L 10 EmergencyGateOps
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Transcript of L 10 EmergencyGateOps
7/21/2019 L 10 EmergencyGateOps
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Hydrologic Engineering Center
Emergency GateOperation(Induced Surcharge)
HEC-ResSim
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Outline
Terms and Background
Theory Basics
When to use the induced surcharge rule How to use the induced surcharge rule
What to look for in operations
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“Surcharge Storage” is water stored
above the top of the flood pool –
above the spillway crest
Surcharge happens naturally with any
overflow structure
We can “induce” surcharge storage in a
controlled way with a gated spillway
Terms and Background
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Background
Why induced surcharge operation?
Allows maximum use of the available flood
storage space in the reservoir
AND
Allows evacuation of flood waters in a
planned manner as the reservoir rises,before the flood pool has filled
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Gated Spillway Operation
Flood Control Objectives
1. Do not endanger the dam
Do not let water flow over the spillway
gates2. Do not make the flood worse: do not let
the peak outflow exceed the pre-project
natural peak discharge (or peak inflow)
3. Do not let the rate-of-increase of outflow
exceed acceptable limits
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Spillway Gate Section
Max Pool
Top of Flood Pool
Max Induced Surcharge
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Maximum
PermissibleElevation
Release With GatesFully Open
R e
s e r v o i r E l e v a t i o n
[ f t ]
Top Of Flood Pool
Spillway Discharge [1000 cfs]
Minimum
PermissibleRelease
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Induced Surcharge Envelope
The Induced Surcharge Envelope is: the maximum permissible reservoir elevation at
any rate of release
OR
the minimum release at any extreme reservoirelevation
Steeper slope in more-used portion
– required release increases more slowly
Flatter slope for more extreme events/elevations – required release increases rapidly w/elevation
– save the dam!
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Emergency Spillway ReleaseDiagram
The Emergency Spillway Release Diagram(ESRD) provides instructions for emergencyoperation (a.k.a. Induced SurchargeOperation)
Required release is based on volume ofremaining inflow expected during the event
For a given pool elevation and inflow (or rateof rise), indicated release ensures the pooldoes not rise above the surcharge envelopecurve before the end of the event
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Decision
Point
Recession,Defined By Ts
Current
Release
Induced Surcharge Computation
Time
S t r e a m f l o w
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Decision
Point
Current
Release
Induced Surcharge Computation
Time
S t r e a m f l o w
Recession,Defined By Ts
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Induced Surcharge Computation
Decision
Point
Time
S t r e a m f l o w
Smaller
Value Of Ts
Larger Value
Of Ts
Recession,Defined By Ts
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Induced Surcharge Computation
Decision
Point
Recession,Defined By Ts
Time
S t r e a m f l o w
Later Decision
Points
Recession
Hydrographs
Larger Value
Of Ts
Smaller
Value Of Ts
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Time
S t r e a m f l o w
Decision
Point
Current
Release
Recession,Defined By Ts
Volume ToBe Managed
Induced Surcharge Computation
o
ieoiS
Q
Qlog 1QQT 2Vol
Qi
Qo
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Time
S t r e a m f l o w
Decision
Point
Current
Release
Induced Surcharge Computation
volume of
release
inflow drops
below releasevolume to
be stored
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Questions:
Will the “volume to be stored” put the reservoir
above the allowable surcharge envelope (at current
release)?
What elevation is low enough that the volume willfit?
For many inflows and outflows, plot that elevation.
Plotting and connecting points for a given inflow
creates the surcharge diagram. For a real-time inflow and elevation, the surcharge
diagram provides the operating instructions of what
release to make.
Induced Surcharge Computation
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Induced Surcharge Envelope Curve
Spillway DischargeCurve (Free Overflow)
Reservoir Outflow [1,000 cfs]
R e s e r v o i r E l e v a t i o n
[ f t ]
InflowLevel
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Induced Surcharge Envelope Curve
Reservoir Outflow [1,000 cfs]
R e s e r v o i r E l e v a t i o n
[ f t ] Spillway Discharge
Curve (Free Overflow)
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How is the recession
constant Ts defined?
Plot recession limb of
project (or spillway) design
storm on semi-log paper,
and fit a straight line
Find time needed to
decrease from some flow
Q A to Q B, where
Q B= Q A/e (or Q B= Q A/2.71)
l o g e
s t r e a m f l o w
timeTS
Recession Constant, Ts
QAQA
QB =
QA /2.71QB
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When is Induced SurchargeOperation Needed?
When one or more of the following conditions
are present…
Large to very large inflow event
Rapidly rising Multi-peak
Long duration
Small or rapidly decreasing flood pool
Dam stability concerns
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Top Of Conservation
Top Of Flood Pool
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Top Of Conservation
Top Of Flood Pool
Top Of Flood Dam
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Top Of Conservation
Top Of Flood Pool
Top Of Flood Dam
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What’s wrong?
The problem:
The model doesn’t know what to do when the
reservoir is full
AND, is letting the reservoir become full
The Solution:We need a rule to allow a higher release when
the reservoir is close to full
Release as function of elevation?…but also depends on high inflow…
Use the Induced Surcharge Rule
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How do we produce induced surcharge
operation in the ResSim environment?
with the Induced Surcharge Rule
In which zones should we put the rule?in those zones that appear in the diagram
Does the IS Rule apply to the Pool or Dam?
the pool
What type of limit is the IS rule?
the induced surcharge rule is a MINIMUM rule
Induced Surcharge in ResSim
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What information is needed?
Surcharge envelope curve
Time of Recession, Ts
Inflow (Time-series) Option
Falling Pool instructions
Decrease time
Transition elevation Falling pool release option
Induced Surcharge in ResSim
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Top Of Conservation
Top Of Flood Pool
Top Of Flood Dam
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More to know
The Induced Surcharge rule is a MINIMUM
release rule
It must be paired with a maximum rule at a
lower priority to produce the right operationA decreasing rate of change rule may also be
desirable to temper the transition between
the IS operation and normal flood control
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Top Of Conservation
Top Of Flood PoolTop Of Flood Dam
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Analyzing Results
Induced Surcharge operation can often bedifficult to analyze because…
The release decision report does not identify the IS
rule as the controlling rule
If the inflow event has multiple peaks, the IS rule
may turn on and off sporatically
Use DSSVue
Plot the FLOW-MIN and FLOW-MAX records forthe relevant rules together with the release (Pool,
FLOW-OUT) or FLOW-DECISION record.
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I ESRD C
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Input ESRD Curves
Originally, only the Induced Surcharge Function Rulewas available in ResSim.
The newest form of this rule now allows the user to
select either the original function method for
describing the rule or direct entry of the ESRD familyof curves.
The original function form is appropriate for designing this
operation from scratch.
The new ESRD form is appropriate for describing this
operation when the curves have been altered from those
produced by the function.
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