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Hydrology > Test 2 > Flashcards

Test 2 Flashcards

1
Q

What does routing flow do?

A

Determine Time & Magnitude of Flow at a point
downstream from an upstream hydrograph

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2
Q

Why do we route flow?

A
  • Account for changes in flow hydrograph as a flood wave
    passes downstream
  • This helps in
    – Accounting for storages
    – Studying the attenuation of flood peaks
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3
Q

What is flow routing?

A
  • Procedure to
    determine the flow
    hydrograph at a
    point on a
    watershed from a
    known hydrograph
    upstream
  • As the hydrograph
    travels, it
    – attenuates or
    gets delayed
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4
Q

What are the two routing methods?

A

Hydrologic [Lumped] and Hydraulic [Distributed]

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5
Q

Hydrologic [Lumped]

A

– Use inflow to calculate outflow
– Apply Continuity & Storage Eqs.
–Assumes level pool
– Flow is calculated as a function of time alone
at a particular location
– Governed by continuity equation and
flow/storage relationship

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6
Q

Hydraulic [Distributed]

A

– Examine Cross-Sections along stream
– Unsteady Flow Routing
– Saint Venant Equations (Kinematic, Diffusive,
Dynamic Wave)
– Uses Continuity & Momentum
– Flow is calculated as a function of space and
time throughout the system
– Governed by continuity and momentum
equations

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7
Q

Effects of routing

A

-Peak discharge is lower at downstream end
-Time to peak is greater at downstream due to lag and attenuation
-Volume is equal except for seepage

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8
Q

Level pool routing (Reservoir routing)

A

Procedure for calculating outflow
hydrograph Q(t) from a reservoir with
horizontal water surface, given its inflow
hydrograph I(t) and storage-outflow
relationship
* Given:
– Inflow Hydrograph
– Reservoir Characteristics
– Initial Conditions
* Find: Outflow Hydrograph Q(t)

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9
Q

What are the Storage discharge elevation inputs and out puts?

A
  • Input:
    1. Elevation – Storage (topography)
    2. Elevation – Discharge (hydraulics)
    *Output
    Storage indication curve
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10
Q

What are the impacts/ uses of river routing?

A

D/S impacts such as Flooding
- Local Impacts – such as for recreation, ecologic (fish)
- Energy / Hydro Power
- Water Quality / Chemical Spills (Gold King Mine,
Durango)

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11
Q

How do we calculate River Storage?

A

Muskingum Method
Method developed in Ohio River Basin to address
flood routing.
McCarthy (1938)
Most widely used method (Ponce 1989)

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12
Q

Muskingum Method

A

-River Channel Routing
- Variable Q and S relationship
- Prism and Wedge Storage

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13
Q

Total storage (muskingum)

A

Prism+ wedge

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14
Q

What do K and X in the muskingum

A

K = travel time through the reach
X = weighting factor based on channel shape

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15
Q

Why do we model Hydrology

A

● Planning, design, operation, and management of water resources
projects
● Watershed management
● Environmental protection
● Climate change
● And more!

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16
Q

What are some examples of Hydrologic/Hydraulic Modeling

A

● Flood protection projects
● Reservoir release planning
● Rehabilitation of aging dams
● Water supply forecasting
● Urban development
● Irrigation water management
● Wetland/Stream restoration
● Habitat/Riparian assessment
● Hydropower development
● Response to disturbance:
wildfire, bark beetle infestation

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17
Q

What do models simulate and predict?

A

● Streamflow/runoff
● Soil moisture
● Groundwater flow
● Contaminant transport
○ Nitrate, phosphate, TSS, TDS, E. coli, and more
● Latent heat flux (ET)
● Sensible heat flux
● And more!

18
Q

Open Channel Flow

A
  • Driven by gravity and geometry
  • Features a free surface with atmospheric
    pressure
19
Q

What is open channel flow characterized by?

A
  1. Position of free surface changes with time
    and space.
  2. Flow depth (y), flowrate (Q), slope of WS
    (Sw) and bed slope (So).
  3. Physical Condition of the channel:
    Slope, Roughness, etc.
20
Q

What are the three regimes of flow

A

Supercritical, sub critical, and critical

21
Q
  • Fr < 1
A

– Subcritical Flow
– Gravity dominates
– Waves can propagate upstream

22
Q
  • Fr > 1
A

– Supercritical Flow
– Inertial Forces dominate
– Waves propagate downstream only!

23
Q

Is open channel flow laminar or turbulent?

A

turbulent

24
Q

What are the open channel flow assumptions?

A

Pressure is zero (atmospheric)

25
Q

Specific energy

A

energy per lbf of water

26
Q

What is critical depth

A

The depth of flow corresponding to the
minimum E is the critical depth, yc

27
Q

What do we avoid critical flow in design?

A

it is unstable

28
Q

Flow Profile and Critical
Depth/Slope

A
  • Mild Slope / Subcritical slope
    – Depth due to Backwater
  • Critical Slope
    – Horizontal Level Pool
  • Steep / Supercritical slope
    – Hydraulic Jump
29
Q

Channel Control

A
  • Definition:
    – Establishment of definitive flow conditions for a
    channel
30
Q

Why do we control channels

A
  1. Gaging Stations
  2. Flow Meters: Weirs, Flumes
  3. GVF – Starts @ Control
31
Q

Hydraulic Structures

A
  • Hydraulic structures are used to regulate, measure, and/or
    transport water in OCs.
    –Flow-measuring structures (ex. Weirs)
    –Regulation structures (ex. Gates and stilling basins)
    –Discharge structures (ex. Culverts)
32
Q

Weirs

A

–Hydraulic structure to control flow with known stage
discharge relationship

33
Q

What is the purpose of a weir

A

–To measure and control flow
–Impound water
–Store energy

34
Q

What are the types of weirs

A

–Sharp crested (Rectangular, V-notch, Trapezoidal)
–Not sharp crested (Broad crested, spillway)

35
Q

Parshall flume

A

A specially shaped open channel flow that restricts the channel area and/or
changes the channel slope, resulting in change in the level of the liquid
flowing through the flume.

36
Q

Upstream conditions of Parshall flumes

A

laminar flow condition

37
Q

The crest of a parshall flume…

A

must be
level both longitudinally
and transversely.

38
Q

Downstream channel in a parshall flume…

A
  • avoid submerged flow
    conditions
  • No impoundment of flow
39
Q

Flume

A

A channel with a lateral constriction of the width

40
Q

What is sizing of flumes based on?

A

anticipated normal and maximum flows

41
Q

What is the difference between a weir and an orifice?

A

and orifice is completely submerged

Hydrology (3 decks)

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