 0. 24% 210 21. 03 20. 61 0. 42 26. 22 3. 0 -5. 18 14. 48 6. 55 80 -063 80 -060 36 0. 15% 20 16. 69 20. 61 -3. 92 26. 22 3. 1 -9. 52 14. 48 2. 21 80 -071 80 -063 36 0. 18% 150 18. 29 20. 52 -2. 23 26. 19 3. 4 -7. 90 14. 45 3. 84 113 -007 80 -071 36 0. 23% 350 20. 61 20. 52 0. 09 26. 19 3. 9 -5. 58 14. 45 6. 16 113 -017 113 -007 36 0. 26% 380 22. 11 20. 45 1. 66 26. 14 4. 2 -4. 02 14. 40 7. 72 113 -021 113 -017 36 0. 15% 325 16. 91 20. 16 -3. 26 25. 20 4. 7 -8. 29 13. 39 3. 51 113 -028 113 -021 36 0. 08% 265 11. 84 20. 08 -8. 23 25. 17 4. 0 -13. 33 0. 00 11. 84 NW-4

Sanitary Sewer Analysis Basin Flows n n 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 Design Stormwater NPDES Permit requires treatment of average annual storm AND provide capacity for 100 -year storm Bioswale (grass lined ditch) is a prescriptive method of water quality treatment allowed by the Washington State Department of Ecology Stormwater Management Manual for Western Washington.

Open Channel – Bioswale Design Develop Hydrologic Flows Runoff from precipitation events (WWHM) Model Input to determine flows 10 acres 6. 5 Dwelling units/acre Moderate slopes C 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. 61 800 12% 1. 19 Total Impervious Areas 4650 69% 6. 94 Total Lot + Frontage 6700 100% Total Pervious Areas (Lawn) 2050 31% Patios, decks, hardscapes 3. 06

Open Channel – Bioswale Design Develop Hydrologic Flows = Run the model Flow Frequency - Flow(CFS) WQ On-line BMP = 1. 4276 2 Year = 3. 0153 5 Year = 4. 0518 10 Year = 4. 7903 25 Year = 5. 7848 50 Year = 6. 5714 100 Year = 7. 3980 Treatment Storm Runoff = 1. 43 cfs 100 -year Storm Runoff = 7. 40 cfs

Solve for b with simplifying assumptions (see DOE Manual) Top of swale >>y Z^2 >>1 R~y (hydraulic radius ~ depth)

Open Channel – Bioswale Design Calculate bottom width based on: Mannings “n” = 0. 2 for WQ event Design depth of flow = 2” (typical mower height) Longitudinal slope = 0. 02 ft/ft b= 26 ft Manual allows no greater than 10 ft Increase depth of flow to 4” b= 8. 12 ft Okay

Open Channel – Bioswale Design Calculate flow velocity and residence time Calculate area of flow (trapezoid) = 3. 162 sf Calculate velocity = 0. 4515 ft/s Velocity must be < 1 ft/s Okay Requires 9 minutes residence time ÞLength = 540 s * 0. 4515 ft/s = 244 ft Do you have that much space?

Open Channel – Bioswale Design Check 100 year flow velocity Mannings Equation again to find depth of flow (n value will change) Calculate area of flow (trapezoid) = 2. 944 sf Calculate velocity = 2. 5128 ft/s Velocity must be < 3 ft/s Okay

Open Channel – Bioswale Design Spreadsheet greatly simplifies the math. But 4” of grass and length of bioswale may not be acceptable to the client. Alternative treatment method may be needed, even if the capital cost is much higher.

Flow Splitter Design Filtration treatment requires much less real estate but has a much higher capital cost. Biowswale cost ~$2, 000 Filtration Unit ~$75, 000

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

Flow Splitter Design Plan Treated Stormwater Outfall High flow Bypass Water Quality flow Incoming flow

Flow Splitter Design Section WQ Discharge Orifice

Open Channel – Primary Equations Orifice Discharge

Flow Splitter As-built Section WQ Discharge Orifice

Flow Splitter As-built Plan WQ Discharge Orifice

Flow Splitter Retrofit Plan WQ Discharge Orifice

Flow Splitter Retrofit Section Sharp crested weir WQ Discharge Orifice

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

Open Channel – Primary Equations Weir Discharge

Sediment Control Vault

Questions?