Test 2 Flashcards
What does routing flow do?
Determine Time & Magnitude of Flow at a point
downstream from an upstream hydrograph
Why do we route flow?
- Account for changes in flow hydrograph as a flood wave
passes downstream - This helps in
– Accounting for storages
– Studying the attenuation of flood peaks
What is flow routing?
- 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
What are the two routing methods?
Hydrologic [Lumped] and Hydraulic [Distributed]
Hydrologic [Lumped]
– 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
Hydraulic [Distributed]
– 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
Effects of routing
-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
Level pool routing (Reservoir routing)
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)
What are the Storage discharge elevation inputs and out puts?
- Input:
1. Elevation – Storage (topography)
2. Elevation – Discharge (hydraulics)
*Output
Storage indication curve
What are the impacts/ uses of river routing?
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)
How do we calculate River Storage?
Muskingum Method
Method developed in Ohio River Basin to address
flood routing.
McCarthy (1938)
Most widely used method (Ponce 1989)
Muskingum Method
-River Channel Routing
- Variable Q and S relationship
- Prism and Wedge Storage
Total storage (muskingum)
Prism+ wedge
What do K and X in the muskingum
K = travel time through the reach
X = weighting factor based on channel shape
Why do we model Hydrology
● Planning, design, operation, and management of water resources
projects
● Watershed management
● Environmental protection
● Climate change
● And more!
What are some examples of Hydrologic/Hydraulic Modeling
● 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
What do models simulate and predict?
● 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!
Open Channel Flow
- Driven by gravity and geometry
- Features a free surface with atmospheric
pressure
What is open channel flow characterized by?
- Position of free surface changes with time
and space. - Flow depth (y), flowrate (Q), slope of WS
(Sw) and bed slope (So). - Physical Condition of the channel:
Slope, Roughness, etc.
What are the three regimes of flow
Supercritical, sub critical, and critical
- Fr < 1
– Subcritical Flow
– Gravity dominates
– Waves can propagate upstream
- Fr > 1
– Supercritical Flow
– Inertial Forces dominate
– Waves propagate downstream only!
Is open channel flow laminar or turbulent?
turbulent
What are the open channel flow assumptions?
Pressure is zero (atmospheric)
Specific energy
energy per lbf of water
What is critical depth
The depth of flow corresponding to the
minimum E is the critical depth, yc
What do we avoid critical flow in design?
it is unstable
Flow Profile and Critical
Depth/Slope
- Mild Slope / Subcritical slope
– Depth due to Backwater - Critical Slope
– Horizontal Level Pool - Steep / Supercritical slope
– Hydraulic Jump
Channel Control
- Definition:
– Establishment of definitive flow conditions for a
channel
Why do we control channels
- Gaging Stations
- Flow Meters: Weirs, Flumes
- GVF – Starts @ Control
Hydraulic Structures
- 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)
Weirs
–Hydraulic structure to control flow with known stage
discharge relationship
What is the purpose of a weir
–To measure and control flow
–Impound water
–Store energy
What are the types of weirs
–Sharp crested (Rectangular, V-notch, Trapezoidal)
–Not sharp crested (Broad crested, spillway)
Parshall flume
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.
Upstream conditions of Parshall flumes
laminar flow condition
The crest of a parshall flume…
must be
level both longitudinally
and transversely.
Downstream channel in a parshall flume…
- avoid submerged flow
conditions - No impoundment of flow
Flume
A channel with a lateral constriction of the width
What is sizing of flumes based on?
anticipated normal and maximum flows
What is the difference between a weir and an orifice?
and orifice is completely submerged
