Equation Quick List

Flow Through


Suggested Equation
(Ac-Ft)*(0.01676)=CFS
or
(Ac-Ft)*(7.54)=GPM

When to use:
Flow through can only be permitted using the SW-1 and SW-2 forms and are used to supply off channel reservoirs with the use of fish with oxygenated water.

How to use:
You will need the capacity of the reservoir in acre-feet.


On Channel Reservoir Capacity


Suggested Equation
(Area*Depth)/3=Capacity

When to use:
Use this formula to calculate the capacity of a reservoir located in the channel of a water way when filing an SW-3 or SW-4.

How to use:
Calculate the area of the reservoir in acres
Use the maximum depth of water in feet
The results will be in acre-feet


Pit Reservoir Capacity Formula


Suggested Equation
((D/6)(area of top + area of bottom + 4* average area))/43560=Capacity in acre-feet

When to use:
Use this formula when applying for a reservoir on either SW-3 or SW-4 form and no water is to be stored above ground or against a berm.

How to use:
D is the maximum depth of the pit
Area of the top for a rectangular reservoir is length multiplied by the width
Area of bottom for a rectangular reservoir is the length multiplied by the width
Average area is the area of the top plus the area of the bottom divided by 2


Pump Formula


Suggested Equation
Q=HP(3960E)/T.D.H.

When to use:
When using a pump to apply water to lands using an SW-1 or SW-2 application not covered under Special Applications filings rules. If the filing falls in the category of Special Application the maximum amount of water that can be diverted is 0.056 Cubic Feet Per Second.

How to use:
HP is the horsepower of the pump which is typically found on the pump
T.D.H. is the total dynamic head (Total dynamic head includes the friction in the pipe as well as the lift it has to make. The friction in the pipe will vary by type of pipe used.)
E is the efficiency of the pump
Q is the discharge flow rate


Flow Rate Ditches


Suggested Equation Mannings
Q=(1.486AR^0.667S^.5)/n

When to use:
Use this formula for open channel earthen ditches filed for on an SW-1 or SW-2 form

How to use:
Q is the discharge flow rate
A is the area of the channel
R is the hydraulic radius, which is the area divided by the wetted perimeter
S is the slope
n is the Manning’s number


Gravity Flow Pipeline


Suggested Equations either Hazen-Williams or Weirs
Hazen-Williams
Q=VA
Q=A*(1.318*C)*(R^063)*(S^0.54)

Weirs
Q=CLH^(3/2)

When to use:
Use either of these equations for filing SW-1 or SW-2 forms for gravity and pressure flow pipelines

How to use:
Q is the discharge flow rate
V is the velocity
A is the Area
C is the Hazen-Williams Coefficient
R is the hydraulic radius
S is the slope
C is the coefficient of discharge
L is the length of the crest in feet
H is the feet of head