Screen and Bypass Design

Bryan Nordlund, P.E.National Marine Fisheries Service

Lacey, WashingtonNote: this presentation represents the views of the presenter, and in most

cases, is based on fishway design experience in working for NMFS. Special thanks to Larry Swenson for the assistance with slide content.

Hydrology and Hydraulics

Hydrology and Hydraulics

Hydrology relates to the science dealing with the occurrence, circulation and distribution of water on the earth's lands and in the atmosphere.

Hydraulics refers to fluids in motion.

Hydrology doesn't make fish barriers (unless streamflow gets too low or too high), but hydraulics can create a barrier.

Determining Fishway Design Flows

Determining Fishway Design flows1. Locate daily average streamflow records (USGS,

BOR, other) and import into Excel.2. Determine Passage Season by discussion with

agency fish biologists. 3. Truncate daily flow records outside of Passage

Season.4. Sort remaining records by highest to lowest flow,

keeping date associated with flow record.5. Fishway Design Flow range is the stream flow range where all criteria should be achieved with design. 6. NMFS Design Flow Ranges: 95% - 5% exceedence flows (90% of Passage Season flows)

Example: Determining Fishway Design flows

For example, if the truncated flow records contain 2000 records:

The 5% exceedence flow (Q5) is the streamflow exceeded 5% of the days in the passage season.

The 95% exceedence flow (Q95)is the streamflow exceeded 95% of the days in the passage season.

Q5 is the 100th highest flow record of the sorted data set. (0.05 x 2000 = 100)

Q95 is the 1900th highest (or 100th lowest) flow record of the sorted data set. (0.95 x 2000 = 1900)

• Suppose assessment using previously demonstrated method yields: Q5 = 11,250 cfs and Q95 = 210 cfs.

• Using a tailwater rating curve, the water surface elevations for an bypass outfall location can be determined.

Example: Using 5% and 95% exceedence flow range in fish passage design

Some Dam Tailwater Rating Curve

River Flow, in CFS

Tailw

ater

Wat

er S

urfa

ce E

leva

tion,

in F

eet

Q5 = 11,250 cfsWSE = 628.8 ft

Q95 = 210 cfsWSE = 624.4 ft

More About Design Flow guidelines

• Fishway design flow should consider specific migration timing information for all species and life stages intended to pass.

• This will contract, expand or shift the design flow range.

• Providing optimal passage for 90% of the passage season does not mean that 10% of the run is not passed.

In some rivers, passage may be impaired by extreme flow events.

Note: Flow in lower ladder is flowing UP the ladder

Bonneville Dam – May31, 1948 985,000 CFS

More About Design Flow guidelines (continued)

• Passage of the entire run is expected to occur as streamflow conditions improve.

• Passage facilities can provide passage beyond the design flow range even if the facility is not within design criteria.

Data needs for determining screen and bypass flows

• Rating curves (flow vs.water surface elevation) and flow records for point of diversion, canal (if applicable), and bypass outfall. The greater the data range - the better, but often you will need to work with what you have.

• Maximum and minimum diverted flow.• Canal cross sections, at least at the proposed

screen site.

Hydraulic Calculations in Fishway Design

Hydraulics - Objective:

Given: hydrology, biological criteria, and the design criteria --1. Determine: size and hydraulic

capacity of key fishway components2. Calculate: Flow rates for

a) Weirsb) Orificesc) Open Channels

Properties of Water

16

Calculating Discharge (Q)

LJ SNOAA Fisheries4-28-03

Velocity Head• When water moves from point A to point B,

velocity head, is calculated by :• (equation 1) hv = V2 / 2g , where

• hv is velocity head differential from A and B• V is water velocity between A and B• g is the gravitational constant 32.2 feet per

second squared.

Velocity Head• Why does Velocity Head matter?

• Because if velocity is fast enough, the water surface will decrease downstream.

Example: velocity head as flow approaches a weir

If water velocity at point B is 4 fps, and at point A is nearly zero, then velocity head at point B is calculated as:

hv = V2 / 2g (equation 1) = (4 fps)2 /(2 x 32.2 ft/s2 ) = 16/64.4 (do units check?) = 0.25 feet

A velocity head of 0.25 feet means that the water surface will drop 0.25 feet from A to B, assuming that velocity at A is nearly zero.

Weir Flow – Free Discharge

Weir Flow – Free Discharge

Q=CwL(H +2 )3/2Vo

2g

Sharp crested weir

Where: Cw = Weir Coefficient (handbook) L = Weir Length H= Head across weir Vo

2/2g = Velocity Head

Equation 2:

Submerged Weir Flow

Submerged Weirs

Weir Flow – Submerged Discharge

Qsubmerged = Q/Q1 x Qunsubmerged

Example: Submerged Weir

Then Qsubmerged = 0.85 x Qunsubmerged,

with Qunsubmerged from equation 2

If H1=1 ft and H2 = .33 ft, then H2/H1=.33If H2/H1=.33, then Q/Q1= 0.85 (chart)

Orifice Flow – Free Discharge

Orifice Flow –Free Discharge

Free Discharge Orifice

DH

Orifice Flow – Contraction (Cc), Velocity (Cv) and Discharge (Cd) Coefficients

Thin Wall Orifices Short Tube Bell Mouth

(Circular) Orifice Flow – Free Discharge

Q = AV = CdAo(2gDH)0.5

Where :Cd is orifice discharge coefficient Ao is the area of the orificeΔH is the water surface drop through the orifice to impact point

Orifice Flow – Submerged Discharge

Orifice Flow – Submerged Discharge

Orifice Flow – Submerged Discharge

Orifice Flow – Submerged Discharge

Orifice Flow – Submerged Discharge

(Circular) Orifice Flow – Submerged Discharge

Cd = CcCv

Q = AV = CdAo(2gDH)0.5

Example: Priest Rapids Fishway Orifices

The entire fishway flow passes through two 18” x 24” orifices with a 0.75 foot difference in water surface elevation. The forebay velocity is 0.1 ft/s. Calculate the orifice flow rate.

Example: calculation of orifice flow• First, calculate the velocity head (equation 2): • hv = 0.12 / (2 x 32.2) = .00016 ft• Using equation 4: Q = 0.61 x A x [2g(H+ hv)] ½

• Q = 0.61 x 18/12 ft x 24/12 ft x [2 x 32.2 x (9/12 + 0.00016) ft] ½

• = 0.61 x 1.5 x 2 x 6.95 = 12.7 cfs, • Or, Q = 25.4 cfs for both orifices • Note that the calculated velocity head is negligible (slow

forebay velocity)• Note that the coefficient of 0.61 is only for a rectangular

orifice.• For further guidance on various orifice coefficients for a

variety of shapes, see “Water Measurement Manual”, U.S. Bureau of Reclamation, Denver, Colorado, 1981.

Open Channel Flow – Manning’s Equation

n = Manning’s Roughness Coefficient (find using Google)Rh = Hydraulic radius in feet = flow area (A) ÷ flow perimeter (p)So = Slope of channel in feet/feet

Note: Flow perimeter is where flow contacts the channel sides (not the water surface)

Open Channel Flow – Hydraulic Variables

Manning’s Equation – Rectangular Channel

Flow --->

250 feet

Elev. 1.0’

Elev.0.0’

Elevation View - Concrete channel

Cross section

3 feet

1 foot

Ao = 3 x 1 = 3 square feetSo = (1.0 – 0.0)/250 = 0.004 ft/ft

Rh = 1 +1 +3 = 5 feet

V= 1.49 0.015

N = 0.015 (smooth concrete)

x 52/3

x 0.0041/2

= 18.4 feet per second

Flow (Q) = V x A = 18.4 x 3 = 55 cubic feet per second

Modeling ToolsComputational Fluid Dynamics (CFD) Models Scaled Physical Models

Hydraulic Modeling

Numerical Modeling

Numerical Modeling

Handy Conversions1 cubic feet per second = 448.8 gallons per minute1 gallon per minute = 1440 gallons per day1 cubic meter per second = 35.31 cubic feet per second1 cubic foot per second = 2 acre-feet per day1 acre-foot per day = 0.504 cubic feet per second1 cubic feet = 7.48 gallons1 cubic foot of water = 62.4 pounds1 gallon of water = 8.34 pounds1 foot per second = 0.3048 meters per second(degrees F – 32) x 5/9 = degrees Celsius1 kilogram = 2.2 pounds1 foot per second = 1.097 kilometers per hour

= 0.682 miles per hour = 16.4 miles per day

Or e-mail me at Bryan.Nordlund@noaa.gov for a handy conversions freeware

The End