Exam 3 Vocab

Question 1

The most common means used to indicate the probability of an event is to assign a return period, this is sometimes called a what?

Answer 1

Recurrence interval

Question 2

The probability that the event is equaled or exceeded in any one given year

Answer 2

1/T

Question 3

Probability of non-exceedance in a any year

Answer 3

(1-(1/T))

Question 4

Probability of non-exceedance in n years

Answer 4

(1-(1/T))^n

Question 5

Probability of a T storm occuring in n years

Answer 5

1 - (1-(1/T))^n1

Question 6

i =a/(t+b)^n
what unit is t?

Answer 6

minutes

Question 7

What is NRCS

Answer 7

National resources conservation service
Also known as SCS

They make synthetic hydrographs

Question 8

What is the purpose of the synthetic rainfall distribution (scs)

Answer 8

to approximate the temporal variation of the storm

Question 9

Huff distribution

Answer 9

1st quartile storms are intense early
4th quartile storms are most intense later

Question 10

Factors that affect Tc

Answer 10

surface roughness
rainfall intensity
distances
slopes

Question 11

As time of concentration decreases, peak flow blank?

Answer 11

increases

Question 12

Types of surface runoff

Answer 12

Sheet flow
shallow concentration
open channel

Question 13

Max distance of sheet flow

Answer 13

100 feet

Question 14

What is the difference between an open channel and a shallow concentrated flow

Answer 14

A shallow concentrated cross-sectional area is not defined

Question 15

What design storm is used for sheet flow NRCS method

Answer 15

depth for 2 year 24 hr

Question 16

Units of sheet flow NRCS
Tt =0.007(nL)^0.8/((P2^0.5)(S^0.4)

Answer 16

Tt = hours
n - unitless
L - feet
P2 - in
S - ft/ft

Question 17

Kinematic wave units
Tt = 0.94*n^0.6 * L^0.6 /((i^0.4 * S ^0.3

Answer 17

Tt = minutes
L =feet
i = in/hr
S = ft/ft

Question 18

Velocity equations for shallow flow

Answer 18

V = 20.238S^0.5 - pavement
V = 16.135S^0.5 - grass

Question 19

Tt equation for shallow flow and open channel

Answer 19

Tt = L/ 3600*V

Question 20

Mannings equation

Answer 20

Programmed in calculator

Question 21

What is a unit hydrograph

Answer 21

That if the hydrograph is for one inch of rain
2 inches of rain will have the same shape but double the flow rate

Question 22

Fa + Ia =

Answer 22

storage
Ia = initial abstraction (before flow can begin)
Fa = retention that does not contribute to flow

Question 23

P = Pe + Fa + Ia

Answer 23

P = total precipiation
Pe = excess precipitation (contributes to flow)

Question 24

** know these equation
Pe = ?
S = ?
CNw = ?

Answer 24

([P-0.2(S)]^2)/[P+ 0.8S] in inches

1000/CN - 10

CNw= Sum(CN*A)i / total A

Question 25

Units of qp = 484AQ/ tp

Answer 25

qp = cfs
A - mi^2
Q = Pe - inches
tp - hours

Question 26

Tp = ?

Answer 26

time to peak
=0.67*tc

Question 27

Qp = ?

Answer 27

Qp = C* i * A
Qp -cfs
C - none
i - in/hr
A - acres

Question 28

Limitations of the rational method

Answer 28

used for small drainage basins

Not applicable if ponds of wetlands in the area

cannot predict time to peak

Question 29

Cw = ?

Answer 29

Sum (C*A)i / Sum Ai

Question 30

Why is there a min V is storm sewers

Answer 30

prevent sediments 2.5 ft/s

Question 31

why is there a max V in storm sewers

Answer 31

15 ft/s
Momentum forces structural damage

Question 32

Minimum slope for storm sewers

Answer 32

0.001 ft/ft

Question 33

circumfrence of a circle

Answer 33

2 * pi * r