hydraulics E1

What are the components of the hydrologic cycle (7)

Precipitation, Evaporation, Infiltration, Depression Storage, Detention Storage, Runoff

What is the watershed/river basin/basin definition

All the runoff within that area flows out at a single point

What are the different methods of converting Point Precipitation into areal precipitation (3)

Arithmetic Average Method, Thiessen Polygon Method, Isohyetal Method,

Advantages and disadvantages of Arithmetic Average Method

Advantages: simple

Disadvantages: the area served by each gage isn’t taken into account

Advantages and disadvantages of the Thiessen Polygon Method

Advantages: Area weighted average

Disadvantages: Variation of rainfall within polygon is ignored

Advantages and disadvantages of the Isohyetal Method

Advantages: Area weighted average and variation of precipitation between gages is taken into account

Disadvantages: None

What does IDF curve stand for

Intensity duration frequency curves

What are IDF curves used for

IDF curves are used to find rainfall intensity given rainfall duration and the return period

What are the factors that effect evaporation (8)

Solar radiation

Wind speed

Air temperature

Relative humidity

Atmospheric pressure

Water quality

Geometry of the evaporating surface

What factors affect infiltration based on the NRCS method (4)

Hydrologic soil group

Hydrologic condition

Antecedent moisture condition

Land cover

What are the components of a stream flow hydrograph

know the diagram

Base flow

Rising limb

Peak discharge

Recession limb

What is a base flow

Existing flow in the stream before the storm event

What is the difference between streamflow and direct stream flow hydrographs

DSFH = SFH - BF

How do we determine excess rainfall or direct runoff from stream flow hydrograph

1) find DSFH = SFH - BF

Runoff or excess rainfall = area under the curve

What is a unit hydrograph

A unit hydrograph is a DSFH produced by a storm of tr-duration on a given watershed and has excess rainfall of 1 unit

How are unit hydrographs used

-UH is used to find SFH for a given storm event over the same watershed.

-The duration of UH and the duration of the storm event must be the same

Why do we need to change the duration of a unit hydrograph

Since the UH reflects the characteristics of the watershed, we must have a UH for the same watershed for which a SFH is required

What is the difference in derivation for a UH for gauged and ungauged watersheds

• for a gauged watershed we use storm event of tr duration and corresponding SFH to generate a UH of tr-duration

• For an ungauged watershed we use watershed physical characteristics to find key features of UH

How do you determine a stream flow hydrograph for a rainfall of tr-1-hour duration in a watershed, if a unit hydrograph tr-2- hour duration for the same watershed is given

• find a UH fr tr1 duration from a UH of tr2 duration using s-curve method

• Find ER in the rain event using NRCS or phi index

• (UH of tr1 duration)*ER= DSFH

• DSFH+BF= SFH

Define pressure, pressure head, elevation head, hydraulic head, or piezometric head

know the equations

What is piezometer and what does it measure

A tube that is open to the atmosphere at one end and is connected to liquid at the other end

What does a piezometer measure

It measures pressure head or hydraulic head at its opening in the liquid

What is the difference between hydraulic conductivity and intrinsic permeability

-hydraulic conductivity is a function of both fluid properties and soil properties

• intrinsic permeability is a fraction of only soil properties and is independent of fluid properties

What is the difference between Darcy’s velocity and seepage velocity

-Darcy’s velocity assumes flow takes place through the whole area of soil (ignoring the area occupied by soil properties)

-seepage velocity correctly assumes flow only takes place through the voids in the total area representing the actual velocity

What physical principles govern flow in multilayered systems (layering parallel and perpendicular to flow)

Laying parallel to flow: Qt = Q1 + Q2 + Q3 + …

Laying perpendicular to flow: Qt = Q1 = Q2 = Q3 = Q3