Design of a Dam Sediment Mitigation System to Aid Water
Quality Restoration of the Chesapeake Bay
Sheri Gravette
Kevin Cazenas
100%
80%
150,000,000
60%
100,000,000
Sediment Deposition
Expected
Threshold
50,000,000
0
40%
20%
Percent Capacity
Conowingo Reservoir Sediment Deposition
200,000,000
0%
Alternatives
1. No mitigation (baseline)
•
Sediment continues accumulation
at Conowingo Reservoir
•
•
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
•
•
•
Island made using processed dredged sediment (after 2 years)
Flow velocity increases, Rouse number decreases around island
(i.e. more sediment through dam at steady-state)
Same sub-alternatives above apply (after island construction)
Island, 5 million
5 million
Island, 3 million
3 million
•
1
0.9
0.8
0.7
Plasma
HighGrade
Utility
0.6
0.5
Lightweight
Aggregate
0.4
0.3
0.2
•
0.1
0
-$1
$0
$1
•
•
2% initial decrease in scour
0.4% decrease in scour after maximum dredging for 20 years .

Ecological
Impact

Simulates monetary value of
Chesapeake Bay impact
Business Reuse Model
(0.5)

Simulates cost of processing
dredged sediment into products
Recommendation
$2
Cost (Billions, Net Present Value, discount factor=5%)
•
•
Sediment
Scour
potential
(0.5)
- Amount of
Product(s)
Produced
- Product Revenue
- Annual Cost
 Sediment Removal Model
 Simulates reservoir activity after
mitigation alternatives applied
 Ecological Impact Model
Minimize
Susquehanna
Sediment Impact
to Chesapeake
Bay
3. Dredging & Artificial Island
Island, 1 million
For every 1 million cubic yards dredged:
Business
Reuse
Model
Value Hierarchy
Analysis
Percent Decrease in Scour After 20 years
Compared to Baseline
Product
Alternatives
Sediment Amount
(removed)
Mechanical removal of sediment via
pipeline (1, 3, 5 million cubic yards per year)
Sub-alternatives (action taken with sediment):
• Quarry (baseline)
• Low-Temp Washing – Topsoil
• Rotary Kiln – Lightweight Aggregate
• Plasma Arc Vitrification –
• Low Grade Tile
• High Grade Tile
Results
Total Percent Decrease in Scour
Rouse Number (particle
fall velocity divided by
bed shear stress) with
artificial island location
Yellow-Blue is trapped
sediment (at 30,000 cfs.)
Primary Design Alternatives
- Flow Rates
- Sediment Deposition
Costs of
- Velocity
Profiles
Remediation/
Sediment
Ecological Recovery
- Reservoir Bathymetry Sediment Scoured
Removal
Impact
Model
Model
2. Hydraulic Dredging
•
Scouring events occur due to sediment
build-up at Conowingo Reservoir (area
behind dam)
•
• Sediment scour exponentially increases
as flow rate increases
• Max Recorded Flow Rates:
•
1. (1972) Hurricane Agnes:
1,120,000 cubic ft. per second
2. (2011) Tropical Storm Lee:
709,000 cubic ft. per second
Stakeholder Tension: Sediment needs to be managed. Dam owners do not want to
take responsibility. Relicensing may result in payment for system.
Major storms (>300,000cfs)
cause scouring events
Scouring events cause
sediment plumes along
Chesapeake Bay
Sediment plumes cause large
algae blooms which damages
aquatic ecosystem health
Method of Analysis
Need to create a system to reduce the environmental
impact of scouring events while facilitating current
(Chesapeake Bay TMDL) ecological regulations.
Year
•
Rayhan Ain
Need & Design Alternatives
1929
1936
1943
1950
1957
1964
1971
1978
1985
1992
1999
2006
2013
2020
2027
Sediment Deposition (tons)
Context
Said Masoud
Plasma high-grade is only alternative with a chance to turn a
profit, but has high variability
Lightweight aggregate does not have a chance to turn a profit,
but has a low uncertainty
Best option
• Dredge 5 million cubic
yards annually
Rank
• Produce high-grade
architectural tile for
maximum product and
1
profit potential
• Further analysis on
plasma gas arc vitrification
is needed to solidify
2
profitability.
Best (non-Plasma) option –
• Construct an artificial
island* from sediment
dredged
• After island construction,
dredge 1 million cubic
yards annually
• Produce lightweight
aggregate.
• This is the safest option,
as it provides low
uncertainty and beneficial
reuse
Department of System Engineering & Operations Research George Mason University
Alternative Combo
(Product, Mitigation)
Plasma - High-Grade Tile,
5 million
Plasma - High-Grade Tile,
5 million with Island
3
Plasma - High-Grade Tile,
3 million with Island
4
Plasma - High-Grade Tile,
3 million
5
Lightweight Aggregate,
1 million with Island