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Basics of Reservoir Operations. Computer Aided Negotiations Fall 2008 Megan Wiley Rivera. 0:10. 1:45. Watershed water balance. 2:40. Water Budgets—Conservation of Mass. Mass is not created or destroyed What goes in – what comes out = change in what’s inside. 3:30. $50. ATM $2000 in

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Basics of reservoir operations

Basics of Reservoir Operations

Computer Aided Negotiations

Fall 2008

Megan Wiley Rivera



Watershed water balance

1:45

Watershed water balance


Water budgets conservation of mass

2:40

Water Budgets—Conservation of Mass

  • Mass is not created or destroyed

  • What goes in – what comes out = change in what’s inside


Apply conservation of mass to an atm interaction

3:30

$50

ATM

$2000 in

account

$30

Apply conservation of mass to an atm interaction

  • Starting balance: $2000

  • Deposit a check for $50

  • Take out $30

  • Ending balance: $2020

What goes in – what comes out = change in what’s inside (final balance – initial balance)

$50 – $30 = $2020 - $2000


A dollar is easier to track than a unit of water

4:05

A dollar is easier to track than a unit of water

  • Water is “incompressible”

  • a unit volume of water is not created or destroyed

  • Must define boundaries to apply equation (control volume)


Time must be considered as well

5:15

Time must be considered as well

  • Often times, inflows and outflows are measured as flow rates

  • The change in storage must therefore also be specified over some length of time


Try it for a britta filter

6:20

Try it for a Britta Filter

  • How long can you leave your Britta pitcher filling in the sink before it starts overflowing?


Draw a control volume

6:50

Draw a Control Volume


Some numbers

Inflow, Qin = 2.5 gpm

Outflow, Qout = 1 gpm (note, this is a cheat. The outflow flow rate increases as the chamber fills)

Chamber dimensions: 8” tall, 24 in2 cross sectional area

1 cubic in = 0.00433 gals

7:00

Some Numbers


The equation

What goes in – what comes out = change in what’s inside

Qin – Qout = dV/dt

Work with a partner to figure it out

8:40

The Equation


Feel free to ask someone else if you get stuck there are different approaches

Inflow, Qin = 2.5 gpm

Outflow, Qout = 1 gpm (note, this is a cheat. The outflow flow rate increases as the chamber fills)

Chamber dimensions: 8” tall, 24 in2 cross sectional area

1 cubic in = 0.00433 gals

Feel free to ask someone else if you get stuck (there are different approaches)

Qin – Qout = dV/dt


The answer

Initial volume = 0

Final volume = 24 in2 * 8” = 192 in3

Convert to gallons: 192 in3 * (0.00433 gal/1 in3) = 0.83 gal

Apply equation: 2.5 gpm – 1 gpm = 0.83 gal/x min

Solve equation: x min = 0.83 gal/(1.5 gpm) = 0.55 min or about 30 second

12:30

The Answer


Now let s apply it to a reservoir

13:00

town

dam

lake

river

Now Let’s Apply It to a Reservoir



Draw control volume and specify inflows and outflows1

14:50

Draw Control Volume and Specify Inflows and Outflows

evaporation

Effluent (returns)

precipitation

Water supply diversions (demands)

Dam release

runoff

Groundwater exchange


An aside identifying consumptive uses water removed from the basin

16:15

An Aside: Identifying Consumptive Uses (water removed from the basin)

evaporation

evaporation

irrigation

infiltration

runoff

Groundwater exchange


An aside identifying consumptive uses water removed from the basin1
An Aside: Identifying Consumptive Uses (water removed from the basin)

evaporation

Effluent (returns)

Water supply diversions (demands)

Other consumptive uses (e.g. manufacturing)

runoff


Back to conservation of mass

24:45

Back to Conservation of Mass

Net demands, D

Net Evapotransporation, ET

evaporation

Effluent (returns)

precipitation

Water supply diversions (demands)

Dam release

runoff

Groundwater exchange

Qout

Unimpaired inflow, I


What is unimpaired inflow

25:35

What Is Unimpaired Inflow?


Why might we want to calculate it

26:25

Why Might We Want to Calculate It

  • If you want to model different operational scenarios, you need to know how much water is reaching the river via runoff (as opposed to upstream operations)

  • Also gives information about flow in the river without the presence of reservoirs (possible point of comparison)


Use the equation to calculate unimpaired inflows daily average

32:20

Use the equation to calculate unimpaired inflows (daily average)

Net demands, D

Net Evapotransporation, ET

evaporation

Effluent (returns)

precipitation

Water supply diversions (demands)

Dam release

runoff

Groundwater exchange

Qout

Unimpaired inflow, I


Use the equation to calculate unimpaired inflows daily average1
Use the equation to calculate unimpaired inflows (daily average)

Measured/modeled/estimated from meteorological info

measured

Net Evapotransporation, ET

Net demands, D

measured

Qout

Beginning and end of day stages

measured

Unimpaired inflow, I


Storage area elevation table

32:30 average)

Storage-Area-Elevation Table

Surface area

elevation

Storage = volume of water

Mean sea level


Use the equation to calculate unimpaired inflows daily average2

32:40 average)

Net Evapotransporation, ET

Net demands, D

Qout

Beginning and end of day stages

Unimpaired inflow, I

Use the equation to calculate unimpaired inflows (daily average)

  • What goes in – what comes out = change in what’s inside

  • Qin – Qout = dV/dt, or over the day:

  • Qin,daily ave – Qout, daily ave = Storageend of day – Storagebeginning of day

  • I – ET – Qout – D = Storageend of day – Storagebeginning of day

  • I = ET + Qout + D + Storageend of day – Storagebeginning of day

Work with your partner again


Use the equation to calculate unimpaired inflows daily average3

35:20 average)

Net Evapotransporation, ET

Net demands, D

Qout

Beginning and end of day stages

Unimpaired inflow, I

Use the equation to calculate unimpaired inflows (daily average)

  • What goes in – what comes out = change in what’s inside

  • Qin – Qout = dV/dt, or over the day:

  • Qin,daily ave – Qout, daily ave = Storageend of day – Storagebeginning of day

  • I – ET – Qout – D = Storageend of day – Storagebeginning of day

  • I = ET + Qout + D + Storageend of day – Storagebeginning of day


Fun with units

Net Evapotransporation, ET average)

Net demands, D

Qout

Beginning and end of day stages

Unimpaired inflow, I

Fun with units

  • I = ET + Qout + D + Storageend of day – Storagebeginning of day

0.3”

50 mgd

100 cfs

Stage = 54’

Stage = 53’

Do calculations first in af/day and then mgd


Basics of reservoir operations

39:30 average)

Net Evapotransporation, ET

Net demands, D

Qout

Beginning and end of day stages

Unimpaired inflow, I

  • I = ET + Qout + D + Storageend of day – Storagebeginning of day

0.3”

50 mgd

100 cfs

Stage = 54’

Stage = 53’

Do calculations first in af/day and then mgd


Basics of reservoir operations

0.3” average)

50 mgd

  • I = ET + Qout + D + Storageend of day – Storagebeginning of day

100 cfs

Stage = 54’

Stage = 53’

ET: Multiply by average surface area for the day (see SAE) = 2026 acres

0.3” * 2026 acres = 0.025’ * 2026 acres = 50.7 af in one day

Outflow: 100 cfs * 1.98 af/day / 1cfs = 198 af/day

Demands: 50 mgd * 1 af/day / 3.069 mgd = 16 af/day

I = 50.7 af/day + 198 af/day + 16 af/day + (11957 af – 9930 af)/day = 2292 af/day

This is 747 mgd